MULTISTATIC COHERENT LIDAR

Abstract

Device that includes: at least one transmitter comprising a transmitting aperture (202A, 400A, 400B, 611) configured to provide at least one beam of a transmitted optical wave (714, 718) along a transmission angle to a destination (204), wherein the optical wave (714, 718) comprises at least one first section of the optical wave (714, 718); and two or more receivers (2402), wherein at least one receiver (2402) comprises: a receiving aperture (100, 202B, 612, 613) located near at least one of the transmitting apertures (202A, 400A, 400B, 611) or a receiving aperture (100, 202B, 612, 613) of a different receiver, an optical phased array within the receiving aperture (100, 202B, 612, 613), wherein the optical phased array is configured to receive at least one section of a collected optical wave (714, 718) arriving at the receiving aperture (100, 202B, 612, 613) along a respective collecting angle, characterized by the fact that the optical wave (714, 718) comprises a second section which has a different feature from a feature of the first section of the optical wave (714, 718) and, that the device further includes: a filter configured to filter the received section of the collected optical wave (714, 718) according to the characteristic of the first section of the optical wave (714, 718), and a detector (704) configured to provide a signal (2604) based on the filtered section of the collected optical wave (714, 718).

Description

TECHNICAL AREA

[0001] This disclosure concerns a multistatic coherent LiDAR. STATE OF THE ART

[0002] Some LiDAR systems use a single aperture to transmit and receive light (referred to here as a "monostatic" aperture configuration). Alternatively, some LiDAR systems use two apertures in close proximity—one for transmitting and one for receiving (referred to here as a "bistactic" aperture configuration). Different systems optimize various aspects of the LiDAR configuration based on different criteria. An optical wave is transmitted from an optical source to target object(s) at a given distance, and photons backscattered by the target object(s) are collected.The optical source used in a continuous wave (CW) LiDAR system is typically a laser that provides an optical wave with a narrow linewidth and a peak wavelength falling within a specific range (for example, between about 100 nm and about 1 mm, or a subrange thereof), referred to here simply as "light." Some LiDAR systems may be designed to use either a monostatic or bistatic aperture configuration, depending on a variety of trade-offs made regarding system performance and / or system design.

[0003] US 2018 / 0348592 A1 discloses systems, methods and structures for speckle reduction in photonic phased-array structures. SUMMARY

[0004] The invention relates to a device according to independent claim 1, a method according to independent claim 34, and a LiDAR system according to independent claim 35. Some of the preferred embodiments are described in the dependent claims, the description, and the figures.

[0005] In one aspect, a device generally includes: at least one transmitter comprising a transmitting aperture configured to provide at least one beam of a transmitted optical wave along a transmission angle to a destination, the optical wave comprising at least a first section of the optical wave and a second section of the optical wave having a feature different from a feature of the first section of the optical wave;and two or more receivers, wherein at least one receiver comprises: a receiving aperture located near at least one of the transmitting apertures or a receiving aperture of a different receiver, an optical phased array within the receiving aperture, wherein the optical phased array is configured to receive at least one section of a collected optical wave arriving at the receiving aperture along a respective collecting angle, a filter configured to filter the received section of the collected optical wave according to the characteristic of the first section of the optical wave, and a detector configured to provide a signal based on the filtered section of the collected optical wave.

[0006] In another aspect, a method generally involves: providing at least one beam of a transmitted optical wave along a transmission angle to a destination from a transmitting aperture of a transmitter, wherein the optical wave comprises at least a first section of the optical wave and a second section of the optical wave having a feature different from a feature of the first section of the optical wave;and receiving a collected optical wave at receiving apertures of two or more receivers, wherein at least one receiver comprises: a receiving aperture located near at least one of the transmitting aperture or a receiving aperture of a different receiver, an optical phased array within the receiving aperture, wherein the optical phased array is configured to receive at least one section of a collected optical wave arriving at the receiving aperture along a respective collecting angle, a filter configured to filter the received section of the collected optical wave according to the characteristic of the first section of the optical wave, and a detector configured to provide a signal based on the filtered section of the collected optical wave.

[0007] Aspects may include one or more of the following characteristics.

[0008] Each detector includes a coherent detector configured to combine the received portion of the collected optical wave with an optical local oscillator wave to provide a combined optical wave, and to capture the combined optical wave to provide the signal.

[0009] There is a frequency shift between the local oscillator and the transmitted optical wave to enable heterodyne detection in coherent detectors.

[0010] Each signal comprises an amplitude and a phase angle, and the respective component corresponding to that signal comprises a quantity based on the amplitude and independent of the phase angle.

[0011] The circuits are configured to convert each signal into digital form and to process the signals in digital form in order to eliminate dependence on phase angles.

[0012] At least one coherent detector is configured to use a first optical local oscillator wave to provide a combined optical in-phase wave and to use a second optical local oscillator wave, shifted relative to the first local oscillator wave, to provide a combined optical quadrature wave and to provide the amplitude and phase angle in an in-phase / quadrature (I / Q) space.

[0013] The circuits are configured to perform a transformation on a real-valued signal provided by one of the detectors to provide the amplitude and phase angle in a complex space of a resulting complex transform of the real-valued signal.

[0014] Each detector is configured to generate a current that represents a difference between photocurrents generated by a pair of balanced photodetectors.

[0015] The total number of receiving apertures is between 3 and 20.

[0016] The total number of receiving apertures is between 4 and 10.

[0017] The total number of transmitting apertures is 1.

[0018] The area of ​​each receiving aperture is equal to the area of ​​the transmitting aperture within a factor of between 4 / 9 and 9 / 4.

[0019] The receiving apertures are arranged along an axis in a plane in which the optical phased arrays are configured to provide steering of the respective collecting angles using phases of elements of the optical phased arrays.

[0020] Each of the receiver's optical phase-controlled arrays is configured to align its respective collecting angle with the target location.

[0021] The transmitter includes an optical phased array within the transmitting aperture.

[0022] The area of ​​each optical phased array within the receive apertures is equal to the area of ​​the optical phased array with the transmit aperture within a factor between 4 / 9 and 9 / 4.

[0023] At least one optical phased array within the transmit aperture or at least one of the receive apertures is configured to steer a first angle using phases of elements of the optical phased array and to steer a second angle using wavelength.

[0024] The receiver is a first receiver, the receiving aperture is a first receiving aperture, the optical phased array is a first optical phased array, the filter is a first filter, the detector is a first detector, and the two or more receivers include a second receiver comprising: the transmitting aperture configured as a second receiving aperture, a second optical phased array within the transmitting aperture, the second optical phased array being configured to receive at least one section of a collected optical wave arriving at the transmitting aperture along a respective collecting angle, and a second filter configured to filter the received section of the collected optical wave according to a feature different from the feature of the first section of the optical wave and different from the feature of the second section of the optical wave.to filter, and a second detector configured to provide a signal based on the filtered portion of the collected optical wave that has been filtered by the second filter.

[0025] The device further includes circuits configured to determine an estimated distance associated with the collected optical wave, at least in part based on a combination that includes a respective component corresponding to each of the two or more signals provided by the detectors of the two or more receivers.

[0026] The transmitter applies linear frequency modulation to the transmitted optical wave to enable the circuits to determine the estimated distance.

[0027] The transmitting aperture is further configured as a receiving aperture in which an optical phased array is used to receive at least one section of an optical wave having a different feature from a feature of the transmitted optical wave, and at least one of the receiving apertures is used as a transmitting aperture to provide a beam of an optical wave having the different feature.

[0028] The features include at least one: a special wavelength, a special time slot, or a special polarization.

[0029] The features include a specific wavelength.

[0030] One or more optical sources provide a variety of spectral components that can be tuned over different respective spectral bands, and the first section of the optical wave includes a first spectral component, and the second section of the optical wave includes a second spectral component that is different from the first spectral component.

[0031] The device also includes one or more optical sources.

[0032] The transmit aperture is configured wider than a receive aperture, in which an optical phased array is used to receive a third spectral component that is different from the first spectral component and different from the second spectral component.

[0033] The third spectral component has a wavelength between a wavelength of the first spectral component and a wavelength of the second spectral component, and the transmitted optical wave has no significant power at the wavelength of the third spectral component.

[0034] The transmitting aperture is a first transmitting aperture and the transmitted optical wave is a first transmitted optical wave, and the device comprises a second transmitting aperture configured to provide at least one beam of a second transmitted optical wave comprising at least a third spectral component that is different from the first spectral component and different from the second spectral component.

[0035] The second transmit aperture is configured further away as a second receive aperture, in which an optical phased array is used to receive the first spectral component.

[0036] The device further comprises a coherent receiver configured to capture the first spectral component received from the second receiving aperture by coherent mixing with a local oscillator derived from at least one optical source providing the first spectral component to the first transmitting aperture.

[0037] The third spectral component has a wavelength between a wavelength of the first spectral component and a wavelength of the second spectral component, and the first transmitted optical wave has no significant power at the wavelength of the third spectral component.

[0038] The first transmitting aperture and the second transmitting aperture are located near the center of an arrangement of apertures, and at least some of the receiving apertures are located near the edges of the arrangement of apertures.

[0039] The number of receiving apertures in the arrangement of apertures is greater than the number of transmitting apertures.

[0040] In another aspect, a LiDAR system generally includes: an arrangement of two or more apertures configured to provide at least one beam of a transmitted optical wave to a destination from at least two of the two or more apertures, wherein the two or more apertures comprise: a first aperture containing a first optical phased array within the first aperture, and a second aperture containing a second optical phased array within the second aperture; a transmitter subsystem configured to: provide a first segment of the transmitted optical wave to a first subset consisting of fewer than all of the two or more apertures, wherein the first subset includes the first aperture, and to a second subset consisting of fewer than all of the two or more apertures.to provide a second section of the transmitted optical wave, wherein the second section is different from the first section and includes the second aperture, and the second section of the optical wave has a feature different from a feature of the first section of the optical wave, and a receiver subsystem comprising: a first filter configured to filter a section of a collected optical wave arriving at at least one of the two or more apertures in the arrangement according to the feature of the second section of the optical wave, and a first detector configured to provide a signal based on the section of the collected optical wave that is filtered by the first filter.

[0041] Aspects may include one or more of the following characteristics.

[0042] The features include a special wavelength, and the first section of the transmitted optical wave includes light having a wavelength in a first spectral band, and the second section of the transmitted optical wave includes light having a wavelength in a second spectral band that is different from the first spectral band.

[0043] The first filter is configured to filter a section of the collected optical wave arriving at the first aperture, and the receiver subsystem further comprises: a second filter configured to filter a section of the collected optical wave arriving at the second aperture according to the characteristic of the first section of the optical wave, and a second detector configured to provide a signal based on the section of the collected optical wave filtered by the second filter.

[0044] The transmitter subsystem includes a wavelength multiplexing component configured to combine light having a wavelength in the first spectral band with light having a wavelength in a third spectral band, the second spectral band being located between the first and third spectral bands.

[0045] The arrangement of two or more apertures includes a third aperture which contains a third optical phased array within the third aperture, and the first filter is configured to filter a section of the collected optical wave arriving at the third aperture.

[0046] The transmitter subsystem includes a first wavelength multiplexing component configured to combine light having a wavelength in a first spectral band with light having a wavelength in a third spectral band, and a second wavelength multiplexing component configured to combine light having a wavelength in the second spectral band with light having a wavelength in a fourth spectral band, the second spectral band being located between the first and third spectral bands, and the third spectral band being located between the second and fourth spectral bands.

[0047] The first filter comprises a tunable filter having a passband that is tunable over the second spectral band, and the receiver subsystem is configured to tune the first filter at least partially based on the light having the wavelength in the second spectral band.

[0048] Aspects may have one or more of the following advantages.

[0049] Using the techniques described herein, a LiDAR system can be optimized in various ways. For example, some implementations, for a given total device area (e.g., for both the transmit and receive apertures combined) and a given optical source output power, collect an increased number of backscattered photons from the target object(s) while reducing background leakage light. Some implementations enable improved tolerance to speckle effects resulting from interference of light backscattered from rough (non-reflective) surfaces, and improved performance for both long-range and short-range targeting distances to a location where target objects might be expected.

[0050] Other features and advantages will emerge from the following description as well as from the figures and requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The revelation is best understood by reading the following detailed description together with the accompanying drawings. It is emphasized that, in accordance with common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features have been arbitrarily enlarged or reduced for clarity. Fig. Figure 1 is a schematic representation of an example of a monostatic LiDAR system. Fig. Figure 2 is a schematic representation of an example of a bisstatic LiDAR system. The Fig. 3A, Fig. 3B and Fig. 3C are graphical representations of exemplary simulated data acquisition results. The Fig. 4A and Fig. Figure 4B shows schematic representations of examples of apertures and corresponding speckle patterns received from a target. The Fig. 5A, Fig. 5B and Fig. Figure 5C are schematic representations of exemplary aperture arrays. Fig. Figure 6 is a schematic representation of an example of a multistatic LiDAR system. The Fig. 7A, Fig. 7B, Fig. 8 and Fig. Figure 9 shows schematic representations of various sections of examples of multistatic coherent LiDAR systems. Fig. Figure 10 is a schematic representation of a WDM version of a multistatic aperture configuration. The Fig. 11A and Fig. Figure 11B shows schematic representations of a WDM laser system that uses more than one aperture for different regions of a spectrum. Fig. 11C is a schematic representation of exemplary WDM components that are associated with the system described in the Fig. 11A and Fig. 11B is shown, they can be used. Fig. Figure 11D is an exemplary graphical representation of safety bands in spectral sensitivities of WDM components. The Fig. 12A and Fig. Figure 12B shows graphical representations of exemplary spectral sensitivities of drop and pass-through ports of WDM components. Fig. Figure 13 is a graphical representation of an example of further transmission tapes. Fig. Figure 14 is a graphical representation of closely aligned transmission bands. Fig. Figure 15 is a schematic representation of a generalized WDM version of a multistatic aperture configuration. Fig. Figure 16A is a schematic representation of an exemplary WDM system for a particular aperture. Fig. 16B is a graphical representation of exemplary wavelength bands used in the system of Fig. 16A can be transmitted and received. Fig. Figure 17 is a schematic representation of an alternative WDM system. Fig. Figure 18 is a schematic representation of an alternative WDM system. Fig. Figure 19 is a graphical representation of an exemplary wavelength band for a WDM multiplexer with a dead zone between the bands. Fig. Figure 20 is a graphical representation of exemplary nested wavelength bands for two WDM multiplexers. Fig. Figure 21 is a schematic representation of a section of a LiDAR system. Fig. Figure 22 is a schematic representation of a section of a LiDAR system with calibration elements and other photonic circuit elements. Fig. Figure 23 is a graphical representation of exemplary nested wavelength bands for two WDM multiplexers. Fig. Figure 24 is a schematic representation of an example of an optical WDM configuration. Fig. Figure 25 is a schematic representation of an optical circuit configuration. Fig. Figure 26 is a schematic representation of an optical receiver configuration. Fig. Figure 27 is a schematic representation of an example of a section of a LiDAR system. Fig. Figure 28 is a schematic representation of an example of a section of a LiDAR system. Fig. Figure 29 is a schematic representation of an example of a section of a WDM system. Fig. Figure 30 is a schematic representation of an example of an optical transmitter configuration. DETAILED DESCRIPTION

[0052] In the case of a monostatic aperture configuration, there are several approaches to multiplexing the aperture for both the transmission and reception processes. Some approaches include, for example: (1) using a polarizer to transmit light with one polarization and receive light with the opposite (i.e., orthogonal) polarization, (2) time-domain multiplexing, and / or (3) using non-reciprocal devices, such as a circulator.While monostatic aperture configurations can utilize the entire available aperture space for both a transmit aperture, which carries a beam of light to a target, and a receive aperture, which collects any backscattered light arriving at the same aperture, achieving sufficient isolation between the transmit and receive paths within the LiDAR system can be challenging. This isolation is necessary for the receiver to detect small reflections from a target without becoming saturated with leaked transmitted light. In a frequency-modulated continuous wave (FMCW) LiDAR system, backscattering within the monostatic system results in strong low-frequency peaks that can reduce the signal-to-noise ratio (SNR) for actual target detection at higher frequencies.In a bistastatic aperture configuration, light is transmitted from one aperture and received from a different aperture, overcoming the isolation challenges of a monostatic aperture configuration at the cost of reduced size for both the transmitting and receiving apertures within the available aperture space.

[0053] The Fig. 1 and Fig. Figure 2 shows examples of LiDAR systems, each using a monostatic aperture configuration 100 and a bistatic aperture configuration 200, respectively. Both systems include a laser 10 and a coherent receiver 20, which are used to mix received light with light from a local oscillator (LO) 30. The laser 10 can be a CW laser, for example, one with a narrow linewidth and low phase noise sufficient to provide a temporal coherence length long enough to perform coherent acquisition across the timescales of interest. The monostatic aperture configuration 100 also includes a circulator 40 for deflecting light in different directions.In the monostatic aperture configuration 100, an aperture 102 serves as both a transmitting and a receiving aperture such that the transmission angle of the path from the aperture 102 to a destination and the collecting angle of the path from the destination back to the aperture 102 are essentially the same, regardless of the distance to the destination (. Fig. 1) In contrast, in a bista-static aperture configuration 200, the path from a transmitting aperture 202A to a destination 204 and the path from the destination 204 to a receiving aperture 202B are different and result in different transmission and collection angles ( Fig. 2) In some LiDAR systems, the gathering angles are aligned for operation at an optimal target distance to the target location 204. As a result, operation at a greater target distance 206 or a shorter target distance 208 may provide suboptimal performance. Since the available area for the apertures is divided between transmit and receive in a bistatic configuration, the bistatic configuration has lower space efficiency than a monostatic configuration.

[0054] If the surface of a target object is not polished (for example, like the surface of a metallic mirror), or if it is otherwise configured as a back-reflective surface, the backscattered light experiences random phase fluctuations imposed by the surface roughness of the target object. The microscopic features on most rough surfaces result in a randomized phase for the light backscattered from each point on the surface. This, in turn, leads to the speckle phenomenon responsible for the interference patterns observed at the receiving aperture.Due to the random-walk nature of the interference pattern created by scattering from an extended surface with a randomized phase, the collected light exhibits Rayleigh scattering, and the strength of the collected light (proportional to the number of photons entering the receiving aperture) has an exponential statistical distribution. Consequently, if a transmitted light beam has traveled across a wall and an average of 10 photons are collected back, the aperture will collect far fewer than 10 photons for most target positions, and occasionally the receiver could collect tens of photons, saturating the receiver system's circuitry. If the LiDAR system collects too few photons, the collected light could be buried under background noise, and if too many photons are collected, the light could be outside the linear gain range of the detection system. Fig. 3A, Fig. 3B and Fig. 3C shows examples of simulated acquisition results for speckle effects in a LiDAR system. Fig. Figure 3A shows a graphical representation of the Rayleigh probability density for a particular normalized value of the amplitude of an electric field. Fig. Figure 3B shows a corresponding graphical representation of a probability density for the strength of an electric field, which is exponential. Fig. 3C presents a Monte Carlo simulation of 1000 randomized trials for a normalized strength. A normalized mean strength value of 1 is shown in the graphical representations of the Fig. 3B and Fig. 3C shown (300). How Fig. 3C shows that when the mean strength is normalized to 1, most studies correspond to a value less than one, while a few separate studies result in much greater strengths.

[0055] Both the monostatic and bistatic aperture configurations of a LiDAR system are potentially susceptible to detrimental effects due to speckle in the system's coherent receiver. If there is only one receive aperture whose size is approximately the same as the transmit aperture, only a portion of a particular interference pattern (also called a "speckle realization") will be detected by the receiver. This limits the detection probability at the receiver due to the exponential probability distribution of the signal collected from a single speckle realization.

[0056] For a given LiDAR system, the total usable area available for a number of transmit and receive apertures is typically limited by the size of the system or the size of the reticle allowed in a given manufacturing process if the LiDAR system is fabricated in a planar integrated optical flow. In a LiDAR system with a multistatic aperture configuration, this usable area is used for one or more transmit apertures and two or more receive apertures in an aperture array. The total area used for one or more transmit apertures divided by the total area used for the two or more receive apertures is referred to as the transmit-to-receive ratio.The total area used for the two or more receiving apertures, divided by the total area used for the entire aperture array, is called the "receiving fill factor." This and other parameters can be optimized in various ways by appropriately designing the number of apertures and their sizes.

[0057] The Fig. 4A and Fig. Figure 4B shows examples of different transmitting apertures with varying sizes. The transmitting apertures can, for example, be a square-shaped region essentially filled by the area of ​​a two-dimensional optical phased array (OPA) transmitting a beam of light directed by features of the array, as described in more detail below. Assuming there are no aberrations in the system for a particular transmitting aperture 400A, 400B, the size W is A , W BThe diffraction-limited transmitted light beam 402A, 402B in the far field is inversely proportional to the size of the transmitting aperture 400A, 400B. This transmitted light beam 402A, 402B strikes the surface 404 of a target object and illuminates a specific area on the surface of this target object. The backscattered light from the illuminated area of ​​the target object creates a speckle pattern 408A, 408B on the aperture array 410A, 410B. The correlation length of the speckle pattern created on the aperture array 410A, 410B is inversely proportional to the size of the illuminated area 406A, 406B.Consequently, the smaller transmit aperture 400B results in a faster-changing speckle pattern 408B (for example, with smaller light / dark features of the speckle pattern created by constructive / destructive interference), and the larger transmit aperture 400A results in a slower-changing speckle pattern 408A (for example, with larger light / dark features of the speckle pattern). The optimal number and size of the two or more receive apertures within each aperture arrangement may vary depending on the size of the transmit aperture. In some implementations, for example, the size of each of the receiving apertures is the same or comparable in size to the size of the transmitting aperture (for example, with a factor of 1 / 2 to 2 in diameter and within a factor of 1 / 4 to 4 in area; or within a factor of 2 / 3 to 3 / 2 in diameter and within a factor of 4 / 9 to 9 / 4 in area).In some implementations, the sizes of the receiving apertures are approximately the same, but the size of the transmitting aperture may be slightly larger (for example, 10% larger or 20% larger) than the sizes of the receiving apertures.

[0058] In some implementations, the aperture array comprises a collection of at least three apertures for use in a coherent LiDAR system. At least one of the apertures is used as a transmit aperture to direct light to a destination, and at least two of the apertures are used as receive apertures to receive backscattered light emanating from that transmit aperture. In a multi-wavelength LiDAR system, there may be different apertures selected as a single transmit aperture for a given central wavelength, and all of the remaining apertures are selected as receive apertures for that given central wavelength (potentially with a frequency chirp imposed around that central wavelength).In a LiDAR system that uses optically phased arrays, a receiving aperture can use an optically phased array to steer a gathering angle, and a transmitting aperture can use a phased optical array to steer a transmission angle, as described in more detail below. These optically phased arrays can have an array size (number of individual optically dispersive phased elements) and resulting cross-beam size that are matched (or nearly matched) in size.

[0059] The Fig. 5A, Fig. 5B and Fig. Figure 5C shows examples where the apertures are arranged linearly along one dimension, with the aperture shown being larger than the width of identical square-shaped apertures (where the other dimension of the aperture height in these examples lies in the side). This type of linear aperture arrangement of N apertures can use a transmitting aperture of size 1 / N as a fraction of the total available space (for example, along one long side of a rectangular area available for the aperture arrangement) and can fill the remainder of the available aperture space with N-1 apertures, also of size 1 / N, as a fraction of the available aperture space. The percentage of the total available aperture space used for receiving light approaches 100% as the number of receiving apertures increases. As can be seen from the Fig. 5A, Fig. 5B and Fig. 5C, in which N of 2 ( Fig. 5A) on 3 ( Fig. 5B) to 10 ( Fig. As can be seen in Figure 5C), while the number of receive apertures increases (from 1 to 2 to 9), the relative size of the transmit aperture decreases (from 1 / 2 to 1 / 3 to 1 / 10), and the fraction representing the receive fill factor increases (from 1 / 2 to 2 / 3 to 9 / 10). The transmit-to-receive ratio also decreases (from 1 to 1 / 2 to 1 / 9). A compromise can be made between the receive fill factor and the transmit-to-receive ratio such that an optimal number of apertures can be selected for each given system design. For some system implementations, for example, a value of N somewhere between 5 and 11 may provide an acceptable compromise. In other implementations, a wider range of N values ​​may be tolerated (for example, between 4 and 20), or there may be a value of N that maximizes certain performance parameters for given tolerances (for example, N = 9).For an odd value of N, the transmitting aperture can be located anywhere in the middle of the aperture array, which can be desirable in some implementations (for example, to reduce errors due to parallax effects for receiving apertures furthest from the transmitting aperture). Similar properties would also hold for a two-dimensional array of apertures within an available aperture space of square shape, with the transmitting aperture still being closer to the center in both dimensions. Other examples can also use more than one aperture as a transmitting aperture, with the remaining apertures being used as receiving apertures, and can place the transmitting aperture(s) at locations other than near the center.

[0060] In some implementations, the coherent detectors used to capture the light received at each receiving aperture are also coupled to perform incoherent combination (also called "incoherent averaging"), where coherently captured pointers are processed to obtain amplitudes, the absolute or squared values ​​of which are then added together as different contributions to the combination, optionally with different weights. For example, in some implementations, the coherent capture of each receiving aperture may use an in-phase / squared capture configuration (I / Q capture configuration) that employs two versions of the local light element (LO) that are 90 degrees out of phase with each other. This results in a two-dimensional pointer in an I / Q space with an angle and an amplitude.In some implementations, the coherent acquisition of each receiving aperture can yield a complex-valued transform (for example, in the frequency domain) of the time-domain signal (for example, a photostream from a single photodetector or a pair of balanced detectors), which also results in a two-dimensional phasor (in complex space) with an angle and an amplitude. In both cases, the angle of this phasor can be discarded, and the amplitude of the phasor can be obtained for each of the coherent receivers. Over each of the (N-1) receivers, this amplitude (the absolute value of the phasor) or the square of this amplitude can then be summed or otherwise combined. In some implementations, the summed values ​​can be weighted differently for different receiving apertures, with the weights depending on various parameters (for example, designated target distance).This discarding of the pointer's angle can sacrifice how quickly the mean of a captured signal increases, but it can also provide a more stable signal (for example, with a lower standard deviation).

[0061] Even with a relatively large number of receive apertures, the size of the receive apertures can be kept large enough so that each receive aperture measures an uncorrelated speckle realization, thus increasing the speckle diversity of the LiDAR receivers compared to a monostatic or bistastatic LiDAR system using a single receive aperture. As mentioned above, the probability distribution of the number of photons collected at each receive aperture is exponential. The noise at each coherent detector also has an exponential distribution. Without being bound by theory, an expression for the incoherent combination of k spatially incoherent apertures leads to Erlang distributions for both signal and noise: Noise~Erlang(k,1) Signal~Erland(kkSNRLeistung+k)

[0062] For higher detection probabilities (that is, a threshold for a detected power level or a certain number of photons detected), there is consequently a higher false alarm probability (that is, the threshold being exceeded due to noise photons rather than signal photons) without incoherent averaging (for example, with a single receive aperture) than with the same size as with multiple receive apertures using incoherent averaging. However, for lower detection probabilities, incoherent averaging exhibits the higher false alarm rate. In other words, fewer speckle realizations (lower speckle diversity) are preferable when the false alarm probability requirement is less stringent (that is, a higher false alarm probability is acceptable).More speckle realizations (higher speckle diversity) are better if the false alarm probability requirement is stricter (i.e., a lower false alarm probability is acceptable).

[0063] Another useful feature enabled by the multistatic aperture configuration is that the mixing efficiency of the LiDAR system can be improved in short ranges, while the Fraunhofer distance required for far-field operation is achieved more quickly with smaller apertures. With other systems, the far-field Fraunhofer distance may not be achieved for objects at shorter distances than the assumed target distance. However, if the aperture size is smaller, as with some multistatic LiDAR systems, an object at a shorter distance can still be considered to be in the far field, and some of the advantages still apply.

[0064] A variety of optimizations can also be made to the individual receiving apertures and the optical elements (for example, OPAs) used within each receiving aperture. The collecting angle for each receiving aperture can, for instance, be tilted independently. The light collected by each receiving aperture can also be focused to optimize performance in a different area.

[0065] Fig. Figure 6 shows an example of a LiDAR system using a multistatic aperture configuration 600. For a given transmission angle 601 from a transmitting aperture 611, a first collecting angle 602 into a receiving aperture 612 and a second collecting angle 603 into a receiving aperture 613 can be tilted independently. The potential interference from the light of the laser 10 into the detectors of the coherent receivers 20A, 20B is reduced by using separate apertures for transmission and reception (as in bista-static configurations). In the case that each aperture uses an OPA, the tilting (for example, using phase steering and wavelength steering to control different angles) and focusing (for example, also using phase steering) of each OPA can be adjusted spontaneously to set the region where the LiDAR has the highest mixing efficiency.

[0066] Another example of a multistatic aperture configuration for a coherent LiDAR system is in Fig. Figure 7A shows an example. In this example, the laser 10 provides an optical wave which is transmitted by a transmit (Tx) OPA through a transmit aperture after being modulated by a modulator 702 (for example, using FMCW modulation, which imposes a linear chirp at the peak frequency corresponding to the transmitted wavelength). A group of OPAs 703 within respective apertures, arranged close to one another, includes 8 receive (Rx) OPAs that provide different received segments of a collected optical wave arriving at the receive apertures containing the Rx OPAs. The LO 30 combines each of the received segments, and the resulting combined optical waves are coherently detected by detectors 704.The detectors 704 can be implemented, for example, using balanced detection with photodetectors connected to produce an output current that is the difference between the photocurrents generated by the two photodetectors, and / or homogeneous detection, which imposes a frequency shift on the LO 30 with respect to the peak frequency. The resulting electrical signals provided by the detectors 704 can then be processed in processing modules 706, which include processing using analog-to-digital conversion (A / B conversion), whereby the processing to gain the amplitude and discard the phase angle can be performed digitally. These gained amplitudes (or the squares of the amplitudes) can also be weighted using amplitude control modules 708.These potentially weighted amplitudes are then combined using 710 circuits configured to perform the incoherent averaging described herein.

[0067] Fig. Figure 7B shows an example of a detector 704 for detecting an optical wave 714 received at a receiving aperture, in the context of a LiDAR system 716, which includes other elements, including: the laser 10, which is coupled to the modulator 717 for transmitting a modulated optical wave 718 from a transmitting aperture, and other receiving apertures and corresponding detectors. The detector 704 includes a 90-degree phase shifter 720 for providing a phase-shifted version LO_2 of an incoming optical local oscillator wave LO_1. A set of 50 / 50 splitters 721 is capable of combining the optical wave 714 with the different versions of the LO to perform I / Q detection.The detector 704 includes a first pair of photodetectors 722A, 722B for detecting an in-phase (I) signal based on a corresponding pair of photostreams that can be subtracted in a balanced detection arrangement, and a second pair of photodetectors 724A, 724B for detecting a quadrature (Q) signal based on a corresponding pair of photostreams that can be subtracted in a balanced detection arrangement. A processing module 726 can derive a phase angle and amplitude associated with the optical wave 714 from all four of these photostreams. Other implementations of the detector 704 are also possible.

[0068] Fig. Figure 8 shows an example of a section of a multistatic aperture configuration for a coherent LiDAR system 800, which includes a beam steering and focusing arrangement and optical couplers for a transmit OPA (Tx-OPA) 802 and two receive OPAs (Rx-OPAs) 804, 806. Steering can be performed along angular transverse directions (for example, altitude and azimuth) in a polar coordinate system, with steering in one angular direction being performed by phase shifters 808, and steering in the other angular direction by wavelength (as in Fig. (shown in Figure 8). The adjustment of the transmission angle for the Tx-OPA 802 and the collecting angles for the Rx-OPAs 804 and 806 in the phased angular direction can be performed dynamically, since the phases imposed by the phase shifters 808 can be rapidly adjusted. The light beam transmitted by the Tx-OPA 802 can have a non-linear phase front imposed on it by the phase shifters 808. This dynamically adjusted phase front can also tune the focal length of the Rx-OPAs 804 and 806. In the longitudinal direction, the phased arrays can be directed in predetermined or dynamically adjusted directions, but tuning the gratings in this way could be more challenging or consume more power.Nevertheless, the fact that multiple receiving apertures are available allows the designer to optimize the system for detecting objects at different distances as required by the situation.

[0069] Fig. Figure 9 shows an example of a section of a multistatic aperture configuration for a coherent LiDAR system 900, showing a transmission path to an object 902 from a transmission OPA 904 and resulting collection paths from the object 902 to the receiving OPAs 906A, 906B, 906C, and 906D. The paths are spread within a plane parallel to an axis along which the apertures containing the OPAs are arranged. In this example, the plane is the same plane in which the phased angular direction is directed. These paths can be collectively configured to be aligned to a particular target location, shown in this example as the target object 902 at a particular convergence distance 908. The OPAs can also be focused according to the assumed convergence distance 908.

[0070] In some implementations, the apertures within an aperture array can be multiplexed for different center wavelengths (to enable frequency modulation and / or frequency steering). In this way, a wavelength division multiplexing (WDM) version of a multistatic aperture configuration can assign different combinations of apertures as a transmit aperture and corresponding receive apertures for different center wavelengths. Thus, for a given center wavelength, the operation is capable of achieving the operating characteristics described above, since the center wavelengths of each wavelength band are sufficiently spaced, with appropriate safety bands in between, to ensure strong isolation (e.g., low leakage) between optical waves (and resulting signals) using different center wavelengths.

[0071] Fig. Figure 10 shows an example of a WDM version of a multistatic aperture configuration 1000, in which each aperture transmits a set of one or more wavelength bands and receives all other wavelength bands. In this example, there are four wavelength bands: a first band from 1500 nm to 1525 nm, a second band from 1525 nm to 1550 nm, a third band from 1550 nm to 1575 nm, and a fourth band from 1575 nm to 1600 nm. A suitable portion of the ends of each band can be used as safety bands. Some apertures can use a WDM coupler to combine multiple spectral components (or "wavelengths") of an optical wave within different respective spectral bands (or "wavelength bands") for transmission.Aperture 1001, for example, combines a first and a third wavelength band using a WDM coupler 1010, while apertures 1002 and 1003 each transmit only one wavelength band (the second and fourth bands, respectively) and therefore do not use a WDM coupler. In this example, the optical paths include microring resonators as wavelength direction filters to receive specific wavelengths within specific wavelength bands, as described in more detail below. Alternatively, other wavelength filters can be used on the receive path to select wavelengths that are not transmitted for that aperture.

[0072] Some implementations of a multistatic coherent LiDAR system can be configured to use other forms of diversity in addition to, or instead of, the diversity provided by WDM by employing different optical waves with distinct characteristics. For example, time-division multiplexing within different time slots can be used, polarization diversity can be provided by using orthogonal polarizations, and spatial diversity can be used by dividing the area of ​​an aperture into distinct regions along a first dimension, which are used for transmitting or receiving for different sets of apertures along a second dimension.

[0073] As above with reference to the Fig. 1 and Fig. As described in section 2, some coherent LiDAR systems use a single aperture for transmitting and receiving light (monostatic), while others use two apertures in close proximity, one for transmitting and one for receiving (bistastatic). If, instead, the size of each aperture is kept constant by using three or more apertures, it is possible to achieve the high aperture utilization of a monostatic system while maintaining the high isolation of a bistatic system. Furthermore, a multistatic optical phased array configuration (such as in [reference to be added]) represents Fig. 6 shown) speckle diversity is provided for the system (increasing the detection probability) and reduces or eliminates angular slits in the far field.

[0074] For optical phased arrays that use dispersive antenna elements, steering along an axis is achieved by changing the wavelength of the source (as in, for example, in Fig. (8 shown). A widely tunable high-power laser source, enabling a LiDAR built around such an optical phased array, can be challenging for silicon photonics due to (1) the limited spectral range of available laser amplification media, (2) nonlinear losses in silicon waveguides, and (3) the achievable saturation output power of semiconductor optical amplifiers. Coupling a wavelength division multiplexer on transmit and receive modules with a multistatic aperture configuration reduces the complexity of the LiDAR by, for example, potentially reducing the power input to a waveguide, reducing the spectral coverage requirement of any laser line, and reducing the output power required from each laser line.

[0075] A remaining challenge in a WDM system is achieving high (for example, close to 100%) wavelength band coverage with low loss. In the transition region between two bands of a typical WDM system, there is a loss penalty between the two sub-bands. By transmitting different wavelengths from different sub-apertures in a multistatic system, this transition region is significantly reduced or completely eliminated, thereby reducing or eliminating angular gaps during transmission. Angular gaps can also be eliminated during reception. A time-varying narrowband wavelength division multiplexer allows for high isolation between receive and transmit channels and can be bound to the local oscillator.

[0076] In a system with a multistatic aperture configuration, if speckle reflections are present and reflected from a target, each of these sub-apertures can measure an independent speckle realization and can be incoherently combined to increase the speckle diversity of the receiver and consequently the system's detection probability. In the example of the Fig. 7A the receiver area is 89% of the total aperture area of ​​the system, which provides a 2.5 dB increase in the receiver area relative to a bisstatic system, or only a -0.5 dB penalty compared to a monostatic system.

[0077] Configurations such as those described herein can serve any number of purposes, including: (1) increasing the speckle diversity of the receiver; (2) increasing the partial utilization of a receiver relative to the total aperture area (for example, by using WDM); (3) reducing the size of angular slits of a system in the far field by increasing the spot size (discussed below in the section on spectral coverage); and (4) maintaining high isolation between transmit and receive by partitioning apertures.

[0078] As mentioned above, WDM is a technique for improving the field of view and spectral coverage of the laser by inserting more than one aperture and connecting each aperture to a different source (for example, different lasers or different lines of the same laser), thus covering a different section of the total optical spectrum.

[0079] The following are additional examples of a photonic chip with an optical phased array LiDAR or other laser system that transmits light with different wavelength bands from different apertures, with at least two apertures being used in the transmission system. Fig. 11A and Fig. Figure 11B shows an example of such a structure 1100 which can provide a variety of advantages, including one or more of the following: (1) increasing the total emitted power of the system while keeping individual waveguide power low, (2) distributing emitted power at lower emitted intensity and supporting eye safety (if the total emitted power is the same), and (3) increasing the field of view of OPA by increasing wavelength coverage.

[0080] The receiving process can be performed at one or more of the apertures. For example, one wavelength (λ1) can be transmitted from laser 1 through aperture 1101, while the same aperture 1101 receives the other wavelength (λ2), and the other wavelength can be transmitted from laser 2 through another aperture 1102, while the same aperture 1102 receives the first wavelength (λ1). This approach optimizes space utilization, as all available apertures actively transmit and receive light, albeit at different wavelengths. Fig. Figure 11A shows an example of different tuning ranges for the two wavelengths of different lasers. As can be seen in Fig. As 11B sees, the light sent from one aperture is scattered back by an object and received at the other aperture, reducing cross-coupling, as explained in more detail below.

[0081] Fig. Figure 11C shows an example of two WDM multiplexer components that can be used for wavelength multiplexing (WDM1 and WDM2) in the 1100 structure. These components are configured such that component WDM1 transmits λ1 and receives on λ2, and component WDM2 transmits on λ2 and receives on λ1 in an add / drop multiplexer configuration.

[0082] Typically, the spectral sensitivity of WDM components, such as the wavelength-dependent coupling components WDM1 and WDM2, as well as other wavelength-dependent filters, does not necessarily exhibit an ideal box-like shape. Therefore, there is a surface between adjacent alternating spectral sensitivities of the WDM components WDM1 and WDM2, which is described in Fig. Figure 11D shows a higher loss rate and cross-coupling (between the shaded high-transmission regions (T) as a function of wavelength). As shown Fig. As can be seen in Figure 12A, the lasers driving each of the apertures can be scanned via the respective laser sweep regions 1201 and 1202, which are shown in the shaded areas. The sweep regions (also called “scan regions”) of the lasers can overlap or can be aligned to be adjacent to each other without overlapping, as shown in Figure 12A. Fig. 12. The drop responses for the transmit port (i.e., the drop port) of the two WDM components are shown with the curves exhibiting high power (around 0 dB) across laser sweep regions 1201 and 1202, resulting in little or no transmission loss. The pass responses for the receive port (i.e., the pass-through port) of the two WDM components are shown with the curves exhibiting low power across laser sweep regions 1201 and 1202. As can be seen in Fig. As can be seen in 12B, which each only show the pass / receive responses 1203 and 1204 from the WDM1 component and the WDM2 component, even if the sweep area of ​​the two lasers is perfectly aligned, there is still a dead area 205 in which there is no adequate receive coverage because the WDM spectral sensitivities are low (below -3 dB) at the receive power level.

[0083] As in Fig. 13 is visible, if the laser sweeps through the further shaded areas in each of the apertures, extending to the -3 dB power reduction levels of the spectral sensitivities of the WDM components, there are no actual high-loss dead zones, but the laser light can experience up to 3 dB power reduction on transmission and 3 dB power reduction on reception.

[0084] One technique for reducing high-loss safety band dead zones is to increase the number of apertures and ensure that the wavelength ranges not covered by apertures / receivers in one part of the system are covered by one or more of the other apertures / receivers in the system.

[0085] As in Fig. As shown in Figure 14, for example, three WDM devices with shifts in their spectral sensitivities can create a system in which all wavelengths are covered with relatively high transmission power levels (shown across the shaded areas), and each laser is detected by at least one aperture / receiver at a time with a relatively high receive power level. However, these systems can still suffer from a lack of spatial efficiency, as at certain wavelengths only one-third of the total lidar area covers a given channel.

[0086] In some implementations of the techniques disclosed herein, the receiving circuits include a tunable WDM component (for example, a tunable filter) that is bound to the corresponding transmission wavelength being received. One way to solve this problem is to have only transmitted light passing through the WDM multiplexers (for example, non-tunable WDM multiplexers), and the received light is captured before it reaches the WDM multiplexers.

[0087] A general example of a transmit and receive WDM architecture for the system includes, for instance, at least two apertures and transmits light at a set of one or more wavelength bands in each of these apertures. Each aperture is also configured to receive light at a set of wavelength bands complementary to the transmit band(s) for that aperture. Such an architecture can be used, for example, to configure a LiDAR system to achieve advantages that may include: a speckle diversity receiver, high aperture fill factor, wide field of view, low loss, and / or no field-of-view gaps.

[0088] Such an architecture can be implemented, for example, on a photonic silicon chip to provide a LiDAR system with an optical phased array that uses wavelength division multiplexing during transmission to combine multiple laser lines into a single optical phased array aperture.

[0089] In some implementations, a tunable optical wavelength division multiplexing circuit can be configured to use a tunable photonic ring and light detectors to bind a receiving circuit to the wavelength of the local oscillator, as described in more detail below.

[0090] As a generalization of the example given in Fig. 10 is shown, shows Fig. 15 a configuration 1500, which is set up in such a way that each aperture transmits one set of wavelength bands and receives all other wavelength bands. Each wavelength band defines a channel that can be used for transmitting (as a transmit band) at one aperture and for receiving (as a receive band) at another aperture. To prevent loss in transmission from the WDM multiplexers, each of the transmit bands (such as Tx1 and Tx3) is separated by at least one channel as a safety band. Receive bands are tuned to follow a wavelength of a transmit laser sent from other apertures. In Fig. Aperture 15 transmits (Tx1, Tx3, ...) and receives (Rx2, Rx4, ...). The channels received at aperture 1 are not transmitted by the same aperture, and the feedback from the tunable WDM (filter bank) follows the wavelengths (Tx2, Tx4, ...) emitted by other apertures. It is worth noting that if only one wavelength (for a particular channel / wavelength band) is transmitted by each aperture, all other channels can be received by the same aperture, and no WDM multiplexer is required in the transmission section of the optical system (i.e., the transmitting subsystem) for that aperture. For example, from Fig. As can be seen in Figure 10, if the system is configured to transmit λ1 (in the range of 1500 to 1525 nm) from the first aperture 1001, the second range of wavelengths transmitted from the same aperture 1001 should have some wavelength separation from this range (for example, λ3 lies in the wavelength range of 1550 to 1575 nm). The WDM coupler 1010 (for example, a non-adjustable WDM multiplexer) used in the first aperture can therefore provide lossy feedback in the λ2 range (in the range of 1525 to 1550 nm, which serves as a safety band for this aperture) without performing the transmission power in the λ1 or λ3 ranges. The fourth wavelength range in this example corresponds to λ4 in the range of 1575 to 1600 nm.It should be noted that these wavelength ranges are given as examples, and that the actual wavelength ranges may be what is appropriate for the application and design constraints.

[0091] At the in Fig. In the example shown, not all apertures require a WDM coupler, such as coupler 1010 used for aperture 1001 (or another non-tunable WDM multiplexer), for the transmission channels. Apertures 1002 and 1003, for example, each transmit only one channel and therefore do not require a non-tunable WDM multiplexer. The microrings (or other tunable wavelength drop filters) can be used on the receive paths of the receiving section of the optical system (i.e., the receiver subsystem) to select the wavelengths that are not transmitted by that aperture.For example, in the case of a microring used as a tunable filter, the free spectral range (FSR), which corresponds to the wavelength distance between high transmission peaks, can be selected to be large enough to span each wavelength band (for example, at least 25 nm for the exemplary wavelength bands given above).The potential reasons for not attempting to receive light in a special channel, transmitted from a special aperture in the same channel and collected at the same aperture, include the following: 1) the transmitted light is usually orders of magnitude stronger than the collected light, and tuning a filter to the wavelength being transmitted may damage the filter or cause nonlinearity in its optical feedback; 2) if the receiving filter receives a particular wavelength in the return path, it will not affect the same wavelength in the transmission path and will induce unwanted loss in transmission; 3) because the transmitted light is much stronger, any backscatter from the aperture will dominate the received light at the same wavelength.

[0092] A potential technical challenge lies in ensuring that the tunable receiving WDM components (e.g., tunable filter) are synchronously tuned (e.g., bound) to the transmission wavelengths of other apertures. Some implementations can be configured to use local oscillator light generated by the transmitted light as a tuning reference. Referring to the Fig. 16A and Fig. 16B is, for example, a WDM system 1600 ( Fig. 16A) designed for a special aperture to direct light into the shaded wavelength ranges ( Fig. 16B) of the laser sweep range SR2 (1525 to 1550 nm) and the laser sweep range SR4 (1575 to 1600 nm). The wavelength ranges of the receive range RR1 (1500 to 1525 nm) and the receive range RR3 (1550 to 1575 nm) can therefore be received in the return path. A tunable microring is used to receive the return signals in each receive range RR1 and RR3. The microring M3 is tuned to the laser LP3 in the range RR3 (1550 to 1575 nm), and the microring M1 is tuned to the laser LP1 in the range RR1 (1500 to 1525 nm). A portion of the laser light from this laser (used for transmission to other apertures and for "picking off" at this aperture) is injected into the receiving blocks as local oscillators (LOs). As indicated by the arrow at a wavelength near the center of the receiving area RR3 in Fig. 16B indicated and according to the arrows shown in Fig. As shown in Figure 16A, following the path of light of this wavelength, if the portion of the local oscillator light picked up by the 5% directional couplers is minimized at photodetector D1 (for example, a photodiode detector) by tuning microring M3, microring M3 becomes bound to the local oscillator signal and consequently picks up the correct return signal from the aperture. A similar tuning procedure can be performed to tune microring M1 by minimizing photodetector D3. A potential advantage of this tuning procedure over one that attempts to maximize the collected return signal is that it eliminates the chance of binding to the wrong laser line, since there are multiple transmitted / backscattered and collected laser lines on the return path.

[0093] A similar but slightly different WDM system configuration 1700 is in Fig. Figure 17 shows the difference between systems 1600 and 1700. The difference lies in the fact that photodetectors D2 and D4 in system 1700 are minimized to ensure binding to the transmitted laser. This particular aperture of system 1700 is also designed to transmit light in the wavelength ranges SR2 (1525 to 1550 nm) and SR4 (1575 to 1600 nm). The wavelength ranges RR1 (1500 to 1525 nm) and RR3 (1550 to 1575 nm) can therefore be received in the return path. A microring M1 and M3 are used to each receive the return signal in each wavelength range. The microring M3 is tuned to the laser in the RR3 range (1550 to 1575 nm), and the microring M1 is tuned to the laser in the RR1 range (1500 to 1525 nm). A portion of the laser light from these lasers is injected into the receiver blocks as local oscillators (LOs). As shown in Fig. 16A, show in Fig. 17 The arrows indicate the path of the injected light, and if the portion of the local oscillator light picked up by the 5% directional couplers is minimized at photodetector D2 by tuning microring M3, microring M3 will be bound to the local oscillator signal and consequently will receive the correct return signal from the aperture. A similar tuning procedure can be performed to tune microring M1 by minimizing photodetector D4.

[0094] A similar but slightly different WDM system configuration 1800 is in Fig. 18 shown. Similar to the system in Fig. 16A the photodetectors D1 and D3 are minimized to ensure binding of the tunable wavelengths of the microrings M1 and M3 to the transmitted laser wavelength (which is transmitted from another aperture) that is being recorded.

[0095] A variety of other techniques can be used to ensure that apertures in a LiDAR system can simultaneously transmit and receive light in different parts of the optical spectrum. The wavelength ranges can be adjusted in a way that does not block any spectral range. Non-adjustable WDM devices can be used to combine the transmitted light into the output, and tunable filters can be used on the receive path to selectively capture each received band. To bind the tunable filters to the transmitted laser wavelength (for other apertures) at any given time, a portion of the local oscillator light can be used as a wavelength reference. It is advantageous to minimize the local oscillator light at the reference photodetector to ensure that no other laser line is inadvertently captured.

[0096] In LiDAR systems that rely on wavelength sweeping to cover a large field of view, the techniques described herein for combining different respective wavelength ranges from multiple lasers to increase the overall wavelength range and field of view beyond what is possible with a single laser and amplification medium can offer a variety of advantages.

[0097] Some implementations, for example, offer one or more of the following advantages: Ability: Many laser lines increase points per second. Robustness: Partial spectral coverage per laser improves performance over temperature. Capability: In silicon waveguides, 200 nm total spectral coverage is enabled around 1550 nm with a vertical 24°+ FOV. Cost savings: Receiving apertures use 75% of the total aperture area. Robustness: Self-calibration structures ensure performance across temperature and lifetime. Security: Multi-aperture receivers with speckle diversity can double the detection probability.

[0098] As explained above, a challenge in the multichip sweeping system is achieving 100% coverage of the wavelength band with low loss.

[0099] As in Fig. As shown in Figure 19, for a single WDM multiplexer 1900 there can be a dead zone 1902 between the laser tuning ranges 1904 for channels that are combined by the WDM multiplexer 1900 as described above.

[0100] Alternatively, as in Fig. As shown in Figure 20, the use of more than one WDM multiplexer for different respective apertures can ensure that more of the spectrum (for example, including the dead-zone portion of the spectrum between the WDM channels) is covered by the other WDM multiplexers. A dead zone in one WDM device (used as a first multiplexer 2000) is thus essentially aligned with a passband into another WDM device (used as a second multiplexer 2002). Within each passband, the wavelength of a corresponding laser can be swept to cover essentially the entire passband.This pair of multiplexers then provides an essentially continuous range of wavelength tunability for a transmitter system, as shown by the 2004 laser tuning ranges of the first multiplexer 2000 and the 2006 laser tuning ranges of the second multiplexer 2002, which in this example are interleaved without any dead zones. The resulting optical wave can be used for a transmission signal and for a corresponding local oscillator signal used for coherent reception in a receiver system. A filter in the receiver system (for example, a microring resonator) can also allow its narrow passband to be swept along with the sweep of a corresponding laser, as described above.

[0101] In some implementations, multiple apertures can be used for receiving and transmitting different sets of wavelengths, but the receiving apertures and transmitting apertures can be separate. Fig. Figure 21 shows an example of a section of a LiDAR system that includes a WDM system 2100, which includes: transmit apertures (Tx apertures) Tx aperture 1 and Tx aperture 2 in the middle of a set of 8 apertures; receive apertures (Rx apertures) Rx aperture 1, Rx aperture 2, Rx aperture 3, Rx aperture 4, Rx aperture 5 and Rx aperture 6 on each side of the transmit apertures; 8 wavelength sources (for example, multiple lasers or multiple lines of a laser) and circuits for connecting to an application-specific integrated circuit (ASIC) 2102 and an analog front-end ASIC 2104 of a LiDAR system. Receive apertures 1 to 6 are configured with coherent receivers, and their electronic output is combined with the analog front-end ASIC 2104. The phase-shift driver ASIC 2102 controls the phase of all phase shifters in both the transmit and receive apertures.

[0102] Fig. Figure 22 shows a section 2200 of such a LiDAR system (showing only 4 of the 6 receive apertures) into which calibration elements are incorporated. A set of calibration elements 2202, coupled to the end (or beginning) of each phased array within each aperture, ensures that the beam to / from each aperture is diffraction-limited and that the apertures are directed in the correct directions. Various types of photonic circuit elements, for example, elements on a photonic integrated circuit (PIC), can be used on the transmit-side photonic circuits 2204A and 2204B and the receive-side photonic circuits 2206.The type of WDM filtering / routing performed on the receive side can differ from that performed on the transmit side because power levels are lower on the receive side than on the transmit side. For example, microring-based resonator filters can be used on the receive side (without a significant spectral dead zone), while on the transmit side, their use is limited due to the power handling restrictions of microring-based resonator filters. Since the receivers cannot operate with a dead zone, each receive aperture can pick up the signal from all transmit apertures (in this case, two transmit apertures). The receive apertures can be coherent and can use a local oscillator (LO) derived from the same light as that transmitted by the Tx apertures. As described in... Fig. As shown in Figure 22, some of the light can be collected after the transmitting WDM multiplex circuits 2204A and 2204B and fed to the receiving WDM filter circuits 2206. One waveguide branch carries the LOs from the output of WDM multiplex circuit 2204B with light from the even-numbered lasers, and another waveguide branch carries the LOs from the output of WDM multiplex circuit 2204A with light from the odd-numbered lasers. As shown in Figure 22, a portion of the light can be collected after the transmitting WDM multiplex circuits 2204A and fed to the receiving WDM filter circuits 2206. One waveguide branch carries the LOs from the output of WDM multiplex circuit 2204B with light from the even-numbered lasers, and another waveguide branch carries the LOs from the output of WDM multiplex circuit 2204A with light from the odd-numbered lasers. Fig. Figure 23 shows that, in a generalized example of such WDM multiplexing circuits, an odd-numbered range multiplexer 2300A combines light from odd-numbered lasers sent to Tx aperture 1 and is branched off to provide LO_1, and an even-numbered range multiplexer 2300B combines light from even-numbered lasers sent to Tx aperture 2 and is branched off to provide LO_2. The lasers feeding the Tx arrays are all tunable and are swept over their specific spectral bands, so that the collection of laser lines on the LO paths resembles combs of laser lines, with each tooth of the comb moving independently forwards and backwards in that range, the number of each laser and the corresponding spectral band indicating where it occurs in uniformly spaced and offset sets of spectral bands. Fig. Figure 23 shows, for example, the laser tuning range 2302 for the first spectral band, which occurs between the laser tuning ranges 2304 for the second and fourth spectral bands.

[0103] With reference to Fig. 24 includes an optical WDM configuration 2400 coherent receivers 2402, which contain microrings that can be continuously / constantly tuned to the instantaneous wavelength of the received light 2404. Each microring can, for example, be tuned to an individual line of the received comb 2406. There are also LO microrings in the coherent receivers 2402 that can be used to track the wavelength of the corresponding line in the LO lines (within odd-numbered spectral bands) or LO lines 2 (within even-numbered spectral bands).

[0104] Fig. Figure 25 shows an alternative optical circuit configuration 2500 for delivering the LO lines to the receivers. A 2x2 coupler 2502 can combine the two collections of LO lines branched off after the two WDM multiplexers 2504 with interleaved / staggered safety bands. Each output of the coupler receives half of the light from each branch, and the two outputs contain all the laser lines required by the coherent receivers. The LO light is then distributed to the receivers in such a way that all receivers receive all laser lines. The 2500 configuration also includes demultiplexers and in-phase and quadrature detectors (IQ detectors) 2506 that utilize the LO light.

[0105] With reference to Fig. In an example of an optical receiver configuration 2600, the LO signal 2604, which contains a multiplexed collection of LO lines, is fed to the IQ receivers and mixed with the light 2602 collected by the optical phased receive arrays (Rx lines) using a microring tuned for that particular IQ receiver. In this example configuration, all IQ receivers are cascaded on the same waveguide using different microrings for each receiver. Each receive aperture includes such an optical receiver configuration 2600, which contains a series of such receiver filters (IQ 1, IQ 2, ...) covering all wavelengths received at that aperture. The microring (or other selective filter) is tuned in synchronization with the tunable lasers such that each microring receives one LO line and one Rx line.Since the received signal is merely a delayed and attenuated version of the laser light emitted into the environment, the wavelengths of the LO line and the corresponding received signal are essentially the same. The same filter, which has sufficient bandwidth to accommodate the laser chirp, can receive them simultaneously. As with frequency-modulated continuous wave (FMCW) systems, the laser frequency can be chirped as a function of time, so that the instantaneous frequency of the delayed feedback signal and the emitted light (and LO) are slightly different, resulting in beat frequency notes at the receiver. This slight frequency chirp allows the two laser lines to be slightly different in frequency, which, as mentioned above, can be covered by the filter.

[0106] As in Fig. As shown in Figure 26, when fed from two sides, the LO signal and the Rx signal propagate counterclockwise (CCW) and clockwise (CW) within each of the microring filters, respectively, and are truncated to a left and right waveguide of each IQ detector. The filter can be another narrowband dual-output filter, including higher-rank resonance-based filters or other filter types. The filter can be configured to have a passband narrow enough not to interfere with the other WDM lines and wide enough to pass through the LO and the delayed, frequency-offset signal.

[0107] The Fig. 27 and Fig. Figure 28 shows sections of exemplary LiDAR systems that use couplers to route WDM light in different ways. Fig. The receiving section of the WDM system 2700 can be configured to include 2x2 couplers 2702 after different pairs of receiving apertures. The WDM light collected from adjacent apertures can be coupled into odd-numbered and even-numbered output ports for coherent acquisition. In other words, for each laser line, if the light collected from apertures 1-2, 3-4, etc., is in phase or out of phase, all the light for that particular wavelength is fed to one set of receivers, increasing the noise ratio for that receiver while the other receiver receives no light of that wavelength.

[0108] As in Fig. As shown in Figure 28, this can be further extended into a receive section of the WDM system 2800, which is configured to include 4x4 couplers 2802 according to different sets of four receive apertures. Alternatively, with reference to Fig. 29 a series of 2x2 splitters, 3 dB couplers 2902 are placed in the return path to collect more higher-order room modes of the higher-order phase front 2904, which are received via a super aperture consisting of the collection of four adjacent Rx apertures (Rx_1, Rx_2, Rx_3, Rx_4) with even and odd-numbered modes provided to different respective Rx rings (Rx_1 rings, Rx_2 rings, Rx_3 rings, Rx_4 rings) which are combined with LO combs.

[0109] Fig. Figure 30 shows an exemplary optical transmitter configuration 3000 in which a 2x2 coupler 3002 is placed between two WDM multiplexers 3004A and 3004B, one for even and one for odd wavelengths respectively, and two transmitter OPAs 3006, appear to be in a line with all wavelengths from both transmitters (Tx_1 and Tx_2).

[0110] Although the disclosure was described in connection with certain embodiments, it must be understood that the disclosure is not limited to the disclosed embodiments, but on the contrary aims to cover various modifications and equivalent arrangements that are included in the scope of the attached claims, the scope being to be interpreted in the broadest possible way, so that it includes such modifications and equivalent structures as being permissible under the law.

Claims

[1] Device that includes: at least one transmitter comprising a transmitting aperture (202A, 400A, 400B, 611) configured to provide at least one beam of a transmitted optical wave (714, 718) along a transmission angle to a destination (204), wherein the optical wave (714, 718) comprises at least one first section of the optical wave (714, 718); and two or more receivers (2402), wherein at least one receiver (2402) comprises: a receiving aperture (100, 202B, 612, 613) located near at least one of the transmitting apertures (202A, 400A, 400B, 611) or a receiving aperture (100, 202B, 612, 613) of a different receiver, an optical phased array within the receiving aperture (100, 202B, 612, 613), wherein the optical phased array is configured to receive at least one section of a collected optical wave (714, 718) arriving at the receiving aperture (100, 202B, 612, 613) along a respective collecting angle, characterized by , that the optical wave (714, 718) comprises a second section which has a different feature from a feature of the first section of the optical wave (714, 718) and, that the device further includes: a filter configured to filter the received section of the collected optical wave (714, 718) according to the characteristic of the first section of the optical wave (714, 718), and a detector (704) configured to provide a signal (2604) based on the filtered section of the collected optical wave (714, 718). [2] Device according to claim 1, wherein each detector (704) comprises a coherent detector configured to combine the received portion of the collected optical wave (714, 718) with an optical local oscillator wave to provide a combined optical wave (714, 718) and to capture the combined optical wave (714, 718) to provide the signal (2604). [3] Device according to claim 2, wherein a frequency shift exists between the local oscillator and the transmitted optical wave (714, 718) to enable heterodyne detection in coherent detectors (704). [4] Device according to claim 2, wherein each signal (2604) comprises an amplitude and a phase angle, and the respective component corresponding to that signal (2604) comprises a quantity based on the amplitude and independent of the phase angle. [5] Device according to claim 4, wherein the circuits (710, 2204A, 2204B, 2206) are configured to convert each signal (2604) into digital form and to process the signals (2604) in digital form to eliminate dependence on the phase angles. [6] Device according to claim 4, wherein at least one coherent detector is configured to use a first optical local oscillator wave to provide a combined optical in-phase wave, and to use a second optical local oscillator wave which is shifted relative to the first local oscillator wave to provide a combined optical quadrature wave, and to provide the amplitude and phase angle in an in-phase / quadrature space (I / Q space). [7] Device according to claim 4, wherein the circuits (710, 2204A, 2204B, 2206) are configured to perform a transformation on a real-valued signal provided by one of the detectors (704) to provide the amplitude and phase angle in a complex space of a resulting complex transform of the real-valued signal. [8] Device according to claim 2, wherein each detector (704) is configured to generate a current that represents a difference between photocurrents generated by a pair of balanced photodetectors. [9] Device according to claim 1, wherein the total number of receiving apertures (100, 202B, 612, 613) is between 3 and 20. [10] Device according to claim 9, wherein the total number of receiving apertures (100, 202B, 612, 613) is between 4 and 10. [11] Device according to claim 9, wherein the total number of transmitting apertures is (202A, 400A, 400B, 611) 1. [12] Device according to claim 1, wherein an area (406A, 406B) of each receiving aperture (100, 202B, 612, 613) is equal to an area (406A, 406B) of the transmitting aperture (202A, 400A, 400B, 611) within a factor of between 4 / 9 and 9 / 4. [13] Device according to claim 1, wherein the receiving apertures (100, 202B, 612, 613) are arranged along an axis in a plane in which the optical phased arrays are configured to provide steering of the respective collecting angles using phases of elements of the optical phased arrays. [14] Device according to claim 1, wherein each of the optical phase-controlled arrays of the receivers (2402) is configured to align the respective collecting angle with the target location (204). [15] Device according to claim 1, wherein the transmitter comprises an optical phased array within the transmitting aperture (202A, 400A, 400B, 611). [16] Device according to claim 15, wherein an area (406A, 406B) of each optical phased array within the receive apertures (100, 202B, 612, 613) is equal to an area (406A, 406B) of the optical phased array with the transmit aperture (202A, 400A, 400B, 611) within a factor between 4 / 9 and 9 / 4. [17] Device according to claim 15, wherein at least one optical phased array is configured within the transmit aperture (202A, 400A, 400B, 611) or at least one of the receive apertures (100, 202B, 612, 613) to steer a first angle using phases of elements of the optical phased array and to steer a second angle using wavelength. [18] Device according to claim 1, wherein the receiver (2402) is a first receiver, the receiving aperture (100, 202B, 612, 613) is a first receiving aperture, the optical phased array is a first optical phased array, the filter is a first filter, the detector (704) is a first detector, and the two or more receivers (2402) include a second receiver comprising: the transmit aperture (202A, 400A, 400B, 611), which is configured as a second receive aperture, a second optical phased array within the transmitting aperture (202A, 400A, 400B, 611), wherein the second optical phased array is configured to receive at least one section of a collected optical wave (714, 718) arriving at the transmitting aperture (202A, 400A, 400B, 611) along a respective collecting angle, a second filter configured to filter the received section of the collected optical wave (714, 718) according to a feature that is different from the feature of the first section of the optical wave (714, 718) and different from the feature of the second section of the optical wave (714, 718), and a second detector configured to provide a signal (2604) based on the filtered section of the collected optical wave (714, 718) filtered by the second filter. [19] Device according to claim 1, further comprising circuits (710, 2204A, 2204B, 2206) configured to determine an estimated distance associated with the collected optical wave (714, 718) at least partly based on a combination that includes a respective component corresponding to each of the two or more of the signals (2604) provided by the detectors (704) of the two or more receivers (2402). [20] Device according to claim 19, wherein the transmitter applies linear frequency modulation to the transmitted optical wave (714, 718) to enable the circuits (710, 2204A, 2204B, 2206) to determine the estimated distance. [21] Device according to claim 1, wherein the transmitting aperture (202A, 400A, 400B, 611) is further configured as a receiving aperture (100, 202B, 612, 613) in which an optical phased array is used to receive at least one section of an optical wave (714, 718) having a feature different from a feature of the transmitted optical wave (714, 718), and at least one of the receiving apertures (100, 202B, 612, 613) is used as a transmitting aperture (202A, 400A, 400B, 611) to provide a beam of an optical wave (714, 718) having the different feature. [22] Device according to claim 1, wherein the features include at least one: a particular wavelength, a particular time slot or a particular polarization. [23] Device according to claim 22, wherein the features include a particular wavelength. [24] Device according to claim 23, wherein one or more optical sources provide a plurality of spectral components which are tunable over different respective spectral bands, and the first section of the optical wave (714, 718) comprises a first spectral component, and the second section of the optical wave (714, 718) comprises a second spectral component which is different from the first spectral component. [25] Device according to claim 24, further comprising one or more optical sources. [26] Device according to claim 24, wherein the transmit aperture (202A, 400A, 400B, 611) is further configured as a receive aperture (100, 202B, 612, 613) in which an optical phased array is used to receive a third spectral component that is different from the first spectral component and different from the second spectral component. [27] Device according to claim 26, wherein the third spectral component has a wavelength between a wavelength of the first spectral component and a wavelength of the second spectral component, and the transmitted optical wave (714, 718) has no significant power at the wavelength of the third spectral component. [28] Device according to claim 24, wherein the transmitting aperture (202A, 400A, 400B, 611) is a first transmitting aperture and the transmitted optical wave (714, 718) is a first transmitted optical wave (714, 718), and the device comprises a second transmitting aperture configured to provide at least one beam of a second transmitted optical wave (714, 718) comprising at least one third spectral component that is different from the first spectral component and different from the second spectral component. [29] Device according to claim 28, wherein the second transmit aperture is further configured as a second receive aperture in which an optical phased array is used to receive the first spectral component. [30] Device according to claim 29, further comprising a coherent receiver (20, 20A, 20B, 2402) configured to capture the first spectral component received from the second receiving aperture by coherent mixing with a local oscillator derived from at least one optical source providing the first spectral component to the first transmitting aperture. [31] Device according to claim 28, wherein the third spectral component has a wavelength between a wavelength of the first spectral component and a wavelength of the second spectral component, and the transmitted optical wave (714, 718) has no significant power at the wavelength of the third spectral component. [32] Device according to claim 31, wherein the first transmitting aperture and the second transmitting aperture are located near a center of an arrangement of apertures, and at least some of the transmitting apertures (202A, 400A, 400B, 611) are located near edges of the arrangement of apertures. [33] Device according to claim 31, wherein a quantity of receiving apertures (100, 202B, 612, 613) in the arrangement of apertures is larger than a quantity of transmitting apertures (202A, 400A, 400B, 611). [34] Procedure that includes: Providing at least one beam of a transmitted optical wave (714, 718) along a transmission angle to a destination (204) from a transmitting aperture (202A, 400A, 400B, 611) of a transmitter, wherein the optical wave (714, 718) comprises at least a first section of the optical wave (714, 718), and a second section of the optical wave (714, 718) has a feature different from a feature of the first section of the optical wave (714, 718); and Receiving a combined optical wave (714, 718) at receiving apertures (100, 202B, 612, 613) from two or more receivers (2402), wherein at least one receiver (2402) comprises: a receiving aperture (100, 202B, 612, 613) located near at least one of the transmitting apertures (202A, 400A, 400B, 611) or a receiving aperture (100, 202B, 612, 613) of a different receiver (2402), an optical phased array within the receiving aperture (100, 202B, 612, 613), wherein the optical phased array is configured to receive at least one section of a collected optical wave (714, 718) arriving at the receiving aperture (100, 202B, 612, 613) along a respective collecting angle, a filter configured to filter the received section of the collected optical wave (714, 718) according to the characteristic of the first section of the optical wave (714, 718), and a detector (704) configured to provide a signal (2604) based on the filtered section of the collected optical wave (714, 718). [35] LiDAR system, which includes: an arrangement of two or more apertures configured to provide at least one beam of a transmitted optical wave (714, 718) from at least two of the two or more apertures to a destination (204), wherein the two or more apertures comprise: a first aperture (1001) which includes a first optical phased array within the first aperture (1001), and a second aperture which includes a second optical phase-controlled array within the second aperture; a transmitter subsystem configured to: to provide a first subset consisting of less than all of the two or more apertures of a first section of the transmitted optical wave (714, 718), wherein the first subset includes the first aperture (1001), and to provide a second section of the transmitted optical wave (714, 718) consisting of less than all of the two or more apertures, wherein the second section is different from the first section and the second aperture includes characterized by , that the optical wave (714, 718) comprises a second section which has a different feature from a feature of the first section of the optical wave (714, 718) and, that a receiver subsystem of the LiDAR system includes: a first filter configured to filter a section of a collected optical wave (714, 718) arriving at at least one of the two or more apertures in the arrangement according to the feature of the second section of the optical wave (714, 718), and a first detector configured to provide a signal (2604) based on the section of the collected optical wave (714, 718) filtered by the first filter. [36] LiDAR system according to claim 35, wherein the features include a particular wavelength, and the first section of the transmitted optical wave (714, 718) comprises light (2404, 2602) having a wavelength in a first spectral band, and the second section of the transmitted optical wave (714, 718) comprises light (2404, 2602) having a wavelength in a second spectral band that is different from the first spectral band. [37] LiDAR system according to claim 36, wherein the first filter is configured to filter a section of the collected optical wave (714, 718) arriving at the first aperture (1001), and the receiver subsystem further comprises: a second filter configured to filter a section of the collected optical wave (714, 718) arriving at the second aperture according to the characteristic of the first section of the optical wave (714, 718), and a second detector configured to provide a signal (2604) based on the section of the collected optical wave (714, 718) that is filtered by the second filter. [38] LiDAR system according to claim 37, wherein the transmitter subsystem includes a wavelength division multiplexing component configured to combine the light (2404, 2602) having a wavelength in the first spectral band with light (2404, 2602) having a wavelength in a third spectral band, wherein the second spectral band lies between the first spectral band and the third spectral band. [39] LiDAR system according to claim 36, wherein the arrangement of two or more apertures includes a third aperture which includes a third optical phased array within the third aperture, and the first filter is configured to filter a section of the collected optical wave (714, 718) arriving at the third aperture. [40] LiDAR system according to claim 39, wherein the transmitter subsystem includes a first wavelength division multiplexing component configured to combine the light (2404, 2602) having a wavelength in a first spectral band with light (2404, 2602) having a wavelength in a third spectral band, and a second wavelength division multiplexing component configured to combine the light (2404, 2602) having a wavelength in the second spectral band with light (2404, 2602) having a wavelength in a fourth spectral band, where the second spectral band lies between the first spectral band and the third spectral band, and the third spectral band lies between the second spectral band and the fourth spectral band. [41] LiDAR system according to claim 36, wherein the first filter comprises a tunable filter having a passband that is tunable over the second spectral band, and the receiver subsystem is configured to tune the first filter at least partially based on the light (2404, 2602) having the wavelength in the second spectral band. [42] Device according to claim 1, wherein the filter is located outside the optical phased array. [43] Method according to claim 34, wherein the filter is located outside the optical phase-controlled array.

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