A method and system for matching a longitudinal mode of a ring resonator

Abstract

The application discloses a kind of decay cavity longitudinal mode matching method and system, it is related to the field of cavity ring-down spectroscopy, including CRDS platform and light detector, wherein, the CRDS platform includes ring-down cavity and for producing detection laser laser, the detection laser is incident to ring-down cavity inside;When carrying out ring-down cavity longitudinal mode matching, the frequency of detection laser is fluctuated in frequency fluctuation range by adjusting the operating parameter of laser, the light beam in ring-down cavity is detected using the light detector and generates light detection electrical signal, the frequency fluctuation range of detection laser is adjusted according to the light detection electrical signal generated by light detector, until detection laser is formed in frequency fluctuation range with ring-down cavity Single longitudinal mode matching.The application makes detection laser realize single longitudinal mode matching with ring-down cavity in the process of frequency dynamic change, reduces the adjustment difficulty of detection laser, improves the speed of ring-down cavity longitudinal mode matching.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cavity ring-down spectroscopy, in particular to a method and system for matching longitudinal modes of a ring-down cavity. BACKGROUND

[0002] Cavity ring-down spectroscopy (CRDS) is a high-precision, non-calibration trace gas detection technology, which is widely used in the fields of atmosphere, medical treatment, power and the like. The cavity ring-down spectroscopy is an absorption spectroscopy technology taking ring-down time as a measurement parameter. A ring-down event is generated in a ring-down cavity, and a ring-down curve is formed by measuring the exponential decay of the transmission light intensity of the ring-down cavity with time. The ring-down time is only related to the reflectivity of the mirrors of the ring-down cavity and the absorption of the medium in the ring-down cavity, and is independent of the intensity of the incident light, and thus the cavity ring-down spectroscopy has the advantages of high sensitivity, high signal-to-noise ratio and strong anti-interference capability.

[0003] In the CRDS technology, the precondition for generating the ring-down event is that the laser is matched with the ring-down cavity in the longitudinal mode. Generally, a mode capable of forming a stable standing wave in the ring-down cavity is referred to as a longitudinal mode of the ring-down cavity. When a standing wave is formed in the ring-down cavity, the light wave repeatedly forms multiple-beam interference in the ring-down cavity, so that the light energy is concentrated in the ring-down cavity, thereby forming a strong cavity ring-down signal. The formation of the standing wave can be associated with the wavelength or frequency of the incident laser. The laser frequency capable of forming a standing wave in the ring-down cavity is the longitudinal mode frequency v, v=cN / 2nL, wherein c is the speed of light, N is an arbitrary integer, n is the refractive index of the gas, and L is the cavity length of the ring-down cavity. When the type of the gas in the ring-down cavity is fixed, according to the different values of N, there are multiple longitudinal mode frequencies v in the same ring-down cavity, that is, there are multiple longitudinal modes in the same ring-down cavity.

[0004] In the prior art, the longitudinal mode matching can be achieved by adjusting the cavity length or adjusting the laser. The adjustment of the cavity length causes the movement of the ring-down cavity, which affects the detection accuracy and is not conducive to the miniaturization of the detection instrument. Meanwhile, due to the precision of the laser and environmental factors, it is difficult to stabilize the laser frequency at a fixed value, which makes the existing laser adjustment scheme have the problems of large adjustment difficulty, slow matching speed and matching with multiple longitudinal modes, and thus the frequency of the ring-down event is too low, and the mode noise is introduced, which affects the measurement accuracy and response speed of the CRDS platform. SUMMARY

[0005] In view of the above problems and technical requirements, the present application provides a method and system for matching longitudinal modes of a ring-down cavity.

[0006] A method for matching a longitudinal mode of a ring-down cavity, comprising providing a CRDS platform and a light detector, wherein the CRDS platform comprises a ring-down cavity and a laser for generating a detection laser, the detection laser being incident into the ring-down cavity;

[0007] During the matching of the longitudinal mode of the ring-down cavity, the working parameters of the laser are adjusted to make the frequency of the detection laser fluctuate in a frequency fluctuation range, the light detector is used to detect the light beam in the ring-down cavity and generate a light detection electrical signal, the frequency fluctuation range of the detection laser is adjusted according to the light detection electrical signal generated by the light detector until the detection laser forms a single longitudinal mode matching with the ring-down cavity in the frequency fluctuation range.

[0008] Further, the working parameters of the laser are adjusted by a periodic signal wave, the signal wave being generated by a signal wave generator;

[0009] During the matching of the longitudinal mode of the ring-down cavity, the light detection electrical signal generated by the light detector is transmitted into the signal wave generator, the signal wave generator adjusts the amplitude of the signal wave according to the light detection electrical signal to adjust the frequency fluctuation range of the detection laser.

[0010] Further, when the amplitude of the periodic signal wave is adjusted according to the light detection electrical signal, the method comprises:

[0011] The number of times of matching the longitudinal mode of the ring-down cavity by the detection laser in one period of the signal wave is determined according to the light detection electrical signal, and the number of times of mismatching n between the detection laser and the ring-down cavity is obtained based on the number of times of matching the longitudinal mode of the ring-down cavity by the detection laser in one period of the signal wave and a target matching number.

[0012] When the number of times of mismatching n is greater than k1, the amplitude of the signal wave is adjusted by a first step, wherein k1 is a matching threshold.

[0013] When the number of times of mismatching n is less than or equal to k1, the amplitude of the signal wave is adjusted by a second step, the second step being smaller than the first step.

[0014] Further, the working parameters of the laser include a working current or a working voltage.

[0015] When the working parameters of the laser are the working current, the working parameters of the laser are adjusted by the periodic signal wave, which comprises forming a signal wave current based on the signal wave, and superimposing the signal wave current on the original driving current of the laser to adjust the working current of the laser based on the superimposed signal wave current.

[0016] Further, when the detection laser forms a single longitudinal mode matching with the ring-down cavity, the frequency fluctuation range of the detection laser is less than the FSR of the ring-down cavity.

[0017] A further technical solution is that the periodic signal wave includes a triangular wave.

[0018] A ring-down cavity longitudinal mode matching system, for implementing the above-mentioned ring-down cavity longitudinal mode matching method, the ring-down cavity longitudinal mode matching system comprising a light detector connected to a CRDS platform, the CRDS platform comprising a ring-down cavity and a laser for generating a detection laser, the detection laser being incident on the ring-down cavity;

[0019] When performing longitudinal mode matching of the ring-down cavity, the operating parameters of the laser are adjusted so that the frequency of the detection laser fluctuates within the initial frequency fluctuation range. The light beam in the ring-down cavity is detected by the optical detector and an optical detection electrical signal is generated. The frequency fluctuation range of the detection laser is adjusted according to the optical detection electrical signal generated by the optical detector until the detection laser forms a single longitudinal mode matching with the ring-down cavity within the frequency fluctuation range.

[0020] Its further technical solution is to include a power supply module, a signal wave generator and a driving module;

[0021] The power supply module is connected to the signal wave generator and the driving module, and is used to supply power to the signal wave generator and the driving module;

[0022] The signal wave generator is connected to the driving module and the light detector, and the driving module is connected to the laser. The signal wave generator generates a signal wave voltage according to the light detection electrical signal and inputs it into the driving module. The driving module converts the signal wave voltage into a signal wave current and inputs the signal wave current into the laser.

[0023] A further technical solution is that the signal wave generator includes a matching detection unit, a main control unit, a parameter adjustment unit and an output unit that are adaptively connected;

[0024] The matching detection unit is used to receive the light detection electrical signal generated by the light detector, and determine the number of mismatches n between the detection laser and the ring-down cavity according to the light detection electrical signal;

[0025] The main control unit is used to compare the relationship between the number of mismatches n and the matching threshold k1, the parameter adjustment unit adjusts the amplitude of the signal wave voltage according to the relationship between the number of mismatches n and the matching threshold k1, and the output unit is used to output the signal wave voltage to the driving module.

[0026] A further technical solution is that it also includes an interaction module, which is connected to the signal wave generator through a communication interface.

[0027] The beneficial technical effects of the present invention are:

[0028] The application actively adjusts the working parameters of the laser to make the frequency of the detection laser fluctuate, and adjusts the frequency fluctuation range of the detection laser according to the light detection electric signal generated by the light detector until the detection laser forms single longitudinal mode matching with the decayed cavity in the frequency fluctuation range, so that the detection laser realizes single longitudinal mode matching with the decayed cavity in the process of frequency dynamic change, the adjustment difficulty of the detection laser is reduced, the adjustment speed of the decayed cavity longitudinal mode matching is improved, and the situation of multiple longitudinal mode matching of the detection laser and the decayed cavity is avoided, so that the measurement accuracy and response speed of the CRDS platform are improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of an embodiment of the decayed cavity longitudinal mode matching system provided by the application.

[0030] Figure 2 is a schematic diagram of an embodiment of the signal wave generator structure provided by the application.

[0031] Figure 3 is a schematic diagram of an embodiment of the triangular wave current amplitude adjustment provided by the application.

[0032] The drawings show that: 1 is a driving module, 2 is a power supply module, 3 is a communication interface, 4 is a signal wave generator, 5 is an interaction module, 6 is a laser, 7 is a decayed cavity, and 8 is an optical fiber. DETAILED DESCRIPTION

[0033] The specific embodiments of the application will be further described in combination with the drawings.

[0034] In order to solve the problems of low efficiency and poor stability of decayed cavity longitudinal mode matching, the application provides a decayed cavity longitudinal mode matching method, and in an embodiment of the application, the decayed cavity longitudinal mode matching method comprises:

[0035] A CRDS platform and a light detector are provided, wherein the CRDS platform comprises a decayed cavity 7 and a laser 6 for generating a detection laser, and the detection laser is incident into the decayed cavity 7;

[0036] When the decayed cavity longitudinal mode matching is performed, the working parameters of the laser 6 are adjusted to make the frequency of the detection laser fluctuate in an initial frequency fluctuation range, after the detection laser is incident into the decayed cavity 7, the light detector is used to detect the light beam in the decayed cavity 7 and generate a light detection electric signal, the frequency fluctuation range of the detection laser is adjusted according to the light detection electric signal generated by the light detector, until the detection laser forms single longitudinal mode matching with the decayed cavity 7 in the frequency fluctuation range.

[0037] Specifically, the CRDS platform, i.e., a platform for detecting trace gas by using cavity ring-down spectroscopy technology, generally comprises a ring-down cavity 7 and a laser 6 for generating detection laser incident into the ring-down cavity 7. In implementation, the ring-down cavity 7 and the laser 6 can adopt common forms in the technical field, and the detection laser generated by the laser 6 is generally transmitted into the ring-down cavity 7 through an optical fiber 8. In particular, since a DFB (Distributed Feedback Laser) laser has a wide frequency adjustable range and good frequency adjustability, the laser 6 in the embodiment preferably adopts a DFB laser.

[0038] As known from the background, in the CRDS technology, a prerequisite for the ring-down event is that the detection laser and the ring-down cavity achieve good longitudinal mode matching. There are multiple longitudinal modes in the ring-down cavity 7, and the detection laser only forms matching with one longitudinal mode, which is single longitudinal mode matching. In the prior art, the frequency of the detection laser is difficult to be fixed at a stable value, i.e., the frequency of the detection laser will oscillate irregularly. During the oscillation of the frequency of the detection laser, the detection laser and several longitudinal modes of the ring-down cavity 7 often sequentially form matching, i.e., the detection laser and the ring-down cavity 7 form multiple longitudinal mode matching, which will produce mode noise, thereby reducing the measurement accuracy of the CRDS platform.

[0039] To solve the above problem, in the embodiment, when the ring-down cavity longitudinal mode matching is performed, the working parameters of the laser 6 are actively adjusted to make the frequency of the detection laser fluctuate, and the light detection signal generated by the light detector is used to judge the longitudinal mode matching of the detection laser and the ring-down cavity 7. Then, the frequency fluctuation range of the detection laser is continuously adjusted according to the longitudinal mode matching, until the detection laser forms single longitudinal mode matching with the ring-down cavity 7 in the frequency fluctuation range. At this time, in the frequency fluctuation range of the detection laser, the frequency of the detection laser will only coincide with a certain longitudinal mode frequency v. After the frequency fluctuation range of the detection laser is adjusted, the frequency of the detection laser is continuously fluctuated in the frequency fluctuation range, so as to coincide with the same longitudinal mode frequency v multiple times in the fluctuation process, thereby forming multiple single longitudinal mode matching.

[0040] When the detection laser and the ring-down cavity 7 form the longitudinal mode matching, the light energy in the cavity will accumulate, at this time, the light detection electric signal generated by the light detector will be greatly enhanced, therefore, according to the strength change of the light detection electric signal detected by the light detector, whether the detection laser and the ring-down cavity 7 form the longitudinal mode matching can be judged. In the embodiment, when the light detection electric signal strength is greater than the signal threshold, it is judged that the detection laser and the ring-down cavity 7 form the longitudinal mode matching once, wherein the signal threshold can be set according to the detection requirement of the to-be-detected gas. According to the fluctuation state of the detection laser and the number of times of the longitudinal mode matching formed by the detection laser and the ring-down cavity 7, whether the detection laser and the ring-down cavity 7 form the single longitudinal mode matching in the frequency fluctuation range can be judged, and the specific judgment method of the single longitudinal mode matching formed in the embodiment can be referred to the following description.

[0041] In the specific implementation, other technical means can also be used to determine whether the detection laser and the ring-down cavity 7 form the single longitudinal mode matching. The light detector is usually formed by the adaptation connection of a photodiode, a signal amplification circuit and a signal filtering circuit, and is used to convert the light signal into a light detection electric signal and amplify it. In the specific implementation, the light detector can adopt the existing common form, and the way of detecting the light beam in the ring-down cavity 7 by the light detector can also be consistent with the existing technology, which will not be described here.

[0042] In the present application, when the ring-down cavity longitudinal mode matching is performed, the working parameters of the laser 6 are actively adjusted to make the frequency of the detection laser fluctuate, and the frequency fluctuation range of the detection laser is adjusted according to the light detection electric signal generated by the light detector, until the detection laser and the ring-down cavity 7 form the single longitudinal mode matching in the frequency fluctuation range. The present application makes the detection laser and the ring-down cavity 7 realize the single longitudinal mode matching in the process of frequency dynamic change, reduces the adjustment difficulty of the detection laser, improves the adjustment speed of the ring-down cavity longitudinal mode matching, and avoids the multiple longitudinal mode matching of the detection laser and the ring-down cavity 7, thereby improving the measurement accuracy and response speed of the CRDS platform.

[0043] Preferably, in order to further improve the frequency of the single longitudinal mode matching, when the detection laser and the ring-down cavity 7 form the single longitudinal mode matching, the frequency fluctuation range of the detection laser is less than the FSR (Free Spectral Range) of the ring-down cavity 7. It can be understood that the frequency fluctuation range of the detection laser is less than the FSR of the ring-down cavity 7, which means that the difference between the maximum value and the minimum value of the frequency of the detection laser in the fluctuation process is less than the FSR of the ring-down cavity 7. The FSR represents the interval Δv between adjacent longitudinal mode frequencies, FSR = Δv = c / 2nL, wherein c is the speed of light, n is the gas refractive index, and L is the cavity length of the ring-down cavity 7. For a ring-down cavity 7 containing a to-be-detected gas, the cavity length L and the gas refractive index n of the ring-down cavity 7 can be determined, at this time, the FSR of the ring-down cavity 7 can be determined by the above formula, and the FSR is a constant value.

[0044] Further, the working parameters of the laser 6 are adjusted by a periodic signal wave, which is generated by the signal wave generator 4.

[0045] When the longitudinal mode matching of the ring-down cavity is performed, the optical detection electric signal generated by the optical detector is transmitted to the signal wave generator 4, and the signal wave generator 4 adjusts the amplitude of the signal wave according to the optical detection electric signal to adjust the frequency fluctuation range of the detection laser.

[0046] Specifically, to ensure the frequency of the single longitudinal mode matching, the working parameters of the laser 6 are adjusted by the periodic signal wave, so that after the adjustment of the detection laser frequency fluctuation range, the detection laser forms the single longitudinal mode matching with the ring-down cavity 7 periodically in the frequency fluctuation range. Preferably, the signal wave is a triangular wave. Since the change rate of the instantaneous value of the triangular wave remains unchanged when the triangular wave rises or falls, the change rate of the detection laser frequency when the detection laser frequency rises or falls also remains unchanged when the detection laser frequency rises or falls. Therefore, when the longitudinal mode matching occurs at any time of the rising or falling of the detection laser frequency, i.e., when the detection laser frequency coincides with the longitudinal mode frequency v, the time for the accumulation of optical energy in the ring-down cavity 7 is fixed, the intensity of the optical detection electric signal generated by the optical detector is the same each time the longitudinal mode matching occurs, and the condition of the longitudinal mode matching can be judged according to the change of the intensity of the optical detection electric signal. In specific implementation, the type of the signal wave can be selected according to actual requirements, such as a sine wave, and the specific type is subject to the condition that the detection laser frequency can be adjusted to fluctuate.

[0047] In the embodiment, the signal wave is a triangular wave. To improve the adjustment efficiency of the detection laser frequency, in specific implementation, a relatively large initial amplitude of the triangular wave is first set to make the detection laser frequency fluctuate in a large initial frequency fluctuation range. During the longitudinal mode matching of the ring-down cavity, the amplitude of the triangular wave is gradually reduced to gradually reduce the frequency fluctuation range of the detection laser, until the detection laser forms the single longitudinal mode matching with the ring-down cavity in the frequency fluctuation range. The initial frequency fluctuation range is the fluctuation range of the detection laser frequency under the adjustment of the triangular wave when the amplitude of the triangular wave is the initial amplitude. Generally, the initial frequency fluctuation range can be set according to actual requirements.

[0048] As can be seen from the above description, in the embodiment, the single longitudinal mode matching of the detection laser with the ring-down cavity 7 in the frequency fluctuation range is judged by combining the fluctuation state of the detection laser and the number of times of the longitudinal mode matching of the detection laser with the ring-down cavity 7. Specifically, the target matching number of times of the detection laser with the ring-down cavity 7 is determined by the fluctuation state of the detection laser. When the number of times of the longitudinal mode matching in one period of the signal wave is equal to the target matching number of times, it is judged that the single longitudinal mode matching of the detection laser with the ring-down cavity 7 in the frequency fluctuation range is formed.

[0049] The target matching times refer to the corresponding longitudinal mode matching times in one period of the signal wave when the single longitudinal mode matching is realized under the adjustment of the current signal wave type. In the embodiment, the signal wave is a triangular wave. Under the adjustment of the triangular wave, the working parameters of the laser 6 change with the instantaneous value of the triangular wave in one period of the triangular wave, so that the frequency of the detection laser generated by the laser 6 first increases and then decreases in one period of the triangular wave, and the detection laser frequency at each time in the rising edge corresponds to and is equal to the detection laser frequency at each time in the falling edge. When the detection laser realizes the single longitudinal mode matching under the adjustment of the triangular wave, the frequency of the detection laser coincides with the longitudinal mode frequency v only once at the frequency peak value in one period of the triangular wave, or the frequency of the detection laser coincides with the longitudinal mode frequency v once at a certain time in the rising edge and at the corresponding time in the falling edge, that is, when the single longitudinal mode matching is realized under the adjustment of the triangular wave, the corresponding longitudinal mode matching times in one period of the signal wave are 1 or 2 times. However, since the probability that the frequency of the detection laser coincides with the longitudinal mode frequency v only at the frequency peak value is very small, and since the range of the fluctuation of the detection laser frequency changes from large to small in the embodiment, and the step of the change of the frequency fluctuation range is generally much smaller than the FSR of the ring-down cavity 7, therefore, the case that the frequency of the detection laser coincides with the longitudinal mode frequency v once at a certain time in the rising edge and at the corresponding time in the falling edge will occur before the case that the frequency of the detection laser coincides with the longitudinal mode frequency v only at the frequency peak value. Therefore, in the embodiment, when the detection laser forms 2 longitudinal mode matchings with the ring-down cavity 7 in one period of the triangular wave, it means that the detection laser has formed the single longitudinal mode matching with the ring-down cavity 7, that is, the target matching times in the embodiment are 2 times.

[0050] Further, the working parameter of the laser 6 includes a working current or a working voltage;

[0051] When the working parameter of the laser 6 is the working current, the working parameter of the laser 6 is adjusted by the periodic signal wave, including forming a signal wave current based on the signal wave, and superimposing the signal wave current on the original driving current of the laser 6, so as to adjust the working current of the laser 6 based on the superimposed signal wave current.

[0052] Specifically, the working parameter of the laser 6 includes a working current or a working voltage, and the modulation type of the laser 6 can be a current modulation type or a voltage modulation type. Correspondingly, when the laser 6 is of the current modulation type, the adjusted working parameter is the working current of the laser 6; and when the laser 6 is of the voltage modulation type, the adjusted working parameter is the working voltage of the laser 6.

[0053] In the embodiment, the laser 6 is a current modulation type, and the working current of the laser 6 is adjusted by a periodic signal wave, the signal wave current is superimposed on the original driving current of the laser 6, and the working current of the laser 6 is adjusted based on the superimposed signal wave current, that is, the working current of the laser 6 is the sum of the signal wave current and the original driving current, and the change of the working current of the laser 6 is caused by the change of the signal wave current.

[0054] The skilled in the art can know that for the current modulation type laser 6, the frequency of the detection laser generated by the laser 6 can be controlled by configuring the working current of the laser 6, therefore, in the embodiment, the working current of the laser 6 is configured by the signal wave current, so as to control the frequency of the detection laser generated by the laser 6. At this time, adjusting the amplitude of the signal wave specifically refers to adjusting the amplitude of the signal wave current, the signal wave is generally a waveform formed by the change of the signal wave voltage with time, and the signal wave current is generally converted from the signal wave voltage, therefore, the amplitude of the signal wave current is generally adjusted by adjusting the voltage amplitude of the signal wave. In the embodiment, the signal wave is a triangular wave, and the signal wave current is superimposed on the original driving current of the laser 6, that is, the triangular wave current is superimposed on the original driving current of the laser 6. Generally, the change range of the triangular wave current value is 0-10 mA. The conversion mode of the signal wave voltage to the signal wave current can adopt the existing common mode.

[0055] Further, when adjusting the amplitude of the signal wave according to the optical detection electric signal, the number of mismatching times n of the detection laser and the decay cavity is obtained based on the number of times that the detection laser matches the longitudinal mode of the decay cavity in one period of the signal wave and the target matching times;

[0056] When the number of mismatching times n is greater than k1, the amplitude of the signal wave is adjusted by a first step, wherein k1 is a matching threshold;

[0057] When the number of mismatching times n is less than or equal to k1, the amplitude of the signal wave is adjusted by a second step, and the second step is smaller than the first step.

[0058] Specifically, the number of mismatching times n refers to the number of longitudinal mode matching times exceeding the target matching times in one period of the signal wave, that is, the number of mismatching times n is the difference between the number of longitudinal mode matching times in one period of the signal wave and the target matching times. Specifically, the number of mismatching times n of the detection laser and the decay cavity 7 is determined according to the optical detection electric signal, that is, in one period of the signal wave, the number of times that the intensity of the optical detection electric signal detected by the optical detector is greater than a signal threshold is recorded, so as to obtain the number of longitudinal mode matching times in one period of the signal wave, and the number of longitudinal mode matching times is subtracted from the target matching times to obtain the number of mismatching times n of the detection laser and the decay cavity 7.

[0059] As can be seen from the above description, the signal wave used in the embodiment is a triangular wave, and in the longitudinal mode matching process of the ring-down cavity, the frequency fluctuation range of the detection laser is changed from large to small by adjusting the amplitude of the triangular wave current. Specifically, when the amplitude of the triangular wave current is large, the frequency fluctuation range of the detection laser is also large, and the detection laser will coincide with multiple longitudinal mode frequencies v in one period of the triangular wave, and the number of false matching is large. At this time, a larger first step is used to reduce the amplitude of the triangular wave current, and the frequency fluctuation range of the detection laser is coarsely adjusted to improve the efficiency of longitudinal mode matching adjustment.

[0060] With the gradual reduction of the amplitude of the triangular wave current, the frequency fluctuation range of the detection laser is also gradually reduced. At this time, the number of longitudinal mode matching of the detection laser in one period of the triangular wave gradually approaches the target matching number, that is, the number of false matching n gradually approaches zero. When the number of false matching n is less than or equal to the matching threshold k1, a smaller second step is used to continue to reduce the amplitude of the triangular wave current, so as to finely adjust the frequency fluctuation range of the detection laser, until the number of false matching n is equal to zero, that is, the detection laser forms single longitudinal mode matching with the ring-down cavity 7.

[0061] In the embodiment, the matching threshold k1=2, and in the process of adjusting the amplitude of the triangular wave current, the first step can be 1 mA, and the second step can be 0.5 mA. Figure 3 A schematic diagram of the adjustment of the amplitude of the triangular wave current in the embodiment is shown in FIG. 3. Figure 3As shown, the initial amplitude of the triangular wave current is 10 mA, and the initial frequency is 10 Hz. In 0-0.6 s, the number of mismatching times n > 2, and the amplitude of the triangular wave current is reduced by a first step of 1 mA. In 0.6-1.1 s, the number of mismatching times n ≤ 2, and the amplitude of the triangular wave current is reduced by a second step of 0.5 mA. When the amplitude of the triangular wave current is reduced to 2.5 mA, the number of mismatching times = 0, at this time, the detection laser and the ring-down cavity 7 form a single longitudinal mode matching in the frequency fluctuation range, that is, the adjustment of the frequency fluctuation range of the detection laser is completed. Thereafter, the amplitude of the triangular wave current is maintained, so that the detection laser realizes periodic single longitudinal mode matching with the ring-down cavity 7 under the adjustment of the triangular wave current. During the adjustment of the frequency fluctuation range and after the adjustment is completed, the frequency of the triangular wave current can always remain unchanged. In the embodiment, the amplitude of the triangular wave current is adjusted every three periods of the triangular wave. In actual implementation, the initial amplitude of the triangular wave current, the initial frequency of the triangular wave current, the adjustment frequency of the amplitude of the triangular wave current, the matching threshold k1, the first step, and the second step can all be selected according to actual requirements. The first step and the second step can be set according to the cavity length L of the ring-down cavity 7. As can be seen from the above FSR = c / 2nL, the larger the cavity length L of the ring-down cavity 7, the smaller the value of FSR, that is, the smaller the adjacent longitudinal mode frequency interval Δv. The smaller the adjacent longitudinal mode frequency interval Δv, the higher the accuracy requirement for the frequency adjustment of the detection laser. Therefore, the larger the cavity length L, the smaller the values of the first step and the second step should be.

[0062] In order to implement the above ring-down cavity longitudinal mode matching method, the application further provides a ring-down cavity longitudinal mode matching system, which comprises an optical detector connected with a CRDS platform, the CRDS platform comprising a ring-down cavity 7 and a laser 6 for generating a detection laser, the detection laser being incident into the ring-down cavity 7;

[0063] When the ring-down cavity longitudinal mode matching is performed, the working parameters of the laser 6 are adjusted so that the frequency of the detection laser fluctuates in an initial frequency fluctuation range. After the detection laser is incident into the ring-down cavity, the optical detector is used to detect the light beam in the ring-down cavity and generate an optical detection electrical signal. The frequency fluctuation range of the detection laser is adjusted according to the optical detection electrical signal generated by the optical detector, until the detection laser forms a single longitudinal mode matching with the ring-down cavity 7 in the frequency fluctuation range.

[0064] Specifically, Figure 1 A schematic diagram of an embodiment of the ring-down cavity longitudinal mode matching system is shown, wherein the optical detector is not shown in the figure, and the specific forms of the laser 6, the ring-down cavity 7, and the optical detector can all refer to the above description.

[0065] Further, the ring-down cavity longitudinal mode matching system further comprises a power supply module 2, a signal wave generator 4, and a driving module 1.

[0066] The power supply module 2 is connected with the signal wave generator 4 and the driving module 1, and is used for supplying power for the signal wave generator 4 and the driving module 1.

[0067] The signal wave generator 4 is connected with the driving module 1 and the light detector, the driving module 1 is connected with the laser 6, the signal wave generator 4 generates a signal wave voltage according to the light detection electric signal and inputs the signal wave voltage into the driving module 1, the driving module 1 converts the signal wave voltage into a signal wave current and inputs the signal wave current into the laser 6.

[0068] Specifically, the power supply module 2 is connected with the power supply of the CRDS platform, the power supply module 2 has a level conversion capability, is used for converting the power supply voltage provided by the CRDS platform into a driving voltage, and the driving voltage is loaded to the signal wave generator 4 and the driving module 1 to provide a working voltage for the signal wave generator 4 and the driving module 1. The signal wave generator can adopt an ARM chip of STM32F1 series, when the signal wave is a triangular wave, the ARM chip outputs a triangular wave voltage to the driving module 1 through step-by-step adjustment of DA code value, the driving module 1 converts the triangular wave voltage into a triangular wave current and inputs the triangular wave current into the laser 6, the triangular wave current is superimposed into the original driving current of the laser 6, so as to adjust the working current of the laser 6 based on the superimposed triangular wave current, and the original driving current of the laser 6 is provided by the power supply of the CRDS platform. The specific way of outputting the triangular wave voltage to the driving module 1 through step-by-step adjustment of DA code value is the same as the existing way of outputting the triangular wave voltage through step-by-step adjustment of DA code value, and will not be described here.

[0069] Further, the signal wave generator includes a matching detection unit, a main control unit, a parameter adjustment unit and an output unit which are adaptively connected.

[0070] Specifically, the matching detection unit is connected with the light detector and the main control unit, the main control unit is connected with the parameter adjustment unit, the parameter adjustment unit is connected with the output unit, and the output unit is connected with the driving unit. The matching detection unit is used for receiving the light detection electric signal detected by the light detector, and judging the number n of mismatching times of the detection laser and the ring-down cavity in one period of the signal wave according to the light detection electric signal. The main control unit is used for comparing the relationship between the number n of mismatching times and a matching threshold k1, the parameter adjustment unit adjusts the amplitude of the signal wave voltage according to the relationship between the number n of mismatching times and the matching threshold k1, so as to adjust the amplitude of the signal wave current, and the output unit is used for outputting the signal wave voltage to the driving module 1.

[0071] Further, the ring-down cavity longitudinal mode matching system further includes an interactive module 5 which is connected with the signal wave generator 4 through the communication interface 3.

[0072] Specifically, the power supply module 2 is connected with the interaction module 5 to provide working voltage for the interaction module 5. The communication interface 3 can be a serial communication interface, and the interaction module 5 can be a serial resistance screen. When the longitudinal mode matching of the ring-down cavity is performed, the interaction module 5 can be used to input an adjusting instruction of the initial value of the signal wave amplitude and frequency to the signal wave generator 4 to configure the initial value of the signal wave amplitude and frequency.

[0073] In an embodiment of the present application, the specific working steps of performing the longitudinal mode matching of the ring-down cavity by using the ring-down cavity longitudinal mode matching system are as follows.

[0074] S1, after the ring-down cavity longitudinal mode matching system is connected with the CRDS platform, the initial frequency of the detection laser is determined according to the absorption spectrum of the to-be-detected gas, so as to configure the initial working parameters of the laser 6 according to the initial frequency of the detection laser.

[0075] Specifically, the absorption of light by the gas is selective, and the absorption effect of the same gas on light is different at different frequencies. Therefore, the initial frequency of the detection laser needs to be determined according to the absorption spectrum of the gas, so that the detection laser can be absorbed by the to-be-detected gas. The initial working parameters of the laser 6 include the original driving current and the working temperature.

[0076] S2, the power supply module 2 converts the power supply voltage provided by the CRDS platform into a driving voltage to supply power to the driving module 1, the signal wave generator 4 and the interaction module 5.

[0077] S3, after the signal wave generator 4 is powered on and started, the initial value of the signal wave voltage amplitude and frequency is configured.

[0078] Specifically, since the signal wave current in the system is converted from the signal wave voltage, after the initial value of the signal wave current amplitude and frequency is determined, the initial value of the signal wave voltage amplitude and frequency needs to be configured according to the conversion relationship between the signal wave current and the signal wave voltage. Alternatively, the initial value of the signal wave voltage amplitude and frequency can be configured by inputting an adjusting instruction of the initial value of the signal wave voltage amplitude and frequency to the signal wave generator 4 through the interaction module 5, or the initial value of the signal wave voltage amplitude and frequency can be directly preset in the signal wave generator 4.

[0079] S4, the signal wave generator 4 outputs the signal wave voltage to the driving module 1, and the driving module 1 converts the signal wave voltage into the signal wave current and superimposes it on the original driving current of the laser 6, so that the frequency of the detection laser starts to fluctuate.

[0080] S5, the light detector detects the light beam in the ring-down cavity 7 and transmits the generated light detection electrical signal to the signal wave generator 4, the signal wave generator 4 adjusts the amplitude of the signal wave voltage and the adjustment step of the amplitude according to the light detection electrical signal, so as to adjust the amplitude of the signal wave current and the adjustment step of the amplitude, until the detection laser and the ring-down cavity 7 form single longitudinal mode matching.

[0081] The ring-down cavity longitudinal mode matching system adopts modular design and can be quickly installed on different CRDS platforms for use. Based on the above ring-down cavity longitudinal mode matching method, the system can quickly realize single longitudinal mode matching between the detection laser and the ring-down cavity 7, and solve the problems of slow adjustment speed and low adjustment precision in the longitudinal mode matching.

[0082] It should be noted that the words "front", "back", "left", "right", "up" and "down" used in the above description refer to the directions in the drawings of the present application, and the words "front" and "back", "inner" and "outer" refer to the directions towards or away from a particular component. In addition, the terms "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features.

[0083] The above description is only the preferred embodiments of the present application, and the present application is not limited to the above embodiments. It can be understood that other improvements and changes directly derived or thought by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A ring-down cavity longitudinal mode matching method, characterized in that: A CRDS platform and a light detector are provided, wherein the CRDS platform includes a ring-down cavity and a laser for generating a detection laser, wherein the detection laser is incident on the ring-down cavity; When performing longitudinal mode matching of the ring-down cavity, the operating parameters of the laser are adjusted so that the frequency of the detection laser fluctuates within a frequency fluctuation range, the light beam in the ring-down cavity is detected by the photodetector and a light detection electrical signal is generated, and the frequency fluctuation range of the detection laser is adjusted according to the light detection electrical signal generated by the photodetector until the detection laser forms a single longitudinal mode matching with the ring-down cavity within the frequency fluctuation range; Adjusting the operating parameters of the laser by a periodic signal wave, wherein the signal wave is generated by a signal wave generator; When performing ring-down cavity longitudinal mode matching, the light detection electrical signal generated by the photodetector is transmitted to the signal wave generator, and the signal wave generator adjusts the amplitude of the signal wave according to the light detection electrical signal to adjust the frequency fluctuation range of the detection laser; When the amplitude of the periodic signal wave is adjusted according to the light detection electrical signal, it includes: The number of longitudinal mode matches between the detection laser and the ring-down cavity within one cycle of the signal wave is determined based on the optical detection electrical signal. The number of mismatches n between the detection laser and the ring-down cavity is obtained based on the number of longitudinal mode matches between the detection laser and the ring-down cavity within one cycle of the signal wave and the target number of matches. When the number of mismatches n>k1, the amplitude of the signal wave is adjusted with the first step length, wherein k1 is the matching threshold; When the number of mismatches n≤k1, the amplitude of the signal wave is adjusted with a second step length, and the second step length is smaller than the first step length.

2. The ring-down cavity longitudinal mode matching method according to claim 1, characterized in that: The operating parameters of the laser include operating current or operating voltage; When the operating parameter of the laser is the operating current, the operating parameter of the laser is adjusted by a periodic signal wave, including forming a signal wave current based on the signal wave, and superimposing the signal wave current on the original driving current of the laser, so as to adjust the operating current of the laser based on the superimposed signal wave current.

3. The ring-down cavity longitudinal mode matching method according to claim 1, characterized in that: When the detection laser forms a single longitudinal mode match with the ring-down cavity, the frequency fluctuation range of the detection laser is made smaller than the FSR of the ring-down cavity.

4. The ring-down cavity longitudinal mode matching method according to claim 1, characterized in that: The periodic signal wave includes a triangular wave.

5. A ring-down cavity longitudinal mode matching system, characterized in that: for implementing the ring-down cavity longitudinal mode matching method according to any one of claims 1 to 4, wherein the ring-down cavity longitudinal mode matching system comprises a light detector connected to a CRDS platform, the CRDS platform comprises a ring-down cavity and a laser for generating a detection laser, the detection laser being incident on the ring-down cavity; When performing longitudinal mode matching of the ring-down cavity, the operating parameters of the laser are adjusted so that the frequency of the detection laser fluctuates within a frequency fluctuation range, the light beam in the ring-down cavity is detected by the photodetector and a light detection electrical signal is generated, and the frequency fluctuation range of the detection laser is adjusted according to the light detection electrical signal generated by the photodetector until the detection laser forms a single longitudinal mode matching with the ring-down cavity within the frequency fluctuation range; The ring-down cavity longitudinal mode matching system includes a signal wave generator and a driving module. The signal wave generator is connected to the driving module and the light detector. The driving module is connected to the laser. The signal wave generator generates a signal wave voltage according to the light detection electrical signal and inputs it into the driving module. The driving module converts the signal wave voltage into a signal wave current and inputs the signal wave current into the laser. The signal wave generator includes a matching detection unit, a main control unit, a parameter adjustment unit and an output unit that are adaptively connected; The matching detection unit is used to receive the light detection electrical signal generated by the light detector, and determine the number of mismatches n between the detection laser and the ring-down cavity according to the light detection electrical signal; The main control unit is used to compare the relationship between the number of mismatches n and the matching threshold k1, the parameter adjustment unit adjusts the amplitude of the signal wave voltage according to the relationship between the number of mismatches n and the matching threshold k1, and the output unit is used to output the signal wave voltage to the driving module.

6. The ring-down cavity longitudinal mode matching system according to claim 5, characterized in that: It includes a power supply module, which is connected to the signal wave generator and the driving module and is used to supply power to the signal wave generator and the driving module.

7. The ring-down cavity longitudinal mode matching system according to claim 6, characterized in that: It also includes an interaction module, which is connected to the signal wave generator through a communication interface.

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