CN116642837A - Photothermal spectrum gas detection device and method based on micro-nano optical fiber array - Google Patents

Abstract

The application provides a photothermal spectrum gas detection device and a method based on a micro-nano optical fiber array, wherein the device comprises the following components: the optical fiber array comprises an optical emission component, a first single-mode optical fiber coupler, a micro-nano optical fiber array air chamber, an optical narrow-band filter, an optical frequency shift module and an optical 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 fiber coupler, the micro-nano fiber array air chamber, the optical narrow-band filter and the light conversion component; the micro-nano optical fiber array air chamber comprises a micro-nano optical fiber sensing array structure. The application uses micro-nano optical fiber as core sensing element, which can realize high-sensitivity and quick-response gas sensing and can realize mass production with lower cost.

Description

A photothermal spectroscopy gas detection device and method based on a micro-nano fiber array

technical field

The invention belongs to the field of optical gas detection, and in particular relates to a gas detection device and method based on a micro-nano optical fiber array.

Background technique

Photothermal spectroscopy (PTS) technology has attracted extensive attention of researchers due to its advantages such as ultra-high detection sensitivity. It adopts a "pump light-probe light" dual light source configuration. The pump light is absorbed by the gas to heat the sensing medium and cause the phase modulation of the probe light. This process is called "photothermal effect". The harmonic signal can be demodulated from the phase of the probe light and used to invert the concentration of the gas to be measured. The current sensing media are mostly based on free-space light beams and hollow-core optical fibers. The former has poor resistance to industrial strong vibration environments, and the latter will cause longer response times. Both are large in size and high in cost. conducive to large-scale production.

Contents of the invention

The purpose of the present invention is to provide a photothermal spectroscopy gas detection device and method based on a micro-nano optical fiber array, which can realize highly sensitive and fast-response gas sensing, and can be mass-produced at a lower cost.

Technical scheme of the present invention is as follows:

A photothermal spectroscopic gas detection device based on a micro-nano optical fiber array, comprising:

Optical emission components, the first single-mode fiber coupler, micro-nano fiber array gas chamber, optical narrowband filter, optical frequency shift module, optical conversion components;

The light emitting component is connected with the optical frequency shifting module and the light converting component;

The light emitting component is sequentially connected with the first single-mode fiber coupler, the micro-nano fiber array gas chamber, the optical narrowband filter, and the light conversion component;

Wherein, the micro-nano fiber array gas chamber includes a micro-nano fiber sensing array structure.

Further, the light emitting component includes a pumping light emitting module, a detection light emitting module and a second single-mode fiber coupler;

The second single-mode fiber coupler is used to split the detection light emitted by the detection optical module into two beams;

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

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

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

Further, the signal processing module 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.

Further, the micro-nano optical fiber array air chamber includes: air port, screen, glass plate, U-shaped glass groove, tapered micro-nano optical fiber, standard single-mode optical fiber; wherein, a plurality of The U-shaped glass groove and the micro-nano optical fiber encapsulated inside constitute the micro-nano optical fiber sensing array structure.

Further, the preparation process of the micro-nano fiber sensing array structure is as follows:

Take a standard single-mode optical fiber of appropriate length, remove the coating layer on its surface for about 4-5cm in length with a wire stripper, and then wipe the surface of the optical fiber with a dust-free paper dipped in high-concentration alcohol; use a hydrogen-oxygen flame fusion tapered machine The single-mode optical fiber with the coating layer stripped is tapered, and the appropriate parameters are set to draw a micro-nano optical fiber with a tapered waist diameter of about 1 μm, a transition zone length of 3-4 cm, and a tapered waist length of about 1 cm; The drawn micro-nano optical fiber is fixed in the U-shaped glass groove, and the glass groove is fixed on the glass plate with double-sided tape; repeating the above operations can make an S-shaped micro-nano optical fiber array on a single glass plate.

The present invention also provides a photothermal spectroscopy gas detection method based on a micro-nano optical fiber array, including:

Input the probe light and pump light into the gas chamber of the micro-nano fiber array;

The local refractive index modulation caused by the selective absorption of the pump light by the gas to be measured will modulate the phase of the probe light accordingly, obtain the phase change 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 inversion of the amplitude of the second harmonic signal.

Further, the probe light and the pump light are combined through a single-mode fiber coupler and then input into the gas chamber of the micro-nano fiber array.

Technical effect of the present invention:

1. Using tapered micro-nano optical fibers with sub-wavelength diameters to replace traditional space beams and hollow-core optical fibers greatly reduces the volume of the sensing gas chamber and the response recovery time of the system. The stable structure of the micro-nano fiber also enhances the stability of the sensor system, and its relatively simple preparation also greatly reduces the process cost.

2. Several tapered micro-nano optical fibers are packaged and fixed on a unified base in an S-type cascading manner to form a micro-nano optical fiber array sensing gas chamber. This increases the effective sensing length to a certain extent and further increases the sensing sensitivity of the system.

3. The structure of "pump light-probe light transmission in the same direction" is adopted, which avoids the risk of damage to laser components by high-power pump light and probe light in the "double light source relative transmission" structure. The "codirectional transmission" structure can eliminate passive components such as optical isolators and optical circulators, reducing system cost and making it more compact.

4. Use optical frequency shifter to build optical heterodyne interference structure, extract sensing signal caused by gas absorption and use harmonic signal to represent gas concentration information. The active control elements used to stabilize the orthogonal working point in the homodyne interferometer (such as the PZT-based servo control loop) are eliminated, and the system stability is increased by reducing the system mechanical structure.

Description of drawings

The drawings illustrate various embodiments, generally by way of example and not limitation, and together with the description and claims serve to describe embodiments of the invention. Where appropriate, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Such embodiments are illustrative, and not intended to be exhaustive or exclusive embodiments of the apparatus or method.

Figure 1 shows a schematic diagram of the principle of micro-nano fiber-guided "photothermal phase modulation" of the present invention;

Fig. 2 shows the micro-nano fiber array sensing air chamber structural diagram of the present invention;

Fig. 3 shows the structural diagram of the photothermal spectroscopy gas detection device based on the micro-nano optical fiber array of the present invention;

Figure 4 shows the second harmonic signals corresponding to different concentrations of the gas to be measured.

Detailed ways

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

A photothermal spectroscopic gas detection device based on a micro-nano optical fiber array, comprising:

Light emitting component, first single-mode fiber coupler 81, micro-nano fiber array gas chamber 9, optical narrowband filter 10, optical frequency shift module 12, light conversion component;

The light emitting component is connected with the optical frequency shifting module 12 and the light conversion component;

The light emitting component is sequentially connected with the first single-mode fiber coupler 81, the micro-nano fiber array gas chamber 9, the optical narrowband filter 10, and the light conversion component;

Wherein, the micro-nano fiber array gas chamber 9 includes a micro-nano fiber sensing array structure.

The light emitting component includes a pumping light emitting module 7, a detection light emitting module 11 and a second single-mode fiber coupler 82;

The second single-mode fiber coupler 82 is used to split the detection light emitted by the detection optical module 11 into two beams;

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

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

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

The signal processing module 14 includes an oscilloscope, a spectrum analyzer, and a lock-in amplifier for demodulating the beat frequency electrical signal into a second harmonic signal.

The micro-nano optical fiber array air chamber 9 includes: gas port 1, screen 2, glass plate 3, U-shaped glass groove 4, tapered micro-nano optical fiber 5, standard single-mode optical fiber 6; wherein, is fixed on the glass plate A plurality of U-shaped glass grooves 4 on the 3 and micro-nano optical fibers 5 encapsulated inside constitute a micro-nano optical fiber sensing array structure.

The invention proposes to use the micro-nano optical fiber as the core sensing element, which can realize highly sensitive and fast-response gas sensing, and can be mass-produced at a lower cost. As shown in Figure 1, a biconical micro-nano fiber with a subwavelength diameter can be divided into two parts: a tapered transition zone and a tapered waist. The length of the tapered transition zone is about 3–4 cm, its diameter gradually changes from 125 μm to 1 μm, and the diameter of the cone waist is about 1 μm. As shown in the figure, the pump light and the probe light are incident into the micro-nano fiber at the same time, and the modulated pump light generates an evanescent field in the cone waist region, which accounts for about 25% of the total pump light power. The evanescent field on the surface of the micro-nano fiber is absorbed by the surrounding gas molecules to generate thermal relaxation, and the heat is periodically transferred to the micro-nano fiber through the heat conduction effect, thus causing the refractive index modulation of the local sensing medium, that is, the micro-nano Fiber-guided "photothermal effect". At this time, the probe light passing through the micro-nano fiber carries "photothermal phase modulation", which can be expressed as:

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, P _pump , D _pump (r) and M(t) are the average light intensity of the pump light, normalized Intensity distribution and time-varying modulation waveform. The normalized intensity distribution of the pump light D _pump (r) can be further expressed as:

Among them, R _pump is the effective mode field radius of the pump light (the power drops to 1/e ² of the peak value). From the above two formulas, 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 of the pump light transmitted in free space, hollow-core fiber, and micro-nano fiber are on the order of mm, 10 μm, and 1 μm, respectively, within the same pump light average power and unit effective sensing length, the micro The phase modulation intensity of probe light provided by nanofiber can be improved by 2 to 6 orders of magnitude compared with free space beam and hollow core fiber. Therefore, an ultra-compact sensor made of a micro-nano optical fiber with a waist length of centimeters can achieve the effect of a spatial phosgene chamber with a meter-level optical path, and the micro-nano optical fiber array made of it can further increase the effective Sensing length and improving detection sensitivity.

The invention provides a micro-nano optical fiber array sensing gas chamber. As shown in Figure 2, it includes: air inlet (air outlet) port 1, screen 2, glass plate 3, U-shaped glass groove 4, tapered micro-nano optical fiber 5, and standard single-mode optical fiber 6. Among them, the air chamber is equipped with two air inlet (air outlet) ports 1, and the two sides of the tank body are sealed by rubber plugs to ensure airtightness, and the screen 2 placed at each air inlet (air outlet) port is used to prevent large air in the air. Particle dust enters the air chamber and damages the micro-nano fiber. A plurality of U-shaped glass grooves 4 fixed on the glass plate 3 and micro-nano optical fibers 5 encapsulated inside constitute a micro-nano optical fiber sensing array structure. The standard single-mode optical fiber 6 left at both ends of the gas chamber is used to connect with other modules in the gas sensing system.

The detailed preparation process of the micro-nano optical fiber array structure is as follows: Take a standard single-mode optical fiber of appropriate length, remove the coating layer on its surface with a length of about 4-5cm with a wire stripper, and then use a dust-free paper dipped in high-concentration alcohol to wipe the surface of the optical fiber. Wipe clean. Use a hydrogen-oxygen flame fusion tapering machine to taper the single-mode optical fiber stripped of the coating, set appropriate parameters to draw a tapered waist with a diameter of about 1 μm, a transition zone length of about 3-4cm, and a tapered waist diameter of about 1 μm micro-nano fiber. Fix the drawn micro-nano optical fiber in the U-shaped glass groove with ultraviolet glue, and fix the glass groove on the glass plate with double-sided adhesive. By repeating the above operations, an S-shaped micro-nano fiber array can be made on a single glass plate, and the array structure is placed in a glass jar to make a micro-nano fiber array air chamber.

A photothermal spectroscopic gas detection device based on a micro-nano fiber array. As shown in Figure 3, it includes: pumping light emitting module (DFB laser) 7, single-mode fiber coupler 8 (including 8-1, 8-2, 8-3), micro-nano fiber array gas chamber 9, optical Narrowband filter 10 , detection light emission module (narrow linewidth laser) 11 , optical frequency shift module (acousto-optic modulator AOM) 12 , photodetector (PD) 13 , and signal demodulation analysis module 14 . Among them, 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 include three ports A, B, and C, and light enters port B from port A. , C two out, or from B, C two into A port out.

The function of the second single-mode fiber coupler 8-2 is to divide the detection light emitted by the detection optical module 11 into two beams, one of which enters the optical frequency shift module (acousto-optic modulator AOM) 12, and the other enters the first single The mode fiber coupler 8-1 merges with the pump light. The role of the first single-mode fiber coupler 8-1 is to combine the probe light with the pump light emitted by the pump light emitting module 7 and introduce it into the gas chamber 9 of the micro-nano fiber array, and each section of micro-nano fiber in the array The evanescent field guided by the cone waist region can interact with the gas to be measured. The optical narrow-band 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 band-pass range of the filter. The function of the third single-mode fiber coupler 8 - 3 is to combine the two detection lights to obtain a mixed frequency light, which is then converted into a beat frequency electrical signal in the photodetector 13 . The signal processing module 14 includes functions of an oscilloscope, a spectrum analyzer, and a lock-in amplifier, which demodulate the beat-frequency electrical signal output by the photodetector 13 into a second harmonic signal. The demodulated second harmonic signals corresponding to different concentrations of the gas to be measured are shown in Figure 4.

A photothermal spectroscopy gas detection method based on a micro-nano optical fiber array, comprising:

Fill the gas to be measured into the gas chamber of the micro-nano fiber array;

Input the probe light and pump light into the gas chamber of the micro-nano fiber array;

The local refractive index modulation caused by the selective absorption of the pump light by the gas to be measured will modulate the phase of the probe light accordingly, obtain the phase change 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 inversion of the amplitude of the second harmonic signal.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention and its Any equivalent replacement or change of the inventive concept shall fall within the protection scope of the present invention.

Claims (8)

1. A photothermal spectroscopy gas detection device based on a micro-nano optical fiber array, characterized in that it comprises: Light emitting component, first single-mode fiber coupler (81), micro-nano fiber array gas chamber (9), optical narrowband filter (10), optical frequency shifting module (12), light conversion component; The light emitting component is connected with the optical frequency shifting module (12) and the light conversion component; The light emitting component is sequentially connected with the first single-mode fiber coupler (81), the micro-nano fiber array gas chamber (9), the optical narrowband filter (10), and the light conversion component; Wherein, the micro-nano fiber array gas chamber (9) includes a micro-nano fiber sensing array structure. 2. The spectroscopic gas detection device according to claim 1, characterized in that, the light emitting assembly comprises a pumping light emitting module (7), a detection light emitting module (11) and a second single-mode fiber coupler (82 ); The second single-mode fiber coupler (82) is used to split the detection light emitted by the detection optical 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 spectral gas detection device according to claim 1, characterized in that, the optical conversion assembly comprises: a third single-mode fiber coupler (83), a photodetector (13), a signal demodulation analysis module (14 ); The third single-mode fiber coupler (83), the photodetector (13), and the signal demodulation and analysis module (14) are connected in sequence. 4. The spectral gas detection device according to claim 1, characterized in that, the signal processing module (14) includes an oscilloscope, a spectrum analyzer, and a lock-in amplifier for demodulating the beat frequency electrical signal into a second harmonic wave signal. 5. The spectroscopic gas detection device according to claim 1, characterized in that, the micro-nano fiber array gas chamber (9) comprises: a gas port (1), a screen (2), a glass plate (3), a U-shaped Glass groove (4), tapered micro-nano optical fiber (5), standard single-mode optical fiber (6); wherein, a plurality of U-shaped glass grooves (4) fixed on the glass plate (3) and its internal package The micro-nano optical fiber (5) constitutes a micro-nano optical fiber sensing array structure. 6. The spectral gas detection device according to claim 1, wherein the preparation process of the micro-nano optical fiber sensing array structure is: Take a standard single-mode optical fiber of appropriate length, remove the coating layer on its surface for about 4-5cm in length with a wire stripper, and then wipe the surface of the optical fiber with a dust-free paper dipped in high-concentration alcohol; use a hydrogen-oxygen flame fusion tapered machine Taper the single-mode optical fiber with the coating stripped off, set appropriate parameters to draw a micro-nano optical fiber with a tapered waist diameter of about 1 μm; fix the drawn micro-nano optical fiber in a U-shaped glass groove with ultraviolet glue , and fix the glass groove on the glass plate; repeat the above operations to make an S-shaped micro-nano optical fiber array on a single glass plate. 7. A photothermal spectroscopy gas detection method based on a micro-nano optical fiber array, characterized in that it comprises: Input the probe light and pump light into the gas chamber of the micro-nano fiber array; The local refractive index modulation caused by the selective absorption of the pump light by the gas to be measured will modulate the phase of the probe light accordingly, obtain the phase change 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 inversion of the amplitude of the second harmonic signal. 8 . The gas detection method according to claim 1 , wherein the probe light and the pump light are combined by a single-mode fiber coupler and then input into the gas chamber of the micro-nano fiber array.