CN113108940B - Temperature sensing system and device - Google Patents
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- CN113108940B CN113108940B CN202110404085.XA CN202110404085A CN113108940B CN 113108940 B CN113108940 B CN 113108940B CN 202110404085 A CN202110404085 A CN 202110404085A CN 113108940 B CN113108940 B CN 113108940B
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- 229920000435 poly(dimethylsiloxane) Polymers 0.000 claims description 52
- CXQXSVUQTKDNFP-UHFFFAOYSA-N octamethyltrisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)O[Si](C)(C)C CXQXSVUQTKDNFP-UHFFFAOYSA-N 0.000 claims description 51
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- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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Abstract
The embodiment of the application provides a temperature sensing system and a temperature sensing device, and belongs to the technical field of optical fiber sensors. The temperature sensing system includes: the broadband light source, the sensor and the spectrometer are all connected with the optical fiber connector, the sensor comprises a first sensing interferometer and a second sensing interferometer which are mutually connected, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, and the sensor senses the temperature based on vernier effects generated by the first sensing interferometer and the second sensing interferometer. That is, the sensor includes two sensing interferometers. And because the first sensing interferometer and the second sensing interferometer have opposite temperature responses to the temperature, the first sensing interferometer and the second sensing interferometer can generate an enhanced vernier effect, the amplification factor of the sensor is effectively improved, and the sensitivity of the sensor is increased.
Description
Technical Field
The embodiment of the application relates to the technical field of optical fiber sensors, in particular to a temperature sensing system and a temperature sensing device.
Background
The temperature is one of seven basic physical quantities manufactured by international units, and the accurate measurement of the temperature plays a significant role in the fields of national economy, national defense construction, scientific research and the like. With the improvement of the application requirement of temperature sensing, the traditional temperature sensor can not meet the measurement requirement of high precision, and the optical fiber temperature sensor has the advantages of small size, high measurement precision, high sensitivity, strong electromagnetic interference resistance, good electrical insulation, large temperature range and the like, and has unique advantages in the aspect of temperature measurement, so the research on the optical fiber temperature sensor is particularly important.
In recent years, the vernier effect has been widely used to improve the sensitivity of the optical fiber temperature sensor. Typically, fiber optic temperature sensors based on the vernier effect include a reference interferometer and a sensing interferometer, where only the sensing interferometer is responsive to temperature changes, and the reference interferometer is not responsive to temperature changes. Such a fiber optic temperature sensor can only produce the conventional vernier effect. Although the sensitivity of the fiber optic temperature sensor is improved by 1 to 2 orders of magnitude relative to a single sensing interferometer, the need for high sensitivity temperature sensing is still not met in many cases.
Disclosure of Invention
In view of the above, embodiments of the present application provide a temperature sensing system and apparatus that overcomes or at least partially solves the above-mentioned problems.
According to an aspect of an embodiment of the present application, there is provided a temperature sensing system including: the system comprises a broadband light source, an optical fiber connector, a sensor and a spectrometer;
the broadband light source, the sensor and the spectrometer are all connected with the fiber optic connector, the sensor comprises a first sensing interferometer and a second sensing interferometer that are interconnected, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, and the sensor senses temperature based on a vernier effect produced by the first sensing interferometer and the second sensing interferometer.
Optionally, the sensor comprises: single mode fiber, hollow fiber and PDMS;
the first end of the single mode fiber is connected with the optical fiber connector, and the second end of the single mode fiber is connected with the first end of the hollow fiber;
a first air hole communicated with the axial through hole of the hollow optical fiber is radially formed in the first end of the hollow optical fiber, the PDMS is injected into the hollow optical fiber from the first air hole, and the first sensing interferometer is formed at the first end of the hollow optical fiber;
and injecting the PDMS into the hollow-core optical fiber from the second end of the hollow-core optical fiber, and forming the second sensing interferometer between the first end and the second end of the hollow-core optical fiber, wherein the free spectral range of the first sensing interferometer is a preset multiple of the free spectral range of the second sensing interferometer.
Optionally, the preset multiple is greater than or equal to 0.9 and less than or equal to 0.99.
Optionally, the preset multiple is greater than or equal to 1.01 and less than or equal to 1.10.
Optionally, an included angle is formed between the end surface of the second end of the hollow-core optical fiber and the cross section of the hollow-core optical fiber, and the degree of the included angle is not equal to zero.
Optionally, the degree of the included angle is greater than or equal to 7 degrees.
Optionally, the hollow-core optical fiber is further provided with a second air hole in the radial direction, and the second air hole is communicated with the second sensing interferometer.
Optionally, a distance between the first air hole and the end face of the first end of the hollow-core optical fiber is greater than or equal to 10 micrometers and less than or equal to 20 micrometers.
Optionally, the optical fiber connector comprises a fiber optic circulator or a fiber optic coupler.
According to another aspect of embodiments of the present application, there is provided an apparatus comprising the temperature sensing system described above.
In an embodiment of the application, the sensor comprises a first sensing interferometer and a second sensing interferometer interconnected. That is, the sensor includes two sensing interferometers. And because the first sensing interferometer and the second sensing interferometer have opposite temperature responses to the temperature, the first sensing interferometer and the second sensing interferometer can generate an enhanced vernier effect, the amplification factor of the sensor is effectively improved, and the sensitivity of the sensor is increased.
The foregoing description is only an overview of the technical solutions of the embodiments of the present application, and in order that the technical means of the embodiments of the present application can be clearly understood, the embodiments of the present application are specifically described below in order to make the foregoing and other objects, features, and advantages of the embodiments of the present application more clearly understandable.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a temperature sensing system according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of the effect of temperature on the interference spectrum according to an embodiment of the present disclosure;
fig. 3 is a schematic structural diagram of a sensor according to an embodiment of the present disclosure;
FIG. 4 is a schematic diagram of a cascade interference spectrum provided by an embodiment of the present application;
fig. 5 is a schematic diagram illustrating an effect of temperature on cascade interference spectrum according to an embodiment of the present application.
Reference numerals:
1: broadband light source, 2: optical fiber connector, 3: sensor, 4: spectrometer, 31: single-mode optical fiber, 32: hollow-core optical fiber, 33: PDMS,321: first air hole, 322: PDMS chamber, 323: air chamber, 324: second air vent, M1: first reflective interface, M2: second reflective interface, M3: third reflective interface, P1: first interference spectrum, P2: second interference spectrum, P3: parallel interference spectrum, P4: envelope spectrum, α: an included angle, R: incident light, F1: first reflected light, F2: second reflected light, F3: and the third reflected light.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
The terms "comprising" and "having," and any variations thereof, in the description and claims of this application and in the description of the figures are intended to cover, but not exclude, other things. The word "a" or "an" does not exclude a plurality.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein may be combined with other embodiments.
The term "and/or" herein is merely an association describing an associated object, meaning that three relationships may exist, e.g., a and/or B, may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
The following description is presented with the directional terms as they are used in the drawings and not intended to limit the specific structure of the temperature sensing system of the present application. For example, in the description of the present application, the terms "central," "longitudinal," "lateral," "length," "width," "up," "down," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in an orientation or positional relationship that is indicated based on the orientation or positional relationship shown in the drawings for ease of description and simplicity of description only, and do not indicate or imply that the device or element so referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present application.
Furthermore, the terms "first," "second," and the like in the description and claims of the present application or in the above-described drawings are used for distinguishing between different objects and not necessarily for describing a particular sequential order, and may explicitly or implicitly include one or more of the features.
In the description of the present application, unless otherwise specified, "plurality" means two or more (including two), and similarly, "plural groups" means two or more (including two).
In the description of the present application, it should be noted that, unless explicitly stated or limited otherwise, the terms "mounted," "connected" and "connected" should be interpreted broadly, for example, the mechanical structures "connected" or "connected" may refer to physical connections, for example, the physical connections may be fixed connections, for example, fixed connections by fasteners, such as screws, bolts or other fasteners; the physical connection can also be a detachable connection, such as a mutual snap-fit or snap-fit connection; the physical connection may also be an integral connection, for example, a connection made by welding, gluing or integrally forming the connection. "connected" or "connected" of circuit structures may mean not only physically connected but also electrically connected or signal-connected, for example, directly connected, i.e., physically connected, or indirectly connected through at least one intervening component, as long as the circuits are in communication, or communication between the interiors of two components; signal connection in addition to signal connection through circuitry, may also refer to signal connection through a media medium, such as radio waves. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.
Fig. 1 is a schematic structural diagram of a temperature sensing system according to an embodiment of the present disclosure, as shown in fig. 1 (arrows in fig. 1 represent transmission directions of optical signals), the temperature sensing system includes: a broadband light source 1, a fiber optic connector 2, a sensor 3 and a spectrometer 4. The broadband light source 1, the sensor 3 and the spectrometer 4 are all connected with the optical fiber connector 2, the sensor 3 comprises a first sensing interferometer and a second sensing interferometer which are interconnected, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, and the sensor 3 senses the temperature based on vernier effect generated by the first sensing interferometer and the second sensing interferometer.
It should be noted that the broadband light source 1 is used to provide a light source, and the broadband light source 1 can provide light with any wavelength, for example, light with a wavelength of 1200nm (nanometers) to 1600 nm.
In addition, the optical fiber connector 2 is used for connecting an optical fiber device, and the optical fiber connector 2 may be any one of an optical fiber circulator and an optical fiber coupler. The optical fiber connector 2 can also transmit light, incident light R emitted by the broadband light source 1 enters the sensor 3 through the optical fiber connector 2, light reflected from the sensor 3 enters the spectrometer 4 through the optical fiber connector 2, and the spectrometer 4 receives the light reflected from the sensor 3 and measures an interference spectrum of the sensor 3 based on the reflected light.
In order to ensure the unidirectionality of optical transmission, an optical fiber isolator may be further disposed between the broadband light source 1 and the optical fiber connector 2, so that light emitted by the broadband light source 1 may enter the optical fiber connector 2 through the optical fiber isolator, but cannot return to the broadband light source 1 from the optical fiber isolator, and thus the broadband light source 1 is not damaged.
Fig. 2 is a schematic diagram illustrating an effect of temperature on an interference spectrum according to an embodiment of the present disclosure, as shown in fig. 2 (a), a first interference spectrum P1 formed by reflected light returned by a first sensing interferometer shifts with a change in temperature, and it can be seen that the first sensing interferometer responds to temperature. As shown in fig. 2 (b), the second interference spectrum P2 formed by the reflected light returned by the second sensing interferometer also shifts with the temperature, and it can be seen that the second sensing interferometer also responds to the temperature. That is, both the first and second sensing interferometers are responsive to temperature. Further, as the temperature increases, the first interference spectrum P1 shifts to the left (i.e., blue-shift) as shown in fig. 2 (a), and the second interference spectrum P2 shifts to the right (i.e., red-shift) as shown in fig. 2 (b), and it can be seen that as the temperature increases, the first interference spectrum P1 and the second interference spectrum P2 shift in opposite directions. That is, the first and second sensing interferometers have opposite temperature responses to temperature. It should be noted that fig. 2 is only an example, and the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, and the first interference spectrum P1 may be red-shifted and the second interference spectrum P2 may be blue-shifted with increasing temperature, which is not limited by the embodiment of the present application.
In the present embodiment, the sensor 3 comprises a first and a second sensing interferometer interconnected. That is, the sensor 3 includes two sensing interferometers. And because the first sensing interferometer and the second sensing interferometer have opposite temperature responses to the temperature, the first sensing interferometer and the second sensing interferometer can generate an enhanced vernier effect, the amplification factor of the sensor 3 is effectively improved, and the sensitivity of the sensor 3 is increased.
In some embodiments, as shown in fig. 3, the sensor 3 comprises: a single mode fiber 31, a hollow core fiber 32, and PDMS33;
the first end of the single mode optical fiber 31 is connected with the optical fiber connector 2, and the second end of the single mode optical fiber 31 is connected with the first end of the hollow-core optical fiber 32. A first air hole 321 communicated with an axial through hole of the hollow-core optical fiber 32 is radially arranged at a first end of the hollow-core optical fiber 32, the PDMS33 is injected into the hollow-core optical fiber 32 from the first air hole 321, and the first sensing interferometer is formed at the first end of the hollow-core optical fiber 32; the PDMS33 is injected into the hollow-core fiber 32 from the second end of the hollow-core fiber 32, and the second sensing interferometer is formed between the first end and the second end of the hollow-core fiber 32, and the free spectral range of the first sensing interferometer is a preset multiple of the free spectral range of the second sensing interferometer.
The single-mode optical fiber 31 includes an optical fiber core and an optical fiber cladding, and the optical fiber cladding is wrapped outside the optical fiber core. The diameter of the single mode fiber 31 may be 125 μm (micrometers) and the core of the single mode fiber 31 may be 10 μm directly. The outer diameter of the hollow core fiber 32 may be 125 μm and the inner diameter (i.e., the diameter of the axial through hole) may be 50 to 70 μm. The embodiments of the present application do not limit this.
In addition, the first air hole 321 serves as an injection passage for injecting the PDMS33 toward the first end of the hollow fiber 32. To ensure that no bubbles are generated when injecting the PDMS33 into the first end of the hollow-core optical fiber 32 to form a good first sensing interferometer (i.e., the PDMS cavity 322. The PDMS cavity 322 will be used in the following description), the first air hole 321 may be disposed on the sidewall of the first end of the hollow-core optical fiber 32 and may be disposed as close to the end face of the first end of the hollow-core optical fiber 32 as possible. That is, the distance between the first air hole 321 and the end face of the first end of the hollow-core optical fiber 32 may be as small as possible, and for example, the distance may be greater than or equal to 10 μm and less than or equal to 20 μm. In addition, the aperture of the first air hole 321 may be set according to the cavity length of the PDMS cavity 322, for example, the aperture of the first air hole 321 may be greater than or equal to 5 μm and less than or equal to 20 μm. The embodiments of the present application do not limit this.
In addition, PDMS33 is polydimethylsiloxane, which is an excellent thermal sensitive material, and has obvious thermal expansion and cold contraction effects. PDMS33 was liquid for a certain period of time immediately after the preparation, and solidified to a colorless transparent solid after heating. In addition, PDMS33 has good light transmission and refraction properties, good adhesion and chemical inertness, and is very suitable for being combined with optical fibers to carry out high-sensitivity temperature measurement.
The first section of PDMS33 is filled in the first end of the hollow-core optical fiber 32, so that a PDMS cavity 322 (the PDMS cavity 322 is a fabry-perot sensing interferometer) may be formed at the first end of the hollow-core optical fiber 32, and thus a first reflective interface M1 is formed between the second end of the single-mode optical fiber 31 and the PDMS cavity 322. When the second section of PDMS33 is filled into the second end of the hollow-core optical fiber 32, the air in the hollow-core optical fiber 32 is compressed and confined between the first end and the second end of the hollow-core optical fiber 32, forming an air cavity 323 (i.e., a second sensing interferometer; the following description will collectively use the air cavity 323. The air cavity 323 is also a fabry-perot sensing interferometer), so that a second reflective interface M2 is formed between the PDMS cavity 322 and the air cavity 323, and a third reflective surface M3 is formed between the air cavity 323 and the second section of PDMS33.
That is, in the sensor 3, two ends of the hollow fiber 32 are respectively a section of PDMS33, and an air cavity 323 is sandwiched between the two sections of PDMS33. When the temperature rises, the two sections of PDMS33 are thermally expanded, the air cavity 323 is simultaneously pressed towards the middle, the cavity length of the air cavity 323 is reduced, the optical path is reduced, when the temperature drops, the two sections of PDMS33 shrink, so that the cavity length of the middle air cavity 323 is increased, the optical path is increased, the temperature response sensitivity of the air cavity 323 is further increased, and the amplification factor of the enhanced vernier effect is further increased.
Based on the sensor 3 provided in the embodiment of the present application, a part of the incident light R entering the single-mode fiber 31 is reflected back to the single-mode fiber 31 at the first reflective interface M1 to generate a first reflected light F1, and the remaining part enters the PDMS cavity 322 through the first reflective interface M1. A portion of the light entering the PDMS cavity 322 through the first reflective interface M1 is reflected back to the PDMS cavity 322 at the second reflective interface M2, generating a second reflected light F2, and the remaining portion enters the air cavity 323 through the second reflective interface M2. Most of the light entering the air cavity 323 through the second reflective interface M2 is reflected back to the air cavity 323 at the third reflective interface M3 to generate third reflected light F3, and the remaining small part of the light enters the second section of PDMS33 through the third reflective interface M3. The spectrometer 4 measures a first interference spectrum P1 based on the first reflected light F1 and the second reflected light F2, and a second interference spectrum P2 based on the third reflected light F3 and the first reflected light F1. The spectrometer 4 can also measure a parallel interference spectrum P3 based on the first interference spectrum P1 and the second interference spectrum P2.
Further, in order to prevent the light entering the second section of PDMS33 through the third reflective interface M3 from being reflected back to the second section of PDMS33 from the end surface of the second end of the hollow-core optical fiber 32 and then entering the air cavity 323, as shown in fig. 3, the end surface of the second end of the hollow-core optical fiber 32 may be arranged as an inclined surface, and an included angle α may be formed between the end surface and the cross section of the hollow-core optical fiber 32, and the degree of the included angle α is not equal to zero. When the angle α is set appropriately, no light will be reflected back from the end face of the second end of hollow core fiber 32.
The included angle α between the end surface of the second end of the hollow-core optical fiber 32 and the cross section of the hollow-core optical fiber 32 may be set according to the principle of optical transmission, and the degree of the included angle α may be any value greater than or equal to 7 degrees, for example, the degree of the included angle α may be 8 degrees, 10 degrees, and the like, which is not limited in this embodiment of the present application.
In some embodiments, to facilitate injecting the PDMS33 from the second end of the hollow-core optical fiber 32 and to facilitate adjusting the cavity length of the air cavity 323, the hollow-core optical fiber 32 may be further provided with a second air hole 324 in communication with the axial through hole in the radial direction, and the second air hole 324 is in communication with the air cavity 323. Wherein, the aperture of the second air hole 324 can be set according to the cavity length of the air cavity 323, for example, the aperture of the second air hole 324 can be greater than or equal to 5 μm and less than or equal to 20 μm. The aperture of the second air hole 324 may be the same as or different from the aperture of the first air hole 321, which is not limited in this embodiment of the present invention.
The second air hole 324 is disposed between the first end and the second end of the hollow-core optical fiber 32 and communicates with the air chamber 323, and on one hand, when injecting the PDMS33 from the second end of the hollow-core optical fiber 32, a part of air between the first end and the second end is discharged from the second air hole 324, thereby facilitating the injection of the PDMS33. On the other hand, by discharging a portion of the air between the first end and the second end from the second air hole 324, the cavity length of the air cavity 323 can be reduced. When it is necessary to increase the cavity length of the air cavity 323, air may also be injected into the air cavity 323 from the second air hole 324. That is, the length of the air chamber 323 can be easily adjusted by exhausting or injecting air from the second air hole 324.
When the sensor 3 provided by the embodiment of the present application is manufactured, the second end of the single-mode fiber 31 may be welded to the first end of the hollow-core fiber 32 to form the first reflection interface M1, and then the hollow-core fiber 32 is cut, so that the cavity length of the hollow-core fiber 32 reaches the first preset cavity length, and an included angle α is formed between the end surface of the second end of the hollow-core fiber 32 and the cross section. Then, a femtosecond laser is used to radially open a first air hole 321 at the first end of the hollow-core optical fiber 32, so that the first air hole 321 is communicated with the axial through hole of the hollow-core optical fiber 32. A second air hole 324 is radially punched between the first end and the second end of the hollow-core optical fiber 32 by the femtosecond laser, so that the second air hole 324 is communicated with the axial through hole of the hollow-core optical fiber 32. Then, the liquid PDMS33 is injected into the first end of the hollow-core fiber 32 from the first air hole 321 by using capillary phenomenon, and the injection process ensures that no air bubble is generated near one end of the single-mode fiber 31, thereby forming a PDMS cavity 322 (the first section of PDMS 33) with a certain cavity length. And then, slowly injecting the liquid PDMS33 from the second end of the hollow fiber 32 by using the capillary phenomenon to form a second section of PDMS33, and forming an air cavity 323 with a certain cavity length between the first end and the second end of the hollow fiber 32. Finally, the PDMS33 is heated and cured.
Wherein the first predetermined cavity length may be 1 to 2mm (millimeters). In addition, the cavity length of the PDMS cavity 322 may be 100 to 150 μm, and the cavity length of the air cavity 323 may be a preset multiple of the cavity length of the PDMS cavity 322, for example, the cavity length of the air cavity 323 may be 1.4 times of the cavity length of the PDMS cavity 322, so that it may be ensured that the optical path length of the air cavity 323 is the preset multiple of the optical path length of the PDMS cavity 322, thereby ensuring that the free spectral range of the PDMS cavity 322 is the preset multiple of the free spectral range of the air cavity 323, and the free spectral range of the PDMS cavity 322 and the free spectral range of the air cavity 323 are close to but not equal to each other, thereby having an enhanced vernier effect. For example, the preset multiple may be greater than or equal to 0.9 and less than or equal to 0.99, or greater than or equal to 1.01 and less than or equal to 1.10, which is not limited in the embodiments of the present application.
In addition, when the liquid PDMS33 is injected into the first end of the hollow-core optical fiber 32, the first interference spectrum P1 (i.e., the interference spectrum of a single PDMS cavity 322) can be monitored by the spectrometer 4 in real time (as shown in the curve in fig. 2 (a)), how much the current cavity length of the PDMS cavity 322 reaches can be determined according to the first interference spectrum P1, and when it is determined that the cavity length of the PDMS cavity 322 reaches 100 to 150 μm, the injection of the PDMS33 into the first end is stopped. Similarly, when the liquid PDMS33 is injected into the second end of the hollow-core optical fiber 32, the second interference spectrum P2 (i.e., the interference spectrum of the single air cavity 323) can be monitored by the spectrometer 4 in real time (as shown in fig. 2 (b)), and it can be determined from the second interference spectrum P2 how much the cavity length of the current air cavity 323 reaches, and when it is determined that the cavity length of the air cavity 323 is a preset multiple of the cavity length of the PDMS cavity 322, the injection of the PDMS33 into the second end is stopped.
Wherein the first interference spectrum P1 and the second interference spectrum P2 can be represented by the following first expression:
wherein, I 1 (λ) is the intensity of the first interference spectrum P1, I 2 (λ) is the intensity of the second interference spectrum P2, A is the amplitude of the first reflected light F1, B is the amplitude of the second reflected light F2, C is the amplitude of the third reflected light F3, n 1 Is PDMRefractive index of S33, about 1.4,n 2 Is the refractive index of air, about 1.0 1 Is the chamber length, L, of the PDMS chamber 322 2 Is the cavity length of the air cavity 323 and λ is the wavelength of the incident light R.
After the first interference spectrum P1 and the second interference spectrum P2 are measured, the spectrometer 4 may superimpose the first interference spectrum P1 and the second interference spectrum P2 to form a parallel interference spectrum P3 (i.e., a parallel interference spectrum P3 generated after the air cavity 323 and the PDMS cavity 322 form a parallel structure) (e.g., the upper curve in fig. 4). Wherein, the parallel interference spectrum P3 can be represented by the following second expression:
I all (λ)＝I 1 (λ)+I 2 (λ)
wherein, I all (λ) is the intensity of the parallel interference spectrum P3.
Since the free spectral range of the PDMS cavity 322 is a preset multiple of the free spectral range of the air cavity 323, i.e., the free spectral range of the PDMS cavity 322 and the free spectral range of the air cavity 323 are close to but not equal, the interference spectrum generated by the parallel dual cavity formed by the air cavity 323 and the PDMS cavity 322 (i.e., the parallel interference spectrum P3) generates an envelope phenomenon (i.e., vernier effect). The lower curve in fig. 4 is an envelope spectrum P4 generated by the parallel interference spectrum P3 (i.e., a connecting line of each valley of the parallel interference spectrum P3), and the envelope spectrum P4 can be represented by the following third expression:
wherein, I envelope (λ) is the intensity of the envelope spectrum P4, E is the amplitude of the envelope spectrum P4, and M is the magnification of the conventional vernier effect.
In some embodiments, when the temperature changes, the refractive index of the PDMS33 changes, and the cavity length of the PDMS cavity 322 also changes, based on which the sensitivity of the PDMS cavity 322 can be determined according to the following formula one:
wherein S is 1 Is the sensitivity of the PDMS chamber 322, and α is the thermo-optic coefficient of PDMS33, which is about-5.0 × 10 -4 /. Degree.C.,. Beta.is the coefficient of thermal expansion of PDMS33, which is about 9.6X 10 -4 /℃，λ m1 Is the wavelength corresponding to the m1 th peak in the first interference spectrum P1. Note that the first interference spectrum P1 has N peaks, N is an integer greater than 0, and m1 is an integer greater than 0 and less than or equal to N.
In addition, when the temperature increases, the first and second PDMS sections 33 and 33 may expand and thus may compress the air chamber 323 to shorten the chamber length of the air chamber 323, and when the temperature decreases, the first and second PDMS sections 33 and 33 may contract and thus the chamber length of the air chamber 323 may lengthen. Based on this, the sensitivity of the air cavity 323 can be determined according to the following equation two:
wherein S is 2 Is the sensitivity, L, of the air cavity 323 1 Is the chamber length, L, of the PDMS chamber 322 2 Is the chamber length, L, of the air chamber 323 3 Is the length, λ, of the second PDMS segment 33 m2 Is the wavelength corresponding to the m2 th peak in the second interference spectrum P2. Note that the second interference spectrum P2 also has N peaks, N is an integer greater than 0, and m2 is an integer greater than 0 and less than or equal to N. Notably, λ m1 And λ m2 And may be equal or unequal, and when they are unequal, the difference between the sensitivity of the PDMS cavity 322 and the sensitivity of the air cavity 323 may be as small as possible.
From the second equation, increasing the length of the PDMS cavity 322 and the length of the second section of PDMS33 both increase the sensitivity of the air cavity 323. However, since increasing the cavity length of the PDMS cavity 322 increases the loss of light transmitted in the PDMS cavity 322, thereby decreasing the intensity of the reflected light and affecting the intensity of the first interference spectrum P1, the cavity length of the PDMS cavity 322 is not too large. The increase of the length of the second section of PDMS33 can prevent light from being reflected from the end surface of the second end of the hollow-core fiber 32, and does not affect the transmission of the effective reflected light, so the sensitivity of the air cavity 323 can be improved by properly increasing the length of the second section of PDMS33.
From the first and second formulas, S 1 >0，S 2 <0, further indicating that the first interference spectrum P1 and the second interference spectrum P2 shift in opposite directions when the temperature changes, the PDMS cavity 322 and the air cavity 323 have opposite temperature responses to the temperature.
Finally, the sensitivity of the temperature sensor 3 can be determined by the following equation three:
wherein M is 1 "is the magnification of the sensitivity of the temperature sensor 3 relative to the sensitivity of the individual PDMS chambers 322, M 2 "is the magnification of the sensitivity of the temperature sensor 3 relative to the sensitivity of the single air cavity 323. M is a group of 1 ' and M 2 ' may be represented by the following formula four:
where M is the magnification of the conventional vernier effect of the temperature sensor 3.
According to the third and fourth formulas, the magnification of the temperature sensor 3 is M relative to the single PDMS cavity 322 and the single air cavity 323 1 ' and M 2 All of M 1 ' and M 2 "is significantly larger than the conventional magnification M of the temperature sensor 3, and therefore, the temperature sensor 3 provided by the embodiment of the present application has sensitivity significantly larger than the sensitivity of the single PDMS cavity 322 and the single air cavity 323. It can be seen that the temperature sensor 3 provided in the embodiment of the present application realizes an enhanced vernier effect. As can be seen from fig. 2 and 5, when the temperature changes from 30 ℃ to 31 ℃, the shift amounts of the first interference spectrum P1 and the second interference spectrum P2 are small, and the shift amount of the envelope spectrum P4 is large, i.e., the translation amount of the envelope spectrum P4 is much larger than that of the first stemThe amount of translation of the interference spectrum P1 and the second interference spectrum P2.
In some embodiments, the present application further provides an apparatus comprising the temperature sensing system of the previous embodiment, wherein the sensor 3 is used for thermometry.
In summary, in the embodiment of the present application, the sensor 3 includes a first sensing interferometer and a second sensing interferometer which are interconnected. That is, the sensor 3 includes two sensing interferometers. And because the first sensing interferometer and the second sensing interferometer have opposite temperature responses to the temperature, the first sensing interferometer and the second sensing interferometer can generate an enhanced vernier effect, the amplification factor of the sensor 3 is effectively improved, and the sensitivity of the sensor 3 is increased.
Those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than others, combinations of features of different embodiments are meant to be within the scope of the application and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.
The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.
Claims (10)
1. A temperature sensing system, comprising: the system comprises a broadband light source, an optical fiber connector, a sensor and a spectrometer;
the broadband light source, the sensor and the spectrometer are all connected with the optical fiber connector, the sensor comprises a first sensing interferometer and a second sensing interferometer which are interconnected, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, the sensor senses the temperature based on a vernier effect generated by the first sensing interferometer and the second sensing interferometer, and the first sensing interferometer and the second sensing interferometer have opposite temperature responses to the temperature, namely, a first interference spectrum and a second interference spectrum are translated in opposite directions along with the change of the temperature; wherein the first interference spectrum is an interference spectrum formed by reflected light returned by the first sensing interferometer, and the second interference spectrum is an interference spectrum formed by reflected light returned by the second sensing interferometer.
2. The temperature sensing system of claim 1, wherein the sensor comprises: single mode fiber, hollow fiber and PDMS;
the first end of the single-mode optical fiber is connected with the optical fiber connector, and the second end of the single-mode optical fiber is connected with the first end of the hollow-core optical fiber;
a first air hole communicated with the axial through hole of the hollow optical fiber is radially formed in the first end of the hollow optical fiber, the PDMS is injected into the hollow optical fiber from the first air hole, and the first sensing interferometer is formed at the first end of the hollow optical fiber;
and injecting the PDMS into the hollow-core optical fiber from the second end of the hollow-core optical fiber, and forming the second sensing interferometer between the first end and the second end of the hollow-core optical fiber, wherein the free spectral range of the first sensing interferometer is a preset multiple of the free spectral range of the second sensing interferometer.
3. The temperature sensing system of claim 2, wherein the predetermined multiple is greater than or equal to 0.9 and less than or equal to 0.99.
4. The temperature sensing system of claim 2, wherein the predetermined multiple is greater than or equal to 1.01 and less than or equal to 1.10.
5. The temperature sensing system of claim 2, wherein an end face of the second end of the hollow-core optical fiber has an angle with a cross-section of the hollow-core optical fiber, the angle being unequal in degree to zero.
6. The temperature sensing system of claim 5, wherein the degree of the included angle is greater than or equal to 7 degrees.
7. The temperature sensing system of claim 2, wherein the hollow-core optical fiber is further radially provided with a second air hole in communication with the axial through hole, the second air hole being in communication with the second sensing interferometer.
8. The temperature sensing system of claim 2, wherein a distance between the first air hole and the end face of the first end of the hollow-core optical fiber is greater than or equal to 10 microns and less than or equal to 20 microns.
9. The temperature sensing system of any one of claims 1-8, wherein the fiber optic connector comprises a fiber optic circulator or a fiber optic coupler.
10. A temperature sensing device, characterized in that it comprises a temperature sensing system according to any one of claims 1-9.
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