In-situ sensor for propane content in air based on optical fiber vernier effect

Abstract

The invention discloses an in-situ sensor for the content of propane in air based on an optical fiber vernier effect. The in-situ sensor comprises a broadband light source, a spectrum analyzer and a propane gas detection unit, the broadband light source, the spectrum analyzer and the propane gas detection unit are respectively connected with three input ports of the optical fiber circulator; the propane gas detection unit comprises a single-mode optical fiber, a multimode optical fiber, a double-core optical fiber and an ultraviolet glue micro tip which are connected in sequence; and the ultraviolet glue micro tip extends along one fiber core of the double-core optical fiber. Reflecting faces are formed on the two micro-tip end faces of the ultraviolet glue and the end face of the middle fiber core of the double-core optical fiber, the vernier effect is formed through Fabry-Perot interference superposition of multiple mode fields, and meanwhile high-sensitivity sensing detection is achieved through the sensitive material characteristic of the micro-tip of the ultraviolet glue.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensing, and particularly relates to an in-situ sensor for propane content in air based on the fiber optic vernier effect. Background Art

[0002] Currently, for the detection of propane gas, methods such as electrochemical sensors, infrared imaging, and catalytic combustion sensors are mainly used, which have problems such as limited sensitivity and poor adaptability to complex environments. Fiber optic sensors have the advantages of a wide range of measurement objects, anti-electromagnetic interference, low operating temperature, small size, and long transmission distance. Therefore, fiber optic sensors have broad prospects in the field of gas sensing.

[0003] Common microstructured fiber optic sensors include Mach-Zehnder sensors, fiber optic Fabry-Perot sensors, Michelson sensors, surface plasmon resonance fiber optic sensors, fused taper fiber optic sensors, etc. However, most fiber optic sensors have limited sensing sensitivity and poor stability, and it is difficult to adapt to the complex and changeable environment of air. Summary of the Invention

[0004] The present invention is proposed to solve the problem of limited sensing sensitivity in the prior art, and its purpose is to provide an in-situ sensor for propane content in air based on the fiber optic vernier effect.

[0005] The present invention is achieved through the following technical solutions:

[0006] An in-situ sensor for propane content in air based on the fiber optic vernier effect, comprising a broadband light source, a spectral analyzer, and a propane gas detection unit;

[0007] The broadband light source, the spectral analyzer, and the propane gas detection unit are respectively connected to three ports of a fiber optic circulator in sequence through fiber optic jumpers;

[0008] The propane gas detection unit includes a single-mode fiber, a multi-mode fiber, a dual-core fiber, and a UV glue microtip connected in sequence; the UV glue microtip extends along one of the cores of the dual-core fiber.

[0009] In the above technical solution, the broadband light source is a supercontinuum light source;

[0010] In the above technical solution, the single-mode fiber is Corning SMF-28, its cladding diameter is 125 μm, the refractive index at 1550 nm is 1.444, the core diameter is 8.2 μm, and the refractive index is 1.449;

[0011] The multi-mode fiber has a cladding diameter of 125 μm, a refractive index of 100, a core diameter of 105 μm, and a refractive index of 1.444;

[0012] The cladding diameter of the dual-core optical fiber is 125 μm, the refractive index is 1.444, the core diameter is 9 μm, and the refractive index is 1.4492.

[0013] In the above technical solution, the ultraviolet glue microtip is formed by polymerizing an ultraviolet light-sensitive resin under ultraviolet light irradiation, and its size is controllable.

[0014] In the above technical solution, the end face of the ultraviolet glue microtip and the end faces of the two cores in the middle of the dual-core optical fiber both form reflecting surfaces. The end face of the ultraviolet glue microtip and the end faces of the two cores of the dual-core optical fiber form three reflecting surfaces, generating multiple groups of Fabry-Perot interference.

[0015] In the above technical solution, the preparation method of the propane gas detection unit specifically includes the following steps:

[0016] (ⅰ) Splice a single-mode optical fiber, a multi-mode optical fiber, and a dual-core optical fiber in sequence to obtain a combined optical fiber;

[0017] (ⅱ) Place the combined optical fiber obtained in step (ⅰ) and another auxiliary single-mode optical fiber with a planar end face into a polarization-maintaining fusion splicer, and adjust the distance between the end faces of the combined optical fiber and the auxiliary single-mode optical fiber by controlling the positions of two motors;

[0018] The planar end face of the auxiliary single-mode optical fiber is arranged opposite to the dual-core optical fiber;

[0019] (ⅲ) Inject an ultraviolet light-sensitive resin into the gap between the combined optical fiber and the auxiliary single-mode optical fiber, transmit ultraviolet light with a wavelength of 395 nm through the optical fiber and transmit it out from the end face of the dual-core optical fiber, so that the ultraviolet light-sensitive resin is cured, and a microcone is formed between the combined optical fiber and the auxiliary single-mode optical fiber;

[0020] Ultraviolet light enters from one side of the combined optical fiber, passes through the single-mode optical fiber, the multi-mode optical fiber, and the dual-core optical fiber in sequence, and finally exits from the cross-section of the dual-core optical fiber and irradiates the ultraviolet light-sensitive resin in the gap between the combined optical fiber and the auxiliary single-mode optical fiber; the role of the auxiliary single-mode optical fiber is positioning and support, and ultraviolet light does not pass through the auxiliary single-mode optical fiber and is transmitted out;

[0021] (ⅳ) Axially stretch by moving the motors in the polarization-maintaining fusion splicer to control the length of the microcone; then adjust the rotation direction to obtain a flat microcone reflection surface; at the same time, keep the distance between the combined optical fiber and the auxiliary optical fiber within 40 μm to 50 μm to ensure that the microcone parameters meet the standards;

[0022] The length of the microcone is 40 μm, and there is no requirement for the taper; the length of the ultraviolet glue microtip is determined by the size of the gap between the combined optical fiber and the auxiliary single-mode optical fiber. The gap can be determined by the moving distance of the motor;

[0023] (ⅴ) Use anhydrous ethanol to clean the uncured photosensitive material remaining on the microcone to obtain a stable microcone structure.

[0024] In the above technical solution, in step (i), the single-mode fiber, multi-mode fiber, and dual-core fiber are spliced using a fiber splicer of model Furukawa, S178A made in Japan to form an FP fiber sensor.

[0025] In the above technical solution, the broadband light source is connected to the input end of the fiber optic circulator; the spectral analyzer is connected to the output end of the fiber optic circulator; the propane gas detection unit is connected to the detection end of the fiber optic circulator; the fiber optic circulator guides the light emitted by the broadband light source to the propane gas detection unit, and then guides the reflected light to the spectral analyzer for analysis. In the fiber optic circulator, after the optical signal enters from one port, it will come out from the next port in a specific order and will not be transmitted in the reverse direction; the fiber optic circulator guides the light emitted by the light source to the structure to be measured (propane gas detection unit), and then guides the reflected light to the spectrometer for analysis, while avoiding the light directly returning to the light source and reducing interference.

[0026] In the above technical solution, the single-mode fiber end of the propane gas detection unit is connected to the fiber optic circulator.

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

[0028] The present invention provides an in-situ sensor for the propane content in the air based on the fiber optic vernier effect. The structure of the propane gas detection unit is simple, and the structure of the probe is convenient for realizing the in-situ real-time monitoring of propane gas in the air at a fixed position. At the same time, the high-sensitivity sensing detection is realized by using the sensitive material characteristics of the ultraviolet glue microtip; the present invention has the advantages of simple operation, low cost, easy installation, etc., and provides a new method for propane gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of the propane gas detection unit in the present invention;

[0030] Figure 2 is a schematic structural diagram of the present invention;

[0031] Figure 3 is a refractive index response reflection spectrogram of the Fabry-Perot fiber sensor.

[0032] Wherein:

[0033] 1. Broadband light source; 2. Spectral analyzer; 3. Propane gas detection unit; 31. Single-mode fiber; 32. Multi-mode fiber; 33. Dual-core fiber; 34. Ultraviolet glue microtip; 4. Fiber optic circulator.

[0034] For those of ordinary skill in the art, without creative efforts, other relevant drawings can be obtained based on the above drawings. Detailed implementation mode

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings of the specification and through specific implementation modes.

[0036] As Figure 1 、 2 shown, an in-situ sensor for propane content in air based on the fiber optic vernier effect, characterized in that it comprises a broadband light source 1, a spectral analyzer 2 and a propane gas detection unit 3;

[0037] The broadband light source 1, the spectral analyzer 2 and the propane gas detection unit 3 are respectively connected to three ports of an optical fiber circulator 4;

[0038] The propane gas detection unit 3 comprises a single-mode optical fiber 31, a multi-mode optical fiber 32, a dual-core optical fiber 33 and an ultraviolet glue microtip 34 which are sequentially fused; the ultraviolet glue microtip 34 extends along one of the cores of the dual-core optical fiber 33.

[0039] The broadband light source 1 is a supercontinuum light source;

[0040] The single-mode optical fiber 31 is Corning SMF-28, its cladding diameter is 125 μm, the refractive index at 1550 nm is 1.444, the core diameter is 8.2 μm, and the refractive index is 1.449; the multi-mode optical fiber 32 has a cladding diameter of 125 μm, a refractive index of 100, a core diameter of 105 μm, and a refractive index of 1.444; the dual-core optical fiber 33 has a cladding diameter of 125 μm, a refractive index of 1.444, a core diameter of 9 μm, and a refractive index of 1.4492.

[0041] The ultraviolet glue microtip 34 is formed by polymerizing ultraviolet light-sensitive resin under ultraviolet light irradiation, and its size is controllable. The ultraviolet light-sensitive resin is used as a sensitive material, and the change in the concentration of propane gas in the external environment can cause a change in its refractive index, thereby realizing the identification and measurement of the content of propane gas.

[0042] The end face of the ultraviolet glue microtip 34 and the end faces of the two cores in the middle of the dual-core optical fiber 33 both form reflecting surfaces, and through the Fabry-Perot interference superposition of multiple mode fields, a vernier effect is formed to realize high-sensitivity sensing detection of propane content in air.

[0043] The preparation method of the propane gas detection unit 3 specifically includes the following steps:

[0044] (ⅰ) The single-mode optical fiber 31, the multi-mode optical fiber 32 and the dual-core optical fiber 33 are sequentially fused to obtain a combined optical fiber; the single-mode optical fiber 31, the multi-mode optical fiber 32 and the dual-core optical fiber 33 are fused using a fiber optic fusion splicer of model Furukawa, S178A made in Japan to form an FP fiber optic sensor;

[0045] (ii) placing the combined optical fiber obtained in step (i) and another section of auxiliary single-mode optical fiber with a planar end face into a polarization-maintaining fusion splicer, and adjusting the distance between the end faces of the combined optical fiber and the auxiliary single-mode optical fiber by controlling the positions of two motors; the planar end face of the auxiliary single-mode optical fiber is arranged opposite to the dual-core optical fiber 33;

[0046] (iii) injecting ultraviolet light photosensitive resin into the gap between the combined optical fiber and the auxiliary single-mode optical fiber, and transmitting ultraviolet light of 395 nm through the optical fiber and out from the end face of the dual-core optical fiber to cure the ultraviolet light photosensitive resin and form a micro-cone between the combined optical fiber and the auxiliary single-mode optical fiber;

[0047] (iv) adjusting the reflective surface of the micro-cone by moving a motor in the welding machine to obtain a flat reflective surface;

[0048] (v) Using anhydrous ethanol to clean the uncured photosensitive material remaining on the micro-cone to obtain a stable micro-cone structure.

[0049] The micro-tip surface and the two core end surfaces of the optical fiber form three reflection surfaces, and the reflected light fields of the three surfaces interfere, thereby forming two Fabry-Perot interference superpositions, realizing cursor amplification and improving the sensitivity of the sensor.

[0050] Principle of the present invention:

[0051] The Fabry-Perot sensor significantly improves its sensitivity through the precise principle of optical interference, can detect tiny environmental changes, and improves the speed and accuracy of signal response. However, because it does not require a high-power light source and the sensor head is compact, its structure is stable and has strong anti-interference capabilities, reducing the impact of external factors on the sensor, thereby improving its overall stability and reliability.

[0052] The present invention utilizes a Fabry-Perot sensor and adopts a method of self-growing ultraviolet glue microtips on dual-core optical fibers to achieve the superposition of multiple groups of Fabry-Perot interferences; utilizing the sensitive material properties of the ultraviolet glue microtips, the prepared propane gas detection unit has high sensitivity to the propane content in the air, effectively improving the sensitivity of the sensor to the surrounding environment; the optical fiber sensing structure in the form of a probe is stable, compact, anti-electromagnetic interference, low operating temperature, small size, long transmission distance and other characteristics, and can achieve high-sensitivity, in-situ real-time monitoring of the propane content in the air.

[0053] The light emitted by the broadband light source 1 passes through the optical circulator 4 and first enters the propane gas detection unit 3 through a single-mode optical fiber and then into the air. The propane gas detection unit 3 is placed in the air in the form of a probe. The propane gas detection unit 3 forms reflection surfaces at the end face of the ultraviolet glue microtip c and the end faces of the two cores in the middle of the dual-core optical fiber. The reflected spectra are superimposed to form the superposition of multiple Fabry-Perot interferences, generating the Vernier effect, and the signal is demodulated through the spectral analyzer 2 to achieve highly sensitive sensing detection of the propane content in the air.

[0054] In the fiber optic sensing system, when the broadband light source 1 enters the multimode optical fiber 32 from the single-mode optical fiber 31 of the propane gas detection unit 3 through the optical circulator 4, mode field mismatch occurs and multiple high-order modes are excited. The high-order modes enter the dual-core optical fiber 33 through the multimode optical fiber 32, and the dual-core optical fiber 33 performs spatial mode regulation to control two main modes to be coupled into the two cores (a and b, as Figure 2 shown). Among them, the core a is connected to the ultraviolet glue microtip c, and reflections occur at the two end interfaces of the ultraviolet glue microtip.

[0055] When the broadband light source enters the multimode optical fiber from the single-mode optical fiber, due to mode field mismatch, multiple high-order modes are excited. The high-order modes enter the dual-core optical fiber through the multimode optical fiber, and two modes are controlled to be coupled into the two cores respectively. The optical field mode reflected at the interface where the core a of the dual-core optical fiber is connected to the ultraviolet glue microtip is called mode a, the optical field mode directly reflected at the end face of the core b of the dual-core optical fiber is called mode b, and the optical field mode reflected at the other interface of the ultraviolet glue microtip is called mode c. Therefore, there is an optical path difference between mode a and mode b, and an optical path difference between mode a and mode c, which can be expressed as:

[0056]

[0057] where n PMC represents the effective refractive index of the ultraviolet glue microtip, n SRI represents the effective refractive index of the surrounding environment, L represents the length of the ultraviolet glue microtip, and λ represents the wavelength. Therefore, the interference intensity I1 between mode a and mode b and the interference intensity I2 between mode a and mode c can be expressed as:

[0058]

[0059]

[0060] where I a 、I b 、I c represent the intensities of mode a, mode b, and mode c respectively. When the optical path differences and When it is an odd multiple of π, the peak value of the interference spectrum can be obtained. From this, the free spectral ranges FSR1 of the interference between mode a and mode b and FSR2 of the interference between mode a and mode c are respectively:

[0061]

[0062] Among them, the interference spectrum between mode a and mode b is used as the reference spectrum, and the interference spectrum between mode a and mode c is used as the sensing spectrum. The free spectral ranges between the two interferences are different. When the spectra are superimposed, the Vernier effect will occur, amplifying the sensitivity of the sensor. The total spectral function formed by the Vernier effect obtained from the spectral superposition of the interference between mode a and mode b and the interference between mode a and mode c is:

[0063] I all = Acos[2πL(n PMC - n SRI ) / λ] (7)

[0064] Where A is the intensity constant. Therefore, the free spectral range of the envelope can be expressed as:

[0065]

[0066] Furthermore, it can be deduced that the magnification factor M of the Vernier effect in this monitor can be expressed as:

[0067]

[0068] Therefore, this sensor can sense the propane content in the air with high sensitivity. Figure 3 For this gas sensor refractive index response reflection spectrogram, it can be seen that as the refractive index increases, the envelope drifts towards the short-wave direction, and then the propane gas content in the sample to be measured can be determined.

[0069] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0070] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. An in-situ sensor for propane content in air based on optical fiber cursor effect, characterized in that: It comprises a broadband light source (1), a spectrum analyzer (2) and a propane gas detection unit (3); The broadband light source (1), the spectrum analyzer (2) and the propane gas detection unit (3) are respectively connected to three ports of the optical fiber circulator (4) in sequence through optical fiber jumpers; The propane gas detection unit (3) comprises a single-mode optical fiber (31), a multi-mode optical fiber (32), a dual-core optical fiber (33), and a UV glue micro-tip (34) which are connected in sequence; the UV glue micro-tip (34) extends along one of the cores of the dual-core optical fiber (33).

2. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The broadband light source (1) is a supercontinuum light source.

3. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The single-mode optical fiber (31) is Corning SMF-28, with a cladding diameter of 125 μm and a refractive index of 1.444 at 1550 nm, a core diameter of 8.2 μm, and a refractive index of 1.449; The multimode optical fiber (32) has a cladding diameter of 125 μm and a refractive index of 100, a core diameter of 105 μm and a refractive index of 1.444; The cladding diameter of the double-core optical fiber (33) is 125 μm, and the refractive index is 1.444; the core diameter is 9 μm, and the refractive index is 1.4492.

4. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The ultraviolet glue micro-tip (34) is formed by polymerization of ultraviolet photosensitive resin under ultraviolet light irradiation, and has a controllable size.

5. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The end face of the ultraviolet glue micro-tip (34) and the end faces of the two middle cores of the dual-core optical fiber (33) both form reflection surfaces, and the end face of the ultraviolet glue micro-tip (34) and the end faces of the two cores of the dual-core optical fiber (33) form three reflection surfaces, generating multiple groups of Fabry-Perot interference.

6. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The method for preparing the propane gas detection unit (3) specifically comprises the following steps: (i) splicing the single-mode optical fiber 31, the multi-mode optical fiber 32 and the dual-core optical fiber 33 in sequence to obtain a combined optical fiber; (ii) placing the combined optical fiber obtained in step (i) and another section of auxiliary single-mode optical fiber with a flat end face into a polarization-maintaining fusion splicer, and adjusting the distance between the end faces of the combined optical fiber and the auxiliary single-mode optical fiber by controlling the positions of two motors; The plane end face of the auxiliary single-mode optical fiber is arranged opposite to the dual-core optical fiber 33; (iii) injecting ultraviolet light photosensitive resin into the gap between the combined optical fiber and the auxiliary single-mode optical fiber, and transmitting ultraviolet light of 395 nm through the optical fiber and out from the end face of the dual-core optical fiber to cure the ultraviolet light photosensitive resin and form a micro-cone between the combined optical fiber and the auxiliary single-mode optical fiber; (iv) axial stretching is performed by moving the motor in the polarization-maintaining fusion splicer to control the length of the micro-cone; then the rotation direction is adjusted to obtain a flat micro-cone reflection surface; at the same time, the distance between the combined optical fiber and the auxiliary optical fiber is maintained at 40 μm to 50 μm to ensure that the micro-cone parameters meet the standards; The length of the micro-cone is 40 μm, and there is no requirement for the taper. The length of the UV glue micro-tip is determined by the gap between the combined optical fiber and the auxiliary single mode. The gap can be determined by the moving distance of the motor. (v) Using anhydrous ethanol to clean the uncured photosensitive material remaining on the micro-cone to obtain a stable micro-cone structure.

7. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 6 is characterized in that: In the step (i), the single-mode optical fiber (31), the multi-mode optical fiber (32) and the dual-core optical fiber (33) are fused using a Japanese fiber fusion splicer model Furukawa, S178A to form a FP optical fiber sensor.

8. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The broadband light source (1) is connected to the input end of the optical fiber circulator (4); the optical spectrum analyzer (2) is connected to the output end of the optical fiber circulator (4); the propane gas detection unit (3) is connected to the detection end of the optical fiber circulator (4); the optical fiber circulator (4) guides the light emitted by the broadband light source (1) to the propane gas detection unit (3), and then guides the reflected light to the optical spectrum analyzer (2) for analysis.

9. The in-situ sensor for propane content in air based on the optical fiber cursor effect according to claim 1 is characterized in that: The single-mode optical fiber (31) end of the propane gas detection unit (3) is connected to the optical fiber circulator (4).

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