High-sensitivity gas detection system based on anti-resonance hollow-core optical fiber

Abstract

The invention discloses a high-sensitivity gas detection system based on an anti-resonance hollow-core optical fiber, relates to the technical field of gas detection structures, and aims to improve the sensitivity of the gas detection system. The system comprises a signal generation module, an optical fiber ring cavity ring-down module and a signal detection module. The first end of the optical fiber coupler is connected with the signal generation module, and the second end of the optical fiber coupler is connected with the signal detection module; the third end of the optical fiber coupler is connected with the first end of the gas chamber, the second end of the gas chamber is connected with the first end of the erbium-doped optical fiber amplifier, the second end of the erbium-doped optical fiber amplifier is connected with the first end of the optical fiber extender, and the second end of the optical fiber extender is connected with the fourth end of the optical fiber coupler. And the optical fiber ring cavity ring-down module is used for receiving the periodic rectangular pulse optical signal, circularly realizing the ring-down effect of the optical signal in the cavity, and coupling and outputting part of the optical signal in the ring-down process to the signal detection module through the third end of the optical fiber coupler.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection structures, and in particular to a high-sensitivity gas detection system based on anti-resonance hollow-core optical fiber. Background Art

[0002] Ultra-high-sensitivity optical gas sensors, leveraging the high sensitivity and low cost of absorption spectroscopy, have become a research hotspot in fields such as environmental monitoring, medical diagnosis, and industrial control. However, the effective absorption pathlength directly determines the sensitivity of gas detection and is a key technical bottleneck that urgently needs to be overcome. Existing technical solutions for extending the effective absorption optical path have their pros and cons. Multi-pass cell technology achieves long optical paths through multiple reflections, but its complex optical path structure requires stringent installation precision, resulting in cumbersome operation and poor stability in practical applications. While hollow-core fiber chambers can extend the optical path by increasing their length and offer the advantage of compactness, their cost increases exponentially with length, limiting their widespread adoption. Fiber ring cavity ring-down spectroscopy systems can achieve an exponential increase in optical path length within a limited space, but to ensure system compactness, the chamber size is limited, impacting detection performance. Summary of the Invention

[0003] The purpose of the present invention is to provide a highly sensitive gas detection system based on antiresonant hollow-core optical fiber, aiming to improve the sensitivity of the gas detection system.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a highly sensitive gas detection system based on an antiresonant hollow-core optical fiber, the system comprising: a signal generation module, a fiber ring cavity ring-down module, and a signal detection module; the fiber ring cavity ring-down module comprises a fiber coupler, an air chamber, an erbium-doped fiber amplifier, and a fiber extender; the first end of the fiber coupler is connected to the signal generation module, and the second end of the fiber coupler is connected to the signal detection module; the third end of the fiber coupler is connected to the first end of the air chamber, the second end of the air chamber is connected to the first end of the erbium-doped fiber amplifier, the second end of the erbium-doped fiber amplifier is connected to the first end of the fiber extender, and the second end of the fiber extender is connected to the fourth end of the fiber coupler; the signal generation module is configured to output a periodic rectangular pulse light signal; the fiber ring cavity ring-down module is configured to receive the periodic rectangular pulse light signal, cyclically realize the ring-down effect of the light signal in the cavity, and couple part of the light signal in the ring-down process to the signal detection module through the third end of the fiber coupler; wherein the light signal circulates through the air chamber; and the signal detection module is configured to detect the signal coupled out by the third end of the fiber coupler.

[0005] The gas chamber in the highly sensitive gas detection system provided in some embodiments of the present application is based on an antiresonant hollow-core fiber. The unique structure of the antiresonant hollow-core fiber allows light to propagate primarily within the air core, resulting in a spot size significantly larger than that of conventional optical fibers. This means that the light energy is distributed over a larger cross-section. This direct, large-area interaction significantly increases the probability that the light signal will be absorbed by the gas under test during a single pass through the gas chamber. According to the principle of ring-down spectroscopy, the stronger the absorption, the more pronounced the reduction in ring-down time. Therefore, even low-concentration gas can result in observable changes in ring-down time, significantly improving detection capabilities for low-concentration gases. The light signal circulates multiple times within the annular cavity, passing through the gas chamber with each pass. This results in multiple interactions between the light signal and gas molecules. Even slight changes in absorption during a single pass are accumulated and amplified over multiple passes, manifesting as significant differences in ring-down time. Furthermore, the multiple-pass design significantly extends the optical path (equivalent optical path = physical cavity length × number of passes), eliminating the need to physically create an extremely long absorption path. This reduces costs while improving detection efficiency.

[0006] In some embodiments, the air chamber includes an antiresonant hollow-core fiber, a ceramic ferrule, and a single-mode fiber; the two ends of the antiresonant hollow-core fiber are respectively mechanically coupled to two single-mode fibers at a certain gap through an open ceramic ferrule having the same outer diameter as the antiresonant hollow-core fiber.

[0007] In some embodiments, the signal generation module includes a continuous wave laser, an optoelectronic modulator, a signal generator, and an isolator; the continuous wave laser is connected to the first end of the optoelectronic modulator, the second end of the optoelectronic modulator is connected to the first end of the isolator, the second end of the isolator is connected to the first end of the optical fiber coupler, and the third end of the optoelectronic modulator is connected to the signal generator.

[0008] In some embodiments, the signal detection module includes a photodetector and an oscilloscope; the second end of the fiber optic coupler is connected to the first end of the photodetector, and the second end of the photodetector is connected to the oscilloscope.

[0009] In some embodiments, the continuous wave laser has a center wavelength of 1567 nm.

[0010] In some embodiments, the fiber coupler includes a first input port, a second input port, a first output port, and a second output port. The first end of the fiber coupler is the first input port. The fourth end of the fiber coupler is the second input port. The second end of the fiber coupler is the first output port. The third end of the fiber coupler is the second output port.

[0011] In some embodiments, the splitting ratio of the input port to the output port of the fiber coupler is 90:10, wherein the input port of the fiber coupler includes a first input port and a second input port, and the output port of the fiber coupler includes a first output port and a second output port.

[0012] In some embodiments, the antiresonant hollow core fiber is 1 m.

[0013] In some embodiments, the gas cell has a limiting loss of 0.92 dB / km at the center wavelength of laser light emitted by a continuous wave laser.

[0014] In some embodiments, the dual-air path interface assembly includes a first single-mode optical fiber and a second single-mode optical fiber; the first single-mode optical fiber is connected to one end of the antiresonant hollow-core optical fiber, and the second single-mode optical fiber is connected to the other end of the antiresonant hollow-core optical fiber to form a cascade structure.

[0015] In some embodiments, the erbium-doped fiber amplifier has a gain of 2 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 A schematic structural diagram of a highly sensitive gas detection system based on antiresonant hollow-core optical fiber provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] In the description of the invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "back," "inner," "outer," and the like, indicating directions or positional relationships, are based on the directions or relative positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction. Therefore, they should not be construed as limitations on the invention. Unless otherwise specified, the above-mentioned directions may be flexibly set in actual application, provided that the relative positional relationships shown in the accompanying drawings are met.

[0020] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," and "communicated" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections. They may be directly connected, indirectly connected through an intermediary, or internally connected between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0022] In embodiments of the present invention, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of other identical elements in the process, article, or apparatus comprising the element.

[0023] In the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present invention should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0024] In cutting-edge fields such as atmospheric environmental monitoring, medical respiratory diagnostics, and industrial process control, ultra-high-sensitivity optical gas sensors based on absorption spectroscopy detection technology have become the focus of academic research and industrial applications due to their dual advantages of high sensitivity and low cost. However, the effective absorption pathlength, a key parameter determining gas detection sensitivity, has become a key technical bottleneck restricting improvements in sensing performance. Existing optical path extension technologies are experiencing diversified development, but all have significant limitations. For example, multi-pass cell technology achieves long optical path detection through a precisely designed, multiple-reflection structure. However, its complex optical architecture requires extremely high optical path calibration accuracy. In practical applications, it often faces problems such as difficult installation and debugging and poor environmental adaptability, which greatly limits the system's engineering applications.

[0025] Hollow-core fiber chambers extend optical path length and offer the advantage of high spatial integration, but their manufacturing costs increase nonlinearly with length, leading to high costs for large-scale deployment. While fiber ring cavity ring-down spectroscopy systems can achieve an exponential increase in optical path length within a limited physical space, the compact design requirements of the system limit the chamber volume, which in turn affects the effective detection concentration range of trace gases. Faced with the contradiction between structural complexity, cost-effectiveness and detection performance of the above technologies, developing a trace gas detection system with a highly integrated structure and excellent detection sensitivity is not only the key to breaking through the existing technological bottleneck, but also an important direction to promote the practical application and industrialization of optical gas sensing technology.

[0026] In view of this, the embodiment of the present application provides a highly sensitive gas detection system based on antiresonant hollow core fiber, for example, Figure 1 The high-sensitivity gas detection system 100 includes: a signal generation module 20 , a fiber ring cavity ring-down module 30 and a signal detection module 40 .

[0027] The signal generation module 20 is used to output a periodic rectangular pulse optical signal. The fiber ring cavity ring-down module 30 is used to receive the periodic rectangular pulse optical signal, cyclically realize the ring-down effect of the optical signal in the cavity, and output part of the optical signal during the ring-down process to the signal detection module 40 through coupling.

[0028] Furthermore, the fiber ring cavity ring-down module 30 includes a fiber coupler 5, an air chamber 6, an erbium-doped fiber amplifier 7, and a fiber extender 8. The first end of the fiber coupler 5 is connected to the signal generation module 20, and the second end of the fiber coupler 5 is connected to the signal detection module 40. The third end of the fiber coupler 5 is connected to the first end of the air chamber 6, the second end of the air chamber 6 is connected to the first end of the erbium-doped fiber amplifier 7, the second end of the erbium-doped fiber amplifier 7 is connected to the first end of the fiber extender 8, and the second end of the fiber extender 8 is connected to the fourth end of the fiber coupler 5.

[0029] As a possible implementation, refer to Figure 1 The signal generation module 20 includes a continuous wave laser 1, an electro-optical modulator 2, a signal generator 3, and an isolator 4. The continuous wave laser 1 is connected to a first end of the electro-optical modulator 2, a second end of the electro-optical modulator 2 is connected to a first end of the isolator 4, a second end of the isolator 4 is connected to a first end of the optical fiber coupler 5, and a third end of the electro-optical modulator 2 is connected to the signal generator 3.

[0030] As a possible implementation, refer to Figure 1The signal detection module 40 includes a photodetector 9 and an oscilloscope 10 . The second end of the fiber optic coupler 5 is connected to the first end of the photodetector 9 , and the second end of the photodetector 9 is connected to the oscilloscope 10 .

[0031] A continuous wave laser (CW laser) 1 is a device that can continuously and uninterruptedly output laser light, providing a constant power output. As one possible implementation, the CW laser 1 provided in the embodiments of this application continuously outputs laser light with a central wavelength of 1567 nm.

[0032] Signal generator 3 is a device capable of providing electrical signals of various frequencies, waveforms, and output levels. It is also known as a signal source or oscillator. It serves as a test signal source or excitation source when measuring the amplitude, frequency, transmission, and other electrical parameters of various telecommunications systems or equipment, as well as when measuring the characteristics and parameters of components. In this embodiment of the present application, the optoelectronic modulator 2 can be used to separate the gas absorption signal from the DC noise by frequency or intensity modulating the continuous laser light. Combined with phase-locked amplification technology, this significantly improves the signal-to-noise ratio.

[0033] As one possible implementation, signal generator 3 generates a continuous, periodic square wave signal. The continuous-wave laser 1, through the coordinated action of electro-optical modulator 2 and signal generator 3, is modulated into periodic rectangular pulses, which are then transmitted to the first end of isolator 4. Isolator 4 prevents electromagnetic interference during the detection process, avoiding signal distortion that could occur due to electromagnetic interference, thereby ensuring accuracy during signal transmission and improving gas detection precision. The isolator also prevents reflected light from returning to the laser, protecting the laser.

[0034] After passing through isolator 4, the rectangular pulse light is transmitted to fiber coupler 5. In some embodiments, the fiber coupler includes an input port and an output port, wherein the input port includes a first input port and a second input port. The output port includes a first output port and a second output port. The first end of the fiber coupler is the first input port. The fourth end of the fiber coupler is the second input port. The second end of the fiber coupler is the first output port. The third end of the fiber coupler is the second output port.

[0035] The optical fiber coupler 5, also known as a splitter, connector, adapter, or fiber flange, is a passive optical component. It utilizes a precisely designed waveguide structure and the coupling effect of optical waveguides to distribute, combine, or extend optical signals within a fiber optic link. Optical signals enter the optical fiber coupler 5 through the input port, where they interfere and couple within the coupler, leaving the coupler 5 through the output port after the predetermined split. For example, the splitting ratio between the input and output ports of the optical fiber coupler 5 is 90:10.

[0036] In the highly sensitive gas detection system 100 provided in the embodiment of the present application, the periodic rectangular pulse light transmitted to the input port of the optical fiber coupler 5 through the isolator 4 enters the optical fiber ring cavity, which includes the optical fiber coupler 5, the gas chamber 6, the erbium-doped fiber amplifier 7 and the optical fiber extender 8. Most of the periodic rectangular pulse light passes through the gas chamber 6, the erbium-doped fiber amplifier 7 and the optical fiber extender 8 in sequence, re-enters the optical fiber coupler 5, and rings down in the optical fiber ring cavity. After the ringing down is completed, a small part of the optical signal is output to the photodetector 9 through the output port of the optical fiber coupler 5. The photodetector 9 converts the optical signal into an electrical signal and outputs it to the oscilloscope 10, which is intuitively displayed by the oscilloscope 10.

[0037] As a possible implementation, the gas chamber 6 in the fiber annular cavity includes an antiresonant hollow-core fiber, a ceramic ferrule, and a single-mode fiber. The two ends of the antiresonant hollow-core fiber are mechanically coupled to two single-mode fibers via open ceramic ferrules with the same outer diameter as the antiresonant hollow-core fiber, with a certain gap between them, allowing gas to flow in and out through the openings.

[0038] For example, the length of the antiresonant hollow core fiber is 1 m. Compared with traditional solid core fibers, antiresonant hollow core fibers have a lower loss ratio, can significantly reduce the dispersion and nonlinear effects of optical signals during transmission, and improve signal quality.

[0039] Since the detection system provided by the present application follows the Lambert-Beer law, it can be deduced from the law that the detection accuracy of the gas is related to the effective optical path length. The longer the effective optical path length of the gas absorption, the higher the detection accuracy. Therefore, the present application designs a fiber ring cavity ring-down module to effectively enhance the effective optical path of gas absorption. Since the sensitivity of gas detection is positively correlated with the effective optical path length of the light signal through the gas chamber, extending the anti-resonant hollow core fiber can increase the effective optical path length of the gas chamber, and the fiber can be coiled into a small diameter ring to reduce the volume of the system. However, considering that an excessively long anti-resonant hollow core fiber will significantly increase the cost, in order to further increase the effective optical path length of the gas chamber, the present application proposes to allow the light signal to circulate through the gas chamber multiple times through a fiber ring cavity ring-down structure.

[0040] A periodic rectangular pulse signal enters the ring cavity through a fiber coupler. Within the gas chamber, it absorbs a portion of the measured gas. An erbium-doped fiber amplifier increases the light intensity, while a fiber extender prevents pulse overlap. The majority of the light signal entering the ring cavity decays within the cavity. A small portion is coupled out through the second end of the fiber coupler, detected by a photodetector and converted into an electrical signal. This signal appears on an oscilloscope as a series of exponentially decaying periodic rectangular pulses.

[0041] In some embodiments, the loss of gas chamber 6 at the center wavelength of the laser light emitted by the continuous wave laser is limited to 0.92 dB / km. 0.92 dB / km means that for every kilometer of light transmission, the power decreases by approximately 10^(-0.92 / 10) ≈ 0.914 times, or a loss of approximately 8.6%. This is far lower than the loss of many traditional optical fibers at certain wavelengths or special optical fibers (such as ordinary single-mode optical fibers at non-optimal wavelengths). The limitation of the center wavelength of the laser light emitted by the continuous wave laser in gas chamber 6 can further improve optical transmission efficiency, support long-distance transmission, reduce system power consumption and complexity, and further minimize nonlinear effects.

[0042] In some embodiments, the gain of the erbium-doped fiber amplifier 7 is 2 dB. The erbium-doped fiber amplifier 7 can provide a high gain, helping to increase the transmission distance of optical signals and significantly enhance weak optical signals. Furthermore, the erbium-doped fiber amplifier 7 has a low noise figure, introducing less noise while amplifying the signal. This helps maintain high-quality signal transmission and improves the signal-to-noise ratio, thereby ensuring detection accuracy.

[0043] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0044] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A highly sensitive gas detection system based on antiresonant hollow core fiber, characterized in that: It includes a signal generation module, a fiber ring cavity ring-down module and a signal detection module; The fiber ring cavity ring-down module includes a fiber coupler, an air chamber, an erbium-doped fiber amplifier, and a fiber extender; the first end of the fiber coupler is connected to the signal generation module, and the second end of the fiber coupler is connected to the signal detection module; the third end of the fiber coupler is connected to the first end of the air chamber, the second end of the air chamber is connected to the first end of the erbium-doped fiber amplifier, the second end of the erbium-doped fiber amplifier is connected to the first end of the fiber extender, and the second end of the fiber extender is connected to the fourth end of the fiber coupler; The signal generating module is configured to: output a periodic rectangular pulse light signal; The fiber ring cavity ring-down module is configured to: receive the periodic rectangular pulse optical signal, cyclically realize the ring-down effect of the optical signal in the cavity, and couple part of the optical signal in the ring-down process to the signal detection module through the third end of the optical fiber coupler; wherein, the optical signal circulates through the gas chamber; The signal detection module is configured to detect a signal coupled and outputted from the third end of the optical fiber coupler.

2. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 1, characterized in that: The air chamber includes an anti-resonant hollow core optical fiber, a ceramic ferrule and a single-mode optical fiber; The two ends of the antiresonant hollow-core optical fiber are respectively mechanically coupled to the two single-mode optical fibers at a certain gap through an open ceramic ferrule having the same outer diameter as the antiresonant hollow-core optical fiber.

3. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 1, characterized in that: The signal generation module includes a continuous wave laser, an optoelectronic modulator, a signal generator and an isolator; The continuous wave laser is connected to the first end of the optoelectronic modulator, the second end of the optoelectronic modulator is connected to the first end of the isolator, the second end of the isolator is connected to the first end of the optical fiber coupler, and the third end of the optoelectronic modulator is connected to the signal generator.

4. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 1, characterized in that: The signal detection module includes a photodetector and an oscilloscope; The second end of the optical fiber coupler is connected to the first end of the photodetector, and the second end of the photodetector is connected to the oscilloscope.

5. The high-sensitivity gas detection system based on anti-resonant hollow-core fiber according to claim 3, characterized in that: The central wavelength of the continuous wave laser is 1567 nm.

6. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 3, characterized in that: The optical fiber coupler includes a first input port, a second input port, a first output port and a second output port; The first end of the optical fiber coupler is the first input port; the fourth end of the optical fiber coupler is the second input port; the second end of the optical fiber coupler is the first output port; and the third end of the optical fiber coupler is the second output port.

7. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 6, characterized in that: The splitting ratio between the input port and the output port of the optical fiber coupler is 90:10; The input ports of the optical fiber coupler include the first input port and the second input port; the output ports of the optical fiber coupler include the first output port and the second output port.

8. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 2, characterized in that: The antiresonant hollow core optical fiber is 1 m long.

9. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 5, characterized in that: The limiting loss of the gas cell at the central wavelength of the laser light emitted by the continuous wave laser is 0.92 dB / km.

10. The highly sensitive gas detection system based on antiresonant hollow core fiber according to claim 1, characterized in that: The gain of the erbium-doped fiber amplifier is 2 dB.

Images