Long-range high-precision frequency-modulated continuous wave ranging system with fast optical path switching using optical switches

Abstract

The present invention provides a long-range, high-precision frequency-modulated continuous wave (FMCW) ranging system that uses an optical switch to rapidly switch optical paths, and relates to the field of interferometric ranging technology. This system, based on existing FMCW interferometric ranging systems, adds a time-of-flight (TOF) infrared ranging module and a semiconductor optical switch switching module. The TOF infrared ranging module measures the approximate distances between different parts of a workpiece to be measured and the measurement module. When the interferometric ranging module measures a beat frequency signal, the semiconductor optical switch switching module switches the optical path of a reference beam to delay lines with different optical path differences based on the distance measured by the TOF infrared ranging module. This matches the optical path of the measurement path and the reference path, maintaining them at the coherent length, thereby ensuring that measurement accuracy does not degrade with increasing distance. Finally, the distance to the workpiece to be measured is demodulated using the ratio of the optical path difference to the actual optical path, thereby completing the distance measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of interference distance measurement, and in particular to a long-range high-precision frequency-modulated continuous wave distance measurement system with an optical switch that quickly switches the optical path. Background Art

[0002] Currently, the commonly used ranging products on the market, including 3D cameras (ToF), use ranging methods such as direct pulse ranging, random pulse correlation ranging, and phase ranging.

[0003] Among them, the ranging principle of the direct pulse ranging method is to calculate the distance information by measuring the flight time between the pulse emitted from the transmitter, passing through the target and returning to the detector. This method is generally used for long-range ranging, not suitable for close-range ranging, and has low accuracy.

[0004] The ranging principle of random pulse correlation ranging is to calculate the distance information by calculating the cross-correlation function between the emitted random pulse signal and the returned random pulse signal. This method has strong anti-interference ability and is generally suitable for long-range ranging. Its ranging accuracy is limited by the modulation frequency of the random signal and has low accuracy.

[0005] The ranging principle of the phase ranging method is to calculate the distance information by detecting the phase displacement between the periodic signal sent from the transmitter, passing through the target and returning to the detector. This method has high measurement accuracy, but because it is a periodic signal, its maximum measurement distance is limited by the maximum phase displacement of 2π. The later proposed multi-frequency phase ranging method uses periodic signals of two or more frequencies to expand the ranging range, but it is still limited by the period of the periodic signal. Therefore, the phase ranging method is generally used in short-distance, high-precision measurement occasions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a long-range, high-precision frequency-modulated continuous wave ranging system with an optical switch that quickly switches the optical path, thereby solving or alleviating at least one of the problems existing in the prior art, namely, the large amount of collected data, the degradation of measurement accuracy with distance, and the large amount of data.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: the present invention provides a long-range, high-precision frequency-modulated continuous wave ranging system with fast optical switch switching, comprising a frequency-modulated continuous wave laser emission module, an interferometric ranging module, a time-of-flight infrared ranging module, a semiconductor optical switch switching module, a beat frequency signal acquisition module, a signal processing module, and a distance demodulation module;

[0008] The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module;

[0009] The interference ranging module measures the beat frequency signals of different positions of the workpiece to be measured based on the large-bandwidth linear frequency modulated laser emitted by the frequency modulated continuous wave laser emission module;

[0010] The time-of-flight infrared ranging module measures the distance between different parts of the workpiece to be measured and the measuring module, and feeds back the distance to the semiconductor optical switch module;

[0011] The semiconductor optical switch module switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module when the interferometric ranging module measures the beat frequency signal, matches the optical path of the measurement path and the reference path, and keeps the measurement path and the reference path at a coherent length, thereby ensuring that the measurement accuracy does not deteriorate with increasing distance, and transmits the optical path difference to the distance demodulation module;

[0012] The beat frequency signal acquisition module collects the beat frequency signals of the interferometric ranging system at different positions of the workpiece to be measured and sends them to the signal processing module;

[0013] The signal processing module demodulates the interference distance based on the beat frequency signal collected by the beat frequency signal collection module;

[0014] The distance demodulation module adds the interference distance demodulated by the signal processing module to the optical path difference transmitted by the semiconductor optical switch switching module, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference to the actual optical path, thereby completing the distance measurement.

[0015] Preferably, the frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference ranging module.

[0016] Preferably, the semiconductor optical switch module includes a semiconductor package and a data feedback line encapsulated in the semiconductor package, an acquisition card fast switching switch, and delay lines with different optical path differences; one end of the data feedback line is connected to the time-of-flight infrared ranging module for direct communication through a data interface, and the other end is connected to the signal acquisition card to collect feedback results from the time-of-flight infrared ranging module; the acquisition card is connected to the fast switching switch as a signal generator; the fast switching switch is connected to the delay lines with different optical path differences to achieve switching between different optical path differences according to the signal sent by the acquisition card.

[0017] Preferably, the beat signal is a frequency offset generated when the reference light and the measurement light interfere with each other.

[0018] Preferably, the interference optical path structure in the interference ranging module includes a coupler 1, a circulator, a coupler 2, a detector 1, a detector 2, a flange, and a zoom lens; wherein the coupler 1 receives the large-bandwidth linear tuned laser emitted by the frequency-modulated continuous-wave laser emission module and divides the tuned laser into a measuring beam and a reference beam; wherein the measuring beam passes through the circulator flange and the zoom lens connected in sequence and is emitted onto the workpiece to be measured, and then returns to the circulator and is transmitted to the coupler 2; the reference beam is switched to delay lines with different optical path differences by a semiconductor optical switch module and is then transmitted to the coupler 2; the coupler 2 recouples the two beams and then divides them into two beams and transmits them respectively to the detector 1 and the detector 2; the detector 1 and the detector 2 respectively collect the beat frequency signal and the optical path difference signal and transmit them to the signal processing module and the distance demodulation module.

[0019] The beneficial effects of the above technical solution are as follows: The present invention provides a long-range, high-precision frequency-modulated continuous wave ranging system that uses an optical switch to rapidly switch optical paths. This method reduces the pressure of long-range acquisition and improves ranging stability and accuracy. It enables rapid, micron-level, high-precision ranging, increasing measurement speed. It also features a simple structure, ease of implementation, convenient adjustment, and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A structural block diagram of a long-range, high-precision frequency-modulated continuous wave ranging system with fast optical path switching using an optical switch provided by an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of the fast switching optical path of a semiconductor optical switch provided by an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the optical path structure of the interferometric ranging module provided in an embodiment of the present invention.

[0023] In the figure: 1. Time-of-flight infrared ranging module; 2. Semiconductor optical switch switching module; 3. Frequency-modulated continuous wave laser emission module; 4. Interference ranging module; 5. Beat frequency signal acquisition module; 6. Signal processing module; 7. Distance demodulation module; 22. Semiconductor package; 21. Data feedback line; 23. Fast switching switch; 24. Delay line with different optical path difference; 41. Coupler 1; 42. Circulator; 43. Coupler 2; 44. Detector 1; 45. Detector 2; 46. Flange; 47. Zoom lens. DETAILED DESCRIPTION

[0024] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0025] In this embodiment, a long-range high-precision frequency-modulated continuous wave ranging system with a fast optical switch switching optical path is provided. Figure 1 As shown, it includes a frequency modulated continuous wave laser emission module 3, an interference ranging module 4, a time-of-flight infrared ranging module 1, a semiconductor optical switch switching module 2, a beat frequency signal acquisition module 5, a signal processing module 6 and a distance demodulation module 7;

[0026] The frequency modulated continuous wave laser emission module 3 emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module; in this embodiment, the frequency modulated continuous wave laser emission module 3 emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference ranging module 4.

[0027] The interference ranging module 4 measures the beat frequency signals at different positions of the workpiece to be measured based on the large-bandwidth linear frequency modulated laser emitted by the frequency modulated continuous wave laser emitting module 3; the beat frequency signal is the frequency offset generated when the reference light and the measuring light interfere.

[0028] The time-of-flight infrared ranging module 1 measures the distance between different parts of the workpiece to be measured and the distance between the measuring module ...

[0029] In this embodiment, the time-of-flight infrared ranging module 1 uses the GYTOF10M ranging module to measure the approximate distance between different parts of the workpiece being measured and the measurement system. The GYTOF10M is a low-cost infrared laser ranging sensor module with an operating voltage of 3.7V-5V, low power consumption, compact size, and easy installation. Its operating principle is to use the time phase difference between the emitted light and the reflected light from the object being measured, and then use a sophisticated algorithm to obtain direct distance data. The module has two data reading modes: serial UART (TTL level) + IIC (2-wire) mode. The serial port baud rate is configurable from 2400bps to 230400bps, with continuous and query output modes, and the settings can be saved during power-down. Communication programs for Arduino, 51, and STM32 microcontrollers are provided. The GYTOF10M module can set the module distance alarm value and switch output. If the set distance alarm value is exceeded, the OUT pin directly outputs a high level. In IIC mode, if necessary, the internal IIC addresses can be set to different levels to allow multiple sensors to be directly connected to the same bus. GYTOF10M distance measurement uses dynamic time filtering, and the data will be more stable when the output frequency is lower.

[0030] The semiconductor optical switch module 2 switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module 1 when the interferometric ranging module 4 measures the beat frequency signal, matches the optical path of the measurement path and the reference path, and keeps the measurement path and the reference path at a coherent length, thereby ensuring that the measurement accuracy does not deteriorate with increasing distance, and transmits the optical path difference to the distance demodulation module 7;

[0031] In this embodiment, the semiconductor optical switch module is as follows: Figure 2 The device shown includes a semiconductor package 22 and a data feedback line 21 encapsulated in the semiconductor package 22, an acquisition card fast switching switch 23 and delay lines 24 with different optical path differences; one end of the data feedback line 21 is connected to the time-of-flight infrared ranging module 1 for direct communication via the 232 data interface, and the other end is connected to the signal acquisition card to collect the feedback results of the time-of-flight infrared ranging module 1; the acquisition card is connected to the fast switching switch 23 as a signal generator; the fast switching switch 23 is connected to the delay lines 24 with different optical path differences to achieve switching between different optical path differences according to the signal sent by the acquisition card; according to the feedback results of the time-of-flight infrared ranging module 1, the fast switching switch 23 can quickly switch between delay lines with different optical path differences to match the measurement optical path.

[0032] The beat signal acquisition module 5 collects the beat signals of the interferometric ranging system at different positions of the workpiece to be measured and sends them to the signal processing module 6;

[0033] The signal processing module 6 obtains the optical path difference through Fourier transform based on the beat frequency signal collected by the beat frequency signal collection module 5, and then demodulates the interference distance;

[0034] The distance demodulation module 7 (GPU) adds the interference distance demodulated by the signal processing module 6 to the optical path difference transmitted by the semiconductor optical switch switching module 2, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference and the actual optical path, thereby completing the distance measurement.

[0035] In this embodiment, the interference optical path structure in the interference ranging module 4 is as follows: Figure 3 As shown, it includes a coupler 1 41, a circulator 42, a coupler 2 43, a detector 1 44, a detector 2 45, a flange 46, and a zoom lens 47; wherein, the coupler 1 41 receives the large-bandwidth linear tuned laser emitted by the frequency-modulated continuous-wave laser emission module 3, and divides the tuned laser into a measurement beam and a reference beam; wherein, the measurement beam passes through the circulator 42 flange 46 and the zoom lens 47 connected in sequence, and then is emitted onto the workpiece to be measured, and then returns to the circulator 42 and is transmitted to the coupler 2 43; the reference beam is switched to different optical path difference delay lines by the semiconductor optical switch switching module 2 and is transmitted to the coupler 2 43; the coupler 2 43 recouples the two beams and then divides them into two beams, which are respectively transmitted to the detector 1 44 and the detector 2 45; the detector 1 44 and the detector 2 45 respectively collect the beat frequency signal and the optical path difference signal and transmit them to the signal processing module 6 and the distance demodulation module 7.

[0036] The core idea of ​​FM laser ranging technology is to use the time-varying frequency of the emitted light beam (linear modulation) to introduce a frequency offset between the reference light and the measurement light. By measuring this offset, the distance to the object being measured can be inferred. The following are the detailed working steps:

[0037] 1. Linear frequency modulated light source: The laser emits a beam whose frequency changes linearly with time. The frequency f(t) is expressed as:

[0038]

[0039] Among them, f0 is the initial frequency, Δf is the frequency modulation range (the difference between the maximum frequency and the minimum frequency), T is the linear frequency modulation period, and t is the current time (0 <t≤T);

[0040] 2. Interference between reference and measurement light: The transmitted light beam is split into two beams by a beam splitter: the reference beam and the measurement beam. The reference beam returns along a fixed path, while the measurement beam reflects off the surface of the object being measured and returns to the interferometer. These two beams converge in the interferometer, forming interference fringes. Due to the varying distances to the object being measured, the measurement light returns to the interferometer with a time delay τ, which is proportional to the distance d to the object:

[0041]

[0042] Where c is the speed of light (about 3×10 8 m / s), d is the distance to the object.

[0043] 3. Formation of frequency offset (beat frequency): When the reference light and the measurement light are recombined in the interferometer, there is an optical path difference Δd when the measurement beam returns, which causes the reference light and the measurement light to produce a frequency offset (beat frequency) when interfering. Due to the time delay τ of the measurement light, there is a frequency difference between the two beams when interfering. For a linear frequency modulation signal, the frequency difference Δf beat The relationship with the time delay τ is as follows:

[0044]

[0045] Where Δf beat is the interference fringe frequency offset (beat frequency), Δf is the sweep range, T is the sweep period, and τ is the time delay caused by the optical path difference;

[0046] 4. Distance calculation: by measuring the frequency shift Δf of the interference fringes beat , we can find the time delay τ and then get the distance d of the target:

[0047]

[0048] So the distance

[0049] The long-range, high-precision frequency-modulated continuous wave ranging system of the present invention with fast optical path switching of an optical switch is based on the above-mentioned frequency-modulated laser ranging technology. By switching the optical path of the reference beam to a delay line 24 with different optical path differences, the optical path of the measurement path and the reference path are matched, so that the measurement path and the reference path are kept at the coherent length, thereby ensuring that the measurement accuracy of the interferometric ranging does not deteriorate with increasing distance.

[0050] In this embodiment, it is assumed that the frequency of the light beam emitted by the transmitting laser at time t=0 is f0, and its frequency increases linearly with time, and the frequency change form is:

[0051] f(t)=f(0)+k·t

[0052] Wherein, the modulation rate k is defined as:

[0053]

[0054] When the measuring beam hits the target and reflects back, the optical path delay is τ. The frequency of the returning beam is:

[0055] f(t-τ)=f 0+ +k·(t-τ)=f0+k·tk·τ

[0056] Therefore, the frequency difference between the return beam and the reference beam is:

[0057]

[0058] Substituting the time delay τ and distance relationship The relationship between the frequency shift of the interference fringes and the measured distance is obtained:

[0059]

[0060] Solve for the optical path distance d:

[0061]

[0062] Since the signals to be processed in actual measurements are often affected by noise and multipath effects, frequency domain analysis (such as fast Fourier transform, FFT) is usually used to extract the frequency components of the interference signal to accurately determine the frequency difference Δf beat The intensity of the interference signal can be expressed in the following form:

[0063]

[0064] in, is the initial phase of the laser;

[0065] By performing FFT analysis on the interference signal I(t), the main peak in the spectrum is obtained, and then Δf is determined.beat , and finally the distance d is calculated.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A long-range, high-precision frequency-modulated continuous wave ranging system with fast optical path switching using an optical switch, characterized by: It includes a frequency modulated continuous wave laser emission module, an interference ranging module, a time-of-flight infrared ranging module, a semiconductor optical switch module, a beat frequency signal acquisition module, a signal processing module and a distance demodulation module; The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module; The interference ranging module measures the beat frequency signals of different positions of the workpiece to be measured based on the large-bandwidth linear frequency modulated laser emitted by the frequency modulated continuous wave laser emission module; The time-of-flight infrared ranging module measures the distance between different parts of the workpiece to be measured and the measuring module, and feeds back the distance to the semiconductor optical switch module; The semiconductor optical switch module switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module when the interferometric ranging module measures the beat frequency signal, matches the optical path of the measurement path and the reference path, and keeps the measurement path and the reference path at a coherent length, thereby ensuring that the measurement accuracy does not deteriorate with increasing distance, and transmits the optical path difference to the distance demodulation module; The beat frequency signal acquisition module collects the beat frequency signals of the interferometric ranging system at different positions of the workpiece to be measured and sends them to the signal processing module; The signal processing module demodulates the interference distance based on the beat frequency signal collected by the beat frequency signal collection module; The distance demodulation module adds the interference distance demodulated by the signal processing module to the optical path difference transmitted by the semiconductor optical switch switching module, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference to the actual optical path, thereby completing the distance measurement.

2. The long-range, high-precision frequency-modulated continuous wave ranging system with fast optical switch switching according to claim 1, characterized in that: The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference ranging module.

3. The long-range, high-precision frequency-modulated continuous wave ranging system with fast optical switch switching according to claim 1, characterized in that: The semiconductor optical switch module includes a semiconductor package and a data feedback line encapsulated in the semiconductor package, an acquisition card fast switching switch, and delay lines with different optical path differences. One end of the data feedback line is connected to the time-of-flight infrared ranging module for direct communication via a data interface, and the other end is connected to the signal acquisition card to collect feedback results from the time-of-flight infrared ranging module. The acquisition card serves as a signal generator and is connected to the fast switching switch. The fast switching switch is connected to delay lines with different optical path differences to achieve switching between different optical path differences based on the signal sent by the acquisition card.

4. The long-range, high-precision frequency-modulated continuous wave ranging system with fast optical switch optical path switching according to claim 1, characterized in that: The beat signal is a frequency shift generated when the reference light and the measurement light interfere with each other.

5. The long-range, high-precision frequency-modulated continuous wave ranging system with fast optical switch optical path switching according to claim 3, characterized in that: The interference optical path structure in the interference ranging module includes a coupler 1, a circulator, a coupler 2, a detector 1, a detector 2, a flange, and a zoom lens. The coupler 1 receives a large-bandwidth linearly tuned laser emitted by a frequency-modulated continuous-wave laser emission module and divides the tuned laser into a measurement beam and a reference beam. The measurement beam passes through the circulator flange and the zoom lens connected in sequence, is emitted onto the workpiece to be measured, and then returns to the circulator and is transmitted to the coupler 2. The reference beam is switched to delay lines with different optical path differences by a semiconductor optical switch module and is then transmitted to the coupler 2. The coupler 2 recouples the two beams and then splits them into two beams, which are respectively transmitted to the detector 1 and the detector 2. The detectors 1 and 2 respectively collect beat frequency signals and optical path difference signals and transmit them to the signal processing module and the distance demodulation module.

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