Method for imaging an area and device for imaging an area

Abstract

Light is provided to optical antennas (OAs) separated by a first set of intervals within a first OPA. The phase of the light provided to each OA is controlled to form a transmission beam whose angle is manipulated such that the first and second lobes of a first angular intensity distribution (AID) scan across the entirety of the first and second portions of the region, respectively. The light is received from OAs separated by a second set of intervals within a second OPA, and the light is received from directions associated with a second AID. The first lobe of the first AID and the first lobe of the second AID are substantially angularly overlapping during the scan of the first lobe, and the second lobe of the first AID and the second lobe of the second AID are substantially angularly overlapping during the scan of the second lobe.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit and priority of U.S. Provisional Application No. 63 / 340,526, filed May 11, 2022, titled "MITIGATION OF SPURIOUS RETURNS IN OPTICAL PHASED ARRAYS", which is hereby incorporated by reference in its entirety.

[0002] This disclosure relates to managing optical phased array performance based on angular intensity distribution.

Background Art

[0003] An optical phased array (OPA) LiDAR (Light Detection and Ranging) system can generate a return intensity map (also called angular intensity distribution) that includes spurious signal peaks associated with lobes other than the intended lobes of the OPA radiation pattern. For example, light associated with the main lobe can be reflected to provide a main signal peak that triggers a detection event, but the radiation pattern typically also includes side lobes on both sides of the main lobe (e.g., based on the finite extent of the OPA) and many grating lobes at several angular intervals (e.g., based on the finite spacing between the optical antennas that make up the OPA). The grating lobes can be larger than the side lobes, and light from either the grating lobes and / or the side lobes can be reflected to provide spurious (e.g., false or unwanted) signal peaks. If the intensity of these spurious signals exceeds the digitization - after noise floor of the LiDAR system, these spurious signals can be registered as false detection events, which can be problematic for typical LiDAR applications.

Summary of the Invention

Means for Solving the Problems

[0004] In one aspect, generally, a method of imaging an area includes providing light to a plurality of optical antennas separated by a first set of spacings within a first optical phased array (OPA), wherein the phase of the light provided to each optical antenna is controlled to form a transmission beam from the first OPA, the transmission beam being characterized by a first angular intensity distribution including a first lobe and a second lobe; steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the area and the second lobe of the first angular intensity distribution scans across a second portion of the area; and receiving light from a plurality of optical antennas separated by a second set of spacings within a second OPA, wherein at least one spacing within the second set of spacings is different from at least one spacing within the first set of spacings, and the phase of the light received from each optical antenna is controlled to receive light into the second OPA from various directions related to a second angular intensity distribution including a first lobe and a second lobe. The phase of the first OPA and the phase of the second OPA are configured such that the first lobe of the first angular intensity distribution and the first lobe of the second angular intensity distribution are substantially angularly overlapping during the scan of the first lobe across the first portion of the area, and the second lobe of the first angular intensity distribution and the second lobe of the second angular intensity distribution are substantially angularly overlapping during the scan of the second lobe across the second portion of the area.

[0005] In another aspect, generally, an apparatus for imaging a region includes a first optical phased array (OPA) having a plurality of optical antennas separated by a first set of spacings, and a plurality of phase shifters configured to impose a phase shift on light provided to respective optical antennas to form a transmission beam from the first optical phased array (OPA), the transmission beam being characterized by a first angular intensity distribution including a first lobe and a second lobe; a first optical phased array (OPA) including a phase shift control module configured to manage the imposed phase shift, the managing including steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across the entirety of a first portion of the region and the second lobe of the first angular intensity distribution scans across the entirety of a second portion of the region; and a second plurality of optical antennas separated by a second set of spacings and a plurality of phase shifters configured to impose a phase shift on light received from respective optical antennas, at least one spacing within the second set of spacings being different from at least one spacing within the first set of spacings, the phase shift of the light received from each optical antenna being controlled to receive light into the second OPA from various directions related to a second angular intensity distribution including a first lobe and a second lobe. The phase shift of the first OPA and the phase shift of the second OPA are configured such that the first lobe of the first angular intensity distribution and the first lobe of the second angular intensity distribution are substantially angularly overlapped during the scan of the first lobe across the first portion of the region, and such that the second lobe of the first angular intensity distribution and the second lobe of the second angular intensity distribution are substantially angularly overlapped during the scan of the second lobe across the second portion of the region.

[0006] Some aspects may include one or more of the following features.

[0007] The first lobe of the first angular intensity distribution has a peak intensity that is at least twice the intensity of each of the two side lobes adjacent to the first lobe of the first angular intensity distribution, and the second lobe of the first angular intensity distribution has (1) a peak intensity that is at least twice the peak intensity of each of the two side lobes adjacent to the second lobe of the first angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the first angular distribution by at least 10 degrees.

[0008] The first lobe of the second angular intensity distribution has a peak intensity that is at least twice the intensity of each of the two side lobes adjacent to the first lobe of the second angular intensity distribution, and the second lobe of the second angular intensity distribution has (1) a peak intensity that is at least twice the peak intensity of each of the two side lobes adjacent to the second lobe of the second angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the second angular distribution by at least 10 degrees.

[0009] The intervals within the first set of intervals and the intervals within the second set of intervals are each greater than 1 / 2 of any wavelength within the spectrum of light provided to the plurality of optical antennas within the first OPA.

[0010] All of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other.

[0011] In another aspect, generally, a method of imaging a region includes providing light to a plurality of optical antennas separated by a first set of spacings within a first optical phased array (OPA), wherein the phase of the light provided to each optical antenna is controlled to form a transmission beam from the first OPA, the transmission beam being characterized by a first angular intensity distribution including a first lobe and a second lobe; steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the region and the second lobe of the first angular intensity distribution scans across a second portion of the region; receiving light from a plurality of optical antennas separated by a second set of spacings within a second OPA, wherein at least one spacing within the second set of spacings is different from at least one spacing within the first set of spacings, and the phase of the light provided to each optical antenna is controlled to receive light into the OPA from various directions related to a second angular intensity distribution; and characterizing a potential detected event during the scan of the first lobe of the first angular intensity distribution across the first portion of the region, at least in part based on whether the detected event is detected during the scan of the second lobe of the first angular intensity distribution across the second portion of the region at a beam angle related to the potential detected event.

[0012] In another aspect, generally, an apparatus for imaging a region includes a first optical phased array (OPA) having a plurality of optical antennas separated by a first set of spacings, and a plurality of phase shifters configured to impose a phase shift on the light provided to each optical antenna to form a transmission beam from the first OPA, wherein the transmission beam is characterized by a first angular intensity distribution including a first lobe and a second lobe; a phase shift control module configured to manage the imposed phase shift, the managing including maneuvering the angle of the beam such that the first lobe of the first angular intensity distribution scans across the first portion of the region and the second lobe of the first angular intensity distribution scans across the second portion of the region; a second OPA having a plurality of optical antennas separated by a second set of spacings and a plurality of phase shifters configured to impose a phase shift on the light received from each optical antenna, wherein at least one spacing within the second set of spacings is different from at least one spacing within the first set of spacings and the phase shift of the light received from each optical antenna is controlled to receive light into the second OPA from various directions related to a second angular intensity distribution; and a control module configured to characterize a potential detection event at least in part based on whether the detection event is detected during the scanning of the second lobe of the first angular intensity distribution across the second portion of the region at the beam angle associated with the potential detection event during the scanning of the first lobe of the first angular intensity distribution across the first portion of the region.

[0013] Some aspects may include one or more of the following features.

[0014] Characterizing includes determining a first detection threshold associated with light received at a beam angle at which no corresponding detection event was detected during scanning of a second lobe of a first angular intensity distribution across an entire second portion of the region, and determining a second detection threshold associated with light received at a beam angle at which no corresponding detection event was detected during scanning of the second lobe of the first angular intensity distribution across the entire second portion of the region.

[0015] The intervals within the first set of intervals and the intervals within the second set of intervals are each greater than one half of any wavelength within the spectrum of light provided to the plurality of optical antennas within the first OPA.

[0016] All of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other.

[0017] Characterizing is further at least partially based on a spatial distance between the first OPA and the second OPA.

[0018] Characterizing is further at least partially based on a beam angle associated with an estimated location of a potential detection event.

[0019] The method further includes determining a first signal at least partially based on light received from a second portion of the region, determining a second signal at least partially based on light received from a first portion of the region, and subtracting at least a portion of the first signal from the second signal.

[0020] Some aspects may have one or more of the following advantages.

[0021] In a LiDAR system, light waves from a light source can be transmitted to a target object at a given distance by using an OPA, and the light backscattered from the target object can be collected by using another OPA. Various techniques such as modulation and / or time-of-flight can be used to determine the distance to the target object based on information related to the detection event. The light source used in such a system can be a laser or other coherent light source that provides light waves (also simply referred to as "light" herein) having a narrow linewidth and a peak wavelength falling within a specific range (e.g., between about 100 nm and about 1 mm or a sub-range thereof).

[0022] In some environments (e.g., automotive environments) where a LiDAR system or other optical systems using a transmitter OPA and a receiver OPA can be used, a return intensity map (e.g., representing the intensity of the collected return light) including spurious signal peaks related to the side lobes and / or grating lobes of the optical phased array (OPA) radiation pattern can be deteriorated by the prevalence of retroreflectors (e.g., road signs, road markers, bicycle safety reflectors, registration stickers, etc.) that can generate return signals orders of magnitude higher than those generated by diffusely scattering surfaces. Accordingly, the return signal related to the mixing of side lobes or grating lobes in distant retroreflectors can easily exceed the noise floor of the phased array LiDAR system, generating false detection events. Mitigation of this effect is useful for the commercialization of phased array LiDAR technology in automotive and other application spaces.

[0023] In some examples, the optical systems described herein can be used to explore and measure an environment or region over a wider range of angles than existing implementations. For example, a configuration in which the grating lobe of the transmitter aperture and the grating lobe of the receiver aperture are aligned while the main lobe of the transmitter aperture and the main lobe of the receiver aperture are misaligned can enable scanning over the entire angle outside the region accessible to the main lobe, as described in detail below.

[0024] Other features and advantages will become apparent from the following description, from the accompanying drawings, and from the claims.

[0025] This disclosure will be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that the various features of the accompanying drawings are not drawn to scale. On the contrary, the dimensions of the various features are arbitrarily enlarged or reduced for clarity.

Brief Description of the Drawings

[0026]

Figure 1A

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DETAILED DESCRIPTION OF THE INVENTION

[0027] An optical phased array (OPA) can form a steerable optical beam based on the phased array principle. For example, an array of optical antennas (sometimes called optical emitters) can each emit light with a controllable (e.g., controlled by a phase shifter coupled to the optical antenna) phase that results in an interference pattern forming one or more optical beams. Usually, each optical antenna can also receive light in addition to emitting light. A transmitting OPA can be characterized by an angular intensity distribution, also called a radiation intensity pattern, that describes the optical beam formed by the transmitting OPA. Thus, the optical beam formed by the transmitting OPA can include light emitted at one or more angles characterized by the angular intensity distribution. A receiver OPA can receive or collect light that can be used to characterize a scene or region surrounding the OPA. The receiver OPA can also be characterized by an angular intensity distribution (radiation intensity pattern), also called a gain pattern. The gain pattern characterizes the angular sensitivity of the receiver OPA to incident light. Both the transmitter angular intensity distribution and the receiver angular intensity distribution can have peaks, also called lobes or array factor peaks, that correspond to maxima where the respective OPA has higher transmission output or reception sensitivity. An optical platform that includes both a receiver OPA and a transmitter OPA can be characterized by a radiation intensity pattern product. In some examples, the radiation intensity pattern product can be determined by multiplying the transmitter radiation intensity pattern and the receiver radiation intensity pattern. In other examples, the radiation intensity pattern product can depend on other factors (e.g., antenna element factors).

[0028] Some of the examples described herein can include an OPA having a receiving aperture (i.e., a receiver OPA, a receiving section, or a receiving subsystem) and a transmitting aperture (i.e., a transmitting OPA, a transmitting section, or a transmitting system). Other examples can include separate structures where the transmitting aperture and the receiving aperture are not physically connected together or are fabricated as stand-alone devices. Further, the transmitting aperture and the receiving aperture can be the same.

[0029] In some exemplary implementations, the optical systems described herein can be designed to operate over a judged range of optical wavelengths (e.g., the λ = 1500 - 1600 nm band or the λ = 1270 - 1330 nm band), and the basic interval pitch between the optical antennas can be of a size similar to the optical wavelength. For example, for operation in the 1500 - 1600 nm band, 1000 nm ≦ a ≦ 2000 nm can be standard. All grating lobes will be removed if a < λ / 2, but the practical lower limit for the grating pitch can be set not only by the refractive index of the available waveguide material but also by the detrimental effects of waveguide - waveguide coupling when the pitch is reduced. For example, individually single - mode silicon waveguides designed for the 1500 - 1600 nm band will couple to each other with a characteristic coupling length of 50 μm - 200 μm if placed at a pitch of 750 nm to completely remove the grating lobes; thus, phase - dependent optical redispersion between the waveguides is inevitable and will thus impair the angular intensity distribution. Accordingly, in practical implementations, the presence of grating lobes within the transmit (TX) radiation pattern and the receive (RX) gain pattern can occur. However, the grating lobes of the TX OPA and the grating lobes of the RX OPA can be misaligned by applying uniform pitch misalignment (Δa), element factor engineering, pitch apodization, random pitch, or other methods.

[0030] FIG. 1A shows an exemplary optical interface 100 that includes a transmit OPA 102 and a receive OPA 104. The transmit OPA 102 includes an array of transmit optical antennas 106 having a separation determined by a first pitch a. The receive aperture includes an array of receive optical antennas 108 having a separation determined by a second pitch a + Δa. The transmit optical antennas 106 and the receive optical antennas 108 can be, for example, optical gratings or waveguide facets (referred to as an “end-fire array” configuration). The exemplary optical interface 100 further includes an array of transmit phase shifters 110 and an array of receive phase shifters 112 that can be, for example, thermal phase shifters, electro-optic phase shifters, or microelectromechanical phase shifters. In some examples, each of the transmit phase shifters 110 and each of the receive phase shifters 112 can be independently controlled. The transmit phase shifter 110 can modulate the direction and the radiation intensity pattern of a transmit beam emitted from the transmit OPA 102, and the receive phase shifter 112 can modulate the receiver radiation intensity pattern (i.e., the gain pattern of the receiver). The transmitter optical output splitter 114 directs the input optical wave 116 to each of the transmit phase shifters 110 optically coupled to the respective transmit optical antennas 106. In this example, the transmitter optical output splitter 114 is connected by waveguides in a binary tree arrangement. A similar or identical binary tree arrangement for accommodating the optical output combiner 118 combines the received light into the output optical wave 120, which can then be further processed, converted, or measured. Similar systems (not depicted) can also include multiple similar or identical transmit OPAs 102 or receive OPAs 104.

[0031] Figure 1B shows an example of a LiDAR system 130 in which an optical interface such as the optical interface 100 shown in Figure 1A using one or more OPAs can be used. The LiDAR system 130 includes a laser system 132, a transmitter module 134 configured to transmit the light provided by the laser system 132 (e.g., by using an OPA) to a target area, and a receiver module 136 configured to receive the light (e.g., by using an OPA) and coherently mix the received light with the light of a local oscillator (LO) 138 in a coherent detector 140 (which can be derived from the laser system 132). The control module 142 is configured to control various aspects of the transmitter module 134 and the receiver module 136 and to estimate the distance to a target associated with a detection event based at least in part on the characteristics of the scattered light received by the receiver module 136. The laser system 132 can provide a continuous wave (CW) optical signal having a narrow linewidth and low phase noise that is sufficient to provide a long enough temporal coherence length to perform coherent detection over the entire relevant time scale. In some implementations, the laser system 132 is a frequency-tunable laser system whose provided optical frequency can be swept to perform frequency modulated continuous wave (FMCW) LiDAR measurements. The specific transmit lobe collection angle 144 from the transmitter module 134 can correspond to the specific receive lobe collection angle 146 into the receiver module 136, as will be described in detail below.

[0032] Any of a wide variety of techniques can be used to steer the transmit or receive angle of a lobe of the radiation intensity pattern. Some OPAs have a linearly distributed optical antenna. Steering about a first axis perpendicular to the linear distribution can be provided, for example, by changing the relative phase shifts in phase shifters coupled to each of the optical antennas. Other techniques can be used to steer about a second axis orthogonal to the first axis (e.g., by changing the frequency of the laser system 132).

[0033] Figures 2A-2E illustrate exemplary hardware configurations and techniques for mitigation of grating lobe signals when the phase shifters are programmed to generate a linear phase front in the near-field (e.g., there is a common phase shift used for each phase shifter). Another exemplary operating configuration or mode involving a phase-apodized phase front is described herein. Referring to Figures 2A-2E, misalignment of the grating lobes can cause a difference between the main lobe and the grating lobe angles of each array factor. However, the direction of the main lobe can still be controlled, for example, by using phase shifters coupled to the optical antenna.

[0034] Figure 2A shows exemplary radiation intensity patterns of transmitter OPA202 and receiver OPA204. While the transmitter main lobe 206 and the receiver main lobe 208 overlap, the transmitter grating lobe 210 and the receiver grating lobe 212 do not overlap or have very little overlap. Such an arrangement of lobe overlaps can be due to tuning the phase shifters associated with the transmitter optical antenna and the receiving optical antenna. In this example, the return signal from an object located near one of the grating lobes is attenuated due to the reduced overlap.

[0035] Figures 2B, 2C, and 2E show an example quantitatively, where the TX OPA pitch and the RX OPA pitch differ by 4 nm such that the grating lobes are misaligned when the main lobes are aligned. Figure 2D shows an example quantitatively, where the TX OPA pitch and the RX OPA pitch are the same such that the grating lobes are aligned.

[0036] Figure 2B shows a plot of a predicted exemplary transmitter radiation intensity pattern 220 (solid line) and an exemplary receiver radiation intensity pattern 222 (dashed line) as a function of the angle with respect to the center of the overlapping main lobes located at 0°.

[0037] FIG. 2C shows a plot of a predicted exemplary transmitter radiation intensity pattern 230 (solid line) and an exemplary receiver radiation intensity pattern 232 (dashed line) as a function of the angle with respect to the midpoint between misaligned grating lobes located at 0°.

[0038] FIGS. 2B - C show the far - field TX array factor pattern and the RX array factor pattern in the main lobe and the grating lobes respectively, depicting the relative shift of the grating lobes when the main lobe is aligned.

[0039] FIG. 2D shows a plot of the predicted exemplary radiation intensity pattern product of the transmitter OPA and the receiver OPA as a function of the angle formed with respect to the alignment where the grating lobes of the transmitter OPA and the receiver OPA are aligned. The radiation intensity pattern product can be determined by multiplying the transmitter radiation intensity pattern by the receiver radiation intensity pattern. In some examples, other factors can contribute to the radiation intensity pattern product (e.g., antenna element factor and parallax). Since the pitch of the transmitter OPA and the pitch of the receiver OPA are the same, the grating lobes of the transmitter OPA and the receiver OPA are aligned, and the main lobes of the transmitter OPA and the receiver OPA are aligned. The aligned grating lobes give rise to a grating intensity peak 240 that can be of equal amplitude of radiation intensity with respect to the main intensity peak 242.

[0040] Figure 2E shows a plot of the predicted exemplary radiation intensity pattern product of the transmitter OPA and the receiver OPA according to the angle formed for an alignment in which the grating lobe of the transmitter OPA and the grating lobe of the receiver OPA are misaligned. Since the pitch of the transmitter OPA and the pitch of the receiver OPA differ by only 4 nm, the grating lobe of the transmitter OPA and the grating lobe of the receiver OPA are misaligned when the main lobe of the transmitter OPA and the main lobe of the receiver OPA are aligned. The misaligned grating lobes give rise to a grating intensity peak 250 that may have a substantially smaller amplitude of radiation intensity compared to the main intensity peak 252.

[0041] Figures 2D - E demonstrate a 24 dB reduction in the return signal from the grating lobe direction for the non - aligned case (Δa = 4 nm) compared to the aligned case. Generally, a larger |Δa| will result in a larger relative reduction of the return signal from the grating lobe.

[0042] Figures 3A - 3C depict an example of an alternative operating configuration that can be used in some optical system implementations. In this example, the antenna array phase shifter is programmed such that one or more grating lobes of the TX OPA overlap one or more grating lobes of the RX OPA, and the main lobe of the TX OPA is misaligned with the main lobe of the RX OPA. In this operating configuration, LiDAR can be overwhelmingly sensitive to return signals from objects within the angular range defined by the grating lobes. The direction of the grating lobes can be controlled, for example, by using an antenna phase shifter.

[0043] Figure 3A shows the exemplary radiation intensity patterns of the transmitter OPA 302 and the receiver OPA 304. While the transmitter main lobe 306 and the receiver main lobe 308 do not overlap, the transmitter grating lobe 310 and the receiver grating lobe 312 overlap. Thus, the return signal from any object located in the main lobe is attenuated relative to the return signal from any object located in the grating lobe.

[0044] Figure 3B shows a plot of a predicted exemplary transmitter radiation intensity pattern 320 (solid line) and an exemplary receiver radiation intensity pattern 322 (dashed line) as a function of the angle with respect to the midpoint between misaligned main lobes located at 0°.

[0045] Figure 3C shows a plot of a predicted exemplary transmitter radiation intensity pattern 330 (solid line) and an exemplary receiver radiation intensity pattern 332 (dashed line) as a function of the angle with respect to the center of the overlapping grating lobes located at 0°.

[0046] Figures 3B - 3C show the far - field TX array factor pattern and the RX array factor pattern in each of the main lobe and the grating lobe, depicting the relative shift of the main lobe when the grating lobe is aligned.

[0047] By expanding the operating range to a configuration where the grating lobes are aligned (e.g., FIGS. 3A - 3C), a plurality of practical capabilities are added to the optical system. First, this expansion effectively enlarges the "addressable field of view" of the system beyond the main lobe range having a half - value width of arcsin(λ / 2a). Here, λ is the wavelength of light, and a is the pitch of the OPA (i.e., the distance between the optical antennas). Such a configuration and technique enable the OPA - based LiDAR system to uniquely address the pointing directions at azimuth angles |θ|≧arcsin(λ / 2a). This effectively expands the azimuth - scanning range of the device. Here, during the process of scanning across the entire scene, first, the TX left grating lobe and the RX left grating lobe overlap while scanning the left grating lobe range, then the TX main lobe and the RX main lobe overlap while scanning the main range, and then the TX right grating lobe and the RX right grating lobe overlap while scanning the right grating range. Generally, the user can choose to scan any subset of the entire 180° hemisphere in front of the LiDAR unit. Second, the ability to uniquely address objects within the main lobe range and the grating lobe ranges enables techniques for retro - reflector grating lobe "image" (or "ghost image" or "spurious image") mitigation.

[0048] FIG. 4 shows an example of spurious image detection and mitigation. By using overlapping TX and RX lobes, over the course of scanning scene 400, if a return signal (a large return signal in some cases) is measured in a certain direction, the system radiation intensity pattern product and antenna element factor model can be used to predict the intensity and direction of spurious "ghost signals" that can occur when the partially non-overlapping TX and RX lobes coincide with an object that generates a reflection and a resulting return signal (which may still be relatively strong despite the reduction due to misaligned TX and RX lobes). For example, objects 402A (and 402B) can generate ghost signals 404A (and 404B). Next, the system can annotate that "the direction is affected by grating lobe ghosts" and then either ignore the data so as not to register only ghost signal 404A as a detected event or locally increase the detection threshold. Such techniques can, in some cases, mitigate the detrimental effects of retroreflectors on application domain performance. In other examples, the system can "subtract" the data corresponding to the ghost signals and obtain an image that is almost ghost-free.

[0049] Using selectively aligned and misaligned TX grating lobes and RX grating lobes can enable an object within the grating lobe range to be uniquely targeted. For example, the left TX grating lobe and the left RX grating lobe can be overlapped to scan the left grating lobe range 406, the TX main lobe and the RX main lobe can be overlapped to scan the main lobe range 408, and the TX right grating lobe and the RX right grating lobe can be overlapped to scan the right grating lobe range 410. Next, the direction in which a strong return signal is detected can be used to annotate the direction in which a spurious "ghost" image is expected. Next, data at points affected by the ghost can be deleted so that the ghost signal alone does not constitute a detection, or alternatively the detection threshold at those points can be increased. In this example, there are two grating lobes (on either side of the main lobe) corresponding to three respective ranges corresponding to different parts of the area being scanned. In other examples, any number of grating lobes can be present on one or both sides of the main lobe, reaching four or more respective ranges corresponding to different parts of the area being scanned.

[0050] FIG. 1, FIGS. 2A, 3A and 4 together show various aspects of a first exemplary method of imaging a region. The first exemplary method of imaging a region includes providing light (e.g., input light wave 116) to a plurality of optical antennas (e.g., transmit optical antennas 106) separated by a first set of spacings (e.g., pitch α if all spacings are equal) within a first optical phased array (e.g., transmit OPA 102), and the phase of the light provided to each optical antenna is controlled (e.g., by an array of transmit phase shifters 110) to form a transmit beam from the first OPA. The transmit beam is characterized by a first angular intensity distribution including a first lobe (e.g., transmitter main lobe 206, transmitter main lobe 306) and a second lobe (e.g., transmitter grating lobe 210, transmitter grating lobe 310). The first exemplary method of imaging a region further includes steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the region (e.g., main lobe range 408) and the second lobe of the first angular intensity distribution scans across a second portion of the region (e.g., left grating lobe range 406, right grating lobe range 410). The first exemplary method of imaging a region further includes receiving light from a plurality of optical antennas (e.g., receive optical antennas 108) separated by a second set of spacings (e.g., pitch α+Δα) within a second OPA (e.g., receive OPA 104), at least one spacing within the second set of spacings being different from at least one spacing within the first set of spacings, and the phase of the light provided to each optical antenna is controlled (e.g., by an array of receive phase shifters 112) to receive light from various directions related to a second angular intensity distribution including a first lobe (e.g., receiver main lobe 208, receiver main lobe 308) and a second lobe (e.g., receiver grating lobe 212, receiver grating lobe 312) into the OPA.The phase of the first OPA and the phase of the second OPA are configured such that the first lobe of the first angular intensity distribution and the first lobe of the second angular intensity distribution are substantially angularly overlapped during the scanning of the first lobe across the entire first portion of the region (e.g., as shown in FIG. 2A), and such that the second lobe of the first angular intensity distribution and the second lobe of the second angular intensity distribution are substantially angularly overlapped during the scanning of the second lobe across the entire second portion of the region (e.g., as shown in FIG. 3A).

[0051] Figures 1, 2A, 3A, and 4 together show various aspects of a second exemplary method of imaging a region. The second exemplary method of imaging a region includes providing light (e.g., input light wave 116) to a plurality of optical antennas (e.g., transmit optical antennas 106) separated by a first set of intervals (e.g., pitch α) within a first optical phased array (e.g., transmit OPA 102), and the phase of the light provided to each optical antenna is controlled (e.g., by an array of transmit phase shifters 110) to form a transmit beam from the first OPA. The transmit beam is characterized by a first angular intensity distribution that includes a first lobe (e.g., transmitter main lobe 206, transmitter main lobe 306) and a second lobe (e.g., transmitter grating lobe 210, transmitter grating lobe 310). The second exemplary method of imaging a region further includes steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the region (e.g., main lobe range 408) and the second lobe of the first angular intensity distribution scans across a second portion of the region (e.g., left grating lobe range 406, right grating lobe range 410). The second exemplary method of imaging a region further includes receiving light from a plurality of optical antennas (e.g., receive optical antennas 108) separated by a second set of intervals (e.g., pitch α + Δα) within a second OPA (e.g., receive OPA 104), at least one interval within the second set of intervals being different from at least one interval within the first set of intervals, and the phase of the light provided to each optical antenna being controlled (e.g., by an array of receive phase shifters 112) to receive light from various directions related to a second angular intensity distribution into the OPA. The second exemplary method of imaging a region further includes characterizing a potential detected event (e.g., ghost signal 404A) during the scan of the first lobe of the first angular intensity distribution across the first portion of the region, at least in part based on whether a detected event (e.g., object 402A) is detected during the scan of the second lobe of the first angular intensity distribution across the second portion of the region at a beam angle related to the potential detected event.

[0052] In the examples depicted in FIGS. 2A-E and 3A-C, the phase shifters for each TX antenna and RX antenna are set to generate a substantially flat phase plane within the near field of the TX aperture and RX aperture. In other examples, the phase shifters may be configured to generate other non-flat phase planes within the near field.

[0053] FIG. 5A shows a schematic diagram of an exemplary transmitter optical phased array (TX OPA) 500 configured to generate a substantially flat transmitter phase plane corresponding to the distribution of phase 502A in the near field of the beam transmitted from transmitter aperture 506, and an exemplary receiver optical phased array (RX OPA) 501 configured to receive a substantially flat receiver phase plane corresponding to the distribution of phase 504A in the near field of the light received at receiver aperture 508. The arrows shown in relation to the near field phase plane of the transmitted beam represent the relative phase shifts applied by the phase shifters to the optical fields emitted from the optical antennas of TX OPA 500. The arrows shown in relation to the near field phase plane of the received beam represent the relative phase shifts applied by the phase shifters to the optical fields received at the optical antennas of RX OPA 501. In this example, as the optical field begins to transition from the near field to the far field of each OPA, three lobes (corresponding to the main lobe and the grating lobes on both sides of the main lobe) begin to appear.

[0054] FIG. 5B shows a plot of a predicted exemplary transmitter radiation intensity pattern 510A (dashed line) and a predicted exemplary receiver radiation intensity pattern 512A (solid line) of the transmitter optical phased array as a function of the angle to the midpoint between the peaks of the grating lobes. Referring to FIG. 5A, if the optical output is distributed substantially uniformly across all the antennas within transmitter aperture 506 and collected uniformly from the antennas within receiver aperture 508 (e.g., by using a binary splitter tree), transmitter optical phased array 500 and receiver optical phased array 501 may generate the sinc 2 radiation intensity pattern shown in FIG. 5B. Referring to FIG. 5B, the sinc 2A possibly gradual decrease in the profile may limit the relative attenuation of ghost images located on the misaligned TX grating lobe and RX grating lobe with respect to the main lobe. This drawback may apply to divider networks other than the binary tree that produce a gradual decrease in the far field due to, for example, a near field amplitude profile.

[0055] Figures 5C-D show additional operating modes that can be used in some implementations to further reduce the effects of ghost images.

[0056] Figure 5C shows a schematic diagram of an example where a phase shifter is configured to generate a spatially varying transmitter phase 502C and a spatially varying receiver phase 504C in the near field of transmitter aperture 506 and receiver aperture 508. The spatially varying phase shift applied by the phase shifter results in a near field profile with a smooth and gradual decrease towards the edge of the aperture.

[0057] Figure 5D shows a plot of a predicted exemplary transmitter radiation intensity pattern 510C (dashed line) of a transmitter optical phased array and a predicted exemplary receiver radiation intensity pattern 512C (solid line) of a receiver optical phased array as a function of the angle relative to the midpoint between the peaks of the grating lobes. The far field beam profile corresponds to the configuration shown in Figure 5C and exhibits a sharper roll-off away from the array factor peak. In some examples, the near field phase is designed such that the relative attenuation of the ghost signal with respect to the main signal can be further reduced compared to the sinc 2 decrease case shown in Figure 5B. In some examples, the near field phase misalignment may reduce the peak intensity of the main lobe, imposing a small link penalty on the overall return signal of the system. A representative value of this penalty is 0 - 10 dB. However, for some phase surface configurations, the relative attenuation of the ghost signal can exceed the induced link penalty significantly (more than 10 dB in some cases).

[0058] Generally, the various phase apodization techniques described herein can be used to improve peak roll-off and reduce ghosts (e.g., the contribution of ghost signals to the received signal, which is the result of reflections from objects outside the region scanned by the intended lobe). Further, the various phase apodization techniques can be implemented in various embodiments. Two possible embodiments (exemplary algorithms for determining the appropriate phase for each antenna) are described as follows.

[0059] FIG. 6A is a plot of an exemplary absolute value of the predicted effective amplitude of apodization versus antenna number, where the antenna number corresponds to the relative position of each antenna within the optical phased array.

[0060] FIG. 6B is a plot of an exemplary phase of apodization versus antenna number, where the antenna number corresponds to the relative position of each antenna within the optical phased array.

[0061] FIGS. 6A - B show an example of apodization by applying random phases to each antenna in the transmitter OPA (TX) and receiver OPA (RX), where each phase is selected from a suitable probability distribution (e.g., a Gaussian probability distribution) having a standard deviation of variation across the width of each aperture by using a suitable function for generating random values (e.g., by using a spurious random number generation function). The procedure for this example is as follows. First, the desired "effective amplitude apodization" profile shown in FIG. 6A is selected with respect to the TX aperture and the RX aperture. The design of this apodization profile can be similar to the design of a finite impulse response low-pass filter insofar as the result (i.e., the far-field profile) can be the Fourier transform of a finite list of values. In some embodiments, a finite impulse response design procedure can be used for this step. Second, for each antenna, the phase is randomly selected from a Gaussian distribution having zero mean and standard deviation σ = sqrt[-2ln(A)], where A is the value of the effective amplitude apodization profile at that antenna and ln is the natural logarithm.

[0062] Figure 6B shows a plot of a predictive example of such an antenna phase profile. The antenna phase configuration shown in Figure 6B generates a far-field profile whose sidelobe intensity is approximately equal to the intensity that would occur if the transmit amplitude of the antenna were apodized by the design amplitude profile shown in Figure 6A (as opposed to the transmit phase shown in Figure 6B). The far-field profile shown in Figure 5D was generated by using this methodology (e.g., the antenna phase configuration shown in Figure 6B).

[0063] Another exemplary methodology for determining the antenna phase configuration involves solving an optimization problem by incorporating a calibration model for each individual OPA LiDAR system, and the optimization performance index can be the minimization of ghost intensity (i.e., the minimization of the TX / RX radiation intensity pattern product within the non-coincidence region) constrained by the radiation intensity pattern product peak or the attenuation of the acceptable amount of the main lobe. A particularly desirable solution to this optimization problem can result in deep (>10 dB) dips in the RX pattern noise floor that coincide with the TX peak within the non-coincidence region and deep (>10 dB) dips in the TX pattern noise floor that coincide with the RX peak within the non-coincidence region, thus resulting in a TX / RX radiation intensity pattern product with highly attenuated ghosts.

[0064] The phase apodization described in Figures 6A - B can result in additional advantages. For example, such phase apodization can lead to the sharpening of the main peak of the TX / RX radiation intensity pattern product as shown in Figure 7.

[0065] Figure 7 shows a plot of an exemplary radiated intensity pattern product with apodization for the transmitter OPA and receiver OPA as a function of the angle with respect to the peak of the intensity pattern product. Comparing with the unapodized linear phase front case that can have about 10 side lobes on both sides where the central lobe at 0° rises above the noise floor, phase apodization reduces this number to 2 side lobes on both sides of the 2048 element TX and RX array in this example. The reduced number of side lobes, in turn, reduces the azimuthal width of the spurious signals associated with the coincidence of these side lobes onto strong reflectors. A practical manifestation of this effect is that the "apparent width" of retroreflectors (which can be many times wider than their physical width in the unrelaxed case) can be significantly reduced. In Figure 7, the distance between side lobes is represented in terms of the angular offset with respect to the center of the angle on the horizontal axis, and the relative width is compared in terms of arbitrary units (labeled as the diameter of a basketball at a distance of 200m).

[0066] Due to the link penalty associated with phase apodization, the practical application of relaxation techniques can involve switching between a non-phase-apodized (e.g., a linear phase profile based on common phase shifts without using a probability distribution or pseudorandom function or other deterministic phase profile (such as a lensed linear / parabolic phase profile)) near-field phase profile and a phase-apodized near-field phase profile depending on the situation. For example, the OPA LiDAR being described currently can be operated in a linear / lensed linear mode during the initial scan of a scene. In regions of the scene where a retroreflector (e.g., recognized by a strong return signal compared to a predetermined threshold) or a ghost (annotated at a known angle relative to the left and right of the strong return signal) is suspected, the system can reconfigure the phase shifter to generate a phase-apodized near-field phase surface and rescan the affected region, obtaining the advantage of reduced side lobe overlap in the former (near the retroreflector) case and the advantage of reduced offset peak overlap in the latter (in the ghost) case, increasing the sensitivity to weaker return signals that might otherwise be masked by spurious return signals. Since the proportion of the scene affected by retroreflectors is expected to be very low (e.g., <5%), a similarly low amount of time overhead is expected in the rescan process.

[0067] FIG. 1 and FIG. 6B together show various aspects of an exemplary apparatus. The exemplary apparatus includes an optical phased array (e.g., a transmission OPA 102) including a plurality of optical antennas (e.g., transmission optical antennas 106) separated by a set of intervals (e.g., pitch α), and a plurality of phase shifters (e.g., transmission phase shifters 110) configured to impose a phase shift on the light provided to each of the plurality of optical antennas. A phase shift control module is configured to manage the imposed phase shift, and managing includes a first mode of operation. The phase shift control module may provide an analog electrical signal to the plurality of phase shifters. For example, a computer processing unit (CPU) is disposed in the vicinity of and electrically connected to the plurality of phase shifters. A digital-to-analog converter (DAC) may be used to convert a digital signal from the exemplary phase shift control module into an analog signal that is then transmitted to the plurality of phase shifters. In other examples, an application-specific integrated circuit (ASIC) may be used as the phase control module. The first mode of operation includes determining a variation in the imposed phase shift that is less than the phase shift variation width for a first subset of optical antennas within a certain distance from the center of the plurality of optical antennas (e.g., the antennas having antenna numbers 800 to 1200 in FIG. 6B), and determining a variation in the imposed phase shift that is greater than the phase shift variation range for a second subset of optical antennas (e.g., the antennas having antenna numbers less than 800 and greater than 1200 in FIG. 6B) that are further from the center of the plurality of optical antennas than the said distance.

[0068] In some implementations, the OPA LiDAR may use multiple receiver OPAs to capture light from one or more transmitter OPAs (e.g., multiple transmitters in a multistatic configuration). In this case, additional measures may be taken to identify or suppress retroreflection. For example, a subset of the receive apertures may be configured to overlap with the main lobe of the transmitter beam while the remainder of the receiver apertures are configured to overlap with the grating lobes. In this case, the receiver apertures configured to overlap within the grating lobes may be monitored for strong return signals and used to reject ghost return signals that appear within the receiver apertures configured to overlap with the main lobe of the TX beam.

[0069] Multistatic LiDAR may also include information used to identify and reject retroreflection, and some or all of the receiver apertures are configured to overlap with the main lobe of the transmitter. Prior to reaching the far field, the offset between the transmitter and the receiver may cause losses at the receiver due to the parallax between the transmitter and the receiver. This loss may be based on the geometry and can be calculated assuming that the target object is also located in the main lobe of the transmitter or in the grating lobe of the transmitter as shown in FIG. 8.

[0070] FIG. 8 shows exemplary predicted parallax as a function of the angle of the target (assumed to be at a distance of 10 m) with respect to the transmitter OPA for various optical system configurations. The difference between the expected parallax and the measurement within the main lobe can be used to mark and reject high-intensity retroreflectors that couple into the grating lobes.

[0071] FIG. 9 shows a plot of exemplary predicted radiation intensity patterns of a transmitter OPA and two receiver OPAs as a function of the angle relative to the lobe reference angle. For a multistatic LiDAR configuration (such as that shown in FIG. 9), each RX aperture may use a different pitch than the TX aperture and also than the other RX apertures. In this case, different grating lobe couplings are expected for each receiver aperture. Return signals having an intensity drop due to an expected mismatch in the grating lobe coupling can be marked as retroreflectors and ignored. In this example, the Rx2 receiver beam grating lobe has a lower predicted overlap with the transmit beam grating lobe than the Rx1 receiver beam grating lobe.

[0072] Another spurious signal that can affect LiDAR systems such as FMCW (Frequency Modulated Continuous Wave) LiDAR is the frequency domain spread of strong reflectors into adjacent frequency bins (as shown in FIG. 10). The data generated by a single FMCW LiDAR acquisition at a single azimuth angle consists of finite-time complex signals. The frequency components of this signal directly reflect the intensity of the light received from various distances from the system, and the frequency bins are approximately proportional to the reflector distance. A strong reflector generates a strong sine wave within the frequency components. The strong sine wave generates a peak with a wide frequency spread after a finite-time Fourier transform, potentially masking the weak signals below the frequency domain shoulders of the peak. One way to remove the peak and its frequency spread is, for example, to infer the phase and amplitude of the original sine wave from the Fourier domain information, subtract the sine wave from the time domain data, and re-evaluate the Fourier transform to reveal the weak signals that were previously ambiguous. However, other algorithms may work equally well.

[0073] FIG. 10 shows a flowchart of an exemplary spurious image detection and mitigation scheme 1000 within an exemplary FMCW LiDAR system. The retroreflector signal 1002, the target signal 1004, and the noise signal 1006 are summed at summer 1008. A Fourier transform 1010 is performed on the output of summer 1008. The Fourier transform signal 1012 indicates that the detection of the target signal 1004 is masked by the retroreflector signal 1002. The mitigation algorithm 1014 attempts to transform the contribution of the retroreflector signal into the Fourier transform signal 1012. One exemplary mitigation algorithm 1014 finds peaks within the zero-padded Fourier transform signal 1012, synthesizes a sine wave and a complex amplitude in alignment, and subtracts the synthesized sine wave from the original output of summer 1008. Finally, the Fourier transform 1010 is re-evaluated, resulting in a retroreflector mitigation signal 1016 that includes the previously ambiguous target signal peak 1018.

[0074] In some aspects, generally, the mitigation techniques described herein include optical phased array systems where the TX optical phased array and the RX optical phased array have non-matching grating lobes. This enables not only linear or lens-shaped linear operating modes characterized by a maximum link budget but also reduction of ghosts (i.e., spurious return signals) associated with multiple grating orders emitted by the TX and RX antenna arrays. This also enables a phase-apodized mode characterized by not only further reduced grating lobe ghosts but also reduced side lobe ghosts (reduced spurious lateral spread of strong reflectors) in exchange for a small link penalty. These techniques may be involved in the use of these modes separately or in tandem, where the scene is first scanned by using the previous operating mode and then regions of the scene suspected of containing spurious signals are re-scanned by using the latter operating mode.

[0075] Although the present disclosure has been described in connection with several embodiments, it should be understood that the present disclosure is not intended to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. The claims should be given the broadest interpretation so as to encompass all such modifications and equivalent configurations as permitted under the law.

Claims

Claim 1 A method of imaging a region, comprising: providing light to a plurality of optical antennas separated by a first set of spacings within a first optical phased array (OPA), wherein the phase of the light provided to each optical antenna is controlled to form a transmission beam from the first OPA, the beam being characterized by a first angular intensity distribution including a first lobe and a second lobe; steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the region and the second lobe of the first angular intensity distribution scans across a second portion of the region; receiving light from a plurality of optical antennas separated by a second set of spacings within a second OPA, wherein at least one spacing within the second set of spacings is different from at least one spacing within the first set of spacings, and the phase of the light received from each optical antenna is controlled to receive light into the second OPA from various directions related to a second angular intensity distribution including a first lobe and a second lobe; comprising: wherein the phase of the first OPA and the phase of the second OPA are configured such that the first lobe of the first angular intensity distribution and the first lobe of the second angular intensity distribution have angles that substantially overlap during the scanning of the first lobe across the first portion of the region, and the second lobe of the first angular intensity distribution and the second lobe of the second angular intensity distribution have angles that substantially overlap during the scanning of the second lobe across the second portion of the region. A method. Claim 2 The first lobe of the first angular intensity distribution has a peak intensity that is at least twice as large as the intensity of each of two side lobes adjacent to the first lobe of the first angular intensity distribution, The second lobe of the first angular intensity distribution has (1) a peak intensity that is at least twice as large as the peak intensity of each of two side lobes adjacent to the second lobe of the first angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the first angular distribution by at least 10 degrees. The method of Claim 1. Claim 3 The first lobe of the second angular intensity distribution has a peak intensity that is at least twice the intensity of each of the two side lobes adjacent to the first lobe of the second angular intensity distribution. The second lobe of the second angular intensity distribution has: (1) a peak intensity that is at least twice the peak intensity of each of the two side lobes adjacent to the second lobe of the second angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the second angular distribution by at least 10 degrees. The method of claim 2. **Claim 4** The interval within the first set of intervals and the interval within the second set of intervals are each greater than 1 / 2 of any wavelength within the spectrum of the light provided to the plurality of optical antennas within the first OPA. The method of claim 1. **Claim 5** All of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other. The method of claim 1. **Claim 6** An apparatus for imaging a region, comprising: a first optical phased array (OPA); a phase shift control module; a second OPA; and wherein the first OPA comprises: a plurality of optical antennas separated by a first set of intervals; a plurality of phase shifters configured to impose a phase shift on the light provided to each respective optical antenna to form a transmission beam from the first OPA, the beam being characterized by a first angular intensity distribution including a first lobe and a second lobe; and the phase shift control module is configured to manage the imposed phase shift, wherein managing includes maneuvering the angle of the beam such that the first lobe of the first angular intensity distribution scans across the entirety of a first portion of the region and the second lobe of the first angular intensity distribution scans across the entirety of a second portion of the region; wherein the second OPA comprises: a plurality of optical antennas separated by a second set of intervals; A plurality of phase shifters configured to impose a phase shift on the light received from each optical antenna, wherein at least one interval within the second set of intervals is different from at least one interval within the first set of intervals, and the phase shift of the light received from each optical antenna is controlled to receive light into the second OPA from various directions related to a second angular intensity distribution including a first lobe and a second lobe. A plurality of phase shifters including the phase shift of the first OPA and the phase shift of the second OPA are such that the first lobe of the first angular intensity distribution and the first lobe of the second angular intensity distribution have angles that substantially overlap during the scanning of the first lobe across the first portion of the region, and the second lobe of the first angular intensity distribution and the second lobe of the second angular intensity distribution have angles that substantially overlap during the scanning of the second lobe across the second portion of the region. configured device. **Claim 7** The first lobe of the first angular intensity distribution has a peak intensity that is at least twice the intensity of each of two side lobes adjacent to the first lobe of the first angular intensity distribution. The second lobe of the first angular intensity distribution has (1) a peak intensity that is at least twice the peak intensity of each of two side lobes adjacent to the second lobe of the first angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the first angular distribution by at least 10 degrees. The device of claim 6. **Claim 8** The first lobe of the second angular intensity distribution has a peak intensity that is at least twice the intensity of each of two side lobes adjacent to the first lobe of the second angular intensity distribution. The second lobe of the second angular intensity distribution has (1) a peak intensity that is at least twice the peak intensity of each of two side lobes adjacent to the second lobe of the second angular intensity distribution, and (2) a peak intensity that is separated from the peak intensity of the first lobe of the second angular distribution by at least 10 degrees. The device of claim 7. **Claim 9** The apparatus according to claim 6, wherein the interval within the first set of intervals and the interval within the second set of intervals are each greater than one half of any wavelength within the spectrum of the light provided to the plurality of optical antennas within the first OPA.

10. The apparatus according to claim 6, wherein all of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other.

11. A method of imaging a region, comprising: providing light to a plurality of optical antennas separated by a first set of intervals within a first optical phased array (OPA), wherein the phase of the light provided to each optical antenna is controlled to form a transmission beam from the first OPA, and the transmission beam is characterized by a first angular intensity distribution including a first lobe and a second lobe; steering the angle of the beam such that the first lobe of the first angular intensity distribution scans across a first portion of the region and the second lobe of the first angular intensity distribution scans across a second portion of the region; receiving light from a plurality of optical antennas separated by a second set of intervals within a second OPA, wherein at least one interval within the second set of intervals is different from at least one interval within the first set of intervals, and the phase of the light provided to each optical antenna is controlled to receive light into the OPA from various directions related to a second angular intensity distribution; characterizing a potential detected event during the scan of the first lobe of the first angular intensity distribution across the first portion of the region, the characterization being at least partially based on whether the detected event is detected during the scan of the second lobe of the first angular intensity distribution across the second portion of the region at a beam angle related to the potential detected event; and a method including the above.

12. The characterizing includes: determining a first detection threshold related to light received at a beam angle at which no corresponding detected event is detected during the scan of the second lobe of the first angular intensity distribution across the second portion of the region; determining a second detection threshold related to light received at a beam angle at which at least one corresponding detected event is not detected during the scan of the second lobe of the first angular intensity distribution across the second portion of the region. The method of claim 11, comprising

13. The method of claim 11, wherein the interval within the first set of intervals and the interval within the second set of intervals are each greater than one half of any wavelength within the spectrum of the light provided to the plurality of optical antennas within the first OPA.

14. The method of claim 11, wherein all of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other.

15. The method of claim 11, wherein the characterizing is further at least partially based on a spatial distance between the first OPA and the second OPA.

16. The method of claim 15, wherein the characterizing is further at least partially based on a beam angle associated with a presumed location of the potential detection event.

17. Determining a first signal based at least in part on light received from a second portion of the region, Determining a second signal based at least in part on light received from a first portion of the region, Subtracting at least a portion of the first signal from the second signal The method of claim 11, further comprising

18. An apparatus for imaging a region, comprising A first optical phased array (OPA), A phase shift control module, A second OPA, A control module Including The first OPA includes A plurality of optical antennas separated by a first set of intervals, A plurality of phase shifters configured to impose a phase shift on the light provided to each optical antenna to form a transmission beam from the first OPA, the beam being characterized by a first angular intensity distribution including a first lobe and a second lobe, a plurality of phase shifters Including The phase shift control module is configured to manage the imposed phase shift, The managing includes maneuvering the angle of the beam such that the first lobe of the first angular intensity distribution scans across an entire first portion of the region and the second lobe of the first angular intensity distribution scans across an entire second portion of the region, The second OPA includes A plurality of optical antennas separated by a second set of intervals, A plurality of phase shifters configured to impose a phase shift on the light received from each optical antenna, wherein at least one interval within the second set of intervals is different from at least one interval within the first set of intervals, and the phase shift of the light received from each optical antenna is controlled to receive light into the second OPA from various directions related to a second angular intensity distribution. A plurality of phase shifters including The control module is configured to characterize a potential detection event during the scanning of the first lobe of the first angular intensity distribution across the first portion of the region, based at least in part on whether the detection event is detected during the scanning of the second lobe of the first angular intensity distribution across the second portion of the region at the beam angle associated with the potential detection event. An apparatus

19. Said characterizing comprises determining a first detection threshold associated with light received at a beam angle at which no corresponding detection event was detected during the scanning of the second lobe of the first angular intensity distribution across the second portion of the region; determining a second detection threshold associated with light received at a beam angle at which no at least one corresponding detection event was detected during the scanning of the second lobe of the first angular intensity distribution across the second portion of the region The apparatus of claim 18, comprising

20. The apparatus of claim 18, wherein the intervals within the first set of intervals and the intervals within the second set of intervals are each greater than one half of any wavelength within the spectrum of the light provided to the plurality of optical antennas within the first OPA.

21. The apparatus of claim 18, wherein all of the intervals within the first set of intervals are identical to each other, and all of the intervals within the second set of intervals are identical to each other.

Images