Electro-optical modulation double-sideband FSI ranging method based on frequency sweeping rate real-time traceability

Abstract

The invention discloses an electro-optical modulation double-sideband FSI distance measurement method based on real-time source tracing of a sweep frequency rate, and mainly solves the problem that the distance measurement precision is reduced due to non-constancy of the sweep frequency rate in the prior art. According to the scheme, the method comprises the following steps: 1) establishing a double-sideband scanning interference ranging system for generating interference signals required for real-time tracing of the frequency sweeping rate; 2) performing electro-optical modulation by using an MZM modulator to generate a double-sideband signal; 3) importing the double-sideband signal into an F-P etalon to generate an F-P signal; 4) constructing a frequency sweep rate resolving algorithm module, carrying out peak value processing on the F-P signal, and obtaining the frequency sweep rate of a single frequency sweep period; and 5) substituting the calculated real-time frequency sweeping rate back to a double-sideband frequency sweeping distance measurement calculation process to obtain a distance measurement result. The method can effectively eliminate the ranging error caused by the change of the frequency sweeping rate during the cycle, improves the anti-interference capability of the system while reducing the cost, and remarkably improves the measurement accuracy and reliability of the system in a complex environment.

Description

Technical Field

[0001] The present invention belongs to the field of optical precision measurement technology, and further relates to an optical frequency scanning interferometry ranging method. Specifically, it is a ranging method of an electro-optically modulated double-sideband optical frequency scanning interferometry system FSI (Frequency Scanning Interferometry) based on real-time tracing of the sweeping rate. The method can be used to achieve high-precision distance measurement by tracing the sweeping rate of the sweeping signal in real time. Background Art

[0002] High-precision absolute distance measurement technology is of vital importance to both basic scientific research and advanced manufacturing. In space science in particular, spacecraft formation flying, exemplified by the European Darwin Project, the Gravitational Wave Project, and the Sound Seeker Project, places extremely high demands on on-orbit measurement accuracy. Double-sideband frequency scanning interferometry (DSBFI) enables high-precision distance measurement. This technology not only eliminates errors introduced by Doppler shift but also exhibits excellent nonlinearity, significantly reducing the impact of frequency scanning nonlinearity on ranging accuracy. It is currently one of the most promising and research-worthy ranging technologies.

[0003] Distance measurement using optical interferometry achieves exceptionally high accuracy because the optical frequency (or wavelength) serves as a measurement reference. The measurement system establishes a connection between the distance being measured and this reference, allowing distance measurement results to be traced back to this reference. For example, single-frequency laser interferometers often achieve extremely high distance measurement accuracy because the wavelength emitted by a He-Ne laser is extremely stable. Its value under vacuum can serve as a length reference, and the system's measurement results can be traced back to this length reference.

[0004] In a double-sideband frequency-scanning interferometry (DSS) ranging system, the sweep rate of the DSS signal modulated by the MZM is considered a constant. However, due to the MZM's extreme sensitivity to temperature and other environmental factors, it is difficult to maintain a constant sweep rate for the DSS signal. The sweep rate varies within different sweep cycles, and there is no traceability reference. The lack of a traceability reference for the DSS sweep rate seriously affects the accuracy of DSS ranging technology, resulting in significant ranging errors. Furthermore, due to the DSS system's lack of traceability for the sweep rate of the DSS signal, the ranging system lacks credibility and reliability. Therefore, how to measure the sweep rate for each sweep cycle and find its traceability reference is an urgent problem that needs to be solved in DSS ranging.

[0005] To mitigate the impact of optical frequency sweep non-constancy on frequency-sweeping ranging systems, several common techniques are available: 1) Reference interferometer resampling: Using an auxiliary reference interferometer to generate equally spaced frequency markers, the measured signal is resampled to suppress nonlinear errors. This can mitigate the impact of optical frequency sweep non-constancy on frequency-sweeping ranging systems, but requires additional optical paths and cannot be processed in real time. Recent research has attempted to accelerate data processing using FPGAs, but this is still limited by system complexity and the dynamic measurement requirements. 2) Phase-locked loop feedback control: Using real-time feedback to adjust the laser drive signal to correct for frequency sweep nonlinearity online. This method requires high-speed circuitry. While it can mitigate the impact of optical frequency sweep non-constancy on frequency-sweeping ranging systems, it is limited by device response speed and requires optimization of stability under electromagnetic interference. 3) Digital pre-distortion compensation: By pre-correcting the input signal, a mathematical model is established to calculate the inverse function of the nonlinear characteristic. This inverse function is then embedded into the drive signal to make the actual output close to linear, thus offsetting the system's nonlinearity. However, this system requires high-precision calibration equipment, and the model is susceptible to environmental drift. 4) FP etalon real-time traceability method: A portion of the double-sideband (DSB) swept signal is introduced into the FP etalon to form an interference signal. Using the DSB sweep rate calculation algorithm, the sweep rate per cycle of the DSB signal is calculated. Substituting this DSB sweep rate result into the distance calculation portion of the DSB ranging system, this produces a more accurate, reliable, and trustworthy ranging result. Summary of the Invention

[0006] The purpose of the present invention is to address the defects of the above-mentioned prior art and propose a double-sideband FSI ranging method based on real-time tracing of the sweep rate to solve the problem of decreased ranging accuracy caused by the non-constancy of the sweep rate. By designing a real-time tracing scheme of the sweep rate, the measurement accuracy and reliability of the system in complex environments are improved.

[0007] The basic idea of ​​implementing the present invention is as follows: first, a double-sideband scanning interferometry ranging system is established to generate the interference signal required for real-time tracing of the sweep rate; an MZM modulator is used to perform electro-optical modulation to generate the double-sideband signal required for real-time tracing of the sweep rate; the double-sideband signal is introduced into an FP etalon to generate an FP signal; the FP signal is processed and analyzed to calculate the sweep rate of each sweep cycle; and the calculated dynamic sweep rate is substituted back into the double-sideband sweep ranging calculation process to obtain a ranging result with higher ranging accuracy.

[0008] To achieve the above objectives, the technical solution of the present invention includes:

[0009] A double-sideband (FSI) ranging method based on real-time traceability of the sweep rate is implemented using a double-sideband (FSI) optical frequency scanning interferometer (FSI) system. The system includes a narrow-linewidth frequency-stabilized laser, a Mach-Zehnder modulator (MZM), a sweep signal source, a driver, a fiber beam splitter (FS), an erbium-doped fiber amplifier (EDFA), a circulator, an optical mixer, a transceiver optical antenna, a corner cube prism, and two balanced photodetectors. The implementation steps are as follows:

[0010] (1) Narrow linewidth frequency-stabilized laser generates a frequency-stabilized laser signal The sweep signal source sends a sweep signal which is processed by the driver and then sent to the MZM. The MZM modulates the incoming signal to generate a double-sideband sweep signal. ;

[0011] (2) The fiber optic splitter FS converts the double-sideband signal First double sideband signal and the second double-sideband signal Two beams; the system introduces a Fabry-Perot FP etalon to convert the two double-sideband signals and Import the circulator and Fabry-Perot FP etalon respectively;

[0012] (3) The second double-sideband signal in the Fabry-Perot etalon Interference is performed to form FP signal;

[0013] (4) Construct a sweep rate calculation algorithm module to perform peak processing on the FP signal and obtain the sweep rate of a single sweep cycle. ;

[0014] (5) The first double-sideband signal entering the circulator It is divided into two parts. One part is sent into the measurement optical path, and the measurement signal is obtained through the optical antenna and the corner cube prism. ; The other part is used as a reference signal ; and and The input is sent to the 90° optical mixer to generate interference, generating four optical signals with a phase difference of 90°. ;

[0015] (6) Two balanced photodetectors are used to eliminate the DC component of the four optical signals and obtain two orthogonal interference signals. ;

[0016] (7) Use the phase extraction algorithm to calculate the time difference between the upper sideband and lower sideband signals from the two orthogonal interference signals. Phase change within and ;

[0017] (8) According to and and sweep rate , calculate and obtain the distance to be measured .

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] First, the present invention establishes a traceability benchmark for the sweep rate of the double-sideband swept frequency signal. By introducing the FP etalon as the traceability benchmark for the sweep rate, the actual sweep rate of each sweep cycle is measured in real time, solving the problem of sweep rate drift caused by environmental factors (such as temperature) in traditional methods.

[0020] Second, since the present invention utilizes the high spectral resolution of the FP etalon to dynamically calculate the sweep rate of each cycle, dynamic compensation for errors is achieved, thereby effectively eliminating the ranging error introduced by the change in sweep rate between cycles.

[0021] Third, the present invention only requires connecting a beam splitter and an FP etalon after the MZM. There is no need to introduce a reference interferometer or a high-speed phase-locked loop circuit, and no additional complex hardware is required, thus greatly reducing the complexity of the system. At the same time, since the use of high-precision calibration equipment or high-speed sampling circuits is avoided, the hardware cost is greatly reduced, and there is no need to rely on complex environmental control.

[0022] Fourth, because the FP etalon used in the present invention has excellent temperature stability, its cavity length is almost unaffected by changes in ambient temperature during the measurement process, thereby ensuring the long-term reliability of the sweep rate measurement; compared with the phase-locked loop feedback method, it does not require high-speed circuits and complex electromagnetic shielding designs, thereby reducing the system's sensitivity to electromagnetic noise and having stronger resistance to environmental interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart for realizing the method of the present invention;

[0024] Figure 2 It is a schematic diagram of the overall structure of the improved double-sideband ranging system in the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Example 1: Refer to the attached Figure 1The present invention proposes a double-sideband (FSI) ranging method based on real-time tracing of the sweeping frequency rate, which is implemented through a double-sideband optical frequency scanning interferometer (FSI) system. The system includes a narrow-linewidth frequency-stabilized laser, a Mach-Zehnder modulator (MZM), a sweeping frequency signal source, a driver, a fiber beam splitter (FS), an erbium-doped fiber amplifier (EDFA), a circulator, an optical mixer, an integrated transceiver optical antenna, a corner cube prism, and two balanced photodetectors. In this embodiment, the laser of the double-sideband optical frequency scanning interferometer FSI system adopts a 1550nm narrow linewidth light source. Its output light beam is frequency-sweep modulated by the Mach-Zehnder modulator MZM and then divided into a main path and a secondary path through an optical fiber beam splitter: the main light path is boosted by the erbium-doped fiber amplifier EDFA, and then guided to the measurement light path and the reference light path carrying the target distance information respectively through a circulator. The two signals are input into the distance resolution module after interference through a 90° optical mixer; the secondary light path introduces the double-sideband signal generated by the MZM into the Fabry-Perot FP standard through an optical fiber beam splitter, generates an FP signal through its interference effect, and resolves the scanning rate parameters through the scanning rate resolution module; finally, the phase interference data of the main light path is combined with the scanning rate calibration value of the secondary light path to realize the target distance resolution. The specific implementation steps include:

[0027] Step 1) The narrow-linewidth frequency-stabilized laser generates a frequency-stabilized laser signal The sweep signal source sends a sweep signal which is processed by the driver and then sent to the MZM. The MZM modulates the incoming signal to generate a double-sideband sweep signal. ;

[0028] Step 2) Fiber optic splitter FS converts the double-sideband signal First double sideband signal and the second double-sideband signal Two beams; the system introduces a Fabry-Perot FP etalon to convert the two double-sideband signals and Import the circulator and Fabry-Perot FP etalon respectively;

[0029] Step 3) The second double-sideband signal is detected in the Fabry-Perot etalon. Interference is performed to form an FP signal. In this embodiment, the signal intensity is expressed as follows:

[0030] ,

[0031] in, is the average light intensity, is the reflectivity of the FP etalon coating, is the phase difference caused by the optical path in the FP etalon cavity, expressed as follows:

[0032] ,

[0033] The transmitted light intensity reaches its output peak when the optical frequency meets the following conditions; when the frequency-tuned laser enters the Fabry-Perot etalon, the standard transmitted light intensity reaches its output peak each time it passes through an FSR:

[0034] ;

[0035] in, is the refractive index of the medium in the FP etalon cavity, is the FP etalon cavity length, is the light frequency, is the speed of light, Is a positive integer.

[0036] Step 4) Build a sweep rate calculation algorithm module, perform peak processing on the FP signal, and obtain the sweep rate of a single sweep cycle ,,The specific implementation steps are as follows:

[0037] (4.1) The peak in the FP signal is intercepted and recorded as , where j represents the sequence number of the peak intercepted from the front to the back;

[0038] (4.2) Yes After denoising and fitting, we can get ;

[0039] (4.3) Yes Perform peak point search and record the time corresponding to each peak point. ;

[0040] (4.4) The frequency change between peaks with an interval of 1 is recorded as FSR, and the corresponding sweep rate is recorded as ,in ; The FSR is the free spectral range of the FP etalon;

[0041]

[0042] in, is the time corresponding to the i-th peak point.

[0043] (4.5) For a frequency sweep cycle Perform the least squares fitting and take the average value as the sweep rate of a single sweep cycle :

[0044] .

[0045] Step 5) The first double-sideband signal entering the circulator It is divided into two parts. One part is sent into the measurement optical path, and the measurement signal is obtained through the optical antenna and the corner cube prism. ; The other part is used as a reference signal ; and and The input is sent to the 90° optical mixer to generate interference, generating four optical signals with a phase difference of 90°. :

[0046] , , , ;

[0047] , ;

[0048] in, is the upper sideband phase of the interference signal, is the lower sideband phase of the interference signal; is the measured optical signal amplitude, is the reference optical signal amplitude; is the target's movement speed, is the starting optical path, is the speed of light, is the frequency of the stabilized laser.

[0049] Step 6) Eliminate the DC component of the four optical signals through two balanced photodetectors to obtain two orthogonal interference signals. :

[0050] ,

[0051] .

[0052] Step 7) Use the phase extraction algorithm to calculate the time difference between the upper sideband and lower sideband signals from the two orthogonal interference signals. Phase change within and ;

[0053] Step 8) According to and and sweep rate , calculate and obtain the distance to be measured :

[0054] .

[0055] Example 2: The overall implementation steps of the ranging method proposed in this example are the same as those in Example 1. The specific implementation process of the front-end optical path structure improvement and the back-end double-sideband signal sweep rate measurement algorithm is now given to further describe the content of the present invention in detail:

[0056] Step 1. The optical signal emitted by the frequency-stabilized laser is:

[0057]

[0058] Where, is the laser signal power, is the frequency of the stabilized laser, and the sweep signal emitted by the sweep signal source is:

[0059]

[0060] Where, is the laser signal amplitude, is the initial frequency of the sweep signal source, is the sweep rate of the swept frequency signal source.

[0061] Double-sideband signal generated by MZM modulator for:

[0062] ,

[0063] is the power of the modulated optical signal.

[0064] Step 2. The double-sideband swept signal generated by MZM modulation is introduced into the Fabry-Pérot etalon to generate an FP signal through interference.

[0065] Fabry-Perot etalons are mostly transmission type. According to the principle of multi-beam interference, the total transmitted light intensity after interference is for:

[0066] ,

[0067] From the above formula, we can see that the transmitted light intensity reaches the output peak when the optical frequency meets the following conditions. When the laser with tuned optical frequency enters the Fabry-Perot etalon, the standard transmitted light intensity will reach the output peak every time it passes through a fixed optical frequency interval (FSR):

[0068]

[0069] Where: is the refractive index of the cavity medium; is the reflectivity of the coating; is the cavity length; is the phase difference caused by the optical path in the cavity, and its magnitude is .

[0070] Step 3. By processing the FP signal, calculate the sweep rate of the double-sideband swept signal and use it as the traceability benchmark for the sweep rate of the double-sideband signal.

[0071] (3.1) The peak in the FP signal is intercepted and recorded as .

[0072] (3.2) Yes After denoising and fitting, we can get .

[0073] (3.3) Yes Perform peak point search and record the time corresponding to each peak point. .

[0074] (3.4) Since the peaks of the double-sideband swept signal appear in pairs, the frequency shift corresponding to the peaks with an interval of 1 is FSR, so the sweep rate between peaks with an interval of 1 is

[0075] , ;

[0076] (3.5) Within a frequency sweep cycle Perform least square fitting and use the optimal solution as the sweep rate of a single sweep cycle, that is:

[0077] .

[0078] Example 3: Reference Figure 2 This embodiment further describes the specific structure of the improved double-sideband ranging system in the present invention as follows:

[0079] The electro-optical modulation sideband ranging system of the present invention is as follows: Figure 2As shown in the figure, the system consists of three components: First, the sideband signal modulation section, which modulates and generates the up and down frequency-sweeping optical signals, consists of components such as a frequency-stabilized laser, a Mach-Zehnder modulator, a frequency-sweeping signal source, a beam splitter, and an erbium-doped optical fiber amplifier (EDFA). Second, the laser alignment transceiver section constructs the measurement optical path. This section uses an integrated transceiver and optical antenna structure. The circulator and optical antenna design enable coupling and conversion between the optical fiber and free space. The corner cube is rigidly attached to the ranging target and dynamically moves with the target. Third, the interference signal processing section, essentially the IQ demodulation process, consists of a 90° mixer, a balanced detector, an AD acquisition card, and a field programmable gate array (FPGA) distance resolution module.

[0080] Step A. Stabilize the frequency of the laser to emit an optical signal , the sweep signal source sends out a sweep signal , the double-sideband signal generated by the MZM modulator .

[0081] Step B: The double-sideband swept frequency signal generated after MZM modulation is introduced into the circulator and then a portion of it enters the measurement optical path. The measurement signal is obtained through the integrated optical antenna and corner cube prism. , the other part is used as reference signal ,Will and The input is sent to the 90° optical mixer to generate interference, generating four optical signals with a phase difference of 90°. ;

[0082] Step C: The four optical signals pass through two balanced photodetectors to eliminate the DC component and obtain two orthogonal interference signals. ;

[0083] Step D: Use the phase extraction algorithm to calculate the time phases of the upper and lower sideband signals from the two orthogonal interference signals. Phase change within and :

[0084] ,

[0085] ;

[0086] Step E. According to and And the sweep rate obtained from the FP etalon , calculate the distance to be measured :

[0087] .

[0088] Parts of the present invention that are not described in detail belong to common knowledge among those skilled in the art.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, for professionals in this field, after understanding the content and principles of the present invention, they may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. An electro-optically modulated double-sideband (FSI) ranging method based on real-time traceability of the sweep rate is implemented using a double-sideband (FSI) optical frequency scanning interferometer (FSI) system. The system includes a narrow-linewidth frequency-stabilized laser, a Mach-Zehnder modulator (MZM), a sweep signal source, a driver, a fiber beam splitter (FS), an erbium-doped fiber amplifier (EDFA), a circulator, an optical mixer, an integrated transceiver optical antenna, a corner cube prism, and two balanced photodetectors. The method is characterized by: The steps include: (1) Narrow linewidth frequency-stabilized laser generates a frequency-stabilized laser signal The sweep signal source sends a sweep signal which is processed by the driver and then sent to the MZM. The MZM modulates the incoming signal to generate a double-sideband sweep signal. ; (2) The fiber optic splitter FS converts the double-sideband signal First double sideband signal and the second double-sideband signal Two beams; the system introduces a Fabry-Perot FP etalon to convert the two double-sideband signals and Import the circulator and Fabry-Perot FP etalon respectively; (3) The second double-sideband signal in the Fabry-Perot etalon Interference is performed to form FP signal; (4) Construct a sweep rate calculation algorithm module to perform peak processing on the FP signal and obtain the sweep rate of a single sweep cycle. ; (5) The first double-sideband signal entering the circulator It is divided into two parts. One part is sent into the measurement optical path, and the measurement signal is obtained through the optical antenna and the corner cube prism. ; The other part is used as a reference signal ; and and The input is sent to the 90° optical mixer to generate interference, generating four optical signals with a phase difference of 90°. ; (6) Two balanced photodetectors are used to eliminate the DC component of the four optical signals and obtain two orthogonal interference signals. ; (7) Use the phase extraction algorithm to calculate the time difference between the upper sideband and lower sideband signals from the two orthogonal interference signals. Phase change within and ; (8) According to and and sweep rate , calculate and obtain the distance to be measured .

2. The method according to claim 1, wherein: In the double-sideband optical frequency scanning interferometry (FSI) system, a laser uses a 1550nm narrow-linewidth light source. Its output beam is frequency-sweep modulated by a Mach-Zehnder modulator (MZM) and then divided into a primary and a secondary path through an optical fiber beam splitter. The primary path is boosted in power by an erbium-doped fiber amplifier (EDFA) and then guided by a circulator to a measurement path and a reference path carrying target distance information. The two signals are then input into a distance calculation module after interference through a 90-degree optical mixer. The secondary path introduces the double-sideband signal generated by the MZM into a Fabry-Perot etalon through an optical fiber beam splitter, generates an FP signal through its interference effect, and calculates the sweep rate parameter through a sweep rate calculation module. Finally, the target distance is calculated by combining the phase interference data of the primary path with the calibrated sweep rate value of the secondary path.

3. The method according to claim 1, wherein: The FP signal in step (3) is After the Fabry-Perot etalon is introduced and interference is generated, the signal intensity is expressed as follows: ， in, is the average light intensity, is the reflectivity of the FP etalon coating, is the phase difference caused by the optical path in the FP etalon cavity.

4. The method according to claim 3, wherein: Phase difference caused by the optical path in the FP etalon cavity , which is expressed as follows: ， The transmitted light intensity reaches its output peak when the optical frequency meets the following conditions; when the frequency-tuned laser enters the Fabry-Perot etalon, the standard transmitted light intensity reaches its output peak each time it passes through an FSR: ， in, is the refractive index of the medium in the FP etalon cavity, is the FP etalon cavity length, is the light frequency, is the speed of light, Is a positive integer.

5. The method according to claim 1, wherein: In step (4), the peak value of the FP signal is processed. The specific implementation steps are as follows: (4.1) The peak in the FP signal is intercepted and recorded as , where j represents the sequence number of the peak intercepted from the front to the back; (4.2) Yes After denoising and fitting, we can get ; (4.3) Yes Perform peak point search and record the time corresponding to each peak point. ; (4.4) The frequency change between peaks with an interval of 1 is recorded as FSR, and the corresponding sweep rate is recorded as ,in ; The FSR is the free spectral range of the FP etalon; (4.5) For a frequency sweep cycle Perform a least squares fit and take the average value as the sweep rate of a single sweep cycle .

6. The method according to claim 5, characterized in that: The frequency sweep rate corresponding to the peak interval of 1 in step (4.4) , which is expressed as follows: ， in, is the time corresponding to the i-th peak point.

7. The method according to claim 5, characterized in that: The sweep rate of a single sweep cycle described in step (4.5) , which is expressed as follows: 。 8. The method according to claim 1, wherein: The four optical signals described in step (5) , which is expressed as follows: ， ， ， ， ， ； in, is the upper sideband phase of the interference signal, is the lower sideband phase of the interference signal; is the measured optical signal amplitude, is the reference optical signal amplitude; is the target's movement speed, is the starting optical path, is the speed of light, is the frequency of the stabilized laser.

9. The method according to claim 8, characterized in that: The two orthogonal interference signals in step (6) , which is expressed as follows: ， 。 10. The method according to claim 8, characterized in that: The distance to be measured in step (8) , calculated according to the following formula: 。

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