A high repetition frequency double optical fiber comb spectrum measurement system based on repetition frequency difference locking

Abstract

The application discloses a high-repetition-frequency double-fiber optical comb spectrum measurement system based on repetition frequency difference locking. The system comprises a double-mode fiber laser, an optical coupler, a first photoelectric detector, a high-speed oscilloscope, a second photoelectric detector, a first low-pass filter, an electric amplifier, a signal generator, a frequency mixer, a second low-pass filter and a proportional-integral-derivative controller. For the double-fiber optical comb spectrum measurement system, two independent GHz high-repetition-frequency mode-locked fiber lasers are packaged in the same shared environment, and the relative repetition frequency difference of the two lasers is locked, so that the GHz high-repetition-frequency double-fiber optical comb spectrum measurement system is realized. The system has the advantages of high long-term stability, rapid acquisition, compact structure and low cost, and solves the problems of slow data acquisition speed, low long-term stability and complex structure of the double-fiber optical comb system.

Description

Technical Field

[0001] This invention belongs to the field of optical frequency comb technology, specifically relating to a high repetition rate dual fiber optical comb spectral measurement system based on repetition rate difference locking. Background Technology

[0002] In recent years, optical frequency comb (hereinafter referred to as "optical comb") technology has become an important tool in research fields such as absolute optical frequency metrology, astronomical spectrometer calibration, and precision measurement due to its highly stable characteristics. Dual-comb spectroscopy, with its advantages of high resolution, rapid measurement, and wide spectral range, has attracted much attention and is one of the most active application areas of optical combs. A dual-comb spectral measurement system is based on two pulse sequences with slightly different repetition rates. One pulse sequence encodes spectral information, while the other pulse sequence is combined with heterodyne detection to extract information. In dual-comb spectral measurements, the difference in repetition rates between the two pulse sequences directly determines the radio frequency comb spacing of the dual-comb, thus affecting the information acquisition speed. With the expansion of cutting-edge applications, the demand for rapid acquisition in dual-comb spectral measurement systems is constantly increasing. To obtain a larger repetition rate difference, within a limited spectral bandwidth, it is usually necessary to increase the repetition rate of the dual-comb source. In particular, compared to kHz or MHz repetition rates, high repetition rate (>1 GHz) dual-comb spectral measurement systems simultaneously offer high spectral resolution and rapid acquisition, making them more advantageous in analyzing spectral absorption characteristics and transient response events, and thus the best choice for spectral measurements.

[0003] To realize high-repetition-rate dual-comb spectroscopic measurement systems at GHz, many dual-comb techniques have been explored, such as electro-optic dual-combs and on-chip integrated microcavity dual-combs. However, these methods typically involve expensive devices or have poor system robustness, making them unsuitable for many scenarios outside the laboratory. In contrast, mode-locked fiber lasers offer advantages such as high beam quality, compact structure, strong anti-interference capability, and low cost, making them ideal light sources for dual-comb spectroscopic measurement systems. A common approach is to use two phase-locked mode-locked fiber lasers as the dual-comb source. For example, in Coherent's multi-heterodyne spectrocopy using stabilized optical frequency combs, two independently locked combs were used to achieve a dual-fiber comb source with a repetition rate of 100 MHz and a repetition rate difference of 1 kHz. However, this method requires a bulky and complex phase-locking system to ensure high coherence between the combs, which hinders the simplification of dual-fiber comb spectroscopic measurement systems. Another approach is to generate two pulse sequences with slightly different repetition rates within the same fiber optic resonator using a pulse-forming mechanism that multiplexes wavelength, polarization, or direction, thereby constructing a single-cavity dual-fiber optical comb system. This method can effectively suppress common-mode noise and improve the relative stability between light sources. For example, CN202210555841.3 utilizes a polarization-multiplexed asynchronous dual-pulse generation mechanism to realize a single-cavity dual-fiber optical comb. However, residual non-common-mode noise caused by environmental fluctuations can lead to long-term drift in the relative repetition rate difference between the two optical combs, hindering the system's high signal-to-noise ratio and long-term stability, thus making it unsuitable for field applications requiring high reliability.

[0004] Although dual-fiber comb systems based on mode-locked fiber lasers have high application potential, the repetition rates (RFs) of currently reported dual-fiber comb systems are typically in the MHz range, resulting in small RF differences, usually between 10 Hz and 10 kHz. This severely limits the data acquisition speed of dual-fiber combs. To date, no GHz high RF dual-fiber comb spectral measurement system with a RF difference greater than 100 kHz has been reported internationally. Therefore, researching and implementing a GHz high RF dual-fiber comb spectral measurement system with fast acquisition, high long-term stability, and low cost has significant research and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a high repetition rate dual fiber comb spectral measurement system based on repetition rate difference locking. This system is achieved by encapsulating two independent GHz high repetition rate mode-locked fiber lasers in the same shared environment and locking their relative repetition rate difference.

[0006] The objective of this invention is achieved by at least one of the following technical solutions.

[0007] A high-repetition-rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking includes a dual-mode-locked fiber laser, an optical coupler, a first photodetector, a high-speed oscilloscope, a second photodetector, a first low-pass filter, an electrical amplifier, a signal generator, a mixer, a second low-pass filter, and a proportional-integral-differential controller.

[0008] In this system, two asynchronous pulse sequences output from the dual-mode-locked fiber laser are respectively connected to the two input terminals of the optical coupler. One output terminal of the optical coupler undergoes photoelectric conversion by the second photodetector, then passes through the first low-pass filter to filter out the repetition frequency difference signal, which is then amplified by the electrical amplifier. The amplified repetition frequency difference signal is mixed with a reference signal provided by the signal generator in the mixer, and then passes through the second low-pass filter to obtain the difference frequency signal. The proportional-integral-derivative controller processes the difference frequency signal and loads the generated feedback voltage signal onto the piezoelectric actuator of the dual-mode-locked fiber laser. The other output terminal of the optical coupler serves as a signal detection terminal to detect the spectral information carried by the object under test. After photoelectric conversion by the first photodetector, the signal is displayed as a time-domain interferogram on a high-speed oscilloscope. The high-speed oscilloscope acquires the displayed time-domain interferogram and performs Fourier transform processing to achieve rapid measurement of spectral information.

[0009] Furthermore, the splitting ratio of the two input terminals and the output terminal of the optical coupler is 50:50.

[0010] Furthermore, the cutoff frequency of the first low-pass filter is between 1MHz and 10MHz to effectively filter out the repetition rate difference signal of the dual fiber optic comb.

[0011] Furthermore, the cutoff frequency of the second low-pass filter is 100kHz to effectively filter out the difference frequency signal output by the mixer.

[0012] Furthermore, the dual-mode-locked fiber laser employs two independent linear resonant cavities, each of which includes a gain fiber, a semiconductor saturable absorber mirror, and a dielectric film.

[0013] In each linear resonant cavity, a semiconductor saturable absorber mirror is in contact with the end face of the first ferrule, and a dielectric film is deposited on the end face of the third ferrule and in contact with the end face of the second ferrule.

[0014] Furthermore, in the dual-mode-locked fiber laser, the pigtails of the third ferrules in the two linear resonant cavities are each connected to the common terminal of a wavelength division multiplexer; the pump terminals of the two wavelength division multiplexers are connected to a pump source, and the signal terminals of the two wavelength division multiplexers are connected to an isolator.

[0015] A piezoelectric actuator is bonded to the surface of the gain fiber of one of the linear resonant cavities via epoxy resin, and stretches the gain fiber according to the feedback voltage signal of the proportional-integral-derivative controller to achieve repetition rate difference locking of the dual fiber comb.

[0016] Furthermore, all components of the dual-mode-locked fiber laser are located in an environmental interference isolation module to share environmental conditions such as temperature and mechanical vibration noise. The environmental interference isolation module can greatly protect the dual-mode-locked fiber laser from the influence of external environmental interference and ensure that the two resonant cavities have a high degree of environmental consistency, thereby improving the coherence of the dual-fiber comb system.

[0017] Furthermore, the lengths of the gain fibers in the two linear resonant cavities are less than 10 cm, and the lengths of the gain fibers in the two linear resonant cavities differ by 10 μm, so as to achieve a dual fiber comb with a repetition rate difference greater than 100 kHz.

[0018] Furthermore, the pump source is a semiconductor laser or a fiber laser, which simultaneously provides pump light to two linear resonant cavities to reduce the coupling differences in pump noise.

[0019] Furthermore, the dynamic response bandwidth of the piezoelectric actuator is between 10kHz and 100kHz to ensure that the repetition rate difference signal of the dual fiber optic comb can be effectively locked within the corresponding frequency bandwidth.

[0020] Compared with existing technologies, the advantages of this invention are:

[0021] This invention provides a high-repetition-rate (PRR) dual-fiber comb spectral measurement system based on repetition rate difference locking. On one hand, only one frequency-locking active feedback device is needed to lock the relative repetition rate difference between two independent GHz high-PRR mode-locked fiber lasers, thus simplifying the structure of the dual-fiber comb spectral measurement system and significantly reducing system cost. On the other hand, this invention uses two independent GHz high-PRR mode-locked fiber lasers sharing a common environment, thus enabling a GHz high-PRR dual-fiber comb spectral measurement system with a repetition rate difference greater than 100 kHz. This system offers advantages such as high long-term stability, fast acquisition, compact structure, and low cost, solving the problems of slow data acquisition speed, low long-term stability, and complex structure inherent in dual-fiber comb systems. Furthermore, this invention supports flexible adjustment of the repetition rate difference of the dual-fiber comb by changing the length of the gain fiber, which is beneficial for practical applications. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a high repetition rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking, provided in an embodiment of the present invention.

[0023] Figure 2This is a schematic diagram of a dual-mode-locked fiber laser structure provided in an embodiment of the present invention;

[0024] Figure 3 The spectrum of the output of the dual-mode-locked fiber laser provided in an embodiment of the present invention;

[0025] Figure 4 A frequency stability diagram of the repetition rate difference of a high repetition rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking is provided in an embodiment of the present invention.

[0026] Figure 5 A time-domain waveform diagram of a high repetition rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking provided in an embodiment of the present invention;

[0027] Figure 6 Fourier transform spectral spectrum of a high repetition rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking, provided in an embodiment of the present invention;

[0028] Figure 7 The Fourier transform radio frequency comb spacing diagram of the time-domain waveform of a high repetition rate dual fiber optic comb spectral measurement system based on repetition rate difference locking is provided in an embodiment of the present invention. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A high repetition rate dual-fiber optical comb spectral measurement system based on repetition rate difference locking, such as Figure 1 As shown, it includes a dual-mode-locked fiber laser 1, an optical coupler 2, a first photodetector 3, a high-speed oscilloscope 4, a second photodetector 5, a first low-pass filter 6, an electrical amplifier 7, a signal generator 8, a mixer 9, a second low-pass filter 10, and a proportional-integral-differential controller 11.

[0032] In this system, two asynchronous pulse sequences output from the dual-mode-locked fiber laser 1 are respectively connected to the two input terminals of the optical coupler 2. One output terminal of the optical coupler 2 undergoes photoelectric conversion by the second photodetector 5, and then passes through the first low-pass filter 6 to filter out the repetition frequency difference signal, which is then amplified by the electrical amplifier 7. The amplified repetition frequency difference signal is mixed with the reference signal provided by the signal generator 8 in the mixer 9, and then passes through the second low-pass filter 10 to obtain the difference frequency signal. The proportional-integral-derivative controller 11 processes the difference frequency signal and loads the generated feedback voltage signal onto the piezoelectric actuator of the dual-mode-locked fiber laser 1. The other output terminal of the optical coupler 2 serves as a signal detection terminal to detect the spectral information carried by the object under test. After photoelectric conversion by the first photodetector 3, the time-domain interferogram is displayed in the high-speed oscilloscope 4. The high-speed oscilloscope 4 acquires the displayed time-domain interferogram and performs Fourier transform processing to achieve rapid measurement of spectral information.

[0033] In one embodiment, the splitting ratio of the two input terminals and the output terminal of the optical coupler 2 is 50:50.

[0034] In one embodiment, the cutoff frequency of the first low-pass filter 6 is between 1MHz and 10MHz to effectively filter out the repetition rate difference signal of the dual fiber optic comb.

[0035] In one embodiment, the cutoff frequency of the second low-pass filter 10 is 100kHz to effectively filter out the difference frequency signal output by the mixer 9.

[0036] In one embodiment, such as Figure 2 As shown, the dual-mode-locked fiber laser 1 employs two independent linear resonant cavities, each of which includes a gain fiber 15, a semiconductor saturable absorber mirror 16, and a dielectric film 17.

[0037] In each linear resonant cavity, the semiconductor saturable absorber mirror 16 is in contact with the end face of the first ferrule 12, and the dielectric film 17 is deposited on the end face of the third ferrule 18 and is in contact with the end face of the second ferrule 13.

[0038] like Figure 2 As shown, in the dual-mode-locked fiber laser 1, the pigtails of the third ferrules 18 in the two linear resonant cavities are respectively connected to the common terminal of a wavelength division multiplexer 19; the pump terminals of the two wavelength division multiplexers 19 are connected to the pump source 20, and the signal terminals of the two wavelength division multiplexers 19 are connected to the isolator 21.

[0039] A piezoelectric actuator 14 is bonded to the surface of the gain fiber 15 of one of the linear resonant cavities via epoxy resin. The gain fiber 15 is stretched according to the feedback voltage signal of the proportional-integral-differential controller 11 to achieve frequency repetition rate difference locking of the dual fiber comb.

[0040] In one embodiment, all components of the dual-mode-locked fiber laser 1 are located in the environmental interference isolation module 22 to share environmental conditions such as temperature and mechanical vibration noise. The environmental interference isolation module 22 can greatly protect the dual-mode-locked fiber laser 1 from the influence of external environmental interference and ensure that the two resonant cavities have a high degree of environmental consistency, thereby improving the coherence of the dual fiber comb system.

[0041] In one embodiment, the length of the gain fiber 15 in the two linear resonant cavities is less than 10 cm, and the length difference of the gain fiber 15 in the two linear resonant cavities is 10 μm, so as to realize a dual fiber comb with a repetition rate difference greater than 100 kHz.

[0042] Furthermore, the pump source 20 is a semiconductor laser or a fiber laser, which simultaneously provides pump light to the two linear resonant cavities to reduce the coupling differences in pump noise.

[0043] Furthermore, the dynamic response bandwidth of the piezoelectric actuator 14 is between 10kHz and 100kHz to ensure that the repetition rate difference signal of the dual fiber optic comb can be effectively locked within the corresponding frequency bandwidth.

[0044] Figure 1 This is a schematic diagram of a high repetition rate dual fiber optic comb spectral measurement system based on repetition rate difference locking in this embodiment. Figure 2 This is a schematic diagram of the dual-mode-locked fiber laser structure in this embodiment. The dual-mode-locked fiber laser 1 includes two independent ultrashort resonant cavities, both employing a typical Fabry-Perot cavity structure. The semiconductor saturable absorber mirror 16 has a recovery time of 10 ps, ​​a modulation depth of 12%, and a saturation energy of 65 μJ / cm². 2 The dielectric film 17 has a reflectivity greater than 90% for signal light and a transmittance greater than 90% for pump light. The pump source 20 is a dual-port output 1570nm continuous fiber laser with a maximum output power of 500mW, sufficient to pump two independent resonant cavities simultaneously. To ensure the long-term stability of the dual-mode-locked fiber laser 1, isolators 21 with a working wavelength range of 1900nm-2000nm are added at the output end to prevent reflected light from returning to the resonant cavity. A piezoelectric actuator 14 is attached to the surface of the gain fiber 15 of one of the resonant cavities, with a static frequency tuning coefficient greater than 1kHz / V, used to stretch the gain fiber 15 in real time to ensure long-term locking of the repetition rate difference.

[0045] A dual-mode-locked fiber laser 1 outputs two asynchronous pulse sequences with repetition frequencies of 1.051250 GHz and 1.051130 GHz, respectively, and a repetition frequency difference of 120 kHz. These two asynchronous pulse sequences are combined and split by an optical coupler 2 with a splitting ratio of 50:50. One of the split signal beams is detected by a second photodetector 5 and then connected to a first low-pass filter 6 with a cutoff frequency of 1 MHz to filter out the repetition frequency difference signal at 120 kHz. An amplifier 7 with an effective operating frequency range of DC-100 MHz and an amplification gain greater than 30 dB is used to further amplify the intensity of the repetition frequency difference signal. A mixer 9 with an operating bandwidth range of DC-100 MHz mixes the reference signal provided by a signal generator 8 with the amplified repetition frequency difference signal. The difference frequency signal between the two signals is obtained by a second low-pass filter 10 with a cutoff frequency of 1 kHz. Then, the difference frequency signal is input to a proportional-integral-derivative (PID) controller 11 for comparison. The PID controller 11 can realize a high-bandwidth control loop of 100 kHz. If a deviation occurs between the repetition rate difference signal and the reference signal, a feedback signal will be output to the piezoelectric actuator 14 of the dual mode-locked fiber laser 1, thereby driving the gain fiber 15 to stretch, so that the frequency of the repetition rate difference signal is consistent with that of the reference signal, and finally the locking of the repetition rate difference of the GHz high repetition rate dual fiber comb is achieved.

[0046] With the frequency difference of the dual-fiber comb locked, the other signal light after splitting by the optical coupler 2 interferes with the first photodetector 3, forming an RF comb composed of heterodyne beat frequencies between a pair of optical comb teeth, which appears as an asynchronous pulse interferogram in the time domain. The high-speed oscilloscope 4 used to record the time-domain signal has a frequency bandwidth of 20 GHz, a sampling rate of 5 GSa / s, and a sampling time window of 10 ms. By performing Fourier transforms on multiple consecutive interferograms, a high signal-to-noise ratio RF spectrum can be obtained. Therefore, the GHz high-repetition-rate dual-fiber comb can convert the spectral information to be measured from optical frequency to radio frequency through beat frequency and Fourier transform, thereby realizing the downconversion of spectral information. In this embodiment, the frequency difference of the GHz high-repetition-rate dual-fiber comb is 120 kHz, and the acquisition time of a single time-domain interferogram is only 8.3 μs, which can fully utilize the rapid acquisition advantage of the high-repetition-rate dual-fiber comb spectral measurement system.

[0047] Figure 3 This is the spectrum of the dual-mode-locked fiber laser output in this embodiment. The center wavelength of the 1.051250GHz high-repetition-rate first optical comb is 1938nm, and the 3dB bandwidth of the spectrum is approximately 13.7nm; the center wavelength of the 1.051130GHz high-repetition-rate second optical comb is 1942nm, and the 3dB bandwidth of the spectrum is approximately 10.8nm.

[0048] Figure 4This diagram illustrates the frequency stability of the repetition rate difference (RFD) of a high-repetition-rate dual-fiber optical comb spectral measurement system based on RFD locking in this embodiment. After RFD locking of the GHz high-repetition-rate dual-fiber optical comb system, the standard deviation of the 120kHz RFD measured within one hour is only 10mHz, indicating that the GHz high-repetition-rate dual-fiber optical comb system possesses excellent long-term stability, which is beneficial for spectral information measurement.

[0049] Figure 5 This is a time-domain waveform of a high repetition rate (PRR) dual-fiber optical comb spectral measurement system based on repetition rate difference locking in this embodiment. After the PPR difference is locked in the GHz high PPR dual-fiber optical comb system, the time interval between each interferogram remains at 8.3 μs, corresponding to a 120 kHz PPR difference. By performing a Fourier transform on the continuous time-domain interferograms with a sampling time of 10 ms, a high signal-to-noise ratio (SNR) spectral spectrum can be obtained, such as... Figure 6 As shown, this GHz high repetition rate dual-fiber optical comb spectral measurement system can convert optical frequency information to the radio frequency range detectable by electrical devices, thereby achieving down-conversion of spectral information. In addition, from... Figure 6 As can be seen, due to the high repetition rate (RF) of this dual-fiber optical comb spectral measurement system, no RF aliasing occurred while maintaining a RF difference greater than 100 kHz, ensuring the effective measurement application of the dual optical comb. The spacing between each RF comb tooth is 120 kHz. Figure 7 As shown, the high repetition rate dual-fiber optical comb spectral measurement system based on the repetition rate difference locking method has the characteristics of high sampling rate with resolvable comb teeth, and can greatly improve the data acquisition speed of dual optical combs. It has the advantages of high long-term stability and fast acquisition.

[0050] Example 2:

[0051] This embodiment provides a high repetition rate (PRR) dual-fiber optical comb spectral measurement system based on repetition rate difference locking, which has the same system structure as that in Embodiment 1. By adjusting the length of the gain fiber 15 of the two resonant cavities of the dual mode-locked fiber laser 1, a dual-fiber optical comb with repetition rates of 1.027589 GHz and 1.027652 GHz, and a repetition rate difference of 63 kHz is achieved. The center wavelength of the 1.027589 GHz high-PRR first optical comb is 1958 nm, and its spectral 3dB bandwidth is approximately 7.8 nm; the center wavelength of the 1.027652 GHz high-PRR second optical comb is 1942 nm, and its spectral 3dB bandwidth is approximately 12.3 nm. After locking the repetition rate difference of the GHz high-PRR dual-fiber optical comb system, a GHz high-PRR dual-fiber optical comb spectral measurement system with a time interval of 15.8 μs between each interferogram and a comb tooth spacing of 63 kHz in the Fourier transform spectral spectrum can be obtained. This demonstrates that the high-PRR dual-fiber optical comb spectral measurement system of this invention has high spectral resolution and flexible adjustable repetition rate difference characteristics.

[0052] Example 3:

[0053] This embodiment provides a high repetition rate (PRR) dual-fiber optical comb spectral measurement system based on repetition rate difference locking, which has the same system structure as that in Embodiment 1. By shortening the length of the gain fiber 15 in the two resonant cavities within the dual-mode-locked fiber laser 1, asynchronous pulse outputs with repetition rates of 2.944870 GHz and 2.944288 GHz are achieved, respectively. The center wavelength of the 2.944870 GHz high PPR first optical comb is 1932 nm, and its spectral 3dB bandwidth is approximately 9.6 nm; the center wavelength of the 2.944288 GHz high PPR second optical comb is 1934 nm, and its spectral 3dB bandwidth is approximately 8.5 nm. Due to the increased PPR of the dual-fiber optical comb, not only can spectral aliasing be avoided, but a larger PPR difference, i.e., 582 kHz, can also be obtained. After PPR difference locking in the GHz high PPR dual-fiber optical comb system, the time interval between each interferogram can be obtained as 1.7 μs. Therefore, the number of samples of consecutive interferograms can be increased within the same sampling time, which is beneficial for improving the signal-to-noise ratio of GHz high PPR dual-fiber optical comb spectral measurement through averaging processing.

[0054] This invention employs two independent GHz high repetition rate (PRR) mode-locked fiber lasers. Therefore, by adjusting the gain fiber lengths of the two resonant cavities, the repetition rate and difference of the GHz high PPR dual-fiber optical comb can be flexibly adjusted. Furthermore, based on the different operating wavelength parameters of the intracavity fiber, pump source, and fiber optic devices, GHz high PPR dual-fiber optical comb spectral measurement systems in different wavelength bands can be realized.

[0055] This invention addresses the dual-fiber comb spectral measurement system by encapsulating two independent GHz high repetition rate mode-locked fiber lasers in the same shared environment and locking their relative repetition rate difference. This results in a GHz high repetition rate dual-fiber comb spectral measurement system with advantages such as high long-term stability, fast acquisition, compact structure, and low cost. It solves the problems of slow data acquisition speed, low long-term stability, and complex structure of dual-fiber comb systems.

[0056] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking, characterized in that, The application relates to a double-mode fiber laser (1), an optical coupler (2), a first photodetector (3), a high-speed oscilloscope (4), a second photodetector (5), a first low-pass filter (6), an electric amplifier (7), a signal generator (8), a frequency mixer (9), a second low-pass filter (10) and a proportional-integral-derivative controller (11). The two asynchronous pulse sequences output by the double-mode fiber laser (1) are respectively connected to two input ends of the optical coupler (2); one output end of the optical coupler (2) is optoelectronically converted by the second photodetector (5), then filtered by the first low-pass filter (6) to obtain a repetition frequency difference signal, and then connected to the electric amplifier (7) for amplification; the amplified repetition frequency difference signal is mixed with a reference signal provided by the signal generator (8) in the frequency mixer (9), and then a beat frequency signal is obtained by the second low-pass filter (10); the proportional-integral-derivative controller (11) processes the beat frequency signal, and generates a feedback voltage signal which is loaded to a piezoelectric actuator of the double-mode fiber laser (1); the other output end of the optical coupler (2) is used as a signal detection end to detect spectral information carried by an object to be measured, and the spectral information is optoelectronically converted by the first photodetector (3) and displayed as a time-domain interference pattern in the high-speed oscilloscope (4); the high-speed oscilloscope (4) collects the displayed time-domain interference pattern, and realizes rapid measurement of the spectral information through Fourier transform processing. The double-mode fiber laser (1) adopts two independent linear resonant cavities, and each linear resonant cavity comprises a gain fiber (15), a semiconductor saturable absorber mirror (16) and a dielectric film (17). In each linear resonant cavity, the semiconductor saturable absorber mirror (16) is in abutment with the end face of the first plug-in core (12), and the dielectric film (17) is coated on the end face of the third plug-in core (18) and in abutment with the end face of the second plug-in core (13); in the double-mode fiber laser (1), the tail fibers of the third plug-in cores (18) in the two linear resonant cavities are respectively connected to the common end of a wavelength division multiplexer (19); the pump ends of the two wavelength division multiplexers (19) are connected to a pump source (20), and the signal ends of the two wavelength division multiplexers (19) are connected to an isolator (21). A piezoelectric actuator (14) is attached to the surface of the gain fiber (15) of one of the linear resonant cavities through epoxy resin, and the gain fiber (15) is stretched according to the feedback voltage signal of the proportional-integral-derivative controller (11) to realize repetition frequency difference locking of the double-fiber optical comb.

2. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking according to claim 1, wherein, The splitting ratios of the two input ends and the output end of the optical coupler (2) are both 50:

50.

3. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking according to claim 1, wherein, The cut-off frequency of the first low-pass filter (6) is between 1MHz and 10MHz, so as to effectively filter out the repetition frequency difference signal of the double-fiber optical comb.

4. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking of claim 1, wherein, The cut-off frequency of the second low-pass filter (10) is 100kHz, so as to effectively filter out the beat frequency signal output by the frequency mixer (9).

5. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking according to claim 1, wherein, All components in the dual-mode fiber laser (1) are located in an environmental interference isolation module (22) to share environmental conditions such as temperature and mechanical vibration noise.

6. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking according to claim 1, wherein, The length of the gain fiber (15) in the two linear resonators is less than 10 cm, and the length of the gain fiber (15) in the two linear resonators is different by 10 μm to achieve a dual-fiber comb with a repetition rate difference greater than 100 kHz.

7. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking according to claim 1, wherein, The pump source (20) is a semiconductor laser or a fiber laser, which provides pump light for the two linear resonators to reduce the coupling difference of pump noise.

8. The high repetition rate dual-fiber optical comb spectroscopy system based on repetition rate difference locking of claim 1, wherein, The dynamic response bandwidth of the piezoelectric actuator (14) is between 10 kHz and 100 kHz to ensure that the repetition rate difference signal of the dual-fiber comb can be effectively locked within the corresponding frequency bandwidth.

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