Quantum sensing method and quantum sensing device

Abstract

The present disclosure relates to remote sensing devices, remote sensing methods, and remote sensing systems. For example, an exemplary device may include an interferometer including a beam splitter that splits incident time bin pairs having modulated phase signatures imprinted thereon and at least two reflectors. The at least two reflectors generate parallel photon streams from each split incident time bin pair, generating first and second outputs. The device includes at least two paths, each path allowing a respective one of the first and second outputs to travel toward a respective detector.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 478,746, filed January 6, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates generally to the field of quantum sensing. [Background technology]

[0003] In existing remote sensing and ranging systems, a photon source, such as a laser, emits a large number of photon pulses that propagate toward a target scene. Upon impact, some of the photons are reflected or scattered toward a receiver equipped with a camera that captures the reflected or scattered photons. Detection at each pixel of a multi-pixel camera corresponds to a distinct spatial region of the scene, effectively collecting the spatial information encoded in the reflected photons. Furthermore, the arrival time recorded by each pixel provides an additional degree of freedom that can be used to calculate the relative distance between the photon source and objects in the scene. This computational process allows for the reconstruction of a three-dimensional representation of the scene, effectively rendering a three-dimensional remote sensing system. Such sensors have recently attracted significant interest for a variety of applications due to their superior properties, including excellent sensitivity, non-intrusiveness, ultra-high resolution, and rapid response capabilities.

[0004] A challenge in these remote sensing and ranging systems is dealing with inaccuracies and reduced sensitivity caused by noise, which can include noise photons scattered and reflected from the surrounding atmosphere, ambient light, detector dark noise, and thermal noise.

[0005] Previously implemented techniques for distinguishing between signal and noise photons have been inefficient or inaccurate, or require both the emitter and detector to be within the line of sight of the target. Known techniques include polarization filtering, spectral filtering, time filtering, signal averaging, and employing complex signal processing algorithms to distinguish between signal and noise photons. Similarly, in some existing applications, short-pulse lasers are used to transmit pulse trains, and high-speed detectors are used to search for photons arriving within a short time window, thereby using a degree of temporal freedom to filter out noise photons.

[0006] Traditional LiDAR systems, hereafter referred to as intensity-based LiDARs, use degrees of freedom (DoFs), such as time of flight and intensity, to measure the presence, potential range, and / or speed of targets buried in noise (e.g., environmental noise). Intensity-based LiDARs can use a photon source that emits short pulses toward a target (or the target's expected location) and a detector that collects photons reflected or scattered by the target. When a target is not present, the detected photons are from the atmosphere, i.e., noise photons. On the other hand, when a target is present, some of the transmitted photons, i.e., signal photons, are reflected by the target and collected by the detector along with the noise photons. In an intensity-based LiDAR approach, the task of the detection algorithm is to determine with high certainty whether a target is present by analyzing the photons received by the detector. The performance of these types of LiDARs can be limited by detector noise and environmental noise.

[0007] The concept of intensity-based sensing is illustrated in Figure 1A. The top graph shows two cases: when only "noise" photons are detected (I N ) and the case where both "signal" and "noise" photons are detected (I S+N) and the time evolution of the detected signal for . The bottom graph in Figure 1A shows the corresponding histograms of the intensities for the two cases. The ability to distinguish between these two cases depends on the SNR between the two histograms. intensity The separation depends on the signal-to-noise ratio (SNR), denoted by , and can be defined as:

[0008]

number

[0009] where SNR=I s / I n is the ratio of the average signal to the average noise. SNR intensity can be reduced in several ways. The signal strength itself can decrease while the noise remains constant, so I S+N The histograms shift left, whereas as the average background noise increases (mean signal strength remains constant), both histograms shift right, resulting in an increase in SNR intensity If the two histograms are separated, it is easy to distinguish between them.

[0010] The detection probability can be increased by using multiple degrees of freedom (DoFs). For example, to utilize spectral DoF, a narrowband wavelength filter can be used to block noise photons with wavelengths different from those of the signal photons. Another option is to utilize temporal DoF. A combination of a short-pulse laser and a high-speed detector is used to receive photons within a short time window, thus blocking all other photons outside the window. Even with both of the above DoFs, it is not possible to distinguish between noise photons that pass through the wavelength filter and are detected within the same time window. In this case, the two peaks (noise and signal + noise) begin to overlap, as shown in Figure 1B, and the probability of error begins to increase.

[0011] Known systems, such as intensity-based LiDAR methods, that operate in high signal-to-noise ratio (SNR) regimes may require potentially undesirably bright laser pulse energies to overcome environmental noise (e.g., sunlight) to reliably detect the reflected signal. Higher-intensity LiDAR methods may also have narrower field-of-view angles or shorter ranges. LiDAR systems capable of operating at lower laser energies may be subject to reduced accuracy due to environmental noise. Low-energy lasers may not be suitable for low SNR regimes, where ambient noise photons can overwhelm weak signals and complicate detection.

[0012] Effective low-laser-energy LiDAR systems are particularly desirable in covert operations where bright laser sources can reveal the sensor's location or interfere with imaging systems. Additionally, the ability to operate at lower signal levels may enable a wider field of view and / or longer range.

[0013] Another existing technique is shown in FIG. 1C. In FIG. 1C, a photon source 102 emits photons, shown as output 150. The emitted photons pass through an imprinter 104. The imprinter 104 is comprised of an interferometer (comprised of mirrors and beam splitters, as shown). The interferometer and a piezoelectric actuator, as shown, are used together to imprint a phase signature, as shown via time bin pairs output from the imprinter 104 at output 152. The emitted time bin pairs reflect off a target 108 and are then received by an analyzer 106 (shown as output 154). The analyzer 106 includes another interferometer, where the time bin pairs entering the interferometer are further split and directed to a detector 110 (as shown at output 156).

[0014] However, existing techniques have difficulties with accurate or efficient detection, narrow field-of-view angles, and difficulty in filtering out noise photons that pass through wavelength filters and are detected in the same time window as the signal photons. Summary of the Invention

[0015] This disclosure describes systems, methods, and apparatus that operate at least in part based on quantum coherence degrees of freedom, and more specifically, describes an approach that splits received scattered photons into associated discrete time-bin pairs to exploit quantum coherence. The proposed approach may improve the performance, noise immunity, and sensitivity of quantum signal-based sensing and ranging applications.

[0016] The present disclosure contemplates generating, transferring, and measuring quantum coherence via time bin encoding techniques.

[0017] Existing time-bin encoding techniques, such as the approach shown in Figure 1C, can be challenging to implement. For example, the implementation environment can present challenges. Turbulent media can cause photon scattering, as opposed to more controlled environments (e.g., within single-mode optical fiber). One scenario where such challenges exist is implementing time-bin encoding techniques over a free-space channel with a spatially multimode light source. Photon scattering due to atmospheric turbulence and / or diffraction can mix spatial modes, making them distinguishable, resulting in poor interference quality. Even when single-mode light is used in the light source, atmospheric effects can convert photons into multiple distinguishable modes, thereby reducing visibility and performance.

[0018] One exemplary approach disclosed herein can address at least some of the above challenges through an analyzer configuration that improves the recovery of quantum coherence through scattered photons, thereby enabling detection of at least one of the presence or absence of targets at long distances. This approach can mitigate adverse effects in turbulent or high-noise environments. A phase modulator sequentially applies different phase patterns to act as a phase signature, improving the analyzer's ability to distinguish emitted photons from noise photons, for example.

[0019] Correlation performance can be characterized by techniques such as receiver operating characteristic (ROC) curves.

[0020] In summary, the transfer and recovery of quantum coherence via scattered photons enables object recognition, ranging, and velocity measurement of targets at long distances.

[0021] According to one aspect, a method is provided that includes transmitting a plurality of time bin pairs imprinted with a modulated phase signature toward a target and receiving the time bin pairs after scattering from the target. The method includes receiving a first data set with a first detector. The first data set is established based on a first output generated by the plurality of time bin pairs scattered from the target and processed with an analyzer that recovers the modulated phase signature in the generated first and second outputs. The method includes receiving a second data set with a second detector. The second data set is based on the generated second output. The method includes combining the first data set and the second data set and comparing the first and second data sets to a third data set describing the imprinted phase signature. The method includes determining one or more characteristics of the target based on the degree of correlation.

[0022] In an exemplary embodiment, the method includes combining the first data set and the second data set, the combining including at least one of subtracting, adding, multiplying, or dividing the first data set from the second data set.

[0023] In an exemplary embodiment, the one or more characteristics include at least one of presence, range, velocity, acceleration, and vibration.

[0024] In an exemplary embodiment, the comparing includes determining a degree of correlation between (1) the combined first and second data sets and (2) the third data set.

[0025] In an exemplary embodiment, the one or more characteristics include presence or absence, and determining presence further includes determining whether the degree of coherence can be classified into a preset range indicative of the presence of the target.

[0026] In an exemplary embodiment, combining the first and second data sets amplifies the imprinted phase signature and attenuates the received noise signal.

[0027] In an exemplary embodiment, the first and second data sets are related such that the first and second analyzer outputs are at least partially inverse of each other.

[0028] In an exemplary embodiment, the modulation is controlled via a phase modulator.

[0029] In an exemplary embodiment, the method further includes actuating a phase modulator in the analyzer based on the imprinted modulated phase signature.

[0030] In another aspect, an apparatus is disclosed. The apparatus includes an interferometer including a beam splitter that splits incoming time-bin pairs. The incoming time-bin pairs have a modulated phase signature imprinted thereon. The interferometer includes at least two reflectors that generate parallel photon streams from each split incoming time-bin pair. The at least two reflectors and the beam splitter generate a first output and an associated second output, each output combining photons from each of the parallel photon streams. In other words, the at least two reflectors create a spatial walk-off between the split incoming time-bin pairs and generate the first and second outputs. The apparatus includes at least two paths, each path allowing each of the first and second outputs to move toward a respective detector. The first and second outputs can be inverted copies of each other, effectively splitting the incident noise intensity.

[0031] In an exemplary embodiment, each reflector is a respective distance from the beam splitter, and the difference in the respective distances causes a delay.

[0032] In an exemplary embodiment, the apparatus includes a compensator between one of the at least two reflectors and the beam splitter, the compensator being capable of reducing distortion of the spatial modes.

[0033] In an exemplary embodiment, the at least two reflectors include at least one of a combination of flat mirrors, a curved mirror, a Herriott cell, a combination of curved mirrors, or a combination of flat and curved mirrors.

[0034] In an exemplary embodiment, the beam splitter is positioned to receive an off-center incident time bin pair or to receive returns from at least two off-center reflectors.

[0035] In an exemplary embodiment, the apparatus includes a housing that encloses the interferometer and incorporates the at least two paths, and the housing may further enclose an imprinter that imprints the imprinted quantum coherence into time bin pairs.

[0036] In an exemplary embodiment, the device includes a wavelength filter.

[0037] In an exemplary embodiment, the split incident time bin pairs are phase shifted relative to each other by a beam splitter.

[0038] In an exemplary embodiment, the apparatus includes a phase modulator between the beam splitter and at least one of the at least two reflectors.

[0039] In another aspect, a remote sensing system is disclosed. The system includes an imprinter that receives incident photons and generates time bin pairs imprinted with a modulation phase signature. The system includes an analyzer that receives the time bin pairs generated after scattering from a target and generates at least two outputs, each based on a combination of at least two instances of the generated time bin pairs, the at least two instances being delayed relative to one another to at least partially maintain the modulation phase signature. The system includes at least two detectors, each receiving one of the at least two outputs. The system includes an assessor in communication with the at least two detectors and configured to compare the at least two outputs with the imprinted modulation phase signature to determine one or more characteristics associated with the target.

[0040] In an exemplary embodiment, the system further includes an emitter that emits the incident photons.

[0041] In an exemplary embodiment, the at least two detectors are configured for at least one of a desired polarization, time window, and spectral window.

[0042] In an exemplary embodiment, the analyzer includes an interferometer. The interferometer can be an asymmetric Michelson interferometer or an asymmetric Mach-Zehnder interferometer with a phase modulator in one arm. The imprinter can include a second interferometer associated with the interferometer.

[0043] In an exemplary embodiment, the at least two detectors are photodetectors (eg, detect photons, infrared light, etc.) or microwave detectors.

[0044] In exemplary embodiments, the evaluator is housed separately from the detector, housed at least in part with the detector, or housed in combination with and separate from the detector.

[0045] In an exemplary embodiment, the system further includes a phase modulator that communicates the imprinted modulated phase signal to the imprinter. The analyzer can include a second phase modulator that operates based on the phase modulator.

[0046] In an exemplary embodiment, the phase modulator is a piezoelectric actuator connected to a mirror of an imprinter interferometer.

[0047] Upon reading this disclosure, those skilled in the art will recognize many additional features and combinations thereof that will improve upon this invention. [Brief explanation of the drawings]

[0048] [Figure 1A] FIG. 1A shows two example output graphs based on the system's detectors for an example intensity-based system. [Figure 1B] FIG. 1B shows two example output graphs of the detector of an exemplary intensity-based system. [Figure 1C] FIG. 1C shows an example of a remote sensing system. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of a remote sensing system. [Figure 3A] FIG. 3A is an example architecture of the example remote sensing system of FIG. [Figure 3B] FIG. 3B is a schematic diagram of an embodiment of the system of FIG. 3A. [Figure 4A] FIG. 4A is a graph illustrating the different stages of a pulse passing through the exemplary architecture shown in FIG. 3A. [Figure 4B] FIG. 4B is a graph illustrating the different stages of a pulse passing through the exemplary architecture shown in FIG. 3A. [Figure 4C] FIG. 4C is a graph illustrating the different stages of a pulse passing through the exemplary architecture shown in FIG. 3A. [Figure 4D] FIG. 4D is a graph illustrating the different stages of a pulse passing through the exemplary architecture shown in FIG. 3A. [Figure 4E] FIG. 4E is a graph illustrating the different stages of a pulse passing through the exemplary architecture shown in FIG. 3A. [Figure 5A] FIG. 5A shows a diagram of signal and noise photons received by a system relying on quantum sensing. [Figure 5B] FIG. 5B shows a diagram of signal and noise photons received by a system relying on quantum sensing. [Figure 5C] FIG. 5C shows a diagram of signal and noise photons received by a system relying on quantum sensing. [Figure 6] FIG. 6 shows a flow diagram of an example method for remote sensing. [Figure 7A] FIG. 7A shows the simulated intensity histograms, respectively. [Figure 7B] FIG. 7B shows the simulated intensity histograms, respectively. [Figure 7C] FIG. 7C shows an example of a determined ROC curve. [Figure 8A] FIG. 8A shows an example of an interferometer. [Figure 8B] FIG. 8B shows an example of an interferometer.

[0049] [Detailed explanation] Imprinting, as used in this disclosure, includes any process or group of processes that impart properties to optical pulses. The term imprinting, as used in this disclosure, has an expansive meaning and can include, for example, imprinting by a combination of an interferometer and an actuator, imprinting by the use of a compensator, etc.

[0050] The present disclosure includes aspects that incorporate another DoF, namely, inter-pulse quantum coherence (hereafter referred to as phase signature), which can be evaluated alongside the known DoF to improve discrimination capabilities. Coherent photons can be transmitted with a deliberately selected or pre-defined phase signature, which can be recovered from received photons after scattering or reflection from a target. No coherence is observed in received "noise" photons, but some coherence is observed in received "signal" photons. The degree of correlation between received and transmitted photons serves as a parameter for distinguishing between signal and noise photons, thereby improving sensing performance.

[0051] Quantum coherence can be generated by time-bin interferometry to distinguish between signal and noise photons. Such capabilities can be used for a variety of quantum sensing applications, such as target detection, distance detection, and velocity measurement, to name a few (hereafter collectively referred to as remote sensing for ease of reference).

[0052] A schematic diagram of an exemplary embodiment of a remote sensing apparatus is shown in FIG. 2. The illustrated apparatus includes a laser source 102, an imprinter 104, an analyzer 206 (different from the analyzer 106, as described in further detail herein), and a quantum coherence-based evaluator 216. The imprinter 104 creates coherent time bins imprinted with a "phase signature." The time bins created by the imprinter 104 are transmitted (e.g., via a guidance device such as a mirror) toward the target 108, the expected location of the target 208, or a location where target detection is desired. At least some photons scattered or reflected from the target 108 are collected by the analyzer 206. The analyzer 206 can be used to generate two different outputs 212 and 214 from the collected scattered photons. The known imprinted phase signature applied by imprinter 104 (shown as output 218) and outputs 212 and 214 of analyzer 206 are provided to phase-signature-based evaluator 216 to (1) evaluate the correlation of the phase signatures between outputs 212 and 214 and output 218. Based on the determined correlation, evaluator 216 can be further configured to determine one or more characteristics of target 108, such as the presence of target 208, the velocity of the target, etc. The term "characteristic" is intended to capture characteristics that evaluator 216 can derive from outputs 212 and 214, including multiple features, including those used to determine characteristics of an image of target 108, accommodate free-space communications, etc.

[0053] A more detailed exemplary device is shown in Figures 3A and 3B. Figures 4A-4E illustrate the properties of photons as they pass through the exemplary device shown in Figure 3A and are discussed below in conjunction with Figure 3A. For ease of reference, Figure 3A shows the path traveled by a photon, defined in part by outputs 150, 152, 154, 212, and 214, and the properties of these outputs are shown in Figures 4A-4E.

[0054] Photons are emitted from the photon source 102 (shown in FIG. 3A as output 150). FIG. 4A shows an example graph of a pulse emitted from the photon source 102.

[0055] The emitted photons pass through imprinter 104, and the time bin pairs that exit imprinter 104 (output 152 in FIG. 3A) are imprinted with the imprinted phase signature. Imprinter 104 generates the time bin pairs using an unbalanced interferometer. FIG. 4B shows the characteristics of the output time bin pairs resulting from an exemplary imprinting process.

[0056] In at least some exemplary embodiments, the state of a photon exiting imprinter 104 can be described as follows:

[0057]

number

[0058] where |s〉 represents the early time bin shown in FIG. 4B, which arises from the short arm of the interferometer, and |l〉 represents the late time bin shown in FIG. 4B, which arises from the long arm. In this example, θ i (t) ∈ [0, 2π] is the phase signature pattern selected for imprinting and applied between two time bins within the time interval T.

[0059] The time bin pairs present in the imprinter 104 are reflected or scattered from the target 108. It will be appreciated that the configurations shown in Figures 3A and 3B can be used in non-line-of-sight applications, including between multiple users around corners indoors, or in short-range links with mobile systems.

[0060] Photons scattered or reflected from target 108 are received by analyzer 206. The photons received by analyzer 206 may have the characteristics shown in Figure 4C, which illustrates output 154 of Figure 3A.

[0061] As previously mentioned, analyzer 206 generates two outputs, 214 and 212, each related to the other by a phase shift (e.g., caused by passing through beam splitter 312). The phase shift may be a π phase shift, which facilitates subtraction of the outputs and allows for better noise removal and signal discrimination. In at least some exemplary embodiments, analyzer 206 may include an unbalanced interferometer (also referred to as an asymmetric interferometer). The unbalanced interferometer of analyzer 206 may be used in combination with the unbalanced interferometer of imprinter 104 to restore the coherent superposition of time bin pairs of photons. Various configurations of the unbalanced interferometer are possible, including path length differences of different sizes (where the path length difference between different arms of the imprinter 104 interferometer is Δ I and Δ A where σ represents the path length difference between different arms of the analyzer 206 interferometer. The analyzer 206 interferometer (or imprinter interferometer 106) can be, for example, an unbalanced Michelson interferometer, a Mach-Zehnder interferometer, or a combination of an interferometer and a phase modulator that can imprint (recover) the phase signature between time bin pairs with high efficiency. In conclusion, the analyzer 206 can partially recover the imprinted phase signature from photons scattered from the target 208.

[0062] The analyzer 206 may include at least two reflectors (e.g., the illustrated reflectors 312A and 312B, hereinafter referred to simply as reflector 316 in the singular for ease of reference) that generate beam walk-off, one or more compensators (e.g., the illustrated compensator 314), and a beam splitter 312. The reflectors may be combinations of flat mirrors, 3D curved mirrors, one or more Harriott cells, etc. The reflector 316 may be a retroreflector that allows for capture of a wider angle of incidence of the incident light, enabling generation of two outputs 212 and 214. In summary, the analyzer 206 may generate at least two outputs, each based on combining at least two instances of time bin pairs scattered from the target 108. At least two instances can be generated by the analyzer 206 (e.g., via a retroreflector and beam splitter as shown), and the instances can include a delay between them while at least partially preserving the modulation phase signature.

[0063] The analyzer 206 interferometer splits each received time bin pair into two distinct sub-pulses, generating two separate outputs 212 and 214, each consisting of four (4) sub-pulses (or two time pairs), with each output having a distinct pair of sub-pulses separated in time by a delay ΔA. For example, as shown in Figures 4D and 4E, a "short" (or "long") pulse is split into a "short-short" and a "short-long" (or "long-short" and "long-long"). The two distinct sub-pulses can be generated by positioning the beam splitter 312 so that the received time bin pairs are incident off-center on the beam splitter, as shown in Figure 3A.

[0064] The outputs 212 and 214 of the analyzer 206 are emitted or transmitted to at least two detectors (e.g., detectors 310A and 310B), respectively. Various types of detectors are contemplated herein, and different detectors may be selected based on different implementation requirements. It is understood that the detectors 310 may include one or more of a pin photodiode, a single-photon detector (allowing for detection of weak signals down to the single-photon level), an array of single-photon detectors, a superconducting detector, etc.

[0065] In an exemplary embodiment, at least two of the photon source 102, imprinter 104, analyzer 206, and detector(s) 310 are within an integrated housing. For example, the analyzer 206 can include separate paths for receiving light and different paths for each output for outputting each output to a respective detector 310, all within the same housing. The evaluator 216 can be similarly integrated into the housing, or the evaluator 216 can be a processor located at a remote service, such as a cloud computing provider, that ingests the data sets generated by the detectors 310 (e.g., the first and second data sets generated by the detectors 310, respectively).

[0066] In summary, output 150 results from photon source 102 emitting a train of pulses. Each output pulse can be narrowband, broadband, or a combination of narrowband and broadband. The pulses can be multimode or single-mode. Figure 4A shows the characteristics of the photons in output 150.

[0067] The signal from the photon source 102 is collimated and sent through the imprinter 104. The imprinter 104 splits the pulses arriving from the photon source 102 and creates an optical path length asymmetry Δ between the split pulses. IAs described above, the imprinter 104 transforms each incident state of photons into a coherent superposition of two time bins. In this way, the imprinter 104 induces a selected phase signature between the two time bins in a time bin pair, resulting in a coherent superposition of time bins parameterized by the selected phase signature.

[0068] Output 152 exits imprinter 104 and is directed towards target 108. Figure 4B shows the characteristics of an exemplary pulse directed towards target 108, including the imprinted delay.

[0069] Output 154 shows the characteristics of photons scattered or reflected from target 108, which travel towards analyzer 206. Figure 4C shows the characteristics of example photons scattered from target 108 with an imprinted delay and some additional characteristics.

[0070] Photons scattered or reflected from the target 108 are collected by the analyzer 106. The scattered photons can be collected using conventional collection techniques such as telescopes or mirrors.

[0071] The collected photons pass through analyzer 206 and are directed towards detector 310. Detector 310 may be a photodetector (including infrared in an exemplary embodiment), a microwave detector, a radar detector, etc. Photons traveling towards two detectors 310A and 310B (hereafter referred to as detector 310 in the singular for ease of reference) shown at outputs 212 and 214 may exhibit the exemplary characteristics shown in Figures 4D and 4E.

[0072] Thus, photons exiting the analyzer 206 may travel one of four paths (where the first length represents the path within the imprinter 104 and the second path represents the distance traveled by the analyzer 206): short-short (SS), short-long (SL), long-short (LS), and long-long (LL). If the path length asymmetry in the two interferometers is matched, i.e., ΔI ≒Δ A , the probabilities of collected photons coming via the SL and LS paths become indistinguishable, and interference occurs. Thus, as shown in Figures 4D and 4E, eight sub-pulses related to one originally emitted pulse (from output 150) are generated, and each detector 310 receives four pulses. The time delay Δ A The asymmetry can be such that the latest subpulse of the earlier subpulse pair overlaps in time, partially or completely, with the earliest subpulse of the later subpulse pair. This overlap produces at least some interference, the degree of interference being a function of the amount of overlap.

[0073] Detector 310 can be used to measure the degree of interference between the sub-pulses. More specifically, the amount of overlap, and therefore the amount of interference, can vary in a known manner from a pair of sub-pulses earlier in the train to a pair of sub-pulses later in the train based on differences in time delays imparted by imprinter 104, analyzer 206, or both, more specifically as a function of the imprinted phase signature.

[0074] The degree of interference also depends on whether the target 108 is moving. For example, if the target 108 is moving, the Doppler effect can shift the time bin delay by a factor "D," as shown in Figures 4C, 4D, and 4E. For example, if the target 108 is stationary, then D=1.

[0075] The strength of the interference depends on the degree of overlap and can be estimated by the observed contrast and visibility. The analyzer 206 can include a phase modulator, similar to the modulator shown in the imprinter of FIG. 3B, to control the degree of overlap. Because the output intensities of photons from separate paths depend in part on the imprinted phase signatures defined by the interferometer, precise phase manipulation by the analyzer 206 interferometer's phase modulator allows for the determination of the presence (if any) of the imprinted phase signature originally applied by the imprinter 104 on the collected photons as the analyzer 206 output intensity varies over time in response to the imprinted phase signature.

[0076] 5A, 5B, and 5C show the results of a simulated object detection experiment. When the target 108 is not present, the detector 310 receives only noise photons with an average intensity of four (4) arbitrary units, as shown by the middle line of the graph in FIG. 5A. FIG. 5A also shows the results when the target 108 is incorporated into the experiment. Assuming no losses, no noise, and 100% reflection of photons from the target 108, the signal received by the detector 310 is shown by the lower curve in FIG. 5A. The transmitted signal is a sinusoidally modulated wave with an average intensity of two (2) arbitrary units. When both the target and noise are present, the detector 310 receives both the noise and the reflected signal. As shown by the highest line of the graph in FIG. 5A, a sinusoidal wave with an average intensity of six (6) units is displayed.

[0077] Figures 5B and 5C show histograms generated based on experimental examples, where the histograms are generated based on either an intensity or correlation scheme. In the intensity-based scheme of Figure 5B, the histogram of the detected signal is shown as two distinct peaks. Figure 5C shows the histogram resulting from cross-correlating the phase signature of the received photons with the phase signature of the transmitted photons. When no target is present (left), the detected photons are only noise photons that are uncorrelated with the transmitted phase signature, resulting in a low correlation value. In contrast, when an object is present (right), the received photons are a subset of the signal photons, and the observed phase signature is highly correlated with the transmitted one, resulting in a high correlation value, as shown. Therefore, instead of the two histograms shown in the intensity graph of Figure 5B, the disclosed process can result in a more separated histogram, as can be seen by comparing Figures 5B and 5C.

[0078] FIG. 6 shows an example of a flow chart for determining the characteristics of a target.

[0079] In block 602, a plurality of time bin pairs imprinted with a modulation phase signature are transmitted towards a target.

[0080] At block 604, a first data set is received, the first data set being based on a first output generated by a plurality of time bin pairs scattered from a target, the scattered time bin pairs being received and processed by an analyzer that maintains modulation phase signatures in the generated and separated first and second outputs.

[0081] At block 606, a second data set based on the generated second output is received at a second detector.

[0082] At block 608, the first and second data sets are combined.

[0083] In block 610, the first and second data sets are compared to a third data set that describes the phase signatures imprinted on the transmitted time bin pairs.

[0084] A cross-correlation function can be used in the signal processing to determine the presence of an imprinted phase signature pattern, or in other words, to determine whether a reflected signal has been detected.

[0085] JPEG2026501780000004.jpg27170

[0086]

number

[0087] JPEG2026501780000006.jpg22170

[0088] The processing task involves analyzing the received signal to determine the likelihood that a target is present or absent, with greater accuracy and reliability being desired.

[0089] There are various approaches to analyzing the received signal. In at least one exemplary embodiment, a correlation histogram comparison is used (instead of the typical intensity histogram comparison as done in intensity-based LiDAR). When a target is present, the detected signal is composed of both noise photons and photons scattered from the target, resulting in a significantly higher correlation upon cross-correlation with the transmitted signal. Conversely, when the target is removed, the detected signal is composed only of noise photons, resulting in a lower correlation upon cross-correlation analysis. The histogram plot of correlation values ​​depicted in FIG. 5C captures these distinctions. This comparison approach therefore leverages the correlation as a robust indicator of the system's SNR. A higher correlation indicates the presence of photons reflected from the target during the target placement interval. Conversely, a lower correlation means that only noise is detected during target-free intervals.

[0090] Correlation algorithms are faster and more accurate than intensity-based algorithms. One indicator of improvement is the ROC curve. Because both approaches simply determine whether a data point (detector output) belongs to a target-absent or target-present histogram, the approach can be abstracted into "binary classification." When the two histograms begin to overlap, as in high-noise and / or high-loss environments, binary classification becomes nontrivial (e.g., as shown in Figures 7A and 7B).

[0091] One way to compare binary classifiers (in this case, the correlation approach and the intensity approach) is to plot the ROC curve for each classifier. Classes can be defined as target present and target absent. Thus, the ROC plot can be interpreted as a [0,1] x [0,1] space, with the axes representing the proportion of non-overlapping target-absent and target-present histograms in the histogram region. In other words, the ROC graph shows the difference between the discriminant threshold c as the threshold scans the histogram region. t The percentage of target presence histograms that fall to the right of (non-overlapping) can be graphed.

[0092] Figure 7C shows an example ROC curve that can be used to quantify the effectiveness of a binary classification model. The closer the ROC curve is to y=1, the better the classifier. As can be seen, the cross-correlation method (shown in Figure 7A) is consistently the better binary classifier.

[0093] Correlation-based approaches can suffer from poor performance when multimode light enters the interferometer (e.g., the analyzer 206 interferometer) at variable angles of incidence. Variable angles of incidence can cause lateral offsets between the paths entering the exit beam splitter, resulting in degradation of interference visibility, as shown in Figures 8A and 8B. Channel-induced spatial mode distortions can further degrade interference quality. This degradation can be attributed to the inherent asymmetry of the unbalanced interferometer.

[0094] Various techniques have been considered to correct this spatial mode distortion. For example, a compensation technique can involve using a glass material with the appropriate length and refractive index to create a virtual mirror close to the beam splitter (e.g., splitter 312). In at least one exemplary embodiment, a glass cube (e.g., compensator 314) can be placed in the long arm of each unbalanced interferometer to match the distance between the beam splitter and the virtual mirror with the short arm. Another example of a compensation technique is a relay lens setup in which a 4f-lens system is placed in the long arm of each unbalanced interferometer. The relay system serves to project the field of view of the virtual mirror back after propagation.

[0095] More generally, when the angle of incidence of light entering the interferometer is zero, the difference in path length between the two arms is:

[0096]

number

[0097] where l L and l S are the lengths of the long and short paths, respectively. However, for non-zero angles of incidence, the path length difference is a function of the angle of incidence as follows (note that angles are shown in Figures 8A and 8B):

[0098]

number

[0099] where δ(α) = Δl0 tan α / [1 + tan α] is the lateral offset of the beam at the output. In this case, the two paths become distinguishable and the incident beam angle is 2×10 -5 With each change in degree A relative phase difference shifted by π is observed. These properties can be used to adjust the compensation approach described above.

[0100] Such correction may be necessary not only to improve performance at higher angles of incidence, but also to allow for high coherent visibility in multimode beams.

[0101] Referring again to FIG. 6, in block 612, one or more characteristics of the target 108 are determined based on the comparison of block 610.

[0102] Blocks 604 through 612 can be completed by a single processor or by multiple processors. The processor(s) can be located remotely from the detector 310 (e.g., all information collected by the detector 310 is provided to the cloud), integrated or coupled to the detector 302 (e.g., a computer connected to the detector 310), or some combination of the two (e.g., partial processing is performed on the detector 310 and then provided to a cloud processor), etc. The functionality of block 610 can be seamlessly implemented in software, firmware, or hardware.

[0103] The order of the blocks shown in Figure 6 is exemplary and other orders are possible, for example the second data set may be received before the first data set.

[0104] The photon intensity detected at detector 310 may vary depending on the phase coherence pattern imparted by the phase modulator. When the phase applied by the phase modulator of analyzer 206 is zero, the photon intensity at one of the interferometer outputs exactly reflects the phase signature applied by imprinter 104. When a phase is applied simultaneously, the photon intensity at the other output appears as a π-phase-shifted version of the former.

[0105] If the SNR is particularly low, due to high noise and / or high loss, the signal containing the phase signature of block 602 may not be recognized by detector 310 .

[0106] In at least one exemplary embodiment, to avoid problems associated with low SNR, the optical common mode rejection technique can be used to amplify the signal strength and cancel background noise entering the analyzer 206 from the surrounding environment.

[0107] One example approach is to use both outputs of the analyzer 206 interferometer, as shown on the right side of FIG. 3A and shown schematically on the right side of FIG. 2, where the signal photon intensity I at one analyzer 206 output (e.g., output 212) is s (t) is the imprinted phase signature θ within the time interval T applied by the imprinter 104. i (t) accurately reflects the signal photon intensity at the other output (e.g., output 214) - I s (t) is output as a π-phase shifted version of the other output. However, the incident noise photons are inherently incoherent and therefore split symmetrically between the two outputs, resulting in a noise intensity I N As a result, one detector will have a "noise plus signal" (I N +I s (t)) and the other receives the "noise minus signal" (I N -I sBy taking the difference between the outputs of the two detectors, the noise (except for statistical fluctuations) is cancelled out and the signal is amplified as follows:

[0108]

number

[0109]

number

[0110]

number

[0111]

number

[0112] In an exemplary embodiment, a wavelength filter is used in combination with the dual detector noise canceling analyzer 206 shown in Figure 3B. The wavelength filter can increase the amount of noise that is removed.

[0113] More generally, the disclosed method and apparatus, also referred to as optical common mode rejection technology, is inapplicable to traditional intensity-based LiDAR systems due to the absence of a phase-inverted complementary output signal, which relies on interference and is inherently absent from intensity-based approaches but is crucial for optical common mode rejection applications.

[0114] Accordingly, the present disclosure includes a method in which coherent photons are transmitted toward a target along with a first set of phase signature(s). Photons, if any, reflected from the target can be collected and their characteristics detected. The method can include recovering or determining the phase signature from the detected photon characteristics. By matching the observed phase signature with the transmitted phase signature, the method can distinguish whether the incident photons are signal or noise photons. The method can include tuning, such as tuning with a correlation metric that is large when there are more signal photons in the reflected photons compared to noise photons.

[0115] Accordingly, the embodiments described and illustrated above are merely exemplary.

Claims

1. 1. A method for determining a characteristic of a target, comprising: (a) transmitting a plurality of time bin pairs imprinted with a modulation phase signature toward a target; (b) receiving at a first detector a first data set based on the generated first outputs by time bin pairs of the plurality of time bin pairs scattered from the target and processed by an analyzer that recovers the modulation phase signature within the generated first and second outputs; (c) receiving at a second detector a second data set based on the generated second output; (d) combining the first data set and the second data set; (e) comparing the first and second data sets with a third data set describing the imprinted phase signature; (f) determining the one or more characteristics of the target based on the comparison; and A method comprising:

2. 10. The method of claim 1, 10. The method of claim 9, wherein combining the first data set and the second data set comprises at least one of subtracting, adding, multiplying, or dividing the first data set from the second data set.

3. 10. The method of claim 1, The method, wherein the one or more characteristics include at least one of presence, range, velocity, acceleration, rotation, and vibration.

4. 10. The method of claim 1, The method, wherein comparing includes determining a degree of correlation between (1) the combined first and second data sets and (2) the third data set.

5. 10. The method of claim 1, the one or more characteristics include presence or absence; The method, wherein determining the presence further comprises determining whether the degree of coherence can be classified into a preset range indicative of the presence of a target.

6. 10. The method of claim 1, 10. The method of claim 9, wherein the combining of the first and second data sets amplifies the imprinted phase signature and attenuates received noise signals.

7. 10. The method of claim 1, The method of claim 1, wherein the first and second data sets are related such that the first and second outputs are at least partially inverse with respect to each other.

8. 10. The method of claim 1, The method, wherein the modulation is controlled via a phase modulator.

9. 10. The method of claim 1, The method further comprising activating a phase modulator within the analyzer based on the imprinted modulation phase signature.

10. a beam splitter that splits incident time bin pairs, the incident time bin pairs being imprinted with a modulation phase signature; at least two reflectors that generate parallel photon streams from each of the split incident time bin pairs, the at least two reflectors and the beam splitter generating a first output and an associated second output, each output combining photons from each of the parallel photon streams; at least two paths, each path allowing a respective one of the first and second outputs to travel towards a respective detector; 10. An apparatus comprising an interferometer having:

11. 11. The apparatus of claim 10, The apparatus, wherein each reflector is spaced a respective distance from the beam splitter, the difference in the respective distances causing a delay between time bin pairs of the plurality of time bin pairs.

12. 11. The apparatus of claim 10, The apparatus further comprising a compensator between one of the at least two reflectors and the beam splitter.

13. 13. The apparatus of claim 12, The apparatus, wherein the compensator reduces distortion of spatial modes.

14. 11. The apparatus of claim 10, The apparatus, wherein the at least two reflectors include at least one of a combination of flat mirrors, a curved mirror, a Herriott cell, a combination of curved mirrors, or a combination of flat and curved mirrors.

15. 11. The apparatus of claim 10, 10. The apparatus of claim 9, wherein the beam splitter is positioned to receive off-center incident time bin pairs or to receive off-center returns from the at least two reflectors.

16. 11. The apparatus of claim 10, The apparatus further comprising a housing enclosing the interferometer and incorporating the at least two paths.

17. 17. The device of claim 16, The apparatus, wherein the housing further encloses an imprinter that imprints the imprinted phase signature into time bin pairs.

18. 11. The apparatus of claim 10, The apparatus further comprises a wavelength filter and a polarizer.

19. 11. The apparatus of claim 10, The apparatus further comprising a phase modulator between the beam splitter and at least one of the at least two reflectors.

20. 11. The apparatus of claim 10, The apparatus wherein the first and second outputs are inverted copies of each other, effectively dividing the incident noise intensity.

21. an imprinter that receives incident photons and generates time bin pairs imprinted with modulation phase signatures; an analyzer that receives the generated time bin pairs after scattering from a target and generates at least two outputs each based on a combination of at least two instances of the generated time bin pairs, the at least two instances being delayed relative to one another to at least partially preserve the modulation phase signature; at least two detectors, each receiving one of the at least two outputs; an evaluator in communication with the at least two detectors and configured to compare outputs of the at least two detectors with the imprinted modulation phase signature to determine one or more characteristics associated with the target; A system comprising:

22. 22. The system of claim 21, The system further comprises an emitter that emits the incident photons.

23. 22. The system of claim 21, The system, wherein the at least two detectors are configured for at least one of a desired polarization, a time window, and a spectral window.

24. 22. The system of claim 21, The system wherein the analyzer comprises an interferometer.

25. 25. The system of claim 24, The system is characterized in that the interferometer is an asymmetric Michelson interferometer or an asymmetric Mach-Zehnder interferometer with a phase modulator in one arm.

26. 26. The system of claim 25, The system wherein the imprinter comprises a second interferometer associated with the interferometer.

27. 22. The system of claim 21, The system, wherein the at least two detectors are optical detectors or microwave detectors.

28. 22. The system of claim 21, The system, wherein the evaluator is housed separately from the detector, housed at least in part with the detector, or housed in combination with and separately from the detector.

29. 22. The system of claim 21, The system further comprises a phase modulator that conveys an imprinted modulated phase signal to the imprinter.

30. 20. The system of claim 19, The system is characterized in that the analyzer includes a second phase modulator that operates based on the phase modulator.

31. 30. The system of claim 29, The system, wherein the phase modulator is a piezoelectric actuator connected to a mirror of an interferometer of the imprinter.

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