KR20210141512A - Multi-Static Coherent Lidar - Google Patents

Abstract

At least one beam of light waves is transmitted along a transmission angle from a transmission aperture of the transmitter toward a target location. The light wave includes at least a first portion and a second portion having properties different from those of the first portion. The two or more receivers include at least one receiver, which is a receive aperture arranged proximate to at least one of a transmit aperture or a receive aperture of a different receiver, a collecting light wave arriving at the receive aperture along a respective collection angle. an optical phased array in the receive aperture, configured to receive at least a portion of

Description

Multi-Static Coherent Lidar

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a US Provisional Application Serial No. 62/821,427 entitled "Multi-Static Coherent LiDAR", filed on March 20, 2019, and entitled "Multi-Static Coherent LiDAR", filed on October 25, 2019 claims the benefit of U.S. Provisional Application Serial No. 62/926,085. The entire disclosures of each of the applications listed above are incorporated herein by reference.

technical field

The present disclosure relates to multi-static coherent LiDAR.

Some LiDAR systems use a single aperture to transmit and receive light (referred to herein as a “monostatic” aperture configuration). Alternatively, some LiDAR systems use two apertures in close proximity - one for transmitting and one for receiving (referred to herein as a “bistatic” aperture configuration). . Different systems optimize various aspects of LiDAR configuration based on different criteria. The light wave is transmitted to the target object(s) at a given distance from the light source and photons that are backscattered from the target object(s) are collected. The light source used in continuous wave (CW) LiDAR systems is typically a laser, which has a narrow linewidth and has a peak wavelength that falls within a specific range (e.g., between about 100 nm and about 1 mm, or some partial range thereof). Provides a light wave, which is also referred to herein simply as “light”. Some LiDAR systems may be designed to use either a monostatic or bistatic aperture configuration, depending on various tradeoffs that may arise in system performance and/or system design.

In one aspect, generally, an apparatus comprises at least one transmitter comprising a transmit aperture configured to provide at least one beam of a transmit optical wave along a transmit angle toward a target location, the light wave being a first of the light wave. at least comprising a portion and a second portion of the light wave having properties different from properties of the first portion of the light wave; and two or more receivers, wherein at least one receiver comprises: a receive aperture arranged proximate to at least one of a transmit aperture or a receive aperture of a different receiver, an optical phased array in the receive aperture, the optical phased array each configured to receive at least a portion of the collected light wave arriving at the receiving aperture along a collection angle of the filter, configured to filter the receiving portion of the collected light wave according to a characteristic of the first portion of the light wave, and at the receiving portion of the collected light wave and a detector configured to provide a signal based on the detector.

In another aspect, generally a method includes providing at least one beam of a transmit light wave along a transmit angle from a transmit aperture of a transmitter toward a target location, the light wave comprising at least a first portion of the light wave and a first of the light wave comprising a second portion of the light wave having properties different from properties of the portion; and receiving the collection light wave at the receive apertures of the two or more receivers, wherein at least one receiver has a receive aperture arranged proximate to at least one of a transmit aperture or a receive aperture of a different receiver; an optical phased array in the optical phased array configured to receive at least a portion of the collected light wave arriving at the receive aperture along a respective collection angle; and configured to filter the receiving portion of the collected light wave according to a characteristic of the first portion of the light wave. a filter configured to be used, and a detector configured to provide a signal based on the received portion of the collected light wave.

Aspects may include one or more of the following features.

Each detector includes a coherent detector configured to optically couple a receiving portion of the collected light wave with a local oscillator light wave to provide a combined light wave and detect the combined light wave to provide a signal.

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

Each signal includes an amplitude and a phase angle, and each component corresponding to that signal includes a quantity based on the amplitude and independent of the phase angle.

The circuitry is configured to convert each signal into digital form and process the signals in digital form to remove dependence on phase angles.

The at least one coherent detector provides an in-phase coupled light wave using a first local oscillator light wave and provides a quadrature coupled light wave using a second local oscillator light wave that is shifted with respect to the first local oscillator wave, It is configured to provide amplitude and phase angle in (In-phase/Quadrature, I/Q) space.

The circuitry is configured to perform a transform on the real-valued signal provided from one of the detectors to provide amplitude and phase angles in the complex space of the resulting complex transform of the real-valued signal.

Each detector is configured to produce a current representative of a difference between the photocurrents produced by the pair of balanced photodetectors.

The total amount of receive apertures is between 3 and 20.

The total amount of receive apertures is between 4 and 10.

The total amount of transmit apertures is 1.

The area of each receive aperture is equal to the area of the transmit aperture within a factor of 4/9 to 9/4.

The receive apertures are arranged along an axis in a plane in which the optical phased arrays are configured to provide steering of respective collection angles using the phases of the elements of the optical phased arrays.

Each of the optical phased arrays of receivers is configured to align a respective collection angle with a target position.

The transmitter includes an optical phased array within the transmit aperture.

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.

At least one optical phased array in at least one of the transmit aperture or the receive aperture is configured to steer the first angle using the phases of the elements of the optical phased array and steer the second angle using the wavelength.

the receiver is a first receiver, the receive aperture is a first receive 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 are a second a transmitting aperture configured as a second receiving aperture, a second optical phased array in the transmitting aperture, the second optical phased array collecting along a respective collection angle to reach the transmitting aperture; configured to receive at least a portion of the light wave, a second filter configured to filter the receiving portion of the collected light wave according to a property different from a property of the first portion of the light wave and different from a property of the second portion of the light wave, and a second filter and a second detector configured to provide a signal based on the filtered portion of the collected light wave that is filtered by

The apparatus further comprises circuitry configured to determine an estimated distance associated with the collected light wave based at least in part on a combination comprising a respective component corresponding to each of the two or more signals provided from the detectors of the two or more receivers. .

The transmitter applies linear frequency modulation to the transmitted light wave to enable the circuitry to determine the estimated distance.

The transmit aperture is further configured as a receive aperture wherein the optical phased array is used to receive at least a portion of the light wave having a property different from that of the transmit light wave, wherein at least one of the receive apertures receives a beam of the light wave having a different property It is used as a transport aperture to provide.

The characteristic includes at least one of a specific wavelength, a specific time slot, or a specific polarization.

Characteristics include specific wavelengths.

The one or more light sources provide a plurality of spectral components that are tunable across different respective spectral bands, a first portion of the light wave comprising a first spectral component and a second portion of the light wave different from the first spectral component. contains components.

The device further includes one or more light sources.

The transmit aperture is further configured as a receive aperture wherein the optical phased array is used to receive a third spectral component different from the first spectral component and different from the second spectral component.

The third spectral component has a wavelength between the wavelength of the first spectral component and the wavelength of the second spectral component, and the transmitted light wave does not have significant power at the wavelength of the third spectral component.

the transmit aperture is a first transmit aperture and the transmit light wave is a first transmit light wave, and wherein the apparatus comprises at least one of a second transmit light wave that is different from the first spectral component and includes at least a third spectral component different from the second spectral component. and a second transmit aperture configured to provide a beam.

The second transmit aperture is further configured as a second receive aperture through which the optical phased array is used to receive the first spectral component.

The apparatus is configured to detect a first spectral component received from a second receive aperture by coherent mixing with a local oscillator derived from at least one light source providing the first spectral component to the first transmit aperture. It further includes a configured coherent receiver.

The third spectral component has a wavelength between the wavelength of the first spectral component and the wavelength of the second spectral component, and the first transmitted light wave does not have significant power at the wavelength of the third spectral component.

The first transmit aperture and the second transmit aperture are located near the center of the arrangement of apertures, and at least some of the receive apertures are located near edges of the arrangement of apertures.

The amount of receive apertures is greater than the amount of transmit apertures in the array of apertures.

In another aspect, generally a LiDAR system is an arrangement of two or more apertures—two or more apertures, configured to provide at least one beam of a transmit light wave from at least two of the two or more apertures toward a target location. the apertures include a first aperture including a first optical phased array within a first aperture, and a second aperture including a second optical phased array within a second aperture, a first portion of a transmit light wave to a first subset consisting of fewer than all of the two or more apertures, the first subset comprising the first aperture, and a second portion of the transmitted light wave having fewer than all of the two or more apertures. to provide a second subset consisting of the number, the second subset being different from the first subset and comprising a second aperture, the second portion of the light wave having a property different from a property of the first portion of the light wave; a transmitter subsystem configured, a first filter configured to filter a portion of the collection light wave that arrives at at least one of the two or more apertures in the array according to a characteristic of the second portion of the light wave, and a collection filtered by the first filter and a receiver subsystem comprising a first detector configured to provide a signal based on a portion of the light wave.

Aspects may include one or more of the following features.

the characteristic includes a specific wavelength, the first portion of the transmitted light wave includes light having a wavelength in a first spectral band, and the second portion of the transmitted light wave includes light having a wavelength in a second spectral band different from the first spectral band includes

the first filter is configured to filter the portion of the collected light wave arriving at the first aperture, and the receiver subsystem is configured to filter the portion of the collected light wave arriving at the second aperture according to a characteristic of the first portion of the light wave. It further includes a second filter and a second detector configured to provide a signal based on the portion of the collected light wave that is filtered by the second filter.

The transmitter subsystem includes a wavelength division multiplexing component configured to combine light having a wavelength in a first spectral band with light having a wavelength in a third spectral band, wherein the second spectral band comprises the first spectral band and a third spectrum between the bands.

The arrangement of the two or more apertures includes a third aperture including a third optical phased array within the third aperture, the first filter configured to filter a portion of the collected light wave arriving at the third aperture.

The transmitter subsystem includes a first wavelength division 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 light having a wavelength in a second spectral band into a fourth spectral band. a second wavelength division multiplexing component configured to combine light having a wavelength of between the spectral bands.

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

Aspects may have one or more of the following advantages.

Using the techniques described herein, a LiDAR system can be optimized in a variety of ways. For example, in some implementations, for a given total device area (eg, both transmit and receive apertures) and a given light source output power, an increased number of backscattered photons are collected from the target object(s) while Background leakage light is reduced. Some implementations have implemented improved immunity to speckle effects due to interference from backscattered light from rough (eg, non-mirror) surfaces, and improved immunity to target locations where target objects can be expected. Enables improved performance for both long and short target distances.

Other features and advantages will become apparent from the following description, and from the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, in accordance with common practice, various features of the drawings are not to scale. In contrast, the dimensions of various features are arbitrarily enlarged or reduced for clarity.
1 is a schematic diagram of an example of a monostatic LiDAR system.
2 is a schematic diagram of an example of a bistatic LiDAR system.
3A, 3B, and 3C are plots of example simulation detection results.
4A and 4B are schematic diagrams of examples of apertures and corresponding speckle patterns received from a target.
5A, 5B, and 5C are schematic diagrams of example aperture arrays.
6 is a schematic diagram of an example of a multi-static LiDAR system.
7A, 7B, 8, and 9 are schematic diagrams of various portions of examples of multi-static coherent LiDAR systems.
10 is a schematic diagram of a WDM version of a multi-static aperture configuration.
11A and 11B are schematic diagrams of a WDM laser system using two or more apertures for different ranges of the spectrum.
11C is a schematic diagram of example WDM components that may be used with the system shown in FIGS. 11A and 11B .
11D is an example plot of guard bands of spectral responses of WDM components.
12A and 12B are plots of example spectral responses of drop and pass ports of a WDM component.
13 is a plot of an example of wider transmission bands.
14 is an example plot of closely aligned transmission bands.
15 is a schematic diagram of a generalized WDM version of a multi-static aperture configuration.
16A is a schematic diagram of an example WDM system for a particular aperture.
16B is a plot of example wavelength bands transmitted and received in the system of FIG. 16A.
17 is a schematic diagram of an alternative WDM system.
18 is a schematic diagram of an alternative WDM system.
19 is a plot of example wavelength bands for a WDM multiplexer with a dead zone between the bands.
20 is a plot of example interleaved wavelength bands for two WDM multiplexers.
21 is a schematic diagram of a portion of a LiDAR system.
22 is a schematic diagram of a portion of a LiDAR system with calibration elements and other photonic circuit elements.
23 is a plot of example interleaved wavelength bands for two WDM multiplexers.
24 is a schematic diagram of an example of a WDM optical configuration.
25 is a schematic diagram of an optical circuit configuration.
26 is a schematic diagram of an optical receiver configuration;
27 is a schematic diagram of an example of a portion of a LiDAR system.
28 is a schematic diagram of an example of a portion of a LiDAR system.
29 is a schematic diagram of an example of a portion of a WDM system.
30 is a schematic diagram of an example of an optical transmitter configuration.

For monostatic aperture construction, there are several approaches to multiplexing the aperture for both transmit and receive operations. For example, some approaches include (1) using a polarizer to transmit light in one polarization and receive light in an opposite (ie, orthogonal) polarization, (2) time domain multiplexing, and/or (3) This includes using irreversible devices such as circulators. Monostatic aperture configurations can use the entire available aperture space for both a transmit aperture to transmit a light beam towards a target location and a receive aperture to collect any backscattered light arriving at the same aperture; It can be difficult to achieve sufficiently high isolation between the transmit and receive paths in a LiDAR system so that the receiver can detect small reflections from the target object without being saturated by the outgoing transmit light. In a frequency modulated continuous wave (FMCW) LiDAR system, backscattering inside a monostatic system is a powerful low that can reduce the signal-to-noise ratio (SNR) for real target detection at higher frequencies. leading to frequency peaks. In a bistatic aperture configuration, light is transmitted from one aperture and received from a different aperture, forming a monostatic aperture at the cost of reduced sizes for both the transmit and receive apertures within the available aperture space. overcome the isolation challenges of

1 and 2 show examples of LiDAR systems using a monostatic aperture configuration 100 and a bistatic aperture configuration 200, respectively. Both systems include a laser 10 and a coherent receiver 20 used to mix the received light with the light of a local oscillator (LO) 30 . Laser 10 may be, for example, a CW laser with a narrow linewidth and low phase noise sufficient to provide a long enough temporal coherence length to perform coherent detection over time scales of interest. The monostatic aperture configuration 100 also includes a circulator 40 for redirecting light in different directions. In the monostatic aperture configuration 100 , the aperture 102 serves as both a transmit and a receive aperture, so the transmit angle of the path from the aperture 102 to the target location and back from the target location to the aperture 102 . The collection angle of the path to ) is substantially the same irrespective of the distance to the target location ( FIG. 1 ). On the other hand, in the bistatic aperture configuration 200, the path from the transmit aperture 202A to the target location 204 and the path from the target location 204 to the receive aperture 202B are different, and different transmission and collection angles give birth to them (Fig. 2). In some LiDAR systems, the transmission and collection angles are aligned to operate at an optimal target distance to the target location 204 . Consequently, operation at a greater target distance 206 or a shorter target distance 208 may provide sub-optimal performance. Also, since the usable area for apertures is divided between transmit and receive for bistatics, the bistatic configuration has lower space efficiency than the monostatic configuration.

Unless the surface of the target object is unpolished (such as the surface of a metal mirror) or otherwise configured as having a retro-reflective surface, backscattered light may be affected by the surface roughness of the target object. It experiences random phase fluctuations imposed. The fine features of most rough surfaces lead to 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 in the receive aperture. Due to the random walk nature of the interference pattern created by scattering from the extended surface with a randomized phase, the amplitude of the collected light has a Rayleigh distribution and the intensity of the collected light (of photons entering the receive aperture) proportional to the number) has an exponential statistical distribution. Thus, for example, if the transmit light beam is moved across a wall and on average 10 photons are collected again, then for most target locations the aperture will collect much less than 10 photons, and often the receiver will collect tens of photons. It can collect several photons and saturate the circuitry of the receiver's detection system. When the LiDAR system collects too few photons, the collection light may be buried under the background noise, and when too many photons are collected, the light may be outside the linear gain range of the detection system. 3A, 3B, and 3C show examples of simulation detection results on the effects of speckle of a LiDAR system. 3A shows a plot of the Rayleigh probability density for a particular normalized value of the electric field amplitude. 3B shows a corresponding plot of probability density versus exponential electric field strength. 3C shows a Monte-Carlo simulation of 1000 randomized trials for normalized intensity. A normalized average intensity value of 1 is shown in the plots of FIGS. 3B and 3C ( 300 ). As Figure 3c shows, when the average intensity is normalized to one, most trials correspond to values less than one while several separate trials yield much larger intensities.

Both monostatic and bistatic aperture configurations of a LiDAR system potentially suffer from potentially detrimental effects due to the speckle of the system's coherent receiver. When there is only one receive aperture whose size roughly matches the size of the transmit aperture, there is only one portion of a particular interference pattern (also called "speckle realization") that is detected at the receiver. This limits the detection probability of the receiver because of the exponential probability distribution of the signal collected from a single speckle realization.

For a given LiDAR system, typically the total usable area available for any number of transmit and receive apertures is the size or reticle of the system acceptable for a particular manufacturing process if the LiDAR system is fabricated in planar integrated optical flow. ) is limited by the size of In a LiDAR system with a multi-static aperture configuration, this usable area is used for one or more transmit apertures and two or more receive apertures in the aperture arrangement. The total area used for one or more transmit apertures divided by the total area used for two or more receive apertures is referred to as the "transmit-receive ratio". The total area used for the two or more receive apertures divided by the total area used for the total aperture arrangement is referred to as the "receive fill factor". These and other parameters can be optimized in various ways by appropriately designing the number of apertures and their sizes.

4A and 4B show examples of different transmit apertures with different sizes. For example, the transmit apertures may be a square-shaped area substantially filled by the area of a two-dimensional optically phased array (OPA) that transmits a beam of light that is steered by a characteristic of the array, as described in more detail below. have. Assuming there is no aberration in the system, for a particular transmit aperture 400A, 400B, the magnitudes W _A , W _B of the diffraction-limited transmit light beams 402A, 402B in the far field are transmitted It is inversely proportional to the size of the apertures 400A and 400B. These transmit light beams 402A, 402B strike the surface 404 of the target object and illuminate a specific area on the surface of the target object. Backscattered light from the illumination area of the target object creates speckle patterns 408A, 408B on aperture arrays 410A, 410B. The correlation length of the speckle pattern generated on the aperture array 410A, 410B is inversely proportional to the size of the illumination area 406A, 406B. Thus, the smaller transmit aperture 400B is converted to the faster changing speckle pattern 408B (eg, having light/dark features of the smaller size speckle pattern created by constructive/destructive interference). A larger transmit aperture 400A then leads to a slower changing speckle pattern 408A (eg, having the light/dark features of a larger size speckle pattern). The optimal quantity and size of the two or more receive apertures in each of the aperture arrangements may be different depending on the size of the transmit aperture. For example, in some implementations, the size of each of the receive apertures is the same or similar in size to the size of the transmit aperture (eg, within a factor of 1/2 to 2 in diameter and 1 in area to /4 to within a factor of 4 inches, or a diameter within a factor of 2/3 to 3/2 and an area within a factor of 4/9 to 9/4). In some implementations, the sizes of the receive apertures are approximately equal to each other, but the size of the transmit aperture can be larger (eg, 10% larger or 20% larger than the sizes of the receive apertures) by an amount. could be larger).

In some implementations, the aperture arrangement includes a collection of at least three apertures for use in a coherent LiDAR system, disposed in close proximity. At least one of the apertures is used as a transmit aperture for transmitting light towards a target location, and at least two of the apertures are used as receive apertures for receiving backscattered light originating from that transmit aperture. In a multi-wavelength LiDAR system, there may be different apertures selected as a single transmit aperture for a given center wavelength, and all remaining apertures are selected as receive apertures for that given center wavelength (potentially that center wavelength frequency chirp around). In a LiDAR system using optical phased arrays, as described in more detail below, the receive aperture can steer the collection angle using the optical phased array and the transmit aperture adjust the transmit angle using the optical phased array. can be steered Such optical phased arrays may have an array size (number of individual optically dispersed phase control elements) and a resulting transverse beam size that matches (or nearly matches) one another in size.

5A, 5B, and 5C show examples in which apertures are arranged linearly along one dimension, where the aperture size is shown as the width of apertures of the same square shape (in these examples the aperture size is other dimensions of height are towards the inside of the page). This type of linear aperture arrangement of N apertures (e.g., along the long side of the rectangular area available for the aperture arrangement) gives one transmit aperture of size 1/N as a fraction of the total available space. and fill the remainder of the usable aperture space with N-1 apertures whose size is also 1/N as a fraction of the usable aperture space. The percentage of total available aperture space used to receive light approaches 100% as the number of receive apertures increases. 5A, 5B, and 5C, N changes from 2 (FIG. 5A) to 3 (FIG. 5B) to 10 (FIG. 5C), and as the number of receive apertures increases (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). . However, the transmit-receive ratio also decreases (from 1 to 1/2 to 1/9). A tradeoff may occur between the receive fill factor and the transmit-receive ratio so that the optimal number of apertures can be selected for any given system design. For example, in some system implementations any value of N between 5 and 11 may provide an acceptable tradeoff. In other implementations, a wider range of values of N may be tolerated (eg, between 4 and 20), or there may be a value of N that maximizes certain performance parameters for given tolerances (eg, , N = 9). With an odd value of N, the transmit aperture can be located in the center of the aperture array (e.g., errors due to parallax effects on receive apertures furthest from the transmit aperture) to reduce) may be desirable in some implementations. Also, similar properties would hold for a two-dimensional arrangement of apertures in the usable aperture space of a square shape where the transmission aperture could still be near the center in both dimensions. Further, other examples may use two or more apertures as the transmit aperture, the remaining apertures may be used as receive apertures, and place the transmit aperture(s) in locations other than near the center.

In some implementations, the coherent detectors used to detect light received at each receive aperture are coupled together to perform incoherent combining (also called "incoherent averaging"), where detecting as coherent. The phased phasors are processed to recover the amplitudes, then their absolute or square values are optionally added to the different components of the combination with different weights. For example, in some implementations, coherent detection of each receive aperture may use an in-phase/quadrature (I/Q) detection scheme that uses two versions of an LO that are phase shifted 90 degrees with respect to each other. . This yields a two-dimensional phasor (in I/Q space) with angle and amplitude. In some implementations, the coherent detection of each receive aperture comprises a complex-valued transformation (eg, in the frequency domain) of a time domain signal (eg, a photocurrent from a single photodetector or pair of balanced detectors). can be computed, which also yields a two-dimensional phasor (in complex space) with angles and amplitudes. In either case, the angle of that phasor can be discarded and the amplitude of the phasor can be recovered for each of the coherent receivers. Then, across each of the (N-1) receivers, the corresponding amplitude (the absolute value of the phasor) or the square of the corresponding amplitude may be summed or otherwise combined. In some implementations, the summed values may be weighted in the summation differently for different receive apertures, where the weights may depend on various parameters (eg, a designed target distance). Discarding this angle of the phasor may sacrifice how quickly the mean value of the detection signal increases, but may provide a more stable signal (eg, with a lower standard deviation).

Even with a relatively large number of receive apertures, the size of the receive apertures remains large enough for each receive aperture to measure uncorrelated speckle realization, so that a monostatic or bistatic LiDAR system using a single receive aperture and increases speckle diversity of LiDAR receivers. As mentioned above, the probability distribution of the number of photons collected at each receive aperture is exponential. Also, the noise in each coherence detector has an exponential distribution. Without wishing to be bound by theory, one expression for the incoherent combination of k spatially incoherent apertures leads to Erlang distributions for both signal and noise.

Noise to Erlang(k, 1)

)Signal ~ Erlang(k,

)

Thus, when the detection probability is high (i.e., the threshold for the detected power level or the number of detected photons is high), incoherent averaging (e.g., a plurality of receive apertures of the same size as Without one receive aperture), there is a higher probability of a false alarm (ie, the threshold is exceeded due to noise photons rather than signal photons) compared to when there is incoherent averaging. However, when the detection probability is low, incoherent averaging has a higher false alarm rate. That is, when the probability of a false alarm requirement is less stringent (ie, a higher probability of a false alarm is acceptable), fewer speckle realizations (lower speckle diversity) are better. When the probability of a false alarm requirement is stricter (ie, a lower probability of a false alarm is acceptable), more speckle realizations (higher speckle diversity) are better.

Another useful feature enabled by the multi-static aperture configuration is that the mixing efficiency of the LiDAR system will be improved at short distances as the Fraunhofer distance required for far field operation is reached faster for smaller apertures. that it can In other systems, for objects at distances shorter than the assumed target distance, the far-field Fraunhofer distance may not have been reached. However, when the aperture size is smaller, as in some multi-static LiDAR systems, an object at a shorter distance can still be considered in the far field, and some advantages are still applicable.

In addition, various optimizations may be made for the individual receive apertures and the optical elements (eg, OPAs) used within each receive aperture. For example, the collection angle for each receive aperture can be tilted independently. In addition, the light collected by each receive aperture can be focused to optimize performance at different ranges.

6 shows an example of a LiDAR system using a multi-static aperture configuration 600 . For a given transmit angle 601 from transmit aperture 611 , first angle of collection 602 into receive aperture 612 and second angle of collection 603 into receive aperture 613 are independent can be tilted to Potential interference from the laser 10 light into the detectors of the coherent receivers 20A, 20B is reduced by using separate apertures for transmission and reception (as in bistatic configurations). If each aperture uses an OPA, the slope (eg, using phase steering and wavelength steering to control different angles) and focus (eg, using phases as well) of each OPA is , the LiDAR can be tuned on-the-fly to tune the range with the highest mixing efficiency.

Another example of a multi-static aperture configuration for a coherent LiDAR system is shown in FIG. 7A . In this example, laser 10 generates a transmit aperture after being modulated by modulator 702 (eg, using FMCW modulation, which imposes a linear chirp on a peak frequency corresponding to the transmit wavelength). Transmit (Tx) provides a light wave transmitted from the OPA. The group of OPAs 703 in respective apertures arranged proximate to each other includes eight receive (Rx) OPAs that provide different receive portions of the collecting light wave arriving at receive apertures comprising the Rx OPAs. . LO 30 is coupled with each of the receiving portions of the collected light wave, and the resulting combined light waves are detected coherently by detectors 704 . Detectors 704 are, for example, balanced detection using photodetectors coupled to yield an output current that is the difference between the photocurrents produced by the two photodetectors, and/or frequency to peak frequency. It can be implemented using homodyne detection that imposes a shift on the LO 30 . The resulting electrical signals provided by the detectors 704 are then subjected to processing using analog-to-digital (A/D) conversion where processing to recover the amplitude and discard the phase angle can be performed digitally. It may be processed in the including processing modules 706 . Also, these recovered amplitudes (or squares of amplitudes) may be weighted using amplitude control modules 708 . These potentially weighted amplitudes are then combined using circuitry 710 configured to perform the incoherent averaging described herein.

7B shows a LiDAR system 716 including a laser 10 coupled to a modulator 717 for transmitting a modulated light wave 718 from a transmit aperture, and other elements including other receive apertures and corresponding detectors. In this regard, an example of a detector 704 for detecting a light wave 714 received at the receive aperture is shown. The detector 704 includes a 90 degree phase shifter 720 for providing a phase shifted version LO_2 of the incoming local oscillator light wave LO_1. A set of 50/50 dividers 721 may combine lightwave 714 with different versions of the LO to perform I/Q detection. Detector 704 includes a first pair of photodetectors 722A, 722B for detecting an in-phase (I) signal based on a corresponding pair of photocurrents that may be subtracted in the balance detection arrangement, and subtraction in the balance detection arrangement. a second pair of photodetectors 724A, 724B for detecting a quadrature (Q) signal based on a corresponding pair of photocurrents that can be From all four of these photocurrents, the processing module 726 can extract the phase angle and amplitude associated with the light wave 714 . Other implementations of detector 704 are also possible.

8 is a multi-static for a coherent LiDAR system 800 illustrating a beam steering and focusing arrangement and optical couplers for a transmit (Tx) OPA 802 and two receive (Rx) OPAs 804 , 806 . An example of a part of an aperture configuration is shown. Manipulation may be performed along angular directions in a transverse direction (eg, polar and azimuth) of the polar coordinate system, wherein steering in one angular direction is performed by the phase shifters 808 and steering in another angular direction is It is done by wavelength (as shown in Figure 8). Adjustment of the transmit angle for the Tx OPA 802 and the collection angles for the Rx OPAs 804 , 806 in the phase control angular direction allows the phases imposed by the phase shifters 808 to be tuned quickly. So it can be done dynamically. The light beam transmitted by the Tx OPA 802 may have a non-linear phase front imposed on it by the phase shifters 808 . Also, this dynamically adjusted phase front can tune the depth of focus of the Rx OPAs 804 , 806 . Also, in the longitudinal direction, the phased arrays may steer in predetermined or dynamically tuned directions but tuning the gratings in this way may be more challenging or consuming more power. Nevertheless, having multiple receive apertures allows the designer to optimize the system to detect objects at different distances as needed depending on the situation.

9 is a coherent LiDAR system 900 showing the transmit path from transmit OPA 904 to object 902 and the resulting collection paths from object 902 to receive OPAs 906A, 906B, 906C, 906D. shows an example of a part of a multi-static aperture configuration for The paths unfold in a plane parallel to the axis along which the apertures containing the OPAs are arranged. In this example, this plane is the same plane in which the phase control angle direction is steered. These paths may be collectively configured to align to a particular target location, shown in this example hitting the target object 902 at a particular convergence distance 908 . Also, the OPAs may be focused according to the hypothesized convergence distance 908 .

In some implementations, apertures in the aperture arrangement may be multiplexed for different center wavelengths to which frequency modulation and/or frequency steering may be applied. In this way, the wavelength division multiplexing (WDM) version of the multi-static aperture configuration can assign different combinations of apertures as transmit aperture and corresponding receive apertures for different center wavelengths. Thus, the center wavelengths of each wavelength band are sufficiently far apart with appropriate guard bands between them so that there is strong isolation (eg, low emission) between light waves (and resulting signals) using different center wavelengths. Since they are spaced apart, operation for any given central wavelength can achieve the operating characteristics described above.

10 shows an example of a WDM version of a multi-static aperture configuration 1000 where 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, the first band is from 1500 nm to 1525 nm, the second band is from 1525 nm to 1550 nm, the third band is from 1550 nm to 1575 nm, and the fourth band is from 1575 nm to 1600 nm. Appropriate portions of the ends of each band may be used as guard bands. Some apertures may combine a plurality of spectral components (or “wavelengths”) of a light wave within different respective spectral bands (or “wavelength bands”) for transmission using a WDM combiner. For example, aperture 1001 combines first and third wavelength bands using WDM combiner 1010, and apertures 1002 and 1003 each have one wavelength band (second and fourth bands, respectively). ), so the WDM combiner is not used. The optical paths in this example include microring resonators as directional wavelength filters for receiving specific wavelengths within specific wavelength bands as described in more detail below. Alternatively, any other wavelength filters may be used on the receive path to select wavelengths that are not transmitted for that aperture.

Some implementations of a multi-static coherent LiDAR system may be configured to use other forms of diversity by using different light waves with different characteristics in addition to or instead of the diversity provided by WDM. For example, time division multiplexing within different time slots may be used, polarization diversity may be provided by using orthogonal polarizations, and the area of an aperture transmits and receives for different sets of apertures along the second dimension. Spatial diversity may be used by partitioning into different regions along a first dimension used to

As described above with reference to FIGS. 1 and 2 , some systems for coherent LiDAR use a single aperture to transmit and receive light (monostatic), and some systems close the two apertures in close proximity. Use - one for transmitting and one for receiving (bistatic). Instead, by using three or more apertures, it is possible to achieve high aperture utilization of the monostatic system while maintaining the high isolation of the bistatic system, provided that the size of each aperture remains the same. In addition, a multistatic optical phased array configuration (eg, as shown in FIG. 6 ) provides the system with speckle diversity (which increases the probability of detection) and reduces or eliminates angular gaps in the far field.

For optical phased arrays using distributed antenna elements, steering in one axis is achieved by changing the wavelength of the source (eg, as shown in FIG. 8 ). The high power, widely tunable laser source that enables LiDAR to be built around such an optical phased array is (1) limited spectral range of usable laser gain medium, (2) nonlinear losses of silicon waveguides, and ( 3) Can be a challenge for silicon photonics due to the achievable saturated output power of semiconductor optical amplifiers. Combining a wavelength division multiplexer on the transmit and receive modules in a multistatic aperture configuration, for example, reduces the power, perhaps to any one waveguide, and reduces the spectral coverage requirement of any one laser line and , reducing the complexity of the LiDAR by reducing the required output power in any one laser line.

A remaining challenge for WDM systems is to achieve high (eg nearly 100%) coverage of a wavelength band with low losses. In the transition region between the two bands of a typical WDM system, there is a loss penalty between the two subbands. By transmitting different wavelengths from different sub-apertures of the multistatic system, this transition region is greatly reduced or completely eliminated, reducing or eliminating angular gaps in transmission. Upon reception, angular gaps may also be eliminated. The narrow band time-varying wavelength division multiplexer allows high isolation between the receive and transmit channels and can be locked to the local oscillator.

In a system with a multistatic aperture configuration, in the presence of speckle returns reflected from the target, each of these sub-apertures measures an independent speckle realization, increasing the speckle diversity of the receiver and thus of the detection of the system. They can be combined non-coherently to increase the probability. In the example of FIG. 7A, the receiver area is 89% of the total aperture area of the system, which provides a 2.5 dB increase in receive area for a bistatic system or only a -0.5 dB penalty compared to a monostatic system.

Configurations, such as those described herein, are capable of (1) increasing the speckle diversity of a receiver; (2) increasing the fractional utilization of the receiver relative to the total aperture area (eg, using WDM); (3) reducing the size of the angular gaps of the far-field system by increasing the spot size (discussed in the Spectral Coverage section below); (4) It can serve any of a variety of purposes, including maintaining high isolation between transmit and receive by splitting the apertures.

As mentioned above, WDM uses two or more apertures and connects each aperture to a different source (eg, different lasers or different lines of the same laser) that covers a different portion of the total optical spectrum. It is one technique for improving the field of view and spectral coverage of the laser.

The following are further examples of a photonic chip with an optical phased array LiDAR or other laser system that transmits light of different wavelength bands from different apertures with at least two apertures used in the transmission regime. 11A and 11B illustrate examples of such a structure 1100 that may provide various advantages including one or more of the following: (1) increasing the total emission power of the system while keeping the individual waveguide power low. , (2) lowering the emission intensity and distributing the emission power to aid eye safety (if the total emission power is the same), and (3) increasing the field of view of the OPA by increasing wavelength coverage.

)은 하나의 애퍼쳐(1101)가 다른 파장(

)을 수신하는 동안 레이저 1로부터 동일한 애퍼쳐(1101)를 통해 보내질 수 있고, 해당 다른 파장은 또 다른 애퍼쳐(1102)가 제1 파장(

)을 수신하는 동안 레이저 2로부터 동일한 애퍼쳐(1102)를 통해 보내질 수 있다. 이 접근법은, 사용가능한 애퍼쳐 전체가 상이한 파장들에서라도 광을 능동적으로 전송하고 수신하기 때문에, 면적 사용을 최적화한다. 도 11a는 상이한 레이저들로부터의 2개의 파장들의 상이한 튜닝 범위들의 예를 도시한다. 도 11b에서 보여질 수 있는 바와 같이, 하나의 애퍼쳐로부터 전송된 광은 물체로부터 후방산란하고 다른 애퍼쳐에서 수신되며, 이는 아래에서 더 상세히 설명되는 바와 같이 혼신(crosstalk)을 감소시킨다.The receive operation may be performed on one or more apertures. For example, one wavelength (

) indicates that one aperture 1101 has a different wavelength (

) can be sent through the same aperture 1101 from laser 1 while receiving the other aperture 1102 at the first wavelength (

) can be sent through the same aperture 1102 from laser 2 while receiving. This approach optimizes area usage because the entire available aperture actively transmits and receives light even at different wavelengths. 11A shows an example of different tuning ranges of two wavelengths from different lasers. As can be seen in FIG. 11B , light transmitted from one aperture backscatters from the object and is received at the other aperture, which reduces crosstalk as described in more detail below.

에서 송신,

에서 수신하고, 컴포넌트 WDM2가

에서 송신,

에서 수신하는 방식으로 구성된다.11C shows an example of two WDM multiplexer components (WDM1 and WDM2) that may be used for wavelength multiplexing in structure 1100 . These components are configured by component WDM1 in an add/drop multiplexer configuration.

sent from,

Received from, component WDM2

sent from,

It is configured in such a way that it is received from

Typically, the spectral response of WDM components, such as coupling components WDM1 and WDM2 and other wavelength dependent filters, does not necessarily have to have an ideal box-shaped shape. Thus, there is an area between the adjacent alternating spectral responses of the WDM components WDM1 and WDM2 shown in FIG. high. As can be seen in FIG. 12A , the lasers driving each of the apertures may be scanned over respective laser sweep ranges 1201 and 1202 shown in the shaded areas. The sweep ranges of the lasers (also referred to as “scanning ranges”) may overlap, or may be arranged adjacent to each other without overlap as shown in FIG. 12A . The drop responses for the transmit port (ie, drop port) of the two WDM components are shown as curves with high power (about 0 dB) over the laser sweep ranges 1201 and 1202 of the lasers with little or no transmission loss. do. The penetration responses for the receive port (ie, the penetration port) of the two WDM components are shown as curves with low power over the laser sweep ranges 1201 and 1202 . The WDM spectral response at the receive power level, even though the sweep ranges of the two lasers are perfectly aligned, as can be seen in FIG. There is still a dead area 1205 that does not have adequate receive coverage because the values are low (less than -3 dB).

As can be seen in FIG. 13 , when the laser of each of the apertures is swept across wider shaded areas that extend to -3dB power reduction levels of the spectral responses of the WDM components, there are practically no high-loss dead areas, Laser light can experience a power reduction of up to 3 dB at transmit and up to 3 dB at receive.

One technique for mitigating high loss guard band dead regions is to increase the number of apertures, in which wavelength ranges not covered by apertures/receivers in one part of the system are not covered by one or more other apertures of the system. It is guaranteed to be processed by the listeners/receivers.

For example, as shown in FIG. 14 , three WDM components with shifts in spectral responses would create a system in which all wavelengths are covered at relatively high transmit power levels (shown across shaded regions). wherein each laser is detected by at least one aperture/receiver at a time at a relatively high receive power level. Nevertheless, these systems may still suffer from a lack of space efficiency, as only a third of the total area of the lidar at certain wavelengths detects a particular channel.

In some implementations of the techniques disclosed herein, the receive circuitry includes a tunable WDM component (eg, a tunable filter) that is fixed to a corresponding transmit wavelength being received. One way to achieve this problem is to have only the transmit light pass through WMD multiplexers (eg, fixed WDM multiplexers) and the receive light is detected before reaching the WDM multiplexers.

For example, a typical example transmit and receive WDM architecture for a system includes at least two apertures and transmits light in a set of one or more wavelength band(s) in each of the one or more corresponding apertures. Further, each aperture is configured to receive light in a set of wavelength band(s) that are complementary to the transmit band(s) for that aperture. Such an architecture may be used, for example, to construct a LiDAR system to achieve advantages, which may include a speckle diversity receiver, high aperture fill factor, wide field of view, low loss, and/or absence of a field of view coverage gap. may include

Such an architecture may be implemented, for example, on a silicon photonic chip to provide an optical phased array LiDAR system that uses wavelength division multiplexing in transmission to couple a plurality of laser lines into a single optical phased array aperture.

In some implementations, the tunable wavelength division multiplexing optical circuit can be configured to use a tunable photon ring and photo detectors to lock the receive circuit on the wavelength of a local oscillator as described in more detail below.

을 송신하도록 구성된다면, 동일한 애퍼쳐(1001)로부터 송신되는 파장들의 제2 범위는 이 범위로부터의 소정의 파장 분리를 가져야 한다(예를 들어,

는 1550-1575nm 범위에 있다). 따라서, 제1 애퍼쳐에서 이용되는 WDM 결합기(1010)(예를 들어, 고정 WDM 다중화기)는

,

범위들 중 어느 하나의 송신 파워에도 영향을 주지 않고 (1525-1550nm 범위의, 이 애퍼쳐에 대한 보호 대역 역할을 하는)

에서 손실 응답을 가질 수 있다. 이 예의 제4 파장 범위는 1575-1600nm 범위의

에 대응한다. 이러한 파장 범위들은 예들로 주어지며 실제 파장 범위들은 응용 및 설계 제한들에 적합한 것일 수 있다는 것에 주목해야 한다.As a generalization of the example shown in FIG. 10 , FIG. 15 shows a configuration 1500 in which each aperture is arranged in such a way that it transmits a set of wavelength bands and receives all other wavelength bands. Each wavelength band defines a channel that can be used to transmit at one aperture (as transmit band) and receive at another aperture (as receive band). To avoid loss of transmission from WDM multiplexers _{, each of the transmission bands (such as Tx 1} and Tx ₃ ) is separated by at least one channel as a guard band. The receive bands are tuned to follow the wavelength of the transmit laser transmitted from the different apertures. For example, in FIG. 15 , the topmost aperture transmits (Tx ₁ , Tx ₃ , ...) and receives (Rx ₂ , Rx ₄ , ...). The channels received at aperture 1 are not transmitted from the same aperture, and the tunable WDM (filter bank) response follows the wavelengths of (Tx2, Tx4, ...) emitted from the different apertures. If only one wavelength (for a particular channel/wavelength band) is transmitted from each aperture, all other channels can be received from the same aperture, and the transmitting portion of the optical system for that aperture (i.e., the transmitter Subsystem) is not required for any WDM multiplexers. For example, as can be seen in FIG. 10 , the system can be installed from the first aperture 1001 (in the range of 1500-1525 nm).

A second range of wavelengths transmitted from the same aperture 1001 must have some wavelength separation from this range (eg,

is in the range of 155-1575 nm). Thus, the WDM combiner 1010 (eg, a fixed WDM multiplexer) used in the first aperture is

,

without affecting the transmit power of any of the ranges (which serves as a guard band for this aperture, in the range 1525-1550 nm)

may have a lossy response. The fourth wavelength range in this example is in the range of 1575-1600 nm.

respond to It should be noted that these wavelength ranges are given as examples and that actual wavelength ranges may be suitable to application and design limitations.

In the example shown in FIG. 10, not all apertures require a WDM combiner, such as combiner 1010 used in aperture 1001 (or other fixed WDM multiplexer) for transmit channels. For example, apertures 1002 and 1003 each transmit only one channel and thus do not require a fixed WDM multiplexer. Microrings (or any other tunable wavelength drop filters) may be used on the receive paths of the receive portion of the optical system (ie, the receiver subsystem) to select wavelengths that are not transmitted from that aperture. For the examiner, in the case of a microring used as a tunable filter, the free spectral range (FSR) corresponding to the wavelength distance between the high transmission peaks is equal to each wavelength band (e.g., of the example wavelength bands given above). may be chosen large enough to span at least 25 nm). Potential reasons not to attempt to receive a particular channel of light transmitted from a particular aperture from the same channel of light collected at the same aperture include: 1) The transmitted light is usually several orders of magnitude stronger than the collected light and , tuning the filter to the transmitted wavelength can damage the filter or cause nonlinearities in the optical response; 2) if the receive filter picks up a specific wavelength in the return path, it affects the same wavelength in the transmit path and induces unwanted losses in the transmission; 3) The transmit light is much stronger, and any backscatter from the aperture dominates the receive light at the same wavelength.

A potential technical problem is that receive tunable WDM components (eg, tunable filters) must be tuned (eg, fixed) synchronously to transmit wavelengths from different apertures. Some implementations may be configured to use the local oscillator light generated from the transmit light as a reference for tuning. For example, referring to FIGS. 16A and 16B , the WDM system 1600 ( FIG. 16A ) for a particular aperture has a shaded wavelength in the laser sweep range SR2 (1525-1550 nm) and laser sweep range SR4 (1575-1600 nm). It is designed to transmit light in the areas (FIG. 16B). Accordingly, the wavelength regions of the reception range RR1 (1500-1525 nm) and the reception range RR3 (1550-1575 nm) can be received on the return path. One tunable microring is used to pick up the return signals in each of the respective reception ranges RR1 and RR3. Microring M3 is tuned to laser LP3 in the range RR3 (1550-1575 nm), and microring M1 is tuned to laser LP1 in the RR1 (1500-1525 nm) range. A portion of the laser light from these lasers (used for transmission at other apertures and “pickoff” at this aperture) is injected into the receive blocks as local oscillators (LO). of the local oscillator light picked off by the 5% directional couplers, as indicated by the arrow at a wavelength near the middle of the reception range RR3 in FIG. 16B and the corresponding arrows shown in FIG. 16A along the path of light at that wavelength. If the portion is minimized at the photodetector D1 (eg photodiode detector) by tuning the microring M3, it will pick up the correct return signal from the aperture as the microring M3 will be locked to the local oscillator signal. A similar tuning procedure can be performed to tune the microring M1 by minimizing the photodetector D3. A potential advantage of this tuning procedure, compared to trying to maximize the collection return signal, is that it eliminates the probability of being stuck on the wrong laser line because there are multiple transmit/backscatter and collection laser lines in the return path.

A similar but slightly different WDM system configuration 1700 is shown in FIG. 17 . The difference between systems 1600 and 1700 is that the photodetectors D2 and D4 of system 1700 are minimized to ensure that they are fixed relative to the transmit laser. Also, this particular aperture of the system 1700 is designed to transmit light in the wavelength ranges SR2 (1525-1550 nm) and SR4 (1575-1600 nm). Thus, the wavelength ranges RR1 (1500-1525 nm) and RR3 (1550-1575 nm) may be received in the return path. One microring M1 and M3 is used to pick up the return signal in each of the respective wavelength ranges. Microring M3 is tuned to a laser in the RR3 (1550-1575 nm) range, and Microring M1 is tuned to a laser in the RR1 (1500-1525 nm) range. A portion of the laser light from these lasers is injected into receiving blocks as local oscillators (LO). As in Fig. 16a, the arrows in Fig. 17 show the path of the injected light, and if the portion of local oscillator light picked off by the 5% directional couplers is minimized at photodetector D2 by tuning microring M3, then microring M3 is Since it will be locked to the local oscillator signal, it will pick up the correct return signal from the aperture. A similar tuning procedure can be performed to tune the microring M1 by minimizing the photodetector D4.

A similar but slightly different WDM system configuration 1800 is shown in FIG. 18 . Similar to the system of FIG. 16A , the photodetectors D1 and D3 are minimized to ensure locking the tunable wavelengths of the microrings M1 and M3 to the transmitted laser wavelength being picked off (transmitted from another aperture). .

Various other techniques can be used to ensure that the apertures of the LiDAR system can transmit and receive light simultaneously in different parts of the optical spectrum. The wavelength ranges can be adjusted in such a way that neither spectral range is blocked. Fixed WDM devices may be used to couple the transmit light to the output, and tunable filters may be used on the receive path to selectively detect each receive band. To lock the tunable filters to the transmit laser wavelength at each instant (for different apertures), 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 picked up accidentally.

In LiDAR systems that rely on wavelength sweeping to cover a large field of view, the present invention 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 gain medium. The techniques described herein may have any of a variety of advantages.

For example, some implementations have 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, 200nm total spectral coverage around 1550nm enables 24°+ vertical FOV.

Cost savings: Receive apertures use 75% of the total aperture area.

Robustness: Self-calibrating structures ensure performance over temperature and lifetime.

Safety: A multi-aperture receiver with speckle diversity can double the detection probability.

The challenge of multichip sweeping systems is to achieve 100% coverage of the wavelength band with low loss as described above.

19, for a single WDM multiplexer 1900, a dead zone 1902 between the laser tuning ranges 1904 for channels coupled by the WDM multiplexer 1900 as described above. )This can be.

Alternatively, as shown in FIG. 20 , using two or more WDM multiplexers for different respective apertures results in more spectrum (eg, including the dead zone portion of the spectrum between WDM channels). It can ensure that it is covered by other WDM multiplexers. Thus, the dead zone of one WDM component (used as the first multiplexer 2000) is substantially aligned with the passband of another WDM component (used as the second multiplexer 2002). Within each passband, the wavelength of the corresponding laser may be swept to cover substantially the entire passband. This pair of multiplexers is then, in this example, interleaved with laser tuning ranges 2004 of first multiplexer 2000 and laser tuning ranges 2006 of second multiplexer 2002 without any dead zone. As shown, it provides a substantially continuous range of wavelength tunability for the transmitter system. The resulting light wave can be used for a transmit signal and a corresponding local oscillator signal to be used for coherent reception in a receiver system. Also, the filter (eg, microring resonator) of the receiver system may have a narrow passband that is swept with the sweep of the corresponding laser as described above.

In some implementations, multiple apertures may be used to receive and transmit different sets of wavelengths, but the receive apertures and transmit apertures may be separated. 21 shows an example of a portion of a LiDAR system including a WDM system 2100 comprising: transmit (Tx) apertures in the middle of a set of 8 apertures Tx Aperture 1 and Tx Aperture 2; receive (Rx) apertures on either side of the transmit apertures Rx Aperture 1, Rx Aperture 2, Rx Aperture 3, Rx Aperture 4, Rx Aperture 5 and Rx Aperture 6; 8 wavelength sources (eg, a plurality of lasers or a plurality of lines of one laser), a circuit for coupling to a phase shifter driver application specific integrated circuit (ASIC) 2102 , and a LiDAR The system's analog front-end ASIC (2104). Receive apertures 1-6 consist of coherent receivers whose electronic output is coupled by an analog front-end ASIC 2104 . The phase shifter driver ASIC 2102 controls the phase of the overall phase shifters of both the transmit and receive apertures.

22 shows a portion 2200 of such a LiDAR system (showing only 4 of 6 receive apertures) that includes calibration elements. A set of calibration elements 2202 coupled to the end (or start) of each phased array within each aperture ensures that the beam from/to each aperture is diffraction limited and the apertures are correct. ensure that they are oriented in the directions. Various types of photonic circuit elements, eg, elements of a photonics integrated circuit (PIC), may be used on transmit side photonic circuits 2204A and 2204B and receive side photonic circuits 2206 . Since the power levels of the receiving side are lower than that of the transmitting side, the type of WDM filtering/routing performed at the receiving side may be different from the WDM filtering/routing performed at the transmitting side. For example, microring-based resonator filters that cannot be used on the transmit side due to the power processing limitations of microring-based resonator filters can be used on the receive side (without a large spectral dead zone). Since the receivers can operate without a dead zone, each receive aperture can pick up a signal from all of the transmit apertures (in this case, two transmit apertures). The receive apertures may be coherent and may use a local oscillator (LO) derived from the same light being transmitted from the Tx apertures. As can be seen in FIG. 22 , the portion of light after transmit WDM multiplexing circuits 2204A and 2204B may be collected and fed to receive WDM filter circuits 2206 . One waveguide tap will carry the LOs from the output of WDM multiplexing circuit 2204B with light from even numbered lasers, and another waveguide tap will carry the LOs from the output of WDM multiplexing circuit 2204A with light from odd numbered lasers. will pass on 23, in a generalized example of such WDM multiplexing circuits, odd range multiplexer 2300A combines light from odd numbered lasers, which is transmitted to Tx aperture 1 and tapped to provide LO_1 , an even range multiplexer 2300B combines the light from the even numbered lasers, which is transmitted to Tx aperture 2 and tapped to provide LO_2. Since the lasers fed to the Tx arrays are all tunable and swept across their specific spectral band, the collection of laser lines in the LO paths is such that each tooth of the comb independently moves back and forth within that range. It will look like combs of laser lines, where the number of each laser and corresponding spectral band indicates where it occurs in evenly spaced and offset sets of spectral bands. For example, FIG. 23 shows a laser tuning range 2302 for a first spectral band occurring between the laser tuning ranges 2304 for the second and fourth spectral bands.

Referring to FIG. 24 , a WDM optical configuration 2400 includes coherent receivers 2402 comprising microrings that can be continuously/constantly tuned to the instantaneous wavelength of receive light 2404 . For example, each microring may be tuned to an individual line of receive comb 2406 . There are also LO microrings of coherent receivers 2402 that can be used to track the wavelength of the LO lines (in odd-numbered spectral bands) or the corresponding line of LO lines 2 (in even-numbered spectral bands).

25 shows an alternative optical circuit configuration 2500 for delivering LO lines to receivers. The 2x2 combiner 2502 may combine the two collections of tapped LO lines with interleaved/staggered guard bands after the two WDM multiplexers 2504 . Each output of the coupler will receive half of the light from each tap and the two outputs will contain all the laser lines needed by the coherent receivers. The LO light is then split between the receivers in such a way that all the laser lines are provided to all the receivers. Configuration 2500 also includes demultiplexers using LO light and in-phase and quadrature (IQ) detectors 2506 .

Referring to FIG. 26 , which is an example of an optical receiver configuration 2600 , an LO signal 2604 comprising a multiplexed collection of LO lines is fed to IQ receivers using a microring tuned for that particular IQ receiver. It is mixed with light 2602 that is collected from the receive optical phased arrays (Rx lines). In this example configuration, all of the IQ receivers are cascaded to the same waveguide using different respective microrings. Each receive aperture includes such an optical receiver configuration 2600 comprising a series of such filtering receivers IQ 1 , IQ 2 , ... covering all wavelengths received at that aperture. The microring (or other optional filter) is tuned in synchronization with the tunable lasers in such a way that each microring picks up one LO line and one Rx line. Since the received signal is only a delayed and attenuated version of the laser light transmitted into the environment, the wavelengths of the LO line and the corresponding received signal are essentially the same. Thus, given enough bandwidth to accommodate the chirps of the laser, the same filter can pick them up simultaneously. As in frequency-modulated continuous-wave (FMCW) systems, the frequency of the laser can be chirped as a function of time so that the instantaneous frequency of the delayed return signal and the emitted light (and LO) is slightly different leading to beat frequency notes at the receiver. This fine frequency chirp allows the two laser lines to be slightly mismatched in frequency as mentioned above, which can be covered by the filter.

26, the LO and Rx signals when supplied from both sides will propagate counterclockwise (CCW) and clockwise (CW), respectively, inside each of the microring filters, to the left of each IQ detector. and to the right waveguides, respectively. The filter may be any other narrow band filter with two outputs, including higher order resonance based filters or other types of filter. The filter may be configured to have a passband narrow enough not to interfere with other WDM lines and wide enough to pass the LO and frequency offset delay signals.

27 and 28 show portions of example LiDAR systems that use combiners to route WDM light in different ways. In FIG. 27 , the receive portion of the WDM system 2700 may be configured to include 2x2 combiners 2702 after different pairs of receive apertures. WDM light collected by adjacent apertures may be coupled to odd and even output ports for more coherent detection. That is, for each laser line, if the phases of the light collected by apertures 1-2, 3-4, etc. are the same or different, the entire light for that specific wavelength is supplied to one set of receivers, and to one receiver. The signal-to-noise ratio for that is increased while the other receivers get no light at that wavelength.

As shown in FIG. 28 , this can be further extended in the receive portion of the WDM system 2800 configured to include 4x4 combiners 2802 after different sets of four receive apertures. Alternatively, referring to FIG. 29 , a series of 2x2 dividers, 3dB combiners 2902 , is a higher-order phase received at a super-aperture consisting of a collection of four adjacent Rx apertures Rx_1 , Rx_2 , Rx_3 , Rx_4 . Can be placed in the return path to collect the higher order spatial modes of the front 2904, the even and odd modes are combined with the LO combs in different respective Rx rings (Rx_1 ring, Rx_2 ring, Rx_3 ring, Rx_4 ring) is provided on

30 shows two WDM multiplexers 3004A and 3004B for even-numbered and odd-numbered wavelengths, respectively, in which a 2x2 combiner 3002 illuminates a line at all wavelengths from both transmitters (Tx_1 and Tx_2). An example optical transmitter configuration 3000 is shown disposed between two transmitter OPAs 3006 .

Although the present disclosure has been described in connection with specific embodiments, the present disclosure is not intended to be limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, the scope of which is It should be understood that the broadest interpretation is intended to be accorded so as to encompass all such modifications and equivalent structures permitted by law.

Claims (43)

As a device,
at least one transmitter comprising a transmit aperture configured to provide at least one beam of a transmit optical wave along a transmit angle towards a target location, the light wave comprising a first portion of the light wave and the light wave at least a second portion of said light wave having properties different from properties of said first portion; and
2 or more receivers
comprising, at least one receiver
a receive aperture arranged proximate to at least one of the transmit aperture or a receive aperture of a different receiver;
an optical phased array within the receive aperture, the optical phased array configured to receive at least a portion of a collection light wave arriving at the reception aperture along a respective collection angle;
a filter configured to filter a receiving portion of the collected light wave according to a characteristic of the first portion of the light wave, and
a detector configured to provide a signal based on a filtered portion of the collected light wave
A device comprising a. The coherent detector of claim 1 , wherein each detector optically couples a receiving portion of the collected light wave with a local oscillator light wave to provide a combined light wave and detects the combined light wave to provide the signal. Including device. 3. The apparatus of claim 2, wherein there is a frequency shift between the local oscillator and the transmitted light wave to enable heterodyne detection in coherent detectors. 3. The apparatus of claim 2, wherein each signal comprises an amplitude and a phase angle, and each component corresponding to that signal comprises a quantity based on the amplitude and independent of the phase angle. 5. The apparatus of claim 4, wherein the circuitry is configured to convert each signal to digital form and process the signals in digital form to remove dependence on the phase angles. 5. The second local oscillator of claim 4, wherein the at least one coherent detector provides an in-phase combined optical wave using a first local oscillator light wave and is shifted relative to the first local oscillator wave. An apparatus configured to provide a quadrature combined optical wave using an oscillator light wave and to provide the amplitude and phase angle in in-phase/quadrature (I/Q) space. 5. The circuit of claim 4, wherein the circuitry is configured to perform a transformation on a real-valued signal provided from one of the detectors to provide the amplitude and phase angles in the complex space of the resulting complex transform of the real-valued signal. Device. The apparatus of claim 2 , wherein each detector is configured to produce a current representative of a difference between photocurrents generated by a pair of balanced photodetectors. 2. The apparatus of claim 1, wherein the total amount of receive apertures is between 3 and 20. 10. The apparatus of claim 9, wherein the total amount of receive apertures is between 4 and 10. 10. The apparatus of claim 9, wherein the total amount of transmit apertures is one. 2. The apparatus of claim 1, wherein the area of each receive aperture is equal to the area of the transmit aperture within a factor between 4/9 and 9/4. The method of claim 1 , wherein the receive apertures are arranged along an axis in a plane in which the optically phased arrays are configured to provide steering of the respective collection angles using phases of the elements of the optical phased arrays. Device. The apparatus of claim 1 , wherein each of the optical phased arrays of the receivers is configured to align the respective collection angle with a target location. The apparatus of claim 1 , wherein the transmitter comprises an optical phased array within the transmit aperture. 16. The apparatus of claim 15, wherein 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. 16. The optical phased array of claim 15, wherein at least one optical phased array in at least one of the transmit aperture or the receive aperture steers a first angle using phases of elements of the optical phased array and a second angle using a wavelength. A device configured to control 2. The method of claim 1, wherein the receiver is a first receiver, the receive aperture is a first receive aperture, the optical phased array is a first optical phased array, the filter is a first filter, and the detector is a first 1 detector, wherein the two or more receivers include a second receiver, the second receiver comprising:
the transmit aperture configured as a second receive aperture;
a second optical phased array in the transmission aperture, the second optical phased array configured to receive at least a portion of a collection light wave arriving at the transmission aperture along a respective collection angle;
a second filter configured to filter the receiving portion of the collected light wave according to a property different from a property of the first portion of the light wave and different from a property of the second portion of the light wave; and
a second detector configured to provide a signal based on a filtered portion of the collected light wave that is filtered by the second filter
A device comprising a. The method of claim 1 , further configured to determine an estimated distance associated with the collected light wave based at least in part on a combination comprising a respective component corresponding to each of the two or more signals provided from the detectors of the two or more receivers. The apparatus further comprising a circuit configured. 20. The apparatus of claim 19, wherein the transmitter applies linear frequency modulation to the transmitted light wave to enable the circuitry to determine the estimated distance. 2. The method of claim 1, wherein the transmit aperture is further configured as a receive aperture wherein the optical phased array is used to receive at least a portion of a light wave having a characteristic different from that of the transmit light wave, at least one of the receive apertures one used as a transmission aperture for providing a beam of light waves with the different characteristics. The apparatus of claim 1 , wherein the characteristic comprises at least one of a specific wavelength, a specific time slot, or a specific polarization. 23. The apparatus of claim 22, wherein the characteristic comprises a specific wavelength. 24. The method of claim 23, wherein one or more light sources provide a plurality of spectral components tunable across different respective spectral bands, the first portion of the light wave comprising a first spectral component and the second portion of the light wave comprises a second spectral component different from the first spectral component. 25. The apparatus of claim 24, further comprising the one or more light sources. 25. The apparatus of claim 24, wherein the transmit aperture is further configured as a receive aperture wherein an optical phased array is used to receive a third spectral component different from the first spectral component and different from the second spectral component. . 27. The method of 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 wherein the transmitted light wave has significant power at the wavelength of the third spectral component. ), which does not have a device. 25. The third spectral component of claim 24, wherein the transmit aperture is a first transmit aperture, the transmit light wave is a first transmit light wave, and the apparatus is different from the first spectral component and different from the second spectral component. a second transmit aperture configured to provide at least one beam of a second transmit light wave comprising at least 29. The apparatus of claim 28, wherein the second transmit aperture is further configured as a second receive aperture through which an optical phased array is used to receive the first spectral component. 30. The method of claim 29, wherein the first spectral component is received from the second receive aperture by coherent mixing with a local oscillator derived from at least one light source providing the first transmit aperture. and a coherent receiver configured to detect the first spectral component. 29. The method of 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 wherein the first transmit light wave exerts significant power at the wavelength of the third spectral component. Don't have the device. 32. The method of claim 31, wherein the first transmit aperture and the second transmit aperture are located proximate to a center of an arrangement of apertures, and at least some of the receive apertures are proximate to edges of the arrangement of apertures. A device that is positioned in a way. 32. The apparatus of claim 31, wherein an amount of receive apertures in the array of apertures is greater than an amount of transmit apertures. As a method,
providing at least one beam of a transmit light wave along a transmit angle from a transmit aperture of the transmitter toward a target location, wherein the light wave has at least a first portion of the light wave and characteristics different from characteristics of the first portion of the light wave a second portion of said light wave having a -; and
receiving the collected light wave at receive apertures of the two or more receivers;
Including, at least one receiver,
a receive aperture arranged proximate to at least one of the transmit aperture or a receive aperture of a different receiver;
an optical phased array within the receive aperture, the optical phased array configured to receive at least a portion of a collection light wave arriving at the reception aperture along a respective collection angle;
a filter configured to filter a receiving portion of the collected light wave according to a characteristic of the first portion of the light wave, and
a detector configured to provide a signal based on the received portion of the collected light wave
A method comprising A LiDAR system comprising:
an arrangement of two or more apertures configured to provide at least one beam of a transmit light wave from at least two of the two or more apertures toward a target location, the two or more apertures comprising:
a first aperture comprising a first optical phased array within the first aperture, and
a second aperture including a second optical phased array within the second aperture
including -;
transmitter subsystem - the transmitter subsystem comprising:
providing a first portion of the transmit light wave to a first subset consisting of fewer than all of the two or more apertures, the first subset comprising the first aperture;
provide a second portion of the transmitted light wave to a second subset consisting of fewer than all of the two or more apertures, the second subset being different from the first subset and comprising the second aperture; the second portion of the light wave has a property different from the property of the first portion of the light wave;
configured -; and
Receiver subsystem - the receiver subsystem comprising:
a first filter configured to filter, according to a characteristic of the second portion of the light wave, the portion of the collected light wave arriving at at least one of the two or more apertures in the array; and
a first detector configured to provide a signal based on a portion of the collected light wave that is filtered by the first filter
including -
Including, LiDAR system. 36. The method of claim 35, wherein the characteristic comprises a specific wavelength, the first portion of the transmitted light wave comprises light having a wavelength in a first spectral band, and the second portion of the transmit light wave comprises the first spectrum A LiDAR system comprising light having a wavelength in a second spectral band that is different from the band. 37. The system of claim 36, wherein the first filter is configured to filter a portion of the collected light wave arriving at the first aperture, the receiver subsystem comprising:
a second filter configured to filter, according to a characteristic of the first portion of the light wave, the portion of the collected light wave arriving at the second aperture; and
a second detector configured to provide a signal based on a portion of the collected light wave that is filtered by the second filter
Further comprising a, LiDAR system. 38. The system of claim 37, wherein the transmitter subsystem comprises a wavelength division multiplexing component configured to combine the light having a wavelength in the first spectral band with light having a wavelength in a third spectral band, and wherein the second spectral band is between the first spectral band and the third spectral band. 37. The method of claim 36, wherein said arrangement of two or more apertures comprises said third aperture comprising a third optically phased array within a third aperture, said first filter reaching said third aperture. and filter a portion of the collected light wave. 40. The method of claim 39, wherein the transmitter subsystem comprises:
a first wavelength division multiplexing component configured to combine the light having a wavelength in a first spectral band with light having a wavelength in a third spectral band; and
a second wavelength division multiplexing component configured to combine the light having a wavelength in the second spectral band with light having a wavelength in a fourth spectral band
wherein the second spectral band is between the first spectral band and the third spectral band, and the third spectral band is between the second spectral band and the fourth spectral band. 37. The method of claim 36, wherein the first filter comprises a tunable filter having a tunable passband over the second spectral band, and wherein the receiver subsystem is at least partially adapted to the light having a wavelength in the second spectral band. and tune the first filter based on The optical phased array of claim 1 , wherein the filter is external to the optical phased array. Device. 35. The method of claim 34, wherein the filter is external to the optical phased array.

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