PATENT DOCUMENT

Publication Number: US-10788366-B2
Application Number: US-201716095311-A
Country: US
Kind Code: B2

Title: Optical system for reference switching

Abstract:
Systems and methods for determining one or more properties of a sample are disclosed. The systems and methods disclosed can be capable of measuring along multiple locations and can reimage and resolve multiple optical paths within the sample. The system can be configured with one-layer or two-layers of optics suitable for a compact system. The optics can be simplified to reduce the number and complexity of the coated optical surfaces, etalon effects, manufacturing tolerance stack-up problems, and interference-based spectroscopic errors. The size, number, and placement of the optics can enable multiple simultaneous or non-simultanous measurements at various locations across and within the sample. Moreover, the systems can be configured with an optical spacer window located between the sample and the optics, and methods to account for changes in optical paths due to inclusion of the optical spacer window are disclosed.

Claims:
What is claimed is: 
     
       1. A system comprising:
 one or more light sources that emit a first light and a second light, the first light directed toward an exterior interface of the system and including a plurality of optical paths, and the second light incident on a reference; 
 one or more first optics that collect at least a portion of a reflection of the first light and change an angle of the first light; 
 one or more second optics configured to receive the first light from the one or more first optics and focus the first light to a detector array; and 
 the detector array including a plurality of detector pixels that detect at least a portion of the focused first light from the one or more second optics. 
 
     
     
       2. The system of  claim 1 , further comprising:
 a plurality of groups, each of the plurality of groups including:
 a launch region configured to reflect or absorb one or more wavelengths different from wavelengths of light emitted from the one or more light sources, 
 a reference region that receives a reflection of the second light, and 
 a measurement region including the one or more first optics. 
 
 
     
     
       3. The system of  claim 2 , wherein each group includes one launch region, one reference region, and a plurality of measurement regions. 
     
     
       4. The system of  claim 2 , wherein at least one group shares at least a portion of the measurement region with another of the plurality of groups. 
     
     
       5. The system of  claim 1 , wherein a first surface of at least one of the one or more first optics is flat and located at the exterior interface of the system, and a second surface of the at least one of the one or more second optics is convex. 
     
     
       6. The system of  claim 1 , further comprising:
 an aperture layer configured to allow one or more first optical paths to pass through to the one or more first optics, the one or more second optics, or both, the one or more first optical paths having a path length in a first range of path lengths, 
 wherein the aperture layer is further configured to reject one or more second optical paths with a path length in a second range of path lengths, different from the first range of path lengths. 
 
     
     
       7. The system of  claim 1 , further comprising:
 an aperture layer configured to allow one or more first optical paths to pass through to the one or more first optics, the one or more second optics, or both, the one or more first optical paths having an angle of incidence in a first range of angles, 
 wherein the aperture layer rejects one or more second optical paths having an angle of incidence in a second range of angles, different from the first range of angles. 
 
     
     
       8. The system of  claim 1 , further comprising:
 a junction located between the one or more light sources and the exterior interface of the system, 
 wherein the junction is further located between the one or more light sources and the reference, and 
 wherein the junction is configured to split light emitted from the one or more light sources into the first light and the second light, wherein an intensity of the first light is greater than an intensity of the second light. 
 
     
     
       9. The system of  claim 1 , further comprising:
 a first outcoupler including a bridge, the first outcoupler positioned to receive and redirect the first light towards the exterior interface of the system; and 
 a second outcoupler including a bridge, the second outcoupler positioned to receive and redirect the second light towards the reference. 
 
     
     
       10. The system of  claim 9 , further comprising one or more third optics coupled to the first outcoupler and the exterior interface of the system, wherein a first surface of the one or more third optics is in contact with a surface of the first outcoupler. 
     
     
       11. The system of  claim 1 , further comprising at least one of one or more integrated tuning elements, one or more multiplexers, optical routing, one or more waveguides, and integrated circuitry, wherein the one or more integrated tuning elements are included in a silicon-photonics chip. 
     
     
       12. The system of  claim 1 , wherein each detector pixel is associated with at least one of the one or more first optics and at least one of the one or more second optics. 
     
     
       13. The system of  claim 1 , wherein each of the one or more first optics is associated with at least one of the one or more second optics and at least two of the plurality of detector pixels. 
     
     
       14. The system of  claim 1 , wherein the one or more first optics includes material different from material included in the one or more second optics. 
     
     
       15. A method of operating a system, the method comprising:
 emitting light using one or more light sources, wherein the light includes a first light and a second light; 
 directing the first light towards an exterior interface of the system; 
 directing the second light towards a reference; 
 collecting at least a portion of a reflection of the first light using one or more first optics; 
 changing an angle of the first light using the one or more first optics; 
 focusing the first light to a detector array using one or more second optics; and 
 detecting at least a portion of the focused first light from the one or more second optics using the detector array. 
 
     
     
       16. The method of  claim 15 , further comprising:
 splitting the light into the first light and the second light using a junction, wherein an intensity of the first light is greater than an intensity of the second light. 
 
     
     
       17. The method of  claim 15 , wherein the system includes a plurality of groups, the plurality of groups including a first group comprising a first launch region, a first reference region, and a first measurement region,
 wherein the one or more first optics and the one or more second optics are associated with the first group, 
 wherein the first light is associated with the first launch region, the second light is associated with the first reference region, and the portion of the reflection of the first light is associated with the first measurement region. 
 
     
     
       18. The method of  claim 17 , wherein the detector array receives the portion of the focused first light from the plurality of groups. 
     
     
       19. The method of  claim 15 , further comprising:
 allowing one or more first optical paths to pass through to the one or more first optics, the one or more second optics, or both, using an aperture layer, wherein the one or more first optical paths have a path length in a first range of path lengths; and 
 rejecting one or more second optical paths with a path length in a second range of path lengths, wherein the second range of path lengths is different from the first range of path lengths. 
 
     
     
       20. The method of  claim 15 , further comprising:
 allowing one or more first optical paths to pass through to the one or more first optics, the one or more second optics, or both, using an aperture layer, wherein the one or more first optical paths have an angle of incidence in a first range of angles; and 
 rejecting one or more second optical paths with an angle of incidence in a second range of angles, wherein the second range of angles is different from the first range of angles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase Patent Application under 35 U.S.C. § 371 of International Application No. PCT/US2017/027353, filed Apr. 13, 2017, and claims priority to U.S. Provisional Patent Application Ser. No. 62/325,908 filed Apr. 21, 2016, which are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     This relates generally to a reference switch architecture capable of detecting one or more substances in a sample, and more particularly, capable of reimaging one or more optical paths in the sample. 
     BACKGROUND 
     Absorption spectroscopy is an analytical technique that can be used to determine one or more properties of a sample. Conventional systems and methods for absorption spectroscopy can include emitting light into the sample. As light transmits through the sample, a portion of the light energy can be absorbed at one or more wavelengths. This absorption can cause a change in the properties of light exiting the sample. The properties of light exiting the sample can be compared to the properties of light exiting a reference, and the one or more properties of the sample can be determined based on this comparison. 
     The properties of light exiting the sample can be determined using measurements from one or more detector pixels. Measurements along multiple locations within the sample may be useful for accurate determination of one or more properties in the sample. These multiple locations can be at different locations in the sample, which can lead to optical paths with different path lengths, angle of incidence, and exit locations. However, some conventional systems and methods may not be capable of discerning differences in path lengths, depths of penetration, angles of incidence, exit locations, and/or exit angles from measurements along multiple locations within the sample. Those systems and methods that can be capable of measurements at multiple depths or multiple locations can require complicated components or detection schemes to associate optical paths incident on the multiple locations within the sample. These complicated components or detection schemes may not only limit the accuracy of reimaging and resolving the multiple optical paths, but can also place limits on the size and/or configuration of the optical system. Thus, a compact optical system capable of accurately reimaging and resolving multiple optical paths within a sample may be desired. 
     SUMMARY 
     This relates to systems and methods for measuring one or more properties of a sample. The systems can include a light source, optic(s), reference, detector array, and controller (and/or logic). The systems and methods disclosed can be capable of measuring one or more properties at multiple locations within the sample. The systems and methods can reimage and resolve multiple optical paths within the sample, including selecting a targeted (e.g., pre-determined) measurement path length such that the spectroscopic signal quality measured by the detector can accurately represent one or more properties of the sample. The system can be configured with one-layer or two-layers of optics suitable for a compact (e.g., less than 1 cm 3  in volume) system. The optics can be simplified to reduce the number and complexity of the coated optical surfaces, etalon effects, manufacturing tolerance stack-up problems, and interference-based spectroscopic errors. The optics can be formed such that the number of moving parts can be reduced or moving parts can be avoided, and robustness can be enhanced. Furthermore, the size, number, and placement of the optics can enable multiple simultaneous or non-simultaneous measurements at various locations across and within a sample, which can reduce the effects of any heterogeneity in the sample. Moreover, the systems can be configured with an optical spacer window located between the sample and the optics, and methods to account for changes in optical paths due to inclusion of the optical spacer window are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a block diagram of an exemplary system capable of measuring one or more properties located at multiple locations within a sample according to examples of the disclosure. 
         FIG. 1B  illustrates an exemplary process flow for measuring one or more properties located at multiple locations within a sample according to examples of the disclosure. 
         FIG. 2  illustrates a cross-sectional view of an exemplary system configured to determine one or more properties of a sample according to examples of the disclosure. 
         FIG. 3  illustrates a cross-sectional view of an exemplary system configured to determine one or more properties of a sample according to examples of the disclosure. 
         FIG. 4A  illustrates a cross-sectional view of an exemplary portion of a system configured for resolving multiple angles of incidence on a sample surface with two-layers of optics according to examples of the disclosure. 
         FIG. 4B  illustrates an exemplary junction coupled to light sources according to examples of the disclosure. 
         FIG. 4C  illustrates an exemplary waveguide coupled to light sources according to examples of the disclosure. 
         FIGS. 4D-4H  illustrate cross-sectional views of exemplary optics layers included in a system configured for resolving multiple optical paths in a sample according to examples of the disclosure. 
         FIG. 4I  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple angles of incidence on a sample surface and reducing or eliminating trapped light from light sources according to examples of the disclosure. 
         FIG. 5  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple angles of incidence on a sample surface with one-layer of optics according to examples of the disclosure. 
         FIG. 6  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple optical path lengths with two-layers of optics according to examples of the disclosure. 
         FIG. 7  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple optical path lengths with one-layer of optics according to examples of the disclosure. 
         FIG. 8  illustrates Snell&#39;s Law according to examples of the disclosure. 
         FIGS. 9A-9B  illustrate top and perspective views of an exemplary group including an optics unit according to examples of the disclosure. 
         FIG. 9C  illustrates a top view of exemplary multiple groups including optics units and detector arrays in a system according to examples of the disclosure. 
         FIG. 10  illustrates an exemplary configuration with light rays having a spatial resolution uncertainty according to examples of the disclosure. 
         FIG. 11  illustrates an exemplary configuration with light rays having an angular resolution uncertainty according to examples of the disclosure. 
         FIG. 12  illustrates an exemplary configuration with an input light beam with a Gaussian angular divergence according to examples of the disclosure. 
         FIG. 13A  illustrates a cross-sectional view of an exemplary system including an optical spacer window and aperture layer located between the optics unit and the sample according to examples of the disclosure. 
         FIG. 13B  illustrates a cross-sectional view of an exemplary system including an optical spacer window located between the optics unit and the sample according to examples of the disclosure. 
         FIG. 14A  illustrates a cross-sectional view of an exemplary system excluding an optical spacer window and corresponding determination of the lateral position of light incident at the exterior interface of the system (e.g., interface where the system contacts the sample) according to examples of the disclosure. 
         FIGS. 14B-14C  illustrate cross-sectional views of an exemplary system including an optical spacer window and corresponding determination of the lateral position of light incident at the exterior interface of the system (e.g., interface where the system contacts the sample) according to examples of the disclosure. 
         FIGS. 14D-14E  illustrate cross-sectional views of an exemplary system including an optical spacer window according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     This disclosure relates to systems and methods for determining one or more properties of a sample. The systems can include a light source, optics, reference, detector array, and controller (and/or logic). The systems and methods disclosed can be capable of measuring along multiple locations within the sample to determine the one or more properties. The systems and methods can reimage and resolve multiple optical paths within the sample, including selecting a targeted (e.g., pre-determined) measurement path length such that the spectroscopic signal quality measured by the detector can accurately represent the one or more properties of the sample. The system can be configured with one-layer or two-layers of optics suitable for a compact (e.g., less than 1 cm 3  in volume) system. The optics can be simplified to reduce the number and complexity of the coated optical surfaces, etalon effects, manufacturing tolerance stack-up problems, and interference-based spectroscopic errors. The optics can be formed such that the number of moving parts can be reduced or moving parts can be avoided, and robustness can be enhanced. Furthermore, the size, number, and placement of the optics can enable multiple simultaneous or non-simultaneous measurements at various locations across and within a sample, which can reduce the effects of any heterogeneity in the sample. Moreover, the systems can be configured with an optical spacer window located between the sample and the optics, and methods to account for changes in optical paths due to inclusion of the optical spacer window are disclosed. 
     Absorption spectroscopy is an analytical technique that can be used to determine one or more properties of a sample. Light can have an initial intensity or energy when emitted from a light source and incident on the sample. As light is transmitted through the sample, a portion of the energy can be absorbed at one or more wavelengths. This absorption can cause a change (or loss) in the intensity of light exiting the sample. Light exiting the sample can be due to light that scatters from one or more locations within the sample, wherein the location can include a substance of interest. In some examples, the substance of interest can be present in some or all of the path of light into and/or out of the sample, where the measured absorbance can include absorption at one or more regions where the light scatters. The amount of light exiting the sample can decrease exponentially as the concentration of the substance of interest in the sample increases. In some examples, the substance can include one or more chemical constituents, and the measurement can be used to determine the concentration of each chemical constituent present in the sample. 
       FIG. 1A  illustrates a block diagram of an exemplary system and  FIG. 1B  illustrates an exemplary process flow for measuring one or more substances located at multiple locations within the sample according to examples of the disclosure. System  100  can include interface  180 , optics  190 , light source  102 , detector  130 , and controller  140 . Interface  180  can include input regions  182 , interface reflected light  184 , reference  108 , and output regions  156 . In some examples, input regions  182  and/or output regions  156  can include an aperture layer including one or more openings configured to limit the location and/or angles of light exiting and/or entering the system. By limiting the location and/or angles of light exiting and/or entering the system, the light incident on or exiting from sample  120  can also be limited. Optics  190  can include an absorber or light blocker  192 , optics  194  (e.g., a negative micro-lens), and light collection optics  116  (e.g., a positive microlens). Sample  120  can be located near, close to, or touching at least a portion of system  100 . Light source  102  can be coupled to controller  140 . Controller  140  can send a signal (e.g., current or voltage waveform) to control light source  102  to emit light towards the surface of sample  120  (step  153  of process  151 ). Depending on whether the system is measuring the one or more properties of the sample or of the reference, light source  102  can emit light towards input regions  182  (step  155  of process  151 ) or reference  108 . 
     Input regions  182  can be configured to allow light to exit system  100  to be incident on sample  120 . Light can penetrate a certain depth into sample  120  and can reflect and/or scatter back towards system  100  (step  157  of process  151 ). The reflected and/or scattered light can enter back into system  100  at output regions  156  (step  159  of process  151 ). The reflected and/or scattered light that enters back into system  100  can be collected by light collection optics  116 , which can redirect, collimate, focus, and/or magnify the reflected and/or scattered light (step  161  of process  151 ). The reflected and/or scattered light can be directed towards detector  130 . Detector  130  can detect the reflected and/or scattered light and can send an electrical signal indicative of the light to controller  140  (step  163  of process  151 ). 
     Light source  102  can, additionally or alternatively, emit light towards reference  108  (step  165  of process  151 ). Reference  108  can reflect light towards optics  194  (step  167  of process  151 ). Reference  108  can include, but is not limited to, a mirror, a filter, and/or a sample with known optical properties. Optics  194  can redirect, collimate, focus, and/or magnify light towards detector  130  (step  169  of process  151 ). Detector  130  can measure light reflected from reference  108  and can generate an electrical signal indicative of this reflected light (step  171  of process  151 ). Controller  140  can be configured to receive both the electrical signal indicative of light reflected/scattered from sample  120  and the electrical signal indicative of light reflected from reference  108  from detector  130 . Controller  140  (or another processor) can determine one or more properties of the sample from the electrical signals (step  173  of process  151 ). 
     In some examples, when the system is measuring the one or more substances in the sample and in the reference, light emitted from the light source  102  can reflect off a surface of the sample back into system  100 . Light reflected off the exterior interface of the system (e.g., interface where the system contacts the sample) can be referred to as interface reflected light  184 . In some examples, interface reflected light  184  can be light emitted from light source  102  that has not reflected off sample  120  or reference  108  and can be due to light scattering. Since interface reflected light  184  can be unwanted, absorber or light blocker  192  can prevent interface reflected light  184  from being collected by optics  194  and light collection optics  116 , which can prevent interface reflected light  184  from being measured by detector  130 . 
       FIG. 2  illustrates a cross-sectional view of an exemplary system configured to determine one or more properties of a sample according to examples of the disclosure. System  200  can be close to, touching, resting on, or attached to sample  220 . Sample  220  can include one or more locations, such as location  257  and location  259 . System  200  can include a light source  202 . Light source  202  can be configured to emit light  250 . Light source  202  can be any source capable of generating light including, but not limited to, a lamp, laser, light emitting diode (LED), organic light emitting diode (OLED), electroluminescent (EL) source, quantum dot (QD) light emitter, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  202  can be capable of emitting a single wavelength of light. In some examples, light source  202  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  202  can be any tunable source capable of generating a SWIR signature. In some examples, a plurality of light sources can be included in the system with each light source  202  emitting a different wavelength range of light (e.g., different colors in the spectrum). In some examples, light source  202  can include a III-V material, such as Indium Phosphide (InP), Gallium Antimonide (GaSb), Gallium Arsenide Antimonide (GaAsSb), Aluminum Arsenide (AlAs), Aluminum Gallium Arsenide (AlGaAs), Aluminum Indium Arsenide (AlInAs), Indium Gallium Phosphide (InGaP), Indium Gallium Arsenide (InGaAs), Indium Arsenide Antimonide (InAsSb), Indium Phosphide Antimonide (InPSb), Indium Arsenide Phosphide Antimonide (InAsPSb), and Gallium Indium Arsenide Antimonide Phosphide (GaInAsSbP). 
     System  200  can include input region  282  located close to or near sample  220  or an external surface of the system. Input region  282  can include one or more transparent components including, but not limited to, a window, an optical shutter, or a mechanical shutter. 
     Light  250  can exit system  200  through input region  282 . In some examples, light  250  can be a collimated beam. Light that exits system  200  and travels through sample  220  to location  257  can be referred to as light  252 . Light  252  can be incident on location  257  at any angle including, but not limited to, 45°. In some examples, light  252  can have an angle of incidence at location  257  between 20° to 30°. In some examples, light  252  can have an angle of incidence at location  257  of 35°. Location  257  can include one or more properties of sample  220 . Light  252  can be partially absorbed prior to reaching location  257 , at location  257 , and/or after being partially reflected and/or scattered at location  257 , and can be referred to as light  254 . In some examples, light  254  can be formed by light transmitting through sample  220 . Light  254  can penetrate through sample  220  and can enter system  200  at location  213  of optic  210 . In some examples, optic  210  can be in contact or near sample  220 . In some examples, optic  210  can be any type of optical component such as a window. In some examples, optic  210  can be any optical component, such as a lens, capable of changing the behavior and properties of the incoming light. In some examples, optic  210  can include a transparent material. Optic  210  can include a plurality of locations, including location  213  and location  217 , where light can be allowed to enter. In some examples, optic  210  can be a lens configured with a large aperture (e.g., an aperture larger than the size of the incoming light beam) and a short focal length (e.g., the focal length can be such that a sample within 10 mm proximity to the system is in focus). In some examples, optic  210  can be a Silicon lens or a lens including silicon dioxide. 
     System  200  can include optics to magnify or reimage the incoming light beam. The optics in system  200  can be capable of reimaging the optical paths including path lengths, angles of incidences, and exit locations to another plane closer to the detector array  230 . To reduce the differences in any fluctuations, drifts, and/or variations between a light path (e.g., light  252  or light  253 ) penetrating through sample  220  and a light path reflecting off a reference  222  (e.g., a reflector), system  200  can share the optics between the two different light paths. System  200  can include optic  210 , optic  216 , and/or optic  218  for reimaging both light that has penetrated and light that has not penetrated through sample  220 . In some examples, optic  216  and optic  218  can be configured such that a reimage of the incident optical paths at the exterior interface of the system (e.g., interface where the system contacts the sample) can be reimaged onto another plane (e.g., plane where detector array  230  is located) without magnification. In some examples, optic  216  and optic  218  can be configured such that a magnification, such as a 2.5×-5× magnification, is introduced into the image. 
     Light  254  can be transmitted through optic  216  and optic  218  and can be incident on optic  223 . Optic  223  can be included in optics unit  229 . Optics unit  229  can comprise a plurality of optics, such as optic  223  and optic  227 , attached to a substrate. In some examples, the optics can be of any type and can include any type of material conventionally used in optics. In some examples, two or more of the optics can have the same optical (e.g., reflectance, refractive index, and transparency range) and/or geometric properties (e.g., curvature/focal length or pitch). One skilled in the art would appreciate that the same optical properties and the same geometric properties can include tolerances that result in a 15% deviation. In some examples, optics unit  229  can be coupled to one or more aperture layers. In some examples, optics unit  229  can be coupled to a patterned aperture layer, such as an aperture layer including locations between adjacent optics are opaque to prevent light mixing. 
     Light  254  can be transmitted through optic  223 , and optic  223  can converge light  254  to be detected by detector pixel  233  included in detector array  230 . In some examples, optic  223  can converge light  254  to a center location (not shown) or an edge location of the detector pixel. Detector array  230  can include one or more detector pixels, such as detector pixel  233 , detector pixel  235 , and detector pixel  237 , disposed on a substrate. A detector pixel can include one or more detector elements with a common footprint (e.g., same size and shape). A detector element can be an element designed to detect the presence of light and can individually generate a signal representative of the detected light. In some examples, at least one detector pixel can be independently controlled (e.g., measured, observed, or monitored) from other detector pixels in detector array  230 . In some examples, at least one detector pixel can be capable of detecting light in the short-wave infrared (SWIR) range. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 2.0-2.5 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be associated with a particular sample position and/or angle of light incident on a surface of system  200 . Detector pixel  233  can detect light  254  and can generate an electrical signal indicative of the properties of detected light  254 . Detector array  230  can transmit the electrical signal to controller  240 , and controller  240  can process and/or store the electrical signal. 
     System  200  can determine one or more properties of sample  220  by utilizing the information from light reflected from the sample in conjunction with information from light reflecting off a reference  222 , such as a reflector. Light source  202  can emit light  264 . Light  264  can be directed at reference  222 . Reference  222  can include any type of material capable of at least partially reflecting incident light. Exemplary reflective materials can include, but are not limited to, Titanium (Ti), Cobalt (Co), Niobium (Nb), Tungsten (W), Nickel Chrome (NiCr), Titanium Tungsten (TiW), Chrome (Cr), Aluminum (Al), Gold (Au), and Silver (Ag). In some examples, reflective materials can include one or more dielectric layers. One or more properties (e.g., thickness) of reference  222  can be determined based on the wavelength of light, type of material, and/or composition of reference  222 . In some examples, the size and shape of reference  222  can be configured to be larger or the same size and/or shape of light beam of light  264 . One skilled in the art would appreciate that the same size and shape can include tolerances that result in a 15% deviation. In some examples, the optical and/or physical properties of reference  222  can be such that the reflectivity of light  264  is greater than 75%. In some examples, the optical and/or physical properties of reference  222  can be such that the reflectivity of light  264  can be greater than 90%. In some examples, the size and shape of reference  222  can be such that less than 15% of light  264  is allowed to transmit through the reference  222  and light  264  is prevented from reaching sample  220 . In some examples, the reference  222  can be configured to reflect light  264  as a specular reflection. In some examples, reference  222  can be a spectroscopically neutral blocker. In some examples, the reference signal can include chopping light  264  between light  252  entering sample  220  and light  264  incident on reference  222 . Although  FIG. 2  illustrates reference  222  as located at the exterior interface of the system (e.g., interface where the system contacts the sample), examples of the disclosure can include the reference located at other locations including, but not limited to, an interior wall of the system, a side of the optics, and the like. 
     Light  264  can reflect off reference  222  towards optic  216 . Light  264  can be transmitted through optic  216  towards optic  218 . Light  264  can be transmitted through optic  218  and can be incident on optic  219 , included in optics unit  229 . Optic  219  can be any type of optics configured for spreading out the incoming light beam. In some examples, optic  219  can be a negative lens, which can be a lens with a focal length that is negative. In some examples, optic  219  can be a prism. In some examples, optic  219  can include a prism wedge angled for each detector pixel in detector array  230 . In some examples, optic  219  can be a beamsplitter. In some examples, optic  219  can be configured to spread out or divide light into multiple beams, such as light  266  and light  267 . In some examples, optic  219  can spread out light such that each light beam can be directed to a different detector pixel in detector array  230 . In some examples, optic  219  can uniformly spread out light such that the properties of each light beam can be the same. One skilled in the art would appreciate that the same properties can include tolerances that result in a 15% deviation. In some examples, optic  219  can spread out light such that intensities of at least two light beams are different. In some examples, optic  219  can comprise multiple optics. In some examples, the size and/or shape of optic  219  can be based on the number of detector pixels that light is spread to, the properties of the one or more light beams exiting optic  219 , or both. In some examples, an aperture layer can be coupled to optic  219  to control the properties and/or direction of light exiting optic  219 . In some examples, optic  219  or system  200  can be configured such that light that reflects off a surface of the sample back into the system (i.e., light that has not penetrated through sample  220 ) is prevented from being incident on optic  219 , although stray light or background light can be incident on optic  219 . 
     Light  264  can transmit through optic  219  to form light  266 . Light  266  can be incident on detector pixel  233 . Detector pixel  233  can detect light  266  and can generate an electrical signal indicative of the properties of detected light  266 . In some examples, the number of detector pixels configured to detect a light beam can be different for different light beams. For example, light  255  can be detected by two detector pixels (e.g., detector pixel  235  and detector pixel  237 ), while light  254  can be detected by one detector pixel (e.g., detector pixel  233 ). The electrical signal can be transmitted from detector array  230  to controller  240 . Controller  240  can process and/or store the electrical signal. Controller  240  can utilize the signal information measured from light  254  to determine the reflectivity or one or more sample properties along the light path directed to location  257  and can utilize the signal information from light  266  to detect any fluctuations or drift in light source  202  and/or detector array  230 . Using any of the above discussed methods, controller  240  can process the electrical signal and the signal information to determine the one or more properties of sample  220 . 
     The same components in system  200  can be used for measurements at other locations, such as location  259 , in sample  220 . Light  252  that is not absorbed or reflected along the light path directed to location  257  can be referred to as light  253 . Light  253  can be incident on location  259  and can reflect and/or scatter into system  200  as light  255 . In some examples, the angle of incidence of light  255  at the surface of system  200  can be different from the angle of incidence of light  254 . Light  255  can enter system  200  through optic  210  at location  217 . Light  255  can be transmitted through optic  216  and optic  218  and can be incident on optic  227 , included in optics unit  229 . Light  255  can be transmitted through optic  227 , and optic  227  can converge, redirect, collimate, focus, and/or magnify light such that light  255  is detected by detector pixel  235  and detector pixel  237 , included in detector array  230 . Detector pixel  235  and detector pixel  237  can detect light  255  and can generate electrical signals indicative of the properties of detected light  255 . In some examples, optic  227  can converge, redirect, collimate, focus, and/or magnify light such that light  255  is incident on a center location or an edge location of the detector pixel. Any number of detector pixels can be configured to detect a light beam. Detector array  230  can transmit the electrical signal to controller  240 . Controller  240  can process and/or store the electrical signal. 
     Controller  240  can utilize the signal information measured from light  255  to determine one or more properties of sample  220  and can utilize the signal information from light  267  to detect any fluctuations or drift in light source  202  and/or detector array  230 . In some examples, controller  240  can detect light  266  incident on detector pixel  233  and light  267  incident on detector pixel  235  and/or detector pixel  237  simultaneously without the need for separate measurements. In some examples, location  257  and location  259  can have the same depth from the surface of sample  220  or the exterior interface of the system (e.g., interface where the system contacts the sample). One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, location  257  and location  259  can have different depths from the surface of sample  220 . Controller  240  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, or absorbance at both location  257  and location  259  and can average the values. 
     Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. In some examples, light can be incident on the multiple locations at the same angle of incidence. In some examples, the light source can be configured to generate one light beam exiting the system that results in multiple input light beams reflected and/or scattered back into the system. In some examples, the system can be configured with one or more light sources that emit light at locations with different angles of incidence, where the light can be emitted at the same time or at different times. 
     In some examples, system  200  can further include a light blocker  292 . Light blocker  292  can include any material capable of absorbing or blocking light. In some examples, light blocker  292  can include any material (e.g., an anti-reflection coating) that prevents incident light from reflecting. That is, light blocker  292  can prevent unwanted light from reaching and being measured by detector array  230 . In some examples, light blocker  292  can include any material that reflects at wavelengths different from the detection wavelengths of detector array  230 . 
     As illustrated in the figure, system  200  can include a plurality of optics and a plurality of detector pixels, where each optic can be associated to one or a plurality of detector pixels. Each optics-detector pixel pair can be associated with an optical path in sample  220 . In some examples, the association can be one optics-detector pixel pair to one optical path in sample  220 . For example, optic  223  and detector pixel  233  can be associated with the optical path from light  254 , and optic  227  and detector pixel  237  can be associated with the optical path from light  255 . Since controller  240  can associate detector pixel  233  and detector pixel  237  with different locations (e.g., location  257  and location  259 ) and/or different light paths in sample  220 , controller  240  can discern differences in path lengths, depths of penetration, angles of incidence, exit locations, and/or exit angles. 
       FIG. 3  illustrates a cross-sectional view of an exemplary system configured to determine one or more properties of a sample according to examples of the disclosure. System  300  can be close to, touching, resting on, or attached to a surface of sample  320 . Sample  320  can include one or more locations, such as location  357  and location  359 . In some examples, the one or more locations can be associated with one or more scattering events. 
     System  300  can include a light source  302 . Light source  302  can be configured to emit light  350 . Light source  302  can be configured to emit light  350 . Light source  302  can be any source capable of generating light including, but not limited to, a lamp, laser, light emitting diode (LED), organic light emitting diode (OLED), electroluminescent (EL) source, quantum dot (QD) light emitter, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  302  can be capable of emitting a single wavelength of light. In some examples, light source  302  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  302  can be any tunable source capable of generating a SWIR signature. In some examples, a plurality of light sources can be included in the system with each light source  302  emitting a different wavelength range of light (e.g., different colors in the spectrum). In some examples, light source  302  can include a III-V material, such as Indium Phosphide (InP), Gallium Antimonide (GaSb), Gallium Arsenide Antimonide (GaAsSb), Aluminum Arsenide (AlAs), Aluminum Gallium Arsenide (AlGaAs), Aluminum Indium Arsenide (AlInAs), Indium Gallium Phosphide (InGaP), Indium Gallium Arsenide (InGaAs), Indium Arsenide Antimonide (InAsSb), Indium Phosphide Antimonide (InPSb), Indium Arsenide Phosphide Antimonide (InAsPSb), and Gallium Indium Arsenide Antimonide Phosphide (GaInAsSbP). 
     System  300  can also include an input region  382  located close to or near sample  320  or an external surface of the system. Input region  382  can include one or more transparent components including, but not limited to, a window, optical shutter, or mechanical shutter. 
     Light  350  can exit system  300  through input region  382 . In some examples, light  350  can be a collimated beam. Light that exits system  300  and travels through sample  320  to location  357  can be referred to as light  352 . Light  352  can be incident on location  357  at any angle including, but not limited to, 45°. In some examples, light  352  can have an angle of incidence at location  357  between 20° to 30°. In some examples, light  352  can have an angle of incidence at location  357  of 35°. Location  357  can include one or more properties of sample  320 . Light  352  can be partially absorbed prior to reaching location  357 , at location  357 , and/or after being partially reflected and/or scattered at location  357 , and can be referred to as light  354 . In some examples, light  354  can be formed by light transmitting through sample  320 . Light  354  can penetrate through sample  320  and can enter system  300  at location  313  of optic  310 . In some examples, optic  310  can be in contact or near sample  320 . Optic  310  can be any type of optical component, such as a lens, capable of changing the behavior and properties of the incoming light. Optic  310  can include a plurality of locations, such as location  313  and location  317 , where light exiting sample  320  is allowed to enter into system  300 . In some examples, optic  310  can include a transparent material. In some examples, optic  310  can be a lens configured with a large aperture (e.g., an aperture larger than the size of the incoming light beam) and a short focal length (e.g., the focal length can be such that a sample  220  within 10 mm proximity to system is in focus). In some examples, optic  310  can be a Silicon lens or a lens including silicon dioxide. 
     System  300  can include optics, such as optic  316  and optic  318 . In some examples, optic  316  and optic  318  can be objective lenses. An objective lens is a lens capable of collecting incident light and magnifying the light beam, while having a short focal length. Optic  316  can collect light  354  and direct light  354  towards opening  385  included in aperture layer  386 . Aperture layer  386  can include one or more openings, such as opening  385  and opening  387 , configured to allow light to transmit through. Aperture layer  386  can be capable of selecting light with one or more specific path lengths, angles of incidence, or both and rejecting or attenuating light with other path lengths or angles of incidence. Selection and rejection of light based on path length, angle of incidence, or both can be optimized by adjusting the aperture size (i.e., the size of an opening in the aperture layer). The selected light (i.e., light with one or more specific path lengths, angles of incidence, or both) can be in focus when it reaches an opening in the aperture layer, and rejected light can be out of focus. Light that is out of focus can have a beam size that is larger than the aperture size, can have an angle of incidence that is outside the collection range, or both, and therefore can be rejected. Light that is in focus can have a light beam that is within a range of path lengths and range of collection angles, and therefore can be allowed to transmit through the aperture layer. 
     Light  354  exiting opening  385  in aperture layer  386  can be transmitted through optic  318  and can be incident on optic  323 . Optic  323  can be included in optics unit  39 . Optics unit  39  can comprise a plurality of optics, such as optic  323  and optic  327 , attached to a substrate. In some examples, the optics can be of any type and can include any type of material conventionally used in optics. In some examples, two or more of the optics can have the same optical and/or geometric properties. One skilled in the art would appreciate that the same optical properties and the same geometric properties can include tolerances that result in a 15% deviation. In some examples, optics unit  39  can be coupled to one or more aperture layers. In some examples, optics unit  39  can be coupled to a patterned aperture layer, such as an aperture layer including locations between adjacent optics are opaque to prevent light mixing. 
     Light  354  can be transmitted through optic  323  and can be incident on detector pixel  333  included in detector array  330 . Detector array  330  can include a plurality of detector pixels, such as detector pixel  333 , detector pixel  335 , and detector pixel  337 . A detector pixel can include one or more detector elements with a common footprint (e.g., same size and shape). A detector element can be an element designed to detect the presence of light and can individually generate a signal representative of the detected light. In some examples, at least one detector pixel can be independently controlled (e.g., measured, observed, or monitored) from other detector pixels in detector array  330 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR range. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 1.5-2.5 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be associated with a particular sample position and/or angle of light incident on a surface of system  300 . Detector pixel  333  can detect light  354  and can generate an electrical signal indicative of the properties of the detected light  354 . Detector array  330  can transmit the electrical signal to controller  340 , and controller  340  can process and/or store the electrical signal. 
     System  300  can determine the one or more properties in sample  320  by utilizing the information from light penetrating through sample  320  (and reflecting off locations within the sample) in conjunction with the information from light reflecting off reference  322 . Light source  302  can emit light  364 . Light  364  can be directed at reference  322 . Reference  322  can include any type of material capable of at least partially reflecting light. Exemplary reflective materials can include, but are not limited to, Ti, Co, Nb, W, NiCr, TiW, Cr, Al, Au, and Ag. In some examples, reflective materials can include one or more dielectric layers. One or more properties (e.g., thickness) of reference  322  can be determined based on the wavelength of light, type of material, and/or composition of the reference. In some examples, the size and shape of reference  322  can be configured to be larger or the same size and/or shape of light  364 . One skilled in the art would appreciate that the same size and same shape can include tolerances that result in a 15% deviation. In some examples, the optical and/or physical properties of reference  322  can be such that the reflectivity of light  364  is greater than 75%. In some examples, the optical and/or physical properties of reference  322  can be such that the reflectivity of light  364  is greater than 90%. In some examples, the size and shape of reference  322  can be such that less than 15% of light  364  is allowed to transmit through reference  322  and light  364  is prevented from reaching sample  320 . In some examples, reference  322  can be configured to reflect light  364  as a specular reflection. In some examples, reference  322  can be a spectroscopically neutral blocker. In some examples, the reference signal can include chopping light  364  between sample  320  and reference  322 . 
     Light  364  can reflect off reference  322  towards optic  316 . Light  364  can be transmitted through optic  316  towards aperture layer  386 . Aperture layer  386  can be configured with opening  389 , whose size and shape can be configured to allow light  364  to transmit through. Light  364  exiting opening  389  can be incident on optic  318 . Light  364  can be transmitted through optic  318  and be incident on optic  319 . Optic  319  can be any type of optics configured for spreading out the incoming light beam. In some examples, optic  319  can be a negative lens, which is a lens with a focal length that is negative. In some examples, optic  319  can be a prism. In some examples, optic  319  can include a prism wedge angled for each detector pixel in detector array  330 . In some examples, optic  319  can be a beamsplitter. In some examples, optic  319  can be configured to spread out or divide light into multiple light beams, such as light  366  and light  367 . In some examples, optic  319  can spread out light such that each light beam is directed to a different detector pixel on detector array  330 . In some examples, optic  319  can uniformly spread out light such that one or more properties of each light beam are the same. One skilled in the art would appreciate that the same properties can include tolerances that result in a 15% deviation. In some examples, optic  319  can spread out the light beam such that intensities of at least two light beams are different. In some examples, optic  319  can comprise multiple optics. In some examples, the size and/or shape of optic  319  can be based on the number of detector pixels and/or the properties of the one or more light beams exiting optic  319 . In some examples, an aperture layer can be coupled to optic  319  to control the properties and/or direction of light exiting optic  319 . 
     Light  364  can be transmitted through optic  319  to form light  366 . Light  366  can be incident on detector pixel  333 . Detector pixel  333  can detect light  366  and can generate an electrical signal indicative of the properties of detected light  366 . In some examples, the number of detector pixels configured to detect a light beam can be different for different light beams. For example, light  355  can be detected by two detector pixels (e.g., detector pixel  335  and detector pixel  337 ), while light  354  can be detected by one detector pixel (e.g., detector pixel  233 ). The electrical signal can be transmitted from detector array  330  to controller  340 . Controller  340  can process and/or store the electrical signal. Controller  340  can utilize the signal information measured from light  354  to determine the reflectivity or one or more properties along the light path directed to location  357  and can utilize the signal information from light  366  to detect any fluctuations or drift in light source  302  and/or detector array  330 . Using any of the above discussed methods, the controller  340  can process both the electrical signal and the signal information to determine the one or more properties of sample  320 . 
     The same components can be used for measurements at other locations, such as location  359 , in sample  320 . Light  352  that is not absorbed or reflected along the light path directed to location  357  can be referred to as light  353 . Light  353  can be incident on location  359  and can reflect and/or scatter into system  300  as light  355 . In some examples, the angle of incidence of light  355  at the surface of system  300  can be different from the angle of incidence of light  354 . Light  355  can enter system  300  through optic  310  at location  317 . Light  355  can be transmitted through optic  316  and can be incident on aperture layer  386 . Aperture layer  386  can include opening  387  configured to allow light  355  (and any light with the same path length, angle of incidence, or both) to transmit through. One skilled in the art would appreciate that the same path length and same angle of incidence can include tolerances that result in a 15% deviation. In some examples, since light reflected from location  357  can have a path length different from light reflected from location  359 , aperture layer  386  can include multiple openings with different sizes and/or shapes to account for the different properties (e.g., path length and angle of incidence) of the optical paths. For example, opening  385  can be configured with a size and shape based on the path length and angle of incidence of light  354 , and opening  387  can be configured with a size and shape based on the path length and angle of incidence of light  355 . Light  355  can be transmitted through opening  387  in aperture layer  386 , can be transmitted through optic  318 , and can be incident on optic  327  included in optics unit  39 . Light  355  can be transmitted through optic  327 , and optic  327  can converge, redirect, collimate, focus, and/or magnify light such that light  355  is detected by detector pixel  335  and detector pixel  337 . Detector pixel  335  and detector pixel  337  can detect light  355  and can generate an electrical signal indicative of the properties of detected light  355 . The detector array  330  can transmit the electrical signal to controller  340 , and controller  340  can process and/or store the electrical signal. 
     Controller  340  can utilize the signal information measured from light  355  to determine one or more properties of sample  320  and can utilize the signal information from light  367  to detect any fluctuations or drift in light source  302  and/or detector array  330 . Controller  340  can process both of the collections of signal information to determine one or more properties along the light path directed to location  359  located in sample  320 . In some examples, controller  340  can detect light  366  incident on detector pixel  333  and light  367  incident on detector pixel  335  and detector pixel  337  simultaneously without the need for separate measurements. In some examples, location  357  and location  359  can have the same depth from the surface of sample  320 . One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, location  357  and location  359  can have different depths from the surface of sample  320 . Controller  340  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, or absorbance at both location  357  and location  359  and can average the values. 
     Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. In some examples, light can be incident on the multiple locations at the same angle of incidence. In some examples, the light source can be configured to generate one light beam exiting the system that results in multiple input light beams reflected and/or scattered back into the system. In some examples, the system can be configured with one or more light sources that emit light at locations with different angles of incidence, where the light can be emitted at the same time or at different times. 
     As illustrated in the figure, system  300  can include a plurality of openings in the aperture, a plurality of optics, and a plurality of detector pixels, where each opening and optics can be coupled to a detector pixel. Each opening/optics/detector pixel trio can be associated with an optical path in sample  320 . In some examples, the association can be one opening-optics-detector pixel trio to one optical path in the sample  320 . For example, opening  385 , optic  323 , and detector pixel  333  can be associated with the optical path from light  354 . Similarly, opening  387 , optic  327 , and detector pixel  337  can be associated with the optical path from light  355 . Since controller can associate detector pixel  333  and detector pixel  337  with different locations (e.g., location  357  and location  359 ) in sample  320  and different depths or path lengths, the controller  340  can discern differences in path lengths, depths of penetration, angles of incidence, exit locations, and/or exit angles. 
     In some examples, system  300  can further include a light blocker  392 . Light blocker  392  can include any material capable of absorbing or blocking light. In some examples, light blocker  392  can include any material (e.g., an anti-reflection coating) that prevents incident light from reflecting. In some examples, light blocker  392  can include any material that reflects at wavelengths different from the detection wavelengths of detector array  330 . 
       FIG. 4A  illustrates a cross-sectional view of an exemplary portion of a system configured for resolving multiple angles of incidence on a sample surface with two-layers of optics according to examples of the disclosure. System  400  can be close to, touching, resting on, or attached to sample  420 . Sample  420  can include one or more locations, such as location  457 . In some examples, the one or more locations can be associated with one or more scattering events. System  400  can be configured to reimage the optical paths in sample  420 . For example, system  400  can be configured to reimage the angles of incident light and the exit locations to another plane (e.g., a plane located closer to detector array  430 ). Reimaging of the optical paths can be performed using one or more layers of optics. System  400  can include two layers of optics, for example. Located below (i.e., opposite the surface of sample  420 ) the layers of optics can be a detector array  430 , and the two-layers of optics can be supported by support  414 . Located between the two layers of optics can be air, a vacuum, or any medium with a refractive index that contrasts the refractive index of the optics. Although the figures illustrates a system including two-layers of optics, examples of the disclosure can include, but are not limited to, any number of layers of optics including one layer or more than two layers. 
     System  400  can include light sources  402 . Light sources  402  can be configured to emit light  450 . Light sources  402  can be any source capable of generating light including, but not limited to, a lamp, laser, light emitting diode (LED), organic light emitting diode (OLED), electroluminescent (EL) source, quantum dot (QD) light emitter, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light sources  402  can be capable of emitting a single wavelength of light. In some examples, light sources  402  can be capable of emitting a plurality of wavelengths of light. In some examples, light sources  402  can be any tunable source capable of generating a SWIR signature. In some examples, each of light sources  402  can emit a different wavelength range of light (e.g., different colors in the spectrum). In some examples, light sources  402  can include a III-V material, such as Indium Phosphide (InP), Gallium Antimonide (GaSb), Gallium Arsenide Antimonide (GaAsSb), Aluminum Arsenide (AlAs), Aluminum Gallium Arsenide (AlGaAs), Aluminum Indium Arsenide (AlInAs), Indium Gallium Phosphide (InGaP), Indium Gallium Arsenide (InGaAs), Indium Arsenide Antimonide (InAsSb), Indium Phosphide Antimonide (InPSb), Indium Arsenide Phosphide Antimonide (InAsPSb), and Gallium Indium Arsenide Antimonide Phosphide (GaInAsSbP). 
     Light from light sources  402  can be combined using integrated tuning elements  404 , optical traces (not shown), and one or more multiplexers (not shown). In some examples, integrated tuning elements  404 , the optical traces, and the multiplexer(s) can be disposed on a substrate  442  or included in a single optical platform, such as a silicon photonics chip. System  400  can also include a thermal management unit  401  for controlling, heating, or cooling the temperature of light sources  402 . Coupled to one or more multiplexers can be outcouplers  409 . Outcouplers  409  can optionally be configured to focus, collect, collimate, and/or condition (e.g., shape) the light beam from the multiplexer(s) towards optic  416 . In some examples, outcouplers  409  can be configured as a single mode waveguide that directs a well-defined (i.e., directional) light beam towards optic  416 . In some examples, light  450  from outcouplers  409  can be a light beam with any suitable shape (e.g., conical, cylindrical, etc.). In some examples, light  450  from outcouplers  409  can become totally internally reflected (TIR) and “trapped” between substrate  442  and one or both of the layers of optics. Optic  416  can receive light  450  and can collimate and/or tilt the light beam towards one or more locations in sample  420 . In some examples, optic  416  can include a bottom surface (i.e., surface facing outcouplers  409 ) that is flat (or within 10% from flat) and a top surface (i.e., surface facing away from outcouplers  409 ) that is convex. Light that is emitted from light sources  402 , collimated by outcouplers  409 , transmitted through optic  416 , and then exits system  400  can be referred to as light  452 . 
     In some examples, outcouplers  409  can be coupled to a waveguide including in a junction.  FIG. 4B  illustrates an exemplary junction coupled to the light sources according to examples of the disclosure. Junction  403  can be configured to split or divide light emitted from light sources  402 , where a portion of light can be directed to waveguide  405  and a portion of light can be directed to waveguide  407 . Waveguide  405  can be coupled to an outcoupler  409 , which can direct light to sample  420 . Waveguide  407  can also be coupled to an outcoupler  409 , which can direct light to reference  422 . In some examples, light from light sources  402  can split at junction  403 , and light can be split equally among waveguide  405  and waveguide  407 . In some examples, junction  403  can be an asymmetric y-junction, and light can be split such that the intensity of light through waveguide  405  is greater than the intensity of light through waveguide  407 . 
     In some examples, the height and width of waveguide  405 , waveguide  407 , or both can be configured based on the size and shape of the light beam and divergence properties. For example, for an elliptical light beam, the aspect ratio of waveguide  405  can be configured to be greater than one. In some examples, the aspect ratio of waveguide  405  can be equal to one, and the light beam can be circular in shape. In some examples, the aspect ratio of waveguide  405  can be less than one. In some examples, the height of the waveguide can be less than the width of the waveguide such that the light beam diverges asymmetrically. 
     As discussed above, reference switching can include alternating between transmitting light to sample  420  and transmitting light to reference  422 . While this switching can be performed using mechanical moving parts, examples of the disclosure can include non-moving parts that block light, such as diode  411 . Diode  411  can be coupled to a source  413 , which can be configured to supply a current through waveguide  405 . With a current through waveguide  405 , the electrons in the current can absorb the photons in light traveling through waveguide  405 , which can prevent light from being output from waveguide  405 . Light through waveguide  407  can also be modulated with another diode  411  coupled to another source  413 , which can be configured to supply a current through waveguide  407 . In some examples, waveguide  405  and/or waveguide  407  can include be configured such that the current passes through multiple locations along the waveguide, as illustrated in  FIG. 4C . By passing current through multiple locations along the waveguide, a lower current supplied from source  413  may be needed to block light, which can lead to lower power consumption. Although  FIG. 4B  illustrates two diodes (e.g., diode  411  coupled to waveguide  405  and another diode  411  coupled to waveguide  407 ), examples of the disclosure can include any number of diodes. 
     Referring back to  FIG. 4A , light  452  can be directed at sample  420  and can be incident on location  457 . A portion of light  452 , referred to as light  454 , can reflect back and/or scatter to system  400  with an angle of incidence θ 1 . In some examples, light  452  exiting system  400  can be a collimated light beam, where one or more scattering events can occur along the light path directed to location  457  and can lead to light  454  becoming a scattered light beam. Light  454  can enter system  400  and can be incident on optic  418 , included in optics unit  410 . In some examples, light  454  can be a collimated light beam. 
     System  400  can include one or more optics units. In some examples, the optics units can have one or more different functionalities and/or can include one or more different materials. For example, optics unit  410  can change the general direction of light, while optics unit  429  can focus the light. In some instances, optics unit  410  can include sapphire lenses, while optics unit  429  can include silicon lenses. 
     Optics unit  410  can include one or more optics (e.g., lenses, micro-optics, or micro-lens) configured to collect incident light, condition the size and shape of the light beam, and/or focus incident light. For example, optic  418  can collect light  454  incident on system  400  with an angle of incidence θ 1 . Optic  418  can change the angle (i.e., redirect the light beam) of light  454  such that light  454  is directed towards the optics unit  429  and has an angle of incidence on the optics unit  429  less than the angle of incidence θ 1 . In some examples, the medium between optics unit  410  and optics unit  429  can be configured with a refractive index such that the change in angle (i.e., bending) of light  454  decreases. In some examples, the medium can be multi-functional and can include a conformal material that provides mechanical support. In some examples, optic  418  can focus light  454  at least partially. In some examples, optics unit  410  can preferentially collect light rays included in light  454  with an angle of incidence within a range of collection angles. In some examples, optics unit  410  can include plurality of silicon lenses. In some examples, optics unit  410  can include one or more optics. Although  FIG. 4A  illustrates optics unit  410  attached to support  414 , examples of the disclosure can include optics unit  410  attached to or coupled to optics unit  429  through mechanical features etched into optics unit  410 , optics unit  429 , or both. In some examples, at least two optics included in optics unit  410  can have different geometric properties. A detailed discussion of the properties of the optics in optics unit  410  is provided below. 
     System  400  can also include an aperture layer  486 . Aperture layer  486  can include an opening  487  configured to allow light  454  (or any light with the same angle of incidence θ 1 ) to transmit through. One skilled in the art would appreciate that the same angle of incidence can include tolerances that result in a 15% deviation. Light  454  that has been transmitted through opening  487  can be directed towards optic  423 , included in optics unit  429 . Optics unit  429  can comprise a plurality of optics, such as optic  423  and optic  427 , attached to a substrate. In some examples, optic  423  and optic  427  can be any type of optics and can include any type of material conventionally used in optics. In some examples, two or more of the optics in optics unit  429  can have the same optical and/or geometric properties. One skilled in the art would appreciate that the same optical properties and geometric properties can include tolerances that result in a 15% deviation. In some examples, optic  416  and the optics (e.g., optic  423  and optic  427 ) included in the optics unit  429  can be disposed and/or formed on the same substrate. In some examples, optic  416  and optics unit  429  can be fabricated at the same time using lithography and the same etching process. The lithographic patterning can define the alignments of the optics, which can reduce the number of alignment steps and the number of separately fabricated components. Although  FIG. 4A  illustrates optics unit  429  attached to support  414 , examples of the disclosure can include optics unit  429  attached to or coupled to optics unit  410  through mechanical features etched into optics unit  410 , optics unit  429 , or both. In some examples, at least two optics included in optics unit  429  can have different geometric properties. A detailed discussion of the properties of the optics in optics unit  429  is provided below. 
     Optic  423  can focus light  454  towards detector array  430 . In some examples, light  454  can undergo at least partial refraction from optic  418 . Optic  423  can recollimate light  454  and focus light  454 . In some examples, system  400  can be configured such that light  454  is turned by optics unit  410  and focused by optics unit  429 . In some examples, system  400  can be configured such that light  454  is turned by both optics unit  410  and optics unit  429 . In some examples, optics unit  429  can include a plurality of silicon micro-optics. 
     Light  454  can transmit through optic  423  and can be detected by detector pixel  433 , included in detector array  430 . Detector array  430  can include one or more detector pixels, such as detector pixel  433  and detector pixel  437 , disposed on a substrate. In some examples, the substrate can be a silicon substrate. A detector pixel can include one or more detector elements with a common footprint (e.g., same size and shape). A detector element can be an element designed to detect the presence of light and can individually generate a signal representative of the detected light. In some examples, at least one detector pixel can be independently controlled from other detector pixels in detector array  430 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR range. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 1.5-2.5 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a position and/or angle of light incident on a surface of the detector pixel. Detector pixel  433  can be coupled to an integrated circuit, such as read-out integrated circuit (ROIC)  441 . Each circuit in ROIC  441  can store charge corresponding to the detected light (or photons of light) on the detector pixel in an integrating capacitor to be sampled and read out by a processor or controller (not shown). The stored charge can correspond to one or more optical properties (e.g., absorbance, transmittance, and reflectance) of light  454 . In some examples, ROIC  441  can be fabricated on a silicon substrate. 
     Another portion of light  452  incident on location  457  can reflect back into system  400  with an angle of incidence θ 3 , and can be referred to as light  455 . Light  455  can enter system  400  and can be incident on optic  419 , included in optics unit  410 . Similar to optic  418 , optic  419  can collect incident light, condition the beam size and shape (e.g., redirect the light beam), and/or focus incident light. Light  455  can be transmitted through opening  489  included in aperture layer  486 . Light  455  can be directed towards optic  427  included in optics unit  429 . Optic  427  can focus light  455  towards detector pixel  437  included in detector array  430 . In some examples, system  400  can be configured such that light  455  is redirected by optics unit  410  and focused by optics unit  429 . In some examples, system  400  can be configured such that light  455  is redirected by both optics unit  410  and optics unit  429 . 
     As discussed earlier, system  400  can include a plurality of optics (e.g., optic  418  and optic  419 ) included in optics unit  410  and a plurality of optics (e.g., optic  423  and optic  427 ) included in optics unit  429 , where each of the optics can be coupled to a detector pixel (e.g., detector pixel  433  or detector pixel  437 ) included in detector array  430 . Each first optics-second optics-detector pixel trio can be associated with an optical path in sample  420 . In some examples, the association can be one first optics-second optics-detector pixel trio to one optical path in sample  420 . For example, optic  418 , optic  423 , and detector pixel  433  can form a first optics-second optics-detector pixel trio that is associated with the optical path from light  454 . Similarly, optic  419 , optic  427 , and detector pixel  437  can form another first optics/second optics/detector pixel trio that is associated with the optical path from light  455 . In this manner, system  400  can be capable of reimaging and resolving the multiple optical paths with different angles of incidence in sample  420 , where each detector pixel in detector array  430  can be dedicated to a different optical path. 
     Although  FIG. 4A  illustrates detector pixel  433  and detector pixel  437  as single detector pixels, each individually associated with optics, examples of the disclosure can include multiple detector pixels associated with the same optics and multiple optics associated with the same detector pixel. 
     In some examples, system  400  can integrate the path lengths within a range of path lengths and associate the integrated path lengths with a detector pixel. By integrating the path lengths, different azimuthal angles can be resolved. Since there can be multiple sources (e.g., incident light from a single scattering event or incident light from multiple scattering events that change the path length) to optical paths that can have the same azimuthal angle, system  400  can resolve the different sources. In some examples, resolving the different azimuthal angles can require a large format (e.g., more than a hundred detector pixels) detector array. 
     In some examples, system  400  can be configured such that at least two first optics/second optics/detector pixel trios can resolve different angles of incidence. For example, as discussed earlier, light  454  can have an angle of incidence θ 1 , and light  455  can have an angle of incidence θ 3 . In some examples, angle of incidence θ 1  can be different from angle of incidence θ 3 . In some examples, light  454  can have a different angle of incidence than light  455 , but can have the same path length, for example. One skilled in the art would appreciate that the same path length can include tolerances that result in a 15% deviation. System  400  can associate different detector pixels or the same detector pixels in detector array  430  with different angles of incidence. For example, detector pixel  433  can be associated with angle of incidence θ 1 , and detector pixel  437  can be associated with angle of incidence θ 3 . In some examples, the optical system can operate at infinite conjugate (i.e., infinite distance where the light rays collimate), so the properties (e.g., focal length, working distance, aperture, pitch, fill-factor, tilt, and orientation) of the optics included in optics unit  410  can be determined based on the angle of incidence. 
     In some examples, aperture layer  486  can be located between optics unit  410  and optics unit  429 . Aperture layer  486  can be located a focal length away from optics unit  410  and a focal length away from optics unit  429 . Additionally, system  400  can be configured with detector array  430  located a focal length away from optics unit  429 . This configuration can require at least four layers in the stackup of system  400 : optics unit  410  on a first layer, aperture layer  486  on a second layer, optics unit  429  on a third layer, and detector array  430  on a third layer. However, fewer numbers of layers may be desired for a system with a thinner stackup, for example. 
       FIGS. 4D-4H  illustrate cross-sectional views of exemplary optics included in a system configured for resolving multiple optical paths in a sample according to examples of the disclosure. System  400  can include one or more aperture layers located on the same layer as one or more optics or components in the system. As illustrated in  FIG. 4D , aperture layer  486  can be located on the same layer as optics unit  410 . In some examples, aperture layer  486  can be located on a surface of optics unit  410 . Although the figure illustrates aperture layer  486  as being located on the bottom surface (i.e., surface facing optics unit  429 ) of optics unit  410 , examples of the disclosure can include aperture layer  486  located on the top surface of optics unit  410 . In some examples, aperture layer  486  can be located on the same layer as optics unit  429 , as illustrated in  FIG. 4E . Examples of the disclosure can also include aperture layer  486  located on two layers: the same layer as optics unit  410  and the same layer as optics unit  429 , as illustrated in  FIG. 4F . In some examples, the aperture layer can comprise an opaque element, such as a metal, at least in part. In some examples, the aperture layer can be a lithographically patterned layer applied to one or more surfaces of the optics unit(s). 
       FIG. 4G  illustrates one or more optics integrated into the structure of system  400 . The integrated optics can be configured to selectively transmit light through the optics based on one or more properties, such as path length or angle of incidence of incident light. In some examples, system  400  can include one or more integrated optics included in the optics unit  429 , as illustrated in  FIG. 4H . In some examples, the integrated optics illustrated in  FIGS. 4G-4H  can be continuous with the surface of optics unit  410  and optics unit  429 . 
     Although  FIGS. 4D-4H  illustrate optic  416  located on the same layer (e.g., integrated with) as optics unit  429 , examples of the disclosure can include optic  416  located on the same layer (e.g., integrated with) as optics unit  410 . Additionally, although  FIGS. 4D-4F  illustrate aperture layer  486  located on either the bottom side of optics unit  410  or the top side of optics unit  429 , examples of the disclosure can include the same or an additional aperture layer located on the other side. 
       FIG. 4I  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple angles of incidence on a sample surface and reducing or eliminating TIR trapped light from the light sources according to examples of the disclosure. System  400  can be configured such that outcoupler  409  is in contact with the bottom surface (i.e., the flat surface) of optics unit  429 . System  400  can also be configured such that detector array  430  is located below (i.e., opposite optics unit  429 ) substrate  442 . By placing the top surface (i.e., surface where light exits outcouplers  409 ) of outcouplers  409  in contact with the bottom surface of optics unit  429  and locating detector array  430  below the (i.e., away from the direction of light exiting the outcouplers  409 ) substrate  442 , detector array  430  can be prevented from erroneously detecting TIR trapped light that has directly exited outcouplers  409 . Furthermore, locating detector array  430  below substrate  442  can prevent light reflected off the bottom surface (i.e., the flat surface) of optics unit  429  from being detected by detector array  430  and erroneously changing the measured signal. 
       FIG. 5  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple angles of incidence on a sample surface with one-layer of optics according to examples of the disclosure. System  500  can include one or more components as discussed in the context of and illustrated in  FIGS. 4A-4I . Additionally, system  500  can include optics unit  512 , which can be capable of combining the functionality of optics unit  410  and optics unit  429  illustrated in  FIGS. 4A-4I . Optics unit  512  can include one or more optics, micro-optics, microlens, or a combination of optics configured to collect incident light, condition the beam size and shape, and focus incident light. Optics unit  512  can collect light  554  and light  555  incident on system  500  with the angles of incidence θ 1  and θ 3 , respectively. The optics included in optics unit  512  can change the angle (i.e., redirect the light beam) of light (e.g., light  554  and light  555 ) such that light is directed towards detector array  530 . Turning light  554  and light  555  can lead to an angle of incidence on detector array  530  that is less than angles of incidence θ 1  and θ 3 , respectively. In some examples, the medium between optics unit  512  and detector array  530  can be configured with a refractive index such that the changes in angle (i.e., bending) of light  554  and light  555  increase. In some examples, the medium can be multi-functional and can include a conformal insulating material that provides mechanical support. In some examples, the optics included in optics unit  510  can preferentially collect light rays, included in light  554  and light rays included in light  555  with angles of incidence within a range of collection angles. In some examples, the range of collection angles for the optics coupled to light  554  can be different from the range of collection angles coupled to light  555 . 
     Additionally, optic  518  and optics  519 , included in optics unit  512 , can focus light  554  and light  555  towards detector pixel  533  and detector pixel  537 , respectively, included in detector array  530 . Although a system (e.g., system  400  illustrated in  FIGS. 4A-4I ) with two-layers of optics can include an optics unit (e.g., optics unit  410 ) that can be configured for light collection, turning the beam, and focusing incident light, optics unit  512  can be configured with a higher focusing power (i.e., degree which the optics converges or diverges incident light) than the system with the two-layers of optics. In some examples, optics unit  512  can include a plurality of silicon lenses or lenses including silicon dioxide. In some examples, at least two optics included in optics unit  512  can have different geometric properties. A detailed discussion of the properties of the optics in the optics unit  512  is provided below. 
     System  500  can also include an aperture layer  586 . Aperture layer  586  can include a plurality of openings configured to allow light  554  and  555  (e.g., any light with an angle of incidence within a range of collection angles), respectively, to transmit through. In some examples, aperture layer  586  can be located on an external surface (e.g., the housing) of system  500  and can be configured to allow light to enter into system  500 . Although  FIG. 5  illustrates aperture layer  586  located on an external surface of the system  500 , examples of the disclosure can include aperture layer  586  located on another side (e.g., an internal surface of the system  500 ) or another layer. 
     Each optics included in optics unit  512  can be coupled to a detector pixel (e.g., detector pixel  533  or detector pixel  537 ), included in detector array  530 . Each optics-detector pixel pair can be associated with an optical path in sample  520 . In some examples, the association can be one optics-detector pixel pair to one optical path. For example, optic  517  and detector pixel  533  can form an optics-detector pixel pair that is associated with the optical path from light  554 , and optic  518  and detector pixel  537  can form another optics-detector pixel pair that is associated with the optical path from light  555 . Although  FIG. 5  illustrates detector pixel  533  and detector pixel  537  as single detector pixels, each individually associated with optics, examples of the disclosure can include multiple detector pixels associated with the same optics and multiple optics associated with the same detector pixel. 
     In some examples, the system can be configured with one-layer of optics to reduce the stackup or height of the system. In some examples, the system can be configured with two-layers of optics for higher angular resolution, larger angular range of incident light, or both. In some examples, the system can be configured with the number of layers of optics being different for light emitted from the light sources than for light collected from the sample. For example, the system can be configured with one-layer of optics for light emitted from the light sources and two-layers of optics for light reflected from the sample, or the system can be configured with two-layers of optics for light emitted from the light sources and one-layer of optics for light reflected from the sample. 
       FIG. 6  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple optical path lengths with two-layers of optics according to examples of the disclosure. System  600  can be close to, touching, resting on, or attached to sample  620 . Sample  620  can include one or more locations, such as location  657  and location  659 . System  600  can be configured to reimage and/or resolve the optical paths in sample  620 . For example, system  600  can be configured to reimage the path lengths of the optical paths to another plane (e.g., a plane located closer to detector array  630 ). Reimaging of the optical paths can be performed using one or more layers of optics. System  600  can include two layers of optics and a detector array  630  located below (i.e., opposite the surface of sample  620 ) with the multiple layers supported by support  614 , for example. Located between the two layers of optics can be air, a vacuum, or any medium with a refractive index that contrasts from the refractive index of the optics. 
     System  600  can include light sources  602 . Light sources can be configured to emit light  650 . Light source  602  can be any source capable of generating light including, but not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light sources  602  can be capable of emitting a single wavelength of light. In some examples, light sources  602  can be capable of emitting a plurality of wavelengths of light. In some examples, light sources  602  can be tunable sources capable of generating a SWIR signature. In some examples, at least one of light sources  602  can include a III-V material, such as InP or GaSb. 
     Light from light sources  602  can be combined and amplified using integrated tuning elements  604 , optical traces (not shown), and a multiplexer (not shown). In some examples, integrated tuning elements  604 , optical traces, and multiplexer can be disposed on a substrate or included in a single optical platform, such as a silicon photonics chip. System  600  can also include a thermal management unit  601  for controlling, heating, or cooling the temperature of light sources  602 . Coupled to the multiplexer can be outcouplers  609 . Outcoupler  609  can be configured to focus and/or condition (e.g., shape) light  650  from the multiplexer towards optic  616 . In some examples, outcouplers  609  can be configured as a single mode waveguide that directs a well-defined (i.e., directional and sharp) light beam towards optic  616 . In some examples, light  650  from outcouplers  609  can be a light beam with any suitable shape (e.g., conical, cylindrical, etc.). Optic  616  can collect light  650  and collimate and/or tilt the light beam towards one or more locations in sample  620 . In some examples, optic  616  can include a bottom surface (i.e., surface facing outcouplers  609 ) that is flat and a top surface (i.e., surface facing away from outcouplers  609 ) that is convex. One skilled in the art would appreciate that a flat surface can include tolerances that result in a 15% deviation. Light that is emitted from light sources  602  that is collimated by outcouplers  609 , transmits through optic  616 , and then exits system  600  can be referred to as light  652 . 
     Light  652  can be directed at sample  620  and can be incident on location  657 . A portion of light  652 , referred to as light  654 , can reflect back towards system  600 . Additionally, a portion of light  652  can be incident on location  659  and can reflect back towards system  600 , and can be referred to as light  655 . Although light  652  exiting system  600  can be a collimated light beam, scattering events can occur along the light path directed to location  657  and location  659 , which can lead to light  654  and light  655  becoming scattered beams. Both light  654  and light  655  can enter system  600 , and can be incident on optic  618  and optic  619 , included in optics unit  610 , respectively. Optics unit  610  can include one or more optics, micro/or focus incident light. For example, optic  618  can collect light  654 , and optic  619  can collect light  655 . Optic  618  can change the angle (i.e., redirect the light beam) of light  654  such that light  654  is directed towards (i.e., closer to normal incidence than the angle of incidence) optic  623  included in optics unit  629 . In some examples, the medium between optics unit  610  and optics unit  629  can be configured with a refractive index such that the change in angle (i.e., bending) of light  654  increases. In some examples, the medium can be multi-functional and can include a conformal insulating material that provides mechanical support. Similarly, optic  619  can change the angle of light  655  such that light  655  is directed towards optic  627  included in optics unit  629 . In some examples, optic  618 , optic  619 , or both can be configured to focus incident light (e.g., light  654  and light  655 ). In some examples, optics unit  610  can preferentially collect light rays included in light  654 , light  655 , or both with an angle of incidence within a range of collection angles. In some examples, optics unit  610  can include a plurality of silicon lenses or lenses including silicon dioxide. Although  FIG. 6  illustrates optics unit  610  attached to support  614 , examples of the disclosure can include optics unit  610  attached to or coupled to optics unit  629  through mechanical features etched into optics unit  610 , optics unit  629 , or both. In some examples, at least two optics included in optics unit  610  can have different geometric properties. A detailed discussion of the properties of the optics in optics unit  610  is provided below. 
     System  600  can include an aperture layer  686 . Aperture layer  686  can include an opening  687  and opening  689  configured to allow light  654  and light  655  (e.g., any light with an angle of incidence within the range of collection angles), respectively, to transmit through. Light  654  that has been transmitted through opening  687  can be directed towards optic  623  included in optics unit  629 . Similarly, light  655  that has been transmitted through opening  689  can be directed towards optic  627  included in optics unit  629 . Optics unit  629  can comprise a plurality of optics, such as optic  623  and optic  627 , attached to a substrate. In some examples, optic  623  and optic  627  can be any type of optics and can include any type of material conventionally used in optics. In some examples, two or more of the optics in optics unit  629  can have the same optical and/or geometric properties. One skilled in the art would appreciate that the same optical properties and geometric properties can include tolerances that result in a 15% deviation. 
     Light  645  can undergo some refraction from optic  618 . Optic  623  can recollimate light  654  and/or focus light  654  onto detector pixel  633  included in detector array  630 . Similarly, optic  627  can recollimate light  655  and/or focus light  655  onto detector pixel  637  included in detector array  630 . In some examples, system  600  can be configured such that light  654  is redirected by optics unit  610  and focused by optics unit  629 . In some examples, system  600  can be configured such that light  654  is redirected by both optics unit  610  and optics unit  629 . In some examples, optics unit  629  can include a plurality of silicon lenses or lenses including silicon dioxide. Although  FIG. 6  illustrates optics unit  629  attached to support  614 , examples of the disclosure can include optics unit  629  attached to or coupled to optics unit  610  through mechanical features etched into optics unit  610 , optics unit  629 , or both. In some examples, at least two optics included in optics unit  629  can have different geometric properties. A detailed discussion of the properties of the optics in optics unit  629  is provided below. 
     Light  654  can be transmitted through optic  623  and can be detected by detector pixel  633  included in detector array  630 . Detector array  630  can include one or more detector pixels, such as detector pixel  633  and detector pixel  637  disposed on a substrate. In some examples, the substrate can be a silicon substrate. In some examples, at least one detector pixel can be independently controlled from other detector pixels in detector array  630 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR range. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 1.5-2.5 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a position and/or angle of incidence. 
     Additionally, light  655  can be transmitted through optic  627  and can be detected by detector pixel  637 . Detector pixel  633  and detector pixel  637  can be coupled to an integrated circuit, such as ROIC  641 . In some examples, detector pixel  633  and detector pixel  637  can be coupled to the same circuitry. In some examples, detector pixel  633  and detector pixel  637  can be coupled to different circuitry. Each circuit in ROIC  641  can store charge corresponding to the detected light (or photons of light) on the corresponding detector pixel in an integrating capacitor to be sampled and read out by a processor or controller. The stored charge can correspond to one or more optical properties (e.g., absorbance, transmittance, and reflectance) of the detected light. 
     System  600  can include a plurality of optics (e.g., optic  618  and optic  619 ) included in optics unit  610  and a plurality of optics (e.g., optic  623  and optic  627 ) included in optics unit  629 , where each of the optics can be coupled to a detector pixel (e.g., detector pixel  633  or detector pixel  637 ) included in detector array  630 . Each first optics/second optics/detector pixel trio can be associated with an optical path in the sample. In some examples, the association can be one first optics/second optics/detector pixel trio to one optical path. For example, optic  618 , optic  623 , and detector pixel  633  can be associated with the optical path from light  654 . Optic  619 , optic  627 , and detector pixel  637  can be associated with the optical path from light  655 . In this manner, system  600  can be capable of reimaging and resolving the multiple optical paths with different path lengths in sample  620 , where each detector pixel in detector array  630  can be associated with a different optical path. Although  FIG. 6  illustrates detector pixel  633  and detector pixel  637  as single detector pixels, each individually associated with optics, examples of the disclosure can include multiple detector pixels associated with the same optics and multiple optics associated with the same detector pixel. 
     As illustrated in the figure, system  600  can be configured such that at least two first optics/second optics/detector pixel trios can resolve different path lengths. For example, light  654  can have a first optical path length, and light  655  can have a second optical path length. The first optical path length associated with light  654  can be different from the second optical path length associated with light  655  due to the different depths of the different locations (e.g., location  657  and location  659 ) that the light rays reflect off. In some examples, light  654  can have the same angle of incidence as light  655 , but can have a different path length. One skilled in the art would appreciate that the same angle of incidence can include tolerances that result in a 15% deviation. System  600  can couple different detector pixels in detector array  630  with different path lengths. For example, detector pixel  633  can be associated with the first optical path length, and detector pixel  637  can be associated with the second optical path length. In some examples, the optical system can operate at finite conjugate (i.e., a finite distance where the light rays collimate), and the properties (e.g., focal length, working distance, aperture, pitch, fill-factor, tilt, and orientation) of the optics included in optics unit  610  can be determined based on the range of collection angles. In some examples, at least two optics included in optics unit  610  can have the same geometric properties, but can be located in different areas of optics unit  610 . A detailed discussion of the properties of the optics in optics unit  610  is provided below. 
     In some examples, the shapes, sizes, and geometric properties of the optics included in optics unit  610  can be different for an optical system (e.g., system  400  illustrated in  FIGS. 4A-4I  or system  500  illustrate in  FIG. 5 ) configured to resolve different angles of incidence than an optical system (e.g., system  600  illustrated in  FIG. 6 ) configured to resolve different path lengths. 
     In some examples, each first optics/second optics/detector pixel trio can be associated with a range of collection angles. As illustrated in the figure, light  654  can scatter from location  657  with a shape that resembles a cone, for example. System  600  can integrate the angles of the light rays included in light  654  azimuthally. Since the path lengths of the light rays can be the same, the integration of the angles within the range of collection angles can reduce the number of angle bins, number of detector pixels, and the complexity of the optics needed for the optical system. One skilled in the art would appreciate that the same path length can include tolerances that result in a 15% deviation. For example, an optical system that does not integrate the angles can require a minimum of eight detector pixels, whereas an optical system that does integrate the angles can require fewer number of detector pixels. 
     In addition to needing a smaller number of detector pixels, system  600  can utilize a smaller format (i.e., less than a hundred pixels) detector array that can have better performance (e.g., optical efficiency, fill-factor, and/or reliability) than a large format detector array. Additionally, by integrating the angles of the light rays, system  600  inherently performs spatial averaging of nominally equivalent optical paths incident on a detector pixel. The spatial averaging of nominally equivalent optical paths can lead to more light being incident on a detector pixel, which can lead to a higher signal-to-noise ratio (SNR). Spatial averaging also can lead to better measurement accuracy because unimportant light rays can be “canceled” or averaged out. 
     Although aperture layer  686  is illustrated in  FIG. 6  as located between optics unit  610  and optics unit  629 , examples of the disclosure can include aperture layer  686  located on the same layer as one or more optics or components in the system. Similar to the examples illustrated in  FIGS. 4D-4I , system  600  can be configured with aperture layer  686  located on a surface of optics unit  610 . In some examples, aperture layer  686  can be located on the same layer (e.g., a surface) as optics unit  629 . In some examples, aperture layer  686  can be located on the same layers as optics unit  610  and the same layer as optics unit  629 . In some examples, system  600  can include one or more recessed optics in optics unit  610 . The recessed optics can be configured to selectively transmit light through the optics based on one or more properties, such as path length and/or angle of incidence of incident light. In some examples, system  600  can include one or more recessed optics in optics unit  629 . One or more of the recessed optics can be continuous with the surface of optics unit  610  and optics unit  629 . In some examples, system  600  can include one or more etched or drilled holes for selectively transmitting light through the two-layers of optics to detector array  630 . With one or more etched or drilled holes used as an aperture layer, system  600  can include one or more spacers located between the surfaces of the two-layers of optics. The one or more spacers can be used to mechanically support the optics. 
       FIG. 7  illustrates a cross-sectional view of a portion of an exemplary system configured for resolving multiple optical path lengths with one-layer of optics according to examples of the disclosure. System  700  can include one or more components as discussed in the context of and illustrated in  FIG. 6 . Additionally, system  700  can include an optics unit  712  that can be capable of combining the functionality of optics unit  610  and optics unit  629  illustrated in  FIG. 6 . Optics unit  712  can include one or more optics, micro-optics, microlens, or a combination configured to collect incident light, condition the light beam size and shape, and focus incident light. Optic  718 , included in optics unit  712 , can collect light  754  reflected off location  757 . Optic  719 , included in optics unit  712 , can collect light  755  reflected off location  759 . The optics (e.g., optic  718  and optic  719 ) included in optics unit  712  can change the angle (i.e., redirect the light beam) of light (e.g., light  754  and light  755 ) such that light is directed towards detector array  730 . In some examples, the angles of incidence of light  754  and light  755  can be the same, and optic  718  and optic  719  can be configured to redirect incident light by the same degree. One skilled in the art would appreciate that the same angles of incidence and same degree can include tolerances that result in a 15% deviation. In some examples, the medium between optics unit  712  and detector array  730  can be configured with a refractive index such that the change in angle (i.e., bending) of light  754  and light  755  increases. In some examples, the medium can be multi-functional and can include a conformal insulating material that provides mechanical support. In some examples, the optics unit  712  can preferentially collect light rays included in light  754  and light rays included in light  755  with angles of incidence within a range of collection angles. 
     Additionally, optic  718  and optic  719 , included in optics unit  712 , can focus light  754  and light  755  towards detector pixel  733  and detector pixel  737 , respectively, included in detector array  730 . Although a system (e.g., system  600  illustrated in  FIG. 6 ) with two-layers of optics can include an optics unit (e.g., optics unit  610 ) that can be configured for light collection, turning the beam, and focusing incident light, optics unit  712  can be configured with a higher focusing power (i.e., degree which an optics converges or diverges incident light) than the system with the two-layers of optics. In some examples, optics unit  712  can include a plurality of silicon optics. 
     System  700  can also include an aperture layer  786 . Aperture layer  786  can include a plurality of openings configured to allow light  754  and  755  (e.g., any light with an angle of incidence within a range of collection angles), respectively, to transmit through. In some examples, aperture layer  786  can be located on an external surface (e.g., the housing) of system  700  and can be configured to allow light to enter into system  700 . Although  FIG. 7  illustrates aperture layer  786  located on an external surface of the system  700 , examples of the disclosure can include aperture layer  786  located on another side (e.g., an internal surface of the system  700 ) or another layer. 
     Each optics included in optics unit  712  can be coupled to a detector pixel (e.g., detector pixel  733  or detector pixel  737 ), included in detector array  730 . Each optics-detector pixel pair can be associated with an optical path in sample  720 . In some examples, the association can be one optics-detector pixel pair to one optical path. For example, optic  718  and detector pixel  733  can form an optics-detector pixel pair that is associated with light  754  (or light with the same optical path length as light  754 ), and optic  719  and detector pixel  737  can form another optics-detector pixel pair that is associated with light  755  (or light with the same optical path length as light  755 ). One skilled in the art would appreciate that the same optical path length can include tolerances that result in a 15% deviation. Although  FIG. 7  illustrates detector pixel  733  and detector pixel  737  as single detector pixels, each individually associated with optics, examples of the disclosure can include multiple detector pixels associated with the same optics and multiple optics associated with the same detector pixel. 
     In some examples, the system can be configured with one-layer of optics to reduce the stackup or height of the system. In some examples, the system can be configured with two-layers of optics for higher angular resolution, larger angular range of incident light, or both. In some examples, the system can be configured with the number of layers of optics being different for light emitted from the light sources and for light collected from the sample. For example, the system can be configured with one-layer of optics for light emitted from the light sources and two-layers of optics for light collected from the sample, or the system can be configured with two-layers of optics for light emitted from the light sources and one-layer of optics for light collected from the sample. 
     Although  FIGS. 2-7  illustrate the system close to the sample, examples of the disclosure can include a system configured for touching a surface of the sample. In some examples, a surface of the optics unit (e.g., optics unit  410 , optics unit  512 , optics unit  610 , or optics unit  712 ) can be touching a surface of the sample. Generally, closer proximity of the sample to the optics unit can lead to fewer and smaller optical components needed in the system, better measurement accuracy, and lower power consumption of the system. 
     The close proximity of the device can exploit a reduced effective numerical aperture (NA) of the light rays exiting the sample. The reduced effective NA can be used to characterize the range of angles that the system can accept as reflected light from the sample. This reduced effective NA can be due to angles of incidence on the optics and detector that are closer to normal incidence due to Snell&#39;s Law. With angles of incidence closer to normal, the aperture size and the pitch of the optics can be made smaller, leading to a smaller system. Additionally, the detector can receive a higher optical power, which can lead to better measurement accuracy and a system that can be configured for lower power consumption. 
       FIG. 8  illustrates Snell&#39;s Law according to examples of the disclosure. Snell&#39;s law can describe the properties of a light ray that refracts at an interface between two materials with different refractive indices. Snell&#39;s law is stated as:
 
 n   1  sin θ 1   =n   2  sin θ 2   (1)
 
     Material  810  can have a refractive n 1 , and material  812  can have a refractive index n 2 , where the refractive index n 1  can be different from the refractive index n 2 . The light ray can be incident on the material  810 -material  812  interface at angle of incidence θ 1 . Due to the refractive index difference between the two materials, the light ray can refract and can enter material  812  at an angle of refraction θ 2  different from the angle of incidence θ 1 . If material  810  has a refractive index less than the refractive index of material  812 , then the angle of refraction θ 2  can be reduced (i.e., closer to normal incidence). 
     With a high enough optical power, the optics unit can act like an immersion lens objective. An immersion lens objective can be a system where the optics and sample are surrounded or immersed in a medium with a contrasting refractive index. A contrasting refractive index can lead to a larger change in reduced effective NA than a non-immersed (e.g., the optics and sample are surrounded by air) system. A larger change in reduced effective NA can lead to more light refraction, which can reduce the optical aberrations and can lead to better measurement accuracy. The optical immersion can also eliminate or reduce TIR at the exterior interface of the system (e.g., interface where the system contacts the sample), which can lead to more light reaching the detector. As a result of more light reaching the detector, the light sources included in the system can be driven with less power, and thus, the system can require less power. 
     Additionally, the close proximity of the optics unit to the sample can allow the system to employ a well-defined (i.e., definite and distinct) interface, such as the exterior interface of the system (e.g., interface where the system contacts the sample), as a reference. The system may need to accurately reference the “beginning” or “edge” of the sample in order to reimage and resolve the multiple optical paths within the sample. With the exterior interface of the system (e.g., interface where the system contacts the sample) as a reference, fewer optical elements or components (e.g., a separate window) may be needed, since otherwise an additional optical component can be required to create the well-defined interface. Fewer optical components can lead to a more compact system. 
     In addition to locating the device in close proximity (e.g., touching) to the sample, the measurement region of the sample can affect the system&#39;s capability of accurately reimaging and resolving multiple optical paths within the sample. One factor that can affect the accurate reimaging and resolution can be the measurement path length. The measurement path length can be selected based on a targeted (e.g., pre-determined) path length, which can be a path length such that the spectroscopic signal measured by the detector accurately represents the desired one or more properties of the sample. The targeted measurement path length can be determined based on the scale lengths of the sample. The scale lengths of the sample can be based on the mean absorption length in the sample and the reduced scattering length in the sample. 
     The mean absorption length in a sample can be the distance over which light can attenuate. If the measurement path length is longer than the mean absorption length, the remaining signal (i.e., signal that has not scattered) or the measured signal intensity can be reduced, while any noise sources may not attenuate by an equivalent amount. As a result of the imbalance in attenuation, the SNR can be lower. The mean absorption length can be defined by the Beer-Lambert Law, which can mathematically describe the absorption A of light by a substance in a sample at a given wavelength as:
 
 A=ecL   (2)
 
where e is the molar absorptivity (which can vary with wavelength), L is the path length through the sample that light has to travel, and c is the concentration of the substance of interest.
 
     If the background absorption (i.e., absorption by substances different from the substance of interest) is high, the path length through the sample that light has to travel can be less than the mean absorption length. If the background absorption is negligible, the path length can be the same as the mean absorption length. One skilled in the art would appreciate that the same path length can include tolerances that result in 15% deviation. In some examples, the mean absorption length can be selected such that the mean absorption length is greater than or equal to the path length through the sample that light has to travel. 
     The reduced scattering length can be the distance over which information about the optical path is lost (i.e., randomized or decorrelated). The reduced scattering length can be determined by:
 
μ s ′=μ s (1− g )  (3)
 
where 1/μ s  is the mean free path between scattering events and g is the scattering anisotropy. If the measurement path length is greater than the reduced scattering length, the measurement accuracy can be compromised. In some examples, the measurement path length can be selected such that the measurement path length is less than the reduced scattering length.
 
     In some examples, the mean absorption length can be different from the reduced scatter length, and the measurement path length can be selected based on the smaller of the mean absorption length and reduced scattering length. In some examples, the mean absorption length can be short or absorption of light in the sample can be strong such that the signal of reflected light is undetected, and the system can be configured to increase the optical power of the light sources or increase the sensitivity of the detector to compensate. In some examples, the amount of compensation can be based on the power consumption, optical damage to the sample, unwanted heating effects in the sample, effects to the photon shot-noise, detected stray light that has not transmitted through the sample, or any combination of effects. Therefore, the selection of the measurement path length can affect not only the measurement accuracy, but also the power consumption, reliability, and lifetime of the system. 
     Additionally or alternatively, the system can be configured to utilize the effective scale length when the optical parameters of the sample vary (e.g., by more than 10%) with wavelength, for example. The effective scale length can be determined by calculating individual scale length for each wavelength, and taking an average of the individual scale lengths across the wavelengths of interest. In some examples, the individual scale length for each wavelength can be calculated to determine the range of individual scale lengths. The system can be configured to select the minimum scale length (among the range of individual scale lengths), the maximum scale length (among the range of individual scale lengths), or any scale length between the minimum scale length and the maximum scale length. In some examples, the measurement path length can be selected based on the mean absorption length, reduced scattering length, minimum scale length, maximum scale length, or any combination. 
     As discussed above, the scale length can be used to determine the size of the measurement region on the sample. Light outside of the measurement region can be light rays that have undergone multiple random scattering events within the sample, and as a result, these light rays can be decorrelated from the optical path traveled within the sample. Decorrelated light rays may not contribute useful information for an accurate measurement, and as a result, can be discarded or ignored without sacrificing an accurate measurement. 
     For example, the wavelengths of interest can be between 1500 nm-2500 nm (i.e., SWIR range), and the mean absorption length and reduced scattering length averaged over the wavelengths of interest can be 1 mm, which can correspond to a scale length of 1 mm. This scale length can correspond to a region of the sample with a diameter of 1-2 mm to be used for collecting light exiting the sample. That is, the majority (e.g., greater than 70%) of the optical power that exits the sample can be concentrated within this 1-2 mm diameter region, and the light rays exiting the sample outside of this region can be ignored. 
     The scale length can be also used to determine the size of the input light beam emitted from the outcoupler. The size of the light beam can affect the optical power (i.e., optical intensity) and diffraction effects. Measurement accuracy can favor a collimated input light beam in order for the system to operate with a sufficient optical power (e.g., a signal with a high enough SNR that can be detected by the detector) and minimal diffraction effects. For example, a scale length of 1 mm can correspond to a collimated input light beam with a beam diameter between 100-300 μm. In some examples, the input light beam can be configured with a beam diameter of less than 175 μm. 
     Similar to the properties of the input light beam, the properties of the optics unit(s) can also affect the system. The optics unit(s) can be formed on a single substrate or layer or can be formed on two or more substrates or layers. In some examples, the optics unit(s), detector array, light sources, or any combination can be mounted onto the same optical platform. In some examples, the optics unit(s) can have a plano (i.e., flat) surface contacting the sample. Configuring the optics with a plano surface can reduce wafer handling and fabrication complexity. In some examples, the other surface (i.e., the surface opposite the sample) can be convex to enhance the optics power. In some examples, this other surface can be a single convex refracting surface. In some examples, the thickness of the optics unit(s) can be based on the amount of light bending. In some examples, the thickness can be between 100-300 μm. 
       FIGS. 9A-9B  illustrate top and perspective views of an exemplary optics unit according to examples of the disclosure. A group  900  can include a plurality of units, each unit including at least three regions: launch region  916 , reference region  922 , and measurement region  929 . 
     Launch region  916  can be configured to prevent any specular reflection from reaching the detector array. Launch region  916  can include a light blocker or light absorber capable of blocking or absorbing light. In some examples, the light blocker can include any material that prevents incident light from reflecting (e.g., an anti-reflection coating). In some examples, the light blocker can include any material that reflects at wavelengths different from the detection wavelengths of the detector array. In some examples, launch region can include an opaque mask. 
     Reference region  922  can include any type of optics (e.g., a negative microlens) configured for spreading out incident light beams. Light emitted from the light source can be directed at a reference (e.g., reference  222  included in system  200 ), which can relay light to reference region  922 . Reference region  922  can spread out that light such that one or more light beams are directed to detector pixels on the detector array. In some examples, reference region  922  can include a negative lens or a lens with a focal length that is negative. In some examples, reference region  922  can include a prism. In some examples, reference region  922  can include a different prism wedge angled for each detector pixel in the detector array. In some examples, reference region  922  can include a beamsplitter. In some examples, reference region  922  can be configured to spread out or divide light into multiple beams. In some examples, reference region  922  can be configured to uniformly spread out light such that one or more properties of each light beam is the same. One skilled in the art would appreciate that the same properties can include tolerances that result in a 15% deviation. In some examples, reference region  922  can be configured to spread out the light beam such that intensities of at least two light beams are different. In some examples, reference region  922  can include multiple optics. In some examples, the size and/or shape of optics included in reference region  922  can be based on the number of detector pixels and/or the properties of the one or more light beams exiting reference region  922 . In some examples, one or more aperture layers can be located in reference region  922  to control the properties and/or direction of light exiting reference region  922 . 
     Measurement region  929  can include one or more collection optics (e.g., a positive microlens). The collection optics can be configured to reimage and resolve multiple optical paths in the sample, as discussed above. The system can be configured to chop or alternate between emitting light from the light source to be incident on reference region  922  and emitting light from the light source to be incident on measurement region  929 . The properties of the collection optics will be discussed below. 
     Although  FIGS. 4A-7  illustrate units included the system, where each unit can include one light beam from the outcoupler that exits the sample and is collected by a conjugate optic system and detector array, examples of the disclosure include systems with multiple units.  FIG. 9C  illustrates a top view of an exemplary optics unit and detector array included in multiple groups included in a system according to examples of the disclosure. The system can include a plurality of groups  900  coupled to a detector array  930 . In some examples, one or more optics included in measurement region  929  can be “shared” between adjacent groups  900 . In some examples, the system can be configured with one or more groups with light sources that alternate emitting light to the shared optics. In some examples, the system can be configured with 27 groups  900  and a 9×3-detector array  930 . In some examples, each group  900  can be separated from another group  900  by at least 2 mm. Although  FIGS. 9A-9B  illustrate groups  900  arranged with the reference region  922  located between the launch region  916  and a grid of 3×3 optics included in the measurement region  929 , examples of the disclosure can include any arrangement of the three regions and any arrangement of the optics included in the measurement region  929 . For example, the launch region  916  can be located in the center of group  900 , and the optics can surround the outer edges of the launch region  916 . 
     As discussed above, the configuration and properties of the optics included in the optics unit(s) can be based on numerous factors. These properties can include the effective focal length, working distance, material of the optics, the fill-factor, the aperture size, the pitch, the tilt (or decenter), and the orientation (or rotation), as will be discussed. 
     The system can be configured with an effective focal length based on the relationship between the range of collection angles and the location on the surface of the detector (or detector pixel) that the light ray is incident upon. The system can also be configured based on the integration of the detector array. 
     Since the optics unit(s) is located in the path between the sample and the detector, the material of the optics can affect the optical properties of the detected light, and thus, the measurement accuracy. To allow light exiting the sample to reach the detector array, the optics can be configured with a material that is transparent over the wavelength range of interest such that light can be prevented from reflecting off the surfaces of the optics. Additionally, in examples where the optics unit is in contact with the sample, the material of the optics can be based on resistance to material degradation from chemical and physical exposure of the optics to the sample. Furthermore, other considerations, such as compatibility with wafer-scale processing for creating any patterns (e.g., etch profiles) for the optics unit, availability of a material, and cost can be considered. 
     The material of the optics unit can also be selected based on the refractive index of the sample. For example, the system can be configured with an optics unit with a refractive index of 3.4 (e.g., an unit of silicon lenses) (or within 10%) when the sample has a refractive index 1.42 (or within 10%). Incident light can have an angle of incidence of 45° at the exterior interface of the system (e.g., interface where the system contacts the sample), which can lead to an angle of refraction of 16.9°. In this manner, the material of the optics unit can be selected such that the angle of incidence on the surface of the detector array can be closer to normal, which can be lead to the detector receiving a higher optical power, better measurement accuracy, and a system that can be configured for lower power consumption. 
     Furthermore, the material of the optics unit can be selected such that less “spreading” (i.e., dispersion of the bundles of light between the exterior interface of the system (e.g., interface where the system contacts the sample) and the surface of the detector) of light rays occurs. For example, light incident on the exterior interface of the system (e.g., interface where the system contacts the sample) with an angle of incidence of 60° can lead to an angle of refraction of 20.9°. Without a refractive index contrast between the optics unit and the sample, the spreading would be 15° (i.e., 60°-45°), whereas with a refractive index contrast between the optics unit and the sample, the spreading of light rays can be 4° (i.e., 20.9°-16.9°). A smaller spread of light rays can lead to a narrower range of collection angles, which can result in smaller optics and a more compact system. 
     In some examples, the wavelength range of interest can be SWIR (i.e., 1500 nm-2500 nm), and the optics unit can include single-crystal Silicon, Sapphire, fused Silica, oxide glasses, chalcogenide glasses, gallium arsenide (GaAs), Zinc Selenide (ZnSe), Germanium (Ge), or any combination of these materials. 
     The diameters of the optics can be based on the size of the light beam emitted from the light source. For example, a system configured with a light beam diameter between 100-300 μm can also be configured with an optics unit with diameters between 100-300 μm. 
     The fill-factor of the optics unit can represent the percentage or fraction of light rays exiting the sample that is collected. In general, reduced spreading of bundles of incident light can lead to a higher fill-factor (i.e., ratio of the area of light directed at the detector to the total area of the optics) at the optics unit, and hence, can lead to a higher optical efficiency. The fill-factor of an optic can be determined by: 
                   FF   =       π   4     ⁢       (       A   ⁢           ⁢   D     pitch     )     2               (   4   )               
where AD is the aperture size. The fill-factor FF of a lens or micro-lens can represent the amount of light that exits the sample, refracts into the system, and transmits through an aperture. In some examples, the aperture size of an aperture associated with an optics included in the optics unit(s) included in the optics unit can be based on the spread of the incident light rays. With a lower amount of spreading of incident light rays, the aperture size and optics pitch can be decreased such that a high fill-factor is achieved without loss of incident light rays that include pertinent information (e.g., information that can contribute to better measurement accuracy). In some examples, the optics unit can be configured with a fill-factor FF of 25% or greater. In some examples, the optics unit can be configured with a fill-factor FF of 50% or greater. In some examples, the optics unit can be configured with a fill-factor FF of 60% or greater.
 
     The pitch of the optics unit can be the distance between adjacent optics, which can affect the size of the optics. In some examples, the pitch can be based on the fill-factor of the optics unit. As illustrated in Equation 4, the fill-factor of the optics unit can be related to the aperture size, so pitch of the optics unit can be also based on the aperture size. To increase the fill-factor and the efficiency of capturing light rays exiting the sample, the pitch can be greater than the aperture size. For example, for an aperture size between 100-300 μm, the optics can be configured with a pitch between 125-500 μm. In some examples, the aperture size can be configured to be 175 μm in diameter, the pitch can be 250 μm, and the fill-factor can be 38.4%. 
     Additionally or alternatively, the optics pitch and the aperture size can be based on the range of collection angles. The aperture size can determine which among the light rays exiting the sample are accepted (i.e., transmitted through to the detector) by the optics and which are rejected (i.e., prevented from reaching the detector). The sample material and substances in the sample can lead to a high anisotropy of scattering. As a result, the collection efficiency (i.e., efficiency of the collected scattered light) can be based on the range of collection angles. While a wider range of collection angles can lead to more light collection (i.e., higher optical power), the collected light may include a larger proportion of unwanted light (e.g., noise or decorrelated light). Different angles of collected light rays can have a different importance or relevance to an accurate measurement. In some examples, the optical power of the light rays can be lower as light deviates (e.g., greater than 70° from normal incidence on the detector surface. The light rays with angles of incidence that deviate from normal incidence can include light rays with smaller crossing angles with light emitted from the light source (which can lead to a larger uncertainty in the scattering location or path length) and light rays with a large number of scattering events. As a result, light rays with angles of incidence that deviate from normal incidence can be less relevant and can lead to less accurate measurements. Furthermore, light rays that deviate from normal incidence can include light scattered from locations at shallow depths within the sample. In some applications, substances of interest in a sample may be located deep within the sample, so light rays scattered from locations at shallow depths within the sample may not contribute relevant information to the measurement. 
     Affected by the range of collection angles can be the aperture size, optics or optics pitch, collection efficiency, optical power incident on the detector, and the power of the system. The range of collection angles that the system can be configured to measure can be based on a targeted (e.g., pre-determined) range of collection angles. The targeted range of collection angles can be determined based on several factors, such as the collection efficiency, geometrical path uncertainty, number of scattering events likely to occur within the sample, depth of penetration, and limitations of the optics design, which can be determined based on the path length of a light ray. To determine the path length of a light ray, multiple uncertainties that exist can be considered. The total path length uncertainty ΔPL can include spatial resolution uncertainty Δspatial, angular resolution uncertainty Δangular, input Gaussian angular divergence Ainput, and low-angle sample scatter uncertainty Δmultiple scatter, and can be defined as:
 
Δ PL   2 =(Δspatial) 2 +(Δangular) 2 +(Δinput) 2 +(Δmultiple_scatter) 2   (5)
 
     The properties of one or more of the optics and aperture layers in the system can be configured based on the spatial resolution uncertainty.  FIG. 10  illustrates an exemplary configuration with light rays having a spatial resolution uncertainty according to examples of the disclosure. System  1000  can be touching or in close proximity to sample  1020 . Light can exit system  1000  at location  1006  and can travel a length d 11  through sample  1020  to location  1010 . The angle of the incidence of light at location  1010  can be angle of incidence θ 1 . A portion of light can scatter at a scattering angle θ 4 , travel a length d 12  through sample  1020 , and can reach the exterior interface of the system (e.g., interface where the system contacts the sample) at location  1016 . The distance between location  1006  and location  1016  can be referred to as distance x. Another portion of light can travel further into the sample  1020 , traveling a total length d 21 , to location  1040 . In some examples, the angle of incidence of light at location  1040  can also be the angle of incidence θ 1 , and light can also scatter at the scattering angle θ 4 . The scattered light can travel a length d 22  through sample  1020  and can reach the exterior interface of the system (e.g., interface where the system contacts the sample) at location  1046 . The spatial resolution or the distance between location  1016  and location  1046  can be referred to as spatial resolution or distance Ax. 
     The spatial resolution uncertainty Δspatial can be based on the difference in optical path lengths between scattered light incident at location  1016  and scattered light incident at location  1046  and can be defined as:
 
Δspatial= d   21   +d   22   −d   11   −d   12   (6)
 
Based on the law of sines:
 
                     x     sin   ⁡     (       θ   1     +     θ   4       )         =         d   12       sin   ⁡     (       90   ⁢   °     -     θ   1       )         =       d   11       sin   ⁡     (       90   ⁢   °     -     θ   4       )                   (   7   )                 d   11     =         sin   ⁡     (       90   ⁢   °     -     θ   4       )         sin   ⁡     (       θ   1     +     θ   4       )         ⁢   x             (   8   )                 d   12     =         sin   ⁡     (       90   ⁢   °     -     θ   1       )         sin   ⁡     (       θ   1     +     θ   4       )         ⁢   x             (   9   )                 d   21     =         sin   ⁡     (       90   ⁢   °     -     θ   4       )         sin   ⁡     (       θ   1     +     θ   4       )         ⁢     (     x   +     Δ   ⁢           ⁢   x       )               (   10   )                 d   22     =         sin   ⁡     (       90   ⁢   °     -     θ   1       )         sin   ⁡     (       θ   1     +     θ   4       )         ⁢     (     x   +     Δ   ⁢           ⁢   x       )               (   11   )               
Therefore, the spatial resolution uncertainty Δspatial can be reduced to:
 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     spatial 
                   
                   = 
                   
                     
                       
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             
                               
                                 90 
                                 ⁢ 
                                 ° 
                               
                               - 
                               
                                 θ 
                                 1 
                               
                             
                             ) 
                           
                         
                         + 
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             
                               
                                 90 
                                 ⁢ 
                                 ° 
                               
                               - 
                               
                                 θ 
                                 4 
                               
                             
                             ) 
                           
                         
                       
                       
                         sin 
                         ⁡ 
                         
                           ( 
                           
                             
                               θ 
                               1 
                             
                             + 
                             
                               θ 
                               4 
                             
                           
                           ) 
                         
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         x 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     As illustrated in Equation 12, the spatial resolution uncertainty Δspatial can decrease as the angle of incidence θ 1 , and scattering angle θ 4  can increase. Additionally, the spatial resolution uncertainty Δspatial can increase as the spatial resolution Δx (i.e., distance between light incident at location  1016  and light incident at location  1046 ) increases. In some examples, the aperture size, tilt, or orientation of the optics, or a combination can be configured based on the spatial resolution uncertainty Δspatial. In some examples, the spatial resolution uncertainty Δspatial can be between 150-200 μm, which can coincide with an angle of incidence θ 1 =45° and collection angle (which can be equal to the scattering angle θ 4 ) of 45°. 
     The properties of one or more of the optics in the system can also be configured based on the angular resolution uncertainty.  FIG. 11  illustrates an exemplary configuration with light rays having an angular resolution uncertainty according to examples of the disclosure. System  1100  can be touching or in close proximity to sample  1120 . Light can exit system  1100  at location  1106 , and can travel a length d 11  through sample  1120  to location  1110 . The angle of incidence of at location  1110  can be angle of incidence θ 1 . A portion of light can scatter from location  1110  at a scattering angle θ 5 , travel a length d 12  through sample  920 , and reach the exterior interface of the system (e.g., interface where the system contacts the sample) at location  1146 . The change in refractive index at the exterior interface of the system (e.g., interface where the system contacts the sample) can lead to an angle of refraction θ 8 . Another portion of light can travel further into sample  1120 , traveling a total length d 21 , to location  1140 . In some examples, the angle of incidence of light at location  1140  can also be angle of incidence θ 1 , and light scattered from location  1140  can have a scattering angle θ 6 . In some examples, scattering angle θ 6  can be different from scattering angle θ 1 . Light scattered from location  1140  can travel a length d 22  through sample  1120  and reach the exterior interface of the system (e.g., interface where the system contacts the sample) at location  1146 . The change in refractive index at the exterior interface of the system (e.g., interface where the system contacts the sample) can lead to an angle of refraction θ 7 . The distance between location  1106  and location  1146  can be referred to as distance x. In some examples, angle of refraction θ 8  can be different from angle of refraction θ 7  by an angular resolution of Δθ. 
     The angular resolution uncertainty Δangular can be based on the difference in angles of refraction between the two scattered light beams (e.g., light scattered from location  1110  and light scattered from location  1140 ) and can be defined as:
 
Δangular= d   21   +d   22   −d   11   −d   12   (13)
 
     Based on the law of sines and Snell&#39;s law: 
                     d   11     =         sin   ⁡     (       90   ⁢   °     -     θ   6       )         sin   ⁡     (       θ   1     +     θ   6       )         ⁢   x             (   14   )                 d   12     =         sin   ⁡     (       90   ⁢   °     -     θ   1       )         sin   ⁡     (       θ   1     +     θ   6       )         ⁢   x             (   15   )                 d   21     =         sin   ⁡     (       90   ⁢   °     -     θ   5       )         sin   ⁡     (       θ   1     +     θ   5       )         ⁢   x             (   16   )                 d   22     =         sin   ⁡     (       90   ⁢   °     -     θ   5       )         sin   ⁡     (       θ   1     +     θ   5       )         ⁢   x             (   17   )               
Therefore, the angular resolution uncertainty Δangular can be reduced to:
 
     
       
         
           
             
               
                 
                   Δangular 
                   = 
                   
                     
                       [ 
                       
                           
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       90 
                                       ⁢ 
                                       ° 
                                     
                                     - 
                                     
                                       θ 
                                       6 
                                     
                                   
                                   ) 
                                 
                               
                               + 
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       90 
                                       ⁢ 
                                       ° 
                                     
                                     - 
                                     
                                       θ 
                                       1 
                                     
                                   
                                   ) 
                                 
                               
                             
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     θ 
                                     6 
                                   
                                   + 
                                   
                                     θ 
                                     1 
                                   
                                 
                                 ) 
                               
                             
                           
                           ) 
                         
                         - 
                         
                           ( 
                           
                             
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       90 
                                       ⁢ 
                                       ° 
                                     
                                     - 
                                     
                                       θ 
                                       5 
                                     
                                   
                                   ) 
                                 
                               
                               + 
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       90 
                                       ⁢ 
                                       ° 
                                     
                                     - 
                                     
                                       θ 
                                       1 
                                     
                                   
                                   ) 
                                 
                               
                             
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     θ 
                                     5 
                                   
                                   + 
                                   
                                     θ 
                                     1 
                                   
                                 
                                 ) 
                               
                             
                           
                           ) 
                         
                       
                       ] 
                     
                     ⁢ 
                     x 
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
     As illustrated in Equation 18, the angular resolution uncertainty Δangular can increase as the distance x between light emitted from the light source and the exit location increases. In some examples, the system can be configured with a distance between the light source and the corresponding optics included in the optics unit that is based on the angular resolution uncertainty Δangular. In some examples, the system can be configured with a range of collection angles (i.e., angle bin) based on the angular resolution uncertainty Δangular. In some examples, the tilt, orientation, or both of the optics in the system can be configured based on the angular resolution uncertainty Δangular. In some examples, the angular resolution uncertainty can be between 40-100 μm, and the range of collection angles can be between 5° and 10°. 
     The properties of the light beam in the system can be configured based on the Gaussian angular divergence.  FIG. 12  illustrates an exemplary configuration with an input light beam with a Gaussian angular divergence according to examples of the disclosure. System  1200  can be touching or in close proximity to sample  1220 . Light can exit system  1200  at location  1206  and can have an angle of incidence θ 1  (measured relative to the half-angle divergence θ 12 ). In some examples, a portion of light emitted from the light sources can diverge with a portion of light having an angle of incidence θ 10  at location  1210  and travel a length d 21  through sample  1220  to location  1210 . Another portion of light emitted from the light sources can diverge with an angle of incidence θ 11  also at location  1210  and travel a length d 12  through sample  1220  to location  1210 . Light can scatter from location  1210  to location  1246  on the exterior interface of the system (e.g., interface where the system contacts the sample) at a scattering angle θ 13 . A portion of the scattered light can travel a length d 12  through sample  1220 , and the other portion of the scattered light can travel a length d 22  through sample  1220 . The change in refractive index at the exterior interface of the system (e.g., interface where the system contacts the sample) can lead to angle of refraction θ 14 . 
     The Gaussian angular divergence Ainput can be based on the difference in optical path lengths between the diverged light rays and can be defined as:
 
Δinput= d   21   +d   22   −d   11   −d   12   (19)
 
Based on the law of sines:
 
                     d   11     =         sin   ⁡     (       90   ⁢   °     -     θ   13       )         sin   ⁡     (       θ   13     +     θ   1     +     θ   12       )         ⁢   x             (   20   )                 d   12     =         sin   ⁡     (       90   ⁢   °     -     θ   1     -     θ   12       )         sin   ⁡     (       θ   13     +     θ   1     +     θ   12       )         ⁢   x             (   21   )                 d   21     =         sin   ⁡     (       90   ⁢   °     -     θ   13       )         sin   ⁡     (       θ   13     +     θ   1     -     θ   12       )         ⁢   x             (   22   )                 d   22     =         sin   ⁡     (       90   ⁢   °     -     θ   1     +     θ   12       )         sin   ⁡     (       θ   13     +     θ   1     -     θ   12       )         ⁢   x             (   23   )               
As the Gaussian angular divergence Ainput increases, the path length uncertainty ΔPL can become dominated by the angular resolution uncertainty Δangular. In some examples, the spatial resolution uncertainty can contribute to more than half of the path length uncertainty ΔPL. In some examples, the system can be configured with a range of collection angles of 50° with 5-10 angle bins.
 
     The tilt of the optics can be configured based on the collection efficiency, which can affect measurement accuracy and the power consumption of the system. By tilting (i.e., orienting the axis) of the optics such that the collection direction is parallel to the axis of incident light (i.e., the collection direction faces incident light direction), the collection efficiency can be increased. For example, the axis of incident light can be at 45°, and the collection direction can be at −45°. In some examples, the tilt of the optics can be based on the range of collection angles. For example, the collection angles can range from 0° to −75°, and the collection direction can be at −37.5°. In some examples, the collection angles can range from −25° to −70°, and the collection direction can be at −47.5°. In some examples, the collection angles can range from −30° to −60°, and the collection direction can be at −45°. In some examples, the optics can include a convex surface, which can be tilted (or decentered) to account for any asymmetry (i.e., bias) in the range of collection angles. Compensating for any asymmetry can reduce the magnitude or effects of the optical aberrations of the optics. In some examples, all the optics can be tiled in the same direction from normal incidence. 
     In addition to optics, the system performance can be affected by the properties of one or more other components included in the system. In some examples, the system can include a spacer located between the optics unit and the optical platform. In some examples, the optics unit and optical platform can include single-crystal Silicon. In some examples, the light sources, optical traces, or both can include silicon waveguides formed on the optical platform. In some examples, the ROIC coupled to the detector can be fabricated on silicon. By configuring one or more of the optics unit, optical platform, and ROIC to include silicon, the thermal expansion of the components can be similar, which can minimize any mechanical weaknesses, and the robustness of the system can be improved. Additionally, silicon can be a material with many desirable properties, such as good mechanical strength, good thermal conductance, low cost, and good reliability. 
     In some examples, the system can include an optical spacer window located between the optics and the sample.  FIG. 13A  illustrates a cross-sectional view of an exemplary system including an optical spacer window and aperture layer located between the optical spacer window and the sample according to examples of the disclosure. System  1300  can include light sources  1302 , optics unit  1312 , aperture layer  1386 , and optical spacer window  1321 , where optical spacer window  1321  can be in contact with sample  1320 . Light sources  1302  can emit light  1352  exiting sample  1320 . Light, referred to as light  1354 , can reflect off location  1357  within sample  1320 , can be transmitted through aperture layer  1386 , and can reach optics unit  1312 . 
     As illustrated in  FIG. 13A , placement of aperture layer  1386  can lead to stray light generated by scattering at the edge interfaces and optical aberrations, which could degrade the imaging properties of optics unit  1312 .  FIG. 13B  illustrates a cross-sectional view of an exemplary system including an optical spacer window and aperture layer located between the optical spacer window and the optics unit according to examples of the disclosure. With aperture layer  1387  located between optical spacer window  1321  and optics unit  1312 , light rays light  1354  can propagate to the appropriate optics included in optics unit  1312  and stray light generated by scattering at the edge interfaces can be reduced or eliminated. 
     In some examples, optical spacer window  1321  can be multi-functional and can be configured to provide mechanical support to the optics. The thickness of optics unit  1312  can be configured based on the amount of light bending performed by optics unit  1312  and the ability to separate different angles of refraction. As the thickness of optics unit  1312  decreases, the performance of optics unit  1312  increases. However, a decrease in thickness of the optics unit  1312  can lead to an optics unit that is fragile, costly, and can require complicated fabrication schemes with low yields. The system can be configured such that the optical spacer window  1321  compensates for the fragility of a thin optics unit  1312  without compromising optical performance. In some examples, the thickness of optical spacer window  1321  can be between 400-700 μm. In some examples, the thickness of optical spacer window  1321  can be 650 μm. 
     In some examples, optical spacer window  1321  can be configured with a thickness such that thermal crossover effects between sample  1320  and the active components (e.g., detector, light source, and electronics) can be reduced. The active components can generate heat and can also be sensitive to any temperature fluctuations, and the temperature of sample  1320  can vary or can be different from the operating temperature of the active components. As a result, a difference in temperature of sample  1320  and operating temperature of the active components can lead to thermal crossover effects, which can degrade the measurement accuracy. In some examples, sample  1320  can be skin, for which any difference in temperature can cause discomfort if the thermal crossover effects are not otherwise mitigated. 
     In some examples, optical spacer window  1321  can include an intermediate coating (i.e., a dielectric material with a refractive index between the refractive index of sample  1320  and the refractive index of optics unit  1312 ). Without an intermediate coating, optics unit  1312  or any anti-reflection coating disposed on optics unit  1312  would be configured such that a high refractive index contrast between optics unit  1312  and sample  1320  would result or the angle of refraction in the system would be compromised. The inclusion of an intermediate coating, on the other hand, can reduce the complexity and increase the angle of refraction in the system. 
     In some examples, optical spacer window  1321  can include a dielectric material. In some examples, the dielectric material can have higher chemical durability, higher physical durability, or both compared to the optics. In some examples, optical spacer window  1321  can include sapphire. By including an optical spacer window between the optics and the sample, the system can have enhanced mechanical robustness, enhanced device durability, and reduced thermal crossover. 
     The inclusion of optical spacer window  1321  can alter the manner in which light is distributed among the optics and detector pixels in the detector array. However, this alteration can be accounted for and light incident on the detector array can still allow each detector pixel to describe a trajectory or optical path in the sample.  FIG. 14A  illustrates a cross-sectional view of an exemplary system excluding an optical spacer window and corresponding determination of the lateral position of light incident at the exterior interface of the system (e.g., interface where the system contacts the sample) according to examples of the disclosure. System  1400  can include light sources  1402 , optics unit  1412 , aperture layer  1486 , and detector array  1430 . Light sources  1402  can emit light  1452  exiting sample  1420  at location  1406 . Light  1453 , light  1454 , and light  1455  can reflect off location  1457  within sample  1420  and can be incident on the exterior interface of the system (e.g., interface where the system contacts the sample) at location  1446 , which can be located a distance x away from location  1406 . Light  1453 , light  1454 , and light  1455  can transmit through aperture layer  1486  and can reach optic  1418  included in optics unit  1412 . Detector array  1430  can include detector pixel  1433 , detector pixel  1435 , and detector pixel  1437 . Light  1453  can be incident on detector pixel  1433 , light  1454  can be incident on detector pixel  1435 , and light  1455  can be incident on detector pixel  1437 . Therefore, optic  1418 , detector pixel  1433 , detector pixel  1435 , and detector pixel  1437  can be associated with location  1446 . In this manner, the lateral position of incident light at the exterior interface of the system (e.g., interface where the system contacts the sample) can be associated with the optics included in the optics unit. 
     Inclusion of the optical spacer window can lead to a determination of the lateral position of incident light at the exterior interface of the system (e.g., interface where the system contacts the sample) based on both the optics included in the optics unit and the detector pixel included in the detector array.  FIG. 14B  illustrates a cross-sectional view of an exemplary system including an optical spacer window and corresponding determination of the lateral position of light incident at the exterior interface of the system (e.g., interface where the system contacts the sample) according to examples of the disclosure. System  1490  can include light sources  1402 , optics unit  1412 , aperture layer  1487 , optical spacer window  1421 , and detector array  1430 . Light sources  1402  can emit light  1452  exiting system  1490  at location  1406 . Light  1452 , light  1451 , and light  1453  can reflect off location  1457  within sample  1420 , can transmit through aperture layer  1487 , and can travel through optical spacer window  1421 . In some examples, the scattering angles of light  1452 , light  1451 , and light  1453  can be different. Sample  1420  can include a plurality of locations, such as location  1447 , location  1448 , and location  1449  at the exterior interface of the system (e.g., interface where the system contacts the sample). Location  1447  can be located a distance x 1  away from location  1406 , location  1448  can be located a distance x 2  away from location  1406 , and location  1449  can be located a distance x 3  away from location  1406 . Light  1452  can be incident at location  1447 , light  1451  can be incident at location  1448 , and light  1453  can be incident at location  1449 . Detector array  1430  can include detector pixel  1434 , detector pixel  1436 , and detector pixel  1438 . Light  1452  can be incident on detector pixel  1434 . Similarly, light  1451  and light  1453  can be incident on detector pixel  1436  and detector pixel  1438 , respectively. Detector pixel  1434  can be associated with location  1447 , detector pixel  1436  can be associated with location  1448 , and detector pixel  1438  can be associated with location  1449 . Each location (e.g., location  1447 , location  1448 , and location  1449 ) can have a different lateral position, which can be associated with a different scattering angle. In this manner, the lateral position of incident light at the exterior interface of the system (e.g., interface where the system contacts the sample) can be associated with both the optics included in the optics unit and the detector pixel included in the detector array. 
     To determine the association of the optics and detector pixel to the lateral position of incident light at the exterior interface of the system (e.g., interface where the system contacts the sample) and the path length of the optical path, the exemplary system with optical spacer window can be simplified, as illustrated in  FIG. 14C . The angle of light exiting system  1450  at location  1406  can be referred to as exiting angle θ 1 , and the angle of scattered light  1451  from location  1457  can be referred to as scattering angle θ 2 . The scattering angle θ 2  can be defined as: 
                     θ   2     =         θ     CA   ⁢           ⁢   1       +       (     j   -   1     )     ⁢     (       θ     CA   ⁢           ⁢   2       -     θ     CA   ⁢           ⁢   1         )         j             (   24   )               
where θ 1  and θ 2  are the range of collection angles and j represents the j th  detector pixel included in the detector array. The corresponding angle of incidence at the spacer-optics unit interface θ 3  can be defined as:
 
                     θ   3     =       sin     -   1       ⁡     (         n   sample       n   spacer       ⁢   sin   ⁢           ⁢     θ   2       )               (   25   )               
where n sample  is the refractive index of sample  1420  and n spacer  is the refractive index of optical spacer window  1421 . The distance between location  1447  and the center of optic  1418  can be defined as:
 
δ( j )= t ×tan(θ 3 )  (26)
 
where t is the thickness of optical spacer window  1421 . The distance x i  (i.e., lateral position of light) can be defined as:
 
                       x   1     ⁡     (     j   ,   m     )       =         (     m   -   1     )     ×   p     +     p   2     -     δ   ⁡     (   j   )                 (   27   )               
where m represents the m th  optics in the optics unit  1412  and p is the pitch of optic  1418 . The optical path length PL(j,m) of a light ray can be defined as:
 
                     PL   ⁡     (     j   ,   m     )       =         d   11     +     d   12       =       (         sin   ⁡     (       90   ⁢   °     -     θ   2       )         sin   ⁡     (       θ   1     +     θ   2       )         +       sin   ⁡     (       90   ⁢   °     -     θ   1       )         sin   ⁡     (       θ   1     +     θ   2       )           )     ⁢       x   1     ⁡     (     j   ,   m     )                   (   28   )               
where d 11  is the path length of light  1452  and d 12  is the path length of light  1451 .
 
     For example, optic  1418  can be configured with a range of collection angles θ CA2  equal to 75° and θ CA1  equal to 25°, and optics included in optics unit  1412  can be configured with a pitch of 150 μm. Optical spacer window  1421  can be configured to include sapphire, which has a refractive index of 1.74, and can be configured with a thickness of 500 μm. Optical spacer window  1421  can be in contact with the sample, which can have a refractive index of 1.4 The detector array can be configured with 10 detector pixels coupled to the same optics in optics unit  1412 . The exiting angle θ 1  can be 45°, which can lead to scattering of a light ray with a scattering angle of 45°. The refractive index difference between optical spacer window  1421  and sample  1420  can lead the light ray being incident on the 8 th  optics in optics unit  1412  with angle of incidence θ 3  at the optical spacer window-optics unit interface to be equal to 34.7° at a distance 8 of 346 μm. The lateral position of the light ray x 1 (j,m) can be equal to 779 μm, and the optical path length of the light ray can be 1.1 mm. 
       FIGS. 14D-14E  illustrate cross-sectional views of an exemplary system including an optical spacer window according to examples of the disclosure. As illustrated in  FIG. 14D , the inclusion of the optical spacer window in the system can allow a single optics in the optics unit to collect a range of scattering angles. The range of (different) scattering angles can lead to different locations, together forming a range length, on the exterior interface of the system (e.g., interface where the system contacts the sample) that the light rays are incident upon. In some examples, the thickness of the optical spacer window can be configured based on the total range length. The optics in the optics unit can collect light rays from interleaving portions of the sample, and as a result, the aggregate of the optics in the optics unit can collect multiple angles of incidence and exit location permutations without compromising loss of light rays or information. 
     As illustrated in  FIG. 14E , the inclusion of the optical spacer in the system can also allow a single location on the exterior interface of the system (e.g., interface where the system contacts the sample) to emit light into multiple optics the optics unit. Although the light rays and information can be mixed among multiple optics and multiple detector pixels, the sum total information can be the same. 
     One or more of the functions described above can be performed, for example, by firmware stored in memory and executed by a processor or controller. The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such as a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks and the like. In the context of this document, a “transport medium” can be any medium that can communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium. 
     A system for reimaging a plurality of optical paths in a sample is disclosed. The system can comprise: one or more light sources, each light source configured to emit a first light and a second light, the first light incident on the sample and including the plurality of optical paths, and the second light incident on a reference; a modulator configured to alternate between modulating the first light and the second light; one or more optics units configured to collect at least a portion of a reflection of the first light incident on the sample; a detector array including a plurality of detector pixels and configured to detect at least a portion of the collected reflected first light; and logic configured to resolve at least one of optical path lengths and angles of incidence of the plurality of optical paths and configured to associate a detector pixel in the detector array with an optical path included in the plurality of optical paths. Additionally or alternatively, in some examples, the system further comprises: a plurality of units, each unit including: a launch region configured to reflect or absorb one or more wavelengths different from wavelengths of light emitted from the one or more light sources, a reference region configured to receive a reflection of the second light, and a measurement region including the one or more optics units, wherein each unit included the plurality of units is coupled to a measurement region of the sample. Additionally or alternatively, in some examples, the reference region includes one or more negative lenses configured to spread out the reflection of the second light. Additionally or alternatively, in some examples, each unit is separated from another unit by at least 2 mm. Additionally or alternatively, in some examples, at least one unit included in the plurality of units includes at least a portion of the measurement region shared by another unit included in the plurality of units. Additionally or alternatively, in some examples, each unit includes at least one of the one or more light sources, and at least one unit is configured to measure a region on the sample with a diameter or perimeter less than or equal to 2 mm, the region on the sample including at least 70% of the reflection of the first light. Additionally or alternatively, in some examples, a first surface of at least one of the one or more optics units is flat and in contact with a surface of the sample, and a second surface of the at least one of the one or more optics unit is convex. Additionally or alternatively, in some examples, the system further comprises a spacer located between the one or more optics units and the sample. Additionally or alternatively, in some examples, the spacer includes sapphire. Additionally or alternatively, in some examples, the spacer has a thickness between 400-700 microns. Additionally or alternatively, in some examples, the system further comprises an aperture layer located between the spacer and the one or more optics units. Additionally or alternatively, in some examples, the system further comprises an aperture layer configured to provide the one or more optics units with access to one or more optical paths with a path length in a first range of path lengths and an angle of incidence in a first range of angles, and further configured to reject one or more optical paths with a path length in a second range of path lengths, different from the first range of path lengths, having an angle of incidence in a second range of angles, different from the first range of angles. Additionally or alternatively, in some examples, the aperture layer is located on a same layer as at least the one or more optics units. Additionally or alternatively, in some examples, the one or more optics units include a plurality of recessed optics. Additionally or alternatively, in some examples, the system further comprises a junction located between the one or more light sources and the sample and further located between the one or more light sources and the reference, the junction configured to split light emitted from the one or more light sources into the first light and the second light, an intensity of the first light being greater than an intensity of the second light. Additionally or alternatively, in some examples, the system further comprises: a first outcoupler including a bridge, the first outcoupler configured to receive and redirect the first light towards the sample; and a second outcoupler including a bridge, the second coupler configured to receive and redirect the second light towards the reference. Additionally or alternatively, in some examples, the system further comprises one or more optics coupled to the first outcoupler and the sample, a first surface of the one or more optics in contact with a surface of the first outcoupler. Additionally or alternatively, in some examples, the system further comprises at least one of one or more integrated tuning elements, one or more multiplexers, optical routing, one or more waveguides, and integrated circuitry included in a silicon-photonics chip. Additionally or alternatively, in some examples, a beam size of at least one of the one or more light sources is between 100-300 microns. Additionally or alternatively, in some examples, a thickness of at least one of the one or more optics units is between 100-300 microns. Additionally or alternatively, in some examples, the system is included in a package with a size less than 1 cm 3 . 
     A system is disclosed. The system can comprise: one or more light sources, each light source configured to emit a first light and a second light, the first light directed toward an exterior interface of the system and including a plurality of optical paths, and the second light incident on a reference; one or more first optics configured to collect at least a portion of a reflection of the first light incident on the sample and change an angle of the first light; one or more second optics configured to receive the first light from the one or more first optics and focus the first light to a detector array; and the detector array including a plurality of detector pixels and configured to detect at least a portion of the focused first light from the one or more second optics. Additionally or alternatively, in some examples, the system further comprises: a plurality of groups, each group including: a launch region configured to reflect or absorb one or more wavelengths different from wavelengths of light emitted from the one or more light sources, a reference region configured to receive a reflection of the second light, and a measurement region including the one or more first optics. Additionally or alternatively, in some examples, each group includes one launch region, one reference region, and a plurality of measurement regions. Additionally or alternatively, in some examples, at least one group shares at least a portion of the measurement region with another group. Additionally or alternatively, in some examples, a first surface of at least one first optic is flat and located at the exterior interface of the system, and a second surface of the at least one optic is convex. Additionally or alternatively, in some examples, the system further comprises: an aperture layer configured to allow one or more first optical paths to pass through to the one or more first optics, the one or more second optics, or both, the one or more first optical paths having a path length in a first range of path lengths, wherein the aperture layer is further configured to reject one or more second optical paths with a path length in a second range of path lengths, different from the first range of path lengths. Additionally or alternatively, in some examples, the system further comprises an aperture layer configured to allow one or more first optical paths to pass through to the one or more first optics, the second layer of optics, or both, the one or more first optical paths having an angle of incidence in a first range of angles, wherein the aperture layer is further configured to reject one or more second optical paths having an angle of incidence in a second range of angles, different from the first range of angles. Additionally or alternatively, in some examples, the system further comprises: a junction located between the one or more light sources and the exterior interface of the system, wherein the junction is further located between the one or more light sources and the reference, and wherein the junction is configured to split light emitted from the one or more light sources into the first light and the second light, wherein an intensity of the first light is greater than an intensity of the second light. Additionally or alternatively, in some examples, the system further comprises: a first outcoupler including a bridge, the first outcoupler configured to receive and redirect the first light towards the exterior interface of the system; and a second outcoupler including a bridge, the second coupler configured to receive and redirect the second light towards the reference. Additionally or alternatively, in some examples, the system further comprises one or more third optics coupled to the first outcoupler and the exterior interface of the system, wherein a first surface of the one or more third optics is in contact with a surface of the first outcoupler. Additionally or alternatively, in some examples, the system further comprises at least one of one or more integrated tuning elements, one or more multiplexers, optical routing, one or more waveguides, and integrated circuitry, wherein the one or more integrated tuning elements are included in a silicon-photonics chip. Additionally or alternatively, in some examples, each detector pixel is associated with a first optic and a second optic. Additionally or alternatively, in some examples, each first optic is associated with a second optic and a plurality of the plurality of detector pixels. Additionally or alternatively, in some examples, the one or more first optics includes material different from material included in the one or more second optics. 
     An optical system for determining one or more properties of a sample is disclosed. In some examples, the optical system comprises: a first optics unit disposed on a first substrate and configured for receiving and redirecting a reflection of a first light incident on the sample, the first optics unit including a plurality of first optics, each first optics coupled to a detector pixel included in a detector array and an optical path included in the plurality of optics paths. Additionally or alternatively, in some examples, a surface of the first optics unit is in contact with a surface of the sample and is further configured for focusing the reflection of the first light towards a surface of the detector array. Additionally or alternatively, in some examples, the plurality of first optics is configured with a tilt oriented in a same direction relative to normal incidence. Additionally or alternatively, in some examples, the system further comprises a second optics unit disposed on a second substrate and configured for receiving and focusing the first light from the first optics unit, the second optics unit including a plurality of second optics, each second optics coupled to a first optics included in the first optics unit. Additionally or alternatively, in some examples, the first optics unit is attached to the second optics unit through a plurality of mechanical registration features formed on the first optics unit, the second optics unit, or both. Additionally or alternatively, in some examples, each first optics includes a prism and is configured to have one or more properties different from other first optics. Additionally or alternatively, in some examples, at least one of the first optics includes silicon. Additionally or alternatively, in some examples, each first optics is coupled to a plurality of detector pixels included in a detector array. Additionally or alternatively, in some examples, at least one of the plurality of first optics is configured with a range of collection angles equal to 50° and configured with 5-10 angle bins. Additionally or alternatively, in some examples, at least one of the plurality of first optics is configured with a range of collection angles centered at 45°. 
     An optical system is disclosed. The optical system can comprise: one or more first optics disposed on a first substrate and configured for receiving and redirecting a first light; one or more second optics disposed on a second substrate and configured for receiving the first light from the one or more first optics, the one or more second optics further configured to focus the received first light; and an aperture layer including one or more openings, the aperture layer configured to allow a first portion of incident light to pass through and to prevent a second portion of the incident light from passing through, wherein the aperture layer is located on a same layer as the one or more first optics or the one or more second optics. Additionally or alternatively, in some examples, the aperture layer allows the first portion of incident light to pass through based on an angle of incidence of the incident light. Additionally or alternatively, in some examples, the aperture layer allows the first portion of incident light to pass through based on a path length. Additionally or alternatively, in some examples, the system further comprises: a second aperture layer located on a same layer as the one or more second optics, wherein the first aperture layer is located on a same layer as the one or more first optics. Additionally or alternatively, in some examples, the aperture layer is a lithographic pattern disposed on a surface of the one or more first optics or the one or more second optics. Additionally or alternatively, in some examples, the system further comprises: a third optic located on a same layer as the one or more second optics, wherein the third optic is configured to receive light from a first surface of the system and direct light to a second surface of the system, wherein the one or more first and second optics are configured to receive the first light from the second surface of the system. 
     A method of determining one or more properties of a sample is disclosed. In some examples, the method comprises: determining a first angle of incidence of a first light at a first interface, the first interface including the sample and a spacer, the first light emitted from a light source; determining a second angle of incidence of a second light at the first interface, the second light being a reflection of the first light and including a first information; determining a third angle of incidence of a third light at the a second interface, the second interface including the spacer and one or more optics units; and determining a path length of an optical path based on the first, second, and third angles of incidence. Additionally or alternatively, in some examples, the system further comprises: determining a fourth angle of incidence of a fourth light at the first interface, the fourth light being a reflection of the first light originating from a same location in the sample as the second light originates from and includes a second information, wherein the second light is incident at a first location along the first interface and the fourth light is incident at a second location along the second interface, the second location different from the first location, further wherein the second and fourth light are collected by a first optics; and determining a third information based on an aggregate of the first and second information. Additionally or alternatively, in some examples, the method further comprises: determining a fourth angle of incidence of a fourth light at the first interface, the fourth light being a reflection of the first light originating from a same location in the sample as the second light originates from and includes a second information, wherein the second light and fourth light are incident at a first location along the first interface and incident at a second location along the second interface, further wherein the second light and fourth light are collected by different optics included in the one or more optics units; and determining a third information based on an aggregate of the first and second information. Additionally or alternatively, in some examples, the method further comprises: associating the optical path with a optics included in the one or more optics units and a detector pixel included in a detector array, wherein determining the path length of the optical path is further based on a range of collection angles of the optics and a thickness of the spacer. Additionally or alternatively, in some examples, the optical path is included in a plurality of optical paths, each optical path having a set of information, the set of information including a path length, an angle of incidence, and a location in the sample, wherein each set of information is different from other sets of information included in the plurality of optical paths. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20170413
Publication Date: 20200929
Grant Date: 20200929
Priority Date: 20160421
Inventors: ARBORE, Mark Alan
SHAMBAT, GARY
TERREL, MATTHEW A.
Assignee: APPLE INC
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Family ID: 58641050