WO2025183675A1

WO2025183675A1 - Quarter wave plate lidar

Info

Publication number: WO2025183675A1
Application number: PCT/US2024/017280
Authority: WO
Inventors: Sajan SHRESHTHA; Lawrence Dah Ching Tzuang
Original assignee: Voyant Photonics Inc
Current assignee: Voyant Photonics Inc
Priority date: 2024-02-26
Filing date: 2024-02-26
Publication date: 2025-09-04
Anticipated expiration: 2026-08-26

Abstract

Disclosed are integrated polarization-multiplexed LIDAR (Light Detecting and Ranging) systems which transmit one polarization but receive the orthogonal polarization or both. To measure more power from the target over less-lossy optical pathways through the system, a quarter wave plate is employed.

Description

QUARTER WAVE PLATE LIDAR

FIELD OF THE INVENTION

The present disclosure relates to photonics systems and particularly to polarization- multiplexed LIDAR (Light Detecting and Ranging) systems which transmit one polarization but receive the orthogonal polarization or both.

BRIEF SUMMARY

According to a first aspect, there is provided an integrated photonics polarization- multiplexed LIDAR system comprising: a laser source for generating optical signals of a first linear polarization; an emitter block for receiving optical signals of the first linear polarization generated by the laser source; a quarter wave plate (QWP) for receiving optical signals of the first linear polarization from the emitter block, and for converting them into optical signals of a first circular polarization and forwarding them toward a target of the system, the QWP for receiving return optical signals back-scattered from the target and for converting return optical signals of the first circular polarization into return optical signals of the first linear polarization and converting return optical signals of a second circular polarization orthogonal to the first circular polarization into return optical signals of a second linear polarization orthogonal to the first linear polarization, the emitter block receiving the return optical signals of the first and second linear polarizations from the QWP as received return optical signals of the first and second linear polarizations respectively; and a first receiver for receiving the received return optical signals of the second linear polarization from the emitter block.

Some embodiments further provide for a second receiver for receiving at least a portion of the received return optical signals of the first linear polarization from the emitter block.

Some embodiments further provide for an optical splitter network coupled between the laser source and the emitter block for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into a first and second optical signal, and forwarding the first optical signal to the first receiver as a local oscillator signal, and forwarding the second optical signal to the emitter block.

In some embodiments, the optical splitter network comprises a beamsplitter having a splitting ratio such that a power of the first optical signal is less than a power of the second optical signal.

In some embodiments, the splitting ratio of the beamsplitter is tunable.

Some embodiments further provide for an optical splitter network coupled between the laser source and the emitter block for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into a first optical signal, a second optical signal, and a third optical signal, forwarding the first optical signal to the first receiver as a first local oscillator signal, forwarding the second optical signal to the emitter block, and forwarding the third optical signal to the second receiver as a second local oscillator signal, the optical splitter network further for receiving the received return optical signals of the first linear polarization from the emitter block and forwarding a portion of the received return optical signals of the first linear polarization from the emitter block to the second receiver.

In some embodiments, the optical splitter network comprises a duplexer for receiving at least a portion of the received return optical signal of the first linear polarization from the emitter block and for providing said portion of the received return optical signals of the first linear polarization from the emitter block to the second receiver.

In some embodiments, the optical splitter network further comprises a beamsplitter for receiving at least a portion of the optical signal of the first linear polarization generated by the laser and providing some portion thereof as one of the first or second local oscillator signals to the respective one of the first and second receivers.

In some embodiments, said duplexer is for receiving at least some portion of the of the optical signal of the first linear polarization generated by the laser and for providing a portion thereof as the other one of the first or second local oscillator signals to the respective other one of the first and second receivers.

In some embodiments, the duplexer is for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into the second optical signal and into a fourth optical signal including the first optical signal and the third optical signal, providing the fourth optical signal to a beamsplitter which splits the fourth optical signal into the first and second optical signals and provides them to the first and second receivers as said first and second local oscillator signals.

In some embodiments, the emitter block comprises a polarization splitter rotator (PSR) and a dual polarization emitter.

In some embodiments, a power of the return optical signals of the second circular polarization back-scattered from the target is greater in magnitude than a power of the return optical signals of the second circular polarization back-scattered from the target.

In some embodiments, substantially all of the power of the return optical signals back-scattered from the target is in the form of optical signals of the second circular polarization back-scattered from the target.

Some embodiments further provide for one or more emitter blocks wherein the laser source is coupled to said one or more emitter blocks via an optical switch fabric.

In some embodiments, the optical switch fabric comprises a cascade of binary switches in the form of one or more switch trees.

In some embodiments, the one or more switch trees comprise separate switch trees for switching received return optical signals of the first linear polarization and received return optical signals of the second linear polarization.

In some embodiments, the optical splitting network comprises said beamsplitter absent any duplexer.

The foregoing and additional aspects and embodiments of the present disclosure will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosure will become apparent upon reading the following detailed description and upon reference to the drawings. FIG. 1 is a schematic block diagram of a known integrated photonics polarization- multiplexed LIDAR system.

FIG. 2 is a schematic block diagram of an integrated photonics polarization- multiplexed LIDAR system implemented for receiving the orthogonal polarization of returned optical signals after undergoing transformation via a quarter wave plate into and back from circularly polarized light, according to an embodiment.

FIG. 3 is a schematic block diagram of an example emitter block implementation for an integrated photonics polarization-multiplexed LIDAR system according to an embodiment.

FIG. 4A is a schematic block diagram of an example optical splitter network implementation for an integrated photonics polarization-multiplexed LIDAR system according to one embodiment.

FIG. 4B is a schematic block diagram of an example optical splitter network implementation for an integrated photonics polarization-multiplexed LIDAR system according to another embodiment.

FIG. 4C is a schematic block diagram of an example optical splitter network implementation for an integrated photonics polarization-multiplexed LIDAR system according to a further embodiment.

FIG. 5A is a schematic block diagram of an example mounting of a quarter wave plate to an integrated photonics polarization-multiplexed LIDAR system according to an embodiment.

FIG. 5B is a schematic block diagram of a second example mounting of a quarter wave plate to an integrated photonics polarization-multiplexed LIDAR system according to an embodiment.

FIG. 5C is a schematic block diagram of a third example mounting of a quarter wave plate to an integrated photonics polarization-multiplexed LIDAR system according to an embodiment.

FIG. 5D is a schematic block diagram of a fourth example mounting of a quarter wave plate to an integrated photonics polarization-multiplexed LIDAR system according to an embodiment. FIG. 5E is a schematic block diagram of a fifth example mounting of a quarter wave plate to an integrated photonics polarization-multiplexed LIDAR system according to an embodiment.

While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments or implementations have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of an invention as defined by the appended claims.

DETAILED DESCRIPTION

Photonics systems utilize a host of structural and functional elements to guide, launch, manipulate, or otherwise utilize photonic signals to their desired application. Many LIDAR systems utilize multiple optical receive/transmit locations at the system boundary to direct, like an optical antenna, optical signals into free-space and to receive optical signals scattered back from objects and surroundings of interest. On-chip pixel locations directing optical signals into free-space may also operate to receive optical signals therefrom, and may be referred to as emitters, each often with a unique location. Although reciprocity is a general rule for typical optical systems, in some LIDAR systems, some emitters can be dedicated to either launching LIDAR optical signals into free space or to receiving scattered signals only. In some implementations, the emitters are arranged in an array.

Some chip-based LIDAR systems employ one or more on-chip LIDAR transceiver blocks which launch and receive optical signals for the system. In LIDAR systems implementing beam scanning, typically a controllable optical switch fabric may be implemented between each of the one or more LIDAR transceiver blocks and multiple emitters, to switch the optical signals to and receive optical signals from different emitters at different locations in some sequence. Typically, at any one time, each one of the one or more transceiver blocks is optically coupled via a switch fabric to one emitter or emitter block, for receiving optical signals or transmitting optical signals or both. Operation of the switch fabric in this manner may enable each emitter to function as an addressable “pixel”. Some multiple transceiver block LIDAR systems employing beam steering employ multiple LIDAR transceiver blocks and switch fabrics to address multiple respective emitters in a parallel fashion. In such implementations the switch fabrics may be driven by global drive signals to simultaneously and in a parallel fashion address emitters for each transceiver block at various respective locations simultaneously, for example, by section or row.

In some embodiments, each LIDAR transceiver block sends light out via the switch fabric and then receives the back-scattered signal from the same switch fabric, determining primarily, but not limited to, an object’s distance, reflectance, and velocity. In some embodiments, a LIDAR transceiver block may transmit and receive optical signals through different switch fabrics and emitters, in some cases, the switch fabrics and emitters dedicated to only receive or transmit optical signals. In some embodiments, a LIDAR transceiver may transmit and receive optical signals through different switch fabrics but through the same emitters. In some cases, the different switch fabrics are dedicated to only receive or transmit optical signals. Some of the types of LIDAR transceiver blocks contemplated by the embodiments include time-of-flight LIDAR transceivers, amplitude modulation coded LIDAR transceivers, and Frequency-Modulated-Continuous-Wave (FMCW) LIDAR transceivers.

In many LIDAR systems the polarization states of light are exploited or otherwise put to useful application in whatever manner depending upon the context. One such application is polarization-multiplexed LIDAR, in which the LIDAR system transmits optical signals of one polarization but is configured to receive and process optical signals of the orthogonal polarization or both polarizations. For example, some systems transmit TE but are arranged to receive and process TM, while other systems transmit TE and are arranged to receive and process TE and TM. This is useful in particular contexts, as many targets are often depolarizing, converting some of the optical signals incident on them into the orthogonal polarization upon reflection or back scattering of the optical signals. Sometimes, being able to detect the orthogonal polarization improves the LIDAR system’s ability to see or detect something of interest in connection with the target. In some contexts, using a LIDAR system which detects optical signals of both the orthogonal and the original polarization can provide additional useful information from the ratio of the received polarizations, i.e. information may be gleaned from a target’s “depolarization ratio”. In such systems, however, there is generally a performance hit in terms of optical power. In the case of systems arranged to receive and detect only the orthogonal polarization, potentially half and sometimes more than half the power is lost. In the case of systems arranged to receive and detect both the orthogonal and the original polarization, a 2x2 transmit/receive splitter (duplexer) often used in said architectures can create a further 3dB loss in either direction. Being associated with the optical beams launched toward and received from target objects, these are not insignificant nor inconsequential losses of power. The greater the power associated with optical signals utilized in the detecting and ranging of the target objects the more accurate and potentially the greater the upper range that a LIDAR instrument will have.

With reference to FIG. 1 a known integrated photonics polarization-multiplexed LIDAR system 10 will now be discussed.

A photonics integrated chip 110 of the system 10, includes a laser source 1110 which launches an optical signal having an original linear polarization of TE for example, over waveguide 1191 into an optical splitter network 1120, which splits a portion of the optical signal into two “local oscillator” optical signals TELO and provides them via two waveguides 1193 1195 to a TM receiver 1130 and a TE receiver 1140 respectively. The TE receiver 1140 is also coupled to the optical splitter network 1120 via a waveguide 1196 for receiving return optical signals having the original linear polarization TESIG as described below. The optical splitter network 1120 launches an optical signal TE having the remainder of the optical power over a waveguide 1192 to an emitter block 1150. The emitter block 1150 is arranged to launch the TE polarized optical signal in free space 115 towards an optical lens system 130 after which it traverses the space 135 to a target 140. The return optical signals scattered back from the target 140 include optical signals having the original linear polarization TESIG as well as optical signals having the orthogonal linear polarization TMSIG. These signals traverse back through free space 135, the lens system 130, free space 115, and into the emitter block 1150. The emitter block 1150 converts (rotates) the return optical signals having the orthogonal linear polarization TMSIG into optical signals having the original linear polarization TE and sends them over waveguide 1194 to the TM receiver 1130 as TE optical signals where they are used along with the “local oscillator” TELO signals from waveguide 1193 for detection and ranging. The emitter block 1150 allows the return optical signals of the original linear polarization TESIG to pass over the waveguide 1192 to the optical splitter network 1120 where it is routed and provided over waveguide 1196 to the TE receiver 1140 where they are used along with the “local oscillator” TELO signals from waveguide 1195 for detection and ranging. In some cases some portion of the return optical signals of the original linear polarization TESIG traverse waveguide 1191 back to the laser source 1110 where they are discarded and ignored.

In such a known system 10, although both return optical signals are detected and utilized to analyze the target of interest, i.e. both the orthogonal and original linear polarizations are received respectively in the TM receiver 1130 and the TE receiver 1140, often only half of the power of the optical signals from the laser source 1110 is deployed for use in detection and ranging in the form of an outgoing TE optical signal, due to the at least 3 dB loss caused by typical implementations of the optical splitter network 1120. Moreover, the return optical signals in the original linear polarization TESIG are also reduced in power at least by half (by 3dB) once again at the optical splitter network 1120 prior to being received at the TE receiver 1140.

Single receiver variations of the known integrated photonics polarization- multiplexed LIDAR system 10 are implemented utilizing only the TM receiver for detecting only the orthogonal linear polarization of returned optical signals (after having been rotated). In those systems, the TE receiver 1140 is not present, nor are there any waveguides 1196 and 1195 coupling the TE receiver 1140 to the optical splitter network 1120 for receiving optical signals therefrom. In these single receiver variations the optical splitter network 1120 splits the optical signal received over waveguide 1191 from the laser source 1110 into a single “local oscillator” optical signal TELO and an optical signal TE having the remainder of the optical power. The optical splitter network 1120 provides the local oscillator signal TELO via the waveguide 1193 to the TM receiver 1130 and launches the optical signal TE over the waveguide 1192 toward the emitter block 1150. In these variations of the system 10 the return optical signals of the original linear polarization TESIG traverse waveguide 1192 to the beamsplitter and/or the laser source 1110 where they are discarded and ignored. In these known single receiver variations of the system 10, only return optical signals of the orthogonal linear polarization are received in the TM receiver 1130 (after having been rotated), detected and utilized to analyze the target of interest.

As is clear from the foregoing, with respect to optical signal strength, known polarization-multiplexed LIDAR systems and variations thereof perform better when measuring targets which are depolarizing and more specifically those which convert as much of the incident original linear polarization state into the orthogonal linear polarization state as possible. Contrary to this ideal kind of target for these known systems, almost all targets in reality, and in fact most ideal targets for which LIDAR is implemented to detect and range, reflect the original incident linear polarization more than they rotate the optical signal to an orthogonal state. This tendency is exhibited to an even further degree for metal or mirror-like targets which are highly linear polarization maintaining and reflect or scatter the vast majority of the optical signals with optical signals having the same linear polarization. Generally, rough or diffuse reflectors tend to be linear polarization scattering or depolarizing. Most targets include both diffuse and mirror-like materials and consequently typically a majority of the return signal power is of the original linear polarization.

Polarization-multiplexed LIDAR systems can be varied so as to take advantage of their greater performance with respect to orthogonal linear polarization states while being used on real-world targets of interest which either are linear polarization maintaining or tend to be so, by careful rotation of the linear polarization states. A Faraday rotator can be utilized outside of the photonics integrated chip 110 along one of the free space paths of the optical signals 115 135 to rotate the optical signals of the original linear polarization TE, to optical signals having a 45° linear polarization state. The optical signals at 45° once back- scattered from a linear polarization maintaining target would mostly consist of return optical signals having the same polarization i.e. a linear polarization state of 45°, which would pass back through the Faraday rotator to obtain another 45° rotation in linear polarization state to result in a return optical signal having a 90° linear polarization or a linear polarization orthogonal to the original, by the time it enters the emitter block 1150 going back into the photonics integrated chip 110. This double rotational approach to the linear polarization states provides advantages. In the single receiver variation of system 10, since most of the return optical signal is now orthogonal, e.g. TM, the power of the signal at the TM receiver 1130 has been boosted. In addition to this boost, for the dual receiver system 10 including the TE receiver 1140 and the waveguides 1196 1195, since most of the return optical signal is now orthogonal, e.g. TM, the return optical signal of greater power is directed away from the high-loss path through the optical splitter network 1120 to the TE receiver 1140 and instead goes through the low-loss path to the TM receiver 1130. This general advantage is even greater for particular use in detecting and ranging of metal or mirror-like linear polarization maintaining targets 140.

Although Faraday rotators can represent an improvement in functionality, they are generally very expensive, fundamentally requiring exotic material such as rare-earth doped garnets grown in a single crystal. Linear polarization double rotation also relies on the assumption that in order to solve the problem of real-world targets tending to be linear polarization maintaining, the optical signals must undergo a total rotation of 90° on the round trip between the LIDAR system and the target. Linear polarization double rotation, it turns out, is not the only approach to polarization-multiplexed LIDAR systems that can take advantage of their greater performance with respect to polarization states back scattered from real-world targets of interest. In contrast to expensive rotational approaches using Faraday rotators, the embodiments described herein rely on a different kind of manipulation of polarization states which turn out to be advantageous with targets of interest which are linear polarization maintaining or tend to be so.

The polarization-multiplexed LIDAR systems of the embodiments described below utilize a different approach which, rather than rotating polarization states, transforms the polarization states into different kinds of polarization states, specifically, converts transmitted linear polarization states into circular polarization states and converts received circular polarization states into linear polarization states.

It turns out that most real-world targets, including targets which are diffuse or rough to some extent, do not maintain the circular polarization states upon reflection. In other words, incident circularly polarized optical signals once reflected or scattered back from real-world objects will also be circularly polarized but will have the opposite handedness, i.e. will be orthogonal to the incident circularly polarized optical signals. For most targets tending to be diffuse or rough, the optical power of right hand circularly polarized (RHCP) light once reflected is mostly in the form of return optical signals of left hand circularly polarized (LHCP) light and vice versa, and for metal and mirror-like targets the optical power of RHCP light once reflected is almost entirely in the form of return optical signals of LHCP and vice versa.

Rather than relying on an approach, such as a Faraday rotator which assumes linear polarization is mostly maintained and uses double rotation, the systems of the embodiments herein utilize a quarter wave plate to convert linearly polarized optical signals into circularly polarized optical signals and vice versa, on the premise that targets including relatively diffuse ones, are primarily the opposite of what one would call “circular polarization maintaining”. Quarter wave plates (QWP) are very inexpensive and can be made, for example, from precisely-cut quartz. Placed anywhere between the emitter block (and in fact a PSR if implemented in an emitter block) of the architecture and the target, the QWP converts TE linear polarization to RHCP light which upon backscattering becomes primarily LHCP light, which is converted by the QWP into TM linear polarization which is received by and system and traverses the system over the low-loss TM linear polarization path.

It should be noted that in the embodiments which follow, the QWP is oriented such that the fast and slow axes are properly oriented in relation to the direction of linear polarization of the optical signals so as to enable conversion of TE into RHCP and LHCP into TM. It should be understood that the QWP may be oriented to convert TE into LHCP and RHCP into TM and the embodiments would function the same albeit using different transmit and receive polarization states in free space. It should be understood that the QWP may be of any order, i.e. a zero order or any multi-order QWP as known to persons having ordinary skill in the art. It also should be understood that the system architecture of the following embodiments may be arranged so that TM is the original linear polarization of the optical signals from the laser source with appropriate configuration and types of waveguides and components, i.e. all appearances of TM may be replaced with TE and vice versa. It should be understood that references to TM or TE as well as RHCP or LHCP may be reversed throughout the description, and that generally systems with orthogonal polarization may be implemented in the same manner and with the same interrelationships. With reference to FIG. 2 an integrated photonics polarization-multiplexed LIDAR system 20 for receiving returned optical signals after undergoing transformation into and back from circularly polarized light will now be discussed.

A photonics integrated chip 210 of the system 20, includes a laser source 2110 which launches an optical signal having an original linear polarization of TE for example, over waveguide 2191 into an optical splitter network 2120, which splits a portion of the optical signal into two “local oscillator” optical signals TELO and provides them via two waveguides 2193 2195 to a TM receiver 2130 and a TE receiver 2140 respectively. In some embodiments each of the two “local oscillator” optical signals emerging from the two illustrated outputs of the optical splitter network 2120 are provided to ones of the TM and TE receivers 2130 2140 opposite to that illustrated. One of the TELO optical signals may have a small proportion of the power of the optical beam (for example 3%) and in some embodiments the splitting or tap ratio for that signal is tunable via an electrical control signal provided to the optical splitter network 2120. The TE receiver 2140 is also coupled to the optical splitter network 2120 via a waveguide 2196 for receiving return optical signals having the original linear polarization TESIG as described below. The optical splitter network 2120 launches an optical signal TE having the remainder and typically the majority of the optical power over a waveguide 2192 through an optical switch fabric 212 to any one of one or more emitter blocks 2150. The optical switch fabric 212 in some embodiments comprises a binary tree of optical switches and addresses one emitter block 2150 at a time for each laser source 2110. In some embodiments, the system 20 does not include any optical switch fabric 212. The emitter block 2150 is arranged to launch the TE polarized optical signal into free space 215 towards a quarter wave plate (QWP) 220 where the TE polarized optical signal is converted into a RHCP optical signal and launched in free space 225 to an optical lens system 230 after which it traverses the space 235 to a target 240. The return optical signals scattered back from the target 240 include return optical signals having right hand circular polarization RHCPSIG as well as return optical signals having left hand circular polarization LHCPSIG. These return optical signals traverse back through free space 235, the lens system 230, free space 225, and back through the QWP 220 which converts the return optical signals of the left hand circular polarization LHCPSIG into a return optical signals having the orthogonal linear polarization TMSIG and converts the return optical signals of the left hand circular polarization RHCPSIG into a return optical signals having the original linear polarization TESIG. These return optical signals traverse back through free space 215 and are received by the one or more emitter blocks 2150. Each emitter block 2150 converts (e.g. rotates) the received return optical signals having the orthogonal linear polarization TMSIG into optical signals having the original linear polarization TE and sends them over waveguide 2194 through the optical switch fabric 212 to the TM receiver 2130 as TE optical signals where they are used along with the “local oscillator” TELO signals from waveguide 2193 for detection and ranging. The emitter block 2150 allows the received return optical signals of the original linear polarization TESIG to pass over the waveguide 2192 through the optical switch fabric 212 to the optical splitter network 2120 where it is routed and provided over waveguide 2196 to the TE receiver 1140 where they are used along with the “local oscillator” TELO signals from waveguide 2196 for detection and ranging. A portion of the received return optical signals of the original linear polarization TESIG traverse waveguide 2191 back to the laser source 2110 where they are discarded and ignored.

It should be noted that the optical switch fabric 212 is arranged to separately switch the appropriate optical signals over the waveguide 2192 to and from the appropriate emitter blocks 2150 and to switch appropriate optical signals over the waveguide 2194 to and from the appropriate emitter blocks 2150, and in some embodiments separate switch trees are implemented for the TE and TM paths. In some embodiments the switch fabric 212 is located between the laser source 2110 and the optical splitter network 2120 along waveguide 2191 rather than along waveguides 2192 and 2194. In some embodiments, only one switch tree is implemented between each laser source 2110 and the multiple independent receiver/emitter block structures it powers. Although this represents an increase in the number of receivers, fewer switch trees are utilized (only one polarization) which greatly reduces complexity of the system 20. In some embodiments multiple instances of all the electrical and optical circuitry (effectively a transceiver block) left of the optical switch fabric 212 in FIG. 2 are implemented. Optionally in some embodiments, between the lens system 230 and the target 240 are mirror systems such as a ID mirror for perpendicular-axis steering in the case of a ID array implementation. In embodiments such as the system 20, although both return optical signals received at the emitter blocks 2150 are detected and utilized to analyze the target of interest, i.e. both the received orthogonal and original linear polarizations are detected respectively in the TM receiver 2130 and the TE receiver 2140, often only at most half of the power of the optical signals from the laser source 2110 is deployed for use in detection and ranging in the form of an outgoing TE optical signal, due to the at least 3 dB loss caused by typical implementations of the optical splitter network 2120 to accommodate detection of both received return optical signals. Moreover, the received return optical signals in the original linear polarization TESIG are also reduced in power at least by half (by 3dB) once again at the optical splitter network 2120 prior to being received at the TE receiver 2140.

Single receiver variations of the integrated photonics polarization-multiplexed LIDAR system 20 are implemented utilizing only the TM receiver for detecting only the received orthogonal linear polarization of the received return optical signals. In those systems, the TE receiver 2140, and waveguides 2195 and 2196 coupling the TE receiver 2140 to the optical splitter network 2120 for receiving optical signals therefrom (indicated by the dashed lines of FIG. 2) are not present. In these single receiver variations the optical splitter network 2120 may consist of a single beamsplitter for splitting the optical signal received over waveguide 2191 from the laser source 2110 into a single (rather than two) “local oscillator” optical signal TELO which may have a small proportion of the power of the optical beam (for example 3%) and providing it via the waveguide 2193 to the TM receiver 2130. In some embodiments the splitting or tap ratio of the beamsplitter is tunable via an electrical control signal provided thereto. The beamsplitter launches an optical signal TE having the remainder and majority of the optical power over the waveguide 2192 through the optical switch fabric 212 toward any of one or more of the emitter blocks 2150. Unlike variations described below, the single receiver variations do not employ any duplexer in the optical splitter network 2120 and hence depending upon the beamsplitter ratio, the power of the optical signal TE directed over the waveguide 2192 can be substantially higher, for example closer to 97% versus 50%. In these variations of the system 20, the received return optical signals of the original linear polarization TESIG traverse waveguide 2192 to the beamsplitter and/or the laser source 2110 where they are discarded and ignored. In these single receiver variations of the system 20, only return optical signals received at the emitter block 2150 in the orthogonal linear polarization are detected by the TM receiver 2130 (after having been rotated) and utilized to analyze the target of interest. Moreover, most of the power of the optical signals from the laser source 2110 is retained for use in detection and ranging, often only encountering a small loss (e.g. 3%) at the beamsplitter and other nominal losses throughout the system 20.

With reference to FIG. 3, an implementation of an emitter block 3150 for use within the LIDAR system 20 of FIG. 2 will now be discussed.

An optical signal TE having typically most of the optical power after passing through the optical splitter network from the laser, passes through the optical switch fabric over a waveguide 3192 to a polarization splitter rotator (PSR) 3152 of the emitter block 3150. The PSR 3152 is arranged to pass the TE polarized optical signal over a waveguide 3155 towards a dual polarization emitter 3154 of the emitter block 3150 which launches the TE polarized optical signal into free space 315 towards the QWP, lens system, and target. The return optical signals scattered back from the target through the lens system and QWP, traverse the free space 315 and arrive at the emitter block 3150 as a received return optical signal having the orthogonal linear polarization TMSIG and a received return optical signal having the original linear polarization TESIG. These received return optical signals traverse the dual polarization emitter 3154 and the waveguide 3155 back into the PSR 3152. The PSR 3152 converts (rotates) the received return optical signals having the orthogonal linear polarization TMSIG into optical signals having the original linear polarization TE and sends them over waveguide 3194 through the optical switch fabric to the TM receiver as TE optical signals where they are used for detection and ranging. The PSR 3152 allows the received return optical signals of the original linear polarization TESIG to pass over the waveguide 3192 through the optical switch fabric and the optical splitter network to the TE receiver where they are used for detection and ranging. As noted above, in variations where the LIDAR system has no TE receiver, the received return optical signals of the original linear polarization TESIG pass over the waveguide 3192 through the optical switch fabric and to the optical splitter network and/or the laser where they are discarded and ignored.

Although the emitter block 2150 of FIG. 2 and the implementation of the emitter block 3150 of FIG. 3 output a received return optical signal of the orthogonal linear polarization TMSIG as a TE signal after rotation by for example a PSR, it should be understood that in some embodiments the emitter block 2150 comprises one or more optical elements (e.g. some gratings based dual-polarization emitters) which separate the received return optical signals without rotation of the polarization of the received return optical signals of the orthogonal linear polarization TMSIG, instead only rerouting them over the waveguide 2194 3194 leading to a TM receiver 2130 arranged to receive a signal having the orthogonal linear polarization TM, while rerouting the received return optical signal of the original linear polarization TESIG over the waveguide 3192 through the splitter fabric 212 towards the optical splitter network 2120.

With reference to FIG. 4A, a first implementation of an optical splitter network 4120 A for use within the LIDAR system 20 of FIG. 2 will now be discussed.

Optical signals having an original linear polarization of TE for example, launched by the laser source pass over waveguide 4191 A to a beamsplitter 4122 A of the optical splitter network 4120 A, for splitting the optical signal into a “local oscillator” optical signal TELO which may have a small proportion of the power of the optical beam (for example 3%) and providing it via a waveguide 4195A to one of the TM or TE receivers. In some embodiments the splitting or tap ratio of the beamsplitter 4122A is tunable via an electrical control signal provided thereto. The beamsplitter 4122 A launches an optical signal TE having the remainder and majority of the optical power over a waveguide 4125A toward a duplexer 4124A (e.g. a 2x2 splitter) of the optical splitter network 4120A which splits the optical signal TE into two optical signals of generally equal power. The duplexer 4124 A sends one of these signals, a “local oscillator” TELO signal, via a waveguide 4193 A to the other one of the TM or TE receivers. The duplexer 4124 A forwards the other of the two optical signals having the original linear polarization TE over waveguide 4192 A through the optical switch fabric to one of the emitter blocks. Return optical signals of the original linear polarization TESIG pass over the waveguide 4192A from the optical switch fabric to the duplexer 4124A where the return optical signal of the original linear polarization TESIG is split into two. One of these two optical signals is provided over waveguide 4196A to the TE receiver where they are used for detection and ranging. The other of these optical signals traverses over waveguide 4125 A back to the beamsplitter 4122A and/or the waveguide 4191 A and laser source where they are discarded and ignored. With reference to FIG. 4B, a second implementation of an optical splitter network 4120B for use within the LIDAR system 20 of FIG. 2 will now be discussed.

Optical signals having an original linear polarization of TE for example, launched by the laser source pass over waveguide 4191B to a duplexer 4124B (e.g. a 2x2 splitter) of the optical splitter network 4120B, for splitting the optical signal into two. One of these two optical signals is provided as a “local oscillator” optical signal TELO via a waveguide 4125B to a beamsplitter 4122B (such as a 1 :2 beamsplitter) where it is split into a TELO signal provided along waveguide 4193B to one of the TM or TE receivers and provided along waveguide 4195B to the other one of the TM or TE receivers. The duplexer 4124B launches the second of the two optical signals having the original linear polarization TE over waveguide 4192B through the optical switch fabric to one of the emitter blocks. Return optical signals of the original linear polarization TESIG pass over the waveguide 4192B from the optical switch fabric to the duplexer 4124B where the return optical signal of the original linear polarization TESIG is split into two. One of these two optical signals is provided over waveguide 4196B to the TE receiver where they are used for detection and ranging. The other of these optical signals traverses over waveguide 4191B to the laser source where they are discarded and ignored.

With reference to FIG. 4C, a third implementation of an optical splitter network 4120C for use within the LIDAR system 20 of FIG. 2 will now be discussed.

Optical signals having an original linear polarization of TE for example, launched by the laser source pass over waveguide 4191C to a duplexer 4124C (e.g. a 2x2 splitter) of the optical splitter network 4120C, for splitting the optical signal into two. One of these two optical signals is provided as a “local oscillator” optical signal TELO via a waveguide 4195C to one of the TM or TE receivers. The duplexer 4124C launches the second of the two optical signals having the original linear polarization TE over waveguide 4125C to a beamsplitter 4122C of the optical splitter network 4120C. The beamsplitter 4122C splits the optical signal into two, one being a “local oscillator” optical signal TELO which may have a small proportion of the power of the optical beam (for example 3%) and provides it via a waveguide 4193C to the other one of the TM or TE receivers. In some embodiments the splitting or tap ratio of the beamsplitter 4122C is tunable via an electrical control signal provided thereto. The beamsplitter 4122C launches the second optical signal having the original linear polarization TE and the remainder and majority of the optical power over waveguide 4192C through the optical switch fabric to one of the emitter blocks. Return optical signals of the original linear polarization TESIG pass over the waveguide 4192C from the optical switch fabric to the beamsplitter 4122C which passes on a majority of the optical power of the return optical signal of the original linear polarization TESIG over waveguide 4125C to the duplexer 4124C where the return optical signal of the original linear polarization TESIG is split into two. One of these two optical signals is provided over waveguide 4196C to the TE receiver where they are used for detection and ranging. The other of these optical signals traverses over waveguide 4191 C to the laser source where they are discarded and ignored.

As is clear from the foregoing, with respect to optical signal strength, polarization- multiplexed LIDAR systems 20 with one or two receivers perform better than known solutions when measuring targets which are depolarizing and more specifically those which convert as much of the incident original circular polarization state into the orthogonal circular polarization state as possible. Contrary to the known systems described above, this coincides with the scattering of almost all targets in reality and that of the most ideal targets for which LIDAR is implemented to detect and range.

In the single receiver variation of system 20 of FIG. 2, since most of the received return optical signal is now orthogonal, e.g. TM, the power of the signal at the TM receiver 2130 has been boosted. In addition to this boost, for the dual receiver system 20 of FIG. 2, since most of the received return optical signal is now orthogonal, e.g. TM, the received return optical signal of greater power is directed away from the high-loss path through the duplexer 4124A, 4124B, 4124C of the optical switching network 2120 to the TE receiver 2140 and instead goes through the low-loss path to the TM receiver 2130. This general advantage is even greater for particular use in detecting and ranging of metal or mirror-like “orthogonal circular polarization converting” targets 240.

Generally, it should be noted that single receiver variations of FIG. 2 which comprise a beamsplitter without a duplexer are preferable due to their architectural simplicity and also due to their lower power loss, especially in the transmission of optical signals toward the target, afforded by a relatively low beamsplitter ratio (e.g. 3%) and the absence of any duplexer. It should be understood that the quarter wave plates of the embodiments illustrated in FIGs. 2 and 3 may be positioned anywhere between the target 240 and the PSR 3152 of the implementation of the emitter blocks 3150, within or on the photonics integrated chip 210, before or after or affixed to the lens system 230.

Accordingly, reference is now made to FIGs. 5A-5E which illustrate a non- exhaustive selection of example mounting positions for the quarter wave plate of both architectures. In the system 50A of FIG. 5A, the quarter wave plate 520 is attached e.g. glued to a facet of the photonics integrated chip 510. In the system 50B of FIG. 5B, the quarter wave plate 520 is attached or mounted to a common carrier such as the submount 516 for both the photonics integrated chip 510 and the quarter wave plate 520. In the system 50C of FIG. 5C, the quarter wave plate 520 is attached e.g. glued to a facet of a common carrier such as the submount 516 for both the photonics integrated chip 510 and the quarter wave plate 520. In the system 50D of FIG. 5D, the quarter wave plate 520 is attached e.g. glued to a facet of a lens system 530 between the lens system 530 and the photonics integrated chip 510. In the system 50E of FIG. 5E, the quarter wave plate 520 is attached e.g. glued to a facet of a lens system 530 on the other side of the lens system 530 from the photonics integrated chip 510. The quarter wave plate 520 in embodiments such as that shown in FIG. 5E would generally be larger than the quarter wave plate 520 in embodiments such as that shown in FIG. 5D due to the relatively smaller beam width at the point in the optical chain between the photonics integrated chip 510 and the lens system 530 versus that between the lens system 530 and the target. In yet other systems, the quarter wave plate 520 is located within a multi-element lens system 530 between some of the lens elements thereof. In all embodiments the quarter wave plate is appropriately sized such that all of the outgoing and incoming optical beams, at that point in the optical chain, pass through the quarter wave plate.

While particular implementations and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of an invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An integrated photonics polarization-multiplexed LIDAR system comprising: a laser source for generating optical signals of a first linear polarization; an emitter block for receiving optical signals of the first linear polarization generated by the laser source; a quarter wave plate (QWP) for receiving optical signals of the first linear polarization from the emitter block, and for converting them into optical signals of a first circular polarization and forwarding them toward a target of the system, the QWP for receiving return optical signals back-scattered from the target and for converting return optical signals of the first circular polarization into return optical signals of the first linear polarization and converting return optical signals of a second circular polarization orthogonal to the first circular polarization into return optical signals of a second linear polarization orthogonal to the first linear polarization, the emitter block receiving the return optical signals of the first and second linear polarizations from the QWP as received return optical signals of the first and second linear polarizations respectively; and a first receiver for receiving the received return optical signals of the second linear polarization from the emitter block.

2. The polarization-multiplexed LIDAR system of claim 1, comprising a second receiver for receiving at least a portion of the received return optical signals of the first linear polarization from the emitter block.

3. The polarization-multiplexed LIDAR system of claim 1, further comprising an optical splitter network coupled between the laser source and the emitter block for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into a first and second optical signal, and forwarding the first optical signal to the first receiver as a local oscillator signal, and forwarding the second optical signal to the emitter block.

4. The polarization-multiplexed LIDAR system of claim 3, wherein the optical splitter network comprises a beamsplitter having a splitting ratio such that a power of the first optical signal is less than a power of the second optical signal.

5. The polarization-multiplexed LIDAR system of claim 4, wherein the splitting ratio of the beamsplitter is tunable.

6. The polarization-multiplexed LIDAR system of claim 2, further comprising an optical splitter network coupled between the laser source and the emitter block for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into a first optical signal, a second optical signal, and a third optical signal, forwarding the first optical signal to the first receiver as a first local oscillator signal, forwarding the second optical signal to the emitter block, and forwarding the third optical signal to the second receiver as a second local oscillator signal, the optical splitter network further for receiving the received return optical signals of the first linear polarization from the emitter block and forwarding a portion of the received return optical signals of the first linear polarization from the emitter block to the second receiver.

7. The polarization-multiplexed LIDAR system of claim 6, wherein the optical splitter network comprises a duplexer for receiving at least a portion of the received return optical signal of the first linear polarization from the emitter block and for providing said portion of the received return optical signals of the first linear polarization from the emitter block to the second receiver.

8. The polarization-multiplexed LIDAR system of claim 7, wherein the optical splitter network further comprises a beamsplitter for receiving at least a portion of the optical signal of the first linear polarization generated by the laser and providing some portion thereof as one of the first or second local oscillator signals to the respective one of the first and second receivers.

9. The polarization-multiplexed LIDAR system of claim 8, wherein said duplexer is for receiving at least some portion of the of the optical signal of the first linear polarization generated by the laser and for providing a portion thereof as the other one of the first or second local oscillator signals to the respective other one of the first and second receivers.

10. The polarization-multiplexed LIDAR system of claim 7, wherein the duplexer is for receiving the optical signal of the first linear polarization generated by the laser, splitting the optical signal of the first linear polarization generated by the laser into the second optical signal and into a fourth optical signal including the first optical signal and the third optical signal, providing the fourth optical signal to a beamsplitter which splits the fourth optical signal into the first and second optical signals and provides them to the first and second receivers as said first and second local oscillator signals.

11. The polarization-multiplexed LIDAR system of claim 1 , wherein the emitter block comprises a polarization splitter rotator (PSR) and a dual polarization emitter.

12. The polarization-multiplexed LIDAR system of claim 1, wherein a power of the return optical signals of the second circular polarization back-scattered from the target is greater in magnitude than a power of the return optical signals of the second circular polarization back-scattered from the target.

13. The polarization-multiplexed LIDAR system of claim 1, wherein substantially all of the power of the return optical signals back-scattered from the target is in the form of optical signals of the second circular polarization back-scattered from the target.

14. The polarization-multiplexed LIDAR system of claim 1, further comprising one or more emitter blocks wherein the laser source is coupled to said one or more emitter blocks via an optical switch fabric.

15. The polarization-multiplexed LIDAR system of claim 14, wherein the optical switch fabric comprises a cascade of binary switches in the form of one or more switch trees.

16. The polarization-multiplexed LIDAR system of claim 15, wherein the one or more switch trees comprise separate switch trees for switching received return optical signals of the first linear polarization and received return optical signals of the second linear polarization.

17. The polarization-multiplexed LIDAR system of claim 4, wherein the optical splitting network comprises said beamsplitter absent any duplexer.