High-precision temperature measuring device and method based on double-optical-comb system

Abstract

The invention provides a high-precision temperature measuring device and method based on a double-optical-comb system, which reproduce the response characteristic of external temperature change on an optical signal in a radio frequency domain in a double-optical-comb asynchronous optical sampling mode by using the ultra-stable frequency characteristic of an optical frequency comb; through a mutual fuzzy algorithm, the frequency shift amount of a grating reflection spectrum is accurately extracted, so that temperature change information is obtained with high precision, and the current fiber grating temperature measurement precision is improved by one order of magnitude.

Description

Technical Field

[0001] The present invention relates to the technical field of laser dual-comb spectroscopy detection, and particularly relates to a high-precision temperature measurement device and method based on a dual-comb system. Background Art

[0002] At present, the temperature change sensitivity of the Bragg grating in the fiber grating sensing system can reach 5 pm / °C, and the temperature measurement accuracy can reach 0.1 °C. It mainly uses the fiber grating sensing technology, using the grating as the signal transmission medium and sensing unit. The frequency shift and bandwidth of the grating reflection spectrum signal carry the temperature change information at the measured location. However, limited by the demodulation accuracy, it is difficult to further improve the temperature measurement accuracy.

[0003] An optical frequency comb (OFC) is generated by a mode-locked laser, which closely links its time-domain and frequency-domain characteristics. In the time domain, the optical frequency comb appears as a series of optical pulse trains with the same time interval; in the frequency domain, the optical frequency comb is a series of discrete and equally spaced frequency comb tooth spectral lines. Due to this characteristic of the same frequency interval, the spectral lines form a tooth chain structure like a comb, so it is called an optical frequency comb, abbreviated as an optical comb. In a dual-comb spectrometer (DCS), by locking the dual-comb to an ultra-stable narrow linewidth laser, the linewidth of the comb teeth after the dual-comb beating can reach the Hz level, fundamentally ensuring the stability and mutual coherence of the dual-comb. Then, digital algorithms such as asynchronous optical sampling and mutual ambiguity function can be used to extract the frequency shift amount of the dual-comb spectrum to achieve high-precision measurement.

[0004] If the DCS detection technology is combined with the fiber grating sensing technology, it is expected to break through the demodulation accuracy and further improve the temperature measurement accuracy. However, there is no relevant technical solution design on the market at present. Summary of the Invention

[0005] The purpose of the technical solution of the present invention is to design a high-precision temperature measurement device and method based on a dual-comb system to extract high-precision temperature change information from the spectrum of the DCS.

[0006] The technical solution of the present invention provides a high-precision temperature measurement device based on a dual-comb system, including:

[0007] The first optical frequency comb 1 and the second optical frequency comb 2 are respectively locked on the ultra-stable cavity CW laser 3. The first optical frequency comb 1 and the second optical frequency comb 2 are connected to the first coupler 4, and are successively connected to the isolator 5, the optical band-pass filter 6 and the second coupler 7. The second coupler 7 is respectively connected to the Bragg grating 8 and the second photodetector 11. The Bragg grating 8 is successively connected to the first photodetector 9, the first electrical low-pass filter 10 and the dual-channel AD acquisition card 13. The second photodetector 11 is successively connected to the second electrical low-pass filter 12 and the dual-channel AD acquisition card 13. The dual-channel AD acquisition card 13 is connected to the computer;

[0008] Taking the first optical frequency comb 1 and the second optical frequency comb 2 as light sources to obtain the first light beam and the second light beam. The first light beam and the second light beam are respectively locked in the ultra-stable cavity CW laser 3 for phase locking to obtain the first phase-locked light beam and the second phase-locked light beam. The first phase-locked light beam is emitted by the first optical frequency comb 1 and the second phase-locked light beam is emitted by the second optical frequency comb 2 to the first coupler 4 for coherent coupling and beam combination to obtain the first combined light beam. The first combined light beam passes through the isolator 5 and the optical band-pass filter 6 to obtain the light frequency radio frequency comb tooth corresponding light beam;

[0009] The light frequency radio frequency comb tooth corresponding light beam is divided into the first corresponding light beam and the second corresponding light beam by the second coupler 7. The first corresponding light beam is input to the Bragg grating 8. After reflection, it is successively converted into the first electrical signal by the first photodetector 9. After the first electrical signal passes through the first electrical low-pass filter 10, the digital signal of the temperature change information at the measured place is obtained;

[0010] The second corresponding light beam is input to the second photodetector 11 and the second electrical low-pass filter 12 to obtain the reference digital signal;

[0011] The digital signal of the temperature change information at the measured place and the reference digital signal both complete the acquisition of the signal data and the reference data of the temperature change information through the dual-channel AD acquisition card 13. After the signal data and the reference data pass through the computer 14 to complete the jitter correction and cross-correlation and cross-ambiguity processing, the frequency shift information of the signal path and the reference path can be extracted, so as to inversely deduce the temperature change information at the measured place.

[0012] Preferably, the first optical frequency comb 1 and the second optical frequency comb 2 are optical frequency combs with a small repetition frequency difference.

[0013] Preferably, the optical band-pass filter 6 is selected according to the aliasing-free spectral range. The formula of the aliasing-free spectral range is as follows:

[0014]

[0015] Where f r represents the optical comb repetition frequency, and Δf rRepresents the repetition frequency difference between the first optical frequency comb 1 and the second optical frequency comb 2

[0016] The technical solution of the present invention also provides a high-precision temperature measurement method based on a dual-comb system, which uses a high-precision temperature measurement device based on a dual-comb system as described above, and includes the following steps:

[0017] Step 1: The computer 14 acquires signal data and reference data;

[0018] Step 2: Correct the jitter of the repetition frequency difference between each interference pulse signal in the signal data and the reference data through a resampling algorithm, and locate and extract the peak point positions of each interference pulse signal through a cross-correlation algorithm to estimate the Δf r phase information between the first optical frequency comb 1 and the second optical frequency comb 2, and then based on the peak point positions of each interference pulse signal and the Δf r phase information between the first optical frequency comb 1 and the second optical frequency comb 2, inversely deduce the position information of each interferogram;

[0019] According to the position information of the interferogram, use the cross-ambiguity function to compare the interferograms corresponding to the signal data and the reference data, extract the frequency shift amount between a pair of interferograms, substitute the frequency shift amount δ into the Bragg grating wavelength shift formula to obtain the Bragg grating wavelength shift, and calculate the temperature change sensitivity of the Bragg grating according to the Bragg grating wavelength shift to obtain the temperature change information at the measured location.

[0020] Preferably, the Bragg grating wavelength shift formula is as follows:

[0021]

[0022] where λ is the Bragg wavelength of the grating, c is the speed of light, and Δλ is the Bragg grating wavelength shift caused by temperature change.

[0023] The technical solution of the present invention proposes a high-precision temperature measurement device and method based on a dual-comb system. By borrowing the ultra-stable frequency characteristics of the optical frequency comb, the response characteristics of the external temperature change on the optical signal are reproduced in the radio frequency domain through the asynchronous optical sampling of the dual-comb; through the cross-ambiguity algorithm, the frequency shift amount of the grating reflection spectrum is accurately extracted, so as to obtain the temperature change information with high precision, and the current fiber grating temperature measurement accuracy is improved by one order of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural block diagram of a high-precision temperature measurement device based on a dual-comb system provided by an embodiment of the present invention;

[0025] Reference numerals:

[0026] 1 - First optical frequency comb; 2 - Second optical frequency comb; 3 - Ultra-stable cavity CW laser;

[0027] 4 - First coupler; 5 - Isolator; 6 - Optical band - pass filter; 7 - Second coupler;

[0028] 8 - Fiber Bragg grating; 9 - First photodetector; 10 - First electrical low - pass filter;

[0029] 11 - Second photodetector; 12 - Second electrical low - pass filter; 13 - Dual - channel AD acquisition card;

[0030] 14 - Computer. Detailed implementation mode

[0031] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0032] As Figure 1 shown, an embodiment of the present invention provides a high - precision temperature - measuring device based on a dual - optical - comb system for calculating the temperature change information at the measured location. The high - precision temperature - measuring device based on a dual - optical - comb system includes:

[0033] A first optical frequency comb 1 and a second optical frequency comb 2 are respectively locked on an ultra - stable cavity CW laser 3. The first optical frequency comb 1 and the second optical frequency comb 2 are connected to a first coupler 4, and are sequentially connected to an isolator 5, an optical band - pass filter 6, and a second coupler 7. The second coupler 7 is respectively connected to a Bragg grating 8 and a second photodetector 11. The Bragg grating 8 is sequentially connected to a first photodetector 9, a first electrical low - pass filter 10, and a dual - channel AD acquisition card 13. The second photodetector 11 is sequentially connected to a second electrical low - pass filter 12 and a dual - channel AD acquisition card 13. The dual - channel AD acquisition card 13 is connected to a computer. The branch where the Bragg grating 8 is located is the signal path, and the branch where the second photodetector 11 is located is the reference path.

[0034] Among them, the first optical frequency comb 1 and the second optical frequency comb 2 are optical frequency combs with a small repetition - frequency difference. The first optical frequency comb 1 and the second optical frequency comb 2 are both fiber - mode - locked lasers operating in the 1550 nm band with a repetition frequency of 10 MHz, a spectral linewidth of 0.2 nm, and a 10 dB spectral linewidth of 0.05 nm.

[0035] The first optical frequency comb 1 and the second optical frequency comb 2 are locked on an ultra - stable cavity CW laser 3 with a central wavelength of 1550 nm to achieve a comb - tooth linewidth at the Hz level, ensuring the absolute stability and mutual coherence of the phase - locking of the first optical frequency comb 1 and the second optical frequency comb 2.

[0036] Using the first optical frequency comb 1 and the second optical frequency comb 2 as light sources to obtain a first light beam and a second light beam. The first light beam and the second light beam are respectively locked in the ultra-stable cavity CW laser 3 for phase locking to obtain a first phase-locked light beam and a second phase-locked light beam. The first optical frequency comb 1 emits the first phase-locked light beam and the second optical frequency comb 2 emits the second phase-locked light beam to the first coupler 4 for coherent coupling and beam combination to obtain a first combined light beam. The first combined light beam passes through the isolator 5 and the optical bandpass filter 6 to obtain a light beam corresponding to the optical frequency radio frequency comb teeth to ensure one-to-one correspondence between the optical frequency comb teeth and the radio frequency comb teeth.

[0037] The first coupler 4 is a 50:50 optical coupler. The optical bandpass filter 6 should be selected according to the aliasing-free spectral range calculated from the optical comb repetition frequency and the repetition frequency difference between the first optical frequency comb 1 and the second optical frequency comb 2: where f r represents the optical comb repetition frequency, and Δf r represents the repetition frequency difference between the first optical frequency comb 1 and the second optical frequency comb 2. The repetition frequency difference Δf r between the first optical frequency comb 1 and the second optical frequency comb 2 is adjusted within 0 - 2 kHz, and the actual experimental setting is around 2000 Hz.

[0038] The isolator 5 is used to avoid echo interference with the optical signal, and the optical bandpass filter 6 is used to remove the coherent aliasing phenomenon of the beat frequency between the same comb tooth and multiple comb teeth. The center frequency of the optical bandpass filter 6 is 1550 nm, and the filtering bandwidth is 12 nm.

[0039] The light beam corresponding to the optical frequency radio frequency comb teeth is divided into a first corresponding light beam and a second corresponding light beam by the second coupler 7. The first corresponding light beam is input to the Bragg grating 8. After reflection, it passes through the first photodetector 9 in sequence to be converted into a first electrical signal. After the first electrical signal passes through the first electrical low-pass filter 10, a digital signal of the temperature change at the measured location is obtained. The Bragg grating 8 is a Bragg grating with a center wavelength of 1550 nm and a temperature sensitivity of 5 nm / 100 °C, which is a special doped fiber π-phase shift Bragg grating.

[0040] The second corresponding light beam is input to the second photodetector 11 and the second electrical low-pass filter 12 to obtain a reference digital signal. The first photodetector 9 and the second photodetector 11 are Thorlabs' InGaAs biased detectors DET01CFC with a bandwidth of 1 GHz. The passband frequencies of the first electrical low-pass filter 10 and the second electrical low-pass filter 12 are 0 - 48 MHz, and the 3 dB cut-off frequency is 50 MHz.

[0041] The digital signals of the temperature change at the measured location and the reference digital signals both complete the acquisition of the signal data and reference data of the temperature change through the dual-channel AD acquisition card 13. After the signal data and reference data are processed by the computer 14 to complete jitter correction and cross-correlation and cross-ambiguity processing, the frequency shift information of the signal path and the reference path can be extracted, thereby inversely inferring the temperature change information at the measured location, that is, the temperature change information at different grating positions of the fiber grating.

[0042] The computer 14 has functions of signal acquisition, processing, control, calculation, and display.

[0043] The basic principle is to use the coherence characteristics of lasers for high-precision measurement. Specifically, two optical frequency combs with a small repetition frequency difference are used as signal carriers. When the two optical frequency combs are spatially coherent, their pulse sequences will continuously coincide and reinforce in the time domain, and the pulse pairs of the two beams of light will increase pairwise along the sequence overlap interval, and the coherent part will change accordingly to generate signals with different light intensities. Therefore, the detector outputs a fluctuating voltage signal, which is the interference pattern signal; in the frequency domain, as the pulse sequence is transmitted, the tooth spacing of the two optical frequency combs also increases step by step due to this small repetition frequency difference, so that the frequency spacing between the tooth pairs increases step by step. When the optical frequency combs coincide, parallel multi-heterodyne beat frequency down-conversion occurs between the longitudinal modes, mapping the information recorded on the teeth in the optical frequency domain to the radio frequency domain, generating a comb-shaped interference pattern signal, and the radio frequency spectrum is obtained after Fourier transform of the interference pattern.

[0044] The present invention also provides a high-precision temperature measurement method based on a dual-comb system, which uses a high-precision temperature measurement device based on a dual-comb system as described above, and specifically includes the following steps:

[0045] When the external temperature changes, the thermo-optic effect causes the refractive index of the fiber core of the Bragg grating 8 to change, and at the same time, the thermal expansion effect causes the grating period length to change, thereby causing the reflected Bragg light reflected by the Bragg grating 8 to generate a frequency shift. At this time, the Bragg grating 8 collects the external temperature change information in this process, and the reflected Bragg light is collected after being processed by a photodetector and an electrical low-pass filter; the other part of the light is directly processed and then collected as the reference path.

[0046] Step 1: The computer 14 acquires the signal data and the reference data;

[0047] Step 2: Correct the jitter of the repetition frequency difference between each interference pulse signal in the signal data and the reference data through a resampling algorithm, and locate and extract the peak point positions of each interference pulse signal through a cross-correlation algorithm to estimate the phase information of Δf between the first optical frequency comb 1 and the second optical frequency comb 2, and then combine the peak point positions of each interference pulse signal with Δf between the first optical frequency comb 1 and the second optical frequency comb 2 r of the phase information, and then according to the peak point positions of each interference pulse signal combined with Δf between the first optical frequency comb 1 and the second optical frequency comb 2 rThe phase information is used to inversely deduce the position information of each interferogram (IGM). Since the high-precision temperature measurement device uses a fully reference-type optical frequency comb (the first optical frequency comb 1 and the second optical frequency comb 2), the signal is basically completely coherent after this step.

[0048] Step 3: According to the IGM position information, use the cross ambiguity function to compare the interferograms corresponding to the signal data and the reference data, extract the frequency shift amount between a pair of IGMs, substitute the frequency shift amount δ into the Bragg grating wavelength shift formula to obtain the Bragg grating wavelength shift, and calculate the temperature change sensitivity of the Bragg grating at 1550 nm according to the Bragg grating wavelength shift to obtain the temperature change information (i.e., the temperature change amount) at the measured location.

[0049]

[0050] Among them, λ is the Bragg wavelength of the grating, c is the speed of light, and Δλ is the Bragg grating wavelength shift caused by temperature change.

[0051] Since the accuracy requirement for frequency shift measurement is relatively high, a set of simulations is designed to verify the accuracy of the cross ambiguity function. The basic idea is as follows: First, construct two optical frequency combs that are exactly the same except for having a small repetition frequency difference, so that two IGMs are generated by beating. One of them remains unchanged as the reference path IGM, and the other simulates the frequency shift caused by temperature change by changing the value of fceo as the signal path IGM. Call the cross ambiguity function to measure the frequency offset between the two IGMs and compare it with the input fceo variable to test whether the accuracy of the cross ambiguity function for measuring frequency shift meets the requirements. Through experiments, under the same data conditions as the example, the accuracy error of the cross ambiguity function for measuring a 2500 HZ frequency shift does not exceed 0.005 HZ, meeting the accuracy requirements.

[0052] In the embodiment of the present invention, the temperature change information at the measured location is calculated and deduced by performing calculations such as the repetition frequency difference jitter between each interference pulse signal, extracting the peak point position of each interference pulse signal, and detecting the period change of the Bragg grating on the signal data and the reference data. The reflected signals at different grating positions can be distinguished by different echo times, so as to achieve high-precision temperature change measurement with an accuracy of 0.01 °C, further exerting the detection limit of the existing specially doped fiber π-phase shift Bragg grating, making full use of the high-precision characteristics of the dual optical frequency comb spectrum, and solving the shortcoming of the existing fiber grating sensing technology being limited by the demodulation accuracy.

[0053] The high-precision temperature measurement device and method based on a dual optical frequency comb system provided by the present invention have the following beneficial effects:

[0054] 1. Adopting a fully reference-type DCS system ensures the coherence stability of the light source and reduces the influence of jitter on the signal as much as possible.

[0055] 2. Achieved a higher temperature measurement accuracy than traditional distributed fiber grating sensing systems.

[0056] 3. Combines the advantages of two relatively mature detection systems and is more mature in terms of specific structure.

[0057] It should be understood that although terms such as "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are only used to distinguish one unit from another. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit.

[0058] As described above, it is only the preferred embodiment of the present invention and does not impose any formal or substantial limitations on the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the premise of the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. For those skilled in the art, without departing from the spirit and scope of the present invention, any equivalent changes made by making some modifications, decorations, and evolutions using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes made by making modifications, decorations, and evolutions to the above embodiments based on the essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A high-precision temperature measurement device based on a dual-optical comb system, characterized in that: Used to calculate the temperature change information of the measured location, the high-precision temperature measuring device includes: The ultrastable cavity CW laser 3 is respectively locked with a first optical frequency comb 1 and a second optical frequency comb 2, the first optical frequency comb 1 and the second optical frequency comb 2 are connected to a first coupler 4, and are sequentially connected to an isolator 5, an optical bandpass filter 6 and a second coupler 7, the second coupler 7 is respectively connected to a Bragg grating 8 and a second photodetector 11, the Bragg grating 8 is sequentially connected to a first photodetector 9, a first electrical low-pass filter 10 and a dual-channel AD acquisition card 13, the second photodetector 11 is sequentially connected to a second electrical low-pass filter 12 and a dual-channel AD acquisition card 13, and the dual-channel AD acquisition card 13 is connected to a computer; The first optical frequency comb 1 and the second optical frequency comb 2 are used as light sources to obtain a first light beam and a second light beam, which are respectively locked in an ultrastable cavity CW laser 3 for phase locking to obtain a first phase-locked light beam and a second phase-locked light beam, and the first optical frequency comb 1 emits the first phase-locked light beam and the second optical frequency comb 2 emits the second phase-locked light beam to the first coupler 4 for coherent coupling and beam combination to obtain a first combined light beam, and the first combined light beam passes through an isolator 5 and an optical bandpass filter 6 to obtain a light beam corresponding to an optical frequency radio frequency comb tooth; The light beam corresponding to the optical frequency radio frequency comb teeth is divided into a first corresponding light beam and a second corresponding light beam through the second coupler 7. The first corresponding light beam is input to the Bragg grating 8, and after reflection, it is converted into a first electrical signal by the first photodetector 9 in sequence. After the first electrical signal passes through the first electrical low-pass filter 10, a digital signal of the temperature change at the measured location is obtained. The second corresponding light beam is input to the second photodetector 11 and the second electrical low-pass filter 12 to obtain a reference digital signal; The digital signal of the temperature change at the measured location and the reference digital signal are both acquired through the dual-channel AD acquisition card 13 to complete the acquisition of the signal data and the reference data of the temperature change. After the signal data and the reference data are processed by the computer 14 to complete the jitter correction and cross-correlation and mutual fuzzification processing, the frequency shift information of the signal path and the reference path can be extracted, thereby inferring the temperature change information of the measured location.

2. A high-precision temperature measurement device based on a dual optical comb system as claimed in claim 1, characterized in that: The first optical frequency comb 1 and the second optical frequency comb 2 are optical frequency combs with a small repetition frequency difference.

3. A high-precision temperature measurement device based on a dual optical comb system as claimed in claim 1, characterized in that: The optical bandpass filter 6 is selected according to the alias-free spectral range, and the alias-free spectral range formula is as follows: where f r is the repetition frequency of the optical comb, Δf r represents the repetition frequency difference between the first optical frequency comb 1 and the second optical frequency comb 2.

4. A high-precision temperature measurement method based on a dual-optical comb system, characterized in that: The high-precision temperature measurement device based on the dual optical comb system as claimed in claim 1 specifically comprises the following steps: Step 1: The computer 14 acquires signal data and reference data; Step 2: Use the resampling algorithm to correct the repetition frequency difference jitter between each interference pulse signal in the signal data and the reference data, and use the cross-correlation algorithm to locate and extract the peak point position of each interference pulse signal to estimate the Δf between the first optical frequency comb 1 and the second optical frequency comb 2 r The phase information of each interference pulse signal is then combined with the Δf between the first optical frequency comb 1 and the second optical frequency comb 2 according to the peak position of each interference pulse signal. r The phase information of each interference pattern can be inferred from the position information of each interference pattern; According to the position information of the interference pattern, the interference patterns corresponding to the signal data and the reference data are compared using the mutual ambiguity function, and the frequency shift between a pair of interference patterns is extracted. The frequency shift δ is substituted into the Bragg grating wavelength offset formula to obtain the Bragg grating wavelength offset. The temperature change sensitivity of the Bragg grating is calculated according to the Bragg grating wavelength offset to obtain the temperature change information of the measured location.

5. A high-precision temperature measurement method based on a dual optical comb system as claimed in claim 4, characterized in that: The Bragg grating wavelength shift formula is as follows: Where λ is the Bragg wavelength of the grating, c is the speed of light, and Δλ is the wavelength shift of the Bragg grating caused by temperature change.

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