IL321925A - Method and apparatus for quantum sensing - Google Patents

Description

WO 2024/145721 PCT/CA2024/050011 METHOD AND APPARATUS FOR QUANTUM SENSING CROSS-REFERENCE TO RELATED APPLICATION(S) id="p-1" id="p-1"

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

TECHNICAL FIELD id="p-2" id="p-2"

[0002]This disclosure generally relates to the field of quantum sensing.

BACKGROUND OF THE ART id="p-3" id="p-3"

[0003]In certain existing remote sensing and ranging systems, a photon source, e.g., a laser, emits a pulse of many photons that propagate towards the target scene. Upon impact, a portion of the photons will be reflected or scattered towards a receiver equipped with a camera that captures the reflected or scattered photons. Detection in each pixel on the multipixel camera corresponds to a distinct spatial region of the scene, effectively collecting spatial information encoded in the reflected photons. Additionally, the arrival times recorded by each pixel provides an additional degree of freedom which can be used to calculate the relative distances between the source of the photons and the objects within the scene. This computational process enables the reconstruction of a three-dimensional representation of the scene, effectively rendering a three-dimensional remote sensing system. Such sensors have recently garnered significant interest across various applications owing to their remarkable attributes, including exceptional sensitivity, non-intrusiveness, ultra-high resolution, and rapid response capabilities. id="p-4" id="p-4"

[0004]A challenge for these remote sensing and ranging systems is addressing inaccuracy or insensitivity caused by noise. Noise can include noise photons resulting from scattering and reflection from the surrounding atmosphere, ambient light, detector dark noise, thermal noise etc. id="p-5" id="p-5"

[0005]Techniques have been implemented to delineate between signal photons and noise photons are not sufficiently efficient, accurate, or require both the emitter and detector to be within a line of sight of the target. Known techniques include polarization filtering, spectral filtering, temporal filtering, signal averaging, and employing complex signal processing algorithms to delineate between signal photons and noise photons. Similarly, in some existing applications a short-pulsed laser is used to send trains of pulses and a fast detector is used to look for photons that arrive within a short temporal window, thus rejecting noise photons using the temporal degree of freedom.1 WO 2024/145721 PCT/CA2024/050011 id="p-6" id="p-6"

[0006]Conventional LiDAR systems, referred to hereinafter as intensity-based LiDARs, use degrees of freedoms (DoFs) such as time-of-flight and intensity to measure the presence, and potentially range and/or velocity of a target immersed in noise (e.g., ambient noise). Intensity based LiDARs can use a photon source to emit short pulses towards the target (or expected position of a target), and a detector to collect any photons reflected or scattered off the target. When the target is absent, the detected photons are from the atmosphere, i.e., noise photons. On the other hand, if the target is present, a portion of the transmitted photons, i.e., signal photons, are reflected off the target and collected by the detector along with noise photons. In intensity-based LiDAR approaches, the task of a detection algorithm is to determine, with a high degree of certainty, whether the target is present or absent by analyzing the photons received by the detector. The performance these types of LiDARs may be limited by detector noise and ambient noise. id="p-7" id="p-7"

[0007]The concept of intensity-based sensing is illustrated in FIG. 1A. The top graph shows the variation of detected signal with time for the two cases: when only ‘noise’ photons are detected (1^, and when both ‘signal ’ and ‘noise’ photons are detected (Is+nY The bottom graph of FIG. 1A shows the corresponding histograms of the intensity for the two cases. The ability to distinguish between these two cases depends on the separation signal to noise ratio (SNR), denoted by SNRintensity, between the two histograms, and can be defined as: id="p-8" id="p-8"

[0008]SNRintensity = ^=1+ ^.= 1+SNR (1) id="p-9" id="p-9"

[0009]Here SNR = IsIIn is the ratio of average signal to average noise. SNRintensity can decrease in several ways. Signal intensity itself can decrease while noise stays constant resulting in a left-shift of the Is+N histogram. On the other hand, an increase in average background noise - while the average signal intensity stays constant - leads to a right-shift of both histograms and a decrease in SNRintensity. If the two histograms are separated, distinguishing between them is easy. id="p-10" id="p-10"

[0010]Several degrees of freedom (DoFs) can be used to enhance the probability of detection. For example, to take advantage of the spectral DoF, a narrowband wavelength filter can be used to block the noise photons which differ in wavelength from the signal photons. Another option is to exploit the temporal DoF. A short-pulsed laser in combination with a fast detector is used to receive photons within a short temporal window thus blocking all other photons outside the window. Even using both the above described DoFs, it still may not be possible to distinguish noise photons that manage to pass through the wavelength filter and happen to be detected in the same temporal window. In this case, the two peaks of WO 2024/145721 PCT/CA2024/050011 noise and signal+noise start to overlap as shown in FIG. 1B, and the probability of error starts to increase. id="p-11" id="p-11"

[0011]In example know systems, such as intensity-based LiDAR schemes that operate in the high Signal-to-Noise Ratio (SNR) regime, potentially undesirable bright laser pulse energies may be required to overcome ambient noise (e.g., daylight) to reliably detect reflected signal. Higher intensity LiDAR schemes may also have a narrower viewing angle or shorter ranges. LiDAR systems capable of operating at lower laser energies can suffer from accuracy resulting from ambient noise. Lower-energy lasers may not be suitable for a low- SNR regime, such as when the ambient noise photons flood the weak signal and complicate detection. id="p-12" id="p-12"

[0012]Effective low laser energy LiDAR systems can be particularly desirable in covert operations, where a bright laser source could reveal the position of the sensor or interfere with imaging systems. Additionally, the capability to operate at lower signal levels may enable a wider angle of view and/or longer ranges. id="p-13" id="p-13"

[0013]Another existing technique is shown in FIG. 1C. In FIG. 1C, a source 102 emits photons, shown as output 150. The emitted photons are passed through an imprinter 104. The imprinter 104 consists of an interferometer (consisting of the shown mirrors and beam splitter). Together, the interferometer and shown piezoelectric actuator are used to imprint a phase signature, as shown via time bin pairs leaving the imprinter 104 at output 152. The emitted time bin pairs reflect off a target 108, and afterwards (shown as output 154) are received by the analyzer 106. The analyzer 106 includes another interferometer, and the time bin pairs that enter the interferometer are further spit and directed towards a detector 110 (as shown in output 156). id="p-14" id="p-14"

[0014]Existing techniques, however, can have difficulty making accurate detections, making those detections efficiently, having suffer from narrow viewing angles, have difficultly with rejecting noise photons that pass through the wavelength filter and are detected in the same time window as signal photons, etc.

SUMMARY id="p-15" id="p-15"

[0015]This disclosure discusses a system, method and apparatus that operate at least in part based on a quantum coherence degree of freedom, and more specifically, approaches that incorporate splitting received scattered photons into separate related time- bin pairs to harness quantum coherence. The proposed approach can potentially enhance the performance, noise resilience, and sensitivity in sensing and ranging applications based on quantum signalling.3 WO 2024/145721 PCT/CA2024/050011 id="p-16" id="p-16"

[0016] This disclosure contemplates creating, transferring, and measuring quantum coherence via a time-bin encoding technique. id="p-17" id="p-17"

[0017] Existing time-bin encoding techniques, such as the approach shown in FIG. 1C, can be challenging to implement. For example, challenges can arise depending on the implementation environment. In turbulent media, in contrast to more controlled environments (e.g., within single mode optical fibers), photon scattering can occur. One scenario where such challenges are present includes implementing time-bin encoding techniques over free- space channels with a spatially multi-mode light source. Photon scattering, resulting from atmospheric turbulence and/or diffraction, may mix the spatial modes and make them distinguishable, leading to poor interference quality. Even when single mode light is used at the source, atmospheric effects may convert photons into distinguishable multiple modes, thus reducing visibility and degrading performance. id="p-18" id="p-18"

[0018] One exemplary approach, disclosed herein, may address at least some of the above challenges via an analyzer configuration that allows improved recovery of quantum coherence via scattered photons, thereby allowing the detection of at least one of the presence or absence of a target at a distance. The approach can mitigate deleterious effects in a turbulent and high noise environment. The phase modulator continuously applies different phase patterns to as which acts as a phase signature. This increases the discern the outgoing photons from any noise photons, for example by the analyzer. id="p-19" id="p-19"

[0019] The correlation performance can be characterized by techniques like the Receiver Operating Characteristic (ROC) curves. id="p-20" id="p-20"

[0020] In summary, the transfer and recovery of quantum coherence can be exploited via scattered photons for object recognition, ranging, and velocimetry of a target at a distance. id="p-21" id="p-21"

[0021] In accordance with one aspect, there is provided a method including transmitting a plurality of time-bin pairs imprinted with a modulated phase signature towards a target and receiving time-bin pairs post scattering off the target. The method includes receiving a first data set at a first detector. The first data set is set based on a first output generated by time- bin pairs of the plurality of the time-bin pairs scattering off the target and being processed with an analyzer that recovers the modulated phase signature within the generated first and second output. The method includes receiving a second data set at 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 set and a WO 2024/145721 PCT/CA2024/050011 third data set that describes the imprinted phase signatures. The method includes determining the one or more properties of the target based on the degree of correlation. id="p-22" id="p-22"

[0022]In example embodiments, the method includes combining the first and second data set comprises at least one of subtracting, adding, multiplying, or dividing the first data set from the second data set. id="p-23" id="p-23"

[0023]In example embodiments, the one or more properties includes at least one of presence, range, velocity, acceleration, and vibration. id="p-24" id="p-24"

[0024]In example embodiments, comparing comprises determining a degree of correlation between (1) the combined first and second data set, and (2) the third data set. id="p-25" id="p-25"

[0025]In example embodiments, the one or more properties comprises a presence or absence, and determining the presence further includes determining whether the degree of coherence can be classified in a preconfigured range indicative of target presence. id="p-26" id="p-26"

[0026]In example embodiments, combining the first data set and the second data set amplifies the imprinted phase-signature and attenuates received noise signal. id="p-27" id="p-27"

[0027]In example embodiments, the first data set and the second data set are related as the first analyzer output and the second analyzer output are at least in part inverted relative to one another. id="p-28" id="p-28"

[0028] In example embodiments, the modulation is controlled via a phase modulator. id="p-29" id="p-29"

[0029] In example embodiments, the method further includes actuating a phasemodulator within the analyzer based on the imprinted modulated phase signature. id="p-30" id="p-30"

[0030]In another aspect, an apparatus is disclosed. The apparatus includes an interferometer that includes a beam splitter splitting incoming time-bin pairs. The incoming time-bin pairs having imprinted thereon a modulated phase signature. The interferometer includes at least two reflectors creating parallel photon streams from respective split incoming time-bin pairs. The at least two reflectors and the beam splitter generate a first output and a related second output, each output combining photons from each of the parallel photon streams. Alternatively stated, the at least two reflectors create spatial walk-off between split incoming time-bin pairs and generate a first output and a second output. The apparatus includes at least two pathways, each pathway enabling a respective one of the first and second outputs to travel towards a respective detector. The first and second outputs can be inverted copies of one another, efficiently splitting incoming noise intensity.5 WO 2024/145721 PCT/CA2024/050011 id="p-31" id="p-31"

[0031]In example embodiments, each reflector is separated from the beam splitter by a respective distance, and a difference between the respective distances creates a delay. id="p-32" id="p-32"

[0032]In example embodiments, the apparatus includes a compensator between one of the at least two reflectors and the beam splitter. The compensator can reduce spatial mode distortion. id="p-33" id="p-33"

[0033]In example embodiments, the at least two reflectors comprise at least one of a combination of flat mirrors, a curved mirror, Harriot cells, a combination of curved mirrors, or a combination of flat and curved mirrors. id="p-34" id="p-34"

[0034]In example embodiments, the beam splitter is positioned to receive incoming time-bin pairs off-centre or to receive returns from the at least two reflectors off-centre. id="p-35" id="p-35"

[0035]In example embodiments, the apparatus including a housing encapsulating the interferometer and incorporating the at least two pathways. The housing can further encapsulate an imprinter that imprints the imprinted quantum coherence on time-bin pairs. id="p-36" id="p-36"

[0036] In example embodiments, the apparatus includes a wavelength filter. id="p-37" id="p-37"

[0037] In example embodiments, the split incoming time-bin pairs are phase shiftedrelative to one another by the beam splitter. id="p-38" id="p-38"

[0038]In example embodiments, the apparatus includes a phase modulator between the beam splitter and at least one of the at least two reflectors. id="p-39" id="p-39"

[0039]In another aspect, a system for remote sensing is disclose. The system includes an imprinter for receiving incoming photons and generating time-bin pairs imprinted with a modulated phase signature. The system includes an analyzer for receiving the generated time-bin pairs after scattering from a target and generating at least two outputs that are each based on combining at least two instances of the generated time-bin pairs, the at least two instances being delayed relative to one another and at least in part maintaining the modulated phase signature. The system includes at least two detectors, each respectively 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 modulated phase signature to determine one or more properties associated with the target. id="p-40" id="p-40"

[0040]In example embodiments, the system further includes an emitter to emit the incoming photons.6 WO 2024/145721 PCT/CA2024/050011 id="p-41" id="p-41"

[0041]In example embodiments, the at least two detectors are configured for at least one of a desired polarization, a temporal window, and spectral window. id="p-42" id="p-42"

[0042]In example embodiments, the analyzer includes an interferometer. The interferometer can be an asymmetric Michelson or Mach-Zehnder interferometer with a phase-modulator in one arm. The imprinter can include a second interferometer related to the interferometer. id="p-43" id="p-43"

[0043]In example embodiments, the at least two detectors are optical (e.g., detect photons, infrared, etc.) or microwave detectors. id="p-44" id="p-44"

[0044]In example embodiments, the assessor is housed separately from the detectors, or at least in part with the detectors, or a combination of with the detectors and separate from the detectors. id="p-45" id="p-45"

[0045]In example embodiments, the system further includes a phase modulator in the imprinter to impart the imprinted modulated phase signal. The analyzer can include a second phase modulated operated based on the phase modulator. id="p-46" id="p-46"

[0046]In example embodiments, the phase modulator is a piezoelectric actuator connected to a mirror of an interferometer of the imprinter. id="p-47" id="p-47"

[0047]Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE DRAWINGS id="p-48" id="p-48"

[0048]FIG. 1A shows two example output graphs based on a detector of an example system for intensity-based system. id="p-49" id="p-49"

[0049]FIG. 1B shows two example output graphs of a detector of an example intensity- based system. id="p-50" id="p-50"

[0050]FIG. 10shows an example system for remote sensing. id="p-51" id="p-51"

[0051] FIG. 2 shows a schematic diagram an example system for remote sensing. id="p-52" id="p-52"

[0052] FIG. 3A is an example architecture of the example system for remote sensing ofFIG. 2. FIG. 3B is a schematic of an example implementation of the system of FIG. 3A. id="p-53" id="p-53"

[0053] WO 2024/145721 PCT/CA2024/050011 id="p-54" id="p-54"

[0054] FIGS. 4A, 4B, 40, 4D, 4E are each a graph representing a different stage of a pulse passing within the example architecture presented in FIG. 3A. id="p-55" id="p-55"

[0055] FIGS. 5A, 5B, 50 each show a diagram of signal and noise photons received by systems which rely on quantum sensing. id="p-56" id="p-56"

[0056]FIG. 6 shows a flow diagram of an example method for remote sensing. id="p-57" id="p-57"

[0057]FIGS. 7A, and 7B each show a simulated intensity histogram. id="p-58" id="p-58"

[0058]FIG. 70 shows a diagram of example determined ROC curves. id="p-59" id="p-59"

[0059]FIGS. 8A and 8B each show an example interferometer.

DETAILED DESCRIPTION id="p-60" id="p-60"

[0060]Imprinting, as used in this disclosure, includes a process or processes to impose characteristics to optical pulses of light. The term imprinting as used herein is intended to be expansive, and can include, for example, imprinting via a combination of an interferometer(s) and actuator(s), with the use of compensators, etc. id="p-61" id="p-61"

[0061]This disclosure includes aspects that incorporate another DoF, that could be assessed alongside known DoFs, to improve the distinguishing ability: quantum coherence between pulses (hereinafter referred to as a phase signature). Coherent photons can be sent with a deliberated selected or pre-configured phase-signature, and that phase-signature can then be recovered from the photons received after scattering from or reflecting off the target. For received ‘noise’ photons, no coherence is observed, while for received ‘signal ’ photons, some coherence is observed. The degree of correlation between received photons and transmitted photons can act as the parameter to distinguish a signal photon from a noise photon, thus improving the performance of sensing. id="p-62" id="p-62"

[0062]Quantum coherence can be generated by time-bin interferometers to distinguish signal photons from noise photons. Such a feature may be used for different quantum sensing applications, such as target detection, range finding and velocity measurement, to name some examples (collectively referred to hereinafter as remote sensing, for ease of reference). id="p-63" id="p-63"

[0063]A schematic of an example embodiment of an apparatus for remote sensing is presented in FIG. 2. The shown apparatus includes a laser source 102, an imprinter 104, an analyzer 206 (different from analyzer 106, as will be discussed in greater detail herein), and a quantum coherence-based assessor 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 directing apparatus such as a mirror, etc.) towards the target 108, an 8 WO 2024/145721 PCT/CA2024/050011 expected position of the target 208, or a position where detection of a target is desired. At least some photons scattered or reflected off the target 108 are collected by the analyzer 206. The analyzer 206 can be used to generate two different outputs 212 and 214 from collected scattered photons. The known imprinted phase signature applied by the imprinter 104 (shown as an output 218), and the outputs 212 and 214 of the analyzer 206 are provided to the phase signature-based assessor 216 to assess phase signature correlation between (1) the outputs 212 and 214, and the output 218. Based on the determined correlation, the assessor 216 can be further configured to determine one or more properties of the target 108, such as the presence of a target 208, a speed of a target. The term ‘properties’ is intended capture properties that can be derived from outputs 212 and 214 that include multiple features, including the assessor 216 being used to determine the property of an image of the target 108, to accommodate free space communication, etc. id="p-64" id="p-64"

[0064]A more detailed example apparatus is presented in FIGS. 3A and 3B. FIGS. 4A to 4E discuss photon properties as they pass through the shown example apparatus of FIG. 3A, and will be discussed alongside FIG. 3A, below. For ease of reference, FIG. 3A shows a path travelled by photons in part defined by outputs 150, 152, 154, 212, 214, and properties of these outputs are shown in FIGS. 4Ato 4E. id="p-65" id="p-65"

[0065]Photons are emitted by the source 102 (shown as output 150, in FIG. 3A). FIG. 4A shows an example graph of a pulse emitted by the source 102. id="p-66" id="p-66"

[0066]The emitted photons are passed through the imprinter 104, such that time-bin pairs exiting the imprinter 104 (output 152 of FIG. 3A) are imprinted with the imprinted phase signature. The imprinter 104 uses an unbalanced interferometer to generate time-bin pairs. FIG. 4B shows properties of the output time-bin pairs resulting from an example imprinting process. id="p-67" id="p-67"

[0067]In at least some example embodiments, the state of photons exiting the imprinter 1can be described as follows: id="p-68" id="p-68"

[0068] |^;) = |s)+ id="p-69" id="p-69"

[0069]Here, |s) denotes the early time-bin shown in FIG. 4B, resulting from the shorter arm of the interferometer, and |I) denotes the late time-bin shown in FIG. 4B, resulting from the longer arm. In the example, 9t(t) g [0,27r] is the phase-signature pattern selected for imprinting and applied between the two time-bins within a time interval T. id="p-70" id="p-70"

[0070]The time-bin pairs existing the imprinter 104 are reflected off or scattered off the target 108. It is understood that the configuration shown in FIG. 3A and 3B can be used in WO 2024/145721 PCT/CA2024/050011 non-line-of-sight applications, including between multiple users such as indoors around corners, or with short range links with moving systems, etc. id="p-71" id="p-71"

[0071]Photons scattered or reflected off the target 108 are received by the analyzer 206. The photons received by the analyzer 206 can have the properties shown in FIG. 40, describing output 154 in FIG. 3A. id="p-72" id="p-72"

[0072]As mentioned above, the analyzer 206 generates two outputs 214 and 212, each output related to the other output by a phase shift (e.g., resulting from passing through the beam splitter 312). The phase shift can be a pi-phase shift, to facilitate the subtracting of the outputs to better remove noise and therefore identify signal. In at least some example embodiments, the analyzer 206 can include an unbalanced interferometer (alternatively referred to as asymmetric interferometer). The unbalanced interferometer of analyzer 206, in combination with an unbalanced interferometer of the imprinter 104, can be used to recover coherent superposition of time-bin pairs of photons. Various configurations of an unbalanced interferometer are contemplated, including different sized path length differences (where the path length differences for different arms for the imprinter 104 interferometer are denoted by A; , and A^ denotes the path length differences for different arms of the analyzer 2interferometer). The analyzer 206 interferometer (or imprinter interferometer 106) can be, for example, an unbalanced Michelson interferometer, a Mach-Zehnder interferometer, or a combination of interferometer and phase-modulator that can imprint (recover) a phase- signature between time-bin pairs with high efficiency, or the like. In conclusion, the analyzer 206 can in part recover imprinted phase signature from photons scattered off a target 208. id="p-73" id="p-73"

[0073]The analyzer 206 can include at least two reflectors that generate beam walk-off (e.g., the shown retroflectors 312A, 312B, and referred hereinafter to as simply a reflector 316, singular, for ease of reference), one or more compensators (e.g., the shown compensator 314), and a beam splitter 312. The reflector can be a combination of flat mirrors, a 3D curved mirror, one or more Harriot cells, etc. The reflector 316 can be a retroreflector to enable for the capture of a wider angle of incidence of incoming light, enabling the generation of the two outputs 212 and 214. To summarize, the analyzer 2can generate at least two outputs that are each based on combining at least two instances of the time-bin pairs that scatter off the target 108. The at least two instances can be generated by the analyzer 206 (e.g., via the shown retroreflectors and beam splitter) and the instances can include a delay between the instances while at least in part maintaining the modulated phase signature.

WO 2024/145721 PCT/CA2024/050011 id="p-74" id="p-74"

[0074]The analyzer 206 interferometer divides each received time-bin pair into two distinct sub-pulses, generating the two separate outputs 212 and 214, each output comprising four (4) sub-pulses (or two time-pairs) with separate pairs of sub-pulses temporally separated by a delay, △a For example, as shown in FIG. 4D and FIG. 4E, the ‘short’ (or long ’) pulse is separated into ‘short-short’ and ‘short-long ’ (or ‘long-short ’ and ‘long-long ’). The two distinct sub-pulses can be generated by positioning the beam splitter 312 such that the received time-bin pairs are incident on the beam splitter off-centre, as shown in FIG. 3A. id="p-75" id="p-75"

[0075]The analyzer 206 outputs 212 and 214 are respectively emitted or directed towards at least two detectors (e.g., detectors 310A and 3106). Various types of detectors are contemplated by this application, and different detectors can be selected based on different implementational requirements. It is understood that the detectors 310 can include one or more of pin photodiodes, single-photon detectors (allowing detection of faint signals down to single photon level), arrays of single-photon detectors, superconducting detectors, among others. id="p-76" id="p-76"

[0076]In example embodiments, at least two of the source 102, the imprinter 104, the analyzer 206, and the detector(s) 310 are within an integrated housing. For example, the analyzer 206 can include separate pathways for receiving the light, at distinct pathways for each output to direct that output to a respective detector 310, all within the same housing. The assessor 216 can similarly be integrated into the housing, or the assessor 216 can be a processor located on a remote service, such as a cloud computing provider, which ingests data sets generated by the detectors 310 (e.g., a first and second data set generated by respectively by the detectors 310). id="p-77" id="p-77"

[0077]In summary, output 150 results from the photon source 102 emitting a train of pulses. Each output pulse can be narrowband, broadband, or combinations in between narrowband and broadband. The pulses can be multimode or single mode. FIG. 4A shows the characteristics of photons at output 150. id="p-78" id="p-78"

[0078]Signal from the photon source 102 is collimated and sent through the imprinter 104. The imprinter 104 splits pulses arriving from the source 102 and introduces path length asymmetry A, between the split pulses. As discussed above, the imprinter 104 converts each incoming state of photons into a coherent superposition of two time-bins. The imprinter 1thus induces a selected phase-signature between the two time-bins in the time-bin pair resulting in a coherent superposition of time-bins parameterized by the selected phase-signature.

WO 2024/145721 PCT/CA2024/050011 id="p-79" id="p-79"

[0079]Output 152 exits the imprinter 104 and is sent towards the target 108. FIG. 4B shows characteristics of example pulses sent towards at the target 108, including the imprinted delay. id="p-80" id="p-80"

[0080]Output 154 shows properties of photons scattered or reflected off the target 1travel, and the output travels towards the analyzer 206. FIG. 4C shows characteristics of example photons scattered off the target 108, having the imprinted delay and some additional properties. id="p-81" id="p-81"

[0081]Photons scattered or reflected off the target 108 are collected by the analyzer 106. The scattered photons can be collected using conventional collection techniques, such as a telescope, mirrors, etc. id="p-82" id="p-82"

[0082] The collected photons pass through the analyzer 206 and are sent towards thedetectors 310. The detectors 310 can be optical (including, in example embodiments, infrared), microwave, radar, etc., detectors. Photons travelling towards the two detectors 310A and 310B (hereinafter referred to in the singular, as detector 310, for ease of reference), shown in outputs 212 and 214, can exhibit the example characteristics shown in FIGS. 4D and 4E. id="p-83" id="p-83"

[0083]Therefore, a photon exiting the analyzer 206 could have traversed one of the four paths (with the first length describing paths within the imprinter 104, and the second path describing the travelled length of 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 match, i.e., A; ~ A^, then the probabilities of the collected photon coming via SL and LS paths become indistinguishable and result in interference. Thus, as shown in FIGS. 4D and 4E, eight sub-pulses associated to a single originally emitted pulse (from output 150) are generated, each detector 310 receiving four pulses. A time delay A^ is imparted between split time-bin pairs received by the detector 310. The asymmetry can be such that the latest sub-pulse of the earlier pair of sub-pulses partially or fully overlaps, in time, with the earliest sub-pulse of the pair of later sub-pulses. This overlap creates at least some interference, the degree of interference being a function of the amount of overlap. id="p-84" id="p-84"

[0084]The detector 310 can be used to measure the degree of interference between sub-pulses. More specifically, the amount of overlap, and thus of interference, can vary in a known manner from the earlier pair of sub-pulses of the train to a later pair of sub-pulses of the train based on the difference in time delay imparted at the imprinter 104, the analyzer 206, or both, and more specifically as a function of the imprinted phase signature.

WO 2024/145721 PCT/CA2024/050011 id="p-85" id="p-85"

[0085]The degree of interference can also depend on whether the target 108 is in motion or not. In instances where the target 108 is in motion, the Doppler effect can shift the time-bin delay by a factor ‘D’, as shown in FIGS. 40, 4D, 4E. In instances where the target 108 is still, then D=1. id="p-86" id="p-86"

[0086]The strength of interference depends on the degree of overlap and can be estimated by the observed contrast or visibility. The analyzer 206 can include a phase modulator similar to the modulator shown in the imprinter in FIG. 3B to control the degree of overlap. As the output intensity of photons from the separate paths is defined in part by the interferometers and is further contingent upon the imprinted phase signature, precise phase manipulation with a phase modulator of the analyzer 206 interferometer can enable determining the presence (if any) of the imprinted phase-signature initially applied by the imprinter 104 on the collected photons as the analyzer 206 output intensity varies in time according to the imprinted phase signature. id="p-87" id="p-87"

[0087]FIGS. 5A, 5B, and 50 show the results of a simulated object detection experiment. In the absence of the target 108, the detector 310 received 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 results based on incorporation of the target 108 into the experiment. Assuming no loss, no noise and 100% reflection of photons from the target 108, the signal received by the detector 310 is shown by the lower curve 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 noise and reflected signal. As shown by the highest line of graph of FIG. 5A, displaying a sinusoidal with an average intensity of six (6) units. id="p-88" id="p-88"

[0088]FIGS. 5B and 50 show histograms generated based on example experiments, where the histograms are prepared based on one of an intensity or correlation scheme. In FIG. 5B, the intensity-based scheme, the histogram of the detected signal is shown as two distinct peaks. In FIG. 50, the histogram results from cross correlating the phase signature of the received photons with the phase signature of the transmitted photons. For the target- absent case (left hand side), the only detected photons are noise photons which have no correlation with the transmitted phase-signature, thereby leading to a low correlation value. In contrast, for the object-present case (right hand side), the received photons are a fraction of the signal photons, and the observed phase-signature is highly correlated with the transmitted ones, thereby resulting in a high correlation value as shown. Thus, instead of the two histograms shown in the intensity graph of FIG. 5B, the disclosed process may lead to further separated histogram as can be seen by comparing FIG. 5B and FIG. 50.13 WO 2024/145721 PCT/CA2024/050011 id="p-89" id="p-89"

[0089] FIG. 6 shows an example flow chart for determining characteristics of targets. id="p-90" id="p-90"

[0090] At block 602, a plurality of time-bin pairs imprinted with a modulated phasesignature is transmitted towards a target. id="p-91" id="p-91"

[0091]At block 604, a first data set is received. The first data set is based on a first output generated by time-bin pairs of the plurality of the time-bin pairs scattering off the target. The post scattering time-bin pairs are received and processed with an analyzer that maintains the modulated phase signature within generated and separate first and second outputs. id="p-92" id="p-92"

[0092]At block 606, a second data set is received at a second detector, the second data set being based on the generated second output. id="p-93" id="p-93"

[0093] At block 608, the first and second data set are combined. id="p-94" id="p-94"

[0094] At block 610, the first and second data set are compared with a third data set thatdescribes the phase signature as imprinted on the transmitted time-bin pairs. id="p-95" id="p-95"

[0095]To determine presence of an imprinted phase signature pattern, or alternatively stated whether any reflected signal is detected, a cross-correlation function can be used in its signal processing. id="p-96" id="p-96"

[0096]A cross-correlation function measures the similarity between a reference-signal and a detected signal. The cross-correlation can measure the similarity between a signal vector, x, and a shifted (lagged) copy of the same detected vector, y, as a function of the lag. Given a reference vector, x, and detected data vector, y, both of length N and both from jointly stationary random processes, we can express the cross-correlation as: id="p-97" id="p-97"

[0097]Rxy(m) = £ n=0 1,־•n+myn’^ — 0 id="p-98" id="p-98"

[0098]The asterisk denotes the complex conjugate and mRxy(m) is lag. Here, Rxy(m) is not normalized. The output of this function on a set of vectors x, y is another vector z(m) = Rxy(m -N),m= 1,2,... ,2/V - 1. id="p-99" id="p-99"

[0099]The processing task involves analyzing the received signal to determine the likelihood of whether the target is present or absent. Higher accuracy and confidence are desirable. id="p-100" id="p-100"

[00100]Analyzing the received signal can include a variety of approaches. In at least one example embodiment, a comparison of correlation histograms is used (instead of the typical comparison of intensity histograms, as is done in intensity-based LiDAR). When a target is present, the detected signal is comprised of both noise photons and photons scattered off 14 WO 2024/145721 PCT/CA2024/050011 the target, resulting in a notably higher degree of correlation upon cross-correlation with the transmitted signal. Conversely, when the target is removed, the detected signal consists solely of noise photons, resulting in a lower degree of correlation during cross-correlation analysis. The plot of the histograms of the correlation values as depicted in FIG. 5C, capture these distinctions. Therefore, the comparison approach leverages the degree of correlation as a robust indicator of the system’s SNR: higher correlation indicates the presence of photons reflected from the target during its placement intervals. Whereas lower correlation signifies the detection of only noise during the intervals when the target is absent. id="p-101" id="p-101"

[00101]The correlation algorithm can be faster and more accurate compared to an intensity-based algorithm. One metric to show the improvement includes the ROC curve. As both approaches reduce to determining whether data points (detector outputs) belong to the target-absent histogram or the target-present histogram, the approaches can be abstracted to ‘binary classification. ’ The binary classification becomes non-trivial when the two histograms start to overlap, as in the case of a high-noise and/or high-loss environment (e.g., as shown in FIGS. 7A and 7B). id="p-102" id="p-102"

[00102]One way to compare binary classifiers (in this case, correlation vs. intensity approaches) is to plot the ROC curves of the respective classifiers. The classes can be defined as target-present, and target-absent. An ROC plot can therefore be construed as a [0,1] x [0,1] space, with the axes representing the proportion of the non-overlapping target- absent to target-present histograms along the histogram ’s domain. In other words, ROC graphs can graph the percentage of the (non-overlapped) target-present histogram that falls to the right of the discrimination threshold, ct, as the threshold scans the histograms domain. id="p-103" id="p-103"

[00103]FIG. 7C shows an example ROC curve, which example ROC curve can be used to quantify the efficacy of binary classification models. The closer the ROC curve is to y = 1, the better the classifier. As shown, the cross-correlation method (shown in FIG. 7A) is consistently a better binary classifier. id="p-104" id="p-104"

[00104]Correlation based approaches can suffer reduced performance when multimode light enters an interferometer (e.g., the analyzer 206 interferometer) with variable angle of incidence. The variable angle can cause a lateral offset between the paths impinging at the exit beam-splitter causing degradation of interference visibility, such as illustrated in FIGS. 8A and 8B. Channel induced spatial-mode distortions can further lower the interference quality. This degradation may result from the inherent asymmetry of the unbalanced interferometers.

WO 2024/145721 PCT/CA2024/050011 id="p-105" id="p-105"

[00105]Various compensation techniques for this spatial mode distortion are contemplated. For example, a compensation technique can include a glass material with appropriate length and refractive index to create a virtual mirror closer to the beam splitter (e.g., splitter 312). In at least one example embodiment, a glass cube (e.g., compensator 314) can be placed in the long arm of each unbalanced interferometer to match the distance between beam-splitter-to-virtual-mirror with the short arm. Another example of a compensation technique includes a relay-lens setup where a 4f-lens system is placed in the long arm of each unbalanced interferometer. The relay system would act as a projector of the virtual mirror plane’s field-of-view back after propagation. id="p-106" id="p-106"

[00106]More generally, given an angle of incidence equal to zero of light entering an interferometer, the path length difference between the two arms can be written as: id="p-107" id="p-107"

[00107]M0 = 2(lL-ls) id="p-108" id="p-108"

[00108]where lL and ls are the length of the long path and short path, respectively. However, given a non-zero-degree angle of incidence, the path-length difference becomes a function of the angle of incidence as follows (note that the angles are shown in FIGS. 8A and 8B): -(, - ta11،، 1 + 5(a)tan(a ־ 1 + — ] - ( 00109 ] A،(a ]Lcosa cosa+smaJ 4 [00110]where 5(a) = AZotana/[l + tana] is the lateral offset of the beams at the output. In this case, the two paths become distinguishable, and a relative phase difference is observed: ~ 7r -pi-shifted for every 2 x 10-5 degrees of variation in the angle of incidence of the incoming beam. These characteristics can be used to tailor the compensation approaches discussed above. id="p-111" id="p-111"

[00111]Such compensation can not only improve performance at a higher angle of incidence but may also be necessary to enable high interference visibility with a multimode beam. id="p-112" id="p-112"

[00112]Referring again to FIG. 6, at block 612, one or more characteristics of the target 108 are determined based on the comparison of block 610. id="p-113" id="p-113"

[00113]Blocks 604 to 612 can be completed by a processor, or by a plurality of processors. The processor(s) can be remote to the detector 310 (e.g., all information collected by the detector 310 is provided to the cloud), integrated into, 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, after which it is provided to a WO 2024/145721 PCT/CA2024/050011 cloud processor), etc. The functionality of block 610 can be seamlessly implemented in software, firmware, or hardware. id="p-114" id="p-114"

[00114]The ordering of blocks shown in FIG. 6 is illustrative, and other sequences are contemplated. For example, the second data set can be received before the first data set. id="p-115" id="p-115"

[00115]The detected photon intensity at the detector 310 can vary according to the phase-coherence pattern imparted by the phase modulator. When the phase applied by the phase modulator in the analyzer 206 is zero, the photon intensity at one of the interferometer outputs precisely mirrors the phase-signature applied at the imprinter 104. When the phase applied is concurrent, the photon intensity at the other output manifests as a pi-phase shifted version of the former. id="p-116" id="p-116"

[00116]When the SNR is particularly low, either due to high-noise or high-loss or both, it is possible for the signal containing the phase signature of block 602 to become imperceptible by the detector 310. id="p-117" id="p-117"

[00117]In at least one example embodiments, to circumvent problems associated with low SNR, an optical common mode rejection technique can be used to amplify the signal intensity and cancel background noise that enters the analyzer 206 from the ambient surroundings. id="p-118" id="p-118"

[00118]An example approach involves using both outputs of the analyzer 2interferometer. In this approach, shown on the right-hand side of FIG. 3A, and schematically depicted on the right-hand side of FIG. 2, the signal photon intensity Is(t) at one analyzer 2output (e.g., at output 212) precisely mirrors the imprinted phase-signature 9t(t) within a time interval T applied at the imprinter 104. Concurrently, the signal photon intensity at the other output (e.g., at output 214), -/s(t) exits as a pi-phase shifted version of the other output. However, the incoming noise photons, being non-coherent in nature, are split symmetrically between the two outputs, resulting in equal noise intensity IN at the two detectors 310. As a result, one detector would receive ‘noise plus signal ’(^ + /s(t)) and the other would receive ‘noise minus signal ’ (1N - /s(t)). By taking the difference of the two detectors’ outputs, the noise can be cancelled out (apart from some statistical fluctuations), and the signal can be amplified as follows: id="p-119" id="p-119"

[00119] ID1 = IN+Is(t) id="p-120" id="p-120"

[00120] ID2 = IN-Is(t) id="p-121" id="p-121"

[00121]ID1-ID2 = IN + Is(t)- IN + Is(t) id="p-122" id="p-122"

[00122] - 2/s(t)17 WO 2024/145721 PCT/CA2024/050011 id="p-123" id="p-123"

[00123]In example embodiments, wavelength filters are used in combination with the dual-detector noise-cancelling analyzer 206 shown in FIG. 3B. The wavelength filters can increase the amount of noise being filtered out. id="p-124" id="p-124"

[00124]More generally, the disclosed method and apparatus, alternatively referred to as the optical common mode rejection technique is not applicable in conventional intensity- based LiDAR systems due to the absence of the phase-inverted complementary output signal. This signal, reliant on interference—an element not inherent in the intensity-based approach —is pivotal for the application of optical common mode rejection. id="p-125" id="p-125"

[00125]Accordingly, the disclosure includes a method where coherent photons are sent towards the target with a first set of phase signature(s). The photons reflected from a target (if any) can be collected and their properties detected. The method can include recovering or determining the phase-signature from the detected photon properties. By matching the observed phase signature with the transmitted phase signature, the method can differentiate incoming photons between signal photons or noise photons. The method can include tuning, such as tuning with a correlation metric that is greater in instances where reflected photons have a higher presence of signal photons as compared to noise photons. id="p-126" id="p-126"

[00126]As can be seen therefore, the examples described above and illustrated are intended to be exemplary only.

Claims (31)

WO 2024/145721 PCT/CA2024/050011 WHAT IS CLAIMED IS:

1. A method for determining properties of targets, comprising: a. transmitting a plurality of time-bin pairs imprinted with a modulated phase signature towards a target; b. receiving a first data set at a first detector, the first data set based on a first output generated by time-bin pairs of the plurality of the time-bin pairs scattering off the target and being processed with an analyzer that recovers the modulated phase signature within the generated first and second output; c. receiving a second data set at a second detector, the second data set being based on the generated second output; d. combining the first data set and the second data set; e. comparing the first and second data set and a third data set that describes the imprinted phase signatures; and f. determining the one or more properties of the target based on the comparison.

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

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

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

5. The method of claim 1, wherein the one or more properties comprises a presence or absence, and determining the presence further comprises: determining whether a degree of coherence can be classified in a preconfigured range indicative of target presence.

6. The method of claim 1, wherein the combining the first data set and the second data set amplifies the imprinted phase signature and attenuates received noise signal. WO 2024/145721 PCT/CA2024/050011

7. The method of claim 1, wherein the first data set and the second data set are related as the first output and the second output are at least in part inverted relative to one another.

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

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

10. An apparatus, comprising: an interferometer comprising; a beam splitter splitting incoming time-bin pairs, the incoming time-bin pairs having imprinted therein a modulated phase signature; at least two reflectors creating parallel photon streams from respective split incoming time-bin pairs, the at least two reflectors and the beam splitter generating a first output and a related second output, each output combining photons from each of the parallel photon streams; and at least two pathways, each pathway enabling a respective one of the first and second outputs to travel towards a respective detector.

11. The apparatus of claim 10, wherein each reflector is separated from the beam splitter by a respective distance, a difference between the respective distances creates a delay between time-bin pairs of the plurality of the time-bin pairs.

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

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

14. The apparatus of claim 10, wherein the at least two reflectors comprise at least one of a combination of flat mirrors, a curved mirror, Harriot cells, a combination of curved mirrors, or a combination of flat and curved mirrors.

15. The apparatus of claim 10, wherein the beam splitter is positioned to receive incoming time-bin pairs off-centre or to receive returns from the at least two reflectors off-centre. WO 2024/145721 PCT/CA2024/050011

16. The apparatus of claim 10, further comprising a housing encapsulating the interferometer and incorporating the at least two pathways.

17. The apparatus of claim 16, wherein the housing further encapsulates an imprinter that imprints the imprinted phase signature on time-bin pairs.

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

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

20. The apparatus of claim 10, wherein the first and second outputs are inverted copies of one another which efficiently split incoming noise intensity.

21. A system comprising:an imprinter for receiving incoming photons, and generating time-bin pairs imprinted with a modulated phase signature;an analyzer for receiving the generated time-bin pairs after scattering from a target, and generating at least two outputs that are each based on combining at least two instances of the generated time-bin pairs, the at least two instances being delayed relative to one another and at least in part maintaining the modulated phase signature;at least two detectors, each respectively receiving one of the at least two outputs; andan assessor in communication with the at least two detectors and configured to compare the at least two outputs with the imprinted modulated phase signature to determine one or more properties associated with the target.

22. The system of claim 21, further comprising an emitter to emit the incoming photons.

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

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

25. The system of claim 24, wherein the interferometer is an asymmetric Michelson or Mach-Zehnder interferometer with a phase-modulator in one arm.21 WO 2024/145721 PCT/CA2024/050011

26. The system of claim 25, wherein the imprinter comprises a second interferometer related to the interferometer.

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

28. The system of claim 21, wherein the assessor is housed separately from the detectors, or at least in part with the detectors, or a combination of with the detectors and separate from the detectors.

29. The system of claim 21, further comprising a phase modulator in the imprinter to impart the imprinted modulated phase signal.

30. The system of claim 19, wherein the analyzer comprises a second phase modulator operated based on the phase modulator.

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