Micrometer-level integrated optical ranging device and method based on on-chip coherent scale and joint demodulation algorithm

Abstract

The application discloses an integrated optical ranging device and method, aiming at solving the problems of large volume, high cost and poor long-term stability of the existing coherent ranging system. The device integrates the core optical components such as light source, reference arm, frequency scale and coherent receiver on a photon chip. On the method, through the on-chip frequency scale (such as micro-ring resonator) combined with the embedded multi-tone phase marker, the coarse and fine two-stage correction of the frequency sweep nonlinearity is realized; the upper and lower double slope sweep is used to construct the differential ratio to suppress the sweep rate fluctuation error; and the optical path thermal drift of the reference arm is estimated and compensated online through the algorithm. The application can also expand the unambiguous ranging range by double-wavelength alternative frequency sweep. The application realizes on-chip integration and algorithm closed loop, significantly reduces the device volume, reduces the dependence on the external environment, maintains the micron-level measurement accuracy, and greatly improves the stability and anti-interference ability of the system.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of precision optical measurement and photonic integrated circuits, and specifically relates to a micrometer-scale integrated optical ranging device and method based on an on-chip coherent scale and a joint demodulation algorithm. Background Technology

[0002] Existing high-precision coherent ranging technologies, especially linear frequency sweep coherent ranging (FMCW), calculate distance by generating beat frequency signals between the reference light and the echo light from the target, possessing the potential for high accuracy and sensitivity. However, conventional systems implementing this technology typically rely on optical paths constructed from discrete optical components, such as using external optical fibers to form a reference arm, and external equipment (such as a Fabry-Perot etalon) to linearize and calibrate the laser's frequency sweep process. This discrete structure not only results in a large, complex, and costly device, but also makes it highly sensitive to environmental temperature changes and mechanical vibrations. These sensitivities lead to two key technical problems: first, the frequency sweep process of the laser source itself is nonlinear, which, without precise calibration, directly introduces ranging errors; second, the optical path length of the reference arm drifts slowly due to environmental factors such as temperature, which can introduce imperceptible systematic measurement biases over long-term operation. Although some components (such as coherent receivers) can be integrated onto photonic chips, the lack of an integrated system that can simultaneously sense and correct the two error sources makes it difficult for existing technologies to achieve miniaturization, low cost, and long-term stability while ensuring micron-level accuracy. This limits their deployment in industrial-grade continuous and reliable applications. Summary of the Invention

[0003] This invention provides an integrated optical ranging device to address the problems existing in the prior art, comprising:

[0004] Photonic integrated chip, wherein the photonic integrated chip integrates:

[0005] A beam splitter is used to split the swept laser light from the light source into a measurement beam and a reference beam;

[0006] The optical path of the measuring arm is used to emit the measuring light to the target under test and receive the returned target echo light;

[0007] An on-chip reference arm is configured to provide a preset optical path delay for the reference light;

[0008] An on-chip frequency scale, coupled to the frequency-sweeping laser optical path, is used to generate a series of discrete frequency reference points during the frequency sweeping process; and

[0009] A coherent receiver is used to coherently mix the target echo light with the reference light after it has been delayed by the on-chip reference arm, and output an electrical signal.

[0010] Furthermore, the on-chip reference arm includes a long delay waveguide made of a material with a low thermo-optic coefficient and integrates a phase adjuster for actively compensating for the optical path drift of the reference arm.

[0011] Furthermore, the on-chip frequency scale is at least one of the following:

[0012] The resonant peak of the transmission or reflection response of a microring resonator (MRR) is used as the frequency reference point.

[0013] Soliton microcomb or electro-optical comb, whose stable comb teeth are used as the frequency reference point.

[0014] Furthermore, it also includes a control and processing unit configured to perform at least one of the following functions:

[0015] Based on the frequency reference point generated by the on-chip frequency scale, the frequency scanning of the swept laser is linearized and corrected.

[0016] The electrical signal output by the coherent receiver is demodulated to extract phase information related to the distance to the target under test;

[0017] Based on the phase information, the distance to the target under test is calculated.

[0018] Furthermore, the control and processing unit is configured to implement the linearization correction through a digital predistortion (DPD) module, which performs reverse correction on the laser drive signal of the next frame based on the frequency scanning nonlinear data of the historical frame or the current frame.

[0019] Furthermore, the control and processing unit is also configured to run a state estimation algorithm that takes the optical path drift of the reference arm as a state variable and performs online estimation and compensation using the readings of the on-chip temperature sensor or the feedback control quantity of the phase adjuster.

[0020] An integrated optical ranging method, characterized by comprising the following steps:

[0021] A frequency-sweeping laser beam is generated and split into a measurement beam and a reference beam;

[0022] The measurement light is emitted to the target and the returned target echo light is received.

[0023] The reference light is passed through an upper reference arm to obtain a preset optical path delay;

[0024] The frequency scanning process of the swept laser is sampled using a frequency scale on a chip to generate a series of frequency reference points;

[0025] The target echo light is coherently mixed with the delayed reference light to generate a beat frequency signal;

[0026] The beat frequency signal is resampled or corrected based on the frequency reference point to compensate for sweep frequency nonlinearity; and

[0027] The distance to the target under test is calculated from the calibrated beat frequency signal.

[0028] Furthermore, the step of generating the swept laser includes performing a dual-slope sweep, i.e., alternately performing an up-sweep and a down-sweep; and the step of calculating the distance includes constructing the difference or ratio of the beat frequency signals generated by the up-sweep and down-sweep to suppress measurement errors caused by changes in the sweep rate.

[0029] Furthermore, it also includes the following steps:

[0030] A micro-amplitude multi-tone phase marker is superimposed on the waveform of the swept laser;

[0031] By demodulating the multi-tone phase marker, high-frequency nonlinear information during the frequency sweep process is obtained, and combined with the macroscopic nonlinear information obtained from the on-chip frequency scale, a fine reconstruction of the frequency sweep rate is achieved.

[0032] Furthermore, it also includes expanding the unambiguous ranging range by alternating frequency sweeps between two different center wavelengths (λ1, λ2) and using their combined wavelength (Λ) for coarse phase unwrapping, followed by fine distance calculation using the measurement results of a single center wavelength.

[0033] The present invention has the following beneficial effects:

[0034] This invention integrates an on-chip reference arm and an on-chip frequency scale onto a single photonic integrated chip, enabling real-time monitoring of the two main error sources affecting ranging accuracy—reference arm optical path drift and laser sweep frequency nonlinearity—within the chip. By combining state estimation and linearization correction algorithms in the control and processing unit, the device can compensate for thermally induced drift and correct sweep frequency nonlinearity online, avoiding reliance on expensive external calibration equipment and significantly improving the long-term stability and resistance to environmental interference of ranging results.

[0035] This invention utilizes digital predistortion (DPD) technology to obtain sweep frequency nonlinear data from an on-chip frequency scale and use it to reverse-correct the laser drive signal of the next frame. This predictive closed-loop control method can improve the linearity of the sweep frequency from the source, thereby improving the quality of the original beat frequency signal. By combining dual-slope sweep frequency, constructing signal difference / ratio, and superimposing multi-tone phase markers on the laser waveform, the error introduced by the sweep rate variation can be effectively suppressed, and the high-frequency fine nonlinear information in the sweep frequency process can be accurately reconstructed and compensated, thereby improving the overall ranging accuracy.

[0036] To address the phase entanglement problem inherent in traditional coherent ranging, this invention can also perform coarse phase unwrapping by alternately sweeping frequencies between two different center wavelengths and using their combined wavelength. This effectively extends the unambiguous measurement range of the device without sacrificing micrometer-level accuracy. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the internal structure of the present invention;

[0038] Figure 2 Flowchart for integrated optical ranging method. Detailed Implementation

[0039] The invention will now be further described with reference to the accompanying drawings.

[0040] Example 1:

[0041] This embodiment discloses a micrometer-level integrated optical ranging device, the specific system structure of which is shown in the attached figure. Figure 1 As shown, the device tightly integrates the core optical link of coherent ranging with the digital processing unit to achieve high-precision and high-stability measurements.

[0042] See attached document Figure 1 The core of the device is a photonic integrated chip that integrates the main optical functions required for coherent ranging. During operation, a swept laser beam from the light source enters the chip and is split by a beam splitter. One path serves as the measurement beam, transmitted to the target via the measurement arm optical path (which may include an on-chip grating coupler). The reflected target echo is received by the chip. The other path serves as the reference beam, entering the on-chip reference arm. This reference arm is a long delay waveguide coiled on the chip, providing a stable and preset optical path delay for the reference beam. To reduce the impact of temperature variations on the optical path, the waveguide is preferably made of a low thermo-optical coefficient material (such as silicon nitride, SiN). Through material stacking and structural optimization, its equivalent optical path temperature coefficient can be controlled at a low level. A phase adjuster (e.g., a microheater) is also integrated on the reference arm waveguide to actively compensate for slow optical path drift caused by temperature or stress in the reference arm.

[0043] The third beam split from the beam splitter is coupled to an on-chip frequency scale to generate a series of discrete frequency reference points during the frequency sweep process. In this embodiment, the scale can be a microring resonator (MRR). Whenever the frequency of the sweeping laser crosses the resonant frequency of the microring, its transmitted power will exhibit a peak or trough. These equally spaced peaks and troughs constitute the frequency reference points. A monitoring detector is connected to the output of the microring to convert these optical signals into electrical signals for subsequent processing.

[0044] The target echo light returning from the target under test and the reference light, after being delayed by the on-chip reference arm, enter the coherent receiver for mixing. The receiver preferably adopts a structure that includes a 90° optical mixer and a balanced photodetector to simultaneously output two beat frequency electrical signals, namely in-phase (I) and quadrature (Q), and can effectively suppress the common-mode intensity noise of the laser.

[0045] This device also includes a control and processing unit (represented in the figure as two functional modules: "Laser Drive & DPD Correction" and "Signal Demodulation & State Estimation," typically implemented by an FPGA / SoC). This unit receives I / Q electrical signals from a coherent receiver and a frequency reference point signal from a monitoring detector. It uses the frequency reference point signal to calibrate the nonlinearity during the laser frequency sweep process. In this embodiment, this is achieved through a digital predistortion (DPD) module, which performs reverse correction on the laser drive signal of the next frame based on currently or historically measured frequency sweep nonlinearity data, thereby improving the linearity of the frequency sweep at its source.

[0046] In the signal demodulation and state estimation stage, this unit demodulates the calibrated or resampled I / Q electrical signals (e.g., via a digital phase-locked loop) to extract phase information related to the distance to the target and ultimately calculates the distance value. Simultaneously, this unit runs a state estimation algorithm (e.g., Kalman filtering). This algorithm treats the optical path drift of the reference arm as a state variable requiring online estimation and uses readings from the on-chip temperature sensor or feedback control from the phase adjuster to estimate and compensate for it in real time, forming a closed-loop control to suppress systematic measurement errors caused by thermal effects or stress.

[0047] Example 2:

[0048] This embodiment describes a specific method for distance measurement using the above-described device. Its core is to use on-chip resources to perform real-time correction of frequency sweep and drift in order to obtain accurate distance information.

[0049] The ranging method begins by generating a swept laser beam, which is then split into a measurement beam, a reference beam, and a calibration beam. The measurement beam is emitted, reflected by the target, and returns to the chip; the reference beam receives a preset optical path delay via an on-chip reference arm. Simultaneously with the sweep, an on-chip frequency scale samples the sweep process to generate a frequency reference point. The target echo and the delayed reference beam are mixed in a coherent receiver to generate an I / Q beat frequency signal. The control and processing unit resamples or corrects the beat frequency signal based on the frequency reference point to compensate for sweep nonlinearity, and demodulates the phase from the corrected signal to calculate the distance.

[0050] To further improve measurement accuracy and reliability, this method may also include one or more of the following optimization steps.

[0051] In the step of generating the swept laser, a dual-slope sweep can be performed, that is, alternating between an upward sweep with linearly increasing frequency and a downward sweep with linearly decreasing frequency. By constructing the difference or ratio of the beat signals of the upward and downward sweeps, measurement errors caused by fluctuations in the sweep rate can be eliminated or suppressed under a first-order approximation.

[0052] To obtain higher-frequency and more refined nonlinear information during the frequency sweep process, micro-amplitude multi-tone phase markers can be superimposed on the driving waveform of the sweep laser. By performing correlation demodulation on the received signal, the phase changes of these markers can be extracted, thereby retrieving the subtle jitter of the sweep rate. Combining this high-frequency nonlinear information with the macroscopic nonlinear information obtained from the micro-ring resonator enables a more accurate reconstruction of the sweep rate, further improving the linearization correction effect.

[0053] When it is necessary to extend the unambiguous ranging range, this method can also alternately sweep frequencies between two different center wavelengths (λ, λ2). This yields a long equivalent composite wavelength. First, this composite wavelength is used for coarse phase unwrapping to determine the integer period range of the measured distance. Then, the measurement results from a single center wavelength are used for fine phase calculation, ultimately extending the unambiguous measurement range while maintaining micrometer-level measurement accuracy.

[0054] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. An integrated optical ranging device, characterized in that, include: Photonic integrated chip, wherein the photonic integrated chip integrates: A beam splitter is used to split the swept laser light from the light source into a measurement beam and a reference beam; The optical path of the measuring arm is used to emit the measuring light to the target under test and receive the returned target echo light; An on-chip reference arm is configured to provide a preset optical path delay for the reference light; An on-chip frequency scale is coupled to the frequency sweep laser optical path and is used to generate a series of discrete frequency reference points during the frequency sweep process; and A coherent receiver is used to coherently mix the target echo light with the reference light after it has been delayed by the on-chip reference arm, and output an electrical signal.

2. The apparatus according to claim 1, characterized in that, The on-chip reference arm includes a long delay waveguide made of a material with low thermo-optic coefficient and integrates a phase adjuster for actively compensating for optical path drift of the reference arm.

3. The apparatus according to claim 1 or 2, characterized in that, The on-chip frequency scale is at least one of the following: The resonant peak of the transmission or reflection response of a microring resonator (MRR) is used as the frequency reference point. Soliton microcomb or electro-optical comb, whose stable comb teeth are used as the frequency reference point.

4. The apparatus according to claim 2, characterized in that, It also includes a control and processing unit configured to perform at least one of the following functions: Based on the frequency reference point generated by the on-chip frequency scale, the frequency scanning of the swept laser is linearized and corrected. The electrical signal output by the coherent receiver is demodulated to extract phase information related to the distance to the target under test; Based on the phase information, the distance to the target under test is calculated.

5. The apparatus according to claim 4, characterized in that, The control and processing unit is configured to implement the linearization correction through a digital predistortion (DPD) module, which performs reverse correction on the laser drive signal of the next frame based on frequency scanning nonlinear data of historical frames or the current frame.

6. The apparatus according to claim 4, characterized in that, The control and processing unit is also configured to run a state estimation algorithm that takes the optical path drift of the reference arm as a state variable and performs online estimation and compensation using the readings of the on-chip temperature sensor or the feedback control quantity of the phase adjuster.

7. An integrated optical ranging method, characterized in that, Includes the following steps: A frequency-sweeping laser beam is generated and split into a measurement beam and a reference beam; The measurement light is emitted to the target and the returned target echo light is received. The reference light is passed through an upper reference arm to obtain a preset optical path delay; The frequency scanning process of the swept laser is sampled using a frequency scale on a chip to generate a series of frequency reference points; The target echo light is coherently mixed with the delayed reference light to generate a beat frequency signal; The beat frequency signal is resampled or corrected based on the frequency reference point to compensate for the sweep frequency nonlinearity. as well as The distance to the target under test is calculated from the calibrated beat frequency signal.

8. The method according to claim 7, characterized in that, The step of generating the frequency-sweeping laser includes performing a dual-slope frequency sweep, that is, alternately performing an up-sweep and a down-sweep; Furthermore, the step of calculating the distance includes: constructing the difference or ratio of the beat frequency signals generated by the upper and lower sweep frequencies to suppress the measurement error caused by the change in sweep frequency rate.

9. The method according to claim 7 or 8, characterized in that, It also includes the following steps: A micro-amplitude multi-tone phase marker is superimposed on the waveform of the swept laser; By demodulating the multi-tone phase marker, high-frequency nonlinear information during the frequency sweep process is obtained, and combined with the macroscopic nonlinear information obtained from the on-chip frequency scale, a fine reconstruction of the frequency sweep rate is achieved.

10. The method according to claim 7, characterized in that, It also includes expanding the unambiguous ranging range by alternating frequency sweeps between two different center wavelengths (λ1, λ2) and using their combined wavelength (Λ) for coarse phase unwrapping, followed by fine distance calculation using the measurement results of a single center wavelength.

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