Patent ID: 12228682

DETAILED DESCRIPTION

According to some embodiments, the described LIDAR system using programmable beam steering compensation may be implemented in a variety of sensing and detection applications, such as, but not limited to, automotive, communications, consumer electronics, and healthcare markets. According to some embodiments, the described LIDAR system using programmable beam steering compensation may be implemented as part of a front-end of frequency modulated continuous-wave (FMCW) device that assists with spatial awareness for automated driver assist systems, or self-driving vehicles. According to some embodiments, the disclosed configuration may be agnostic to specific optical scanning architecture and can be tailored to enhance scanning LIDAR performance for a desired target range and/or to increase frame rate for a given range on the fly.

In a coherent LIDAR system, a frequency-modulated continuous wave (FMCW) transmitted light source (Tx) is used to determine the distance and velocity of objects in the scene by mixing a copy of the Tx source, known as the local oscillator (LO), with the received light (Rx) from the scene. The LO and Rx paths are combined on a fast photodiode (e.g., a photodetector), producing beat frequencies, proportional to object distance, which are processed electronically to reveal distance and velocity information of objects in the scene. To generate a point-cloud image, scanning optics are commonly used to deflect the Tx beam (e.g., signal) through the system field of view (FOV), comprising azimuth and zenith angles. In many applications, it is desirable to simultaneously achieve the highest possible scan rate and a large signal-to-noise ratio (SNR), as these two parameters directly affect the frame-rate of the LIDAR system, its maximum range (e.g., distance), range and velocity resolution, and the lateral spatial resolution.

However, increasing the scan rate produces a larger lag angle between the Rx light from a given object and the corresponding local oscillator (LO) that the LIDAR system uses to process the Rx light. This lag angle effect creates a beam walk-off problem, where the Tx light returned from distant objects are offset from the LO, which limits the achievable scan/frame rate and maximum range of the LIDAR system. Furthermore, the detection of objects at a large range produces large beat frequencies. Therefore, detecting distant objects with high fidelity requires the use of analog-to-digital convertors (ADCs) with very large sampling rates, approaching Giga-samples per second (Gsps), which consume a large amount of power.

Accordingly, the present disclosure addresses the above-noted and other deficiencies by disclosing systems and methods for using beam steering compensation in a frequency-modulated continuous wave (FMCW) LIDAR system to enhance detection of distant objects. As described in the below passages with respect to one or more embodiments, a LIDAR system includes an optical scanner to transmit an optical beam towards an object based on a transmit optical beam that propagates along an optical axis. The LIDAR system includes a first optical element to receive, responsive to the transmit of the optical beam, a returned reflection having a lag angle relative to the optical axis; and steer the returned reflection to generate a first steered beam. The LIDAR system includes a beam steering unit to receive the first steered beam and a local oscillator (LO) signal associated with the transmit optical beam, wherein the first steered beam is propagating at a first beam angle relative to the optical axis and the LO signal is propagating at a first LO angle relative to the optical axis. The beam steering unit is further to steer the first steered beam based on an array voltage to generate a second steered beam at a first location on a photodetector. The beam steering unit is further to steer the LO signal based on the array voltage to generate a steered LO signal at a second location on the photodetector, wherein a beam offset between the first location and the second location is caused by the lag angle. The LIDAR system includes a processor to adjust the array voltage to cause the beam steering unit to reduce the beam offset between the first location and the second location.

FIG.1is a block diagram illustrating an example of a LIDAR system, according to some embodiments. The LIDAR system100includes one or more of each of a number of components, but may include fewer or additional components than shown inFIG.1. One or more of the components depicted inFIG.1can be implemented on a photonics chip, according to some embodiments. The optical circuits101may include a combination of active optical components and passive optical components. Active optical components may generate, amplify, and/or detect optical signals and the like. In some examples, the active optical component includes optical beams at different wavelengths, and includes one or more optical amplifiers, one or more optical detectors, or the like. In some embodiments, one or more LIDAR systems100may be mounted onto any area (e.g., front, back, side, top, bottom, and/or underneath) of a vehicle to facilitate the detection of an object in any free space relative to the vehicle. In some embodiments, the vehicle may include a steering system and a braking system, each of which may work in combination with one or more LIDAR systems100according to any information (e.g., distance/ranging information, Doppler information, etc.) acquired and/or available to the LIDAR system100. In some embodiments, the vehicle may include a vehicle controller that includes the one or more components and/or processors of the LIDAR system100.

Free space optics115may include one or more optical waveguides to carry optical signals, and route and manipulate optical signals to appropriate input/output ports of the active optical circuit. In embodiments, the one or more optical waveguides may include one or more graded index waveguides, as will be described in additional detail below atFIGS.3-6. The free space optics115may also include one or more optical components such as taps, wavelength division multiplexers (WDM), splitters/combiners, polarization beam splitters (PBS), collimators, couplers or the like. In some examples, the free space optics115may include components to transform the polarization state and direct received polarized light to optical detectors using a PBS, for example. The free space optics115may further include a diffractive element to deflect optical beams having different frequencies at different angles along an axis (e.g., a fast-axis).

In some examples, the LIDAR system100includes an optical scanner102that includes one or more scanning mirrors that are rotatable along an axis (e.g., a slow-axis) that is orthogonal or substantially orthogonal to the fast-axis of the diffractive element to steer optical signals to scan an environment according to a scanning pattern. For instance, the scanning mirrors may be rotatable by one or more galvanometers. Objects in the target environment may scatter an incident light into a return optical beam or a target return signal. The optical scanner102also collects the return optical beam or the target return signal, which may be returned to the passive optical circuit component of the optical circuits101. For example, the return optical beam may be directed to an optical detector by a polarization beam splitter. In addition to the mirrors and galvanometers, the optical scanner102may include components such as a quarter-wave plate, lens, anti-reflective coated window or the like.

To control and support the optical circuits101and optical scanner102, the LIDAR system100includes LIDAR control systems110. The LIDAR control systems110may include a processing device for the LIDAR system100. In some examples, the processing device may be one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device may be complex instruction set computing (CISC) microprocessor, reduced instruction set computer (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or processor implementing other instruction sets, or processors implementing a combination of instruction sets. The processing device may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like.

In some examples, the LIDAR control system110may include a processing device that may be implemented with a DSP, such as signal processing unit112. The LIDAR control systems110are configured to output digital control signals to control optical drivers103. In some examples, the digital control signals may be converted to analog signals through signal conversion unit106. For example, the signal conversion unit106may include a digital-to-analog converter. The optical drivers103may then provide drive signals to active optical components of optical circuits101to drive optical sources such as lasers and amplifiers. In some examples, several optical drivers103and signal conversion units106may be provided to drive multiple optical sources.

The LIDAR control systems110are also configured to output digital control signals for the optical scanner102. A motion control system105may control the galvanometers of the optical scanner102based on control signals received from the LIDAR control systems110. For example, a digital-to-analog converter may convert coordinate routing information from the LIDAR control systems110to signals interpretable by the galvanometers in the optical scanner102. In some examples, a motion control system105may also return information to the LIDAR control systems110about the position or operation of components of the optical scanner102. For example, an analog-to-digital converter may in turn convert information about the galvanometers' position to a signal interpretable by the LIDAR control systems110.

The LIDAR control systems110are further configured to analyze incoming digital signals. In this regard, the LIDAR system100includes optical receivers104to measure one or more beams received by optical circuits101. For example, a reference beam receiver may measure the amplitude of a reference beam from the active optical component, and an analog-to-digital converter converts signals from the reference receiver to signals interpretable by the LIDAR control systems110. Target receivers measure the optical signal that carries information about the range and velocity of a target in the form of a beat frequency, modulated optical signal. The reflected beam may be mixed with a second signal from a local oscillator. The optical receivers104may include a high-speed analog-to-digital converter to convert signals from the target receiver to signals interpretable by the LIDAR control systems110. In some examples, the signals from the optical receivers104may be subject to signal conditioning by signal conditioning unit107prior to receipt by the LIDAR control systems110. For example, the signals from the optical receivers104may be provided to an operational amplifier for amplification of the received signals and the amplified signals may be provided to the LIDAR control systems110.

In some applications, the LIDAR system100may additionally include one or more imaging devices108configured to capture images of the environment, a global positioning system109configured to provide a geographic location of the system, or other sensor inputs. The LIDAR system100may also include an image processing system114. The image processing system114can be configured to receive the images and geographic location, and send the images and location or information related thereto to the LIDAR control systems110or other systems connected to the LIDAR system100.

In operation according to some examples, the LIDAR system100is configured to use nondegenerate optical sources to simultaneously measure range and velocity across two dimensions. This capability allows for real-time, long range measurements of range, velocity, azimuth, and elevation of the surrounding environment.

In some examples, the scanning process begins with the optical drivers103and LIDAR control systems110. The LIDAR control systems110instruct, e.g., via signal processing unit112, the optical drivers103to independently modulate one or more optical beams, and these modulated signals propagate through the optical circuits101to the free space optics115. The free space optics115directs the light at the optical scanner102that scans a target environment over a preprogrammed pattern defined by the motion control system105. The optical circuits101may also include a polarization wave plate (PWP) to transform the polarization of the light as it leaves the optical circuits101. In some examples, the polarization wave plate may be a quarter-wave plate or a half-wave plate. A portion of the polarized light may also be reflected back to the optical circuits101. For example, lensing or collimating systems used in LIDAR system100may have natural reflective properties or a reflective coating to reflect a portion of the light back to the optical circuits101.

Optical signals reflected back from an environment pass through the optical circuits101to the optical receivers104. Because the polarization of the light has been transformed, it may be reflected by a polarization beam splitter along with the portion of polarized light that was reflected back to the optical circuits101. In such scenarios, rather than returning to the same fiber or waveguide serving as an optical source, the reflected signals can be reflected to separate optical receivers104. These signals interfere with one another and generate a combined signal. The combined signal can then be reflected to the optical receivers104. Also, each beam signal that returns from the target environment may produce a time-shifted waveform. The temporal phase difference between the two waveforms generates a beat frequency measured on the optical receivers104(e.g., photodetectors).

The analog signals from the optical receivers104are converted to digital signals by the signal conditioning unit107. These digital signals are then sent to the LIDAR control systems110. A signal processing unit112may then receive the digital signals to further process and interpret them. In some embodiments, the signal processing unit112also receives position data from the motion control system105and galvanometers (not shown) as well as image data from the image processing system114. The signal processing unit112can then generate 3D point cloud data (sometimes referred to as, “a LIDAR point cloud”) that includes information about range and/or velocity points in the target environment as the optical scanner102scans additional points. In some embodiments, a LIDAR point cloud may correspond to any other type of ranging sensor that is capable of Doppler measurements, such as Radio Detection and Ranging (RADAR). The signal processing unit112can also overlay 3D point cloud data with image data to determine velocity and/or distance of objects in the surrounding area. The signal processing unit112also processes the satellite-based navigation location data to provide data related to a specific global location.

FIG.2is a time-frequency diagram illustrating an example of an FMCW scanning signal that can be used by a LIDAR system to scan a target environment, according to some embodiments. In one example, the scanning waveform201, labeled as fFM(t), is a sawtooth waveform (sawtooth “chirp”) with a chirp bandwidth ΔfCand a chirp period TC. The slope of the sawtooth is given as k=(ΔfC/TC).FIG.2also depicts target return signal202according to some embodiments. Target return signal202, labeled as fFM(t−Δt), is a time-delayed version of the scanning waveform201, where Δt is the round trip time to and from a target illuminated by scanning waveform201. The round trip time is given as Δt=2R/v, where R is the target range and v is the velocity of the optical beam, which is the speed of light c. The target range, R, can therefore be calculated as R=c(Δt/2). When the return signal202is optically mixed with the scanning signal, a range-dependent difference frequency (“beat frequency”) ΔfR(t) is generated. The beat frequency ΔfR(t) is linearly related to the time delay Δt by the slope of the sawtooth k. That is, ΔfR(t)=kΔt. Since the target range R is proportional to Δt, the target range R can be calculated as R=(c/2)(ΔfR(t)/k). That is, the range R is linearly related to the beat frequency ΔfR(t). The beat frequency ΔfR(t) can be generated, for example, as an analog signal in optical receivers104of system100. The beat frequency can then be digitized by an analog-to-digital converter (ADC), for example, in a signal conditioning unit such as signal conditioning unit107in LIDAR system100. The digitized beat frequency signal can then be digitally processed, for example, in a signal processing unit, such as signal processing unit112in system100. It should be noted that the target return signal202will, in general, also includes a frequency offset (Doppler shift) if the target has a velocity relative to the LIDAR system100. The Doppler shift can be determined separately, and used to correct (e.g., adjust, modify) the frequency of the return signal, so the Doppler shift is not shown inFIG.2for simplicity and ease of explanation. For example, LIDAR system100may correct the frequency of the return signal by removing (e.g., subtracting, filtering) the Doppler shift from the frequency of the returned signal to generate a corrected return signal. The LIDAR system100may then use the corrected return signal to calculate a distance and/or range between the LIDAR system100and the object. In some embodiments, the Doppler frequency shift of target return signal202that is associated with an object may be indicative of a velocity and/or movement direction of the object relative to the LIDAR system100.

It should also be noted that the sampling frequency of the ADC will determine the highest beat frequency that can be processed by the system without aliasing. In general, the highest frequency that can be processed is one-half of the sampling frequency (i.e., the “Nyquist limit”). In one example, and without limitation, if the sampling frequency of the ADC is 1 gigahertz, then the highest beat frequency that can be processed without aliasing (ΔfRmax) is 500 megahertz. This limit in turn determines the maximum range of the system as Rmax=(c/2)(ΔfRmax/k) which can be adjusted by changing the chirp slope k. In one example, while the data samples from the ADC may be continuous, the subsequent digital processing described below may be partitioned into “time segments” that can be associated with some periodicity in the LIDAR system100. In one example, and without limitation, a time segment might correspond to a predetermined number of chirp periods T, or a number of full rotations in azimuth by the optical scanner.

FIG.3is a block diagram illustrating an example environment for using an optical scanner to transmit optical beams towards distant objects and receive returned optical beams having different lag angles, according to some embodiments. The environment300includes the optical scanner102(e.g., a prism, a mirror), an optical beam source340, a collimation lens320(sometimes referred to as, “optical element”), and an optical device328(sometimes referred to as, “optical element”). The optical device328may be a lens, a glass plate (sometimes referred to as, “local oscillator window”), or a beam steering unit. In some embodiments, the glass plate may be reflection coated glass plate or a partially reflective glass plate.

In some embodiments, any of the components (e.g., optical scanner102, optical beam source340, collimation lens320, optical device328, etc.) in the environment300may be added as a component of the LIDAR system100inFIG.1, or be used to replace or modify any of the one or more components (e.g., free space optics115, optical circuits, optical receivers104, etc.) of the LIDAR system100.

The environment300includes one or more objects, such as object308a(e.g., a street sign), object308b(e.g., a tree), and object308c(e.g., a pedestrian); each collectively referred to as objects308. AlthoughFIG.3shows only a select number of objects308, the environment300may include any number of objects308of any type (e.g., pedestrians, vehicles, street signs, raindrops, snow, street surface) that are within a short distance (e.g., 30 meters) or a long distance (e.g., 300 meters, 500 meters and beyond) from the optical scanner102. In some embodiments, an object308may be stationary or moving with respect to the optical scanner102.

In some embodiments, the optical scanner102is configured to receive one or more optical beams304(sometimes referred to as, “transmit optical beam”) transmitted from the optical beam source340along an optical axis305(shown inFIG.3as the X-axis). In some embodiments, the optical scanner102is configured to steer (e.g., redirect, transmit, scatter) the one or more optical beams304into free space toward the one or more objects308, which causes the one or more optical beams to scatter into returned optical beams306a,306b,306c(collectively referred to as, “returned optical beams306”). For example, the one or more optical beams304scatter against the object308ato create a returned optical beam306a, which is returned to the LIDAR system100. As another example, the one or more optical beams304scatter against the object308bto create a returned optical beam306b, which is returned to the LIDAR system100. As another example, the one or more optical beams304scatter against the object308cto create a returned optical beam306c, which is returned to the LIDAR system100.

The collimation lens320is configured (e.g., positioned, arranged) to collect (e.g., receive, acquire, aggregate) the returned optical beams306that scatter from the one or more objects308in response to the optical scanner102steering the one or more optical beams304into free space. In some embodiments, the collimation lens320may be a symmetric lens having a diameter. In some embodiments, the collimation lens320may be an asymmetric lens.

As shown inFIG.3, the lag angle between a respective returned optical beam306and the collimation lens320is indicated by θDS,n, where n is an integer. For example, the lag angle between the returned optical beam306aand the collimation lens320is indicated by θDS,0(not shown inFIG.3), the lag angle between the returned optical beam306band the collimation lens320is indicated by θDS,1, and the lag angle between the returned optical beam306cand the collimation lens320is indicated by θDS,2(shown inFIG.3as, θDS,n). In some embodiments, increasing the scan rate of the optical scanner102produces a larger lag angle between one or more of the returned optical beams306.

As shown inFIG.3, the optical device328receives the returned optical beam306aat a location1(shown inFIG.3as, “L1”) on the optical device328from the collimation lens320as a result of the returned optical beam306ahaving a lag angle of zero degrees with respect to the optical axis305, and the collimation lens320generating a collimated beam from the returned optical beams306. The optical device328also receives the returned optical beam306bat a location2(shown inFIG.3as, “L2”) on the optical device328as a result of the returned optical beam306bhaving a lag angle of θDS,1degrees with respect to the optical axis305, and the collimation lens320generating a collimated beam from the returned optical beams306. The optical device328also receives the returned optical beam306cat a location3(shown inFIG.3as, “L3”) on the optical device328as a result of the returned optical beam306chaving a lag angle of θDS,2degrees with respect to the optical axis305, and the collimation lens320generating a collimated beam from the returned optical beams306.

In other words, the respectively increasing lag angles of the returned optical beams306a,306b,306cfrom the distant objects cause the optical device328to receive the returned optical beams306at different locations on the optical device328. The offset of a location on the optical device328with respect to the optical axis305is referred to as a beam walk-off (e.g., a distance). For example, the difference in distance between location2, where the optical device328receives the returned optical beam306b, and location1, where the optical device328receives the returned optical beam306a, is referred to as beam walk-offs. The difference in distance between location3, where the optical device328receives the returned optical beam306c, and location2, where the optical device328receives the returned optical beam306b, is referred to as beam walk-off2(shown inFIG.3as, “beam walk-offn”).

Although not shown inFIG.3, the optical device328couples to the LIDAR control system110inFIG.1such to be able to pass any of the returned optical beams that are received by the optical device328to the LIDAR control system110for processing by the signal processing unit112.

FIG.4is a block diagram illustrating an example environment for beam steering compensation in the LIDAR system100inFIG.1to enhance detection of distant objects, according to some embodiments. The environment400includes the optical scanner102, the collimation lens320(sometimes referred to as, “lens3”), and the optical beam source340. The environment400includes the optical device328fromFIG.3, but where the optical device328is a glass plate428. In some embodiments, the glass plate428may be reflection coated glass plate or a partially reflective glass plate. The environment400includes a beam steering unit430, a lens334(sometimes referred to as, “lens4”), and a photodetector460. The environment400includes a voltage control unit120that is communicatively coupled to the LIDAR control system110. In some embodiments, as shown inFIG.1, the voltage control unit120may be a component of the LIDAR control system110.

In some embodiments, any of the components (e.g., beam steering unit430, etc.) (e.g., optical scanner102, optical beam source340, collimation lens320, glass plate428, etc.) in the environment400may be added as a component of the LIDAR system100inFIG.1, or be used to replace or modify any of the one or more components (e.g., free space optics115, optical circuits, optical receivers104, etc.) of the LIDAR system100.

The environment400includes an object408, such as object308ainFIG.3(e.g., a street sign), object308binFIG.3(e.g., a tree), or object308cinFIG.3(e.g., a pedestrian); each collectively referred to as objects308. AlthoughFIG.4shows only a single object408, the environment400may include any number of objects408of any type that are within a short distance (e.g., 30 meters) or a long distance (e.g., 300 meters, 500 meters and beyond) from the optical scanner102. In some embodiments, an object408may be stationary or moving with respect to the optical scanner102.

An output terminal of the voltage control unit120is coupled to an input terminal of the beam steering unit430. The LIDAR control system110may send instructions to the voltage control unit120to cause the voltage control unit120to generate a control voltage (e.g., 5V) and provide the voltage to the beam steering unit430via the output terminal of the control voltage control unit120. In some embodiments, a plurality of output terminals of the voltage control unit120may be respectively coupled to a plurality of input terminals of the beam steering unit430. As such, the LIDAR control system110may send instructions to the voltage control unit120to cause the voltage control unit120to generate an array voltage (sometimes referred to as, “control voltages”) and provide the array voltage to the beam steering unit430via the plurality of output terminal of the voltage control unit120. For example, the voltage control unit120may provide 4.5V to its first output terminal that is coupled to a first input terminal of the beam steering unit430, the voltage control unit120may provide 4.8V to its second output terminal that is coupled to a second input terminal of the beam steering unit430, the voltage control unit120may provide 0.0V to its third output terminal that is coupled to a third input terminal of the beam steering unit430, and so on.

The optical scanner102is configured to receive an optical beam304transmitted from the optical beam source340along an optical axis305(shown inFIG.4as the X-axis), where the optical beam304passes through the glass plate428. Furthermore, the glass plate428reflects a portion of the optical beam304to generate a local oscillator (LO) signal418that propagates along the optical axis and toward location2(shown inFIG.4as, “L2”) on the beam steering unit430.

The optical scanner102is configured to steer the optical beam304into free space toward the object408, which causes the optical beam to scatter into returned optical beam306that is returned to the LIDAR system100.

The collimation lens320is configured to collect the returned optical beam306. The scan rate of the optical scanner102and/or the distance of the object408from the LIDAR system100causes the returned optical beam306to have a lag angle θDSwith respect to the optical axis.

As shown inFIG.4, the glass plate428receives the returned optical beam306aat location1(shown inFIG.3as, “L1”) on glass plate428as a result of the returned optical beam306ahaving a lag angle θDSis with respect to the optical axis305, and the collimation lens320generating a collimated beam from the returned optical beam306. The glass plate428steers the returned optical beam306to propagate along the optical axis and toward location1(shown inFIG.4as, “L1”) on the beam steering unit430.

Thus, the lag angle θDSis of the returned optical beam306acauses the beam steering unit430to receive the returned optical beam306and the local oscillator (LO) signal418at different locations (e.g., L1, L2) on the beam steering unit430. This creates a beam walk-off (e.g., an error) that is equal to the distance between L2and L1. This beam walk-off propagates to the LIDAR control system110and negatively affects the ability of the LIDAR control system110to accurately calculate metrics (e.g., distance, velocity, orientation, etc.) related to the object408.

The beam steering unit430, however, may be used to compensate (e.g., mitigate or substantially eliminate) for the beam walk-off, which in turn, improves the processing capability of the LIDAR control system110. The beam steering unit430is an optical device that is transparent to the LIDAR laser wavelength (e.g., 905 nanometers (nm) and 1550 nm). The beam steering unit430may work in a transmissive or a reflective way to allow an optical beam (e.g., light) to pass thru it one or more times in reflection with a mirror. In one embodiment, the beam steering unit430may be a thin liquid crystal filled plate with patterned electrode to apply different voltage profiles on the liquid crystal layer to form a linear phase retardation along one direction. When the optical beam passes thru the beam steering unit430, it experiences a linear spatial phase on its wavefront (e.g., the set of all points having the same phase change between adjacent points), which changes its beam direction depending on the linear phase direction in space. Depending on the angle change (lag angle) of the returned optical beams306that is due at least in part to the scanning optics, the beam steering unit430can be aligned with its linear phase direction in the angle shift direction of the returned optical beams306. Thru its programmable capability, the beam steering unit430can be configured dynamically to optimize the mixing performance thru tuning the angle offset of the returned optical beams306.

The LIDAR control system110may be configured to send instructions to the voltage control unit120to cause the voltage control unit120to generate one or more control voltages (e.g., a single voltage or a voltage array) and provide the one or more control voltages to the beam steering unit430via the output terminal of the voltage control unit120. The one or more control voltages may, depending on the angle of the returned optical beam306at L1on the beam steering unit430, cause the beam steering unit430to change (e.g., adjust, modify) the angle of the returned optical beam306.

For example, the returned optical beam306at L1may have a first angle with respect to the optical axis305. In response to receiving a control voltage V1from the voltage control unit120, the beam steering unit430may generate a returned optical beam306V1that also has the same first angle. The beam steering unit430may provide the returned optical beam306V1to the lens334such that the returned optical beam306V1propagates along the optical axis at the first angle and toward location1(shown inFIG.4as, “L1”) on the lens334. Thus, the control voltage V1causes the beam steering unit430to allow the returned optical beam306to pass through the beam steering unit430without adjusting the first angle of the returned optical beam306.

As another example, in response to receiving a control voltage V2from the voltage control unit120, the beam steering unit430may generate a returned optical beam306V2that has a second angle, where the second angle is different from the first angle. The beam steering unit430may then provide the returned optical beam306V2to the lens334such that the returned optical beam306V2propagates along the optical axis at the second angle and toward location2(shown inFIG.4as, “L2”) on the lens334. Thus, the control voltage V2causes the beam steering unit430to adjust the first angle of the returned optical beam306to steer the returned optical beam306.

As another example, in response to receiving a control voltage V3from the voltage control unit120, the beam steering unit430may generate a returned optical beam306V2that has the third angle, where the third angle is different from both the first angle and the second angle. The beam steering unit430may then provide the returned optical beam306V3to the lens334such that the returned optical beam306V3propagates along the optical axis305at the third angle and toward location3(shown inFIG.4as, “L3”) on the lens334. Thus, the control voltage V3causes the beam steering unit430to adjust the first angle of the returned optical beam306to steer the returned optical beam306.

The one or more control voltages may also, depending on its angle at L2on the beam steering unit430, change the angle of the LO signal418. For example, the LO signal418at L2may have a first angle with respect to the optical axis305. In response to receiving a control voltage V1from the voltage control unit120, the beam steering unit430may generate a LO signal418V1that also has the same first angle. The beam steering unit430may provide the LO signal418V1to the lens334such that the LO signal418V1propagates along the optical axis at the first angle and toward location4(shown inFIG.4as, “L4”) on the lens334. Thus, the control voltage V1causes the beam steering unit430to allow the LO signal418to pass through the beam steering unit430without adjusting the first angle of the LO signal418.

As another example, in response to receiving a control voltage V2from the voltage control unit120, the beam steering unit430may generate a LO signal418V2that has second angle, where the second angle is different from the first angle. The beam steering unit430may then provide the LO signal418V2to the lens334such that the LO signal418V2propagates along the optical axis305at the second angle and toward location5(shown inFIG.4as, “L5”) on the lens334. Thus, the control voltage V2causes the beam steering unit430to adjust the first angle of the LO signal418to steer the LO signal418.

As another example, in response to receiving a control voltage V3from the voltage control unit120, the beam steering unit430may generate a LO signal418V2that has the third angle, where the third angle is different from both the first angle and the second angle. The beam steering unit430may then provide the LO signal418V3to the lens334such that the LO signal418V3propagates along the optical axis305at the third angle and toward location6(shown inFIG.4as, “L6”) on the lens334. Thus, the control voltage V3causes the beam steering unit430to adjust the first angle of the LO signal418to steer the LO signal418.

The lens334is configured to receive one of the returned optical beams306(e.g., returned optical beam306V1, returned optical beam306V2, or returned optical beam306V3) at its corresponding angle (e.g., first angle, second angle, or third angle) and steer the returned optical beam306(shown inFIG.4as, “returned optical beam306s”) to propagate along the optical axis toward location1(shown inFIG.4as, “L1”) on the photodetector460. In some embodiments, depending on the location in which the beam steering unit430receives the returned optical beam306, the lens334may either (a) steer the returned optical beam306by adjusting (e.g., adding or subtracting degrees) the corresponding angle of the returned optical beam306to generate the returned optical beam306s, or (b) allow the returned optical beam306to pass through the lens334without adjusting the corresponding angle of the returned optical beam306.

Similarly, the lens334is configured to receive one of the LO signal418(e.g., LO signal418V1, LO signal418V2, or LO signal418V3) at its corresponding angle (e.g., first angle, second angle, or third angle) and steer the LO signal418(shown inFIG.4as, “LO signal418s”) to propagate along the optical axis305toward location2(shown inFIG.4as, “L2”) on the photodetector460. In some embodiments, depending on the location in which the beam steering unit430receives the LO signal418, the lens334may either (a) steer the LO signal418by adjusting (e.g., adding or subtracting degrees) the corresponding angle of the LO signal418to generate the LO signal418s, or (b) allow the LO signal418to pass through the lens334without adjusting the corresponding angle of the LO signal418.

Although,FIG.4shows that the beam steering unit430steers the returned optical beams306and the LO signal418in the same downward direction (e.g., decreasing beam angle) relative to the optical axis305, the beam steering unit430may be configured to steer the returned optical beam306and the LO signal418in an upward direction. In some embodiments, the beam steering unit430may be configured to steer the returned optical beam306and the LO signal418in opposite directions. For example, the beam steering unit430may be configured to steer the returned optical beam306in an upward direction by adding degrees to the angle of the returned optical beam306, and steer the LO signal418in a downward direction by subtracting degrees from the angle of the LO signal418; or vice versa. In some embodiments, the beam steering unit430may be configured to adjust the angle of the returned optical beam306and the LO signal418by an equal amount (e.g., 10 degrees, −10 degrees, etc.).

The photodetector460receives the returned optical beam306(shown inFIG.4as, “returned optical beam306s”) at L1and the LO signal418(shown inFIG.4as, “LO signal4185”) at L2. The distance between L1and L2corresponds to a compensated beam walk-off because it is less than the beam walk-off at input (e.g., L1and L2) of the beam steering unit430, and which was caused by the lag angle ° DS of the returned optical beam306. The photodetector460can now more accurately detect the returned optical beam306and the LO signal418at its inputs to generate electrical signals having beat frequencies that are indicative of the returned optical beam306. The photodetector460then provides the electrical signals to the LIDAR control system for processing to calculate metrics (e.g., distance, velocity, orientation, etc.) related to the object408.

Although not shown inFIG.4, the output of the photodetector460couples to the LIDAR control system110inFIG.1such to be able to pass any of its outputs (e.g., electrical signals) to the LIDAR control system110for processing by the signal processing unit112.

FIG.5is a block diagram illustrating an example environment for beam steering compensation in the LIDAR system100inFIG.1to enhance detection of distant objects using an additional lens, according to some embodiments. The environment500includes the same arrangement of the components depicted inFIG.4, expect that the optical beam source340is positioned between the beam steering unit430and the lens324, instead of being positioned between the glass plate428and the beam steering unit430, as shown inFIG.4. In this alternate configuration, the optical beam source340is configured to transmit an optical beam304along the optical axis305toward the beam steering unit430. The beam steering unit430is configured to adjust, based the control voltage, an angle of the optical axis305to steer the optical axis305.

The environment500also includes a lens522(sometimes referred to as, “L2”) positioned between the glass plate428and the beam steering unit430to receive one or more optical beams (e.g., optical beam304, LO signal418, returned optical beam306). Depending on the location in which the beam steering unit430receives an optical beam, the lens522may either (a) steer the optical beam by adjusting is angle, or (b) allow the optical beam to pass through the lens522without adjusting its angle.

FIG.6Ais a block diagram illustrating an example beam steering unit430, according to some embodiments. In this embodiment, the beam steering unit430is a thin liquid crystal (LC) plate with a linear spatial phase that is configured (e.g., programmed) to steer or deflect a collimated beam.

FIG.6Bis a block diagram illustrating an example beam steering unit430, according to some embodiments. In this embodiment, the beam steering unit430is a thin prism that is configured to steer or deflect a collimated beam.

FIGS.7A-7Bare block diagrams illustrating an example equation that models the performance of the beam steering unit430inFIG.3, according to some embodiments. That is, the beam steering unit430may be configured as a linear phase shifter to steer the optical beams that pass through the beam steering unit430. The beam steering unit430may set the angle θ of the optical beam by shifting the phase of an optical beam according to the following equations:

θ=λ2⁢π⁢A(1)

where λ=is the optical beam's wavelength; A=is the slope of the linear spatial phase
E˜eikzzeikθx(2)

where E=is the optical field; i=is the notation of the imaginary part of a complex value; k=is the optical wave vector; z=is the coordinate along the optical beam propagation direction

FIG.8is a block diagram illustrating an example structure of a beam steering unit, according to some embodiments. The beam steering unit800(e.g., beam steering unit430inFIG.4) includes a thin layer of LC that is sandwiched between two indium tin oxide (ITO) conductive layers. The first layer is coupled to a ground supply and the second layer is pixellated. In some embodiments, the LC layer thickness is on the order of ten to tens of micrometers. In some embodiments, the ITO is optically transparent. In some embodiments, the whole structure is between two glass substrates that are of several tenth millimeter thick. By applying different voltages on the ITO pixels, it can form a linear phase delay or retardation across the pixels.

FIG.9is a graph illustrating the relationship between control voltage and birefringence phase delay or retardation of a beam steering unit, according to some embodiments. In this embodiment, the beam steering unit includes a thin LC of several micrometers. The graph900shows that the higher the voltage is, then the less the optical birefringence phase delay. To form a linear spatial phase retardation profile across all pixels, the phase retardation at each pixel is calculated with the linear phase function, and the required voltage for each pixel is calculated with the retardation vs. voltage curve.

FIG.10is a flow diagram illustrating an example method for beam steering compensation in an FMCW LIDAR system to enhance detection of distant objects, according to some embodiments. Additional, fewer, or different operations may be performed in the method depending on the particular arrangement. In some embodiments, some or all operations of method1000may be performed by one or more processors executing on one or more computing devices, systems, or servers (e.g., remote/networked servers or local servers). In some embodiments, method1000may be performed by a signal processing unit, such as signal processing unit112inFIG.1. In some embodiments, method1000may be performed by any of the components (e.g., scanner302, GP428, beam steering unit430, voltage control unit120, etc.) in environment400inFIG.4, and/or the components in environment500inFIG.5. Each operation may be re-ordered, added, removed, or repeated.

In some embodiments, the method1000may include the operation1002of transmitting, by an optical scanner, an optical beam towards an object based on a transmit optical beam that propagates along an optical axis. In some embodiments, the method1000may include the operation1004of receiving, by a first optical element responsive to transmitting the optical beam, a returned reflection having a lag angle relative to the optical axis. In some embodiments, the method1000may include the operation1006of steering, by the first optical element, the returned reflection to generate a first steered beam.

In some embodiments, the method1000may include the operation1008of receiving, by a beam steering unit, the first steered beam and a local oscillator (LO) signal associated with the transmit optical beam, wherein the first steered beam is propagating at a first beam angle relative to the optical axis and the LO signal is propagating at a first LO angle relative to the optical axis. In some embodiments, the method1000may include the operation1010of steering, by the beam steering unit, the first steered beam based on an array voltage to generate a second steered beam at a first location on a photodetector.

In some embodiments, the method1000may include the operation1012of steering, by the beam steering unit, the LO signal based on the array voltage to generate a steered LO signal at a second location on the photodetector, wherein a beam offset between the first location and the second location is caused by the lag angle. In some embodiments, the method1000may include the operation1014of adjusting, by a processor, the array voltage to cause the beam steering unit to reduce the beam offset between the first location and the second location.

The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that at least some embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present disclosure. Thus, the specific details set forth are merely exemplary. While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Particular embodiments may vary from these exemplary details and still be contemplated to be within the scope of the present disclosure.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. In addition, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.”

Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent or alternating manner.

The above description of illustrated implementations of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The words “example” or “exemplary” are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words “example” or “exemplary” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Moreover, use of the term “an embodiment” or “one embodiment” or “an implementation” or “one implementation” throughout is not intended to mean the same embodiment or implementation unless described as such. Furthermore, the terms “first,” “second,” “third,” “fourth,” etc. as used herein are meant as labels to distinguish among different elements and may not necessarily have an ordinal meaning according to their numerical designation.