FSI multi-target synchronous dynamic ranging system and method based on electro-optical modulation

Abstract

The invention discloses an electro-optical modulation-based FSI multi-target synchronous dynamic distance measurement system and method, and mainly solves the problems of complex implementation means and poor operation convenience of the existing multi-target dynamic distance measurement technology. Comprising the following steps: 1) generating a double-sideband frequency sweep modulation optical signal through an MZM; 2) establishing a Michelson interference light path, and performing primary power light splitting based on a multi-light-path interference principle; (3) a receiving and transmitting integrated multi-target measurement optical path is used, and multi-target distance measurement information multiplexing is achieved through combination of secondary power light splitting and delay optical fiber design; 4) performing frequency mixing interference on the measuring light and the reference light, and collecting an orthogonal interference signal; and 5) identifying and resolving a target optical path based on a distance spectrum algorithm of time-shifting Ap-FFT phase difference extraction, and calculating the absolute distance of each dynamic target by combining the use length of the delay optical fiber. The method can be used for high-precision multi-target or multi-axis synchronous dynamic absolute distance measurement in a complex environment, the system complexity can be greatly reduced, and miniaturization application is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical precision measurement, and further relates to an optical frequency scanning interference ranging method. Specifically, it is an FSI (Frequency Scanning Interferometry) multi-target synchronous dynamic ranging system and method based on electro-optic modulation, which is used for high-precision multi-target or multi-axis synchronous dynamic absolute distance measurement in complex environments. Background Art

[0002] High-precision absolute distance measurement technology is of crucial significance for both basic scientific research and advanced manufacturing. Especially in the field of space science, spacecraft formation flight technologies represented by the European "Darwin Project", "Gravitational Wave Project" and "Sound Search Project" have extremely high precision requirements for on-orbit measurement. The optical frequency scanning interference absolute ranging technology (FSI) can achieve static single-target absolute distance measurement, and has application advantages such as a simple hardware system structure, no need for a guide rail, high precision, and no non-ambiguous distance limit. It is one of the most promising and valuable absolute ranging technologies at present. The FSI ranging technology can achieve high-precision absolute distance measurement. However, the main factors further restricting the wide application of this technology are the following three: high dynamics, multi-target synchronization, and miniaturization.

[0003] On the one hand, absolutely stationary targets do not exist in real measurement scenarios. Various factors such as mechanical vibration noise of the target and temperature fluctuations of the measurement environment will cause the measured optical path difference of the FSI absolute distance measurement system to change dynamically during the optical frequency scanning process. At the same time, FSI is extremely sensitive to the tiny movement of the target. The Doppler dynamic amplification error of thousands of times will annihilate the ranging accuracy in the absolutely stationary state, causing a huge ranging error. In order to perform high-precision dynamic ranging, the following commonly used technologies are available: 1) Dual-laser dynamic FSI technology, which uses two sweeping lasers to synchronously sweep forward and backward to offset the Doppler dynamic error, but the forward and reverse synchronous sweeping is difficult to achieve and the dual-laser FSI system is relatively complex. 2) Kalman state space model dynamic decoupling technology, which establishes a state space model of displacement, velocity and acceleration, combines Kalman filtering for decoupling, and solves the absolute distance, but this method will cause a large solution error and reduce the ranging accuracy. 3) Double-sideband frequency scanning interferometry ranging technology. In 2017, Di Mo published an article titled "Double-sideband frequency scanning interferometry method for long-distance dynamic absolute measurement" in the journal "Applied Physics Series B: Laser and Optics". It proposed a double-sideband frequency scanning interferometry measurement system, which uses a fixed-frequency laser and a Mach-Zehnder modulator MZM (Mach-Zehnder Modulator) to generate two scanning signals with opposite frequencies, and uses IQ demodulation to distinguish the frequencies of the two signals to offset the ranging error caused by target motion. However, this ranging method directly uses the main spectrum line in the spectrum to calculate the phase difference between the upper and lower sidebands, so it is only applicable to the case where the target is stationary or moving at a uniform speed. For the more common uniform acceleration motion and simple harmonic motion in the actual environment, the frequency of the interference signal will change accordingly, resulting in a large spectrum broadening and the failure of the ranging algorithm.

[0004] On the other hand, actual application scenarios often require high-precision ranging systems to have the ability to synchronously measure multiple targets or multiple axes. There are several commonly used methods: 1) Vehicle-mounted laser radar, based on time-of-flight and optical frequency scanning interference, the system is simple but the ranging accuracy is low, and multi-target measurement is achieved by mechanical asynchronous scanning; 2) Cascade multi-target measurement method, the synchronization of cascade multi-target measurement method requires unified clock control and delay calibration, and there are too many device redundancies; 3) FSI distance spectrum synchronization measurement method based on spectrum estimation, this method is only applicable to static targets, the actual system ranging resolution depends on the frequency sweep bandwidth, and the accuracy is only mm level. It can be seen that the existing methods need to construct two sets of ranging signals about the frequency sweep frequency shift and Doppler frequency shift for the same target without losing ranging accuracy. At the same time, measuring several targets or several axes requires several sets of the above dynamic FSI ranging systems; in order to achieve synchronous measurement, it is also necessary to design unified clock control and delay calibration; in addition, the spatial free optical path requires high-precision internal optical path calibration, which has great restrictions on the measurement environment; the system used is extremely complex and difficult to apply in a small and convenient manner. Summary of the invention

[0005] The purpose of the present invention is to propose a FSI multi-target synchronous dynamic ranging system and method based on electro-optical modulation in view of the shortcomings of the above-mentioned prior art, which mainly solves the problems of complex implementation means and poor operation convenience of the existing multi-target dynamic ranging technology. The scheme proposed by the present invention has the advantages of high precision, high dynamics, multi-target synchronization, and miniaturization, and can be used for high-precision multi-target or multi-axis synchronous dynamic absolute distance measurement in complex environments, which can greatly reduce the complexity of the system and facilitate miniaturization application.

[0006] The basic idea of ​​realizing the present invention is as follows: firstly, an electro-optically modulated double-sideband FSI multi-target synchronous dynamic ranging real system is established, and a swept-frequency electrical signal generated by a swept-frequency signal source is electro-optically modulated with a 1550nm laser generated by a narrow linewidth laser through an MZM to generate a swept-frequency double-sideband optical signal; after power amplification and light splitting, one path is directly transmitted to a mixer as a reference light, and the other path is transmitted to the mixer through a circulator as a measurement light; the measurement light path is divided into multiple paths through an optical fiber coupler according to the number of targets to be measured, and each path is equipped with a delay optical fiber of different lengths and an integrated optical antenna for transceiver, and a corner cube prism is installed on the target to be measured; the reference light and the multi-path measurement light are interfered and beat at a 90° mixer, and are sampled by photoelectric conversion through a balanced detector, and finally, in an FPGA (Field Programmable Gate Array), the absolute distance of each target is solved by a distance spectrum algorithm based on time-shifted Ap-FFT (All-Phase Fast Fourier Transform) phase difference extraction.

[0007] In order to achieve the above-mentioned purpose, the technical solution proposed by the present invention includes:

[0008] An FSI multi-target synchronous dynamic ranging system based on electro-optical modulation includes an electro-optical modulation module, a measuring optical path module and a photoelectric detection module; wherein the electro-optical modulation module provides measuring light and reference light for the measuring optical path module and the photoelectric detection module respectively; the measuring optical path module multiplexes the measuring light carrying distance information and outputs it to the photoelectric detection module;

[0009] The electro-optical modulation module is composed of a frequency sweeping signal source, a driving amplifier, a narrow linewidth laser, a Mach-Zehnder intensity modulator MZM, an optical power amplifier EDFA, and a fiber coupler, and is used to generate a double-sideband frequency sweeping optical signal, and to offset the dynamic amplification error caused by the target motion by constructing a forward and reverse frequency sweeping optical carrier.

[0010] The above-mentioned measurement optical path module is realized by multiple measurement sub-optical paths constructed by an optical fiber circulator, an optical fiber coupler, multiple sections of unequal-length delay optical fibers, multiple groups of optical antennas and corner cube prisms, and is used to convert different optical paths of multiple targets to be measured into the swept frequency delay of the measurement light, and realize the synchronous measurement of multiple targets through the wavelength division multiplexing method;

[0011] The above-mentioned photoelectric detection module is composed of a 90° optical mixer, two balanced detectors BPD, an acquisition card, and an FPGA. It is used to perform optical digital coherent detection on the input measurement light and the reference light, and improve the accuracy of multi-target distance solution through the distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction.

[0012] At the same time, a distance measurement method based on the system described in claim 1 is also proposed, comprising the following steps:

[0013] (1) The swept frequency signal source generates a swept frequency electrical signal, which is amplified by the driver and subjected to carrier suppressed double-sideband modulation at the Mach-Zehnder intensity modulator MZM with the optical carrier generated by the narrow linewidth laser to generate a double-sideband swept frequency optical signal E(t). The bias voltage is set at the minimum bias point.

[0014] (2) The double-sideband frequency-sweep optical signal E(t) is amplified by EDFA and then sent to a 1×2 fiber coupler. r Indicates the reference light amplitude, A m Indicates the measured light amplitude, set to 10A r <A m <40A r Based on the principle of multi-path interference, the first-level power splitting is performed and the optical fiber coupler is used to split the light into two paths, one of which is used as the reference light E r (t) is directly transmitted to the 90° mixer, and the other is used as the measurement light E m (t) transmitted to the measurement optical path module;

[0015] (3) The measurement optical path module uses a transceiver-integrated multi-target measurement optical path, and realizes the multiplexing of ranging information of N targets through the combined design of two-stage power splitting and unequal-length delay fiber design, where N is greater than or equal to 2; the steps are as follows:

[0016] (3.1) The measurement light is transmitted through the fiber optic circulator to a 1×N fiber optic coupler for two-stage power splitting to obtain the measurement optical signal E mi (t) of the i-th target corresponding measurement sub-optical path, where i = 1, 2,..., N;

[0017] (3.2) In each measurement sub-optical path, the measurement light passes through the unequal-length delay fiber, sets the wavelength-division multiplexing distance domain through the length of the delay fiber, and then is coupled to free space through the transceiver-integrated optical antenna, incident on the corner cube prism of the target to be measured, and finally reflected back to the optical antenna parallel to the original optical path, and transmitted back to the 1×N fiber optic coupler through the delay fiber to obtain the reflected measurement optical signal S mi (t) of the i-th target corresponding measurement sub-optical path;

[0018] (3.3) The reflected measurement optical signal S mi (t) carrying the distance information is combined and multiplexed at the 1×N fiber optic coupler, and is transmitted through the fiber optic circulator to the 90° mixer;

[0019] (4) The measurement light and the reference light interfere and beat at the 90° mixer, and the interference light is detected by two balanced photodetectors BPD to obtain the quadrature interference signal I(t) containing the distance measurement information, and it is collected by using a data acquisition card;

[0020] (5) The two-channel quadrature interference signals are sent into the FPGA, and the interference signals are processed by using the time-shifted Ap-FFT phase difference algorithm to identify and obtain N groups of phase differences corresponding to the targets. The steps are as follows:

[0021] (5.1) For the complex signal data within one sweep period, calculate the spectrum and phase spectrum of the time-shifted data points through the time-shifted Ap-FFT algorithm;

[0022] (5.2) According to the spectrum distribution, combined with the spectrum segment division and power design of the delay fiber, identify N groups of positive and negative interference frequencies of N sub-measurement optical paths;

[0023] (5.3) Extract the phases corresponding to the interference signal interval frequencies of N sub-measurement optical paths;

[0024] (5.4) Accumulate the phases of all time-shifted data points to obtain the upper sideband and lower sideband phase differences of the i-th target corresponding measurement sub-optical path and

[0025] (6) Construct the dynamic ranging formula for double-sideband frequency-swept interference, substitute the phase differences corresponding to each target into the dynamic ranging formula, and obtain the optical path L mi ;

[0026] (7) Combine the optical path results solved by each sub-measurement optical path and the length of the delay fiber, calculate the absolute distances of each dynamic target, and achieve multi-target synchronous dynamic ranging.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] First, since the present invention uses the double-sideband frequency-swept interference ranging technology, two scanning signals with opposite frequencies are generated by a fixed-frequency laser and a Mach-Zehnder modulator MZM, and IQ demodulation is used to distinguish the frequencies of the two signals, canceling the ranging error caused by the target movement; for more common situations such as uniformly accelerated motion and simple harmonic motion in the actual environment, the time-shifted Ap-FFT phase difference extraction algorithm is used to solve the problem of the original ranging algorithm failure caused by spectrum broadening, thus truly realizing high-dynamic absolute distance measurement in complex environments.

[0029] Second, the present invention designs a multi-target transceiver integrated measurement optical path, performs synchronous measurement by means of wavelength division multiplexing optical path and interference signal frequency band, designs two-stage power splitting and adds unequal-length delay fibers, jointly divides the distance domain and identifies the target, and can fully realize the measurement and acquisition of multi-target absolute distance information, avoiding the complex unified clock control and delay calibration of the system.

[0030] Third, the present invention performs multi-target measurement based on the frequency-swept interference ranging technology. Compared with the original methods such as the dynamic decoupling of the Kalman state space model and the synchronous measurement method of the FSI distance spectrum based on spectrum estimation, the present invention makes full use of the entire interference signal spectrum, and the distance information is independently presented in the frequency domain. And through the proposed distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction, the ranging resolution and ranging accuracy are further locked from frequency measurement to phase measurement. In the range of one hundred meters, the error is less than one hundred micrometers.

[0031] Fourth, the present invention avoids the problem of redundant device use in the cascaded multi-target measurement method through the wavelength division multiplexing optical path and the interference signal frequency band. It neither requires multiple sets of dynamic FSI ranging systems nor a unified clock control and delay calibration circuit. The system is simple and convenient for miniaturized applications; and fiber connection does not require high-precision internal optical path calibration, and the measurement environment has less restrictions. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the implementation flowchart of the present invention;

[0033] Figure 2 is the schematic diagram of the application scenario of the present invention;

[0034] Figure 3 is a schematic diagram of the internal structure of the three-target synchronous dynamic measurement system provided in the third embodiment of the present invention;

[0035] Figure 4 : is a schematic diagram of a dual-target synchronous dynamic measurement simulation provided in the experimental part of an embodiment of the present invention;

[0036] Figure 5 It is a dual-target synchronous dynamic measurement simulation signal diagram provided in the experimental part of the embodiment of the present invention;

[0037] Figure 6 This is a simulation result diagram of the synchronous measurement of a static optical fiber and a moving guide provided in the experimental part of an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The embodiments and effects of the present invention are further described in detail below with reference to the accompanying drawings:

[0039] Embodiment 1: Refer to the attached Figure 1 The present invention provides an FSI multi-target synchronous dynamic ranging system based on electro-optical modulation, comprising an electro-optical modulation module, a measuring optical path module and a photoelectric detection module; wherein the electro-optical modulation module provides measuring light and reference light for the measuring optical path module and the photoelectric detection module respectively; the measuring optical path module multiplexes the measuring light carrying distance information and outputs it to the photoelectric detection module;

[0040] The electro-optical modulation module is composed of a frequency sweeping signal source, a driving amplifier, a narrow linewidth laser, a Mach-Zehnder intensity modulator MZM, an optical power amplifier EDFA, and a fiber coupler, and is used to generate a double-sideband frequency sweeping optical signal, and to offset the dynamic amplification error caused by the target motion by constructing a forward and reverse frequency sweeping optical carrier;

[0041] The measuring optical path module is realized by a plurality of measuring sub-optical paths constructed by an optical fiber circulator, an optical fiber coupler, multiple sections of optical fibers with unequal length delay, multiple groups of optical antennas and corner cube prisms, and is used to convert different optical paths of multiple targets to be measured into the sweeping frequency delay of the measuring light, and realize the synchronous measurement of multiple targets by the wavelength division multiplexing method;

[0042] The photoelectric detection module consists of a 90° optical mixer, two balanced detectors BPD, an acquisition card, and an FPGA. It is used to perform optical digital coherent detection on the input measurement light and the reference light, and improve the accuracy of multi-target distance solution through a distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction.

[0043] Furthermore, in the above-mentioned electro-optical modulation mode, the swept frequency signal source outputs a periodic sawtooth wave or triangular wave swept frequency electrical signal, which is power-amplified by a driving amplifier and then output to an MZM modulator; the narrow linewidth laser is used to generate an optical carrier with a fixed wavelength of 1550nm and output to the MZM modulator; the MZM modulator intensity-modulates the input swept frequency electrical signal and the fixed wavelength optical carrier, and the generated double-sideband swept frequency optical signal is optically power amplified by an EDFA and then output to an optical fiber coupler, which uses a 1×2 optical fiber coupler to divide the double-sideband swept frequency optical signal into two light beams, one of which is output as a reference light to a 90° mixer in a photoelectric detection module, and the other is output as a measurement light to a circulator in a measurement optical path module.

[0044] Furthermore, the measurement optical path module determines the number of measurement sub-optical paths and the number of components in the module according to the number of targets to be measured. Assuming that the constructed system is an N-target synchronous dynamic ranging system, it is necessary to build N measurement sub-optical paths to form a measurement optical path module, where N is greater than or equal to 2; specifically, it includes an optical fiber circulator, a 1×N optical fiber coupler, N sections of unequal-length delay optical fibers, N groups of optical antennas, and N corner cube prisms;

[0045] Furthermore, the above-mentioned optical fiber circulator includes 3 ports, wherein port 1 receives the measurement light output by the 1×2 optical fiber coupler in the electro-optical modulation module, and sends it to the 1×N optical fiber coupler through port 2; the 1×N optical fiber coupler divides the measurement light into N paths of measurement light according to a preset splitting ratio, and outputs them to the measurement sub-optical paths corresponding to each target to be measured; the unequal length delay optical fibers in each measurement sub-optical path are used to set the wavelength division multiplexing distance domain; the optical antenna couples the measurement light to the free space and incident on the corner cube prism; the corner cube prism is installed on the target to be measured, and reflects the measurement light back to the optical antenna in parallel along the original optical path, and transmits it back to the 1×N optical fiber coupler through the delayed optical fiber; port 2 of the optical fiber circulator receives the measurement light returned by the 1×N optical fiber coupler, and sends the combined measurement light to the 90° mixer in the photoelectric detection module through port 3.

[0046] Furthermore, in the above-mentioned photoelectric detection module, the 90° optical mixer performs interference mixing on the received reference light and the measurement light to generate four optical signals with phase differences of 0°, 90°, 180°, and 270°; the balanced detector is used for photoelectric conversion and elimination of direct current to generate two orthogonal electrical signals with phase differences of 0° and 90°; the acquisition card performs AD sampling to obtain the interference electrical signal; the FPGA integrates a distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction to process the interference signal and synchronously identify and solve the dynamic absolute distance of each target.

[0047] Embodiment 2: Refer to the attached Figure 1, the present invention provides a ranging method based on the system described in Embodiment 1, characterized by including the following steps:

[0048] Step 1) The swept-frequency signal source generates a swept-frequency electrical signal, which is power-amplified by a driver and undergoes carrier-suppressed double-sideband modulation with the optical carrier generated by a narrow-linewidth laser at the Mach-Zehnder intensity modulator MZM to generate a double-sideband swept-frequency optical signal E(t), and the bias voltage is set at the minimum bias point;

[0049] Step 2) The double-sideband swept-frequency optical signal E(t) is power-amplified by an EDFA and then sent to a 1×2 fiber coupler. Let A r represent the amplitude of the reference light, and A m represent the amplitude of the measurement light. Set 10A r <A m <40A r , and based on the multi-optical-path interference principle, perform first-level power splitting. It is divided into two paths through the fiber coupler, where one path serves as the reference light E r (t) and is directly transmitted to a 90° mixer, and the other path serves as the measurement light E m (t) and is transmitted to the measurement optical path module;

[0050] Step 3) The measurement optical path module uses a transceiver-integrated multi-target measurement optical path and jointly realizes the multiplexing of ranging information for N targets through a second-level power splitting design and an unequal-length delay fiber design, where N is greater than or equal to 2; it includes the following steps:

[0051] 3.1) The measurement light is transmitted through an optical fiber circulator to a 1×N fiber coupler for second-level power splitting to obtain the measurement optical signal E mi (t) corresponding to the i-th target's measurement sub-optical path, where i = 1, 2,..., N:

[0052]

[0053] Among them, the power ratio of the N measurement lights is designed as A m1 :A m2 :…:A m3 =1:2:…:N; E mi,upper (t) and E mi,lower (t) respectively represent the upper sideband and the lower sideband of the optical signal E mi (t), f c is the frequency of the narrow-linewidth laser, f0 is the initial frequency of the RF signal source, K is the scanning rate of the frequency; j represents a complex number, and t represents time.

[0054] 3.2) In each measurement sub-optical path, the measurement light passes through unequal-length delay optical fibers. The wavelength-division multiplexing distance domain is set by the length of the delay optical fibers, and then it is coupled into free space through a transceiver-integrated optical antenna, incident on the corner cube prism of the target to be measured, and finally reflected back to the optical antenna in parallel along the original optical path. After being transmitted back through the delay optical fibers to the 1×N fiber coupler, the reflected measurement optical signal S mi (t) is obtained:

[0055]

[0056] where S r (t) is the reference optical signal, τ is the time delay of the relative position of the target, c is the speed of light, and ΔL mi,r (t) is the change in the relative optical path between the target to be measured and the reference optical path at time t. The optical path propagates bidirectionally, and L mi,r = L ti + L ei is the initial relative optical path of the target at the interception moment, L ti is the true optical path, and L ei is the optical path of the additional fiber delay line.

[0057] 3.3) The reflected measurement optical signal S mi (t) is combined and multiplexed at the 1×N fiber coupler and transmitted to the 90° mixer through the fiber circulator;

[0058] Step 4) The measurement light and the reference light interfere and beat at the 90° mixer. The interference light is detected by two balanced photodetectors BPD to obtain the quadrature interference signal I(t) containing distance measurement information, and it is collected by the data acquisition card:

[0059]

[0060] where I 直 is the DC component generated by the interference, and I mr,upper and I mr,lower are respectively the upper sideband interference signals and the lower sideband interference signals generated by the interference between the N sub-measurement lights and the reference light. I mm,upper and I mm,lower are respectively the upper sideband interference signals and the lower sideband interference signals generated by the interference between the N sub-measurement lights. The multiplexing of each sub-signal component in I mr,upper and I mr,lower is realized through the delay fiber distance domain division and power splitting design.

[0061] Step 5) The two-channel quadrature interference signals are sent into the FPGA, and the interference signals are processed by the time-shifted Ap-FFT phase difference algorithm to identify and obtain N groups of phase differences corresponding to the target. The implementation steps are as follows:

[0062] 5.1) For the complex signal data within one sweep period, calculate the spectrum and phase spectrum of the time-shifted data points through the time-shifted Ap-FFT algorithm;

[0063] 5.2) According to the spectrum distribution, combine the division of the delay fiber spectrum segment and the power design to identify N groups of positive and negative interference frequencies for N sub-measurement optical paths;

[0064] 5.3) Extract the phases corresponding to the interference signal interval frequencies of N sub-measurement optical paths;

[0065] 5.4) Accumulate the phases of all time-shifted data points to obtain the phase difference between the upper sideband and the lower sideband of the measurement sub-optical path corresponding to the i-th target and

[0066]

[0067] where T is the measurement time, L mi represents the optical path, and ΔL mi is the change in optical path.

[0068] Step 6) Construct a double-sideband frequency-scanning interference dynamic ranging formula, substitute the phase differences corresponding to each target into the dynamic ranging formula to obtain the optical path L mi :

[0069]

[0070] Step 7) Combine the optical path calculation results and the delay fiber lengths of each sub-measurement optical path, calculate the absolute distances of each dynamic target, and achieve multi-target synchronous dynamic ranging:

[0071]

[0072] where L ti,air represents the absolute free space distance of the i-th target, and n air is the refractive index of the air medium; L mi is the optical path of the sub-measurement optical path corresponding to the i-th target, and L ei is the length of the delay fiber added for the i-th target.

[0073] Example 3: The overall implementation steps of the ranging method proposed in this example are the same as those in Example 2. Now, with reference to Appendix Figures 2-3 , taking the construction of a three-target synchronous dynamic ranging system for ranging as an example, the implementation process of the present invention is further described in detail:

[0074] As Figure 2 and Figure 3As shown in the figure, in this embodiment, a three-target synchronous dynamic ranging system is taken as an example, including an electro-optical modulation module: a frequency-swept signal source, a driver amplifier, a 1550 nm narrow linewidth laser, an MZM modulator, an optical power amplifier EDFA, and a 1×2 fiber coupler; a measurement optical path module: one fiber optic circulator and one 1×3 fiber coupler, three unequal-length delay fibers, three optical antennas, and three corner cube prisms; a photoelectric detection module: a 90° optical mixer, two balanced detectors BPD, a data acquisition card, and an FPGA; the ranging is specifically realized according to the following steps:

[0075] Step 1. The frequency-swept signal source generates a radio frequency electrical signal, which is power-amplified by the driver and undergoes carrier-suppressed double-sideband modulation with the light generated by the 1550 nm narrow linewidth laser at the MZM modulator to generate a double-sideband modulated optical signal E(t), and the bias voltage is set at the minimum bias point;

[0076] The optical signal generated by performing double-sideband carrier suppression modulation on the fixed-frequency laser emitted by the laser through the Mach-Zehnder intensity modulator MZM has the following expression:

[0077] E(t) = E upper (t) + E lower (t)

[0078] = exp[j2π(f c + f0)t + jπKt 2 + exp[j2π(f c - f0)t - jπiKt 2

[0079] Among them, E upper (t) represents the upper sideband of the modulated optical signal, E lower (t) represents the lower sideband of the modulated optical signal, T is the time to complete one frequency sweep, f c is the frequency of the narrow linewidth laser, f0 is the initial frequency of the radio frequency signal source, and K is the frequency sweep rate;

[0080] Step 2. The frequency-swept double-sideband optical signal is power-amplified by the EDFA and split into two paths by the 1×2 fiber coupler. Based on the multi-optical path interference principle, a primary power splitting design is carried out. One path serves as the reference light E r (t) and is directly transmitted to the 90° mixer, and the other path serves as the measurement light E m (t);

[0081] For the primary power splitting, the expressions of the reference optical signal E r (t) and the measurement optical signal E m (t) are as follows:

[0082] E r (t) = E r,upper ​(t) + E r,lower (t)

[0083] = A r {exp[j2π(f c + f0)t + jπKt 2 + exp[j2π(f c - f0)t - jπiKt 2}

[0084] E m (t) = E m,upper (t) + E m,lower (t)

[0085] = A m {exp[j2π(f c + f0)t + jπKt 2 + exp[j2π(f c - f0)t - jπiKt 2}

[0086] Taking into account the influence of the multi-path measurement optical interference problem and the signal-to-noise ratio reduction problem caused by the attenuation of the measurement light in the actual scenario, the primary power splitting ratio is designed to be 10A r < A m < 40A r ;

[0087] Step 3. Use a transceiver-integrated multi-target measurement optical path to jointly implement multi-target ranging information multiplexing through secondary power splitting design and unequal-length delay fiber design. The steps are as follows:

[0088] (3a) For a three-target synchronous dynamic ranging system, the measurement light is transmitted through an optical fiber circulator to a 1×3 optical fiber coupler for secondary power splitting. The three measurement sub-optical paths are respectively E mi (t);

[0089] The measurement light is secondarily power split. The expressions of the measurement light signals E mi (t) of each sub-optical path are as follows:

[0090] E mi (t) = E mi,upper (t) + E mi,lower (t)

[0091] = A mi {exp[j2π(f c + f0)t + jπKt 2 + exp[j2π(f c - f0)t - jπiKt 2}

[0092] Among them, i = 1, 2, 3, representing three sub-optical paths, and the designed optical power ratios of the three measurement paths are A m1 :A m2 :A m3 = 1:2:3;

[0093] (3b) In each measurement sub-optical path, the measurement light passes through unequal-length delay fibers. The wavelength-division multiplexing distance domain is set by the length of the delay fibers, and then it is coupled to free space through a transceiver-integrated optical antenna and incident on the corner cube prism of the target to be measured. Finally, it is reflected back to the optical antenna in parallel along the original optical path and transmitted back to the 1×3 fiber coupler through the delay fibers. The reflected measurement optical signal is S mi (t);

[0094] When the target to be measured makes any movement, at any moment, the reflected measurement optical signals S mi (t) of each sub-optical path are expressed as the reference optical signal S r (t) based on the time delay τ of the target to be measured relative to the position:

[0095]

[0096] Among them, c is the speed of light, and ΔL mi,r (t) is the relative optical path change amount between the target to be measured and the reference optical path at time t. The optical path propagates bidirectionally, and L mi,r = L ti + L ei is the initial relative optical path of the target at the intercepted moment, L ti is the true optical path, and L ei is the optical path of the additional fiber delay line. The measurement optical signal S mi (t) is expanded and expressed as follows:

[0097]

[0098] (3c) The three sub-measurement lights S mi (t) carrying distance information are combined and multiplexed at the 1×3 fiber coupler, and the measurement light is transmitted to the 90° mixer through the fiber circulator;

[0099] Step 4. The measurement light and the reference light interfere and beat at the 90° mixer. The interference light is detected by two balanced photodetectors BPD to obtain the quadrature interference signal I(t) containing distance measurement information, and it is collected by the data acquisition card;

[0100] The reference light and the multi-path measurement light interfere and beat to obtain the interference signal I(t):

[0101]

[0102] Among them, I mr,upper and I mr,lowerThe interference signal generated by the swept-frequency of the Michelson optical path constructed for the three-submeasurement optical path and the reference optical path can calculate the distance through the phase information, I 直 is the DC component generated by the interference, I mm,upper and I mm,lower is the interference signal generated by the mutual interference of the three-submeasurement optical paths, which is realized through the distance-domain division of the delay fiber and the power splitting design. I mr,upper and I mr,lower The multiplexing of each sub-signal component of

[0103] Step 5. Send the two orthogonal interference signals into the FPGA, and use the time-shifted Ap-FFT phase difference algorithm to process the interference signals, identify and obtain the three groups of phase differences corresponding to the target. The implementation steps are as follows:

[0104] (5a) For the complex signal data within a swept-frequency period, calculate the spectrum and phase spectrum of the time-shifted data points through the time-shifted Ap-FFT algorithm;

[0105] (5b) According to the spectrum distribution, combined with the spectrum segment division and power design of the delay fiber, identify the 3 groups of positive and negative interference frequencies of the three-submeasurement optical paths;

[0106] (5c) Extract the phase corresponding to the interference signal interval frequency of the three-submeasurement optical paths;

[0107] (5d) Accumulate the phases of all time-shifted data points, and at the same time obtain the three groups of upper and lower sideband phase differences corresponding to the target and

[0108] According to the interference signal expression I(t), construct the three groups of phase difference expressions corresponding to the three targets within the measurement time T as follows:

[0109]

[0110] Step 6. Construct the double-sideband frequency-scanning interference dynamic ranging formula, substitute the phase differences corresponding to each target into the dynamic ranging formula, and calculate and obtain the optical path L mi ;

[0111] Substitute the phase difference into the ranging formula, and deduce the double-sideband frequency-scanning interference dynamic ranging formula as follows:

[0112]

[0113] Substitute the phase differences of each target extracted from the interference signal into the ranging formula, and the optical path L mi and the optical path change ΔL mi ;

[0114] Step 7. Combine the sub-measurement optical paths to calculate the optical path results and the length of the delay fiber, and calculate the absolute distances of each dynamic target to achieve multi-target synchronous dynamic ranging;

[0115] Calculate the optical path L of each sub-measurement optical path mi , subtract the length L of the added unequal-delay fiber ei , and the absolute free-space distance L of each dynamic target ti,air The expression is as follows:

[0116]

[0117] where n air is the refractive index of the air medium.

[0118] The effects of the present invention can be further illustrated by the following simulation results.

[0119] I. Simulation conditions

[0120] Use the matlab simulation software, set the speed of light to 3×10 8 m / s, the wavelength of the laser is 1550 nm, the initial frequency of the swept-frequency signal source is 8 GHz, the swept-frequency period is 1 ms, the swept-frequency bandwidth is 2 GHz, the number of points for the full-phase FFT calculation is 512, and set the sampling frequency to 20 MHz.

[0121] II. Simulation content and results

[0122] Simulation 1: Under the above simulation conditions, as Figure 4 shown, in order to verify the effectiveness of the multi-target dynamic ranging method of the present invention, a static measurement optical path is designed to simulate the static experimental optical path of fiber combination with fiber end-face reflection, and a uniformly moving measurement optical path is designed to simulate the experimental optical path of fiber combination with spatial reflection guide rail movement, and further simulate the synchronous wavelength division multiplexing at the fiber coupler. The simulation settings can cover the basic application scenarios of the present invention.

[0123] Simulation 2: Using the method of the present invention to design a multi-target dynamic ranging system, as Figure 5 shown, a double-target synchronous dynamic measurement simulation signal can be obtained. Within a swept-frequency time period, the sampled quadrature interference signal is obtained; an Ap-FFT time-delay segment interference signal is amplified. The carrier wave and the signal envelope reflect that the interference signal is a multi-frequency signal with multiple frequency components; further simulation processing gives the signal spectrum, with two sets of positive and negative spectral segments with unequal powers. The low-frequency spectral segment is symmetric, and the high-frequency spectral segment is asymmetric. The frequency magnitude is related to the distance of the target to be measured, and the relative movement will cause an asymmetric Doppler frequency shift. The spectral characteristics are completely consistent with the simulation settings.

[0124] Simulation 3: Using the method of the present invention, synchronous high-precision ranging of static and moving targets can be achieved; as Figure 6As shown, the simulation measurement results of the static optical fiber show that the mean ranging distance is 28.543982 m, and the standard deviation is 21.89 μm. After further Kalman filtering, the mean ranging distance is 28.543983 m, and the ranging standard deviation is reduced to 4.00 μm; the simulation measurement results of the uniform motion of the guide rail can reproduce the motion trajectory of the measured target. The measured speed is 9.968 mm / s, and the standard deviation is 83.43 μm. After further Kalman filtering, the measured speed is 9.990 mm / s, and the standard deviation is 16.60 μm. The ranging errors are all less than one hundred micrometers.

[0125] It can be seen from the above simulation results that the method of the present invention realizes fully synchronized dynamic ranging of multiple targets through a set of laser rangefinders. The ranging accuracy in the range of one hundred meters is better than one hundred micrometers, which can greatly reduce the system complexity and facilitate the application in actual complex scenarios.

[0126] The above simulation analysis proves the correctness and effectiveness of the method proposed by the present invention.

[0127] The parts not described in detail in the present invention belong to the common general knowledge of those skilled in the art.

[0128] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Obviously, for those skilled in the art, after understanding the content and principle of the present invention, various modifications and changes in form and details may be made without departing from the principle and structure of the present invention. However, these modifications and changes based on the idea of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. An FSI multi-target synchronous dynamic ranging system based on electro-optical modulation, characterized in that: include: Electro-optical modulation module, measurement optical path module and photoelectric detection module; The electro-optical modulation module provides measurement light and reference light to the measurement optical path module and the photoelectric detection module respectively; The measuring optical path module multiplexes the measuring light carrying the distance information and outputs it to the photoelectric detection module; The electro-optical modulation module is composed of a frequency sweeping signal source, a driving amplifier, a narrow linewidth laser, a Mach-Zehnder intensity modulator MZM, an optical power amplifier EDFA, and a fiber coupler, and is used to generate a double-sideband frequency sweeping optical signal, and to offset the dynamic amplification error caused by the target motion by constructing a forward and reverse frequency sweeping optical carrier; The measuring optical path module is realized by a plurality of measuring sub-optical paths constructed by an optical fiber circulator, an optical fiber coupler, multiple sections of optical fibers with unequal length delay, multiple groups of optical antennas and corner cube prisms, and is used to convert different optical paths of multiple targets to be measured into the sweeping frequency delay of the measuring light, and realize the synchronous measurement of multiple targets by the wavelength division multiplexing method; The photoelectric detection module consists of a 90° optical mixer, two balanced detectors BPD, an acquisition card, and an FPGA. It is used to perform optical digital coherent detection on the input measurement light and the reference light, and improve the accuracy of multi-target distance solution through a distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction.

2. The system according to claim 1, characterized in that: In the electro-optical modulation module, the frequency sweeping signal source outputs a periodic sawtooth wave or triangular wave frequency sweeping electrical signal, which is power-amplified by a driving amplifier and then output to an MZM modulator; the narrow linewidth laser is used to generate an optical carrier with a fixed wavelength of 1550nm and output to the MZM modulator; the MZM modulator performs intensity modulation on the input frequency sweeping electrical signal and the fixed wavelength optical carrier, and the generated double-sideband frequency sweeping optical signal is optically power amplified by an EDFA and then output to an optical fiber coupler, which uses a 1×2 optical fiber coupler to divide the double-sideband frequency sweeping optical signal into two light beams, one of which is output as a reference light to a 90° mixer in a photoelectric detection module, and the other is output as a measurement light to a circulator in a measurement optical path module.

3. The system according to claim 1, characterized in that: The measuring optical path module determines the number of measuring sub-optical paths and the number of devices in the module according to the number of targets to be measured. Assuming that the constructed system is an N-target synchronous dynamic ranging system, it is necessary to build N measuring sub-optical paths to form a measuring optical path module, where N is greater than or equal to 2; specifically, it includes an optical fiber circulator, a 1×N optical fiber coupler, N sections of unequal-length delay optical fibers, N groups of optical antennas, and N corner cube prisms; The optical fiber circulator includes three ports, wherein port 1 receives the measurement light output by the 1×2 optical fiber coupler in the electro-optical modulation module, and sends it to the 1×N optical fiber coupler through port 2; the 1×N optical fiber coupler splits the measurement light into N measurement light paths according to a preset splitting ratio, and outputs them to the measurement sub-optical paths corresponding to each target to be measured; the unequal-length delay optical fibers in each measurement sub-optical path are used to set the wavelength division multiplexing distance domain; The optical antenna couples the measuring light into the free space and makes it incident on the corner cube prism; the corner cube prism is mounted on the target to be measured and reflects the measuring light back to the optical antenna in parallel along the original optical path and transmits it back to the 1×N optical fiber coupler through the delayed optical fiber; the optical fiber circulator port 2 receives the measuring light returned by the 1×N optical fiber coupler and sends the combined measuring light to the 90° mixer in the photoelectric detection module through port 3.

4. The system according to claim 1, characterized in that: The photoelectric detection module, wherein the 90° optical mixer performs interference mixing on the received reference light and the measurement light to generate four optical signals with phase differences of 0°, 90°, 180°, and 270°; the balanced detector is used for photoelectric conversion and direct current elimination to generate two orthogonal electrical signals with phase differences of 0° and 90°; the acquisition card performs AD sampling to obtain the interference electrical signal; the FPGA integrates a distance spectrum algorithm based on time-shifted Ap-FFT phase difference extraction to process the interference signal and synchronously identify and solve the dynamic absolute distance of each target.

5. A distance measurement method based on the system of claim 1, characterized in that: The steps include: (1) The swept frequency signal source generates a swept frequency electrical signal, which is amplified by the driver and subjected to carrier suppressed double-sideband modulation at the Mach-Zehnder intensity modulator MZM with the optical carrier generated by the narrow linewidth laser to generate a double-sideband swept frequency optical signal E(t). The bias voltage is set at the minimum bias point. (2) The double-sideband frequency-sweep optical signal E(t) is amplified by EDFA and then sent to a 1×2 fiber coupler. r Indicates the reference light amplitude, A m Indicates the measured light amplitude, set to 10A r <A m <40A r Based on the principle of multi-path interference, the first-level power splitting is performed and the optical fiber coupler is used to split the light into two paths, one of which is used as the reference light E r (t) is directly transmitted to the 90° mixer, and the other is used as the measurement light E m (t) transmitted to the measurement optical path module; (3) The measurement optical path module uses a multi-target measurement optical path with an integrated transmitter and receiver, and realizes the multiplexing of N target ranging information through a two-level power splitting design and an unequal-length delay optical fiber design, where N is greater than or equal to 2; The steps include: (3.1) The measurement light is transmitted through the fiber circulator to the 1×N fiber coupler for secondary power splitting to obtain the measurement light signal E corresponding to the measurement sub-path of the i-th target. mi (t), i=1, 2, ..., N; (3.2) In each measurement sub-optical path, the measurement light passes through unequal length delay optical fibers, and the wavelength division multiplexing distance domain is set by the delay optical fiber length. Then, it is coupled to the free space through the integrated transceiver optical antenna, incident on the corner cube prism of the target to be measured, and finally reflected back to the optical antenna along the original optical path in parallel, and transmitted back to the 1×N optical fiber coupler through the delay optical fiber, so as to obtain the reflected measurement light signal S of the measurement sub-optical path corresponding to the i-th target. mi (t); (3.3) Reflected measurement light signal S carrying distance information mi (t) The light is combined and multiplexed at the 1×N fiber coupler and transmitted to the 90° mixer through the fiber circulator; (4) The measuring light and the reference light interfere with each other at the 90° mixer. The interference light is detected by two balanced detectors (BPDs) to obtain the orthogonal interference signal I(t) containing distance measurement information, which is then collected using a data acquisition card. (5) The two orthogonal interference signals are sent to the FPGA, and the interference signals are processed using the time-shifted Ap-FFT phase difference algorithm to identify and obtain N groups of phase differences corresponding to the target. The implementation steps are as follows: (5.1) For the complex signal data within a frequency sweep period, the frequency spectrum and phase spectrum of the time-shifted data points are calculated by the time-shifted Ap-FFT algorithm; (5.2) According to the spectrum distribution, combined with the delayed fiber spectrum segmentation and power design, N groups of positive and negative interference frequencies of N sub-measurement optical paths are identified; (5.3) extracting the phase corresponding to the frequency interval of the interference signal of the N sub-measurement optical paths; (5.4) The phases of all time-shifted data points are accumulated to obtain the phase difference between the upper sideband and the lower sideband of the measurement sub-path corresponding to the i-th target: and (6) Construct a double-sideband frequency scanning interferometer dynamic ranging formula, and substitute the phase difference corresponding to each target into the dynamic ranging formula to obtain the optical path L mi ; (7) Combine the optical path results and delayed fiber length of each sub-measurement optical path to calculate the absolute distance of each dynamic target and realize multi-target synchronous dynamic ranging.

6. The method according to claim 5, characterized in that: In step (3), the secondary power splitting design is used to obtain the measurement light signal E of the i-th measurement sub-optical path according to the following formula: mi (t): E mi (t)=E mi,upper (t)+E mi,lower (t) =A mi {exp[j2π(f c +f0)t+jπKt 2 ]+exp[j2π(f c -f0)t-jπiKt 2 ]}, Among them, the designed N-way measurement optical power ratio is A m1 :A m2 :…:A m3 =1:2:…:N;E mi,upper (t) and E mi,lower (t) represent the optical signal E mi The upper and lower sidebands of (t), f c is the frequency of the narrow linewidth laser, f0 is the initial frequency of the RF signal source, K is the frequency scanning rate; j represents a complex number, and t represents time. The unequal-length delay optical fiber design obtains the reflected measurement optical signal S of the measurement sub-optical path corresponding to the i-th target according to the following formula: mi (t): Among them, S r (t) is the reference light signal, τ is the time delay of the target relative position, c is the speed of light, ΔL mi,r (t) is the relative optical path change between the target and the reference optical path at time t. The optical path propagates in both directions. L mi,r =L ti +L ei is the initial relative optical path of the target at the time of interception, L ti is the real optical path, L ei is the optical path length of the additional fiber delay line.

7. The method according to claim 6, characterized in that: The phase difference between the upper sideband and the lower sideband of the sub-light path corresponding to the i-th target in step (5.4) is and It is expressed as follows; Where T is the measurement time, L mi Indicates the optical path length, ΔL mi is the optical path change.

8. The method according to claim 7, characterized in that: In step (4), the measuring light and the reference light interfere with each other at the 90° mixer to obtain an orthogonal interference signal I(t) containing distance measurement information, which is specifically as follows: I(t)=|S r +S m1 +S m2 +...+S mN | 2 =I 直 +I mr,upper +I mm,upper +I mr,lower +I mm,lower , Among them, I 直 is the DC component generated by interference, I mr,upper with I mr,lower are the upper sideband interference signal and the lower sideband interference signal generated by the interference of N-way measurement light and reference light, I mm,upper with I mm,lower The upper sideband interference signal and the lower sideband interference signal generated by the mutual interference between the N-way measurement lights are respectively realized by delaying the fiber distance domain division and the power splitting design. mr,upper with I mr,lower Multiplexing of the sub-signal components.

9. The method according to claim 8, characterized in that: In step (6), a double-sideband frequency scanning interferometer dynamic ranging formula is constructed, and the phase difference corresponding to each target is substituted into the dynamic ranging formula to obtain the optical path L mi , implemented as follows:

10. The method according to claim 5, characterized in that: The absolute distance of each dynamic target in step (7) is calculated according to the following formula: Among them, L ti,air represents the absolute free space distance of the i-th target, n air is the refractive index of the air medium; L mi is the optical path length of the corresponding sub-measurement optical path of the i-th target, L ei is the delay fiber length added to the i-th target.

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