A fully optical fiber carbon isotope detection system and detection method

Abstract

The present invention discloses a fully optical carbon isotope detection system and method, comprising: a detection light source, a time-delay optical fiber, and an input optical fiber; an optical fiber annular path including a hollow-core optical fiber chamber, with opposite ends of the hollow-core optical fiber chamber connected to the time-delay optical fiber and the input optical fiber, respectively; a detection light propagates in the optical fiber annular path and circulates through the hollow-core optical fiber chamber; the hollow-core optical fiber chamber is filled with a gas to be detected; a pump light source connected to the optical fiber annular path and used to generate pump light and pass it into the hollow-core optical fiber chamber; the gas changes its temperature and refractive index under the action of the pump light, and the detection light changes its phase as it passes through the gas in the hollow-core optical fiber chamber; a photodetector is used to receive the phase-changed detection light transmitted back from the time-delay optical fiber and the input optical fiber; and a data processing controller is electrically connected to the photodetector and the pump light source. This system solves the problems of current carbon isotope detection devices, such as high gas consumption, high cost, and large size, caused by the large optical chamber.

Description

Technical Field

[0001] The present invention relates to the technical field of gas concentration detection, and in particular to an all-fiber carbon isotope detection system and a detection method. Background Art

[0002] Carbon isotope testing plays an important role in atmospheric science, energy exploration, medical testing, and other fields. In atmospheric science, carbon isotope testing is a key method for understanding the global carbon cycle and clarifying changes in carbon sources and sinks. In energy exploration, carbon isotope testing is a crucial means for deducing the characteristics of oil, gas, and coal reservoirs and identifying and locating mineral sources. In the medical field, carbon isotope testing in human exhaled breath has become the gold standard for non-invasive diagnosis of Helicobacter pylori infection.

[0003] The carbon isotope content in nature varies very little. The relative change in isotope abundance ratio is usually characterized by the deviation from the reference standard. The change in the carbon isotope ratio of a sample relative to the reference material can be expressed as:

[0004]

[0005] in( 13 C / 12 C) Sample and( 13 C / 12 C) Reference are the carbon isotope ratios of the sample to be tested and the reference standard substance, respectively. Isotope Ratio Mass Spectroscopy (IRMS) is the most commonly used carbon isotope detection instrument, and its typical detection accuracy can reach 0.01-0.1‰, but it is large in size, complicated to operate, expensive, slow in detection speed, and requires complex sample gas pretreatment, which is not suitable for in-situ detection applications. In addition, for example, CN113109292 discloses a carbon isotope detection system and method based on tunable laser absorption spectroscopy (TDLAS). Through the optimized algorithm, the system can work under normal pressure, but the long optical path space optical gas chamber leads to large gas consumption, and it is difficult to use for detection in high-concentration gas environments.

[0006] The existing carbon isotope detection devices and the optical gas chambers in the commonly used spatial optical resonant cavities are too large, resulting in high gas consumption, high cost, and large volume. Therefore, the existing technology needs to be improved and developed. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a fully optical carbon isotope detection system and detection method to solve the problems of large gas consumption, high cost and large size of current carbon isotope detection devices due to the large optical gas chamber.

[0008] The technical solutions of the present invention are as follows:

[0009] On the one hand, the present application proposes an all-fiber carbon isotope detection system, comprising: a detection light source, the detection light source being used to emit detection light;

[0010] The delay optical fiber and the input optical fiber are both connected to the detection light source, and the detection light has different delays after passing through the delay optical fiber and the input optical fiber;

[0011] An optical fiber annular passage includes a hollow-core optical fiber chamber, wherein opposite ends of the hollow-core optical fiber chamber are respectively connected to an output end of a delay optical fiber and an output end of an input optical fiber, and a detection light propagates in the optical fiber annular passage and circulates through the hollow-core optical fiber chamber; the hollow-core optical fiber chamber is filled with a gas to be detected;

[0012] A pump light source is connected to the fiber ring path and is used to generate pump light and pass it into the hollow-core fiber chamber. The gas changes its temperature and refractive index under the action of the pump light, and the probe light changes its phase when it passes through the gas in the hollow-core fiber chamber.

[0013] A photodetector for receiving the phase-changed detection light transmitted back from the delay optical fiber and the input optical fiber;

[0014] The data processing controller is electrically connected to the photodetector and the pump light source respectively.

[0015] Optionally, the detection light source includes: an amplified spontaneous emission fiber light source, a superluminescent diode or a supercontinuum light source; wherein the 3-dB spectral width of the detection light emitted by the detection light source is not less than 1 nm.

[0016] Optionally, the wavelength of the pump light emitted by the pump light source is tunable, and the tunable range of the wavelength of the pump light is not less than 0.5 nm, so as to cover different carbon isotope absorption lines;

[0017] The wavelength of the pump light is simultaneously modulated at high frequency and scanned at low frequency. The modulation frequency is between 1kHz-100kHz, the scanning frequency is between 1mHz-1 Hz, and the optical power of the pump light is not less than 1mW.

[0018] Optionally, the pump light source includes: a DFB seed laser, the wavelength of the pump light emitted by the DFB seed laser being tunable within a predetermined range;

[0019] Thulium-doped fiber amplifier, thulium-doped fiber amplifier connected to DFB seed laser.

[0020] Optionally, the optical fiber annular passage further comprises: a first optical fiber coupler, the first optical fiber coupler having a first port, a second port and a first common port, the first port being connected to the delay optical fiber, and the first common port being connected to one end of the hollow-core optical fiber air chamber;

[0021] a second optical fiber coupler, the second optical fiber coupler having a third port, a fourth port, and a second common port, the third port being connected to the input optical fiber, and the second common port being connected to the other end of the hollow-core optical fiber air chamber;

[0022] The second port is connected to the fourth port, so that the detection light propagates in the first fiber coupler, the second fiber coupler and the hollow-core fiber air chamber and passes through the hollow-core fiber air chamber multiple times.

[0023] Optionally, the second common port is connected to the other end of the hollow-core optical fiber air chamber via a wavelength division multiplexer, and the wavelength division multiplexer is connected to the pump light source and is used to combine the pump light and the detection light emitted by the pump light source.

[0024] Optionally, a splitting ratio between the second port and the first port of the first optical fiber coupler is not less than 7:3;

[0025] The splitting ratio between the fourth port and the third port of the second optical fiber coupler is not less than 7:3.

[0026] Optionally, the delay optical fiber and the input optical fiber are connected to the detection light source via a fiber coupler;

[0027] The optical fiber coupler includes at least three input ports and two output ports;

[0028] One input port of the fiber coupler is connected to the detection light source, and the other two input ports are connected to the photodetectors respectively;

[0029] One output port of the optical fiber coupler is connected to the delay optical fiber, and the other output port is connected to the input optical fiber.

[0030] Optionally, the carbon isotope detection device further includes a temperature control module, which is used to cool and heat the hollow-core optical fiber gas chamber.

[0031] On the other hand, the present application also proposes an all-fiber carbon isotope detection method for use in the all-fiber carbon isotope detection system described above, the method comprising the following steps:

[0032] A pump light source generates pump light and allows the pump light to enter the hollow-core fiber chamber, which is filled with the gas to be detected. The pump light interacts with the gas molecules to release heat, changing the temperature and refractive index of the gas.

[0033] The detection light source emits a probe light, which enters the fiber ring path through the delay fiber and the input fiber, and enters the hollow fiber gas chamber from opposite ends. The phase of the probe light changes after passing through the gas with changed temperature and refractive index.

[0034] The photodetector receives the phase-changed detection light and performs phase detection on the detection light to obtain the refractive index change after the gas interacts with the pump light.

[0035] The carbon isotope concentration information is obtained based on the relationship between the concentration of gas molecules carrying carbon isotopes and the change in refractive index.

[0036] Optionally, in the step of generating pump light by a pump light source and allowing the pump light to enter a hollow-core optical fiber chamber, and filling the hollow-core optical fiber chamber with a gas to be detected:

[0037] A pump light source generates pump lights of different wavelengths, and the pump lights of different wavelengths are respectively sent into the hollow-core fiber chamber for scanning. The hollow-core fiber chamber is filled with gases with different carbon isotopes, and the gas molecules with different carbon isotopes have different absorption wavelengths.

[0038] In the step of receiving the phase-changed probe light by a photodetector and performing phase detection on the probe light to obtain the refractive index change of the gas after the pump light interacts with the gas, the phase change of the probe light is proportional to the absorption amount of the pump light of different wavelengths;

[0039] In the step of obtaining carbon isotope concentration information based on the relationship between the concentration of gas molecules carrying carbon isotopes and the change in refractive index: different carbon isotope concentration information is obtained based on the relationship between the concentration of gas molecules carrying different carbon isotopes and the change in refractive index.

[0040] Beneficial effect: Compared with the prior art, the present invention proposes an all-fiber carbon isotope detection system and detection method, in which the carbon isotope detection system adopts an optical fiber ring passage method, so that the detection light can circulate into the hollow-core optical fiber air chamber, thereby realizing effective amplification of the phase signal of the detection light, and reducing the volume of the air chamber while meeting the detection accuracy. The ring-shaped light passage method optimizes the structure, so that the gas consumption used for calibration and detection is small, and it can be suitable for application scenarios with small sample gas volume such as breath detection and deep-sea dissolved gas detection. The small air chamber can significantly reduce the power consumption of the temperature control system while ensuring temperature control accuracy; and the use of an all-fiber structure can make the structure of the detection device more compact, without the need for complex spatial optical path alignment, and easy to use and maintain; in addition, the high optical power density in the hollow-core optical fiber is fully utilized to further shorten the effective optical path, so that it can still work normally even under high gas concentrations, and the gas concentration range that can be detected is wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a block diagram of the structural principle of an all-fiber carbon isotope detection system of the present invention;

[0042] Figure 2 This is a block diagram of the structural principle of a hollow-core optical fiber gas chamber of an all-optical carbon isotope detection system of the present invention;

[0043] Figure 3 This is a schematic cross-sectional view of a hollow-core antiresonant optical fiber of an all-fiber carbon isotope detection system according to the present invention;

[0044] Figure 4 The carbon dioxide isotope absorption spectrum line within the wavelength tunable range of the pump light used in the all-fiber carbon isotope detection system of the present invention;

[0045] Figure 5 This is the second harmonic signal of 5% concentration of natural isotope abundance CO2 measured by the all-fiber carbon isotope detection system of the present invention when in use;

[0046] Figure 6 A graph showing changes in carbon isotope absorption peaks within 6 hours measured by an all-fiber carbon isotope detection system of the present invention;

[0047] Figure 7 This is a graph showing relative changes in carbon isotope ratios within 6 hours measured by an all-fiber carbon isotope detection system of the present invention;

[0048] Figure 8 This is a graph showing the carbon isotope detection accuracy of an all-fiber carbon isotope detection system of the present invention under different CO2 concentrations when used;

[0049] Figure 9 This is a flowchart of an all-fiber-based carbon isotope detection method of the present invention.

[0050] The numbers in the figure are: 100, detection light source; 210, delay optical fiber; 220, input optical fiber; 230, optical fiber ring path; 231, hollow-core optical fiber air chamber; 232, hollow-core optical fiber body; 233, solid-core single-mode optical fiber pigtail; 234, first optical fiber coupler; 235, second optical fiber coupler; 236, wavelength division multiplexer; 240, photodetector; 250, optical fiber coupler; 260, temperature control module; 300, pump light source; 400, data processing controller. DETAILED DESCRIPTION

[0051] The present invention provides an all-fiber-based carbon isotope detection system. To further clarify the objectives, technical solutions, and advantages of the present invention, the present invention is described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0052] Example 1

[0053] like Figure 1As shown, this embodiment provides an all-fiber carbon isotope detection system that can be used to detect the concentrations of different carbon isotopes in gas. This all-fiber carbon isotope detection system primarily includes a detection light source 100, a delay fiber 210, an input fiber 220, a fiber annular channel 230, a pump light source 300, a photodetector 240, and a data processing controller 400. The delay fiber 210 and the input fiber 220 are both used to connect to the detection light source 100. The detection light emitted by the detection light source 100 is transmitted through the delay fiber 210 and the input fiber 220 respectively, so that the detection light is divided into two paths. The detection light has different delays after passing through the delay fiber 210 and the input fiber 220, that is, the detection light has different transmission times in the delay fiber 210 and the input fiber 220. Since the other end of the delay fiber 210 and the other end of the input fiber 220 are respectively connected to the optical fiber ring path 230, the time when the two paths of detection light arrive at the optical fiber ring path 230 is different. Such difference can facilitate the processing of different detection lights in the subsequent detection process, and the phase change of the detection light can be obtained. The optical fiber annular passage 230 includes a hollow-core optical fiber chamber 231, the opposite ends of the hollow-core optical fiber chamber 231 are respectively connected to the output end of the delay optical fiber 210 and the output end of the input optical fiber 220. The hollow-core optical fiber chamber 231 is filled with a gas containing carbon isotopes to be detected. The two detection lights pass through the gas to be detected in the hollow-core optical fiber chamber 231 in opposite directions, so that one of the two detection lights propagates in the optical fiber annular passage 230 in a clockwise direction, and the other propagates in the optical fiber annular passage 230 in a counterclockwise direction, passing through the hollow-core optical fiber chamber 231 multiple times during the cyclic propagation process. The pump light source 300 is connected to the fiber annular passage 230 and is used to generate pump light that is passed into the hollow-core fiber chamber 231. The pump light acts on the gas within the hollow-core fiber chamber 231, causing the phase of the probe light to shift. Specifically, the pump light enters the hollow-core fiber chamber 231 and interacts with the gas therein, releasing heat, causing changes in the gas temperature and refractive index. These changes in temperature and refractive index cause the phase of the probe light along the same path to shift. The phase-shifted probe light then passes through the input fiber 220 and the delay fiber 210, respectively, and enters the photodetector 240. The photodetector 240 receives the phase-shifted probe light transmitted back from the delay fiber 210 and the input fiber 220, and converts the received optical signal into an electrical signal for signal processing. By analyzing the phase shift of the received probe light, changes in the refractive index can be detected. A higher concentration of carbon isotopes in the gas molecules corresponds to a greater refractive index shift. Therefore, the refractive index shift can be used to detect the carbon isotope concentration in the gas molecules.The data processing controller 400 is electrically connected to the photodetector 240 and the pump light source 300, respectively, so that the pump light source 300 can be controlled so that the pump light emitted by the pump light source 300 meets the requirements. In addition, the data processing controller 400 can receive the detection light signal received by the photodetector 240 and analyze and process the signal to obtain the concentration information of a certain carbon isotope or the concentration information of different carbon isotopes.

[0054] In this solution, the scanned pump light enters the hollow-core fiber chamber 231 through a wavelength division multiplexer 236, where it interacts with gas molecules, releasing heat and changing the gas's refractive index. This causes the probe light's phase to change after passing through the hollow-core fiber chamber 231. Based on the principle that a higher concentration of carbon isotopes in the gas molecules results in a greater change in the refractive index, the change in refractive index can be determined by detecting the phase change of the probe light after the phase shift, thereby reflecting the carbon isotope concentration. Furthermore, by using two probe lights, one clockwise and one counterclockwise, within the hollow-core fiber chamber 231, the optical paths of the two light paths in the fiber ring path 230 are perfectly matched, thus automatically locking the operating point without any feedback control, thereby improving detection accuracy. The detection light passes through the hollow-core optical fiber chamber 231 multiple times in the optical fiber ring passage 230, which can effectively amplify the photothermal phase signal, thereby obtaining more accurate gas concentration information. The optical fiber ring passage 230 can pass through the hollow-core optical fiber chamber 231 multiple times, thereby extending the optical path within a limited area, meeting the requirement of extending the optical path while greatly reducing the chamber structure.

[0055] In addition to detecting the concentration of a single carbon isotope in a gas molecule by the change in refractive index, this embodiment can detect the concentration of different carbon isotopes in a gas molecule. The working principle is that different carbon isotopes have different absorption wavelengths (such as Figure 4(See the carbon dioxide isotope absorption spectrum shown in Figure 2). When pump light of different wavelengths is scanned into hollow-core fiber chamber 231 and interacts with the gas to release heat, if the wavelength of the current pump light corresponds to the absorption wavelength of a carbon isotope, the gas experiences significant heat and refractive index changes during the input period of that wavelength. This results in a significant phase shift in the probe light after it passes through hollow-core fiber chamber 231. Therefore, by scanning pump light of different wavelengths, the phase shift amplitude is closely related to the wavelength of the pump light. Different carbon isotopes have different absorption wavelengths. Therefore, the phase shift amplitude can reflect the carbon isotope concentration at different absorption wavelengths, thereby reflecting the concentration information of carbon isotopes at different absorption wavelengths. Using the same detection optical path allows simultaneous scanning of different carbon isotope absorption lines, effectively suppressing the effects of common-mode noise such as light source power drift, wavelength drift, and slow environmental perturbations, improving system stability and carbon isotope detection accuracy. Thanks to its short optical path, this method can detect carbon isotopes across a wide range of gas concentrations.

[0056] Furthermore, the 3-dB spectral width of the probe light generated by the detection light source 100 is no less than 1 nm, for example, 30 nm, and the optical power is 10 mW. Using this probe light facilitates subsequent acquisition of the probe light after the phase shift, improving detection accuracy. The detection light source 100 in this embodiment includes, but is not limited to, an amplified spontaneous emission fiber light source, a superluminescent diode, a supercontinuum light source, and the like.

[0057] like Figure 1As shown, further, the fiber ring passage 230 in this embodiment also includes: a first fiber coupler 234 and a second fiber coupler 235. The first fiber coupler 234 has a first port, a second port, and a first common port. The first port is connected to the delay fiber 210, and the first common port is connected to one end of the hollow-core fiber chamber 231. The second fiber coupler 235 has a third port, a fourth port, and a second common port. The third port is connected to the input fiber 220, and the second common port is connected to the other end of the hollow-core fiber chamber 231. The second port is connected to the fourth port, so that the probe light propagates within the first fiber coupler 234, the second fiber coupler 235, and the hollow-core fiber chamber 231 and passes through the hollow-core fiber chamber 231 multiple times. It should be noted that the second port and the fourth port are both ports with relatively high optical splitting ratios and are directly connected. One path of probe light from the delay fiber 210 enters the first port, then enters the hollow-core fiber chamber 231 from the first common port. After passing through the gas and undergoing phase change, the probe light enters the second common port of the second fiber coupler 235. Part of the probe light is then emitted through the input fiber 220, and part enters the second port through the fourth port, forming a loop. Similarly, the second path of probe light also circulates through the fiber annular passage 230 in this manner, passing through the hollow-core fiber chamber 231 multiple times. This annular optical path not only achieves a compact structure but also ensures that the probe light undergoes phase change over a longer distance within the hollow-core fiber chamber 231, thereby improving detection accuracy.

[0058] Furthermore, the splitting ratio between the second port and the first port of the first fiber coupler 234 is no less than 7:3; and the splitting ratio between the fourth port and the third port of the second fiber coupler 235 is no less than 7:3. The two ports with higher splitting ratios are directly connected, so that when the probe light is split, a larger amount of the probe light remains in the fiber annular passage 230. This allows most of the probe light to circulate within the annular optical path, allowing the probe light to pass through the hollow-core fiber chamber 231 multiple times, thereby extending the effective range of the probe light.

[0059] Furthermore, the splitting ratios at the first port are 2%, the splitting ratios at the second port are 98%, the splitting ratios at the third port are 2%, and the splitting ratios at the fourth port are 98%. Using the first fiber coupler 234 and the second fiber coupler 235 with these ratios allows the probe light to circulate more times within the fiber ring path 230, thereby enabling the subsequent effective amplification of the photothermal phase signal of the probe light, thereby obtaining more accurate gas concentration information and more precise detection results.

[0060] like Figure 1As shown, further, in this embodiment, the second common port is connected to the other end of the hollow-core fiber chamber 231 via a wavelength division multiplexer 236. The wavelength division multiplexer 236 is also used to connect to the pump light source 300 and multiplex the pump light and probe light emitted by the pump light source 300. The wavelength division multiplexer 236 is connected to the fiber ring passage 230, allowing the pump light to enter the hollow-core fiber chamber 231, thereby interacting with the gas to be detected in the hollow-core fiber chamber 231 to change its temperature and refractive index.

[0061] To detect the concentrations of different carbon isotopes, the pump light emitted by the pump light source 300 is tuned to a wavelength that covers different carbon isotope absorption lines, with a tunable range of at least 0.5 nm. For example, the pump light wavelength can be adjusted from 1991 to 1995 nm. In the 1991-1995 nm band, 12CO2 and 13CO2 exhibit strong absorption lines with similar frequencies. This allows the concentrations of two different carbon isotopes to be determined by scanning the wavelength with the same pump light source. Furthermore, the pump light wavelength is simultaneously modulated at high frequency and swept at low frequency. The modulation frequency is no less than 1 kHz and can range from 1 kHz to 100 kHz. If the modulation frequency is too low, the system is susceptible to interference from low-frequency ambient noise, resulting in excessive noise. If the modulation frequency is too high, the refractive index change caused by the interaction between light and gas takes a considerable time (typically on the order of μs). This can cause the refractive index change to fail to keep pace with the modulation rate, resulting in a reduced signal and a poor signal-to-noise ratio. Therefore, it is preferred that the modulation frequency is between 1kHz-100kHz, for example, 25kHz can be used. The scanning frequency is not less than 1mHz, and is between 1mHz-1Hz. The scanning frequency mainly determines the time of a single measurement. If the scanning frequency is low, the single measurement time is long and the measurement speed is slow. On the other hand, scanning is achieved through temperature tuning. If the scanning frequency is too high, the temperature adjustment cannot keep up with the scanning speed, which will cause signal distortion. Therefore, it is preferred that the scanning frequency is between 1mHz-1Hz. The optical power is not less than 1mW. Through the above parameters, the signal after the detected detection light changes phase can be made clearer, which greatly improves the detection accuracy of the concentrations of different carbon isotopes.

[0062] The pump light source 300 in this embodiment includes a DFB seed laser and a thulium-doped fiber amplifier, which is connected to the DFB seed laser. The wavelength tuning range of the DFB seed laser is 1991-1995 nm; the output optical power of the thulium-doped fiber amplifier can be 200 mW. The current modulation frequency of the pump light source 300 composed of the DFB seed laser and thulium-doped fiber amplifier of this specification can reach 25 kHz, and the temperature scanning frequency can be 100 mHz. Using this specification, the pump light source 300 can emit pump light of different wavelengths, which are basically suitable for detecting different carbon isotope molecules.

[0063] The white light detection light with a central wavelength of 1550nm and the pump light with a central wavelength of 1993nm are combined through the wavelength division multiplexer 236, wherein the port for passing the 1550nm wavelength is connected to the second fiber coupler 235, and the port for passing the 1993nm wavelength is connected to the pump light source 300.

[0064] Furthermore, the delay fiber 210 and the input fiber 220 are connected to the detection light source 100 via a fiber coupler 250. The fiber coupler 250 can be a 3x3 fiber coupler with three input ports and three output ports. One input port of the fiber coupler 250 is connected to the detection light source 100, while the other two input ports are connected to the photodetector 240. One output port of the fiber coupler 250 is connected to the delay fiber 210, one output port is left unused and beveled to suppress reflection, and the third output port is connected to the input fiber 220. The fiber coupler 250 enables both the emission of the detection light and the reception of the phase-modified detection light. This simple structure and miniaturization of the device facilitate the transmission and reception of the probe light. The ideal splitting ratio of the 3x3 fiber coupler is 1:1:1, with a relative error of no more than 20%, which improves detection accuracy.

[0065] Furthermore, the delay optical fiber 210 is a single-mode optical fiber for communication, and the length thereof is 1 km. In this way, the delay effect is effectively achieved under the premise of limited length, which facilitates the subsequent reception and detection of the detection light.

[0066] like Figure 2 As shown, the hollow-core fiber chamber 231 further includes a hollow-core fiber body 232 and a solid-core single-mode fiber pigtail 233. The solid-core single-mode fiber pigtail 233 is fixed to each end of the hollow-core fiber body 232. The end faces of the solid-core single-mode fiber pigtail 233 are each beveled at an 8° angle. The solid-core single-mode fiber pigtail 233 and the hollow-core fiber body 232 are aligned and connected mechanically or by fusion splicing. The length of the hollow-core fiber body 232 is no less than 1 cm and no longer than 10 meters.

[0067] Furthermore, the hollow core fiber body 232 includes but is not limited to one or more of a hollow core photonic bandgap fiber, a hollow core antiresonant fiber, and a hollow core waveguide. Figure 3 As shown, the hollow-core fiber body 232 in this embodiment may be a hollow-core anti-resonant fiber, and the length of the hollow-core fiber body 232 may be 15 cm.

[0068] Furthermore, the carbon isotope detection device also includes a temperature control module 260, which is used to cool and heat the hollow-core fiber chamber 231. By installing the temperature control module 260 on the hollow-core fiber chamber 231 and controlling the temperature of the hollow-core fiber chamber 231 through the temperature control module 260, the core temperature of the hollow-core fiber body 232 can be precisely controlled, thereby facilitating laser frequency stabilization.

[0069] The temperature control module 260 can use a semiconductor refrigeration chip for heating or cooling, and the current size and direction passing through the semiconductor refrigeration chip are controlled by PID, thereby controlling the temperature of the semiconductor refrigeration chip, and the temperature control accuracy is better than 0.01°C.

[0070] Furthermore, the photodetector 240 is a balanced photodetector 240 having two optical input ports, which are respectively connected to two input ports of the fiber coupler 250 . The common mode noise suppression ratio of the balanced photodetector 240 is not less than 20 dB, and the response bandwidth is 1 MHz.

[0071] Furthermore, the data processing controller 400 has a sampling rate of no less than 1 MB / s, a sampling bit number of no less than 12 bits, and a signal generation module capable of generating arbitrary waveform signals with a maximum output frequency of no less than 10 kHz. The data processing controller 400 in this embodiment is developed based on an FPGA platform and is capable of providing sinusoidal modulation and triangular wave scanning signals, enabling the acquisition and processing of the output signal of the photodetector 240.

[0072] The inspection results of the all-fiber-optic carbon isotope detection system in this solution are as follows:

[0073] like Figure 5 As shown, by scanning with pump light of different wavelengths at a CO2 concentration of 5%, the second harmonic signal corresponding to the absorption spectrum line in the figure can be measured, among which the 12CO2 R(68) and 13CO2 R(38) signals are clearly visible.

[0074] like Figure 6 As shown in , by continuously measuring for 6 hours and extracting the peaks at the corresponding positions of the two spectral lines; Figure 7 As shown, the relative deviation of the carbon isotope ratio is further calculated according to the equation. Under a 60-minute sliding average, the carbon isotope detection accuracy can reach 0.19‰.

[0075] like Figure 8 As shown, further testing of various CO2 concentrations revealed a detection accuracy better than 0.3‰ within the 1%-100% concentration range. Even at a CO2 concentration of 1000ppm, the detection accuracy remained around 3‰. This accuracy could be further improved by increasing the hollow-core fiber length or increasing the pump light source power by 300 ns.

[0076] Example 2

[0077] like Figure 9 As shown, this embodiment provides an all-fiber carbon isotope detection method, which is used in the all-fiber carbon isotope detection system described in Example 1. The method includes the following steps:

[0078] Step S100: Generate pump light through a pump light source and allow the pump light to enter a hollow-core fiber chamber filled with a gas to be detected, wherein the pump light interacts with gas molecules to release heat, changing the temperature and refractive index of the gas.

[0079] Step S200: Detection light is emitted from a detection light source, so that the detection light enters the optical fiber ring path through the delay optical fiber and the input optical fiber respectively, and enters the hollow-core optical fiber air chamber from opposite ends respectively; wherein the phase of the detection light changes after passing through the gas with changed temperature and refractive index.

[0080] Step S300: receiving the phase-changed detection light through a photodetector, and performing phase detection on the detection light to obtain a refractive index change after the gas interacts with the pump light;

[0081] Step S400: Acquire carbon isotope concentration information based on the relationship between the concentration of gas molecules carrying carbon isotopes and the change in refractive index.

[0082] Through the above steps, a fixed wavelength pump light can be used to detect the concentration of a single carbon isotope in gas molecules. If the concentrations of different carbon isotopes in gas molecules need to be detected, different wavelengths of pump light need to be input. The specific solution is as follows:

[0083] In step S100, pump light of different wavelengths is generated by a pump light source, and the pump light of different wavelengths is respectively entered into a hollow-core optical fiber chamber for scanning, wherein the hollow-core optical fiber chamber is filled with gases with different carbon isotopes, and gas molecules with different carbon isotopes have different absorption wavelengths.

[0084] After executing the above step S200, since the phase change of the detection light is proportional to the absorption amount of the pump light of different wavelengths, the detection light after the phase change is received by the photodetector, and the phase of the detection light is detected to obtain the refractive index change after the gas interacts with the pump light.

[0085] Therefore, based on the relationship between the concentration of gas molecules with different carbon isotopes and the change in refractive index, different carbon isotope concentration information can be obtained. Because the phase change amplitude is closely related to the wavelength of the pump light, it can reflect the carbon isotope concentration at different absorption wavelengths.

[0086] In summary, the present invention proposes a fully optical fiber carbon isotope detection system and detection method, wherein an optical fiber annular path is adopted so that the detection light can be circulated into the hollow-core optical fiber air chamber, thereby achieving effective amplification of the phase signal of the detection light, while meeting the detection accuracy and reducing the volume of the air chamber, and the annular light passage optimizes the structure, so that the gas consumption used for calibration and detection is small, which can be applied to application scenarios with small sample gas volume such as breath detection and deep-sea dissolved gas detection, and the small air chamber can significantly reduce the power consumption of the temperature control system while ensuring temperature control accuracy; and the adoption of an all-optical fiber structure can make the structure of the detection device more compact, without the need for complex spatial optical path alignment and easy to use and maintain; in addition, by making full use of the high optical power density in the hollow-core optical fiber, the effective optical path can be further shortened, and it can still work normally even at high gas concentrations, and the gas concentration range that can be detected is wider. The system has the characteristics of simple structure, fast measurement speed, low gas consumption and high stability, and has unique advantages and good application prospects in the fields of Helicobacter pylori breath detection, deep-sea methane hydrate detection, oil and gas exploration, etc.

[0087] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An all-fiber carbon isotope detection system, characterized in that: include: A detection light source, configured to emit detection light; A delay optical fiber and an input optical fiber, wherein the delay optical fiber and the input optical fiber are both connected to the detection light source, and the detection light has different delays after passing through the delay optical fiber and the input optical fiber; An optical fiber annular passage, comprising a hollow-core optical fiber chamber, wherein opposite ends of the hollow-core optical fiber chamber are respectively connected to an output end of the delay optical fiber and an output end of the input optical fiber, the detection light propagates in the optical fiber annular passage and circulates through the hollow-core optical fiber chamber; the hollow-core optical fiber chamber is filled with a gas to be detected; a pump light source connected to the optical fiber annular passage and configured to generate pump light and pass it into the hollow-core optical fiber chamber, wherein the temperature and refractive index of the gas are changed by the pump light, and the phase of the probe light is changed by the gas in the hollow-core optical fiber chamber; a photodetector for receiving the phase-changed detection light transmitted back from the delay optical fiber and the input optical fiber; A data processing controller is electrically connected to the photodetector and the pump light source respectively.

2. The all-fiber carbon isotope detection system according to claim 1, characterized in that: The detection light source includes: an amplified spontaneous emission fiber light source, a superluminescent diode or a supercontinuum light source.

3. The all-fiber carbon isotope detection system according to claim 2, characterized in that: The wavelength of the pump light emitted by the pump light source is tunable, and the tunable range of the wavelength of the pump light covers different carbon isotope absorption lines; The wavelength of the pump light is simultaneously subjected to high-frequency modulation and low-frequency scanning.

4. The all-fiber carbon isotope detection system according to claim 3, characterized in that: The pump light source comprises: a DFB seed laser, wherein the wavelength of the pump light emitted by the DFB seed laser is tunable within a predetermined range; A thulium-doped fiber amplifier is connected to the DFB seed laser.

5. The all-fiber carbon isotope detection system according to claim 1, characterized in that: The optical fiber annular passage further includes: a first optical fiber coupler, the first optical fiber coupler having a first port, a second port and a first common port, the first port being connected to the delay optical fiber, and the first common port being connected to one end of the hollow-core optical fiber air chamber; a second optical fiber coupler having a third port, a fourth port, and a second common port, wherein the third port is connected to the input optical fiber, and the second common port is connected to the other end of the hollow-core optical fiber air chamber; The second port is connected to the fourth port, so that the detection light propagates in the first fiber coupler, the second fiber coupler and the hollow-core fiber air chamber and passes through the hollow-core fiber air chamber multiple times.

6. The all-fiber carbon isotope detection system according to claim 5, characterized in that: The second common port is connected to the other end of the hollow-core optical fiber chamber via a wavelength division multiplexer. The wavelength division multiplexer is connected to the pump light source and is used to combine the pump light and the probe light emitted by the pump light source.

7. The all-fiber carbon isotope detection system according to claim 5, characterized in that: The splitting ratio between the second port and the first port of the first optical fiber coupler is not less than 7:3; The splitting ratio between the fourth port and the third port of the second optical fiber coupler is not less than 7:

3.

8. The all-fiber carbon isotope detection system according to claim 1, characterized in that: The delay optical fiber and the input optical fiber are connected to the detection light source via an optical fiber coupler; The optical fiber coupler includes at least three input ports and two output ports; One input port of the optical fiber coupler is connected to the detection light source, and the other two input ports are connected to the photodetectors respectively; One output port of the optical fiber coupler is connected to the delay optical fiber, and the other output port is connected to the input optical fiber; The carbon isotope detection device further includes a temperature control module, which is used to cool and heat the hollow-core optical fiber air chamber.

9. A fully optical fiber carbon isotope detection method, characterized in that: For the all-fiber-based carbon isotope detection system according to any one of claims 1 to 8, the method comprises the following steps: Generate pump light through a pump light source, and allow the pump light to enter a hollow-core optical fiber air chamber filled with a gas to be detected, wherein the pump light interacts with gas molecules to release heat, thereby changing the temperature and refractive index of the gas; The detection light source emits a probe light, which enters the optical fiber ring path through the delay optical fiber and the input optical fiber, and enters the hollow-core optical fiber air chamber from opposite ends respectively; wherein the phase of the probe light changes after passing through the gas with changed temperature and refractive index; Receiving the detection light after the phase change through a photodetector, and performing phase detection on the detection light to obtain the refractive index change after the gas interacts with the pump light; The carbon isotope concentration information is obtained based on the relationship between the concentration of gas molecules carrying carbon isotopes and the change in refractive index.

10. The all-fiber carbon isotope detection method according to claim 9, characterized in that: In the step of generating pump light by a pump light source and allowing the pump light to enter a hollow-core optical fiber air chamber, and filling the hollow-core optical fiber air chamber with a gas to be detected: generating pump lights of different wavelengths by a pump light source, and allowing the pump lights of different wavelengths to enter a hollow-core optical fiber air chamber for scanning, wherein the hollow-core optical fiber air chamber is filled with gases with different carbon isotopes, and gas molecules with different carbon isotopes have different absorption wavelengths; In the step of receiving the probe light after the phase change by a photodetector and performing phase detection on the probe light to obtain the refractive index change of the gas after the pump light interacts with the gas, the phase change of the probe light is proportional to the absorption amount of the pump light of different wavelengths; In the step of obtaining carbon isotope concentration information based on the relationship between the concentration of gas molecules carrying carbon isotopes and the change in refractive index: different carbon isotope concentration information is obtained based on the relationship between the concentration of gas molecules carrying different carbon isotopes and the change in refractive index.

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