Patent Publication Number: US-2022214454-A1

Title: Optical imaging transmitter with brightness enhancement

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Non-Provisional application Ser. No. 15/979,266, filed May 14, 2018, which claims priority to U.S. Provisional Patent Application No. 62/506,449, filed on May 15, 2017, U.S. Provisional Patent Application No. 62/506,437, filed on May 15, 2017, U.S. Provisional Patent Application No. 62/506,445, filed on May 15, 2017, and U.S. Provisional Patent Application No. 62/515,291, filed Jun. 5, 2017. The disclosures of each of the Ser. No. 15/979,266; 62/506,449; 62/506,437; 62/506,445; and 62/515,291 applications are hereby incorporated by reference in their entirety and for all purposes. 
    
    
     BACKGROUND 
     An imager detects light and creates a digital image of a scene based on that detected light. The image contains a fixed number of rows and columns of pixels where each pixel maps to a different field-of-view within the scene. Electronic imagers typically make use of photodetectors to convert light into electrical signals. Each photodetector is located at a different position on the focal plane and usually corresponds to a single pixel or a component of a pixel in the image. Electronic imagers can typically be classified as one of two types: a passive-illumination imager or an active-illumination imager. A passive-illumination imager collects ambient light such as sunlight reflected by objects in a scene, whereas an active-illumination imager illuminates the scene and collects reflected light generated by the active-illumination imager system itself. 
     A narrowband imager collects light within a limited wavelength range. This is in contrast to a traditional camera which detects light across the entire visible spectrum or into three different wide, RGB color bands, each of which may be 100 nm or wider. Narrowband imagers are harder to develop than traditional cameras due to the characteristics of the optical filters on which they rely. Optical filters serve to prevent some portion of the electromagnetic spectrum from reaching the photodetectors. Most narrowband filters rely on thin-film interference effects to selectively transmit or reflect light (such filters are often referred to as dielectric mirrors or Bragg mirrors). The spectral transmissivity of the narrowband filter depends on the number, thicknesses, ordering, and indices of refraction of the constituent layers forming the filter. The spectral transmissivity of the filter also depends upon the angle of incidence of the light upon the narrowband filter. 
     Current narrowband imagers have either a small field-of-view or are limited in their ability to filter wavelength bands narrower than around 50 nm. Optical filters are sensitive to the angle of incident light making it difficult to achieve a narrow range of wavelengths. For example, an optical filter may accept perpendicular light with wavelength at 940-945 nm and slightly oblique light at a wavelength of 930-935 nm. Since most photodetectors in a traditional camera have a large range of angles of light incident upon them, simply placing an optical filter in front of them would not actually achieve narrowband filtering. Constricting the angle of light incident upon the photodetector usually requires using a lens with a longer focal length, which constricts the field-of-view of the camera. 
     Imagers with a wide field-of-view have difficulty in generating uniformly clear visual images and in making uniform measurements across a scene. For example, the pixels at the center of the image may appear brighter or represent a different wavelength of light compared to the pixels at the scene extremities. A wide field-of-view is desirable for some applications because it provides better situational awareness. For example, a camera-based automotive safety system meant to detect pedestrians around a vehicle might require monitoring in a 360 degree field-of-view around the vehicle. Fewer wide field-of-view sensors are required to do the same job (i.e., generate images of the full 360 degree field-of-view) as many narrow field of view sensors, thereby decreasing the system cost. 
     Narrowband imagers have many applications including geographic mapping, astronomy and in LIDAR (Light Detection and Ranging). Narrowband imagers can detect characteristic light wavelengths such as those generated by plants with chlorophyll or by elements within stars. Narrowband imagers can be used, for example, to determine vegetation health or to discover oil deposits. Optical receiver systems, such as LIDAR, can be used for object detection and ranging. LIDAR systems measure the distance to a target or objects in a landscape, by irradiating a target or landscape with light, using pulses from a laser, and measuring the time it takes photons to travel to the target or landscape and return after reflection to a narrowband imager. Other LIDAR techniques, such as photo-demodulation, coherent LIDAR, and range-gated LIDAR, also rely on the transmission and reflection of photons, though they may not directly measure the time-of-flight of pulses of laser light. For many LIDAR applications, it is beneficial for physical sizes of transmitters and receivers to small and compact, and at the same time relatively low in cost. For applications where objects must be sensed with accuracy at long distances, it is beneficial to increase or maximize the number of photons emitted by the transmitter and reflected back toward the receiver while keeping laser energy emissions within mandated safety limits. 
     Micro-optical systems are systems that include miniaturized, optical components that are typically between a few micrometers and a millimeter in size. Micro-optical receivers arrayed adjacent to each other are susceptible to crosstalk. Stray light caused by roughness of optical surfaces, imperfections in transparent media, back reflections, etc., may be generated at various features within the receiver channel or external to receiver channel. When multiple receiver channels are arrayed adjacent to one another, this stray light in one receiver channel may be absorbed by a photosensor in another channel, thereby contaminating the timing, phase, or other information inherent to photons. Minimizing crosstalk is especially important in active-illumination systems. Light reflected from a nearby retro-reflector (e.g. a license plate) may be thousands or millions of time more intense than light reflected from a distant, dark, lambertian surface (e.g. black cotton clothing). Thus, the stray light photons from a retro-reflector could vastly outnumber photons reflected from other surfaces in nearby photosensors if crosstalk is not minimized. This can result in the inability of a LIDAR system to detect dark objects that occupy fields of view near the field of view occupied by a retro-reflector. 
     SUMMARY 
     Embodiments of the disclosure provide optical imager systems that achieve wide field-of-view, narrowband imaging with micro-optic receiver channel arrays that minimize crosstalk and allow tight spectral selectivity that is uniform across the receiver channel array. Some optical imager systems according to the disclosure can include a light transmission module that provides enhanced spot illumination such that a power level of light returning to a light sensing module is increased, while at the same time improving the spatial resolution of the measured image. 
     In some embodiments, an optical system for performing distance measurements includes a bulk transmitter optic, an illumination source, and a micro-optic channel array disposed between the illumination source and the bulk transmitter optic. The illumination source includes a plurality of light emitters aligned to project discrete beams of light through the bulk transmitter optic into a field ahead of the optical system. The micro-optic channel array defines a plurality of micro-optic channels where each micro-optic channel includes a micro-optic lens spaced apart from a light emitter from the plurality of light emitters with the micro-optic lens being configured to receive a light cone from the light emitter and generate a reduced-size spot image of the emitter at a focal point displaced from the emitter at a location between the emitter and the bulk transmitter optic. The micro-optic lens for each channel can be configured to receive a light cone from a light emitter and generate a reduced-size real spot image of the emitter at a focal point between the micro-optic lens and the bulk transmitter optic. A divergence of the light cone from the light emitter can be less than a divergence of a light cone from the second optical surface of the micro-optic lens for generating the reduced-size real spot image 
     In some additional embodiments, an optical system for performing distance measurements includes a light emission system and a light detection system. The light emission system includes a bulk transmitter optic, an illumination source comprising a plurality of light emitters aligned to project discrete beams of light through the bulk transmitter optic into a field ahead of the optical system, and a micro-optic channel array disposed between the illumination source and the bulk transmitter optic. The micro-optic channel array defines a plurality of micro-optic channels where each micro-optic channel includes a micro-optic lens spaced apart from a light emitter from the plurality of light emitters with the micro-optic lens being configured to receive a light cone from the light emitter and generate a reduced-size spot image of the emitter at a focal point displaced from the emitter at a location between the emitter and the bulk transmitter optic. The light detection system includes a bulk receiver optic configured to receive the discrete beams of light from the field, and an optical assembly having a plurality of micro-optic receiver channels defining a plurality of discrete, non-overlapping fields of view in the field. The optical assembly includes: an aperture layer having a plurality of discrete apertures arranged along a focal plane of the bulk receiver optic; an array of photosensors disposed behind the aperture layer; and a plurality of lenses positioned between the aperture layer and the array of photosensors. 
     In certain embodiments, an optical system for performing distance measurements includes a stationary housing having an optically transparent window, and a light ranging device disposed within the housing. The light ranging device includes an optical transmitter coupled to a platform. The optical transmitter includes a bulk transmitter optic, an illumination source, and a micro-optic channel array disposed between the illumination source and the bulk transmitter optic. The illumination source including a plurality of light emitters aligned to project discrete beams of light through the bulk transmitter optic into a field ahead of the optical system. The micro-optic channel array can be disposed between the illumination source and the bulk transmitter optic, and the micro-optic channel array can define a plurality of micro-optic channels where each micro-optic channel can include a micro-optic lens spaced apart from a light emitter from the plurality of light emitters with the micro-optic lens being configured to receive a light cone from the light emitter and generate a reduced-size spot image of the emitter at a focal point displaced from the emitter at a location between the emitter and the bulk transmitter optic. 
     In some embodiments, an optical system includes a bulk receiver optic configured to receive light rays originating from a field external to the optical system, and an optical assembly having a plurality of micro-optic receiver channels defining a plurality of discrete, non-overlapping fields of view in the field. The optical assembly includes an aperture layer having a plurality of discrete apertures arranged along a focal plane of the bulk receiver optic, an array of photosensors disposed behind the aperture layer, and a non-uniform optical filter layer configured to allow different micro-optic channels to measure different ranges of wavelengths. The non-uniform optical filter can include a graduated optical filter that gradually increases in thickness in one dimension, or increases in thickness in a step-wise fashion in one direction such that each channel has a constant optical filter layer thickness, but where the thicknesses for different micro-optic channels are different. 
     In some additional embodiments, an optical system includes a bulk receiver optic configured to receive light from a field external to the optical system, an aperture layer disposed behind the bulk optic and including a plurality of apertures located at a focal plane of the bulk optic, a lens layer including a plurality of collimating lenses having a focal length, the lens layer disposed behind the aperture layer and separated from the aperture layer by the focal length, a non-uniform optical filter layer behind the lens layer, and a photosensor layer including a plurality of photosensors. The aperture layer, lens layer, non-uniform optical filter layer and photosensor layer are arranged to form a plurality of micro-optic channels defining a plurality of discrete, non-overlapping fields of view in the field with each micro-optic channel in the plurality of micro-optic channels including an aperture from the plurality of apertures, a lens from the plurality of lenses, a filter from the filter layer, and a photosensor from the plurality of photosensors and being configured to communicate light incident from the bulk receiver optic to the photosensor of the micro-optic channel. The non-uniform optical filter layer is configured to allow different micro-optic channels to measure different ranges of wavelengths. 
     In certain embodiments, an optical system includes a bulk receiver optic configured to receive light rays originating from a field external to the optical system, and an optical assembly having a plurality of micro-optic receiver channels defining a plurality of discrete, non-overlapping fields of view in the field. The optical assembly includes a monolithic ASIC including a processor, a memory, and a plurality of photosensors fabricated in the ASIC, an aperture layer having a plurality of discrete apertures arranged along a focal plane of the bulk receiver optic, the array of photosensors disposed behind the aperture layer; a plurality of lenses positioned between the aperture layer and the array of photosensors; and a non-uniform optical filter layer having different center wavelengths across its structure to allow at least two different micro-optic receiver channels to measure different ranges of wavelengths of light, wherein the aperture layer, plurality of lenses, and non-uniform optical filter layer are formed on the ASIC such that they form part of the monolithic structure of the ASIC. 
     In some embodiments, an optical system for performing distance measurements includes a stationary housing having an optically transparent window, a spinning light ranging device disposed within the housing, a motor disposed within the housing and operatively coupled to spin the light ranging device including the platform, optical transmitter, and optical receiver within the housing, and a system controller disposed within the housing, the system controller configured to control the motor and to start and stop light detection operations of the light ranging device. The light ranging device includes a platform, an optical transmitter coupled to the platform, and an optical receiver coupled to the platform. The optical transmitter includes a bulk transmitter optic and a plurality of transmitter channels, each transmitter channel including a light emitter configured to generate and transmit a narrowband light through the bulk transmitter optic into a field external to the optical system. The optical receiver includes a bulk receiver optic and a plurality of micro-optic receiver channels, each micro-optic channel including an aperture coincident with a focal plane of the bulk receiver optic, an optical filter positioned along a path of light from the bulk receiver optic and axially aligned with the aperture, and a photosensor responsive to incident photons passed through the aperture and the optical filter. 
     In some additional embodiments, an optical system for performing distance measurements includes a stationary housing having a base, a top and an optically transparent window disposed between the base and the top, a spinning light ranging device disposed within the housing and aligned with the optically transparent window, a motor disposed within the housing and operatively coupled to spin the light ranging device including the platform, optical transmitter and optical receiver within the housing, and a system controller disposed within the housing, the system controller configured to control the motor and to start and stop light detection operations of the light ranging device. The light ranging device including a platform, an optical transmitter coupled to the platform, and an optical receiver coupled to the platform. The optical transmitter including an image-space telecentric bulk transmitter optic and a plurality of transmitter channels, each channel including a light emitter configured to generate and transmit a narrowband light through the bulk transmitter optic into a field external to the optical system. The optical receiver including an image-space telecentric bulk receiver optic and a plurality of micro-optic receiver channels, each micro-optic channel including an aperture coincident with a focal plane of the bulk receiver optic, a collimating lens behind the aperture, an optical filter behind the collimating lens and a photosensor responsive to incident photons passed through the aperture into the collimating lens and through the filter. 
     In certain embodiments, an optical system for performing distance measurements includes a stationary housing having a base, a top and an optically transparent window disposed between the base and the top, a light ranging device disposed within the housing and aligned with the optically transparent window, a motor disposed within the housing and operatively coupled to spin the light ranging device within the housing; and a system controller disposed within the housing, the system controller configured to control the motor and to start and stop light detection operations of the light ranging device. The light ranging device includes a platform, a plurality of vertical-cavity surface emitting lasers (VCSELs) arranged in an array, and an optical receiver coupled to the platform. Each VCSEL in the plurality of VCSELs are configured to generate and transmit discrete pulses of light into a field external to the optical system. The optical receiver including a bulk receiver optic, a plurality of photosensors, each photosensor comprising a plurality of single-photon avalanche diodes (SPADs) responsive to incident photons, and an optical filter disposed between the bulk receiver optic and the plurality of photosensors and configured to allow a band of light to pass through the filter to the plurality of photosensors while blocking light outside the band from reaching the plurality of photosensors. 
     In some embodiments, an optical system for performing distance measurements includes a rotatable platform, an optical transmitter coupled to the rotatable platform and comprising a bulk transmitter optic and a plurality of transmitter channels, an optical receiver coupled to the rotatable platform and comprising a bulk receiver optic and a plurality of micro-optic receiver channels, a motor disposed within the housing and operatively coupled to spin the platform, optical transmitter, and optical receiver, a system controller mounted to a stationary component of the optical system; and an optical communication link operatively coupled between the system controller and the optical receiver to enable the system controller to communicate with the optical receiver. Each transmitter channel includes a light emitter configured to generate and transmit a narrowband light through the bulk transmitter optic into a field external to the optical system. Each micro-optic channel includes an aperture coincident with a focal plane of the bulk receiver optic, an optical filter positioned along a path of light from the bulk receiver optic and axially aligned with the aperture, and a photosensor responsive to incident photons passed through the aperture and through the filter. The optical communication link can extend between the stationary component of the optical system and the rotatable platform to operatively couple the system controller with the optical receiver. The optical receiver can further include a collimating lens behind the aperture and directly coupled to the optical filter, the optical filter positioned behind the collimating lens. 
     In some additional embodiments, an optical system for performing distance measurements including a rotatable platform, an optical transmitter coupled to the rotatable platform and comprising an image-space telecentric bulk transmitter optic and a plurality of transmitter channels, an optical receiver coupled to the rotatable platform and comprising an image-space telecentric bulk receiver optic and a plurality of micro-optic receiver channels, a motor disposed within the housing and operatively coupled to spin the platform, optical transmitter and optical receiver, a system controller mounted to a stationary component of the optical system, and an optical communication link operatively coupled between the system controller and the optical receiver to enable the system controller to communicate with the optical receiver. Each transmitter channel includes a light emitter configured to generate and transmit a narrowband light through the bulk transmitter optic into a field external to the optical system. Each micro-optic channel includes an aperture coincident with a focal plane of the bulk receiver optic, a collimating lens behind the aperture, an optical filter behind the collimating lens and a photosensor responsive to incident photons passed through the aperture into the collimating lens and through the filter. 
     In certain embodiments, An optical system for performing distance measurements includes a rotatable platform, a plurality of vertical-cavity surface emitting lasers (VCSELs) arranged in an array and coupled to the rotatable platform, an optical receiver coupled to the rotatable platform, a motor disposed within the housing and operatively coupled to spin the platform, the plurality of VCSELs and the optical receiver; a system controller mounted to a stationary component of the optical system, and an optical communication link operatively coupled between the system controller and the optical receiver to enable the system controller to communicate with the optical receiver. Each VCSEL in the plurality of VCSELs are configured to generate and transmit discrete pulses of light into a field external to the optical system. The optical receiver including a bulk receiver optic and a plurality of photosensors, each photosensor comprising a plurality of single-photon avalanche diodes (SPADs) responsive to incident photons. 
     In some embodiments, an optical system for performing distance measurements includes a bulk receiver optic, an aperture layer including a plurality of apertures, a first lens layer including a first plurality of lenses, an optical filter layer configured to receive light after it passes through the bulk receiver optic and pass a band of radiation while blocking radiation outside the band, and a photosensor layer including a plurality of photosensors, Each photosensor includes a plurality of photodetectors configured to detect photons, and a second plurality of lenses configured to focus incident photons received at the photosensor on the plurality of photodetectors. The optical system includes a plurality of receiver channels with each receiver channel in the plurality of receiver channels including an aperture from the plurality of apertures, a lens from the plurality of first lenses, an optical filter from the optical filter layer, and a photosensor from the plurality of photosensors, with the aperture for each channel defining a discrete, non-overlapping field of view for its respective channel. For each receiver channel in the plurality of receiver channels, there can be a one-to-one correspondence between the plurality of photodetectors and the second plurality of lenses in the photosensor for that channel, where each of the lenses in the second plurality of lenses can be configured to focus photons on its corresponding lens in the second plurality of lenses 
     In some additional embodiments, an optical system for performing distance measurements includes a light emission system and a light detection system. The light emission system including a bulk transmitter optic and an illumination source. The illumination source including a plurality of light emitters aligned to project discrete beams of light through the bulk transmitter optic into a field ahead of the optical system. The light detection system including a bulk receiver optic, an aperture layer including a plurality of apertures, a first lens layer including a first plurality of lenses, an optical filter layer configured to receive light after it passes through the bulk receiver optic and pass a band of radiation while blocking radiation outside the band, and a photosensor layer including a plurality of photosensors. Each photosensor includes a plurality of photodetectors configured to detect photons, and a second plurality of lenses configured to focus incident photons received at the photosensor on the plurality of photodetectors. The optical system includes a plurality of receiver channels with each receiver channel in the plurality of receiver channels including an aperture from the plurality of apertures, a lens from the plurality of first lenses, an optical filter from the optical filter layer, and a photosensor from the plurality of photosensors, with the aperture for each channel defining a discrete, non-overlapping field of view for its respective channel. 
     In certain embodiments, an optical system for performing distance measurements including a stationary housing having an optically transparent window, a light ranging device disposed within the housing and aligned with the optically transparent window, a motor disposed within the housing and operatively coupled to spin the light ranging device including the platform, optical transmitter, and optical receiver within the housing, and a system controller disposed within the housing. The system controller configured to control the motor and to start and stop light detection operations of the light ranging device. The light ranging device including a platform, an optical transmitter coupled to the platform, an optical receiver coupled to the platform. The optical transmitter including a bulk transmitter optic and a plurality of transmitter channels, each transmitter channel including a light emitter configured to generate and transmit a narrowband light through the bulk transmitter optic into a field external to the optical system. The optical receiver including a bulk receiver optic, an aperture layer including a plurality of apertures, a first lens layer including a first plurality of lenses, an optical filter layer configured to receive light after it passes through the bulk receiver optic and pass a band of radiation while blocking radiation outside the band, and a photosensor layer including a plurality of photosensors. Each photosensor includes a plurality of photodetectors configured to detect photons, and a second plurality of lenses configured to focus incident photons received at the photosensor on the plurality of photodetectors. The optical system includes a plurality of receiver channels with each receiver channel in the plurality of receiver channels including an aperture from the plurality of apertures, a lens from the plurality of first lenses, an optical filter from the optical filter layer, and a photosensor from the plurality of photosensors, with the aperture for each channel defining a discrete, non-overlapping field of view for its respective channel. 
     A better understanding of the nature and advantages of embodiments of the present disclosure may be gained with reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary passive optical imager system, according to some embodiments of the present disclosure. 
         FIG. 2  is a simplified diagram of an exemplary light detection system for a passive optical imager system, according to some embodiments of the present disclosure. 
         FIGS. 3A and 3B  are perspective views of a simplified diagram of different embodiments of micro-optic receiver layers with graduated filter layers, according to some embodiments of the present disclosure. 
         FIG. 4  is a block diagram of a rotating LIDAR system, according to some embodiments of the present disclosure. 
         FIGS. 5A-5B  are simple illustrations of exemplary implementations of solid state LIDAR systems, according to some embodiments of the present disclosure. 
         FIG. 6A-6B  are simple illustrations of exemplary implementations of scanning LIDAR systems, according to some embodiments of the present disclosure. 
         FIG. 7  is an exemplary perspective view diagram showing an embodiment of a LIDAR system employing a 360 scanning architecture, according to some embodiments of the present disclosure. 
         FIG. 8  is an illustrative example of the light transmission and detection operation for a light ranging system, according to some embodiments of the present disclosure. 
         FIG. 9  is a flowchart illustrating a method of using coded pulses in an optical measurement system, according to embodiments of the present disclosure. 
         FIG. 10  is a simplified diagram illustrating a detailed view of an exemplary active optical imager system having a wide field-of-view and capable of narrowband imaging, according to some embodiments of the present disclosure. 
         FIGS. 11-14  are simplified cross-sectional view diagrams of various exemplary enhanced light emission systems, according to some embodiments of the present disclosure. 
         FIGS. 15A-15C  are cross-sectional views of simplified diagrams of exemplary active imager systems having different implementations of corrective optical structures for astigmatism, according to some embodiments of the present disclosure. 
         FIG. 16A  is a simplified cross-sectional view diagram of part of a light detection system  1600  where there is no cross-talk between channels. 
         FIG. 16B  is a simplified cross-sectional view diagram of part of a light detection system  1601  where there is cross-talk between channels. 
         FIG. 17  is a simplified cross-sectional diagram of an exemplary micro-optic receiver channel structure, according to some embodiments of the present disclosure. 
         FIGS. 18A-18D  are simplified cross-sectional view diagrams of various aperture layers for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 19A-19D  are simplified cross-sectional view diagrams of various spacer structures between the aperture layer and the optical lens layer for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 20A-20G  are simplified cross-sectional view diagrams of various optical filter layers for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 21A-21K  are simplified cross-sectional view diagrams of various photosensor layers with diffusers for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 22A-22I  are simplified cross-sectional view diagrams of various hemispherical receiver structures for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 23A-23E  are simplified cross-sectional view diagrams of various bottom micro lens layers for a receiver channel, according to some embodiments of the present disclosure. 
         FIGS. 24 and 25  are simplified cross-sectional view diagrams of exemplary receiver channels, according to some embodiments of the present disclosure. 
         FIGS. 26-30  are simplified top view diagrams of exemplary micro-optical receiver arrays, according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the disclosure pertain to optical imager systems that can generate an image from ambient light in a field and/or light emitted from an optical transmitter that has reflected off of an object in the field. For instance, in some embodiments an optical imager system can be a passive system that does not actively illuminate a scene or given area and instead detects ambient light in the scene or area reflected off of one or more objects in the scene or area. A passive optical imager system can include a light sensing module for receiving ambient light in the field. The light sensing module can be a wide field-of-view, narrowband optical imaging system (WFNBI) that collects imaging information. The light sensing module can include one or more bulk receiver optics, a micro-optic receiver system, and a system controller for operating the light sensing module. According to some embodiments of the present disclosure, the micro-optic receiver system can include one or more micro-optic receiver layers and one or more photosensors, each photosensor can include one or more photodetectors that can measured received light. 
     A bulk imaging optic as defined herein can be one or more optical surfaces, possibly including multiple lens elements, that have clear apertures greater than one millimeter and that is positioned to receive light projected from, or focus received light on, a micro-optic transmitter/receiver layer. A bulk imaging optic that projects light received from an optical emitter, such as a micro-optic transmitter layer, is sometimes referred to herein as a bulk transmitter optic or as an output bulk imaging optic. A bulk optic layer that focuses light received from a field onto an optical detector, such as a micro-optic receiver layer, is sometimes referred to herein as a bulk receiver optic or as an input bulk imaging optic. An input, image-space telecentric bulk imaging optic allows the system to measure narrowband light uniformly over a wide field-of-view (FOV). The micro-optic receiver layer can include a one- or two-dimensional array of micro-optic receiver channels where each micro-optic receiver channel has multiple components including one or more of an aperture, a collimating micro-lens, an optical filter, and a photosensor. In some instances, the micro-optical receiver channel structure has a columnar arrangement with enclosures having absorbent and/or reflective side walls and/or focusing funnels. The micro-optic receiver channel maximizes the collection of incoming rays through its aperture, collimates the light to make it perpendicular to the optical filter, and minimizes crosstalk with adjacent micro-optic receiver channels due to mixing of inputs from neighboring apertures, as will be discussed in detail below. In various instances, bulk imaging optics according to the present disclosure modify light or other radiation for an entire array of emitters or photosensors. Micro-optic structures can be included as part of the array and can modify light differently for different emitters and/or photosensors in the array. In some embodiments, there is one or more micro-optic elements for each individual array element (photosensor and/or emitter). 
     In some embodiments, the optical imager system can be an active system that can emit light into a field and then detect the emitted light after it has reflected off surfaces of an object in the field. An active optical imager system can include a light transmission module in addition to a light sensing module, and be configured as a light ranging device. The light transmission module can include a transmitter layer that is composed of an array of individual emitters where each emitter can be paired with a corresponding micro-optic receiver channel in the light sensing module, or it can be a uniform illuminator that spreads light evenly across the scene with no specific pairing between individual emitters and receiver channels. In some instances, the light transmission module can include a micro-optic transmitter channel array to enhance light outputted from the array of emitters. During operation, light outputted by the array of emitters (e.g., laser pulses) passes through the micro-optic transmitter channel array and enters a bulk transmitter optic having a large numerical aperture to better capture light from the micro-optic transmitter channel array. The light then exits the bulk transmitter optic and illuminates a plurality of spots at a distant field. The micro-optic transmitter channel array can improve the brightness of beams emanating from the bulk transmitter optic to provide enhanced spot illumination, while at the same time improving the spatial resolution of the measured image, as will be discussed in detail further herein. 
     According to some embodiments of the present disclosure, the imager system is a wide field-of-view, narrowband optical system. Thus, the imager can capture images and detect light across a FOV of at least 10 degrees. In certain embodiments, the imager can capture images and detect light across a FOV of at least 20, and across a FOV of at least 30 degrees in some embodiments. Furthermore, the imager can detect light at a wavelength of approximately 10 nm or less. In some particular embodiments, the light sensing module can detect light at a wavelength of approximately 5 nm or less. In some embodiments, the imager system can capture detect light at a wavelength of less than 5 nm across a FOV of approximately 32 degrees. The FOV can be in the vertical or horizontal direction, or any other angle in between. 
     To better understand the function and configuration of passive and active optical imager systems according to embodiments of the disclosure, each will be discussed in detail herein. 
     I. Passive Optical Imager Systems 
     A passive optical imager system receives ambient light to generate an image.  FIG. 1  is a block diagram of an exemplary passive optical imager system  100 , according to some embodiments of the present disclosure. Passive optical imager system  100  includes a passive light capturing device  102  for capturing light existing within a field. Passive light capturing device  102  can include a system controller  104  and a light sensing module  106 . Imaging data can be generated by passive light capturing device  102  by receiving light existing in a field in which passive optical imager system  100  is positioned. The received light can be light that exists naturally in the field, i.e., ambient light, as opposed to light emitted from a transmitter within system  100 . 
     Light sensing module  106  can include a sensor array  108 , which can be, e.g., a one-dimensional or two-dimensional array of photosensors. Each photosensor (also just called a “sensor” or sometimes referred to by one skilled in the art as a “pixel”) can include a collection of photodetectors, e.g., SPADs or the like, or a sensor can be a single photon detector (e.g., an APD). Light sensing module  106  includes an optical sensing system  110 , which when taken together with sensor array  108  can form a light detection system  112 . In some embodiments, optical sensing system  110  can include a bulk receiver optic  114  and optical components  116 , such as an aperture layer, a collimating lens layer and an optical filter, that can be combined with sensor array  108  to form an array of micro-optic receiver channels where each micro-optic receiver channel measures light that corresponds to an image pixel in a distinct field of view of the surrounding field in which system  100  is positioned. Further details of various embodiments of micro-optic receiver channels according to the present disclosure are discussed in detail in conjunction with  FIGS. 17-30  below. 
     In some embodiments, sensor array  108  of light sensing module  106  is fabricated as part of a monolithic device on a single substrate (using, e.g., CMOS technology) that includes both an array of photosensors, a processor  118 , and a memory  120  for signal processing the measured light from the individual photosensors (or groups of photosensors) in the array. The monolithic structure including sensor array  108 , processor  118 , and memory  120  can be fabricated as a dedicated ASIC. In some embodiments, optical components  116  can also be a part of the monolithic structure in which sensor array  108 , processor  118 , and memory  120  are a part. In such instances, optical components  116  can be formed, e.g., bonded (non-reversibly) with epoxy, on the ASIC so that it becomes part of the monolithic structure, as will be discussed further below. As mentioned above, processor  118  (e.g., a digital signal processor (DSP), microcontroller, field programmable gate array (FPGA), and the like) and memory  120  (e.g., SRAM) can perform the signal processing. As an example of signal processing, for each photosensor or grouping of photosensors, memory  120  of light sensing module  106  can accumulate detected photons over time, and these detected photons can be used to recreate an image of the field. 
     In some embodiments, the output from processor  118  is sent to system controller  104  for further processing, e.g., the data can be encoded by one or more encoders of the system controller  104  and then sent as data packets to user interface  115 . System controller  104  can be realized in multiple ways including, e.g., by using a programmable logic device such an FPGA, as an ASIC or part of an ASIC, using a processor  122  with memory  124 , and some combination of the above. System controller  104  can cooperate with a stationary base controller or operate independently of the base controller (via pre-programed instructions) to control light sensing module  106  by sending commands that include start and stop light detection and adjust photodetector parameters. In some embodiments, system controller  104  has one or more wired interfaces or connectors for exchanging data with light sensing module  106 . In other embodiments, system controller  104  communicates with light sensing module  106  over a wireless interconnect such as an optical communication link. 
     Passive optical imager system  100  can interact with a user interface  115 , which can be any suitable user interface for enabling a user to interact with a computer system, e.g., a display, touch-screen, keyboard, mouse, and/or track pad for interfacing with a laptop, tablet, and/or handheld device computer system containing a CPU and memory. User interface  115  may be local to the object upon which passive optical imager system  100  is mounted but can also be a remotely operated system. For example, commands and data to/from passive optical imager system  100  can be routed through a cellular network (LTE, etc.), a personal area network (Bluetooth, Zigbee, etc.), a local area network (WiFi, IR, etc.), or a wide area network such as the Internet. 
     User interface  115  of hardware and software can present the imager data from the device to the user but can also allow a user to control passive optical imager system  100  with one or more commands. Example commands can include commands that activate or deactivate the imager system, specify photodetector exposure level, bias, sampling duration and other operational parameters (e.g., emitted pulse patterns and signal processing), specify light emitters parameters such as brightness. In addition, commands can allow the user to select the method for displaying results. The user interface can display imager system results which can include, e.g., a single frame snapshot image, a constantly updated video image, and/or a display of other light measurements for some or all pixels. 
     As mentioned herein, one or more components of optical sensing system  110  can be part of a monolithic structure with sensor array  108 , processor  118 , and memory  120 . For example, an aperture layer, collimating lens layer, and an optical filter layer of optical components  116  can be stacked over and bonded with epoxy to a semiconductor substrate having multiple ASICs fabricated thereon at the wafer level before or after dicing. For instance, the optical filter layer can be a thin wafer that is placed against the photosensor layer and then bonded to the photosensor layer to bond the optical filter layer with the photosensor layer to have the optical layer form part of the monolithic structure; the collimating lens layer can be injection molded onto the optical filter layer; and, the aperture layer can be formed by layering a non-transparent substrate on top of a transparent substrate or by coating a transparent substrate with an opaque film. Alternatively, the photosensor layer can be fabricated and diced, and the optical filter layer, collimating lens layer, and the aperture layer can be fabricated and diced. Each diced photosensor layer and optical layers can then be bonded together to form a monolithic structure where each monolithic structure includes the photosensor layer, optical filter layer, collimating lens layer, and the aperture layer. By bonding the layers to the ASIC, the ASIC and the bonded layers can form a monolithic structure. The wafer can then be diced into devices, where each device can be paired with a respective bulk receiver optic  114  to form light sensing module  106 . In yet other embodiments, one or more components of light sensing module  106  can be external to the monolithic structure. For example, the aperture layer may be implemented as a separate metal sheet with pin-holes. A more detailed view of an optical sensing system and a sensor array according to an embodiment of the disclosure is discussed herein with respect to  FIG. 2 . 
       FIG. 2  is a simplified diagram of an exemplary light detection system  200  according to some embodiments of the present disclosure. Light detection system  200  can be representative of light detection system  112  discussed above with respect to  FIG. 1 . Light detection system  200  can include an optical sensing system and a sensor array. The optical sensing system can include bulk receiver optics, an aperture layer, a collimating lens layer, and an optical filter layer; and the sensor array can include an array of photosensors, where each photosensor can include one or more photodetectors for measuring light. According to some embodiments, these components operate together to receive light from a field. For instance, light detection system  200  can include a bulk receiver optic  202  and a micro-optic receiver (Rx) layer  204 . During operation, light rays  206  enter bulk receiver optic  202  from multiple directions and gets focused by bulk receiver optic  202  to form light cones  208 . Micro-optic receiver layer  204  is positioned so that apertures  210  coincide with the focal plane of bulk receiver optic  202 . In some embodiments, micro-optic receiver layer  204  can be a one-dimensional or two-dimensional array of micro-optic receiver channels  212 , where each micro-optic receiver channel  212  is formed of a respective aperture  210 , collimating lens  214 , and photosensor  216  positioned along the same axis in the direction of light flow, e.g., horizontal from left to right as shown in  FIG. 2 . Furthermore, each micro-optic receiver channel  212  can be configured various ways to mitigate interference from stray light between photosensors, as will be discussed further herein. During operation, each micro-optic receiver channel  212  measures light information for a different pixel (i.e., position in the field). 
     At the focal point of bulk receiver optic  202 , light rays  206  focus and pass through apertures  210  in an aperture layer  211  and into respective collimating lenses  214 . Each collimating lens  214  collimates the received light so that the light rays all enter the optical filter at approximately the same angle, e.g., parallel to one another. The aperture and focal length of bulk receiver optic  202  determine the cone angle of respective light rays that come to a focus at aperture  210 . The aperture size and the focal length of collimating lenses  214  determine how well-collimated the admitted rays can be, which determines how narrow of a bandpass can be implemented in optical filter  218 . Apertures  210  can serve various functions during the operation of light detection system  200 . For instance, apertures  210  can (1) constrain the pixel FOV so it has tight spatial selectivity despite a large pitch at the photosensor plane, (2) provide a small point-like source at the collimating lens&#39;s focal plane to achieve tight collimation of rays before passing through the filter, where better collimation results in a tighter band that can pass through the filter, and (3) reject stray light. 
     Optical filter  218  blocks unwanted wavelengths of light. Interference-based filters tend to exhibit strong angle dependence in their performance. For example, a 1 nm wide bandpass filter with a center wavelength (CWL) of 900 nm at a zero-degree angle of incidence might have a CWL of 898 nm at a fifteen-degree angle of incidence. Imaging systems typically use filters several tens of nanometers wide to accommodate this effect, so that the shift in CWL is much smaller than the bandpass width. However, the use of micro-optic layer  204  allows all rays to enter optical filter  218  at approximately the same angle of incidence, thus minimizing the shift in CWL and allowing very tight filters (e.g. less than 10 nm wide) to be used. Photosensor  216  generates electrical currents or voltages in response to incident photons. In some embodiments, optical filter  218  is uniform across the entire array of micro-optic receiver channels  212  so that each individual micro-optic receiver channel  212  in the array receives the same range of wavelengths of light. 
     In some embodiments, photosensors  216  are positioned on a side opposite of collimating lenses  214  so that light rays  206  first pass through collimating lenses  214  and optical filter  218  before exposing on photosensors  216 . Each photosensor  216  can be a plurality of photodetectors, such as a mini-array of multiple single-photon avalanche detectors (SPADs). An array of mini-arrays of SPADs can be fabricated on a single monolithic chip, thereby simplifying fabrication. In some alternative embodiments, each photosensor  216  can be a single photodetector, e.g., a standard photodiode, an avalanche photodiode, a resonant cavity photodiode, or another type of photodetector. 
     In some other embodiments, optical filter  218  is non-uniform. For example, a graduated filter allows different micro-optic channels to measure a different range of wavelengths. In other words, a graduated filter allows different micro-optic channels in an array of micro-optic channels to have different center wavelengths (CWL). A graduated filter typically gradually changes the range of allowed wavelengths in either one or two dimensions. However, a graduated filter could also encompass a filter where the range of allowed wavelengths changes rapidly (e.g., step-wise) in one or both dimensions. The different CWLs for the channels can be created in various ways. For instance, the thickness of the filter can change or the index of refraction can change. The index of refraction can be changed by modifying the filter layer, such as by altering its chemical composition, e.g., by modifying it to have a non-uniform doping concentration. As a result, each channel (or row/column of channels) can have an optical filter layer that has a different doping concentration, thereby resulting in a different CWL for each channel (or row/column of channels) without having a modified thickness. Rotating a one-dimensional array of micro-optic channels with a graduated optical filter allows the system to measure light at different wavelengths for each photosensor. Scanning a two-dimensional array of micro optic channels where the graduated filter is changing along the direction of the scan allows the passive optic imager system to measure light at multiple wavelengths for each position in space, but uses multiple photodetectors in the photosensor to do so. Such optical systems using graduated filters require synchronization of the photosensor sampling so that different wavelength measurements are taken for the same photosensor with the same field-of-view. Imaging systems that differentiate between many different wavelengths are sometimes referred to as hyperspectral imagers. A hyperspectral imager often requires that light from the wavelengths of interest all be focused in approximately the same plane. This can be achieved by using an achromatic, apochromatic, superachromatic, or similar lens that is designed to limit the effects of chromatic aberration. 
     Hyperspectral imagers collect information from multiple wavelength bands across the electromagnetic spectrum. The absolute or relative intensities of the wavelength bands can provide information about chemical concentrations. For example, chlorophyll content of certain crops can be estimated using only a few wavelength bands. Similar techniques can be used to find valuable minerals or identify toxins. Spectral information can also be used to assist in the classification of pedestrians, automobiles, and other objects similarly encountered in an automotive environment. 
     A graduated neutral-density filter has a transmission that varies spatially across the filter, but the transmission is largely independent of wavelength (e.g. just as transmissive to red light as to blue light) at any given location. In a scanning imaging system, a graduated neutral-density filter can be used to image the same point in space with varying degrees of attenuation, thereby enabling a composite measurement with higher dynamic range than would achievable with a non-graduated filter. A better understanding of a micro-optic receiver layer with graduated filter can be achieved with reference to  FIGS. 3A and 3B . 
       FIGS. 3A and 3B  are perspective views of a simplified diagram of different embodiments of micro-optic receiver layers with graduated filter layers, according to some embodiments of the present disclosure. Specifically,  FIG. 3A  is a perspective view of a simplified diagram of a micro-optic receiver layer  300  with a graduated filter layer  302 , and  FIG. 3B  is a perspective view of a simplified diagram of a micro-optic receiver layer  301  with a graduated filter layer  312 . As illustrated in  FIGS. 3A and 3B , micro-optic receiver layer  300  and  301  each includes four micro-optic receiver channels  304 ,  306 ,  308  and  310  arranged in two dimensions as a 2×2 array. Although  FIGS. 3A and 3B  illustrate embodiments having only 2×2 arrays, one skilled in the art understands that such embodiments are not limiting and that other embodiments can be configured to have any number of micro-optic receiver channels. It is to be appreciated that in these diagrams, the thicknesses of filter layers  302  and  312  and the thicknesses of the surrounding layers, which are not drawn to scale, should be interpreted as the thicknesses of layers of refractive material in an interference filter. As these thicknesses change, the characteristics (e.g. passband CWL) of the interference filter change. These embodiments can be used in a hyperspectral passive optic imager system. 
     As shown in  FIGS. 3A and 3B , graduated filter layer  302  has gradually increasing thickness in one dimension across multiple columns of micro-optic receiver channels, and graduated filter layer  312  has a step-wise-increasing thickness in one dimension that has a constant thickness for each micro-optic receiver channel. Micro-optic receiver channels  304  and  308  have the same filter thickness and detect the same wavelength of light. Micro-optic receiver channels  306  and  310  have the same filter thickness and detect the same wavelength of light. Micro-optic receiver channels  304  and  308  can have a different filter thickness than micro-optic receiver channels  306  and  310  and thus detect a different wavelength of light. During a first-time interval, the micro-optic receiver channels  304  and  308  measure the intensity of a first wavelength of light for two pixels respectively. In some embodiments, the hyperspectral passive optic imager system moves or rotates the micro-optic receiver layer so that during a second-time interval, micro-optic receiver channels  306  and  310  measure the intensity of a second wavelength of light for the same two pixels respectively. In other embodiments, a hyperspectral passive optic imager system according to the disclosure can include a stationary micro-optic receiver layer and scan a moving target. 
     II. Active Optical Imager Systems 
     As discussed herein, optical imager systems can also be configured as active optical imager systems. Active optical imager systems can differ from passive optical imager systems in that active optical imager systems emit their own light into a field and detect the emitted light after it has reflected off surface(s) of an object in the field. In some embodiments, active optical imager systems can be utilized as LIDAR devices where emitted and received, reflected light can be correlated to determine a distance to the object from which the emitted light was reflected. A better understanding of an active optical imager system can be ascertained with reference to  FIG. 4 . 
       FIG. 4  illustrates a block diagram of a LIDAR system  400  according to some embodiments of the present disclosure. LIDAR system  400  can include a light ranging device  402  and a user interface  415 . Light ranging device  402  can include a ranging system controller  404 , a light transmission (Tx) module  406  and a light sensing (Rx) module  408 . Ranging data can be generated by light ranging device  402  by transmitting one or more light pulses  410  from the light transmission module  406  to objects in a field of view surrounding light ranging device  402 . Reflected portions  412  of the transmitted light are then detected by light sensing module  408  after some delay time. Based on the delay time, the distance to the reflecting surface can be determined. Other ranging methods can be employed as well, e.g. continuous wave, Doppler, and the like. 
     Tx module  406  includes an emitter array  414 , which can be a one-dimensional or two-dimensional array of emitters, and a Tx optical system  416 , which when taken together with emitter array  414  can form a light emission system  438 . Tx optical system  416  can include a bulk transmitter optic that is image-space telecentric. In some embodiments, Tx optical system  416  can further include one or more micro-optic structures that increase the brightness of beams emanating from the bulk transmitter optic as discussed herein with respect to  FIGS. 11-14  and/or for beam shaping, beam steering or the like. Emitter array  414  or the individual emitters can be laser sources. Tx module  406  can further include an optional processor  418  and memory  420 , although in some embodiments these computing resources can be incorporated into ranging system controller  404 . In some embodiments, a pulse coding technique can be used, e.g., Barker codes and the like. In such cases, memory  420  can store pulse-codes that indicate when light should be transmitted. In some embodiments, the pulse-codes are stored as a sequence of integers stored in memory. 
     Light sensing module  408  can be substantially similar in construction to light sensing module  106  discussed herein with respect to  FIG. 1 . Thus, details of processor  422 , memory  424 , sensor array  426 , and Rx optical system  428  (when taken together with sensor array  426  can form a light detection system  436 ) can be referenced herein with respect to  FIG. 1 , and only differences with respect to those components are discussed herein for brevity. For LIDAR system  400 , each photosensor sensor (e.g., a collection of SPADs) of sensor array  426  can correspond to a particular emitter of emitter array  414 , e.g., as a result of a geometrical configuration of light sensing module  408  and Tx module  406 . For example, in some embodiments, emitter array  414  can be arranged along the focal plane of the bulk transmitter optic such that each illuminating beam projected from the bulk transmitter optic into the field ahead of the system is substantially the same size and geometry as the field of view of a corresponding receiver channel at any distance from the system beyond an initial threshold distance. 
     In some embodiments, processor  418  can perform signal processing of the raw histograms from the individual photon detectors (or groups of detectors) in the array. As an example of signal processing, for each photon detector or grouping of photon detectors, memory  424  (e.g., SRAM) can accumulate counts of detected photons over successive time bins, and these time bins taken together can be used to recreate a time series of the reflected light pulse (i.e., a count of photons vs. time). This time-series of aggregated photon counts is referred to herein as an intensity histogram (or just histogram). Processor  418  can implement matched filters and peak detection processing to identify return signals in time. In addition, Processor  418  can accomplish certain signal processing techniques (e.g., by processor  422 ), such as multi-profile matched filtering to help recover a photon time series that is less susceptible to pulse shape distortion that can occur due to SPAD saturation and quenching. In some embodiments, all or parts of such filtering can be performed by processor  458 , which may be embodied in an FPGA. 
     In some embodiments, the photon time series output from processor  418  are sent to ranging system controller  404  for further processing, e.g., the data can be encoded by one or more encoders of ranging system controller  404  and then sent as data packets to user interface  415 . Ranging system controller  404  can be realized in multiple ways including, e.g., by using a programmable logic device such an FPGA, as an ASIC or part of an ASIC, using a processor  430  with memory  432 , and some combination of the above. Ranging system controller  404  can cooperate with a stationary base controller or operate independently of the base controller (via pre-programed instructions) to control light sensing module  408  by sending commands that include start and stop light detection and adjust photodetector parameters. Similarly, ranging system controller  404  can control light transmission module  406  by sending commands, or relaying commands from the base controller, that include start and stop light emission controls and controls that can adjust other light-emitter parameters (e.g., pulse codes). In some embodiments, ranging system controller  404  has one or more wired interfaces or connectors for exchanging data with light sensing module  408  and with light transmission module  406 . In other embodiments, ranging system controller  404  communicates with light sensing module  408  and light transmission module  406  over a wireless interconnect such as an optical communication link. 
     Light ranging device  402  can be used in both stationary and a scanning architectures. Electric motor  434  is an optional component in LIDAR system  400  that can be used to rotate system components, e.g., the Tx module  406  and Rx module  408 , as part of a scanning LIDAR architecture. The system controller  404  can control the electric motor  434  and can start rotation, stop rotation and vary the rotation speed as needed to implement a scanning LIDAR system. Exemplary stationary LIDAR devices are discussed below with respect to  FIGS. 5A and 5B , while exemplary scanning LIDAR devices are discussed further herein with respect to  FIGS. 6A, 6B, and 7 . 
     LIDAR system  400  can interact with one or more instantiations of a user interface  415 . The different instantiations can vary and can include, but not be limited to, a computer system with a monitor, keyboard, mouse, CPU and memory; a touch-screen in an automobile or other vehicle; a handheld device with a touch-screen; or any other appropriate user interface. User interface  415  can be local to the object upon which LIDAR system  400  is mounted but can also be a remotely operated system. For example, commands and data to/from LIDAR system  400  can be routed through a cellular network (LTE, etc.), a personal area network (Bluetooth, Zigbee, etc.), a local area network (WiFi, IR, etc.), or a wide area network such as the Internet. 
     User interface  415  of hardware and software can present the LIDAR data from the device to the user or to a vehicle control unit (not shown) but can also allow a user to control LIDAR system  400  with one or more commands. Example commands can include commands that activate or deactivate the LIDAR system, specify photodetector exposure level, bias, sampling duration and other operational parameters (e.g., emitted pulse patterns and signal processing), specify light emitters parameters such as brightness. In addition, commands can allow the user to select the method for displaying results. The user interface can display LIDAR system results which can include, e.g., a single frame snapshot image, a constantly updated video image, and/or a display of other light measurements for some or all pixels. In some embodiments, user interface  415  can track distances (proximity) of objects from the vehicle, and potentially provide alerts to a driver or provide such tracking information for analytics of a driver&#39;s performance. 
     In some embodiments, for example where LIDAR system  400  is used for vehicle navigation, user interface  415  can be a part of a vehicle control unit that receives output from, and otherwise communicates with light ranging device  402  and/or user interface  415  through a network, such as one of the wired or wireless networks described above. One or more parameters associated with control of a vehicle can be modified by the vehicle control unit based on the received LIDAR data. For example, in a fully autonomous vehicle, LIDAR system  400  can provide a real time 3D image of the environment surrounding the car to aid in navigation in conjunction with GPS and other data. In other cases, LIDAR system  400  can be employed as part of an advanced driver-assistance system (ADAS) or as part of a safety system that, e.g., can provide 3D image data to any number of different systems, e.g., adaptive cruise control, automatic parking, driver drowsiness monitoring, blind spot monitoring, collision avoidance systems, etc. When user interface  415  is implemented as part of a vehicle control unit, alerts can be provided to a driver or tracking of a proximity of an object can be tracked. 
     A. Solid State Architecture 
     LIDAR systems, according to some embodiments of the present disclosure, can be configured as a solid state LIDAR system that has a stationary architecture. Such LIDAR systems do not rotate, and thus do not need a separate motor, e.g., electric motor  434  in  FIG. 4 , to rotate the sensor and transmitter modules. Example solid state LIDAR systems are shown in  FIGS. 5A and 5B . 
       FIGS. 5A and 5B  are simple illustrations of exemplary implementations of solid state LIDAR systems. Specifically,  FIG. 5A  illustrates an implementation  500  where solid state LIDAR systems  502   a - d  are implemented at the outer regions of a road vehicle  505 , such as an automobile, according to some embodiments of the present disclosure; and  FIG. 5B  illustrates an implementation  501  where solid state LIDAR systems  504   a - b  are implemented on top of road vehicle  505 , according to some embodiments of the present disclosure. In each implementation, the number of LIDAR systems, the placement of the LIDAR systems, and the fields of view of each LIDAR system can be chosen to obtain a majority of, if not the entirety of, a 360 degree field of view of the environment surrounding the vehicle. Automotive implementations for the LIDAR systems are chosen herein merely for the sake of illustration and the sensors described herein may be employed in other types of vehicles, e.g., boats, aircraft, trains, etc., as well as in a variety of other applications where 3D depth images are useful, such as medical imaging, mobile phones, augmented reality, geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. 
     With reference to  FIG. 5A , solid state LIDAR systems  502   a - d  can be mounted at the outer regions of a vehicle, near the front and back fenders. LIDAR systems  502   a - d  can each be positioned at a respective corner of vehicle  505  so that they are positioned near the outermost corners of vehicle  505 . That way, LIDAR systems  502   a - d  can better measure the distance of vehicle  505  from objects in the field at areas  506   a - d . Each solid state LIDAR system can face a different direction (possibly with partially and/or non-overlapping fields of views between units) so as to capture a composite field of view that is larger than each unit is capable of capturing on its own. Objects within the scene can reflect portions of light pulses  510  that are emitted from LIDAR Tx module  508 . One or more reflected portions  512  of light pulses  510  then travel back to LIDAR system  502   a  and can be received by Rx module  509 . Rx module  509  can be disposed in the same housing as Tx module  508 . 
     Although  FIG. 5A  illustrates four solid state LIDAR systems mounted at the four corners of a vehicle, embodiments are not limited to such configurations. Other embodiments can have fewer or more solid state LIDAR systems mounted on other regions of a vehicle. For instance, LIDAR systems can be mounted on a roof of a vehicle  505 , as shown in  FIG. 5B . In such embodiments, LIDAR systems can have a higher vantage point to better observe areas  506   a - d  around vehicle  505 . 
     B. Scanning Architecture 
     In some embodiments, LIDAR systems according to the present disclosure can employ a scanning architecture in which the LIDAR system oscillates between an angle that is less than 360 degrees. For instance, LIDAR systems  504   a - b  in implementation  501  of  FIG. 5B  can each employ a scanning architecture to scan the entire scene in front of, and/or behind, vehicle  505 , e.g., in area  514  between field of view  506   a  and  506   b  and in area  516  between field of view  506   c  and  506   d . The output beam(s) of one or more light sources (not shown, but can be a variety of different suitable sources for emitting radiation including, but not limited to lasers, in any wavelength spectrum suitable for LIDAR systems, such as in the infrared, near-infrared, ultraviolet, visible, e.g., green laser wavelength spectrum, and the like) located in the scanning LIDAR systems, can be outputted as pulses of light and scanned, e.g., rotated between an angle that is less than 360 degrees, to illuminate a scene around the vehicle. In some embodiments, the scanning, represented by rotation arrows  514  and  516 , can be implemented by mechanical means, e.g., by mounting the light emitters to a rotating column or platform or through the use of other mechanical means, such as galvanometers. Chip-based beam steering techniques can also be employed, e.g., by using microchips that employ one or more MEMS based reflectors, e.g., such as a digital micromirror (DMD) device, a digital light processing (DLP) device, and the like. In some embodiments, the scanning can be effectuated through non-mechanical means, e.g., by using electronic signals to steer one or more optical phased arrays. 
     Other embodiments can implement a scanning architecture that scans through the entire 360 degrees of the environment surrounding a vehicle. Such scanning LIDAR systems can repetitively rotate continuously through 360 degrees in a clockwise or counter-clockwise direction, and thus may utilize a separate motor, e.g., electric motor  434  in  FIG. 4 , to rotate the sensor and transmitter modules. Exemplary rotating LIDAR systems are shown in  FIGS. 6A and 6B . 
       FIG. 6A  is a top-down view of a simplified diagram of an exemplary scanning LIDAR system  600  implemented for a vehicle  605 , such as a car, and capable of continuous 360 degree scanning, according to some embodiments of the present disclosure. The output beam(s) of one or more light sources (such as infrared or near-infrared pulsed IR lasers, not shown) located in LIDAR system  600 , can be scanned, e.g., rotated, to illuminate a continuous scene  620  around the vehicle. In some embodiments, the scanning, represented by rotation arrow  615 , can be implemented by any suitable mechanical means discussed herein with respect to  FIG. 5B , e.g., by mounting the light emitters to a rotating column or platform, or any other mechanical means, such as through the use of galvanometers or chip-based steering techniques. During operation, objects around vehicle  605  in any direction and within the view of LIDAR system  600  can reflect portions of light pulses  611  that are emitted from a transmitting module  608  in LIDAR system  600 . One or more reflected portions  617  of light pulses  611  then travel back to LIDAR system  600  and can be detected by its sensing module  609 . In some instances, sensing module  609  can be disposed in the same housing as transmitting module  608 . 
     Although  FIG. 6A  illustrates solid state LIDAR systems mounted on a roof of a vehicle  605 , embodiments are not limited to such configurations. Other embodiments can have solid state LIDAR systems mounted on other regions of a vehicle. For instance, LIDAR systems can be mounted at the corners of a vehicle, as shown in  FIG. 6B .  FIG. 6B  illustrates an implementation  601  where solid state LIDAR systems  604   a - d  are implemented at the outer regions of a road vehicle, such as a car, according to some embodiments of the present disclosure. In this implementation, each LIDAR system  604   a - d  can be a spinning LIDAR system that can measure distances around the full 360 degrees. However, since at least some of those measurements will be measured with respect to vehicle  605 , those measurements can be ignored. Thus, each LIDAR system  605   a - d  can only utilize a subset of the measurements from 360 degree scanning, e.g., only the angles covering regions  619   a - d  that do not capture vehicle  605  are utilized. 
       FIG. 7  is a simplified exemplary perspective view of a LIDAR system  700  that employs a 360 scanning architecture, according to some embodiments of the present disclosure. In some embodiments, LIDAR system  700  can include a light ranging device  701  that spins in a clockwise or counter-clockwise direction to observe the surrounding field around a vehicle. System  700  can include a stationary housing  702 , an optically transparent window  704 , and a stationary lid  706  for providing protection for the internal components of LIDAR system  700 . Window  704  can extend fully around a periphery of stationary housing  702 , which can be configured to have a cylindrical shape. The internal components of system  700  can include light ranging device  701 , which can include a rotating platform  708  and sensing and transmitting modules  710  mounted on rotating platform  708 . In some embodiments, light ranging device  701  is aligned with window  704  such that modules  710  are positioned to emit and receive light through window  704 , and that emitted light is not emitted onto stationary housing  702  or stationary lid  706 . For instance, in the aligned positioned, the horizontal center of light ranging device  701  coincides with the horizontal center of window  704 . Sensing and transmitting modules  710  can be, for example, light sensing module  408  and light transmission module  406 , and can optionally include a heat sink (not shown) to cool the micro-optic layers. LIDAR system  700  can also include a system controller  712  (e.g., controller  404 ) and electric motor  714  (e.g., motor  434 ) that reside within stationary housing  702 . Electric motor  714  rotates platform  708 , thereby rotating sensing and transmitting modules  710  in a spinning manner, e.g., continuously through 360 degrees in a clockwise or counter-clockwise direction. System controller  712  can communicate with sensing and transmitting modules  710  using an optical communication link  716 . Optical communication link  716  allows sensing and transmitting modules  710  to communicate with stationary system controller  712 , which is mechanically coupled to stationary housing  702  and does not rotate with platform  708 , through optical communication link  716  without mechanical wear and tear. In some embodiments, system controller  712  can control the motor and to start and stop light detection operations of LIDAR system  700 . System controller  712  can include two or more stacked planar circuit boards arranged in a parallel relationship, which is discussed in more detail in commonly-owned and concurrently-filed Patent Application entitled “Compact Lidar System”, attorney docket number 103033-P010US1-1073278, which is herein incorporated by reference in its entirety for all purposes. 
     III. Operation of Active Imager Systems 
       FIG. 8  is an illustrative example of the light transmission and detection operation for a light ranging system according to some embodiments.  FIG. 8  shows a light ranging system  800  (e.g., solid state or and/or scanning system) collecting three-dimensional distance data of a volume or scene that surrounds the system.  FIG. 8  is an idealized drawing to highlight relationships between emitters and sensors, and thus other components are not shown. 
     Light ranging system  800  includes a light emitter array  810  and a light sensor array  820 . The light emitter array  810  includes an array of light emitters, e.g., an array of vertical-cavity surface-emitting lasers (VCSELs) and the like, such as emitter  812  and emitter  816 . Light sensor array  820  includes an array of photosensors, e.g., sensors  822  and  826 . The photosensors can be pixelated light sensors that employ, for each photosensor, a set of discrete photodetectors such as single photon avalanche diodes (SPADs) and the like. However, various embodiments can deploy other types of photon sensors. 
     Each emitter can be slightly offset from its neighbor and can be configured to transmit light pulses into a different field of view from its neighboring emitters, thereby illuminating a respective field of view associated with only that emitter. For example, emitter  812  emits an illuminating beam  814  (formed from one or more light pulses) into the circular field of view  832  (the size of which is exaggerated for the sake of clarity). Likewise, emitter  816  emits an illuminating beam  818  (also called an emitter channel) into the circular field of view  834 . While not shown in  FIG. 8  to avoid complication, each emitter emits a corresponding illuminating beam into its corresponding field of view resulting in a 2D array of fields of view being illuminated (21 distinct fields of view in this example). 
     Each field of view that is illuminated by an emitter can be thought of as a pixel or spot in the corresponding 3D image that is produced from the ranging data. Each emitter channel can be distinct to each emitter and be non-overlapping with other emitter channels, i.e., there is a one-to-one mapping between the set of emitters and the set of non-overlapping fields or view. Thus, in the example of  FIG. 8 , the system can sample 21 distinct points in the 3D space. A denser sampling of points can be achieved by having a denser array of emitters or by scanning angular position of the emitter beams over time such that one emitter can sample several points in space. As described above, scanning can be accomplished by rotating the entire emitter/sensor assembly. 
     Each sensor can be slightly offset from its neighbor and, like the emitters described above, each sensor can see a different field of view of the scene in front of the sensor. Furthermore, each sensor&#39;s field of view substantially coincides with, e.g., overlaps with and is the same size as a respective emitter channel&#39;s field of view. 
     In  FIG. 8 , the distance between corresponding emitter-receiver channels is exaggerated relative to the distance to objects in the field of view. In practice, the distance to the objects in the field of few is much greater than the distance between corresponding emitter-receiver channels and thus the path of light from the emitter to the object is approximately parallel to the path of the reflected light back from the object to the sensor (i.e., it is almost “back reflected”). Accordingly, there is a range of distances in front of the system  800  over which the fields of view of individual sensors and emitters are overlapped. 
     Because the fields of view of the emitters are overlapped with the fields of view of their respective sensors, each receiver channel ideally can detect the reflected illumination beam that originates from its respective emitter channel with ideally no cross-talk, i.e., no reflected light from other illuminating beams is detected. Thus, each photosensor can correspond to a respective light source. For example, emitter  812  emits an illuminating beam  814  into the circular field of view  832  and some of the illuminating beam reflects from the object  830 . Ideally, a reflected beam  824  is detected by sensor  822  only. Thus, emitter  812  and sensor  822  share the same field of view, e.g., field of view  832 , and form an emitter-sensor pair. Likewise, emitter  816  and sensor  826  form an emitter-sensor pair, sharing field of view  834 . While the emitter-sensor pairs are shown in  FIG. 8  as being in the same relative locations in their respective array, any emitter can be paired with any sensor depending on the design of the optics used in the system. 
     During a ranging measurement, the reflected light from the different fields of view distributed around the volume surrounding the LIDAR system is collected by the various sensors and processed, resulting in range information for any objects in each respective field of view. As described above, a time-of-flight technique can be used in which the light emitters emit precisely timed pulses, and the reflections of the pulses are detected by the respective sensors after some elapsed time. The elapsed time between emission and detection and the known speed of light is then used to compute the distance to the reflecting surface. In some embodiments, additional information can be obtained by the sensor to determine other properties of the reflecting surface in addition to the range. For example, the Doppler shift of a pulse can be measured by the sensor and used to compute the relative velocity between the sensor and the reflecting surface. The pulse strength can be used to estimate the target reflectivity, and the pulse shape can be used to determine if the target is a hard or diffuse material. 
     In some embodiments, the LIDAR system can be composed of a relatively large 2D array of emitter and receiver channels and operate as a solid state LIDAR, i.e., it can obtain frames of range data without the need to scan the orientation of the emitters and/or sensors. In other embodiments, the emitters and sensors can be scanned, e.g., rotated about an axis, to ensure that the fields of view of the sets of emitters and sensors sample a full 360 degree region (or some useful fraction of the 360 degree region) of the surrounding volume. The range data collected from the scanning system, e.g., over some predefined time period, can then be post-processed into one or more frames of data that can then be further processed into one or more depth images or 3D point clouds. The depth images and/or 3D point clouds can be further processed into map tiles for use in 3D mapping and navigation applications. 
     According to some embodiments, a light ranging system (also called a coded-pulse optical receiver system) can transmit multiple pulses of light. In some embodiments, each coded-pulse has an embedded positive-valued pulse-code formed by the light intensity. The system can determine the temporal position and/or amplitude of optical pulses in the presence of background light by creating an intensity histogram of detected, reflected light at different time bins. For each time bin, the system adds a weighted value to the intensity histogram that depends on the intensity of detected light. The weighted values can be positive or negative and have varying magnitudes. 
     By selecting different combinations of positive-valued pulse-codes and applying different weights, the system can detect positive-valued and negative-valued codes suitable for standard digital signal processing algorithms. This approach gives a high signal-to-noise ratio while maintaining a low uncertainty in the measured temporal position of the reflected light pulses. 
       FIG. 9  is a flowchart illustrating a method  900  of using coded pulses in an optical measurement system according to embodiments of the present disclosure. The optical measurement system may be a light ranging system. Method  900  can detect the temporal position of a reflected pulse from a target using multiple coded-pulses. In a real-time three-dimensional application, method  900  can constantly detect distances to objects in the surrounding environment. Method  900  may be implemented by any of the optical measurement systems described herein. 
     At  910 , a coded-pulse optical system (CPOS) performs an initialization. For example, the CPOS can respond to user interface commands for starting, stopping, and changing parameters. The CPOS can initialize an optical transmitter to indicate parameters, e.g., pulse-codes, light power level, and various time intervals (e.g., for a detection interval, an interval for pausing between detection intervals, and an overall measurement time interval). The CPOS can initialize a light sensing module to indicate parameters such as pulse-time-interval and light-sampling-interval. The CPOS can also clear histogram values. 
     At  920 , a pulse train is transmitted from a light source (e.g., a laser) as part of an optical measurement. The pulse train can be transmitted as part of N pulse trains transmitted for the measurement. The N pulse trains can reflect from an object, thereby allowing a ranging measurement to the object. Each of the N pulse trains can include one or more pulses from the light source (e.g., VCSELs) and correspond to a different time interval that is triggered by a start signal. 
     In some embodiments, the CPOS can wait for a specified time to allow a previous pulse train (coded-pulse transmission) to dissipate. The CPOS can then transmit a next pulse train of the N pulse trains of a measurement, where the N pulse trains form a code. Once a measurement is complete, e.g., a last of the N pulse train has dissipated (e.g., after a predetermined time expected for any reflections), the CPOS can then start the first/next coded-pulse transmission using the appropriate pulse-code. N can be an integer greater than one, e.g., 2, 3, 4, 5, or higher. 
     At  930 , optical detection can be started, e.g., in response to the start signal that triggers the pulse train to be transmitted. Thus, the CPOS can start light detection at the same time that it started coded-pulse transmission. As part of the optical detection, a pulse train can be detected by a photosensor (e.g., corresponding to a pixel) of the optical measurement system, thereby generating data values at a plurality of time points. In some embodiments, the photosensor is a collection of photodetectors (e.g., SPADs). The data values may be of various forms, e.g., counts of a number of SPADs that triggered at a time point (e.g., within a time bin of a histogram). As other examples, the data values can be a digitized value from an ADC that follows an analog photosensor (e.g., an APD). Both examples can correspond to an intensity. In total, N pulse trains can be detected. Further, the process can be performed separately for each photosensor of the optical measurement device. 
     At  940 , a weight is assigned to the data values at time points within the time interval corresponding to the pulse train, thereby obtaining weighted values. A weight can be assigned for each of the N pulse trains. Some of such weights for different pulse trains can be the same as other pulse trains. In some embodiments, at least two of the N pulse trains are assigned different weights and have a different pulse pattern. Two pulse trains can have some similarity (e.g., portions of pulses can overlap), but there is at least some times where one pulse train is ON and the other pulse train is OFF. Such different pulse patterns can have a similar shape but have a different delay, e.g., {1, 0, 1, 1, 0} has a similar shape of non-zero values to {0, 1, 0, 1, 1}, but they are different pulse patterns due to an offset as may be achieved by a delay in the second signal relative to the first signal. 
     Accordingly, the CPOS can detect light and create a digitized intensity value for each light-sampling-interval. For each light-sampling-interval, the CPOS can apply a pulse-weight to the digitized intensity value and add the result to the appropriate time-bin of the intensity histogram. 
     At  950 , the CPOS tests if it has sent the required number of coded-pulses. If the CPOS has sent the required number of coded-pulses it continues at block  960 , otherwise it loops back to block  920 . 
     At  960 , a histogram corresponding to the weighted values in a plurality of time bins is determined. As described above, a counter of the histogram at a particular time bin can be determined by accumulating the weighted values at time points within the particular time bin across a plurality of time intervals. 
     At  970 , the histogram is used to detect a signal corresponding to the N pulse trains. For example, the CPOS can determine whether the histogram has a sequence of values that match the match-code (filter). The CPOS can report whether the match-code was found and the amplitude of the match. The match may allow detection of the desired signal relative to noise or interference from other light sources. 
     As an example, a filter can include a set of values to be applied to a window of time bins of a histogram. The filter can be slid over the histogram to calculate a filtered histogram having counters corresponding to different sliding positions of the profile filter relative to the histogram. Each of the counters of the filtered histogram can correspond to an overlap of the profile filter and the histogram at a particular sliding position. A maximum value of the counters of the filtered histogram can be identified, thereby allowing detection, e.g., when the maximum value is above a threshold. The particular sliding position for the maximum value of the counters can correspond to the received time, which may be used for ranging measurements. 
     In some embodiments, the signal may be a reflected signal caused by the N pulse trains reflecting from an object, e.g., when the optical measurement system is configured to perform ranging measurements. In other embodiments, the signal may be a communication signal, e.g., when the light source is at one location and the photosensors are at a different location. Such a configuration can be used for communication purposes. For example, a microwave transmission tower can transmit data to a receiving tower. The transmitted data can include coded pulses, which may help to reduce errors in data reception as may be caused by noise or interference from other sources. The receiving tower can identify pulse trains and create a histogram by selecting an arbitrary time between two pulse trains as a start time for a first time bin. A match filter can then be applied (e.g., by sliding over the histogram); and if a sufficient match is found, then that communication signal can be detected. A sufficient match can be measured by the maximum value obtained the filtered histogram. As a further embodiment, the system can detect an interference signal from another CPOS in a similar manner used to detect the communication signal. If interference is measured, some implementations can change the transmitted code, e.g., of the interference code is similar to the code currently being used. 
     At  980 , a distance to the object can be determined. For example, a received time corresponding to the N pulse trains relative to the start signal can be determined. A distance to the object can be determined using the received time. The received time may be offset from the transmission times of the pulse trains, but such an offset can be taken into account. Accordingly, the CPOS can report the time at which it was detected. The distance can corresponds to a round trip time between the received time and a start time of the start signal, and thus the distance may be expressed in time. 
     The detected signal can be used for other purposes than ranging. For example, the quality of the detected signal can be used to measure the reflectivity of an object. For example, if the detected signal has a strong intensity, then the system can determine that the object has a high reflectivity. Implementations for communications and interference measurements are discussed above. For detection of interference from another light source, the detected signal would be from another set of pulse trains transmitted by the interfering light source. 
     As a generalization, embodiments can transmit N+1 unique codes with N+1 unique weights to generate an N dimensional vector space histogram. For example, instead of a bin holding a signed number, the bin can hold a 1-D vector (e.g., equivalent to a signed number), by transmitting at least two unique codes: one positive and one negative. To store a 2-D vector (e.g., in polar or Cartesian coordinates), the system can transmit at least three unique codes, which could be weighted with three different polar angles and sum to a single 2-D vector. An N-D vector (defined with N separate numbers all held within a single “bin”) would require N+1 different codes, each weighted at a different angle (in other worlds having a component to its weight that is orthogonal to all other weights) when doing the vector summation. By increasing the dimensionality, more advanced coding techniques like quadrature phase coding or code division multiple access (CDMA) that are used in RF communications may be used. An N-dimensional matched filter can be used in this context. 
     As a LIDAR system implements method  900  during its operation, the LIDAR system can continuously measure distances to objects in the field. Accordingly, once the distance to an object is determined, method  900  can loop back to block  920  to begin another series of emitting pulse trains and detecting the emitted pulse trains to determine a histogram for determining a distance to an object in the field. Distances may need to be constantly measured by method  900  because the LIDAR system may need to be constantly measuring distances to objects in the field, such as when the LIDAR system is used for navigational purposes and the LIDAR system is moving within the field. 
     In some embodiments, after determining the distance to the object at block  980 , method  900  can determine whether an exit command has been received by CPOS at block  990 . If an exit command has been received, then method  900  can stop measuring distances at block  999 , otherwise method  900  can continue measuring distances to objects by looping back to block  920 . 
     As mentioned above, method  900  can be used to reduce interference among channels. For example, method  900  can be repeated for a plurality of channels of light sources and photosensors as part of a plurality of optical measurements. The plurality of optical measurements can overlap in time, e.g., performed substantially simultaneously. Thus, each channel can perform a measurement at the same time. To reduce interference, the codes can be different for at least some of the channels. For example, the pulse patterns of the N pulse trains of at least two channels of the plurality of channels can be different, thereby causing different histogram patterns for different channels. In addition or instead, the weights assigned to the N pulse trains of at least two channels of the plurality of channels can be different, thereby causing different histogram patterns for different channels. 
     IV. Construction of Active Imager Systems 
       FIG. 10  is a simplified diagram illustrating a detailed view of an exemplary active optical imager system  1000  having a wide field-of-view and capable of narrowband imaging, according to some embodiments of the present disclosure. Active optical imager system  1000  can employ solid state or scanning architectures as aforementioned herein. In some embodiments, active optical imager system  1000  can include a light detection system  1001  and a light emission system  1002 , which is unlike passive optical imager systems. Light emission system  1002  provides active illumination of at least a portion of a field in which system  1000  is positioned with narrowband light rays  1004 . Light detection system  1001  detects the narrowband light emitted from the light emission system  1002  after it has been reflected by objects in the field as reflected light rays  1006 . Light detection system  1001  can be substantially similar to light detection system  200  discussed herein with respect to  FIG. 2 . Thus, details of bulk receiver optic  1008 , light cone  1010 , micro-optic receiver channel  1012  in micro-optic receiver layer  1014 , and photodetectors  1016  can be referenced herein with respect to  FIG. 2 , and are not discussed herein for brevity. 
     In some embodiments, light emission system  1002  includes a bulk transmitter optic  1018  and a light emitting layer  1020  formed of a one- or two-dimensional array of light emitters  1022 . Each light emitter  1022  can be configured to generate discrete beams of narrowband light. In some embodiments, light emitting layer  1020  is configured to selectively project the discrete beams of light through bulk transmitter optic  1018  according to an illumination pattern that matches, in size and geometry across a range of distances from light emission system  1002 , the fields of view of the receiver channels in micro-optic receiver channel array  1014 . Light emitters  1022  can be any suitable light emitting device, such as a vertical-cavity surface-emitting lasers (VCSELS) integrated on one or more monolithic chip, or any other type of laser diode. Light emitters  1022  can produce cones of narrowband light  1024  that are directed to bulk transmitter optic  1018 , which can collimate cones of light  1024  and then output the collimated light to distant targets in the field as emitted light rays  1004 . In some embodiments, bulk transmitter optic  1018  is image-space telecentric. 
     In additional and alternative embodiments, light rays  1004  from light cones  1024  are focused on an intermediate plane in space by a micro-optic transmitter layer (not shown) before being directed to distant targets by the bulk transmitter optic  1018  to enhance the brightness and intensity of light emitted from light emission system  1002 . In such embodiments, embodiments, light emission system  1002  and light detection system  1001  are configured such that each micro-optic transmitter channel (not shown) is paired with a corresponding micro-optic receiver channel  1012  and the centers of their fields-of-view are aligned to be overlapping at a certain distance from the sensor or their chief rays are made parallel. In further additional and alternative embodiments, the far-field beams of light emitted by light emission system  1002  are of similar size and divergence angle to the far-field fields-of-view of each micro-optic receiver channel  1012 . Details of light emission systems  1002  having the micro-optic transmitter layer for enhancing brightness and intensity of outputted light will be discussed in detail below. 
     As is evident from the illustration of parallel light rays  1004  and  1006  in  FIG. 10 , each micro-optic receiver channel  1012  has a non-overlapping field of view beyond a threshold distance. As shown in  FIG. 10 , each micro-optic receiver channel  1012  includes an aperture from the plurality of apertures, a lens from the plurality of lenses, and a photodetector from the plurality of photodetectors, where the aperture of each channel defines a discrete field of view for the pixel in the channel that is non-overlapping beyond a threshold distance within the fields of view of the other micro-optic receiver channels. That way, each micro-optic receiver channel receives reflected light corresponding to a discrete position in the field that is not measured by any other micro-optic receiver channel in micro-optic receiver channel layer  1014 . 
     A. Enhancing Brightness and Intensity of Transmitters in Active Imager Systems 
     Embodiments of the present disclosure pertain to a LIDAR sensor that can, among other uses, be used for obstacle detection and avoidance in autonomous vehicles. Some specific embodiments pertain to LIDAR sensors that include design features that enable the sensors to be manufactured cheaply enough and with sufficient reliability and to have a small enough footprint to be adopted for use in mass-market automobiles, trucks and other vehicles. For example, some embodiments include a set of vertical-cavity surface-emitting lasers (VCSELs) as illumination sources that emit radiation into a field and include arrays of single-photon avalanche diode (SPAD) detectors as a set of photosensors (detectors) that detect radiation reflected back from a surface in the field. Using VCSELs as the emitters and SPADs as the detectors enables multiple measurements to be taken at the same time (i.e., the VCSEL emitters can be fired simultaneously) and also enables the set of emitters and the set of photosensors to each be fabricated using standard CMOS processes on a single chip, greatly simplifying the manufacturing and assembly process. 
     Using VCSELs and SPADs in certain embodiments presents challenges, however, that various embodiments of the present disclosure overcome. For example, VCSELs are much less powerful than typical lasers used in existing LIDAR architectures and SPADs are much less efficient than the typical detectors used in the existing LIDAR architectures. To address these challenges, as well as challenges presented by firing multiple emitters simultaneously, certain embodiments of the disclosure include various optical components (e.g., lenses, filters, and an aperture layer), which may work in concert with multiple arrays of SPADs, each array corresponding to a different pixel (e.g., position in the field), as described herein. For example, as discussed herein with respect to  FIG. 2 , a light detection system  200  can include a micro-optic receiver layer  204  for enhancing the light detected by photosensors  216 , e.g., SPADs. 
     Because VCSELs are less powerful than typical lasers in existing LIDAR architectures, in some embodiments, light emission system  1002  can be configured to improve the ability of imager system  1000  to perform light ranging functionality. That is, the quality of light emitted by light emission system  1002  can be enhanced to improve light ranging accuracy and efficiency. The quality of transmitted light for light ranging and imaging purposes can be defined in terms of brightness and intensity. The brightness and intensity of light rays  1004  emitted from bulk transmitter optic  1018  can be enhanced by modifying and/or implementing one or more optic transmitter layers, as will be discussed further herein. 
     Brightness of a transmitting light can be defined by the optical power (in watts) per solid angle. Thus, light sources that output light with tight collimation, i.e., low divergence, produce light that are high in brightness. Conversely, light sources that output light with high divergence produce light that are low in brightness. Intensity of light can be defined by the optical power per area, meaning light emitted with a certain power will have higher intensity if it tightly compacted in a small area. Accordingly, light sources that output light in a tightly compacted ray will have higher intensity than light sources that output light in a less compacted ray, even if both light sources output light that has low divergence. As will be appreciated herein, transmitter components for LIDAR systems in embodiments of the present disclosure can be configured with micro-optical components that enable the transmitter to output light that has enhanced brightness and intensity as compared to a similar transmitter without the micro-optical components. 
       FIG. 11  is a simplified cross-sectional view diagram of a first exemplary enhanced light emission system  1100 , according to some embodiments of the present disclosure. Light emission system  1100  can include a light emitter array  1102  having light emitters  1104  that for example may comprise without limitation any of LEDs, laser diodes, VCSELs, or the like for emitting light  1113 . A VCSEL is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface. Note that the linear array shown in  FIG. 11  can be any geometric form of emitter array, including and without limitation circular, rectangular, linear, or any other geometric shape. 
     Enhanced light emission system  1100  can include a micro-optic transmitter channel array  1106  separated from light emitter array  1102  by an open space  1118 . Each micro-optic transmitter channel  1108  is paired with a corresponding receiver channel (e.g., receiver channel  1012  in  FIG. 10 ) and the centers of their fields-of-view are aligned to be overlapping at a certain distance from the optical imager system. Micro-optic transmitter channel array  1106  can be formed of a substrate  1119  sandwiched between a first optical surface  1120  positioned on a side facing light emitter array  1102  and a second optical surface  1121  positioned on an opposite side facing away from light emitter array  1102 . Both first and second optical surfaces  1120  and  1121  can each be configured as an array of convex, micro-optic lenses where each convex lens of first optical surface  1120  is configured to be optically aligned with a respective convex lenses of second optical surface  1120  so that light transmitting through first optical surface  1120  can subsequently be transmitted through second optical surface  1121 . The corresponding convex lenses from first and second optical surfaces  1120  and  1121  can face away from one another as shown in  FIG. 11 . In certain embodiments, convex lenses of first optical surface  1120  have a first optical power and convex lenses of second optical surface  1121  have a second optical power different from the first optical power. For instance, the second optical power can be greater than the first optical power such that the focal length of the second optical power is shorter than the focal length of the first optical power. Substrate  1119  can be formed of any suitable material that is transmissive in the wavelength range of the light emitters  1104  such silicon, silicon dioxide, borosilicate glass, polymer, and the like. First and second optical surfaces  1120  and  1121  can be formed of a transparent polymer that is imprinted on respective opposite surfaces of substrate  1119 . 
     In some embodiments, micro-optic transmitter channel array  1106  can be formed of a monolithic array of micro-optic transmitter channels  1108 . Each micro-optic transmitter channel  1108  can include a first convex lens from first optical surface  1120 , a corresponding second convex lens from second optical surface  1121 , and a corresponding portion of substrate  1119  positioned between the two convex lenses. Each micro-optic transmitter channel  1108  can correspond with a respective light emitter  1104  so that light outputted from the light emitter  1104  first passes through the first convex lens, through the corresponding region of substrate  1119 , and then through the second convex lens during operation. 
     Once light emits out of the second convex lens of second optical surface  1121 , the light forms a miniature spot image  1110  that is a real image of the corresponding light emitter  1104  but a reduced-size of the corresponding light emitter  1104 . In some embodiments, miniature spot images  1110  are positioned between micro-optic transmitter channel array  1106  and bulk transmitter optic  1114 . For instance, miniature spot images  1110  can be formed within respective apertures of an aperture layer  1109 . Each aperture can be a pin hole in a reflective or opaque layer in which emitted light focuses to form miniature spot images  1110 . From there, continuing away from both the light emitter and micro optic channel, the light forms a light cone  1112  reaching out towards bulk transmitter optic  1114 . 
     According to some embodiments of the present disclosure, the degree of divergence of emitted light  1113  can be smaller than the degree of divergence of light cone  1112 . This discrepancy in divergence can be created by a micro-optic transmitter channel  1108 , specifically by the optical power of second optical surface  1121 . Because the divergence of light out of micro-optic transmitter channel  1108  is larger than the divergence of emitted light  1113  from light emitters  1104 , miniature spot image  1110  can be a real image of light emitter  1104  but a multitude smaller than the size of light emitter  1104  and with the same number of photons as emitted light  1113 . The resulting light cone  1112  formed after the real spot images are formed then gets projected into the field as discrete beams of light for each light emitter  1104  after passing through bulk transmitter optic  1114 . The resulting light rays emanating out of light emission system  1100  are highly collimated beams of light that have a small cross-sectional area (smaller than the surface area of light emitter  1104 ), thereby resulting in a light emission system  1100  that can output light having enhanced brightness and intensity. 
     Note that bulk transmitter optic  1114  can include either a single lens or a cluster of lenses where two or more lenses function together to form bulk transmitter optic  1114 . The use of multiple lenses within the bulk transmitter optic  1114  could increase the numerical aperture, reduce the RMS spot size, flatten the image plane, improve the telocentricity, or otherwise improve the performance of bulk transmitter optic  1114 . Note also that for some embodiments, light cones  1112  may overlap forming cone overlap region  1116 . 
     To better understand the operation and effectiveness of micro-optic transmitter channel array  1106 , a more detailed explanation of the operation of light emission system  1100  is discussed. For enhanced light emission systems  1100  utilizing a light emitter array formed of VCSEL emitters, an exemplary initial radius for an emitter might be 12.5 um with light admitted in a 100 half angle cone. Such emitters would typically output 50 uW per square micron of active area. A diverging light cone from each emitter  1104  is accepted into a micro-optic transmitter channel  1108 , and then a converging light cone is output by that same micro optic channel to produce a converging light cone with a half angle of for example 20°. Thus for some embodiments, the cone angle produced by an emitter  1104  is smaller than the cone angle produced by a corresponding micro-optic transmitter channel  1108 . The converging light cone emanated by micro-optic transmitter channel  1108  then produces a miniature spot image  1110  of the emitter. For the embodiment according to  FIG. 11 , miniature spot image  1110  is a real image and has a size that is smaller than the size of a corresponding light emitter  1104 . Note that all rays from a given emitter may not all be focused into an arbitrarily small spot. The miniature spot image size is typically controlled by an “optical invariant”: 
       Θ s*r _ s &gt;=Θ_ e*r _ e  
 
     where Θ_s is the marginal ray half angle of the focused spot, r_s is the radius of the focused spot, Θ_e is the marginal ray half angle of the original emitter, and r_e is the radius of the original emitter. So, in this example, the smallest miniature spot image radius that could be formed (while still capturing all the rays from the emitter) is: 
       10/20*12.5 um=6.25 um 
     Note that this smaller spot will have one fourth the area of the original emitter, and thus has a power density of 200 uW per square micron of spot area. Each micro-optic transmitter channel  1108  typically has one or more optical surfaces, having characteristics that may for example and without limitation include a focal length of 50 um, and a lens diameter of 80 um. For some embodiments, the distance between light emitter  1104  and a corresponding micro-optic transmitter channel  1108  may be for example and without limitation 150 um. Open space  1118  between emitter array  1102  and micro-optic transmitter channel array  1106  as shown in  FIG. 11  may be, for example and without limitation an air gap such as that produced by methods typically used to manufacture MEMS devices. The distance between emitter array  1102  and micro-optic transmitter channel array  1106  for example may be 150 um. 
     Bulk transmitter optic  1114  is positioned in front of the micro-optic and emitting layers such that the focal plane of the bulk imaging optic coincides with miniaturized spot images  1110 . Bulk transmitter optic  1114  accepts divergent light cone(s)  1112  and outputs a collimated beam. Its numeric aperture can be at least large enough to capture the full range of angles in the divergent ray cone(s), so for example and without limitation the Numerical Aperture (NA)=0.34 in this example. Also, bulk transmitter optic  1114  can be image-space telecentric, since light cone(s)  1112  exiting the micro-optic layer may all be parallel (rather than having their center axes aimed towards the center of the bulk optic). In one embodiment, light can exit bulk transmitter optic  1114  approximately collimated. Note that the quality of beam collimation relates to the size of the “emitting object” (miniature spot images  1110 ) at the focal plane. Since this “emitting object” size has been reduced by using a micro-optic stack, a better collimation angle is obtained than if the emitter object was simply imaged directly. 
     Although  FIG. 11  shows an enhanced light emission system having a micro-optic channel array formed of a substrate sandwiched between first and second optical surfaces, and positioned a distance away from a light emitter array by an open space to improve the brightness and intensity of light outputted by the light emission system, embodiments are not limited to such configurations. Rather, other embodiments may not necessarily implement an open space or two optical surfaces, as discussed further herein with respect to  FIG. 12 . 
       FIG. 12  is a simplified cross-sectional view diagram of a second exemplary enhanced light emission system  1200 , according to some embodiments of the present disclosure. Similar to first exemplary enhanced light emission system  1100 , second exemplary enhanced light emission system  1200  can include bulk imaging optic  1214  and light emitter array  1202 . However, unlike first exemplary light emission system  1100 , second exemplary light emission system  1200  can include a micro-optic transmitter channel array  1206  that is positioned directly upon an emission surface of light emitter array  1202  instead of being separated by an open space/air gap, as shown in  FIG. 12 . 
     In such embodiments, micro-optic transmitter channel array  1206  can be formed of a substrate  1219  and an optical surface  1220 . Optical surface  1220  can be positioned on a first surface  1230  of substrate  1219 . Second surface  1231  of substrate  1219  can be located opposite of first surface  1230  and positioned against light emitter array  1202  so that light emitted from emitters  1204  can first pass through substrate  1219  before passing through optical surface  1220 . Optical surface  1220  can be configured as an array of convex lenses where each convex lens of optical surface  1220  is configured to be optically aligned with a respective light emitter  1204  so that light outputted by the respective light emitter  1204  can transmit through the respective convex lens of optical surface  1220 . Convex lenses from optical surface  1220  can face away from their respective light emitters  1204  as shown in  FIG. 12  so that their focal points are positioned further from light emitter  1204 . In certain embodiments, convex lenses of optical surface  1220  have an optical power suitable for converging the emitted light into real miniature spot images  1210  that are real images of corresponding light emitters  1204  but reduced-size images of the corresponding light emitters  1204  like the convex lenses of second optical surface  1121  in  FIG. 11 . Optical surface  1120  enables the emitted light to diverge into light cones  1212  before projecting through bulk imaging optic  1214 . Substrate  1219  and optical surface  1220  can be formed of similar materials as substrate  1119  and optical surfaces  1120  and  1121  discussed herein with respect to  FIG. 11 . In some embodiments, light cones  1212  may overlap forming cone overlap region  1216 . 
     Embodiments herein can also implement micro-optic channel arrays that do not include convex lenses and that do not generate real images of the light emitters. Rather, some embodiments may implement concave surfaces to generate virtual images of the light emitters, as discussed further herein with respect to  FIG. 13 . 
       FIG. 13  is a simplified cross-sectional view diagram of a third exemplary enhanced light emission system  1300 , according to some embodiments of the present disclosure. Similar to first and second exemplary enhanced light emission systems  1100  and  1200 , third exemplary enhanced light emission system  1300  can include bulk imaging optic  1314  and light emitter array  1302 . However, unlike first and second exemplary light emission systems  1100  and  1200 , third exemplary light emission system  1300  can include a micro-optic transmitter channel array  1306  that includes an array of concave surfaces instead of an array of convex lenses, as shown in  FIG. 13 . 
     In such embodiments, micro-optic transmitter channel array  1306  can be formed of a substrate  1319  and an optical surface  1320 . Optical surface  1320  can be a first surface  1330  of substrate  1319  positioned toward bulk imaging optic  1314  and away from light emitters  1304 . Second surface  1331  of substrate  1319  can be located opposite of first surface  1330  and positioned against light emitter array  1302  so that light emitted from emitters  1304  can first pass through substrate  1319  before passing through optical surface  1320 . Optical surface  1320  can each be configured as an array of concave surfaces where each concave surface of optical surface  1320  is configured to be optically aligned with a respective light emitter  1304  so that light outputted by the respective light emitter  1304  can transmit through the respective concave surface of optical surface  1320 . In certain embodiments, the concave surfaces of optical surface  1320  have an optical power suitable for forming virtual miniature spot images  1310  that are virtual images of corresponding light emitters  1304  but reduced-size images of the corresponding light emitters  1304 , and further enable the emitted light to diverge into light cones  1312  before projecting through bulk imaging optic  1314 . In some embodiments, virtual miniature spot images  1310  are formed within substrate  1319  as shown in  FIG. 13 . In some embodiments, light cones  1312  may overlap forming cone overlap region  1316 . Substrate  1319  can be formed of similar materials as substrate  1119  discussed herein with respect to  FIG. 11 . 
     Note that the lens configurations for the micro-optic channels for embodiments described in each of  FIGS. 11, 12 and 13  differs with respect to how many surfaces have optical power and the shapes of those surfaces. The first embodiment shown in  FIG. 11  benefits from the ability to use two optical power surfaces on opposite sides of a substrate, which could allow each surface to be shallower, spherical rather than aspherical, or otherwise more easily manufactured. This embodiment includes a spacer structure (not shown) to maintain an offset between the micro-optic channel array  1106  and the light emitter array  1102 . An example of such a spacer structure would be a silicon wafer with channels formed via deep reactive ion etching. The second embodiment shown in  FIG. 12  benefits from having only one optical power surface on a substrate that is attached to the light emitter array. This type of configuration simplifies fabrication while also achieving enhanced brightness and intensity. The third embodiment shown in  FIG. 13  shares the benefits of the embodiment shown in  FIG. 12  but has a single optical surface that is formed of concave surfaces rather than convex lenses; concave features can often be easier to fabricate at the micro-scale. 
     In some embodiments, bulk imaging optics for light emission systems can include one or more aperture stops to reduce stray light emitted by the system. For instance,  FIG. 14  is a simplified cross-sectional view diagram of an exemplary enhanced light emission system  1400  configured with bulk optics that have aperture stops, according to some embodiments of the present disclosure.  FIG. 14  is substantially similar to  FIG. 1  with the addition of aperture stop variants  1403 ,  1405 , and  1406  for bulk transmitter optic  1414 . Aperture stop(s) shown in  FIG. 14  can be used with any of  FIGS. 11 through 13 . In  FIG. 14 , aperture stops  1403 ,  1405 , and  1407 , can have circular or oval openings for light to pass through, although any opening shape may be utilized without deviating from the spirit and scope of the present disclosure. 
     In some embodiments, aperture stop  1403  can be located on a side of bulk transmitter optic  1414  facing away from light emitter array  1402  and micro-optic transmitter channel array  1406 . In some additional and alternative embodiments, aperture stop  1405  can be located on a side of bulk transmitter optic  1414  facing toward light emitter array  1402  and micro-optic transmitter channel array  1406 . In yet some additional and alternative embodiments where bulk receiver optic  114  includes a plurality of lenses working together, aperture stop  1407  can be formed of one or more aperture stops placed within the plurality of lenses that form bulk transmitter optic  1414 . 
     The various configurations and locations of aperture stops  1403 ,  1405 , and  1407  can dictate the way each aperture stop functions in the light emitting system. For example, if all the light cones  1412  are compressed to be substantially overlapping near the location of aperture stop  1407 , then the size of the aperture stop  1407  would be able control both the initial diameter of the emitted collimated beams as well as reject the marginal rays emitted by light emitters  1404 . Rejecting certain ray angles could effectively narrow the spectrum of light emitted out of the bulk optic, since the wavelength of light emitted by many types of lasers varies with angle. Alternatively, perhaps this best location for the aperture stop would occur at  1402  or  1403 , depending upon the design of the bulk transmitter optic  1414 . Multiple aperture stops may be used simultaneously—e.g.  1402 ,  1403 , and  1404  all in one bulk transmitter optic  1414 —to reduce stray light emitted by light emitting system  1400 . 
     B. Optical Corrections for Astigmatism 
     As mentioned herein with respect to  FIG. 7 , light detection systems and light emission systems can be enclosed within the same protective structure, e.g., stationary housing  702 , optically transparent window  704 , and stationary lid  706  in  FIG. 7 . Light emitted from the light emission system, in some embodiments, exits out of transparent window  704 , and light detected by light detection system may first enter into transparent window  704 . The curvature of transparent window  704  can induce some optical aberrations, such as astigmatism. Because the transparent window can have a cylindrical structure and be well-controlled, it can be corrected with one or more additional optical structures. In some embodiments, light emission and/or detection systems can be configured with corrective optical structures to compensate for the astigmatism caused by the transparent window, as discussed further herein. 
       FIGS. 15A-15C  are cross-sectional views of simplified diagrams of exemplary active imager systems having different implementations of corrective optical structures for astigmatism, according to some embodiments of the present disclosure. Specifically,  FIG. 15A  is a simplified cross-sectional view diagram of an active imager system  1500  having a corrective optical structure as part of the bulk imaging optic,  FIG. 15B  is a simplified cross-sectional view diagram of an active imager system  1501  having a corrective optical structure as part of the micro-optic receiver channel array, and  FIG. 15C  is a simplified cross-sectional view diagram of an active imager system  1502  having a corrective optical structure as part of the micro-optic transmitter channel array. Active imager systems  1500 ,  1501 , and  1502  each include a light detection system  1504  and a light emission system  1506 . Components of active imager systems  1500 ,  1501 , and  1502  are substantially similar to active optical imager system  1000  in  FIG. 10  with the addition of the corrective optical structures. Thus, the components that are shared with active optical imager system  1000  are not discussed for brevity. 
     As shown in  FIG. 15A , active imager system  1500  can be housed within an enclosure containing a transparent window  1508 . Transparent window  1508  is at least transparent to the wavelength of light at which emitters  1510  operate. The curved shape of transparent window  1508  can induce an optical aberration, such as an astigmatism, in light rays  1511  emitted from light emission system  1506  when light rays  1511  exit the enclosure through transparent window  1508 . Light rays  1512  then enter back into the enclosure through transparent window  1508  after reflecting off of an object in the field, which can induce an additional optical aberration to the received light rays. To correct for these optical aberrations, light detection system  1504  can include corrective bulk imaging optic  1514  specifically designed to compensate for the expected astigmatism induced by transparent window  1508 . For example, corrective bulk imaging optic  1514  can include a corrective lens  1516  in addition to bulk receiver optic  1518 . Corrective lens  1516  can be any suitable lens capable of negating the astigmatism caused by transparent window  1508 , such as a cylindrical lens. Corrective lens  1516  can be positioned between transparent window  1508  and bulk receiver optic  1518  in some embodiments, or between bulk receiver optic  1518  and micro-optical receiver channel array  1505  in some other embodiments. Similarly, a corrective bulk optic could be included in the bulk transmitter optic of the light emission system  1506 . 
     Instead of incorporating the corrective optics into the bulk imaging optics, the corrective optics can be implemented into a micro-optical receiver channel array in some embodiments. For instance, with reference to  FIG. 15B , light detection system  1504  can include a corrective lens array  1520  in front of apertures  1522 , e.g., on the opposite side of apertures  1522  from where photosensors  1526  are positioned. That way, light cones  1524  can propagate through respective corrective lenses to compensate for astigmatism caused by transparent window  1508  before projecting on photosensors  1526 . In some embodiments, corrective lens array  1520  is formed of an array of cylindrical lenses that can negate the astigmatism caused by transparent window  1508 . Each corrective lens of corrective lens array  1520  can be positioned in alignment with a respective aperture  1522  so that corrective lens array  1520  can negate the astigmatism caused by transparent window  1508  for light received by each photosensor  1526 . 
     Although  FIGS. 15A and 15B  illustrate ways in which a light detection system portion of a LIDAR system can be modified to correct for astigmatism caused by transparent window  1508 , embodiments are not limited to such configurations and corrective optics can be implemented in light emission systems as well. For example, with reference to  FIG. 15C , active imager system  1502  can include a corrective lens array  1528  in front of aperture layer  1530 , e.g., on the opposite side of aperture layer  1530  from where light emitters  1510  are positioned. That way, light emitted from light emitters  1510  can propagate through respective corrective lenses  1528  before emitting to bulk transmitter optics  1534 . In this case, respective corrective lenses  1528  can induce a corrective degree of astigmatism in the emitted light in anticipation of, and to compensate for, the astigmatism caused by transparent window  1508  as light is emitted out of light emission system  1506 . In some embodiments, corrective lens array  1528  is formed of an array of biconical lenses that can induce an equal but opposite degree of astigmatism caused by transparent window  1508 . Thus, the amount of astigmatism induced by corrective lens layer  1528  can be offset by the degree of astigmatism caused by transparent window  1508 , thereby effectively achieving little to no net astigmatism during operation of active imager system  1502 . Each corrective lens of corrective lens array  1528  can be positioned in alignment with a respective aperture  1532  so that corrective lens array  1528  can induce a corrective degree of astigmatism to negate the astigmatism caused by transparent window  1508  for light received by each photosensor  1526 . In some embodiments, corrective lens array  1528  may not be needed. Instead, optical surface  1536  can be an array of biconical lenses instead of an array of cylindrical lenses. The biconical structure of the lenses can induce an amount of astigmatism to offset the degree of astigmatism caused by transparent window  1508 . In these embodiments, corrective lens array  1528  may not be implemented in light emission system  1506 . Furthermore, in some embodiments, instead of (or in conjunction with) a corrective micro-optic lens array, a corrective bulk cylindrical lens can be implemented with bulk receiver optic  1534  (similar to the embodiment shown in  FIG. 15A  for light detection system  1504 ). Thus, light emission system  1506  can include a corrective bulk imaging optic in front of its bulk receiver optic  1534  to negate the astigmatism caused by transparent window  1508 . 
     V. Mitigating Receiver Channel Cross-Talk 
     As can be appreciated by disclosures herein, channels in the micro-optic receiver and are positioned very close to one another, often times within microns of one another. This small spacing between each channel can invite the opportunity for problems to arise. For instance, light propagating through bulk imaging optic can occasionally cause stray light to bleed into neighboring channels, thereby resulting in inaccurate readings of reflected light for each pixel in the field. Ideally, no stray light should be received by any channel, as shown in  FIG. 16A . 
       FIG. 16A  is a simplified cross-sectional view diagram of part of a light detection system  1600  where there is no cross-talk between channels. During operation, perpendicular light rays  1602  and chief ray  1604  enter the bulk imaging optic  1606  and produce light cone  1608 . Light rays  1602  and  1604  enter an aperture of aperture layer  1610  and enter collimating lens  1611 . Collimating lens  1611  accepts a limited range of incident light angles. For example, collimating lens  1611  can accept light rays at incident angles between +25 to −25 degrees relative to the perpendicular.  FIG. 16A  shows light cone  1608  with incident angles between +25 to −25 degrees. The chief ray  1604  is the light ray that passes through the center of the aperture. In this example, the chief ray  1604  has an incident angle of 0 degrees on the collimating lens  1611 . 
       FIG. 16B  is a simplified cross-sectional view diagram of part of a light detection system  1601  where there is cross-talk between channels. In this case, during operation, oblique light rays  1612  and chief ray  1614  enter bulk receiver optic  1616  and later enter collimating lens  1621 . In this example, collimating lens  1621  belongs to a micro-optic channel that corresponds to a photosensor further from the center of the image. In this example, chief ray  1614  has an incident angle of −12 degrees and the cone of focused light has incident angles between +12 degrees to −35 degrees. Collimating lens  1621  rejects some of the light rays because it only accepts light with incident angles between +25 to −25 degrees. Additionally, the rays that are outside of the collimating lens acceptance cone can travel to other optical surfaces and become stray light. Thus, a non-telecentric bulk imaging optic will deliver significantly fewer signal photons to the photodetector, while potentially polluting other channels with errant light rays  1622 . A telecentric bulk imaging optic, on the other hand, will produce light cones with incident angles approximately between +25 to −25 degrees and chief rays with incident angles on the collimating lens of approximately 0 degrees, regardless of the angle of the oblique rays  1612  and chief ray  1614 . A telecentric bulk imaging optic has similar benefits for the transmitter when the lasers are telecentric (their chief rays are all parallel) as is the case for VCSELS or a side emitter diode laser bar. 
     In some embodiments, the light detection system of a light sensing module uses an input image-space telecentric bulk imaging optic. In some other embodiments, for example where cost or increased field of view is more important than performance, the light detection system may use a more standard input bulk imaging optic such as a bi-convex lens. For any given input field into an image-space telecentric lens, the resulting chief rays are parallel to the optical axis, and the image-side ray cones all span approximately the same set of angles. This allows micro-optic channels far from the optical axis in the light detection system to achieve similar performance to the on-axis micro-optic channel. The light detection system does not need perfect image space telecentricity for this to work, but the closer to perfect telecentricity the better. For a micro-optic receiver optical layer lens that can only accept +/−25 degree light, the preference is that the input bulk imaging optic produce image-side rays that are no greater than 25 degrees in angle for every point on the focal plane. 
     In certain embodiments, specific light detection systems having wide field of view and narrowband imaging can have an input image-space telecentric bulk imaging optic with a numerical aperture (NA) equal to 0.34 and focal length of 20 mm. Similarly, some other embodiments could have a 1 nm wide bandpass filter, thereby enabling it to detect light of a very specific wavelength. The light detection system is capable of supporting FOVs greater than 30 degrees. 
     According to some embodiments of the present disclosure, the design of each channel of the micro-optic receiver channel array can be specifically configured to have features that minimize the intrusion of stray light onto a respective photodetector, thereby reducing or eliminating any detrimental effects caused by the occurrence of stray light.  FIG. 17  is a simplified cross-sectional diagram of an exemplary micro-optic receiver channel structure  1700 , also called a micro-optic receiver channel in discussions herein. Receiver channel  1700  can be representative of micro-optic receiver channels  232  and  1032 , among others, shown in  FIGS. 2 and 10 , respectively, and serves to accept an input cone of light containing a wide range of wavelengths, filters out all but a narrow band of those wavelengths centered at the operating wavelength, and allows photosensor  1771  to detect only or substantially only photons within the aforementioned narrow band of wavelengths. According to some embodiments of the present disclosure, micro-optic receiver channel structures, such as receiver channel  1700 , can include the following layers:
         An input aperture layer  1740  including an optically transparent aperture  1744  and optically non-transparent stop region  1746  configured to define a narrow field of view when placed at the focal plane of an imaging optic such as bulk receiver optic  202  or  1008  (shown in  FIGS. 2 and 10 , respectively; not shown in  FIG. 17 ). Aperture layer  1740  is configured to receive the input marginal ray lines  1733 . The term “optically transparent” herein refers to as allowing most or all light to pass through. Light herein refers to spectrum of light in the near-ultraviolet, visible, and near-infrared range (e.g. 300 nm to 5000 nm). Optically non-transparent herein refers to as allowing little to no light to pass through, but rather absorbing or reflecting the light. Aperture layer  1740  can include optically transparent apertures separated from each other by optically non-transparent stop regions. The apertures and stop regions can be built upon a single monolithic piece such as an optically transparent substrate. Aperture layer  1740  can optionally include a one-dimensional or two-dimensional array of apertures  1744 .   An optical lens layer  1750  including a collimating lens  1751  characterized by a focal length, offset from the plane of aperture  1744  and stop region  1746  by the focal length, aligned axially with aperture  1744 , and configured to collimate photons passed by the aperture such that they are traveling approximately parallel to the axis of collimating lens  1751  which is aligned with the optical axis of receiver channel  1700 . Optical lens layer  1750  may optionally include apertures, optically non-transparent regions and tube structures to reduce cross talk.   An optical filter layer  1760  including an optical filter  1761 , typically a Bragg reflector type filter, adjacent to collimating lens  1751  and opposite of aperture  1744 . Optical filter layer  1760  can be configured to pass normally incident photons at a specific operating wavelength and passband. Optical filter layer  1760  may contain any number of optical filters  1761 . Optical filter layer  1760  may optionally include apertures, optically non-transparent regions and tube structures to reduce cross talk.   A photosensor layer  1770  including a photosensor  1771  adjacent to optical filter layer  1760  and configured to detect photons incident on photosensor  1771 . Photosensor  1771  herein refers to a single photodetector capable of detecting photons, e.g., an avalanche photodiode, a SPAD (Single Photon Avalanche Detector), RCP (Resonant Cavity Photo-diodes), and the like, or several photodetectors, such as an array of SPADs, cooperating together to act as a single photosensor, often with higher dynamic range, lower dark count rate, or other beneficial properties as compared to a single large photon detection area. Each photodetector can be an active area that is capable of sensing photons, i.e., light. Photosensor layer  1770  refers to a layer made of photodetector(s) and contains optional structures to improve detection efficiency and reduce cross talk with neighboring receiver structures. Photosensor layer  1770  may optionally include diffusers, converging lenses, apertures, optically non-transparent tube spacer structures, optically non-transparent conical spacer structures, etc.       

     Stray light may be caused by roughness of optical surfaces, imperfections in transparent media, back reflections, and the like, and may be generated at many features within the receiver channel  1700  or external to receiver channel  1700 . The stray light may be directed: through the filter region  1761  along a path non-parallel to the optical axis of collimating lens  1751 ; reflecting between aperture  1744  and collimating lens  1751 ; and generally taking any other path or trajectory possibly containing many reflections and refractions. If multiple receiver channels are arrayed adjacent to one another, this stray light in one receiver channel may be absorbed by a photosensor in another channel, thereby contaminating the timing, phase, or other information inherent to photons. Accordingly, receiver channel  1700  may feature several structures to reduce crosstalk between receiver channels. 
     As will be understood further herein, each layer of a micro-optic channel layer structure can be designed a specific way to mitigate the detrimental effects of stray light. Various different designs for each layer will now be discussed in further detail below. 
     A. Aperture Layer 
     In an embodiment having aperture layer  1740 , as shown in  FIG. 17 , optically transparent aperture  1744  and optically non-transparent stop region  1746  can be formed from a single monolithic piece, such as a metal foil with a pinhole or from a single layer of a deposited opaque or reflective material having apertures etched therethrough. 
       FIG. 18A  is a simplified cross-sectional view diagram of a different embodiment  1800  where aperture layer  1840  has two apertures  1844 . Both the optically transparent apertures  1844  and corresponding optically non-transparent optical stop regions  1846  are supported on an optically transparent substrate  1845 . Bottom aperture  1844  can be smaller and be positioned at the focal plane of the bulk optic. Aperture layer  1840  can be followed by optically transparent spacer structure  1856  positioned between aperture  1844  and collimating lens  1851  in the receiver channel. Optically transparent spacer structure  1856  forms a tube of substantially similar or larger diameter to collimating lens  1851 . 
       FIG. 18B  is a simplified cross-sectional view diagram of a different embodiment  1801  of aperture layer  1840 . Optically transparent aperture  1844  and optically non-transparent stop region  1846  are supported on optically transparent substrate  1845 . Optically transparent spacer structure  1856  that follows aperture layer  1840  and positioned between aperture  1844  and collimating lens  1851  forms a tube of substantially similar or larger diameter to collimating lens  1851 . 
       FIG. 18C  is a simplified cross-sectional view diagram of an embodiment  1802  of aperture layer  1840  consisting of multiple optically non-transparent stop regions  1846  that are supported on optically transparent substrate  1845 . These layers (stop regions  1846 ) follow the contour of marginal light rays (not shown, but similar to light rays  1733  in  FIG. 17 ) to reduce stray light into the receiver channel. Optically transparent spacer structure  1856  below aperture layer  1840  forms a tube of substantially similar or larger diameter to collimating lens  1851 . 
       FIG. 18D  is a simplified cross-sectional view diagram of an embodiment  1803  of aperture layer  1840  having multiple optically non-transparent stop layers  1846  supported on multiple optically transparent substrate  1845 . Aperture layer  1840  follows the contour of marginal light rays (not shown, but similar to light rays  1733  in  FIG. 17 ) to reduce stray light into the receiver channel. Optically transparent spacer structure  1856  below aperture layer  1840  forms a tube of substantially similar or larger diameter to collimating lens  1851 . 
     In some other embodiments of the present disclosure, spacer structure  1856  shown in  FIGS. 18A-D , can be optically non-transparent. The optically non-transparent spacer structure in this instance could be formed by etching a silicon or glass wafer and may be coated with an optically non-transparent material (e.g. black chrome). Additionally, the spacer structure in this instance would prevent any light in the spacer region from traveling outside the receiver channel. 
     B. Spacer Structure Between Aperture Layer and Optical Lens Layer 
       FIG. 19A  is a simplified cross-sectional view diagram of an embodiment  1900  of the present disclosure with an optically non-transparent spacer structure between the aperture layer and the lens layer.  FIG. 19A  depicts an optically non-transparent spacer structure  1956  positioned between aperture  1944  and collimating lens  1951  in the receiver channel. Optically non-transparent spacer structure  1956  forms a tube of substantially similar or larger diameter to collimating lens  1951  and prevents any light from traveling outside the receiver channel in the region between aperture  1944  and collimating lens  1951 . Optically non-transparent spacer structure  1956  could be formed by etching a silicon or glass wafer and may be coated with an optically non-transparent material (e.g. black chrome). Alternatively, optically non-transparent spacer structure  1956  could be a solid non-transparent structure that is fabricated from molded polymer or any other suitable method.  FIG. 19A  shows the aperture layer having optically transparent substrate  1945  on the top, followed by the optically non-transparent stop region  1946  and aperture  1944 , and then by optically non-transparent spacer structure  1956 . 
       FIG. 19B  is a simplified cross-sectional view diagram of an embodiment  1901  of the present disclosure with an optically non-transparent structure between the aperture layer and the lens layer.  FIG. 1901  depicts an optically non-transparent spacer structure  1956  positioned between aperture  1944  and collimating lens  1951 . Optically non-transparent spacer structure  1956  forms a tube of substantially similar or larger diameter to collimating lens  1951  and prevents any light from traveling outside of the receiver channel in the region between aperture  1944  and collimating lens  1951 .  FIG. 19B  shows multiple optically non-transparent stop regions  1946  supported on optically transparent substrate  1945 . 
       FIG. 19C  is a simplified cross-sectional view diagram of an embodiment  1902  of aperture layer  1940  where aperture  1944  is conically aligned, and where the conical structure as an optically non-transparent layer coated on an optically transparent material. 
       FIG. 19D  is a simplified cross-sectional view diagram of an embodiment  1903  of aperture layer  1940  where the aperture  1944  is conically aligned, and where the conical structure is a solid structure formed of an optically non-transparent material. As shown in  FIGS. 19C and 19D  the optically transparent aperture  1944  and optically non-transparent stop region  1946  are combined into a monolithic layer with a conical cavity aligned with the optical axis of the receiver channel and configured to conform to the shape of marginal ray lines (not shown, but similar to light rays  1733  in  FIG. 17 ). 
     C. Optical Filter Layer 
       FIG. 20A  is a simplified cross-sectional view diagram of an embodiment  2000  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. 
     Optical filter layer  2060  can include a single optical filter  2061  supported on an optically transparent substrate  2065 . Optical filter layer  2060  can be placed on top of optically transparent substrate  2065  or below optically transparent substrate  2065 . Optical filter  2061  can be a bandpass filter that blocks incident light outside of a defined set of wavelengths (e.g. 945-950 nm). However, in some other embodiments, optical filter  2061  can be an edge pass filter or any other suitable type of filter that selectively allows light within a wavelength range to pass through itself. 
       FIG. 20B  is a simplified cross-sectional view diagram of an embodiment  2001  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can include two optical filters  2061  sandwiching and supported by an optically transparent substrate  2065 . Optical filter layer  2060  can contain any number of optical filters  2061  on any number of substrates  2065 . One of the optical filters  2061  as shown in  FIG. 20B  can be a bandpass filter and can be positioned on either on top of or directly below optically transparent substrate  2065  that blocks all of the incident light for a defined set of wavelengths (e.g. 900-945 nm and 950-995 nm). The other optical filter  2061  placed on the opposite side of the optical substrate  2065  can be a wide spectrum blocking filter (except for the region covered by the bandpass filter), for example covering 200-915 nm and 980-1600 nm. The bandpass filter and blocking filter are designed such that there is no leakage in the transition region between the two filters. However, the filters could be two edge pass filters designed to work in conjunction as a bandpass filter or any other types of filters. 
     In some other embodiments of the present disclosure, the bandpass filter and wide spectrum blocking filter are merged into a single optical filter  2061  and placed on either the top or bottom of optically clear substrate  2065 . 
     1. Filter Layer with Apertures 
       FIG. 20C  is a simplified cross-sectional view diagram of an embodiment  2002  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can have an additional aperture  2049  on top and an additional aperture  2054  on the bottom of optical filter layer  2060  along with the corresponding optically non-transparent stop regions  2063  &amp;  2055 . Aperture  2049  defines the maximal cylinder of light desired to be passed into optical filter layer  2060  by optical filter  2061 , and stop region  2063  an absorb or reflect any incident stray light outside the diameter of aperture  2049 . Aperture  2054  defines the maximal cylinder of light desired to be passed out of optical filter layer  2060  and stop region  2055  absorbs or reflects any incident stray light outside the diameter of aperture  2054 . Optical filters  2061  can be supported on an optically transparent substrate  2065 . 
     In some embodiments of the present disclosure, filter layer  2060  can have a single aperture  2049  placed on the top of the optical filter layer  2060 . In some additional and alternative embodiments of the present disclosure, filter layer  2060  can have a single aperture  2054  placed on the bottom of optical filter layer  2060 . 
       FIG. 20D  is a simplified cross-sectional view diagram of an embodiment  2003  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can include multiple optically transparent substrates  2065 , and multiple optically non-transparent aperture layers between them in an alternating order.  FIG. 20D  shows an additional aperture  2049  and corresponding optically non-transparent stop region  2063  positioned on top of optical filter  2061  and supported by optically transparent substrates  2065 . Aperture  2049  can define the maximal cylinder of light desired to be passed into optical filter layer  2060  by optical filter  2061 , and stop region  2063  absorbs or reflects any incident stray light outside diameter of aperture  2049 .  FIG. 20D  shows an additional aperture  2054  and corresponding optically non-transparent stop region  2055  positioned between optical filter layer  2060  and a photosensor layer (not shown, but similar to photosensor layer  1770  in  FIG. 17 ). Aperture  2054  can define the maximal cylinder of light desired to be passed out of optical filter layer  2060  toward the photosensor, and stop region  2055  can absorb or reflect any incident stray light outside the diameter of aperture  2054 . Collectively, these interleaved layers prevent stray light in one optical filter layer  2060  from traveling into an optical filter region of an adjacent receiver channel in a multi receiver channel system. 
     2. Filter Layer with Tube Structure 
       FIG. 20E  is a simplified cross-sectional view diagram of an embodiment  2004  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can include optical filter  2061  and optically transparent substrate  2065  and be surrounded by an optically non-transparent tube structure  2111 , which prevents stray light in one optical filter layer  2060  from traveling into an optical filter region of an adjacent receiver channel in a multi receiver channel system. Tube structure  2111  can be formed of a variety of materials, including but not limited to silicon, metals, polymers, or glasses. 
       FIG. 20F  is a simplified cross-sectional view diagram of an embodiment  2005  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can include optical filter  2061  and optically transparent substrate  2065  and is surrounded by an optically non-transparent tube structure  2111 , which prevents stray light in one optical filter layer  2060  from traveling into an optical filter region of an adjacent receiver channel in a multi receiver channel system. Tube structure  2111  can be formed of a variety of materials, including but not limited to silicon, metals, polymers, or glasses. As shown in  FIG. 20F , tube structure  2111  may only pass partially through optical filter layer  2060 . This type of structure can be formed by performing deep anisotropic etches on each side of filter substrate  2065  and selectively depositing metal or polymer afterwards. 
       FIG. 20G  is a simplified cross-sectional view diagram of an embodiment  2006  of filter layer  2060  for a receiver channel, according to some embodiments of the present disclosure. Optical filter layer  2060  can include two optical filters  2061  supported on optically transparent substrates  2065  and surrounded by an optically non-transparent tube structure  2111 , which prevents stray light in one optical filter layer  2060  from traveling into an optical filter region of an adjacent receiver channel in a multi receiver channel system. However, the optical filter region may contain any number of optical filters  2061  on any number of substrates  2065  within the optical filter layer  2060 .  FIG. 20G  illustrates an additional aperture  2049  and corresponding optically non-transparent stop region  2063  positioned on top of optical filter  2061  and supported by optically transparent substrate  2065 . Aperture  2049  can define the maximal cylinder of light desired to be passed into optical filter layer  2060  and stop region  2063  can absorb or reflect any incident stray light outside the diameter of aperture  2049 . 
     Embodiment  2006  of optical filter layer  2060  in  FIG. 20G  can have an additional aperture  2054 , and corresponding optically non-transparent stop region  2055  can be positioned between optical filter layer  2060  and the photosensor layer (not shown, but similar to photosensor layer  1770  in  FIG. 17 ). Aperture  2054  can define the maximal cylinder of light desired to be passed out of optical filter layer  2060  toward the photosensor, and stop region  2055  can absorb or reflect any incident stray light outside the diameter of aperture  2054 . Tube structure  2111  can be formed of a variety of materials, including but not limited to silicon, metals, polymers, or glasses. 
     D. Photosensor Layer 
     As can be appreciated herein, various different photosensor layer designs can be implemented in a micro-optic receiver channel. 
     1. Photosensor Layer with Diffuser 
       FIG. 21A  is a simplified cross-sectional view diagram of an embodiment  2100  of receiver channel  2132  containing an optional diffuser  2181  located in photosensor layer  2170  between optical filter  2161  and photosensor  2173 , according to some embodiments of the present disclosure. Diffuser  2181  can be configured to spread collimated photons that are output from collimating lens  2151  and passed by optical filter region  2160 , across the full width of a corresponding photosensor  2173 . Photosensor  2173  may be non-square or non-circular in geometry (e.g., short and wide) in order to extend the sensing area of photosensor  2173  to be wider or taller than width or height of the other components in receiver channel  2132 . 
     Diffuser  2181  is configured to spread light rays across the area of photosensor  2173  such that photosensor  2173  is able to detect the incident photons across its full width and height, thereby increasing the dynamic range of receiver channel  2132 , even where the overall height of receiver channel  2132  has to be limited for practical considerations. In particular, in this embodiment, receiver channel  2132  may include widened photosensors exhibiting greater photodetectors  2171  (i.e., areas sensitive to incident photons) and a diffuser  2181  arranged over photosensor  2173  that spreads light passed by optical filter  2161  across the full area of photosensor  2173 , thereby yielding increased dynamic range. 
     In some embodiments, photosensor  2173  includes an array of single-photon avalanche diode detectors  2171  (hereinafter “SPADs”). The height and width of the receiver channel (usually defined by the diameter of collimating lens  2151 ) may accommodate only a relatively small number of (e.g., two) vertically-stacked SPADs. Photosensor  2173  can therefore define an aspect ratio greater than 1:1, and diffuser  2181  can spread light rays passed by the optical filter region  2160  according to the geometry of photosensor  2173  in order to accommodate a larger sensing area per photosensor. By incorporating more SPADs per photosensor, the dynamic range of the photosensor can be increased, as it less likely for all SPADs to be unable to detect photons (i.e., to be “dead”) simultaneously. 
     In some other embodiments, photosensor  2173  includes an array of photodetectors  2171 . The height and width of the receiver channel (usually defined by the diameter of collimating lens  2151 ) may accommodate only a relatively small number of (e.g., two) vertically-stacked photodiodes. Photosensor  2173  can therefore define an aspect ratio greater than 1:1, and diffuser  2181  can spread light rays passed by the optical filter region  2160  according to the geometry of photosensor  2173  in order to accommodate a larger sensing area per photosensor. By incorporating more photodiodes per photosensor, the dynamic range of the photosensor can be increased, as it is unlikely for all photodiodes to be saturated simultaneously. 
     Receiver channel  2132  can additionally or alternatively include an aperture layer interposed between optical filter region  2160  and diffuser  2181  or between the optical filter region  2160  and photosensor  2173 , where aperture  2144  is aligned with a corresponding collimating lens  2151 . In this variation, aperture  2144  can absorb or reflect errant light rays passed by the light filter or reflected by the photosensor to further reduce crosstalk between receiver channels, thereby further increasing SNR (Signal to Noise Ratio) of the system. 
     2. Photosensor Layer with Converging Lens Set 
       FIG. 21B  is a simplified cross-sectional view diagram of an embodiment  2101  of receiver channel  2132 , according to some embodiments of the present disclosure. A photosensor layer  2170  of embodiment  2100  can include a photosensor  2173  formed of a set of discrete photodetectors  2171  (e.g., SPADs) and a set of inactive regions  2172  (e.g., integrated logic) encompassing the set of photodetectors, where each photodetector is configured to detect incident photons. Photosensor layer  2170  can also include a converging lens set  2191  interposed between optical filter region  2160  and photosensor  2173  with photodetectors  2171 , and including one converging lens  2191  per discrete photodetector  2171  within photosensor  2173 , where each lens of the converging lens set  2191  is configured to focus incident photons passed by optical filter region  2160  onto a corresponding discrete photodetector  2171 . Each converging lens can exhibit a common focal length, and converging lens set  2191  can be offset above photosensor  2173  by this common focal length (or by a distance substantially similar to this common focal length), and each converging lens can converge incident light—collimated in optical lens layer  2150  and passed by optical filter region  2160 —onto a corresponding photodetector  2171  in photosensor  2173 . 
     In some embodiments, converging lens set  2191  interposed between optical filter region  2160  and photosensor  2173  with photodetectors  2171  employs diffracting elements in addition to or replacement of refractive elements. 
     3. Photosensor Layer with Converging Lens Set and Additional Apertures 
       FIG. 21C  is a simplified cross-sectional view diagram of an embodiment  2102  of photosensor layer  2170 , according to some embodiments of the present disclosure. Photosensor layer  2170  can include a converging lens set  2191 , and a set of apertures  2157 , wherein each aperture  2157  is aligned with a corresponding converging lens  2191 . In this variation, each aperture  2157  can absorb or reflect errant light rays passed by the light filter or reflected by the photosensor to further reduce crosstalk between receiver channels, thereby further increasing the SNR of the system. Set of apertures  2157  and corresponding optically non-transparent stop regions  2159  are built on an optically transparent substrate  2158 . 
       FIG. 21D  is a simplified cross-sectional view diagram of an embodiment  2103  of photosensor layer  2170 , according to some embodiments of the present disclosure. Photosensor layer  2170  can include converging lens set  2191 , and set of apertures  2157 , where each aperture  2157  is aligned with a corresponding converging lens  2191 . Apertures  2157  and corresponding optically non-transparent stop regions  2159  are built on an optically transparent substrate  2158 . In this variation, apertures  2157  do not go all the way through to photodetector  2171 . 
       FIG. 21E  is a simplified cross-sectional view diagram of an embodiment  2104  of photosensor layer  2170 , according to some embodiments of the present disclosure. An additional set of apertures  2157  and corresponding optically non-transparent stop regions  2159  defining desired maximal light cones can be positioned between lens set  2191  and photodetector  2171 . Set of apertures  2157  and corresponding non-transparent stop regions  2159  define a light cone for every lens in lens set  2191  and function to absorb or reflect any stray light traveling along a path not encompassed by the desired light cones. The apertures may be fabricated using standard semiconductor processes. 
     4. Photosensor Layer with Converging Lens Set and Spacer Structure Between the Lens Set and the Photosensor 
       FIG. 21F  is a simplified cross-sectional view diagram of an embodiment  2105  of photosensor layer  2170 , according to some embodiments of the present disclosure. Here, an optically non-transparent spacer structure  2163  is positioned between lens set  2191  and photosensor  2173  having photodetectors  2171  in receiver channel  2132 . Optically non-transparent spacer structure  2163  forms a tube of substantially similar or larger diameter to a collimating lens (e.g., collimating lens  1751  shown in  FIG. 17 ) and prevents any light from traveling outside of receiver channel  2132  in the region between lens set  2191  and photosensor  2173 . Optically non-transparent spacer structure  2163  could be made from optically non-transparent bulk media (e.g. silicon or polymer). 
       FIG. 21G  is a simplified cross-sectional view diagram of an embodiment  2106  of photosensor layer  2170 , according to some embodiments of the present disclosure. Here, optically non-transparent spacer structure  2163  is positioned between lens set  2191  and photosensor  2173 , and is made from an optically non-transparent coating on an optically transparent substrate (e.g. black chrome on glass). Optically non-transparent spacer structure  2163  forms a tube of substantially similar or larger diameter to collimating lens  2151  and prevents any light from traveling outside of receiver channel  2132  in the region between lens set  2191  and photodetector  2171 . 
     5. Photosensor Layer Spacer Structure Between the Filter Layer and the Photosensor Layer 
       FIG. 21H  is a simplified cross-sectional view diagram of an embodiment  2107  of photosensor layer  2170 , according to some embodiments of the present disclosure. Optically non-transparent spacer structure  2163  can be positioned between an optical filter layer (e.g., any of the above-mentioned optical filter layers) and photosensor layer  2170 . Optically non-transparent spacer structure  2163  forms a tube of substantially similar or larger diameter to a collimating lens (e.g., collimating lens  1751  in  FIG. 17 ) and prevents any light from traveling outside of the receiver channel (e.g., channel  1700  in  FIG. 17 ) in the region between the optical filter layer and photosensor layer  2170 . Optically non-transparent spacer structure  2163  can be formed by etching a silicon or glass wafer and may be coated with an optically non-transparent material (e.g. black chrome). Alternatively, optically non-transparent spacer structure  2163  can be fabricated from molded polymer. In this embodiment, lens set  2191  is directly bonded to photosensor  2173 . Similar to its function in previous embodiments, lens set  2191  serves to focus light onto photodetectors  2171  of photosensor  2173 , rather than the inactive areas. These lenses could be integrated directly on top of an ASIC containing photosensor  2173  in a wafer fabrication process, easing production. 
     6. Photosensor Layer with Conical Spacer Structures 
       FIG. 21I  is a simplified cross-sectional view diagram of an embodiment  2108  of photosensor layer  2170 , according to some embodiments of the present disclosure. In this embodiment, photosensor layer  2170  includes a set of conical, optically non-transparent spacer structures  2164  that is positioned between a lens set (not shown but, e.g., lens set  2191  in  FIGS. 21F and 21G ) and photosensor  2173 . Set of conical, optically non-transparent spacer structures  2164  can form tapered tubes, each with substantially similar entrance diameter to individual lenses in the lens set, and each with substantially similar exit diameter to the individual photodetectors  2171  of photosensor  2173 . Set of conical, optically non-transparent spacer structures  2164  prevents any light from traveling outside of the receiver channel in regions between the lens set and photosensor  2173  and also guide light toward the photodetectors  2171  of photosensor  2173 . The set of conical, optically non-transparent spacer structures  2164  can be formed by etching a silicon or glass wafer and may be coated with an optically non-transparent material (e.g. black chrome). Alternatively, set of conical, optically non-transparent spacer structures  2164  can be fabricated from molded polymer. 
       FIG. 21J  is a simplified cross-sectional view diagram of an embodiment  2109  of photosensor layer  2173 , according to some embodiments of the present disclosure. In this embodiment, photosensor layer  2173  includes a set of conical, optically non-transparent spacer structures  2164  that is positioned between a lens set (not shown but, e.g., lens set  2191  in  FIGS. 21F and 21G ) and photodetector  2171 . The inner walls of the set of conical, optically non-transparent spacer structures  2164  are coated with a reflective material (e.g. chrome) in order to further enhance the structures&#39; ability to act as a light pipe. Set of conical, optically non-transparent spacer structures  2164  form tapered tubes, each with substantially similar entrance diameter to individual lenses in the lens set, and each with substantially similar exit diameter to the individual photodetectors  2171  of photosensor  2173 . Set of conical, optically non-transparent spacer structures  2164  prevents any light from traveling outside of the receiver channel in regions between the lens set and photosensor  2171  and also guide light toward the photodetectors  2171  of photosensor  2173 . 
     7. Photosensor Layer with Resonant Photo-Cavity Diodes 
       FIG. 21K  is a simplified cross-sectional view diagram of a receiver channel  2132  including an embodiment  2110  of photosensor layer  2170 , according to some embodiments of the present disclosure. In this embodiment, photosensor layer  2170  is configured with a resonant cavity around a photo sensitive diode to improve the photon detection efficiency. Each photosensor  2173  includes one or more resonant photo-cavity diodes. Each photosensor  2173  includes one or more photo-diodes  2174  (photodetectors) along with highly-reflective (e.g., partially-mirrored) surfaces facing the top and bottom of the area (the resonant cavity). Generally, an photodetector of a non-resonant cavity diode may have a relatively low quantum efficiency. To improve the percentage of photons detected by the photodetector, resonant photo-cavity diode  2174  is used that includes: a first mirrored surface  2175  below and facing the photodetector; and a second partially mirrored surface  2176  above and facing the photodetector, that also allows light to enter the cavity as shown in  FIG. 21K . Thus, when a photon passes through and is not detected by an photodetector of resonant photo-cavity diode  2174 , first mirrored surface  2175  surrounding the photodetector of resonant photo-cavity diode  2174  reflects the photon back toward top reflective surface  2176  of the cavity and through the photodetector again, which may detect the photon upon its second transition through the photodetector. However, if the photodetector fails to detect the photon upon this second collision, the reflection process is repeated with the second mirrored surface reflecting the photon back toward the photodetector, which again may detect the photon upon its third collision with the photodetector. This process may repeat until the photon is detected by the photodetector of the photosensor or the photon escapes or is absorbed by the cavity. Resonant photo-cavity diode  2174  can thus achieve a relatively high rate of photon detection (i.e. approaching 100%). Note that a particle interpretation of light is used in the preceding description, but consideration of wave interference effects are critical for a complete description of resonant cavity photodiodes. Also note that the active region of resonant photo-cavity diode  2174  may be comprised of a standard photodiode, an avalanche photodiode, a SPAD, or any other photosensor. 
       FIG. 21K  further shows that one or more resonant cavity photodiodes (or “RCPs”)  2174  may be combined with aperture  2144 , collimating lens  2151 , optical filter region  2160 , and any combination of the aforementioned diffusers, converging lens sets, or crosstalk mitigation structures to form a variant of receiver channel  2132 . A typical RCP will have similar wavelength sensitivity as optical filter region  2160  and can be designed to be sensitive to a similar set of wavelengths of light as optical filter region  2160 . However, due to fabrication or other limitations, the RCP may have more part-to-part variability of the center wavelength of the RCP&#39;s operating spectrum and thus necessitate a broader operating wavelength band in order for every photosensor to be capable of detecting photons at the system&#39;s operating wavelength. Alternatively, it may simply be impossible to reliably fabricate an RCP with an operating wavelength band as narrow as the filter passband. For instance, optical filter region  2160  may have a passband as narrow as 0.1 nm, while the RCP may have an operating band of 10 nm. With the optical filter region  2160  on top of the RCP  2174 , the combined filter and RCP system has an effective operating wavelength band substantially similar to optical filter region  2160 . In addition, the RCP performance is improved when sensing collimated light, as opposed to focused light, which is provided as a result of collimating lens  2151  as depicted in  FIG. 21K . In this way, a system employing aperture  2144 , collimating lens  2151 , optical filter region  2160 , and RCP  2174  may achieve high photon detection efficiency and narrow wavelength selectivity to maximize the SNR within receiver channel  2132 . 
     E. Hemispherical Receiver Structures 
       FIG. 22A  is a simplified cross-sectional view diagram of an embodiment  2200  of a receiver channel  2232 , according to some embodiments of the present disclosure. Receiver channel  2232  of embodiment  2200  can include convex hemispheres supported on an optically non-transparent material. In this embodiment, an aperture layer  2240  is combined with an optical filter  2261  coated on a convex hemisphere  2267 , with the center of hemisphere  2267  located at or near the focal point of incoming light (marginal ray lines  2233 ). The center of hemisphere  2267  also corresponds to, or nearly corresponds to, the center of aperture  2244 . In some embodiments, hemisphere  2267  can be below aperture  2244 , as shown in  FIG. 22A . An advantage of the embodiment is that for a sufficiently well-focused cone of rays, any ray lines  2233  will pass through optical filter  2261  normal to the filter&#39;s surface, thereby eliminating CWL (Center Wave Length) shift due to variations in incident angle of the light (e.g. light rays  2233 ) on optical filter  2261 , thereby allowing the use of very narrow bandpass (e.g. 850-852 nm) filters. 
     This is further illustrated in  FIG. 22B , which is a simplified cross-sectional view diagram of an embodiment  2201  of receiver channel  2232 , according to some embodiments of the present disclosure. Unlike embodiment  2200  in  FIG. 22A , embodiment  2201  in  FIG. 2B  can be configured so that hemisphere  2267  is positioned above aperture  2244  to achieve similar functionality but with a less compact footprint. As shown in  FIG. 22B , the angle of incidence on optical filter  2261  is normal for marginal ray lines  2233  (and all other ray lines not shown explicitly in  FIG. 22B ) that pass through the center of hemisphere  2267 . Note that, while not shown in  FIG. 22B or 22C , the rays will refract upon exiting the hemisphere structure since they are not normal to the planar exit surface. Similarly, in  FIG. 22A , there will be some amount of refraction when rays enter the flat side of the hemispherical structure. 
     As illustrated in  FIGS. 22A to 22B , receiver channel  2232  includes sidewalls  2263  between optically non-transparent stop region  2246  and photosensor layer  2270  with photodetectors  2271  to reduce crosstalk. Sidewalls  2263  can be made up of optically non-transparent material or made up of optically transparent material. In addition, sidewalls  2263  can also be coated with reflective or absorptive material. 
     A close-up view of the convex hemispherical surface is shown in  FIG. 22C , which is a simplified cross-sectional view diagram of convex hemisphere  2267  of  FIGS. 22A and 22B . Convex hemisphere  2267  can be coated with optical filter  2261  and positioned on a self-supporting, optically non-transparent stop region  2246  such as metal, silicon, polymer etc. In some embodiments where the convex hemispherical surfaces of the micro-optic channels are used for hyperspectral imagers, optical filter  2261  can be configured to be non-uniform. For example, optical filter  2261  can be a graduated filter increasing gradually or in a step-wise manner in one direction (e.g., the thickness direction) that different micro-optic channels have different optical filter layers that have different thicknesses. This allows different micro-optic channels to measure a different range of wavelengths as discussed herein with respect to  FIGS. 3A and 3B . 
       FIG. 22D  is a simplified cross-sectional view diagram of an embodiment  2202  of a receiver channel  2232 , according to some embodiments of the present disclosure. Receiver channel  2232  of embodiment  2202  can include convex hemisphere  2267  supported on a rigid optically transparent layer. In this embodiment, aperture layer  2240  is combined with optical filter  2261  and coated on convex hemisphere  2267 , where the center of hemisphere  2267  is located at or near the focal point of incoming light (ray lines  2233 ). The center of hemisphere  2267  also corresponds to, or nearly corresponds to, the center of the aperture  2244 . As shown in  FIG. 22D , hemisphere  2267  can be below aperture layer  2240 . In some other embodiments, hemisphere  2267  can be above aperture layer  2240 , as shown in  FIG. 22E . 
       FIG. 22E  is a simplified cross-sectional view diagram of an embodiment  2203  of a receiver channel  2232 , according to some embodiments of the present disclosure. Unlike embodiment  2202  in  FIG. 22D , embodiment  2215  in  FIG. 2E  can be configured so that hemisphere  2267  is positioned above aperture  2244  to achieve similar functionality as embodiment  2202  but with a more compact footprint. 
       FIGS. 22D and 22E  show convex hemisphere  2267  as being coated with optical filter  2261  and imprinted on aperture layer  2240  that is supported on a rigid optically transparent layer  2245  (e.g. glass, polymer) with aperture  2244  along with the corresponding optically non-transparent stop regions  2246 . As illustrated in  FIGS. 22D and 22E , receiver channel  2232  includes sidewalls  2263  between optically transparent layer  2245  and photosensor layer  2270  with photodetectors  2271  to reduce crosstalk. Sidewalls  2263  can be made up of optically non-transparent material or made up of optically transparent material. In addition, sidewalls  2263  can also be coated with reflective or absorptive material. Note that, while not shown in  FIGS. 22D and 22E , there may be refraction of rays  2233  entering and exiting the rigid optically transparent layer  2245 . 
       FIG. 22F  is a simplified cross-sectional view diagram of an embodiment  2204  of a receiver channel  2232 , according to some embodiments of the present disclosure. Embodiment  2204  can include a concave hemisphere  2267  made of optically transparent material (e.g. glass, polymer) with a coated optical filter  2261 . Self-supported aperture layer  2240  can overhang concave hemisphere  2267  and can be perforated or etched with an optically non-transparent rigid material (e.g. metal film) to form the optically non-transparent stop regions  2246 . As shown in  FIG. 22F , hemisphere  2267  can be positioned below aperture layer  2240 . The center of aperture  2244  can be located at or near the focal point of the incoming light (rays  2233 ). Additionally, the center of the hemisphere  2267  can be located at or near the focal point of the incoming light (rays  2233 ). As illustrated in  FIG. 22F , receiver channel  2232  includes sidewalls  2263  between optically transparent layer  2245  and photosensor layer  2270  with photodetectors  2271  to reduce crosstalk. Sidewalls  2263  can be made up of optically non-transparent material or made up of optically transparent material. In addition, sidewalls  2263  can also be coated with reflective or absorptive material. 
       FIG. 22G  is a simplified cross-sectional view diagram of an embodiment  2205  of receiver channel  2232 , according to some embodiments of the present disclosure. Unlike embodiment  2204  in  FIG. 22F , embodiment  2205  in  FIG. 2G  can be configured so that hemisphere  2267  is positioned above aperture  2244  to achieve similar functionality as embodiment  2204 , but embodiment  2204  may have a more compact footprint. 
       FIG. 22H  is a simplified cross-sectional view diagram of an embodiment  2206  of receiver channel  2232 , according to some embodiments of the present disclosure. Receiver channel  2232  of embodiment  2206  can include a concave hemisphere  2267  and aperture layer  2240  supported by a rigid, optically transparent layer  2245 . In some embodiments, concave hemisphere  2267  can be below the aperture layer  2240  as shown in  FIG. 22H . Concave hemisphere  267  can be made of optically transparent material (e.g. glass, polymer) with a coated optical filter  2261 . Aperture layer  2240  with optically transparent aperture  2244  and corresponding optically non-transparent stop regions  244  is supported by optically transparent layer  2245  on both top and bottom sides of aperture layer  2240 . The center of aperture  2244  is located at or near the focal point of the incoming light (rays  2233 ). Additionally, the center of concave hemisphere  2267  is located at or near the focal point of the incoming light (rays  2233 ). As illustrated in  FIG. 22H , receiver channel  2232  includes sidewalls  2263  between optically transparent layer  2245  and photosensor layer  2270  with photodetectors  2271  to reduce crosstalk. Sidewalls  2263  can be made up of optically non-transparent material or made up of optically transparent material. In addition, sidewalls  2263  can also be coated with reflective or absorptive material. 
       FIG. 22I  is a simplified cross-sectional view diagram of an embodiment  2207  of receiver channel  2232 , according to some embodiments of the present disclosure. Unlike embodiment  2206  in  FIG. 22H , embodiment  2207  in  FIG. 21  can be configured so that hemisphere  2267  is positioned above aperture  2244  to achieve similar functionality as embodiment  2206 . 
     F. Bottom Micro-Lens Layer 
       FIG. 23A  is a simplified cross-sectional view diagram of an embodiment  2300  of a receiver channel  2332 , according to some embodiments of the present disclosure. Receiver channel  2332  of embodiment  2300  can include a Bottom Micro-Lens Layer (BMLL), which consists of one or more micro-lenses  2391  that are configured to guide divergent light rays into active portion of the photosensors. The BMLL performs ray angle correction to guide light from dissimilar angles into evenly spaced photosensors. Ray angle correction can be achieved by controlling the lateral offset between lens center and the photosensor center, tilting of the lens, or adjusting the form of the lens. A better illustration of this operation can be seen in  FIG. 23B . 
       FIG. 23B  is a simplified cross-sectional view diagram of a close-up view of the propagation of light during ray angle correction by a BMLL, according to some embodiments of the present disclosure. As illustrated, the pitch of the micro-optics is either not constant or is not equal to the pitch of lenses  2391  in order to steer the divergent rays ( 2333 ) to active portions of photodetectors  2371  in the photosensor layer. With reference back to  FIG. 23A , each micro-lens  2391  can be positioned to correspond with a respective photodetector  2371 . 
       FIG. 23C  is a simplified cross-sectional view diagram of an embodiment  2301  of a receiver channel  2332 , according to some embodiments of the present disclosure. Receiver channel  2332  of embodiment  2301  can include a single micro-lens  2391 , instead of a plurality of micro-lenses as shown in  FIG. 23A . Single micro-lens  2391  can be positioned over and centered to a single photodetector  2371 . Micro-lens  2391  can be configured to guide light to single photodetector  2371 . 
       FIGS. 23D and 23E  is a simplified cross-sectional view diagram of embodiments  2302  and  2303 , respectively, of a receiver channel  2332 , according to some embodiments of the present disclosure. Receiver channel  2332  of embodiment  2302  can include a BMLL positioned on the underside of an optically transparent layer  2345  supporting aperture layer  2340  and hemisphere  2367  with optical filter  2361  coated. As shown in  FIG. 23D , the BMLL can be formed of multiple lenses  2393  for guiding divergent light to multiple photodetectors  2371 . As shown in  FIG. 23E , the BMLL can be formed of a single micro-lens  2391  for guiding divergent light to photodetector  2371 . 
     Embodiments  2302  and  2303  in  FIGS. 23D and 23E  each include a convex hemisphere  2367  supported on a rigid optically transparent layer  2345 . In these illustrations, an aperture layer  2340  is combined with an optical filter  2361  coated on hemisphere  2367 , where the center of hemisphere  2367  is located at or near the focal point of incoming light (marginal ray lines  2333 ). The center of hemisphere  2367  can also correspond to, or nearly correspond to, the center of aperture  2344 . Convex hemisphere  2367  can be coated with optical filter  2361  and imprinted on aperture layer  2340  that is supported on rigid optically transparent layer  2345  (e.g. layer formed of glass, polymer) and the corresponding optically non-transparent stop regions  2346 . As illustrated in  FIGS. 23D and 23E , receiver channel  2332  includes sidewalls  2363  between optically transparent layer  2345  and photosensor layer  2370  to reduce crosstalk. Sidewalls  2363  can be made up of optically non-transparent material or made up of optically transparent material. In addition, sidewalls  2363  can also be coated with reflective or absorptive material. 
     G. Additional Exemplary Receiver Channels 
     It is to be appreciated that a receiver channel is a structure at the micro-optic level, e.g., a micro-optic receiver channel discussed above, that can be formed from multiple layers including one or more of an aperture layer, an optical lens layer below the aperture layer, an optical filter layer below the aperture and optical lens layer, and a photosensor layer below all the other layers. Each such layer can be configured in various ways to mitigate cross-talk. i.e., exposing stray light to adjacent receiver channels, as discussed herein with respect to  FIGS. 17-23E . Various examples of receiver channels are discussed above with respect to  FIGS. 17, 22A-22I , and  23 A- 23 E. Two other examples of receiver channels according to the present disclosure are illustrated in  FIGS. 24 and 25 . Embodiments of the present disclosure are not limited to the particular receiver channels described herein. Instead, based on the present disclosure a person of skill in the art will appreciate that in other embodiments a receiver channel according to the disclosure can include, among other options, an aperture layer as described above with respect to any of  FIG. 18A-18D or 19A-19D , a filter layer as described above with respect to any of  FIGS. 20A-20G , and/or a photosensor layer as described above with respect to any of  FIGS. 21A-21K . 
       FIG. 24  is a simplified cross-sectional view diagram of an exemplary embodiment of a receiver channel  2400 , according to some embodiments of the present disclosure. Receiver channel  2400  can include an aperture layer  2440  composed of first and second apertures  2444 , each formed in respective optically non-transparent layers  2446   a  and  2446   b . First and/or second apertures  2444  can be formed of void space defined by openings within layers  2446   a  and  2446   b  in some embodiments, while first and/or second apertures  2444  can be formed by optically transparent materials in some other embodiments. First and second optically non-transparent layers  2446   a  and  2446   b  can be supported by an optically transparent substrate  2445  sandwiched between first and second optically non-transparent layers  2446   a  and  2446   b.    
     Receiver channel  2400  can also include an optical lens layer  2450  disposed below aperture layer  2440 . Optical lens layer  2450  can include a collimating lens  2451  and an optically non-transparent spacer structure  2456 . Collimating lens  2451  can be separated from aperture layer  2440  by optically non-transparent spacer structure  2456 . In some embodiments, optically non-transparent spacer structure  2456  forms a tube having a circumference that surrounds collimating lens  2451  and extends toward aperture layer  2440 . Optically non-transparent spacer structure  2456  can be formed of an optically reflective or absorptive material that prevents any light from traveling outside of receiver channel  2400  in the region between aperture layer  2440  and collimating lens  2451 . 
     In addition to aperture layer  2440  and optical lens layer  2450 , receiver channel  2400  can further include an optical filter layer  2460  positioned directly below optical lens layer  2450 . Optical filter layer  2460  can include two optical filters  2461  sandwiching an optically transparent substrate  2465  that structurally supports optical filters  2461 . Optical filter layer  2460  can contain any number and type of optical filters  2461  on any number of substrates  2065 . For instance, one of optical filters  2461  can be a bandpass filter and be positioned on either on top of or directly below optically transparent substrate  2465  that blocks all of the incident light for a defined set of wavelengths (e.g. 900-945 nm and 950-995 nm). The other optical filter  2461  placed on the opposite side of optically transparent substrate  2465  can be a different filter, such as a wide spectrum blocking filter (except for the region covered by the bandpass filter), for example covering 200-915 nm and 980-1600 nm. The bandpass filter and blocking filter are designed such that there is no leakage in the transition region between the two filters. However, the filters could be two edge pass filters designed to work in conjunction as a bandpass filter or any other type of filter. 
     Immediately below optical filter layer  2460  can be a photosensor layer  2470 . In some embodiments, photosensor layer  2470  of embodiment  2400  can include an optically non-transparent spacer structure  2463  positioned between a converging lens set  2491  and a photosensor  2473 . Photosensor  2473  can be formed of a set of discrete photodetectors  2471  (e.g., SPADs) positioned between a set of inactive regions  2172  (e.g., integrated logic) in an alternating arrangement, where each discrete photodetector is configured to detect incident photons. Converging lens set  2491  can be interposed between optical filter layer  2460  and photosensor  2473  with photodetectors  2471 , and including one converging lens  2491  per discrete photodetector  2471  within photosensor  2173 , where each lens of the converging lens set  2491  is configured to focus incident photons passed by optical filter layer  2460  onto a corresponding discrete photodetector  2471 . Each converging lens can exhibit a common focal length, and converging lens set  2491  can be offset above the sensing plane of the photosensor by this common focal length (or by a distance substantially similar to this common focal length), and each converging lens can converge incident light—collimated in optical lens layer  2450  and passed by optical filter layer  2460 —onto one corresponding photodetector  2471  in photosensor  2473 . Optically non-transparent spacer structure  2463  forms a tube of substantially similar or larger diameter to a collimating lens  2451  and prevents any light from traveling outside of receiver channel  2400  in the region between lens set  2491  and photosensor  2473 . Optically non-transparent spacer structure  2163  could be made from optically non-transparent bulk media (e.g. silicon or polymer). 
     Another exemplary embodiment of a receiver channel is shown in  FIG. 25 .  FIG. 25  is a simplified cross-sectional view diagram of an exemplary receiver channel  2500 , according to some embodiments of the present disclosure. Receiver channel  2500  can include an aperture layer  2540 , an optical lens layer  2550  disposed below aperture layer  2540 , and an optical filter layer  2560  below both aperture layer  2540  and optical lens layer  2550 . Aperture layer  2540 , optical lens layer  2550 , and optical filter layer  2560  can have the same construction and function as corresponding components in  FIG. 24 . 
     Receiver channel  2500  can also include a photosensor layer  2570  positioned immediately below optical filter layer  2560 . In some embodiments, photosensor layer  2570  of embodiment  2400  can include an optically non-transparent spacer structure  2563 , a converging lens set  2591 , and a photosensor  2573 . Unlike converging lens set  2491  of receiver channel  2400  in  FIG. 24 , converging lens set  2591  of receiver channel  2500  can be positioned directly on at top surface of photosensor  2573  instead of directly on an underside of optical filter layer  2560 . Furthermore, optically non-transparent spacer structure  2563  can be formed of an optically non-transparent material (e.g., black chrome) coated on an optically transparent layer, such as a silicon or glass substrate, instead of being a solid optically non-transparent structure, e.g., optically non-transparent spacer structure  2463  of receiver channel  2400  in  FIG. 24 . Lens set  2591  serves to focus light onto photodetectors  2571  of photosensor  2573 , rather than inactive areas  2572 . 
     By implementing a receiver channel according to any of embodiments  2400  and  2500 , errant light can be prevented from exposing on adjacent receiver channels, thereby improving the accuracy of each photosensor&#39;s ability to capture photons for imaging. 
     VI. Micro Optical Receiver Channel Array Variations 
     According to some embodiments of the present disclosure, micro-optical receiver channels can be organized in an array. The array can have various dimensions according to design. For instance, an array of micro-optical receiver channels can be arranged in a M×N array where M and N are equal to or greater than 1. Accordingly, micro-optical receiver channels can be one- and two-dimensional arrays, as will be discussed furthered herein with respect to  FIGS. 26-30 , which illustrate different embodiments of micro-optical receiver channel arrays where each dot represents a micro-optical receiver channel. As aforementioned herein, each receiver channel can include a plurality of layers stacked upon each other. Thus, it can be appreciated that when arranged in an array, each micro-optic receiver channel is part of a monolithic layer composed of the individual elements reproduced many times in the M×N arrangement, e.g., an M×N aperture layer array, an M×N micro lens layer array, and an M×N photosensor layer array. When bonded together, these array layers create a monolithic multi-channel micro optical receiver array. 
       FIG. 26  is a simplified illustration of an exemplary micro-optical receiver array  2600 , according to some embodiments of the present disclosure. Micro-optical receiver array  2600  is configured as a linear (M×1) array, specifically a 16×1 array. This layout can achieve a high resolution (e.g. 16×1024) as the implementation is amenable to scanning the array in one dimension. As an example, for a receiver channel pitch of 500 microns the layout illustrated can be implemented in a chip of a size that is approximately 500 microns by 8000 microns. 
       FIG. 27  is a simplified illustration of an exemplary micro-optical receiver array  2700 , according to some embodiments of the present disclosure. Micro-optical receiver array  2700  is configured as a rectangular (M×N) array, specifically a 16×32 array. Thus, for a receiver channel pitch of 500 microns the layout illustrated can be implemented in a chip of size 8,000 microns by 12000 microns. 
       FIG. 28  is a simplified illustration of an exemplary micro-optical receiver array  2800 , according to some embodiments of the present disclosure. Micro-optical receiver array  2800  is configured as an M×N staggered array. In this illustration, receiver channels  2832  are laid out in a 16×4 staggered array. This layout can achieve a high resolution (e.g. 64×1024) as the implementation is amenable to sweeping. For a receiver channel pitch of 500 microns the layout illustrated in  FIG. 28  can be implemented in a chip of a size that is approximately 2000 microns by 8375 microns. 
       FIG. 29  is a simplified illustration of an exemplary micro-optical receiver array  2900 , according to some embodiments of the present disclosure. Micro-optical receiver array  2900  is configured as a warped linear (M×1) array. In this embodiment, the spacing between receiver channels  2932  is uneven. Receiver channels near the center, shown as  2932 - 01 , are placed close together (e.g. 400 microns apart), while the exterior channels, shown as  2932 - 02 , are placed farther apart (e.g., greater than 400 microns apart), or vice versa. This layout has an advantage of being able to allow for correction of the distortion curve of a lens (i.e. the angles between the receiver channel fields of view are evenly spaced in the object space). The arrangement shown in  FIG. 29  can be used to achieve a high resolution (e.g. 16×1024) as the implementation is amenable to sweeping. For an average receiver channel pitch of 500 microns the layout illustrated can be implemented in a chip of a size that is approximately 500 microns by 8000 microns. 
     In some embodiments, the receiver channels can be configured in a M×N warped array (where N≥1). In such embodiments, the receiver channels in the center are placed further from each other in both the x and y direction than the exterior receiver channels. This corrects for another possible form of lens distortion. 
       FIG. 29  is a simplified illustration of an exemplary micro-optical receiver array  2900 , according to some embodiments of the present disclosure. Micro-optical receiver array  2900  is configured in an arbitrary pattern. This layout arrangement has the advantage of being able to accommodate lens distortion, to make adjustments to compensate for any timing or routing variations, and also to match an arbitrary pattern from an illumination source. 
     Although the present disclosure has been described with respect to specific embodiments, it will be appreciated that the present disclosure is intended to cover all modifications and equivalents within the scope of the following claims.