Patent Description:
Light Detection and Ranging or LIDAR systems are widely used in a number of different applications including automotive, robotics, and unmanned or autonomous vehicles for mapping, object detection and identification, and navigation. Generally, LIDAR systems work by illuminating a target in a far field scene with a light beam from a coherent light source, typically a laser, and detecting the reflected light with a sensor. Differences in light return times and wavelengths are analyzed in the LiDAR system to measure a distance to the target, and, in some applications, to render a digital <NUM>-D representation of the target.

Traditional LiDAR systems used a mechanical scanner, such as a spinning or moving mirror, to steer the light beam over the target. However, these mechanical LIDAR systems are rather bulky and relatively expensive pieces of equipment making them unsuitable for use in many applications.

A more recent technology is solid-state LiDAR systems in which the scanner is replaced by MEMS-based spatial light modulators used to form a MEMS phased-array built entirely on a single substrate or chip. Solid-state LiDAR systems have the potential to provide cheaper, more compact systems, with higher resolution than traditional LiDAR systems. Although capable at least in theory of providing much faster beam steering than a traditional mechanical LiDAR system, achieving large scan angles, needed for larger field of view (FOV) and resolution, requires small dimensions for the MEMS mirror and elements, approaching wavelengths of the light typically used in LiDAR systems. This in turn adds to the cost and complexity of the MEMS phased-array, and makes it difficult to maintain the speed advantage of the DMD-based MEMS phased-array over the mechanical scanner of traditional LiDAR systems. Further prior art is <CIT> and <CIT>. <CIT> is directed on a light ranging and detection system with an analogue receiver that is configured to differentiate and extract range and reflectivity information of reflected beams. The receiver may comprise a single photodiode with a large aperture or an array of detectors to increase the received signal to noise ratio. <CIT> is directed on a capacitive microelectromechanical system, which includes a bottom electrode formed over a substrate; an electrically permeable damping structure formed over the bottom electrode and a plurality of movable members.

Accordingly, it is an object of the invention to provide means to provide fast beam steering and large scan angles for use in LiDAR applications.

This object is achieved by the subject matter of the independent claims. The invention is defined by the independent claims <NUM>, <NUM> and <NUM>. Preferred embodiments are subject-matters of the dependent claims. Aspects of the invention are set out below: According to an aspect of the invention an optical scanner including a micro-electromechanical system (MEMS) based spatial light modular to form a MEMS phased-array (hereinafter MEMS phased-array) suitable for use in a LiDAR system is provided.

According to an aspect of the invention, the optical scanner includes an optical transmitter including a number of first MEMS phased-array configured to receive light from a coherent light source and to modulate phases of at least some of the received light to scan a far field scene in two-dimensions (2D), and an optical receiver including a number of second MEMS phased-array configured to receive light from the far field scene and to direct at least some of the received light onto a detector. Generally, the second MEMS phased-array are configured to de-scan the received light by directing light from the coherent light source reflected from the far field scene onto the detector while rejecting background light.

According to an aspect of the invention, the optical scanner can be implemented using a single shared MEMS phased-array in which the MEMS phased-array is configured to at a first time modulate phases of the light from the coherent light source to scan the far field scene at a first time, and to de-scan the received light at a second time by directing light from the coherent light source reflected from the far field scene onto the detector and rejecting background light.

In another aspect, methods for operating an optical scanner including a number of MEMS phased-array are provided. Generally, the method begins with illuminating a first microelectromechanical system (MEMS) MEMS phased-array with light from a coherent light source. Next, the first MEMS phased-array is controlled to modulate phases of the light from the coherent light source and project modulated light from the first MEMS phased-array to a far field scene to scan the far field scene in two-dimensions (2D). Finally, light from the far field scene is received on a second MEMS phased-array and the received light de-scanned by controlling the second MEMS phased-array to direct light originating from the coherent light source reflected from the far field scene onto a detector while rejecting background light.

Embodiments of the present invention will be understood more fully from the detailed description that follows and from the accompanying drawings and the appended claims provided below, where:.

An optical scanner including a micro-electromechanical system (MEMS) MEMS phased-array suitable for use in a Light Detection and Ranging (LiDAR) system, and methods of making and operating the same are provided. In the following description, numerous specific details are set forth, such as specific materials, dimensions and processes parameters etc. to provide a thorough understanding of the present invention. However, particular embodiments may be practiced without one or more of these specific details, or in combination with other known methods, materials, and apparatuses. In other instances, well-known semiconductor design and fabrication techniques have not been described in particular detail to avoid unnecessarily obscuring the present invention. Reference throughout this specification to "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

<FIG> is a block diagram illustrating an embodiment of a LiDAR system <NUM> including a solid state optical scanning system or optical scanner <NUM> according to the present disclosure. Referring to <FIG> the LiDAR system <NUM> generally includes a microcontroller or controller <NUM> to control operation of other components of the LiDAR system, including the optical scanner <NUM>, and to interface with a host system (not shown). The controller <NUM> includes a processor and data processing circuitry to analyze signals from the optical scanner <NUM> to detect and measure a location of objects in a far field scene <NUM>, estimate a time of flight (TOF) of distance between the objects and the LiDAR system <NUM> or host, and, by repeating the preceding measurements over time, detect and measure a velocity and direction of moving objects in the far field scene. Generally, the controller <NUM> further includes additional circuits and memory to measure a size of and identify discrete objects, such as cars or pedestrians, sensed in the far field scene <NUM>. Optionally, the controller <NUM> can further include memory and circuits to create a three dimensional (3D) model of the far field scene <NUM>.

The optical scanner <NUM> includes an optical transmitter <NUM> to generate, transmit and scan a light over the far field scene <NUM> in at least two dimensions, and an optical receiver <NUM> to receive reflected light from the far field scene. Generally, both the optical transmitter <NUM> and the optical receiver <NUM> are both solid state. By solid state it is meant both a light scanning element of the optical transmitter <NUM> and a light collecting element of the optical receiver <NUM> are made or fabricated on silicon, semiconductor or other type of substrate using microelectromechanical system devices (MEMs) and semiconductor or integrated circuit (IC) fabrication techniques. In particular, a beam steering or light scanning element of the optical scanner <NUM> is made using a number of MEMS phased-arrays in place of the mechanical scanner, such as a spinning or moving mirror used in a conventional LiDAR system. In some embodiments, such as that shown in <FIG>, substantially an entire LiDAR system including the optical scanner <NUM>, controller <NUM>, along with any interfaces (not shown in this figure) to a host system are integrally formed on a single integrated circuit (IC <NUM>). Because the optical scanner <NUM> does not include the moving or rotating elements of conventional LiDAR systems the resulting optical scanner and LiDAR system is more resilient to vibrations, and can be much smaller and cheaper.

The manner or method in which an optical MEMS-based phased-array can be operated to implement beam steering or scanning will now be described with reference to <FIG>. Generally, an optical MEMS-based phased-array (hereinafter MEMS phased-array) uses a row of modulators that can change the direction of a coherent light beam by adjusting the relative phase of the signal from one element to the next. <FIG> show schematically two adjacent light reflective elements <NUM> or pixels which form a MEMS phased-array <NUM>. Although only two pixels or light reflective elements <NUM> are shown, it will be understood that a MEMS phased-array used in LiDAR applications would typically include from several hundred to several thousand light reflective elements. In particular, <FIG> represent the extremes of an angular scan (i.e. from <NUM> degrees or back reflection perpendicular to a long axis <NUM> of the MEMS phased-array <NUM>, to a ±<NUM>st order). As shown in these figures a maximum phase slope possible between adjacent pixels or light reflective elements <NUM> is 1π or quarter wavelength (λ/<NUM>) deflection. <FIG> illustrates a configuration in which the deflection between adjacent pixels or light reflective elements <NUM> is λ/x, where x is a whole number larger than four (<NUM>), to steer the light to intermediate angles between 2A and 2B.

Referring to <FIG> the MEMS phased-array <NUM> is illuminated with a line of coherent incident light <NUM>, and individually addressing or deflecting the light reflective elements <NUM> from quiescent or non-deflected state by different amounts a relative to a wavelength (λ) of incident light <NUM> a wave front <NUM> reflected from the MEMS phased-array <NUM> can be made to propagate away from the MEMS phased-array at angle (φ) relative to a long axis <NUM> of the MEMS phased-array. <FIG> illustrates the light reflective elements <NUM> in the quiescent or non-deflected state in which the reflected light propagated or steered in a direction parallel to the axis <NUM> of the MEMS phased-array. <FIG> illustrates the light reflective elements <NUM> in state in which the light reflective elements <NUM> have been deflected by an amount equal to <NUM> times the wavelength (λ) of incident light <NUM> and causing the reflected light to be steered or propagated away at a first angle (φ') relative to the axis <NUM> of the MEMS phased-array. <FIG> illustrates the light reflective elements <NUM> in state in which the light reflective elements <NUM> have been deflected by an amount equal to x<. <NUM> times the wavelength (λ) of incident light <NUM> and causing the reflected light to be steered or propagated away at a second angle (φ) relative to the axis <NUM> of the MEMS phased-array.

It is noted that <NUM> times the wavelength (λ) of incident light <NUM> is the maximum by which adjacent light reflective elements <NUM> can be deflected without introducing phase ambiguity and results in a binary pattern creating a positive and negative first order beam. Thus, twice φ represents a maximum angular field of view (FOV) over which a line or swath of modulated light can steered or scanned is determined by angle between <NUM>st order reflected light. The actual values for these angles for <NUM>st order reflected light is dependent on a width or pitch between the light reflective elements <NUM> and the wavelength (λ) of the incident light <NUM> but is generally given by the equation: <MAT> where λ is the wavelength of the incident light and d is two widths of the light reflective elements <NUM>.

A method of operating a LiDAR system including a MEMS phased-array to scan a far field scene will now be described with reference to <FIG> is a schematic functional diagram of a portion of a LiDAR system <NUM> including controller <NUM> and a solid state optical scanner <NUM> having an optical transmitter <NUM> with at least one MEMS phased-array <NUM> configured to receive light from a light source through shaping or illumination optics (not shown in this figure), and to modulate phases of at least some of the received light and transmit or project a beam of phase modulated light through projection optics <NUM> to steer a line or swath <NUM> of illumination to scan a far field scene <NUM>. The MEMS phased-array <NUM> steers the beam of light to scan the far field scene <NUM> by changing phase modulation of light incident on different portions of the MEMS phased-array. Generally, the first MEMS phased-array <NUM> is configured to scan the far field scene <NUM> in at least two-dimensions (2D), including an angular dimension (θ), and an axial dimension (indicated by arrow <NUM>) parallel to a long axis of the MEMS phased-array.

It is noted that although the optical scanner <NUM> is shown schematically as including a single MEMS phased-array <NUM> this need not and generally is not the case in every embodiment. Rather, as explained in detail below, it is often advantageous that the optical scanner <NUM> include multiple adjacent MEMS phased-arrays <NUM> operated in unison or a single MEMS phased-array having multiple adjacent arrays to increase either aperture width or length to increase a power or radiant flux of the transmitted or received light and to increase the point spread resolution of the system.

The optical scanner <NUM> further includes an optical receiver <NUM> including collection or receiving optics <NUM> to capture light from the far field scene <NUM>, which is then directed onto a detector <NUM>.

Referring to <FIG>, depth or distance information from the LiDAR system <NUM> to a target or object <NUM> in the far field scene <NUM> can be obtained using any one of a number of standard LiDAR techniques, including pulsed, amplitude-modulated-continuous-wave (AMCW) or frequency-modulated-continuous-wave (FMCW). In pulsed and AMCW LiDAR systems the amplitude of intensity of the light transmitted is either pulsed or modulated with a signal, and the TOF from the LiDAR system <NUM> to the object <NUM> is obtained by measuring the amount by which the return signal is time-delayed. The distance to the reflected object is found by multiplying half this time by the speed of light.

<FIG> is a diagram illustrating a change in frequency of an outgoing pulse of transmitted light over time for a LiDAR system using an FMCW technique. Referring to <FIG>, in a FMCW LiDAR the frequency of an outgoing chirp or pulse <NUM> of transmitted light is continuously varied over time as the swath <NUM> of light is continuously scanned across the far field scene <NUM>. The time to the object <NUM> can be determined by comparing the frequency of light reflected from the object to that of a local oscillator, and the distance to the object is found by using the speed of light as previously described. FMCW LiDAR systems have an advantage over amplitude modulated in that the local oscillator provides an inherent amplification of the detected signal.

With information on TOF the controller <NUM> in the LiDAR system can then calculate a location of the object <NUM> in the far field scene <NUM> along an X-axis <NUM> from the steering direction of the MEMS phased-array <NUM> when the light was transmitted from the MEMS phased-array, and along a Y-axis <NUM> from a sensed location of the object along an axis of the detector <NUM> (indicated by arrow <NUM>) parallel to a long axis of the detector.

Embodiments of optical scanners according to the present disclosure, and which are particularly suitable for use in LiDAR systems to scan and/or identify objects or targets, such as people, buildings and automobiles, in a far field scene will now be described with reference to the block diagrams of <FIG>, and to <FIG>.

Referring to <FIG>, in a first embodiment the optical scanner <NUM> includes an optical transmitter <NUM> and an optical receiver <NUM>. The optical transmitter <NUM> generally includes a light source <NUM>, shaping or illumination optics <NUM> to illuminate a MEMS phased-array <NUM> with light from the light source, and imaging or projection optics <NUM> to transmit or project phase modulated light from the MEMS phased-array into a far field scene <NUM> to scan the far field scene in at least two dimensions.

The light source <NUM> can include any type and number of light emitting devices capable of continuously emitting or pulsing a coherent light at a sufficient power level or power density, and at a single wavelength or frequency, or within a narrow range of wavelengths or frequencies, to enable light from the MEMS phased-array <NUM> to be modulated in phase and/or amplitude. Generally, the light source <NUM> is a continuous-wave light source that continuously emits a light that is modulated either in amplitude, for an AMCW LiDAR, or in frequency, for a FMCW LiDAR. Bcause objects in the far field scene are continuously illuminated; the light source can operate with less power compared to a high peak-power of pulsed systems. The light source <NUM> can include a number of lasers or laser emitters, such as diode lasers, vertical-cavity surface-emitting lasers (VCSELS). In one embodiment the light source the light source <NUM> includes a VCSEL array having a number of laser emitters to increase optical power while meeting or extending an eye-safe power limit. In another embodiment, the light source <NUM> includes a number of high-power lasers producing from about <NUM> to about <NUM>,<NUM> milliwatts (mW) of power at a wavelength (λ) of from about <NUM> to about <<NUM>.

The illumination optics <NUM> can comprise a number of elements including lens integrators, mirrors and prisms, configured to transfer light from the light source <NUM> to the first MEMS phased-array <NUM> to illuminate a line of a specified width and covering substantially a full width and/or length of the MEMS phased-array. In one embodiment, the illumination optics <NUM> include a microlens or lenticular array (described in greater detail below) to individually illuminate one or more modulators in the first MEMS phased-array <NUM>.

The projection optics <NUM> can also include lenses, integrators, mirrors and prisms, and are configured to transfer light from the MEMS phased-array <NUM> to illuminate a line or swath in the far field scene <NUM>. Generally, the projection optics <NUM> includes magnifying optics or elements, such as Fourier Transform (FT) lenses and mirrors, to increase a field of view (FOV) of the optical scanner <NUM>. In one embodiment, the projection optics <NUM> include a lenticular array to disperse the light in a first direction to form the swath of illumination perpendicular to a direction over which the projected light is moved or steered in the far field scene <NUM>.

The optical receiver <NUM> generally includes receiving optics <NUM> to collect or receive light from the far field scene and direct or pass the received light onto a detector <NUM> or detector array. Like the illumination and projection optics the receiving optics <NUM> can include lenses, integrators, mirrors and prisms, and are configured to receive and transfer light from the far field scene <NUM> to the onto the detector <NUM>. In one embodiment, the receiving optics <NUM> includes a lenticular array to increase an effective fill factor of the detector <NUM>.

Generally, the detector <NUM> can comprise any type of detector sensitive to light in the wavelengths generated by the light source <NUM>, including a rolling shutter camera or cameras, a one or two dimensional array of photodiode detectors, or a single photon avalanche diode (SPAD) array. In the embodiment shown in <FIG>, the receiving optics will be 2D, and the detector is a 2D array of detectors or a 2D detector array. LiDAR systems used in automobiles detector <NUM> can use lower density, higher sensitivity devices, such as APDs, for long range detection.

In another embodiment, shown in <FIG>, the optical receiver <NUM> is a pointing optical receiver including a <NUM>nd MEMS phased-array <NUM> to de-scan collected or received light by selectively directing light reflected from a slice of the far field scene <NUM> onto the detector <NUM> while substantially rejecting background light. For example, the <NUM>nd MEMS phased-array directs the light from the light source reflected from the far field scene <NUM> onto the detector <NUM> by adapting the direction to which it steers light based on information on the direction to which the <NUM>st MEMS phased-array <NUM> steers the light beam. Optionally, as in the embodiment shown the optical receiver <NUM> can further include detector optics <NUM> to transfer light from the <NUM>nd MEMS phased-array <NUM> on to the detector <NUM>. As with the illumination optics <NUM>, projection optics <NUM> and receiving optics <NUM>, the detector optics <NUM> can include lenses, integrators, mirrors and prisms, and configured to substantially fill or over fill the detector <NUM>. In one embodiment, the receiving optics <NUM> includes a lenticular array to increase an effective fill factor of a stacked phased-array <NUM>.

In some embodiments in which the wherein the detector <NUM> includes a one dimensional (1D) detector array, and the optical receiver <NUM> is a pointing-receiver in which the <NUM>nd MEMS phased-array <NUM> selectively directs light reflected from a slice of far field scene <NUM> onto the 1D detector array while rejecting light reflected from the far field scene outside of the slice and background light.

As with the embodiment shown in <FIG> the optical scanner <NUM> includes an optical transmitter <NUM> and an optical receiver <NUM>. The optical transmitter <NUM> additionally includes the light source <NUM> and illumination optics <NUM> to illuminate the <NUM>st MEMS phased-array <NUM> with light from the light source and projection optics <NUM> to transmit or project phase modulated light from the MEMS phased-array into the far field scene <NUM>. The optical receiver <NUM> includes in addition to the <NUM>nd MEMS phased-array <NUM> the detector <NUM> and receiving optics <NUM> to collect or receive light from the far field scene <NUM> and to direct or pass the light to the <NUM>nd MEMS phased-array <NUM> and onto the detector <NUM>. As the <NUM>nd MEMS phased-array <NUM> directs the light from the light source reflected from the far field scene onto the detector <NUM>, it is possible to reduce the size or width of the detector <NUM>, compared to the case in which the <NUM>nd MEMS phased-array <NUM> is not provided. That is, because <NUM>nd MEMS phased-array <NUM> is capable of imaging a slice of the 2D scene <NUM> onto the detector <NUM>, the detector can include a 1D array detector. The full scene is reconstructed by scanning the <NUM>nd MEMS phased-array.

In yet another embodiment, shown in <FIG>, the optical scanner <NUM> includes a shared MEMS phased-array <NUM> configured to modulate phases of the light from a light source <NUM> at a first time to scan a far field scene <NUM>, and at a second time to de-scan collected or received light by directing light from the light source reflected from the far field scene onto a detector <NUM> while substantially rejecting background light. As with the embodiments shown in <FIG> and <FIG>, the optical scanner <NUM> includes an optical transmitter <NUM> and an optical receiver <NUM>. The optical transmitter <NUM> includes in addition to the light source <NUM> and shared MEMS phased-array <NUM>, illumination optics <NUM> to illuminate the MEMS phased-array with light from the light source and projection optics <NUM> to transmit or project phase modulated light from the MEMS phased-array into the far field scene <NUM>. The optical receiver <NUM> includes in addition to the detector <NUM> and shared MEMS phased-array <NUM>, receiving optics <NUM> to collect or receive light from the far field scene <NUM> and, optionally, detector optics <NUM> to direct or pass the light to the shared MEMS phased-array and onto the detector <NUM>.

In another embodiment shown in <FIG> the optical scanner <NUM> can include a MEMS phased-array <NUM> in an optical receiver <NUM> of the scanner, and a spatial light modulator (SLM <NUM>) in an optical transmitter <NUM>. The SLM <NUM> in the optical transmitter <NUM> need not include a solid state device, but can alternatively include a mechanical scanner, such as a spinning or moving mirror, to steer the light beam over a far field scene <NUM>. As with embodiments described above, the optical receiver <NUM> includes in addition to the MEMS phased-array <NUM> receiving optics <NUM> to collect or receive light from the far field scene <NUM> and to direct or pass the light to the MEMS phased-array and from there onto a detector <NUM>. The optical transmitter <NUM> additionally includes a light source <NUM> and illumination optics <NUM> to illuminate the SLM <NUM> with light from the light source and projection optics <NUM> to transmit or project phase modulated light from the MEMS phased-array into the far field scene <NUM>.

Embodiments of a MEMS-based spatial light modulator (SLM) to form a MEMS phased-array suitable for use in an optical scanner will now be described.

One type of MEMS-based SLM suitable for use in a MEMS phased-array of a LIDAR system to modulate or steer a beam of light is a ribbon-type SLM or ribbon MEMS phased-array including multiple electrostatically deflectable ribbons, such as a Grating Light Valve (GLV™), commercially available from Silicon Light Machines, in Sunnyvale CA. Ribbon-type SLMs generally include a one dimensional (1D) linear array composed of thousands of free-standing, addressable electrostatically actuated movable structures, such as elongated elements or ribbons, each having a light reflective surface supported over a surface of a substrate. Each of the ribbons includes an electrode and is deflectable through a gap or cavity toward the substrate by electrostatic forces generated when a voltage is applied between the electrode in the ribbon and a base electrode formed in or on the substrate. The ribbon electrodes are driven by a drive channel in a driver, which may be integrally formed on the same substrate with the array. Ribbon-type SLMs are suited for a wide range of LiDAR applications because they are small, fast, low cost systems, which are simple to fabricate, integrate and package while still capable of providing large diffraction angles. Additionally, ribbon-type SLMs are capable of working to produce 3D scans or models when used in combination with rolling shutter cameras, photodiode detector array and SPAD array, and a wide range of illumination sources, including a laser array or bar with multiple semiconductor diode lasers or VCSELs.

An embodiment of a ribbon-type SLM will now be described with reference to <FIG>. For purposes of clarity, many of the details of MEMS in general and MEMS-based SLMs in particular that are widely known and are not relevant to the present invention have been omitted from the following description. The dimensions and the relative dimensions may not correspond to actual reductions to practice of the invention.

Referring to <FIG> in the embodiment shown the SLM is a one dimensional (1D) ribbon-type SLM <NUM> that includes a linear array <NUM> composed of thousands of free-standing, addressable electrostatically actuated ribbons <NUM>, each having a light reflective surface <NUM> supported over a surface of a substrate <NUM>. Each of the ribbons <NUM> includes an electrode <NUM> and is deflectable through a gap or cavity <NUM> toward the substrate <NUM> by electrostatic forces generated when a voltage is applied between the electrode in the ribbon and a base electrode <NUM> formed in or on the substrate. The ribbon electrodes <NUM> are driven by a drive channel <NUM> in a driver <NUM>, which may be integrally formed on the same substrate <NUM> with the linear array <NUM>.

A schematic sectional side view of an elongated element or ribbon <NUM> of the SLM <NUM> of <FIG> is shown in <FIG>. Referring to <FIG>, the ribbon <NUM> includes an elastic mechanical layer <NUM> to support the ribbon above a surface <NUM> of the substrate <NUM>, a conducting layer or electrode <NUM> and a reflective layer <NUM> including the reflective surface <NUM> overlying the mechanical layer and conducting layer.

Generally, the mechanical layer <NUM> comprises a taut silicon-nitride film (SiNx), and is flexibly supported above the surface <NUM> of the substrate <NUM> by a number of posts or structures, typically also made of SiNx, at both ends of the ribbon <NUM>. The conducting layer or electrode <NUM> can be formed over and in direct physical contact with the mechanical layer <NUM>, as shown, or underneath the mechanical layer. The conducting layer or ribbon electrode <NUM> can include any suitable conducting or semiconducting material compatible with standard MEMS fabrication technologies. For example, the electrode <NUM> can include a doped polycrystalline silicon (poly) layer, or a metal layer. Alternatively, if the reflective layer <NUM> is metallic it may also serve as the electrode <NUM>.

The separate, discrete reflecting layer <NUM>, where included, can include any suitable metallic, dielectric or semiconducting material compatible with standard MEMS fabrication technologies, and capable of being patterned using standard lithographic techniques to form the reflective surface <NUM>.

In the embodiment shown, a number of ribbons are grouped together to form a large number of MEMS pixels <NUM>, with or more ribbons in the array driven by a single driver channel <NUM>.

<FIG> is a schematic representation of how the pitch and amplitude of an ensemble of SLM ribbons in <FIG> can be adjusted to steer a beam of light. Referring to <FIG>, in order to steer a normally incident beam <NUM> through a reflected steering angle θ, ribbons <NUM> are arranged in a "blaze" pattern <NUM> of pitch or period A. As the blaze pitch A is reduced, light is steered over larger angles θ. Note that the blaze period A can assume integer or non-integer values to allow continuous modulation of the steering angle θ. The largest steering angle is achieved when the blaze period comprises two ribbons.

<FIG> is a schematic representation of a portion of a linear array <NUM> in a ribbon-type SLM shown in cross-section to long axes of the ribbons. The deflection of ribbons <NUM> is varied to impart a monotonic phase variation along the array. Note that once the phase variation exceeds one wave (i.e. half wave deflection), the deflection pattern is continued via modulo division by the wavelength forming the blaze groupings <NUM>. An SLM with programmable MEMS elements (ribbons <NUM>) allow light to be continuously scanned in angle, making it particularly useful in steering applications, such as LIDAR.

<FIG> is a graph of intensity versus steering angle and illustrates the suitability of the ribbon-type SLM represented schematically in <FIG> for phased-array applications. Referring to <FIG>, it is seen that the periodic spatial pattern along ribbon-type SLM shown in <FIG> creates a phased-array reflection, while varying the spatial period and amplitude of the pattern changes the reflected beam angle, allowing the ribbon-type SLM to rapidly cycle through patterns to sweep beam across field. In particular, it is noted that as the period of the spatial pattern on the array <NUM> increases, i.e., as each period includes a greater number of ribbons, a maximum intensity <NUM> with which light is reflected from the array <NUM> shifts to the left as indicated by arrow <NUM>. As spatial period decreases or the number of ribbons in each period reduced, the maximum intensity <NUM> with which light is reflected from the array <NUM> shifts to the right as indicated by arrow <NUM>.

The high switching speed of the ribbon-type SLM makes it attractive for MEMS phased-array applications such as LiDAR. However, designing a ribbon-type SLM for LiDAR presents two challenges. First, a large stroke, i.e., an amount by which an individual ribbon can be deflected, is generally used. Often it is suggested that the ribbon-type SLM have a stroke up to or exceeding one-half the wavelength of the light being modulated or steered. For example, it has been found a stroke of approximately <NUM> is desirable to achieve adequate phase shift in applications for LIDAR using <NUM> wavelengths. The stroke of the phase modulator scales linearly with the wavelength.

A second challenge for ribbon-type SLMs used for MEMS phased-array is that the ribbons should include narrow ribbon widths to achieve wide angular swing. Generally, it is suggested that a ribbon used in ribbon-type SLMs for MEMS phased-array applications have a ribbon width of about <<NUM> or less, and in some embodiments can be as narrow as <NUM>.

These requirements of a large stroke and a narrow ribbon width make it very difficult to switch the ribbon-type SLM at a high rate of speed, which is desirable for beam steering, because narrow ribbons over large air gaps are very poorly damped and can behave like a guitar string, taking a long time to settle and thereby limiting the rate of speed at which the beam can be steered.

The impact of air gap and ribbon width on settling time will now be described with reference to <FIG> is a schematic diagram modeling a ribbon of ribbon-type SLM as a capacitor-on-a-spring. Referring to <FIG>, a voltage potential V(t) applied between a ribbon <NUM> and a grounded lower or substrate electrode <NUM> creates an electrostatic Coulomb attraction that deflects the ribbon a distance x towards the substrate electrode. The electrostatic force is balanced by an elastic restoring force (represented by a spring <NUM> in <FIG>). The elastic restoring force, which is due to the taut silicon-nitride film the mechanical layer (shown as mechanical layer <NUM> in <FIG>), allows the ribbon <NUM> to revert back to a neutral state or position once the electrostatic force is removed. In addition there is a damping force (represented by a damper <NUM> in <FIG>), arising from squeeze-film effects which is proportional to the instantaneous velocity of the ribbon and slows or damps movement of the ribbon <NUM>. Squeeze-film damping is a strong function of both ribbon width and air-gap thickness. Settling time is proportional to the cube of the air-gap thickness, and inversely proportional to the cube of the ribbon width. Thus, to achieve adequate damping with narrow ribbons, it is suggested to have a very thin air-gap.

The Coulomb attraction force (Fcoulomb) is given by: <MAT> where ε<NUM> is the permittivity of free space, A is the effective capacitive area of the ribbon in square meters (m<NUM>), G is gap thickness, and x is the linear displacement of the ribbon in meters, relative to the substrate electrode.

The Elastic Restoring Force (FElastic) is given by: <MAT> where k is the spring constant of the mechanical layer, and x is the linear displacement of the ribbon <NUM>, in meters, relative to the substrate electrode <NUM>.

The Damping force (FDamping)is given by: <MAT> where b is the damping constant of the air gap, and dx/dt is the velocity of the center of the ribbon <NUM>, in meters/second, relative to the substrate electrode <NUM>.

Thus, at equilibrium these three forces, Coulomb attraction, Elastic restoring force and the Damping force, must balance.

However, as the ribbon <NUM> displaces past <NUM>/<NUM> a total thickness of the gap (G) between the ribbon in the neutral state and substrate electrode <NUM>, the electrostatic force can overwhelm the elastic restoring force. This results in a potentially destructive phenomenon commonly referred to as "snap-down" or"pull-in," in which the ribbon <NUM> snaps into contact with the substrate electrode <NUM> and sticks there even when the electrostatic force is removed. Generally, it has been observed that snap-down occurs at a characteristic displacement of x=G/<NUM>, where the ribbon <NUM> has been deflected by one third of the original gap thickness. Thus, the ribbons in conventional ribbon-type SLM are typically operated or driven to not be deflected by a distance more than G/<NUM> to prevent snap-down. Uunfortunately, this leaves the lower <NUM>/<NUM> of the gap G empty, which in turn leads to poor squeeze-film damping.

Thus, to achieve adequate damping with narrow ribbons, it is desirable to create a very thin squeeze film gap, approaching the physical stroke (x) for the application, while to avoid pull-in it is desirable to create a much larger "electrical gap.

Reducing the squeeze film gap while maintaining or increasing the electrical gap can be done by inserting a dielectric between the ribbon and the substrate electrode. In one embodiment, a solid dielectric film underneath the ribbon is used to improve damping (and heat transfer) in this way. For a dielectric thickness of G, the equivalent electrical thickness is G/εr, where εr is the relative dielectric constant. For example, for silicon dioxide solid dielectric film having a relative dielectric constant of εr = <NUM>, and a vacuum or air gap having a relative dielectric constant of εr =<NUM>, to increase the electrical gap by <NUM>, it is necessary to provide nearly an additional <NUM> of a dielectric material over the substrate electrode between the ribbon and substrate electrode. It is noted that integrating thick films, i.e., films having a thickness greater than about <NUM>, into an existing MEMS process used to fabricate ribbon-type SLMs can be difficult or impractical, since intrinsic film stresses can cause such thick films to void or delaminate, and film roughness can become excessive with increased thickness. For this reason, a low dielectric constant material is frequently used.

In another embodiment, the squeeze film gap is reduced while maintaining or increasing the electrical gap by use of an electrically permeable damping structure formed over the substrate electrode during fabrication. Generally, the electrically permeable damping structure includes a dielectric layer suspended above and separated from the substrate electrode by a first gap or first air-gap, where the dielectric layer defines at least a top surface of the air-gap. It is noted that although this first gap is referred to as an air-gap, it need not be filled with air, but can alternatively be evacuated or filled with a mixture of other gases. In some embodiments, the dielectric layer can substantially surround the air-gap to form a hermetic or hermetically sealed cavity. In other embodiments, the first air gap is open to the MEMs environment, including a second gap or air-gap between the electrically permeable damping structure and a lower surface of the ribbons, and the entire environment of the ribbon-type SLM can be evacuated or filled with fill gases and hermetically sealed. Suitable fill gases can include pure form or mixtures of one or more of Nitrogen, Hydrogen, Helium, Argon, Krypton or Xenon.

In one embodiment, a ribbon-type SLM includes an electrically permeable damping structure to provide a large stroke while maintaining good damping, thereby enabling fast beam steering and large scan angles, and exceeding the wavelength of the light being modulated or steered to accommodate light having long wavelengths of up to about <NUM>. <FIG> is a sectional side view of a portion of the ribbon-type SLM of <FIG> including such a damping structure. Referring to <FIG> the ribbon-type SLM <NUM> includes a bottom or lower electrode <NUM> formed over a substrate <NUM>, and a static, electrically permeable damping structure formed over the bottom electrode. Generally, the electrically permeable damping structure includes a first air-gap <NUM> and a dielectric layer <NUM> suspended above and separated from the lower electrode <NUM> by the first air-gap, and a second air-gap <NUM> above the dielectric layer separating movable lengths of a plurality of ribbons <NUM> of the ribbon-type SLM <NUM> from the dielectric layer. As in the embodiments of the ribbon-type SLM described in connection with FIGs. 6A and 6B, each of the ribbons <NUM> include a mechanical layer, typically formed from a taut layer of silicon nitride, and a ribbon or top electrode coupled through a bus <NUM> to one of number of drive channels (not shown), and are configured to deflect towards the bottom electrode by electrostatic force generated between the top and bottom electrodes. Generally, as in the embodiments of <FIG> the drive channels are integrally formed on the same substrate <NUM> as the linear array of ribbons <NUM>.

Optionally, as in the embodiment shown, the device can further include a thin intermediate dielectric layer <NUM>, such as a silicon-dioxide between the substrate <NUM> and the lower electrode <NUM> to electrically insulate the lower electrode.

In operation, the ribbons <NUM> are independently deflectable towards the bottom electrode <NUM> by a distance substantially equal to a thickness of the second air-gap <NUM>. Generally, the thickness of the second air-gap <NUM> is ~G/<NUM>, and the thickness of the first air-gap <NUM> is ~<NUM>/<NUM>, where G is a distance between the bottom electrode <NUM> and the ribbons <NUM> in an undeflected or quiescent state. It has been found that for a ribbon-type SLM <NUM> with ribbons <NUM> having a width transverse to a long axis of the linear array of from <NUM> to <NUM>, and operating at near infrared wavelengths suitable for LiDAR applications, an electrically permeable damping structure such as described above and having a first air gap <NUM> of about <NUM> and a second air-gap <NUM> up to about <NUM>, improves settling time, while maintaining a high switching speed and substantially preventing pull-in or snap-down of the ribbons <NUM>. Note that the ratio of second air-gap thickness to first air-gap thickness can be decreased to accommodate narrower ribbons which require stronger damping. By changing the thickness ratio but maintaining the same total thickness (first air-gap + second air gap) the total desired stroke is maintained.

In one embodiment, such as that shown in <FIG>, the MEMS phased-array <NUM> can include multiple ribbon-type SLMs 1302a, 1302b, each with a one dimensional (1D) array 1304a, 1304b, arranged in a line along a common or shared long axis <NUM> and operated to increase an area over which modulated light can be scanned, and stacked to increase an axial dimension parallel to the long axis of the arrays. Referring to <FIG>, each of the arrays 1304a, 1304b, includes hundreds or thousands of free-standing, addressable electrostatically actuated ribbons 1308a, 1308b. As with the ribbon-type SLM <NUM> described above with respect to <FIG>, each of the ribbons 1308a, 1308b, has a light reflective surface, includes an electrode and is deflectable through a gap or cavity toward a substrate <NUM> by electrostatic forces generated when a voltage is applied between the electrode in the ribbon and a base electrode in the substrate. Each of the ribbons 1308a, 1308b, is driven by a drive channel 1312a, 1312b in a driver 1314a, 1314b, which may be integrally formed on the same substrate <NUM> with the arrays 1304a, 1304b.

In some embodiments, such as that shown, each of the ribbon-type SLMs 1302a, 1302b, including the arrays 1304a, 1304b and drivers 1314a, 1314b, are integrally formed on a single, shared substrate <NUM>. Alternatively, each of the ribbon-type SLMs 1302a, 1302b, can be integrally formed on separate substrates, which are then packaged in a single, share integrated circuit (IC) package. In yet another alternative embodiment, each of the ribbon-type SLMs 1302a, 1302b, are separately packaged and then mounted to a single, shared printed circuit board (PCB).

In other embodiments, shown in <FIG> and in <FIG>, the MEMS phased-array can include multiple ribbon-type SLMs or a single ribbon-type SLM having multiple one dimensional (1D) arrays arranged and operated in parallel to increase the active aperture of the optical scanner. Increasing the functional area of the MEMS phased-array in this manner allows for simpler optics, enables an increased field of view (FOV) and system point spread resolution, as well as increased sensitivity by collecting more light in de-scan operations.

<FIG> is a diagram illustrating a top view of an embodiment of a MEMS phased-array <NUM> including multiple ribbon-type SLMs 1402A and 1402B each including an array <NUM> of a plurality of ribbons <NUM> arranged in parallel. Generally, as in the embodiment shown the ribbon-type SLM 1402A and 1402B are integrally formed on a shared substrate <NUM>, and the ribbons <NUM> are driven by drive channels <NUM> in drivers <NUM>, which may be integrally formed on the same substrate <NUM> with the arrays <NUM>. Alternatively, in an embodiment not shown all of the multiple ribbon-type SLMs 1402A and 1402B can be driven by a single shared driver <NUM>.

<FIG> are diagrams illustrating another embodiment of a MEMS phased-array <NUM> including a single ribbon-type SLM <NUM> in which each of the ribbons <NUM> of the SLM are divided by posts <NUM> along a long axis thereof to form a plurality of parallel 1D arrays 1508a, 1508b, and 1508c. Although only three parallel 1D arrays 1508a, 1508b, 1508c are shown it will be understood that the ribbon-type SLM <NUM> can be divided into any number of parallel 1D arrays from <NUM> to over <NUM>. A schematic sectional side view of a movable ribbons <NUM> of the SLM <NUM> of <FIG> in an undeflected or quiescent state is shown in <FIG>. A schematic sectional side view of a movable ribbons <NUM> of the SLM <NUM> of <FIG> in a deflected or active state is shown in <FIG>. As with the embodiment of the SLM <NUM> described with respect to <FIG>, the ribbon <NUM> includes an elastic mechanical layer <NUM> to support the ribbon above a bottom electrode <NUM> formed on a surface of a substrate <NUM>, a ribbon or top electrode <NUM> and a reflective layer <NUM> including a light reflective surface overlying the mechanical layer or top electrode. Generally, as shown in the embodiment of <FIG> the SLM <NUM> further includes a number of drive channels <NUM> in a driver <NUM> integrally formed on the same substrate <NUM> as the linear 1D arrays 1508a, 1508b, and 1508c.

In another embodiment, the MEMS phased-array includes a blazed grating ribbon-type or ribbon MEMS array, in which each elongated element or ribbon of a ribbon-type SLM has a reflective surface with a blazed profile. By a blazed profile it is meant wherein each of the ribbons have a reflective surface across a width of the ribbon that is angled at the blaze angle relative to a surface of the SLM or surface of a substrate on which the SLM is fabricated. In some embodiments, the reflective surfaces have a stepped profile to produce an effective blaze at a blaze angle. The blaze angle on the ribbon adjusts a power and contrast in modulated light from the SLM in the zeroth (<NUM>th) and higher orders, providing higher contrast in the <NUM>th order, and higher contrast and/or power in the first (<NUM>st) and higher orders. For scanning operation, using a blazed ribbon in conjunction with the blazed operation or method described above with respect to <FIG>, shifts a center of a "scan envelope" (angles between +/- first orders in an SLM with flat ribbons) towards the first order, and away from the zeroth (<NUM>th) and order or incidence angle. An advantage of shifting the center of a "scan envelope" is that any reflections from any other surfaces of the SLM exposed through gaps between ribbons will appear only in the zeroth order, and therefore will not be scanned resulting in a more optically efficient system with greater or higher contrast.

An embodiment of a ribbon-type SLM including ribbons with a blazed profile will now be described with reference to <FIG> illustrate a cross-sectional view of a single elongated element or ribbon <NUM> having a stepped profile to produce an effective blaze surface <NUM> at a blaze angle γ at a blaze angle. The ribbon <NUM> generally includes a rectangular body <NUM> and a stepped reflector <NUM>. The rectangular body <NUM> can include silicon nitride and the stepped reflector <NUM> can include an optically reflective material such as aluminum. The stepped reflector <NUM> forms first and second surfaces, <NUM> and <NUM>, of the ribbon <NUM>. The first and second surfaces, <NUM> and <NUM>, are generally separated by a height difference of an eighth wavelength λ/<NUM> of an incident light to form a blaze profile <NUM>. The blaze profile <NUM> forms the effective blaze surface <NUM> at blaze angle y, where blaze angle γ is given by the expression: y=arctan (λ/(4A)).

A first cross-sectional view of a portion of a blazed ribbon-type or ribbon MEMS phased-array <NUM> in a non-activated state with the ribbons <NUM> on a grating pitch A and with the first surfaces <NUM> defining a grating plane <NUM> is illustrated in <FIG>. In the non-activated state, there is generally a zero electrical bias between the ribbons <NUM> and a lower or bottom electrode <NUM>. The incident light (I) of wavelength λ illuminates the blazed ribbon MEMS phased-array <NUM> at an angle normal to the grating plane <NUM>, and diffracts light into a number of diffraction orders D<NUM>, D-<NUM> and D<NUM> based on a profile of the blazed ribbons <NUM>. In the non-activated state, the zeroth order diffraction, D<NUM>, is normal to the grating plane <NUM>. The diffraction orders D<NUM> and D-<NUM> are at a first diffraction angle θ<NUM> given by the expression: θ<NUM> =arcsin (λ/A), where A is the grating pitch of the first and second surfaces, <NUM>, <NUM>, of the ribbons <NUM>. For the embodiment shown having first and second surfaces, <NUM>, <NUM>, separated by a height difference of an eighth wavelength λ/<NUM> the diffraction angle θ<NUM> is approximately four times the blaze angle y, or less than about <NUM>°. Neglecting a first light loss due to absorption by the stepped reflectors <NUM> and a second light loss by the incident light I passing through gaps between adjacent pairs of the ribbons <NUM>, half of the light incident on the blazed ribbon MEMS phased-array<NUM> is diffracted into the zeroth diffraction order, D<NUM>, while a quarter of the incident light I is diffracted into each of the first diffraction orders D<NUM> and D-<NUM>.

A second cross-sectional view of the blazed ribbon MEMS phased-array <NUM> in an activated state in which the ribbons <NUM> are moved towards a substrate <NUM> by applying an electrical bias between the ribbons and the bottom electrode <NUM> is illustrated in <FIG>. Generally, as in the embodiment shown the blazed ribbon MEMS phased-array <NUM> is operated using a blazed operation or method similar to that described above with respect to <FIG>. Referring to <FIG>, in order to steer a normally incident beam (I) through a first order of a reflected steering angle θ<NUM>, ribbons <NUM> having a blaze profile <NUM> are arranged in a "blaze" pattern <NUM> of pitch or period A. In the activated state, the incident light I of the wavelength λ is diffracted into a first angle, θ<NUM>, by the profile of the blazed ribbons <NUM> as described above, and further diffracted or steered by a first order diffraction angle θ<NUM> produced by the blaze pattern <NUM>, and given by the expression: θ<NUM> =arcsin (λ/Λ), where A is the blaze pitch A is of the blaze pattern <NUM>. Note, that the blaze period A can assume integer or non-integer values to allow continuous modulation of the steering angle θ<NUM>. As the blaze pitch A is reduced, light is steered over larger angles from θ<NUM> to θ<NUM>.

<FIG> is an optics diagram illustrating illumination optics <NUM> and projection optics <NUM> for an optical scanner including a number of MEMS phased-arrays <NUM> to steer light <NUM> to scan a far field scene <NUM>. In the embodiment shown in <FIG> the illumination optics <NUM> can include a lenticular array or an array of microcylinder lenses <NUM> to form individual columns of light from a coherent light source, and an imaging lens <NUM> to focus the collimated light onto individual modulators of the MEMS phased-array <NUM>. In the embodiment shown, the light coherent light source includes an array of light emitting devices such as VCSEL lasers <NUM>. In a pulsed or flash LiDAR in which the coherent light source is generated using an a VCSEL array <NUM> the illumination optics <NUM> and projection optics <NUM> can achieve greater than <NUM> watts (W) peak power with <NUM> nanosecond (ns) pulse, at a repetition rate of up to <NUM>, while each beam of light projected into the far field scene has an average power less than about <NUM> microwatts (mW) and thus is eye safe.

The projection optics <NUM> can include one or more lenses, such as a Fourier lens <NUM> and a fish-eye lens to spread the light from the MEMS phased-array to the far field scene in at least an angular dimension, transverse to an axial dimension over which light is scanned by phase modulation of the MEMS phased-array <NUM>. Referring to <FIG>, in a pulsed or flash LiDAR in which the coherent light source is generated using an a VCSEL array <NUM> the illumination optics <NUM> and projection optics <NUM> can achieve greater than <NUM> watts (W) peak power with <NUM> nanosecond (ns) pulse, at a repetition rate of up to <NUM>, while each beam of light projected into the far field scene has an average power less than about <NUM> microwatts (mW) and thus is Class <NUM>, eye safe. Furthermore, for a MEMS phased-array <NUM> having an individual element size <NUM> with an enclosure aperture of <NUM> the MEMS phased-array is capable of providing a FOV of <NUM> degrees, with over <NUM> resolvable lines.

In some embodiments, at least one of the illumination optics or the projection optics or receiving optics includes anamorphic optics for focusing light from a light source onto a MEMS phased-array, and/or focusing modulated light from the MEMS phased-array into the far field scene. Anamorphic optics are desirable to provide a vertical or transverse numerical aperture (NA) along a vertical axis of the MEMS phased-array, transverse to the direction over which the light is scanned, that is smaller than a diffraction angle of the modulated light reflected from the array along a vertical or transverse axis of the scan direction, and a horizontal or longitudinal NA along the horizontal or longitudinal axis of the array that is greater than the vertical or transverse NA, as the field of view and resolution requirement for the vertical and horizontal axis may differ. The horizontal axis optics will match the FOV of the phased-array device to the requirements of the horizontal scan of the system, while the FOV of the vertical scan is determined by the vertical numerical aperture as set by the illuminating or detector array system.

<FIG> and <FIG> are an optics diagram illustrating both top and side views of light paths for anamorphic illumination and imaging optics according to an embodiment of the present disclosure. The top view shows an optical paths along a pixel arranged direction. Referring to <FIG>, the light path begins at a light source, such as a laser <NUM> shown, in this embodiment, as including a plurality of light emitting or laser diodes <NUM> arranged as a bar laser to illuminate a substantially linear portion of a 1D or 2D array <NUM> of an SLM through anamorphic illumination optics <NUM>, including a first optical element or lens <NUM> and second optical element or lens <NUM>. Although in the embodiment shown the anamorphic illumination optics <NUM> are depicted or represented by two single lenses <NUM> and <NUM>, it will be appreciated that the anamorphic illumination optics can include any number of prisms, lenses and to refract and transmit light from the laser <NUM> to the linear array <NUM> to fully illuminate the linear array. The lens <NUM> is usually called FAC lens (Fast Axis Collimator) to collimate laser from the emitters along the vertical axis or fast axis of emitters. In the embodiment shown, the laser <NUM> is a bar laser including multiple semiconductor diode lasers or emitter arranged along common long axis. Each emitter of the bar laser works as spatially single mode laser and it has Gaussian beam profile along the vertical axis. As shown in side view in <FIG>, it is possible to achieve a nearly ideal collimated beam. As the size of modulator along the vertical axis is one or several millimeters, focusing optics or reduction optics are not required. This means the beam of illumination NA along the vertical direction is almost zero. If an optical device like Powell lens is inserted to convert the Gaussian to Top-hat profile, it is possible to evenly illuminate modulators which are arranged vertically in a single pixel. In the top view in <FIG> the optical element or lens <NUM> works for illumination of whole a spatial right modulators array along the horizontal axis. A light pipe or a fly eye lens array can be included in the optical element or lens <NUM> to homogenize the light from the light emitting or laser diodes <NUM> of the bar laser. As a bar laser has multiple emitters and generally has <NUM> width along the horizontal axis, it functions to some degree as a NA. In the instance in which the optical element or lens <NUM> is a single cylindrical lens, the NA would be D/2f, where D is size of the bar laser and f is the focal length of the cylindrical lens in the optical element or lens <NUM>. When an optical device to homogenize illumination is inserted in the optical element or lens <NUM>, the NA number would be extended. Thus, while NA along the fast axis or vertical axis is low, NA along the slow axis or horizontal axis could be much bigger than the fast axis.

As disclosed in the <FIG>, the pixel arranged direction of the linear array <NUM> is set parallel to emitter arranged direction of the bar laser <NUM>. Such the configuration enables to use diffraction beams effectively. When the focus is on the horizontal axis, the NA of illumination optics has some number because of the size of emitter array, while the condition to separate diffraction beams by the linear array <NUM> is limited. The imaging optics <NUM> can include magnification elements, such as a Fourier Transform (FT) lens <NUM>, and Fourier aperture <NUM>. As described above, the array includes just one or a few pixels along the horizontal direction and <NUM>st order beams can be separated from <NUM>th order beam only when the illumination NA is almost zero. Therefore a part of <NUM>st order beam interfere the <NUM>th order beam. In <FIG> the dashed lines illustrate <NUM>st order beams while the solid, bold line show the main, <NUM>th order beams. Since the NA of illumination beam is kept after it is diffracted to <NUM>st order beam by the linear array <NUM>, some of the <NUM>st order beams pass through the Fourier aperture <NUM>. On the other hand, NA of illumination optics along the vertical axis is small and the number of modulators in a single pixel is so large that diffraction, main beams are separated.

Modulated light from the linear array <NUM> is then transmitted through imaging optics <NUM> to the imaging plane <NUM>. In some embodiments, such as that shown in <FIG>, the imaging optics <NUM> can also include anamorphic optics, represented here by anamorphic lens <NUM> and microlens or lenticular array <NUM>. This embodiment is particularly advantageous where the pixel size of array <NUM> is not square. By using or adding anamorphic imaging optics to the imaging optics <NUM> a reduced image of the linear array is projected on the imaging plane along the vertical direction, thereby correcting or compensating for any distortion or non-square pixels in the of linear array <NUM>.

<FIG> shows that <NUM>th order beam and diffracted +/- <NUM>st order beams on the Fourier aperture <NUM>. Referring to <FIG>, ellipse <NUM> represents the <NUM>th order beam, while ellipse <NUM> represent <NUM>st order beams along the vertical direction, and ellipse <NUM> represent <NUM>st order beams along the horizontal direction. The aperture size along the vertical axis (vertical NA <NUM>) is equivalent to the diffraction angle of <NUM>st order beam and a size of the <NUM>th order beam (represented by ellipse <NUM>) along the horizontal axis is the same as the horizontal NA <NUM> of illumination optics (lenses <NUM> and <NUM> in <FIG>). Referring again to <FIG>, it is seen that the <NUM>th order beam (represented by ellipse <NUM>) can pass through the Fourier aperture <NUM> while the +/-<NUM>st order beams along the vertical axis (represented by ellipse <NUM>) are completely blocked, and the +/- <NUM>st order beams along the horizontal axis (represented by ellipse <NUM>) are substantially blocked or significantly reduced in power. This results in a slightly degraded contrast ratio (CR). Thus, the illumination and imaging optics of the embodiment of <FIG> is suitable for use in a LiDAR system, such as that shown in <FIG> and <FIG>.

The power of bar lasers including a plurality of laser diodes is not as high as in the examples given above, and is generally equal to or less than <NUM> watts (W). In order to increase a total illumination power multiple bar lasers should be used. Thus, in some embodiments a vertical stack of bar lasers can be used to achieve higher powers.

<FIG> is a schematic block diagram of a compact optical scanner <NUM> shown in a cut-away view, and including one or more MEMS phased-arrays <NUM>, <NUM>, and illustrating folded light paths for illuminating the MEMS phased-arrays, projecting modulate light therefrom, and receiving and de-scanning light onto a detector <NUM>. As shown in <FIG>, the folded light paths enable a compact optical scanner <NUM> size, for example of about <NUM> by <NUM> with a thickness of about <NUM>, or about the size of a deck of cards.

Referring to <FIG>, the optical scanner <NUM> includes a housing or enclosure <NUM>, and one or more openings or apertures <NUM>, <NUM>, through which light can be projected to scan a far field scene (not shown in this figure) and received back from the far field scene. Generally, the apertures <NUM>, <NUM>, are covered or sealed by lenses <NUM>, <NUM>, to further magnify or expand the projected light, to focus the received light, and/or to provide an environmentally sealed enclosure <NUM> for the optical scanner <NUM>. In some embodiments, such as that shown, the lenses <NUM>, <NUM>, can include fish-eye lenses to further increase a field of view (FOV) of the optical scanner <NUM>.

The optical scanner <NUM> further includes illumination optics <NUM> to direct light from a coherent light source <NUM> on to the MEMS phased-array <NUM>, imaging or projection optics <NUM> to transmit or project phase modulated light from the MEMS phased-array into the far field scene, and receiving optics <NUM> to receive and direct light from the far field scene onto the detector <NUM>. As in embodiments described above the light source <NUM> can include any type and number of light emitting devices, such as lasers, diode lasers or VCSELS. The illumination optics <NUM> can comprise a number of elements including one or more lenses 1920a, and integrators, mirrors or prisms 1920b, configured to transfer light from the light source <NUM> to the MEMS phased-array <NUM> to illuminate a line of a specified width and covering substantially a full width length of the MEMS phased-array. The projection optics <NUM> can also include lenses 1924a, and integrators, mirrors or prisms 1924b, configured to transfer light from the MEMS phased-array <NUM> to illuminate a line or swath in the far field scene. Like the illumination and projection optics, the receiving optics <NUM> can include one or more lenses 1926a, 1926b, integrators, mirrors and/or prisms configured to receive and transfer light from the far field scene to the onto the detector <NUM>. Generally, the detector <NUM> can comprise any type of detector sensitive to coherent light in the wavelengths generated by the light source <NUM>, including a rolling shutter camera or cameras, a one or two dimensional array of photodiode detectors, or a SPAD array.

Finally, the enclosure <NUM> of the optical scanner <NUM> can further include or house electronic circuits <NUM> necessary for the operation of the optical scanner, such as a controller, power supplies for the controller, light source <NUM>, MEMS phased-arrays <NUM>, <NUM>, and detector <NUM>, one or more memories and interfaces to a host system.

As noted above, one or more of the illumination optics <NUM>, projection optics <NUM>, receiving optics <NUM>, and detector optics <NUM> can include a microlens or lenticular array. In particular, illumination optics in the transmitter including a lenticular array is useful in conjunction with a light source including a VCSEL array, as shown in <FIG>, to provide independent optical channels. A lenticular optical array is also particularly useful distribute light on the multiple ribbon MEMS phased-arrays, either in the optical transmitter or receiver, such as those shown in <FIG>, to distribute light on the multiple arrays, and/or in projection optics to disperse to form the swath of illumination in the far field scene. Finally, a lenticular array is useful in receiver array optics to increase an effective fill factor of the receiver array.

An embodiment of a lenticular array suitable for use in some or all of these applications will now be described with reference to <FIG> is a schematic block diagram illustrating a top view of an embodiment of a lenticular array, <FIG> is a cross sectional view of the lenticular array of <FIG> illustrates 0th order illumination of a single modulator in a ribbon MEMS phased-array by single element of the lenticular array of <FIG>. Referring to <FIG> the lenticular array <NUM> includes a molded surface forming multiple individual lenses or elements, such as micro-lenses or cylindrical lenses, configured to concentrate, either focus or project, light more in one direction than in another. In the embodiment shown the lenticular array <NUM> is adapted or configured to focus light onto individual ribbons or portions of ribbons divided by posts in a ribbon MEMS phased-array <NUM>, and the individual lenses or elements include cylindrical lenses <NUM>, each having a long axis parallel to a long axis <NUM> of one or more ribbon MEMS phased-array arranged either stacked as shown in <FIG> or arranged in parallel as shown in <FIG> and <FIG>, and perpendicular to a long axis <NUM> of the ribbons. As shown in the cross-sectional view of the lenticular array <NUM> in <FIG> the cylindrical lenses <NUM> focus or concentrate incoming light <NUM> on a center of each individual ribbon or portion of a divided ribbon in the ribbon MEMS phased-array <NUM>.

Referring to <FIG>, when a difference in electrostatic potential is applied between an active ribbon <NUM> and substrate or lower electrode in a ribbon MEMS phased-array, the ribbon is deflected into a parabolic profile as shown. As a result the diffraction grating is established only in a narrow region near the center-line of the ribbon <NUM>. Regions outside this optical "sweet-spot <NUM>" are neither parallel to a surface of the ribbon MEMS phased-array nor displaced by the desired amount and therefore cannot provide efficiency steering. For this reason, it is desirable to use a lenticular array <NUM> to carefully shape or focus illumination onto a central portion of the ribbons of the ribbon MEMS phased-array, or to collimate and project only light modulated from the central portion of the ribbons. A rule of thumb is that a width of sweet-spot <NUM> should be roughly on the order of <NUM>/<NUM>th to <NUM>/<NUM>rd the length the ribbon <NUM>, depending on the contrast ratio. Additionally, with particular regard to light gathered by receiving optics and focused onto a ribbon MEMS phased-array in the optical receiver, or de-scanned by the ribbon MEMS phased-array and focused onto a detector, the individual lenses or elements enable only a <NUM>th order of light <NUM> to focused on or modulated by the sweet-spot <NUM> while rejecting other orders of light <NUM>, thereby increasing contrast and resolution of the optical scanner.

A method of operating an optical scanner including a first microelectromechanical system (MEMS) phased-array for use in a light detection and ranging (LiDAR) system will now be described with reference to the flow chart of <FIG>. Referring to <FIG> the method begins with illuminating a first MEMS phased-array with light from a coherent light source (<NUM>). The first MEMS phased-array is controlled to modulate phases of the light from the coherent light source and project the modulated light from the first MEMS phased-array to a far field scene (<NUM>), and the first MEMS phased-array is further operated or controlled to scan the far field scene (<NUM>). As described above, the first MEMS phased-array is adapted or configured to scan the far field scene in two-dimensions (2D), including an angular dimension and an axial dimension parallel to a long axis of the first MEMS phased-array. Next, light from the far field scene is received on a second MEMS phased-array (<NUM>) and the second MEMS phased-array is controlled to de-scan the received light by directing substantially only light originating from the coherent light source and reflected from the far field scene onto a detector while rejecting background light (<NUM>).

In some embodiments, the first MEMS phased-array and the second MEMS phased-array are the same, shared MEMS phased-array, and controlling the first MEMS phased-array includes controlling the shared MEMS phased-array at a first time to modulate phases of the light from the coherent light source to scan the far field scene in 2D, and controlling the second MEMS phased-array includes controlling the shared MEMS phased-array at a second time to de-scan the received light by directing light from the coherent light source reflected from the far field scene onto the detector and rejecting background light.

Thus, embodiments of a LIDAR system including a 1D MEMS phased-array, and methods for operating the same have been described. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

The Abstract of the Disclosure is provided to comply with <NUM> C. §<NUM>(b), requiring an abstract that will allow the reader to quickly ascertain the nature of one or more embodiments of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claim 1:
An optical scanner (<NUM>) comprising:
an optical transmitter (<NUM>) to receive light from a light source (<NUM>) and to modulate phases of at least some of the received light to project light onto a far field scene (<NUM>) in two-dimensions, the two-dimensions including a first direction over which the light is dispersed to form a swath of illumination and a second dimension over which the swath is steered by modulating phases of the light received from the light source (<NUM>); and
an optical receiver (<NUM>) including a number of first microelectromechanical system (MEMS) phased-arrays (<NUM>) each comprising a ribbon MEMS phased-array having a parallel arrangement of light-reflective ribbons, to receive light from the far field scene and to direct at least some of the received light onto a detector (<NUM>),
wherein the number of first MEMS phased-arrays (<NUM>) are configured to de-scan the received light by directing light from the light source (<NUM>) reflected from the far field scene (<NUM>) onto the detector (<NUM>) while rejecting background light (<NUM>),
wherein the optical receiver (<NUM>) further comprises receiving optics (<NUM>) to receive light from the far field scene (<NUM>) and direct received light onto the number of the first MEMS phased-arrays (<NUM>), and wherein the receiving optics (<NUM>) comprise a lenticular array, to increase an effective fill factor of the number of the first MEMS phased-arrays (<NUM>).