A displacement and temperature dual-parameter sensing system and method based on SNAP structure microcavity

Abstract

The present invention relates to a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity. In this scheme, a tunable laser, a polarization controller, a coupling waveguide, a photodetector and a computer are connected in sequence, a displacement device is fixedly connected to the SNAP structure microcavity, and the displacement device is slidable. The coupling waveguide is provided with an output end and an input end, the output end and the input end are arranged relatively, and the SNAP structure microcavity is arranged between the output end and the input end. The wavelength of the central band of the first-order resonance mode of the SNAP structure microcavity of this scheme does not change with displacement. When the temperature changes, the wavelength of the central band of the SNAP structure microcavity changes with the change of temperature. The displacement is monitored by using the change of the transmittance of the resonance mode, and the temperature is monitored by using the change of the wavelength of the central band of the SNAP structure microcavity, thereby realizing the simultaneous measurement of the two parameters of displacement and temperature. The present invention also includes a method for realizing a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular to a displacement and temperature dual-parameter sensing system and method based on a SNAP structure microcavity. Background Art

[0002] In recent years, with the rapid development of precision and ultra-precision machining technology, the requirements for sensing technology have become increasingly higher. Optical sensing has a series of advantages such as non-physical contact, anti-electromagnetic interference and high sensitivity, so it has important research significance in many aspects such as biosensing, displacement sensing, temperature sensing and force sensing. At present, optical sensing is mainly performed through the following structures: such as Fabry-Perot cavity, surface plasmon and whispering gallery mode microcavity. Among them, the whispering gallery mode microcavity has excellent performance in sensitivity and detection limit due to its ultra-high Q value and extremely small mode volume. As one of them, the SNAP structure microcavity is easy to make and low in cost, so its application prospects are very large. For example, there is an existing displacement sensing system based on a double-chain SNAP structure microcavity array. The displacement sensing system mainly includes a tunable laser, a polarization controller, a coupled waveguide, a double chain of SNAP structure microcavity array, a displacement device, a photodetector, and a computer. The tunable laser generates a swept frequency laser, which enters the double-chain SNAP structure microcavity through the polarization controller and the coupled waveguide. The photodetector obtains the resonance spectrum and sends it to the computer for processing. When the microcavity moves, displacement sensing of half the length of the SNAP structure is achieved based on the resonance spectrum characteristics of a single SNAP structure microcavity; every time half the length of the SNAP structure is crossed, full-range displacement sensing is achieved by switching the resonance spectrum generated by the SNAP microcavities in the double chain in sequence.

[0003] The displacement sensing system can realize high-precision sensing of a large range of displacements. However, the resonant center wavelength of the SNAP structure microcavity of the displacement sensing system makes it difficult to accurately sense displacement and temperature at the same time. Summary of the invention

[0004] The present invention solves the problem that the displacement sensing system of the SNAP structure microcavity array in the above technical solution is difficult to accurately sense displacement and temperature at the same time, and provides a displacement and temperature dual parameter sensing system based on the SNAP structure microcavity. The SNAP structure microcavity sensing system in this solution can achieve accurate sensing of temperature and displacement at the same time.

[0005] The technical solution adopted by the present invention is: a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity, including a tunable laser, a polarization controller, a coupled waveguide, a SNAP structure microcavity, a displacement device, a photodetector and a computer. The tunable laser, the polarization controller, the coupled waveguide, the photodetector and the computer are connected in sequence, the displacement device is fixedly connected to the SNAP structure microcavity, and the displacement device is slidable. The coupled waveguide is provided with an output end and an input end, the output end and the input end are arranged oppositely, and the SNAP structure microcavity is arranged between the output end and the input end. Two protrusions are provided on the SNAP structure microcavity, and the shape and position of the two protrusions on the SNAP structure microcavity are defined by the effective radius of the axial cross-sectional profile of the SNAP structure microcavity as a function of the axial position. The effective radius of the axial cross-sectional profile of the SNAP structure microcavity as a function of the axial position is:

[0006]

[0007] Where: Δr eff is the effective radius change of the axial position of the SNAP structure microcavity; λc is the laser wavelength emitted by the tunable laser; r0 is the radius of the non-convex part of the SNAP structure microcavity; n is the refractive index of the SNAP structure microcavity material; s is the shape adjustment parameter of the SNAP structure microcavity; z is the axial length of the SNAP structure microcavity; L is the distance between the two small protrusions in the middle part of the SNAP structure microcavity.

[0008] Since the axial cross-sectional profile of the SNAP structure microcavity is similar to the shape of a bat, the SNAP structure microcavity of this shape is customarily called a bat-shaped SNAP structure microcavity.

[0009] This scheme uses the principle that the mode field distribution of the microcavity and the characteristic parameters of the resonance spectrum depend on the nanoscale effective radius protrusion of the cavity. Through certain processing means, a SNAP structure microcavity is produced on the optical fiber, and the microcavity is fixed by a displacement device and coupled with the coupling waveguide. Since the radial dimension change of the SNAP structure is extremely small, only at the nanometer level, it can well suppress the excitation of high-order modes. The wavelength of the central band of the SNAP structure microcavity of this scheme will not change with displacement. When the temperature changes, the wavelength of the central band of the SNAP structure microcavity changes with the change of temperature. Among them, the change in the wavelength of the central band of the SNAP structure microcavity is linearly related to the change in temperature, which can be calculated by the following formula:

[0010]

[0011] Where: Δλ represents the wavelength change of the central band of the SNAP structure microcavity, λ0 represents the resonant wavelength when the temperature does not change, ΔT represents the temperature change, represents the thermo-optic coefficient of the SNAP structure microcavity material, represents the thermal expansion coefficient of the SNAP structure microcavity material.

[0012] From the above formula, we can see that the wavelength of the central band of the SNAP structure microcavity changes linearly with temperature, and at the same time, the transmittance of each order resonance mode changes with the displacement. The displacement is monitored by the change of the transmittance of the resonance mode, and the temperature is monitored by the change of the wavelength of the central band of the SNAP structure microcavity, thereby realizing the simultaneous measurement of the two parameters of displacement and temperature.

[0013] The laser generated by the tunable laser enters the polarization controller through the optical fiber. The polarization controller adjusts the polarization state of the laser and inputs the coupling waveguide through the optical fiber. The coupling waveguide is coupled with the SNAP structure microcavity. The laser that meets the resonance condition is coupled into the SNAP structure microcavity. The photodetector is connected to the coupling waveguide to receive the laser from the coupling waveguide and convert the received optical signal into an electrical signal, thereby obtaining the coupled resonance spectrum.

[0014] Preferably, in the function of the effective radius of the axial cross-sectional profile of the SNAP structure microcavity changing with the axial position, the distance between the two protrusions in the middle of the SNAP structure microcavity is L=300 μm; the axial length z of the SNAP structure microcavity is 400 μm; the radius r0 of the non-protruding part of the SNAP structure microcavity is 62.5 μm; the refractive index n of the SNAP structure microcavity material is 1.452; and the SNAP structure microcavity shape adjustment parameter s is 40. The SNAP structure microcavity can be obtained by arc discharge, carbon dioxide laser or ultraviolet light acting on a uniform optical fiber.

[0015] Preferably, the coupling waveguide is in contact with the SNAP structure microcavity during operation. The coupling waveguide can be a micro-nano tapered fiber, a coupling prism, a planar waveguide, a ground angled fiber or a fiber grating. The operating wavelength of the tunable laser is 1550nm, and its line width is 300kHz. The coupling waveguide is a tapered fiber with a waist diameter of 2um. During the operation of the system, the coupling waveguide maintains contact with the SNAP structure microcavity array, and the weak electrostatic force between the two provides stability for the system, so that the entire system has good anti-vibration interference ability.

[0016] A method for realizing a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity comprises the following steps:

[0017] Step 1: The laser emitted from the tunable laser is input into the coupling waveguide after being acted upon by the polarization controller. The light wave in the coupling waveguide is transmitted to the photodetector after passing through the SNAP structure microcavity. The photodetector converts the light wave into an electrical signal and sends it to the computer for processing.

[0018] Step 2: The displacement device moves in a certain direction to cause the SNAP structure microcavity to change its displacement relative to the coupled waveguide. However, the central wavelength of the central band of the first-order resonance mode in the generated resonance spectrum does not change with the displacement. When the temperature changes, the central wavelength of the central band of the first-order resonance mode will change with the temperature, and the transmittance of each order resonance mode will change with the displacement.

[0019] Step 3: Input the generated resonance spectrum data into a computer. The computer monitors the displacement according to the change of transmittance of the resonance mode and monitors the temperature according to the change of the central wavelength in the middle part of the first-order resonance mode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The displacement and temperature dual-parameter sensing system based on the SNAP structure microcavity adopted in the present invention can realize the simultaneous sensing of displacement and temperature, solves the problem that two sets of coupling systems are required for simultaneous sensing of temperature and displacement, simplifies the sensing system, and further reduces the cost.

[0022] 2. The SNAP structure microcavity in the present invention always keeps in contact with the coupled waveguide during operation, and the weak electrostatic force between the two provides stability for the system, so that the entire system has good anti-vibration interference ability.

[0023] 3. The SNAP structure microcavity used in the present invention is small in size, low in cost and suitable for microstructure measurement occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity provided by the present invention.

[0025] Figure 2 It is a schematic diagram of the axial profile of the nano-scale protrusions on the surface of the SNAP structure microcavity provided by the present invention.

[0026] Figure 3 It is the resonant mode spectrum at different positions of the SNAP structure microcavity provided by the present invention.

[0027] Figure 4 It is a curve diagram showing the variation of transmittance of the first 10 order modes of the SNAP structure microcavity provided by the present invention with displacement.

[0028] Figure 5 It is a comparison diagram of the curve of the change of the central wavelength of the first-order resonance mode of the SNAP structure microcavity provided by the present invention with the displacement and the curve of the change of the central wavelength of the first-order resonance mode of the parabolic SNAP structure microcavity with the displacement.

[0029] Figure 6 This is a graph showing the relationship between the center wavelength of the first-order resonance mode and the temperature when the initial wavelength is 1550nm and the initial temperature is set to 298K.

[0030] Figure 7 It is a flow chart of a method for realizing a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity of the present invention. DETAILED DESCRIPTION

[0031] The drawings are only for illustrative purposes and cannot be construed as limiting the present invention. To better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted. The positional relationships described in the drawings are only for illustrative purposes and cannot be construed as limiting the present invention.

[0032] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "long", "short" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0034] Example 1

[0035] like Figure 1-Figure 6The figure shows an embodiment of a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity, a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity, comprising a tunable laser 1, a polarization controller 2, a coupling waveguide 3, a SNAP structure microcavity 4, a displacement device 5, a photodetector 6 and a computer 7. The tunable laser 1, the polarization controller 2, the coupling waveguide 3, the photodetector and the computer 7 are connected in sequence, the displacement device 5 is fixedly connected to the SNAP structure microcavity 4, and the displacement device 5 is slidable. The coupling waveguide 3 is provided with an output end 301 and an input end 302, the output end 301 and the input end 302 are arranged oppositely, and the SNAP structure microcavity 4 is arranged between the output end 301 and the input end 302. The SNAP structure microcavity 4 is provided with two protrusions, and the shapes and positions of the two protrusions on the SNAP structure microcavity 4 are defined by the effective radius of the axial cross-sectional profile of the SNAP structure microcavity 4 as a function of the axial position. The effective radius of the axial cross-sectional profile of the SNAP structure microcavity 4 as a function of the axial position is:

[0036]

[0037] Where: Δr eff is the effective radius change of the axial position of the SNAP structure microcavity; λc is the laser wavelength emitted by the tunable laser; r0 is the radius of the non-convex part of the SNAP structure microcavity; n is the refractive index of the SNAP structure microcavity material; s is the shape adjustment parameter of the SNAP structure microcavity; z is the axial length of the SNAP structure microcavity; L is the distance between the two protrusions of the SNAP structure microcavity.

[0038] Since the axial cross-sectional profile of the SNAP structure microcavity 4 is similar to the shape of a bat, the SNAP structure microcavity 4 of this shape is customarily called a bat-shaped SNAP structure microcavity. The distance between the two protrusions on the SNAP structure microcavity 4 is the central band of the SNAP structure microcavity 4.

[0039] Working principle of this embodiment: This scheme utilizes the principle that the mode field distribution of the microcavity and the characteristic parameters of the resonance spectrum depend on the nanoscale effective radius protrusion of the cavity. A SNAP structure microcavity 4 is produced on the optical fiber through certain processing means, and the SNAP structure microcavity 3 is fixed by a displacement device 5 and coupled with the coupling waveguide 3. Since the radial dimension change of the SNAP structure microcavity 4 is extremely small, only at the nanometer level, it is able to well suppress the excitation of higher-order modes. The wavelength of the central band of the first-order resonant mode of the SNAP structure microcavity 4 of this scheme will not change with displacement. When the temperature changes, the wavelength of the central band of the SNAP structure microcavity 4 changes with the change in temperature. Among them, the change in the wavelength of the central band of the first-order resonant mode of the SNAP structure microcavity 4 is linearly related to the change in temperature, which can be calculated by the following formula:

[0040]

[0041] Where: Δλ represents the wavelength change of the central band of the first-order resonance mode of the SNAP structure microcavity 4, ΔT represents the temperature change, and λ0 represents the resonance wavelength when the temperature does not change. represents the thermo-optic coefficient of the SNAP structure microcavity 4 material, represents the thermal expansion coefficient of the SNAP structure microcavity 4 material.

[0042] From the above formula, it can be seen that the wavelength of the central band of the first-order resonance mode of the SNAP structure microcavity 4 changes linearly with the temperature. At the same time, the transmittance of each resonance mode changes with the displacement. The displacement is monitored by the change of the transmittance of the resonance mode, and the temperature is monitored by the change of the central band wavelength of the first-order resonance mode of the SNAP structure microcavity 4, thereby realizing the simultaneous measurement of the two parameters of displacement and temperature.

[0043] The working process of this embodiment is as follows: the laser generated by the tunable laser 1 enters the polarization controller 2 through the optical fiber, the polarization controller 2 adjusts the polarization state of the laser and inputs the coupling waveguide 3 through the optical fiber, the coupling waveguide 3 is coupled with the SNAP structure microcavity 4, the laser meeting the resonance condition is coupled into the SNAP structure microcavity 4, the photodetector 6 is connected to the coupling waveguide 3, and is used to receive the laser from the coupling waveguide and convert the received optical signal into an electrical signal, so as to obtain the coupled resonance spectrum.

[0044] Beneficial effects of this embodiment: The displacement and temperature dual parameter sensing system based on the SNAP structure microcavity adopted by the present invention can realize the simultaneous sensing of displacement and temperature, solves the problem that two sets of coupling systems are required for simultaneous sensing of temperature and displacement, simplifies the sensing system, and further reduces the cost. The SNAP structure microcavity 4 in the present invention is small in size, low in cost and suitable for microstructure measurement occasions.

[0045] Example 2

[0046] Embodiment 2 of a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity, based on embodiment 1, as Figure 1-Figure 6 As shown, the system is further limited.

[0047] Specifically, in the function of the effective radius of the axial cross-sectional profile of the SNAP structure microcavity 4 changing with the axial position, the distance between the two protrusions in the middle of the SNAP structure microcavity 4 is L=300 μm; the axial length z of the SNAP structure microcavity 4 is 400 μm; the radius r0 of the non-protruding part of the SNAP structure microcavity 4 is 62.5 μm; the refractive index n of the material of the SNAP structure microcavity 4 is 1.452; and the shape adjustment parameter s of the SNAP structure microcavity 4 is 40. The SNAP structure microcavity 4 can be obtained by arc discharge, carbon dioxide laser or ultraviolet light acting on a uniform optical fiber.

[0048] Specifically, the coupling waveguide 3 contacts the SNAP structure microcavity 4 during operation. The coupling waveguide 3 is a tapered optical fiber with a tapered waist diameter of 2 um. The operating wavelength of the tunable laser 1 is 1550 nm and the line width is 300 kHz.

[0049] Beneficial effects of this embodiment: During the operation of the system, the coupling waveguide 3 and the SNAP structure microcavity 4 maintain contact, and the weak electrostatic force between the two provides stability for the system, so that the entire system has a good ability to resist vibration interference.

[0050] Example 3

[0051] Embodiment 3 of a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity, based on embodiment 1 or 2, as Figure 7 As shown, a method for realizing a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity includes the following steps:

[0052] Step 1: The laser emitted from the tunable laser 1 is input into the coupling waveguide 3 after being acted upon by the polarization controller 2. The light wave in the coupling waveguide 3 passes through the SNAP structure microcavity 4 and is transmitted to the photodetector. The photodetector converts the light wave into an electrical signal and sends it to the computer 7 for processing.

[0053] Step 2: The displacement device 5 moves in a certain direction, so that the SNAP structure microcavity 4 produces a displacement change relative to the coupling waveguide 3.

[0054] Step 3: Input the generated resonance spectrum data into the computer 7. The computer 7 monitors the displacement according to the change of the transmittance of the resonance mode and monitors the temperature according to the change of the central wavelength of the middle part of the first-order resonance mode.

[0055] Beneficial effects of this embodiment: This method can realize simultaneous sensing of displacement and temperature based on a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity.

[0056] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A displacement and temperature dual parameter sensing system based on a SNAP structure microcavity, comprising a tunable laser (1), a polarization controller (2), a coupled waveguide (3), a SNAP structure microcavity (4), a displacement device (5), a photodetector (6) and a computer (7), wherein the tunable laser (1), the polarization controller (2), the coupled waveguide (3), the photodetector (6) and the computer (7) are connected in sequence, the displacement device (5) is fixedly connected to the SNAP structure microcavity (4), and the displacement device (5) is slidable, the coupled waveguide (3) is provided with an output end (301) and an input end (302), and the output end (301) is arranged opposite to the input end (302); the SNAP structure microcavity (4) is arranged between the output end (301) and the input end (302), and characterized in that: The SNAP structure microcavity (4) is provided with two protrusions, and the shapes and positions of the two protrusions on the SNAP structure microcavity (4) are defined by a function of the effective radius of the axial cross-sectional profile of the SNAP structure microcavity (4) changing with the axial position. The function of the effective radius of the axial cross-sectional profile of the SNAP structure microcavity (4) changing with the axial position is: Where: Δr eff is the effective radius change of the axial position of the SNAP structure microcavity; λc is the laser wavelength emitted by the tunable laser; r0 is the radius of the non-convex part of the SNAP structure microcavity; n is the refractive index of the SNAP structure microcavity material; s is the shape adjustment parameter of the SNAP structure microcavity; z is the axial length of the SNAP structure microcavity; L is the distance between the two protrusions of the SNAP structure microcavity; The laser light generated by the tunable laser (1) enters the polarization controller (2), the polarization controller (2) adjusts the polarization state of the laser light and inputs it into the coupling waveguide (3), the coupling waveguide (3) is coupled with the SNAP structure microcavity (4), and the laser light that meets the resonance condition is coupled into the SNAP structure microcavity (4), the photodetector (6) can receive the laser light from the coupling waveguide (3) and convert the received optical signal into an electrical signal, thereby obtaining a coupled resonance spectrum. It can be seen from the resonance spectrum that the transmittance of each order resonance mode changes with the displacement of the SNAP structure microcavity (4), and the wavelength of the central band of the first order resonance mode of the SNAP structure microcavity (4) changes linearly with the temperature. The linear relationship between the wavelength change of the central band of the first order resonance mode of the SNAP structure microcavity (4) and the temperature change is as follows: Wherein: Δλ represents the wavelength change of the central band of the first-order resonance mode of the SNAP structure microcavity (4), ΔT represents the temperature change, λ0 represents the resonance wavelength when the temperature does not change, represents the thermo-optic coefficient of the SNAP structure microcavity (4) material, Indicates the thermal expansion coefficient of the material of the SNAP structure microcavity (4).

2. According to claim 1, a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity is characterized in that: The distance L between the two protrusions of the SNAP structure microcavity is 300 μm, and the axial length z of the SNAP structure microcavity is 400 μm.

3. According to claim 2, a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity is characterized in that: The radius r0 of the non-convex part of the SNAP structure microcavity is 62.5 μm.

4. The dual-parameter displacement and temperature sensing system based on the SNAP structure microcavity according to claim 3 is characterized in that: The refractive index of the SNAP structure microcavity material is n=1.452; the SNAP structure microcavity shape adjustment parameter is s=40.

5. The dual-parameter displacement and temperature sensing system based on the SNAP structure microcavity according to claim 1 is characterized in that: The SNAP structure microcavity (4) belongs to a whispering gallery mode microcavity.

6. The displacement and temperature dual parameter sensing system based on SNAP structure microcavity according to claim 5 is characterized in that: The SNAP structure microcavity (4) can be obtained by arc discharge, carbon dioxide laser or ultraviolet light acting on a uniform optical fiber.

7. The displacement and temperature dual parameter sensing system based on SNAP structure microcavity according to claim 1 is characterized in that: The coupling waveguide (3) contacts the SNAP structure microcavity (4) during operation.

8. The dual-parameter displacement and temperature sensing system based on the SNAP structure microcavity according to claim 7 is characterized in that: The coupling waveguide (3) can be a micro-nano tapered optical fiber, a coupling prism, a planar waveguide, a ground angled optical fiber or an optical fiber grating.

9. The displacement and temperature dual parameter sensing system based on SNAP structure microcavity according to claim 1 is characterized in that: The operating wavelength of the tunable laser (1) is 1550 nm and the line width is 300 kHz.

10. A method for realizing a displacement and temperature dual-parameter sensing system based on a SNAP structure microcavity, characterized in that: The displacement and temperature dual parameter sensing system is a displacement and temperature dual parameter sensing system based on a SNAP structure microcavity as described in any one of claims 1 to 9, comprising the following steps: Step 1: The laser light emitted from the tunable laser (1) is input into the coupling waveguide (3) after being acted upon by the polarization controller (2). The light wave in the coupling waveguide (3) is transmitted to the photodetector (6) after passing through the SNAP structure microcavity (4). The photodetector (6) converts the light wave into an electrical signal and sends it to the computer (7) for processing. Step 2: The displacement device (5) moves in a certain direction, so that the SNAP structure microcavity (4) produces a displacement change relative to the coupling waveguide (3); Step 3: Input the generated resonance spectrum data into the computer (7), and the computer (7) monitors the displacement according to the change of the transmittance of the resonance mode, and monitors the temperature according to the change of the central wavelength of the middle part of the first-order resonance mode.

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