A micro-nano fiber array-based photothermal spectral gas detection device and method

Abstract

The application provides a micro-nano optical fiber array-based photothermal spectrum gas detection device and method, and the device comprises a light emitting component, a first single-mode optical fiber coupler, a micro-nano optical fiber array gas chamber, an optical narrowband filter, an optical frequency shift module and a light conversion component; the light emitting component is connected with the optical frequency shift module and the light conversion component; the light emitting component is sequentially connected with the first single-mode optical fiber coupler, the micro-nano optical fiber array gas chamber, the optical narrowband filter and the light conversion component; wherein the micro-nano optical fiber array gas chamber comprises a micro-nano optical fiber sensing array structure. The micro-nano optical fiber is used as a core sensing element, which can realize high-sensitivity and rapid-response gas sensing, and can be mass-produced at a low cost.

Description

Technical Field

[0001] This invention belongs to the field of optical gas detection, specifically relating to a gas detection device and method based on micro-nano fiber arrays. Background Technology

[0002] Photothermal Spectroscopy (PTS) technology has attracted widespread attention from researchers due to its advantages such as ultra-high detection sensitivity. It employs a dual-source configuration of "pump light-probe light." The pump light is absorbed by the gas, heating the sensing medium and causing phase modulation of the probe light—a process known as the "photothermal effect." Harmonic signals can be demodulated from the phase of the probe light and used to invert the concentration of the analyte gas. Current sensing media are mostly based on free-space beams and hollow-core optical fibers. The former has poor resistance to strong industrial vibrations, while the latter results in a long response time. Both are also bulky and expensive, hindering large-scale production. Summary of the Invention

[0003] The purpose of this invention is to provide a photothermal spectroscopy gas detection device and method based on micro-nano fiber arrays, which can achieve highly sensitive and fast-response gas sensing, and can be mass-produced at a low cost.

[0004] The technical solution of the present invention is as follows:

[0005] A photothermal spectroscopy gas detection device based on micro / nano fiber arrays, comprising:

[0006] Optical transmitting component, first single-mode fiber coupler, micro / nano fiber array air cell, optical narrowband filter, optical frequency shifting module, optical conversion component;

[0007] The optical emitting component is connected to the optical frequency shifting module and the optical conversion component;

[0008] The optical emitting component is sequentially connected to the first single-mode fiber coupler, the micro-nano fiber array air cell, the optical narrowband filter, and the optical conversion component.

[0009] The micro-nano fiber array air chamber includes a micro-nano fiber sensing array structure.

[0010] Furthermore, the optical emission assembly includes a pump optical emission module, a probe optical emission module, and a second single-mode fiber coupler;

[0011] The second single-mode fiber coupler is used to split the probe light emitted by the probe light emitting module into two beams;

[0012] The pump light emitting module and the probe light emitting module are arranged on the same side;

[0013] Furthermore, the optical conversion component includes: a third single-mode fiber coupler, a photodetector, and a signal demodulation and analysis module;

[0014] The third single-mode fiber coupler, photodetector, and signal demodulation analysis module are connected in sequence.

[0015] Furthermore, the signal demodulation and analysis module includes an oscilloscope, a spectrum analyzer, and a lock-in amplifier, used to demodulate the beat frequency electrical signal into a second harmonic signal.

[0016] Furthermore, the micro / nano fiber array air chamber includes: an air inlet, a screen, a glass plate, a U-shaped glass groove, a tapered micro / nano fiber, and a standard single-mode fiber; wherein, the multiple U-shaped glass grooves fixed on the glass plate and the micro / nano fiber encapsulated inside them constitute the micro / nano fiber sensing array structure.

[0017] Furthermore, the fabrication process of the micro / nano fiber optic sensing array structure is as follows:

[0018] Take a standard single-mode fiber of appropriate length and remove about 4-5 cm of its surface coating with wire strippers. Then, wipe the fiber surface clean with lint-free paper soaked in high-concentration alcohol. Use an oxyhydrogen flame fusion tapering machine to tape the stripped single-mode fiber, and set appropriate parameters to draw a micro / nano fiber with a waist diameter of about 1 μm, a transition zone length of 3-4 cm, and a waist length of about 1 cm. Fix the drawn micro / nano fiber into a U-shaped glass groove with UV glue, and fix the glass groove to the glass plate with double-sided tape. Repeat the above operations to form an S-shaped micro / nano fiber array on a single glass plate.

[0019] This invention also provides a photothermal spectroscopy gas detection method based on micro / nano fiber arrays, comprising:

[0020] The probe light and pump light are input into the micro-nano fiber array chamber;

[0021] The local refractive index modulation caused by the selective absorption of pump light by the gas under test will correspondingly modulate the phase of the probe light, obtain the change in the phase of the probe light and demodulate it into a second harmonic signal;

[0022] Finally, the concentration of the gas to be measured can be calculated by inverting the amplitude of the second harmonic signal.

[0023] Furthermore, the probe light and pump light are combined using a single-mode fiber coupler and then input into the micro / nano fiber array chamber.

[0024] Technical effects of the present invention:

[0025] 1. By using tapered micro / nano-fibers with subwavelength diameters instead of traditional space beams and hollow-core fibers, the volume of the sensing chamber and the system's response recovery time are significantly reduced. The stable structure of micro / nano-fibers also enhances the stability of the sensor system, and their relatively simple fabrication greatly reduces processing costs.

[0026] 2. Several tapered micro / nano optical fibers are encapsulated and fixed on a unified base using an S-shaped cascade method to create a micro / nano optical fiber array sensing chamber. This increases the effective sensing length to a certain extent, further enhancing the system's sensing sensitivity.

[0027] 3. A "pump light-probe light co-direction transmission" structure is adopted, avoiding the risk of high-power pump light and probe light damaging laser components in the "dual-source relative transmission" structure. The "co-direction transmission" structure eliminates passive components such as optical isolators and optical circulators, reducing system cost and making it more compact.

[0028] 4. An optical heterodyne interferometer structure is constructed using an optical frequency shifter to extract the sensing signal caused by gas absorption and characterize the gas concentration information using harmonic signals. The active control elements (such as PZT-based servo control loops) used to stabilize the orthogonal operating point in the zero-difference interferometer are eliminated, increasing system stability by reducing the mechanical structure of the system. Attached Figure Description

[0029] The accompanying drawings illustrate various embodiments generally by way of example rather than limitation, and are used, together with the specification and claims, to explain embodiments of the invention. Where appropriate, the same reference numerals are used in all drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the apparatus or method.

[0030] Figure 1 A schematic diagram illustrating the principle of micro / nano fiber-guided "photothermal phase modulation" of the present invention is shown.

[0031] Figure 2 A structural diagram of the micro / nano fiber optic array sensing chamber of the present invention is shown.

[0032] Figure 3 A structural diagram of the photothermal spectroscopy gas detection device based on micro-nano fiber array of the present invention is shown;

[0033] Figure 4 The second harmonic signals corresponding to different concentrations of the gas to be tested are shown. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] A photothermal spectroscopy gas detection device based on micro / nano fiber arrays, comprising:

[0036] Optical transmitting component, first single-mode fiber coupler 81, micro-nano fiber array air cell 9, optical narrowband filter 10, optical frequency shifting module 12, optical conversion component;

[0037] The optical emitting component is connected to the optical frequency shifting module 12 and the optical conversion component;

[0038] The optical emitting component is sequentially connected to the first single-mode fiber coupler 81, the micro-nano fiber array air cell 9, the optical narrowband filter 10, and the optical conversion component.

[0039] The micro-nano fiber array air chamber 9 includes a micro-nano fiber sensing array structure.

[0040] The optical emission assembly includes a pump optical emission module 7, a probe optical emission module 11, and a second single-mode fiber coupler 82.

[0041] The second single-mode fiber coupler 82 is used to split the probe light emitted by the probe light emitting module 11 into two beams;

[0042] The pump light emitting module 7 and the probe light emitting module 11 are arranged on the same side;

[0043] The optical conversion component includes: a third single-mode fiber coupler 83, a photodetector 13, and a signal demodulation and analysis module 14.

[0044] The third single-mode fiber coupler 83, photodetector 13, and signal demodulation and analysis module 14 are connected in sequence.

[0045] The signal demodulation and analysis module 14 includes an oscilloscope, a spectrum analyzer, and a lock-in amplifier, which are used to demodulate the beat frequency electrical signal into a second harmonic signal.

[0046] The micro-nano fiber array air chamber 9 includes: an air inlet 1, a screen 2, a glass plate 3, a U-shaped glass groove 4, a tapered micro-nano fiber 5, and a standard single-mode fiber 6; wherein, the multiple U-shaped glass grooves 4 fixed on the glass plate 3 and the micro-nano fiber 5 encapsulated inside them constitute the micro-nano fiber sensing array structure.

[0047] This invention proposes using micro / nano optical fibers as the core sensing element, which enables highly sensitive and fast-response gas sensing and allows for large-scale production at a lower cost. For example... Figure 1As shown, a subwavelength biconical micro / nanofiber can be divided into a tapered transition region and a tapered waist. The tapered transition region is approximately 3–4 cm long, with its diameter gradually decreasing from 125 μm to 1 μm, and the tapered waist has a diameter of approximately 1 μm. As shown, pump light and probe light are simultaneously incident on the micro / nanofiber. The modulated pump light generates an evanescent field in the tapered waist region, which accounts for approximately 25% of the total pump light power. The evanescent field on the surface of the micro / nanofiber is absorbed by the surrounding gas molecules, generating thermal relaxation and periodically transferring heat to the micro / nanofiber through thermal conduction. This results in local refractive index modulation of the sensing medium, i.e., the "photothermal effect" guided by the micro / nanofiber. The probe light passing through the micro / nanofiber then carries "photothermal phase modulation," which can be represented as:

[0048]

[0049] Where α is the absorption coefficient of the gas to be measured, C and L are the concentration of the gas to be measured and the effective sensing length, respectively, and P... pump D pump (r) and M(t) represent the average intensity, normalized intensity distribution, and time-varying modulation waveform of the pump light, respectively. The normalized intensity distribution of the pump light, D... pump (r) can be further expressed as:

[0050]

[0051] Among them, R pump The effective mode field radius of the pump light (power drops to 1 / e of the peak value) 2 From the above two equations, it can be seen that the phase modulation intensity is inversely proportional to the square of the effective mode field radius. Since the effective mode field diameters formed by pump light propagating in free space, hollow fiber, and micro / nano fiber are on the order of mm, 10 μm, and 1 μm, respectively, the phase modulation intensity of the probe light provided by micro / nano fiber can be increased by 2 to 6 orders of magnitude compared to free space beams and hollow fiber beams within the same average pump light power and unit effective sensing length. Therefore, an ultra-compact sensor made from a single micro / nano fiber with a waist length on the order of centimeters can achieve the effect of a space optical gas cell with a meter-level optical path, and micro / nano fiber arrays made from it can further increase the effective sensing length and improve detection sensitivity.

[0052] This invention provides a micro / nano fiber optic array sensing gas chamber. For example... Figure 2As shown, the structure includes: an air inlet (outlet) 1, a screen 2, a glass plate 3, a U-shaped glass trough 4, a tapered micro / nano fiber 5, and a standard single-mode fiber 6. The gas chamber has two air inlets (outlets) 1, and the sides of the chamber are sealed with rubber stoppers to ensure airtightness. Screens 2 placed at each air inlet (outlet) prevent large dust particles from entering the gas chamber and damaging the micro / nano fiber optics. Multiple U-shaped glass troughs 4 fixed to the glass plate 3 and the micro / nano fiber optics 5 encapsulated within them constitute the micro / nano fiber optic sensing array structure. The standard single-mode fiber optics 6 extending from both ends of the gas chamber are used to connect to other modules in the gas sensing system.

[0053] The detailed fabrication process of the micro / nano fiber array structure is as follows: Take a standard single-mode fiber of appropriate length, remove approximately 4-5 cm of its surface coating using wire strippers, and then clean the fiber surface with lint-free paper soaked in high-concentration alcohol. Use an oxyhydrogen flame fusion tapering machine to tape the stripped single-mode fiber, setting appropriate parameters to draw a micro / nano fiber with a waist diameter of approximately 1 μm, a transition region length of approximately 3-4 cm, and a waist diameter of approximately 1 μm. Fix the drawn micro / nano fiber into a U-shaped glass trough using UV glue, and then fix the glass trough to a glass plate with double-sided tape. Repeat the above operations to fabricate an S-shaped micro / nano fiber array on a single glass plate. Placing this array structure in a glass jar creates the micro / nano fiber array gas chamber.

[0054] A photothermal spectroscopic gas detection device based on micro / nano fiber arrays. For example... Figure 3 As shown, it includes: a pump light emitting module (DFB laser) 7, single-mode fiber couplers 8 (including 8-1, 8-2, and 8-3), a micro / nano fiber array gas cell 9, an optical narrowband filter 10, a probe light emitting module (narrow linewidth laser) 11, an optical frequency shifting module (acousto-optic modulator AOM) 12, a photodetector (PD) 13, and a signal demodulation and analysis module 14. The first single-mode fiber coupler 8-1, the second single-mode fiber coupler 8-2, and the third single-mode fiber coupler 8-3 each have three ports: A, B, and C. Light enters from port A and exits from ports B and C, or enters from ports B and C and exits from port A.

[0055] The second single-mode fiber coupler 8-2 splits the probe light emitted from the probe light module 11 into two beams. One beam enters the optical frequency shift module (acousto-optic modulator AOM) 12, and the other beam enters the first single-mode fiber coupler 8-1 to merge with the pump light. The first single-mode fiber coupler 8-1 combines the probe light with the pump light emitted from the pump light emission module 7 and introduces it into the micro / nano fiber array gas cell 9. The evanescent field guided by the tapered waist region of each micro / nano fiber in the array can interact with the gas under test. The optical narrowband filter 10 is used to cut off the pump light output from the gas cell, while the probe light is allowed to pass because its wavelength is within the passband of the filter. The third single-mode fiber coupler 8-3 combines the two probe lights to obtain a mixed light, which is then converted into a beat frequency electrical signal in the photodetector 13. The signal demodulation and analysis module 14 includes the functions of an oscilloscope, spectrum analyzer, and lock-in amplifier, which demodulates the beat frequency electrical signal output from the photodetector 13 into a second harmonic signal. The demodulated second harmonic signals corresponding to different concentrations of the analyte gas are as follows: Figure 4 As shown.

[0056] A photothermal spectroscopy gas detection method based on micro / nano fiber arrays includes:

[0057] The gas to be tested is filled into the gas chamber of the micro-nano fiber array;

[0058] The probe light and pump light are input into the micro-nano fiber array chamber;

[0059] The local refractive index modulation caused by the selective absorption of pump light by the gas under test will correspondingly modulate the phase of the probe light, obtain the change in the phase of the probe light and demodulate it into a second harmonic signal;

[0060] Finally, the concentration of the gas to be measured can be calculated by inverting the amplitude of the second harmonic signal.

[0061] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A photothermal spectroscopic gas detection device based on micro / nano fiber arrays, characterized in that, include: Optical emission assembly, first single-mode fiber coupler (81), micro-nano fiber array air cell (9), optical narrowband filter (10), optical frequency shifting module (12), optical conversion assembly; The optical emitting component is connected to the optical frequency shifting module (12) and the optical conversion component; the optical frequency shifting module is an acousto-optic modulator; The optical emitting component is sequentially connected to the first single-mode fiber coupler (81), the micro-nano fiber array air cell (9), the optical narrowband filter (10), and the optical conversion component. The micro-nano fiber array air chamber (9) includes a micro-nano fiber sensing array structure. The micro-nano fiber array air chamber (9) includes: air inlet (1), screen (2), glass plate (3), U-shaped glass groove (4), tapered micro-nano fiber (5), and standard single-mode fiber (6); The multiple U-shaped glass grooves (4) fixed on the glass plate (3) and the tapered micro-nano optical fibers (5) encapsulated inside them constitute the micro-nano optical fiber sensing array structure.

2. The spectroscopic gas detection device according to claim 1, characterized in that, The optical emission assembly includes a pump optical emission module (7), a probe optical emission module (11), and a second single-mode fiber coupler (82). The second single-mode fiber coupler (82) is used to split the probe light emitted by the probe light emitting module (11) into two beams; The pump light emitting module (7) and the probe light emitting module (11) are arranged on the same side.

3. The spectroscopic gas detection device according to claim 1, characterized in that, The optical conversion component includes: a third single-mode fiber coupler (83), a photodetector (13), and a signal demodulation and analysis module (14). The third single-mode fiber coupler (83), photodetector (13), and signal demodulation analysis module (14) are connected in sequence.

4. The spectroscopic gas detection device according to claim 3, characterized in that, The signal demodulation and analysis module (14) includes an oscilloscope, a spectrum analyzer, and a lock-in amplifier, which are used to demodulate the beat frequency electrical signal into a second harmonic signal.

5. The spectroscopic gas detection device according to claim 1, characterized in that, The fabrication process of the micro / nano fiber optic sensing array structure is as follows: Take a standard single-mode fiber of appropriate length and remove about 4-5 cm of the coating layer from its surface using wire strippers. Then, wipe the surface of the fiber clean with lint-free paper soaked in high-concentration alcohol. Use an oxyhydrogen flame fusion tapering machine to tape the single-mode fiber after stripping the coating layer, and set appropriate parameters to draw a micro / nano fiber with a tapered waist diameter of about 1 μm. Fix the drawn micro / nano fiber into a U-shaped glass groove with UV glue, and fix the glass groove to a glass plate. Repeat the above operations to form an S-shaped micro / nano fiber array on a single glass plate.

6. A photothermal spectroscopic gas detection method based on micro / nano fiber arrays, characterized in that, include: The probe light and pump light are input into the micro-nano fiber array chamber; The local refractive index modulation caused by the selective absorption of pump light by the gas under test will correspondingly modulate the phase of the probe light, obtain the change in the phase of the probe light and demodulate it into a second harmonic signal; Finally, the concentration of the gas to be measured can be calculated by inverting the amplitude of the second harmonic signal.

7. The gas detection method according to claim 6, characterized in that, The probe light and pump light are combined using a single-mode fiber coupler and then input into the micro / nano fiber array chamber.

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