CN113108940B - Temperature sensing system and device - Google Patents

Abstract

Embodiments of the present application provide a temperature sensing system and device, which belong to the technical field of optical fiber sensors. The temperature sensing system includes: a broadband light source, a sensor and a spectrometer are all connected with an optical fiber connector, the sensor includes a first sensing interferometer and a second sensing interferometer interconnected, the first sensing interferometer and the second sensing interferometer The interferometers 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. That is, the sensor includes two sensing interferometers. And because the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, the first sensing interferometer and the second sensing interferometer can produce an enhanced vernier effect, effectively improving the sensor's The magnification increases the sensitivity of the sensor.

Description

A temperature sensing system and device

technical field

The embodiments of the present application relate to the technical field of optical fiber sensors, and in particular to a temperature sensing system and device.

Background technique

As one of the seven basic physical quantities of the International System of Units, temperature plays an important role in the accurate measurement of temperature in the fields of national economy, national defense construction and scientific research. With the increasing demand for temperature sensing applications, traditional temperature sensors have been unable to meet the high-precision measurement requirements, while optical fiber temperature sensors have the advantages of small size, high measurement accuracy, high sensitivity, strong resistance to electromagnetic interference, good electrical insulation, and wide temperature range. It has its own unique advantages in temperature measurement, so the research on optical fiber temperature sensor is particularly important.

In recent years, the vernier effect has been widely used to improve the sensitivity of fiber optic temperature sensors. Generally, a fiber optic temperature sensor based on the vernier effect includes a reference interferometer and a sensing interferometer, where only the sensing interferometer responds to temperature changes, while the reference interferometer does not respond to temperature changes. This fiber optic temperature sensor can only produce the conventional vernier effect. Although the sensitivity of the optical fiber temperature sensor is improved by 1 to 2 orders of magnitude compared with a single sensing interferometer, it still cannot meet the demand for high-sensitivity temperature detection in many cases.

Contents of the invention

In view of the above problems, embodiments of the present application provide a temperature sensing system and device, which overcome the above problems or at least partially solve the above problems.

According to an aspect of an embodiment of the present application, a temperature sensing system is provided, and the temperature sensing system includes: 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 to the fiber optic connector, the sensor includes a first sensing interferometer and a second sensing interferometer interconnected, the first sensing interferometer The sensor senses temperature based on a vernier effect produced by the first sensing interferometer and the second sensing interferometer having an opposite temperature response to temperature.

Optionally, the sensor includes: single-mode fiber, hollow-core fiber and PDMS;

The first end of the single-mode optical fiber is connected to the optical fiber connector, and the second end of the single-mode optical fiber is connected to the first end of the hollow-core optical fiber;

The first end of the hollow-core optical fiber is radially provided with a first air hole communicating with the axial through hole of the hollow-core optical fiber, and the PDMS is injected into the hollow-core optical fiber through the first air hole. a first end of a hollow core fiber forms said first sensing interferometer;

The PDMS is injected into the hollow-core fiber from the second end of the hollow-core fiber, the second sensing interferometer is formed between the first end and the second end of the hollow-core fiber, and the first The free spectral range of the 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, there is an included angle 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 communicating with the axial through hole in the radial direction, and the second air hole is communicating with the second sensing interferometer.

Optionally, the 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.

Optionally, the optical fiber connector includes an optical fiber circulator or an optical fiber coupler.

According to another aspect of the embodiments of the present application, a device is provided, including the above-mentioned temperature sensing system.

In the embodiment of the present application, the sensor includes 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 temperature, the first sensing interferometer and the second sensing interferometer can produce an enhanced vernier effect, effectively improving the sensor's The magnification increases the sensitivity of the sensor.

The above description is only an overview of the technical solutions of the embodiments of the present application. In order to understand the technical means of the embodiments of the present application more clearly, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and characteristics of the embodiments of the present application The advantages can be more obvious and understandable, and the specific implementation manners of the present application are enumerated below.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings that need to be used in the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present application. For Those of ordinary skill in the art can also obtain other drawings based on these drawings without making creative efforts.

FIG. 1 is a schematic structural diagram of a temperature sensing system provided in an embodiment of the present application;

Figure 2 is a schematic diagram of the influence of temperature on the interference spectrum provided by the embodiment of the present application;

FIG. 3 is a schematic structural diagram of a sensor provided in an embodiment of the present application;

FIG. 4 is a schematic diagram of a cascaded interference spectrum provided by an embodiment of the present application;

FIG. 5 is a schematic diagram of an effect of temperature on cascade interference spectrum provided by an embodiment of the present application.

Reference signs:

1: broadband light source, 2: fiber optic connector, 3: sensor, 4: spectrometer, 31: single-mode fiber, 32: hollow-core fiber, 33: PDMS, 321: first air hole, 322: PDMS cavity, 323: air cavity , 324: second air hole, M1: first reflection interface, M2: second reflection interface, M3: third reflection interface, P1: first interference spectrum, P2: second interference spectrum, P3: parallel interference spectrum, P4: Envelope spectrum, α: included angle, R: incident light, F1: first reflected light, F2: second reflected light, F3: third reflected light.

detailed description

In order to make the purposes, 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 in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of this application.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the application; the terms used herein in the description of the application are only to describe specific embodiments purpose, and is not intended to limit the application.

The terms "comprising" and "having" and any variations thereof in the specification, claims and descriptions of the drawings of this application are intended to cover but not exclude other contents. The word "a" or "an" does not exclude the presence of 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 present 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 understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments.

The term "and/or" in this article is just an association relationship describing associated objects, which means that there can be three relationships, for example, A and/or B can mean: A exists alone, A and B exist simultaneously, and there exists alone B these three situations. In addition, the character "/" in this article generally indicates that the contextual objects are an "or" relationship.

The orientation words appearing in the following description are all directions shown in the figure, and do not limit the specific structure of the temperature sensing system of the present application. For example, in the description of this application, the terms "central", "longitudinal", "transverse", "length", "width", "upper", "lower", "inner", "outer", "clockwise" , "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description. It is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed, or operate in a particular orientation, and thus should not be construed as limiting the application.

In addition, the terms "first" and "second" in the specification and claims of the present application or the above drawings are used to distinguish different objects, not to describe a specific order, and may explicitly or implicitly include a or more of this feature.

In the description of the present application, unless otherwise specified, "multiple" means more than two (including two), and similarly, "multiple groups" means more than two (including two).

In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be interpreted in a broad sense, for example, "connection" or "connection" of mechanical structures It may refer to a physical connection, for example, a physical connection may be a fixed connection, such as a fixed connection through a fixture, such as a fixed connection through screws, bolts or other fasteners; a physical connection may also be a detachable connection, such as Mutual clamping or clamping connection; the physical connection may also be an integral connection, for example, welding, bonding or integrally formed connection for connection. The "connection" or "connection" of the circuit structure may not only refer to a physical connection, but also an electrical connection or a signal connection, for example, it may be a direct connection, that is, a physical connection, or an indirect connection through at least one intermediate component, As long as the circuit is connected, it can also be the internal connection of two components; besides the signal connection through the circuit, the signal connection can also refer to the signal connection through the media medium, for example, radio waves. Those of ordinary skill in the art can understand the specific meanings of the above terms in this application in specific situations.

Fig. 1 is a schematic structural diagram of a temperature sensing system provided by the embodiment of the present application, as shown in Fig. 1 (the arrow in Fig. 1 represents the transmission direction of the optical signal), the temperature sensing system includes: a broadband light source 1, an optical fiber connection device 2, sensor 3 and spectrometer 4. The broadband light source 1, the sensor 3 and the spectrometer 4 are all connected to the fiber optic connector 2, the sensor 3 includes a first sensing interferometer and a second sensing interferometer interconnected, the first sensing interferometer and the second sensing interferometer Having an opposite temperature response to temperature, the sensor 3 senses temperature based on the vernier effect produced 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 of any wavelength, for example, can provide light with a wavelength of 1200nm (nanometer) to 1600nm.

In addition, the optical fiber connector 2 is used for connecting optical fiber devices, 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. The incident light R emitted by the broadband light source 1 enters the sensor 3 through the optical fiber connector 2, and the light reflected from the sensor 3 enters the spectrometer 4 through the optical fiber connector 2, and the spectrometer 4 receives the light reflected by the sensor 3. light and based on this reflected light the interference spectrum of the sensor 3 is measured.

Among them, in order to ensure the unidirectionality of optical transmission, an optical fiber isolator can also be set between the broadband light source 1 and the optical fiber connector 2, so that the light emitted by the broadband light source 1 can enter the optical fiber connector 2 through the optical fiber isolator, but cannot be transmitted from The fiber optic isolator returns to the broadband light source 1 so that no damage is done to the broadband light source 1 .

Figure 2 is a schematic diagram of the influence of temperature on the interference spectrum provided by the embodiment of the present application. As shown in Figure 2(a), the first interference spectrum P1 formed by the reflected light returned by the first sensing interferometer increases with the The changes are translated and it can be seen that the first sensing interferometer is responsive 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 as the temperature changes. It can be seen that the second sensing interferometer also responds to temperature. That is, both the first sensing interferometer and the second sensing interferometer are responsive to temperature. And, as the temperature increases, as shown in Figure 2(a), the first interference spectrum P1 shifts to the left (that is, blue shifts), as shown in Figure 2(b), the second interference spectrum P2 moves to the right Translation (that is, red shift occurs), it can be seen that as the temperature increases, the first interference spectrum P1 and the second interference spectrum P2 translate in opposite directions. That is, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature. It is worth pointing out that Fig. 2 is only an example, the first sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, it may also be that as the temperature increases, the first interference spectrum P1 occurs red shift, the second interference spectrum P2 is blue shifted, which is not limited in this embodiment of the present application.

In the embodiment of the present application, the sensor 3 includes a first sensing interferometer 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 temperature, the first sensing interferometer and the second sensing interferometer can produce an enhanced vernier effect, effectively improving the sensor 3 The magnification ratio increases the sensitivity of the sensor 3.

In some embodiments, as shown in FIG. 3 , the sensor 3 includes: a single-mode fiber 31, a hollow-core fiber 32 and a PDMS33;

A first end of the single-mode fiber 31 is connected to the optical fiber connector 2 , and a second end of the single-mode fiber 31 is connected to the first end of the hollow-core fiber 32 . The first end of the hollow-core optical fiber 32 is radially provided with a first air hole 321 communicating with the axial through hole of the hollow-core optical fiber 32, and the PDMS33 is injected into the hollow-core optical fiber from the first air hole 321 32. The first sensing interferometer is formed at the first end of the hollow-core fiber 32; the PDMS33 is injected into the hollow-core fiber 32 from the second end of the hollow-core fiber 32, and the The second sensing interferometer is formed between the first end and the second end of the optical fiber 32, and the free spectral range of the first sensing interferometer is a preset of the free spectral range of the second sensing interferometer multiple.

It should be noted that the single-mode optical fiber 31 includes an optical fiber core and an optical fiber cladding, and the optical fiber cladding is wrapped around the outer side of the optical fiber core. The diameter of the single-mode fiber 31 may be 125 μm (micrometer), and the core of the single-mode fiber 31 may directly be 10 μm. The outer diameter of the hollow-core fiber 32 may be 125 μm, and the inner diameter (ie, the diameter of the axial through hole) may be 50 to 70 μm. This embodiment of the present application does not limit it.

In addition, the first air hole 321 serves as an injection channel for injecting the PDMS 33 into the first end of the hollow-core optical fiber 32 . In order to ensure that no bubbles are generated when PDMS33 is injected into the first end of the hollow-core optical fiber 32, to form a good first sensing interferometer (that is, the PDMS cavity 322. Subsequent descriptions will uniformly use the PDMS cavity 322), the first air hole 321 can be It is arranged on the side wall of the first end of the hollow-core optical fiber 32 and can be arranged as close as possible to the end face of the first end of the hollow-core optical fiber 32 . That is, the distance between the first air hole 321 and the end surface of the first end of the hollow-core optical fiber 32 can be as small as possible, for example, the distance can be greater than or equal to 10 μm and less than or equal to 20 μm. In addition, the diameter of the first air hole 321 can be set according to the cavity length of the PDMS cavity 322 , for example, the diameter of the first air hole 321 can be greater than or equal to 5 μm and less than or equal to 20 μm. This embodiment of the present application does not limit it.

In addition, PDMS33 is polydimethylsiloxane, which is an excellent heat-sensitive material with obvious thermal expansion and contraction effects. PDMS33 is in a liquid state for a period of time after it has been prepared, and will solidify into a colorless and transparent solid after heating. In addition, PDMS33 has good light transmission and refraction, good adhesion and chemical inertness, and is very suitable for combining with optical fiber for high-sensitivity temperature measurement.

Filling the first section of PDMS33 to the first end of the hollow-core fiber 32 can form a PDMS cavity 322 at the first end of the hollow-core fiber 32 (the PDMS cavity 322 is a Fabry-Perot sensor interferometer), thereby in 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 to the second end of the hollow-core fiber 32, the air in the hollow-core fiber 32 will be squeezed and confined between the first end and the second end of the hollow-core fiber 32, forming an air cavity 323 (That is, the second sensing interferometer. Subsequent descriptions will use the air cavity 323 uniformly. The air cavity 323 is also a Fabry-Perot sensing interferometer), thereby forming a The second reflection interface M2 forms a third reflection surface M3 between the air cavity 323 and the second section of PDMS 33 .

That is to say, in the sensor 3 , the two ends of the hollow-core optical fiber 32 are respectively a section of PDMS 33 , and a section of air cavity 323 is sandwiched between the two sections of PDMS 33 . When the temperature rises, the two sections of PDMS33 thermally expand, and the air cavity 323 will be squeezed in the middle at the same time, reducing the cavity length of the air cavity 323, and the optical path becomes smaller. When the temperature decreases, the two sections of PDMS33 shrink, thereby The cavity length of the air cavity 323 in the middle will increase, and the optical path will become longer, which further increases the temperature response sensitivity of the air cavity 323, and then increases the magnification of the enhanced vernier effect.

Based on the sensor 3 provided by the embodiment of the present application, part of the incident light R entering the single-mode fiber 31 is reflected back to the single-mode fiber 31 at the first reflection interface M1 to generate the first reflected light F1, and the remaining part is transmitted through the first reflection The interface M1 enters the PDMS cavity 322 . Part 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 to generate second reflected light F2, and the remaining part 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 the third reflected light F3, and the remaining small part of the light passes through the third reflective interface M3 Enter the second paragraph PDMS33. The spectrometer 4 measures the first interference spectrum P1 based on the first reflected light F1 and the second reflected light F2 , and measures the 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 avoid the light entering the second section of PDMS33 through the third reflection interface M3 from being reflected back to the second section of PDMS33 from the end face of the second end of the hollow-core optical fiber 32, and then entering the air cavity 323, as shown in Figure 3, the hollow core The end surface of the second end of the optical fiber 32 may be set as an inclined plane, and may have an angle α with 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 included angle α is properly set, no light will be reflected back from the end face of the second end of the hollow-core optical fiber 32 .

Wherein, the angle α between the end face of the second end of the hollow-core fiber 32 and the cross-section of the hollow-core fiber 32 can be set according to the principle of light transmission, and the degree of the angle α can be any angle greater than or equal to 7 degrees. The value, for example, the degree of the included angle α may be 8 degrees, 10 degrees, etc., which is not limited in this embodiment of the present application.

In some embodiments, in order to inject PDMS 33 from the second end of the hollow-core fiber 32 and adjust the cavity length of the air cavity 323, the hollow-core fiber 32 can also be provided with a second hole communicating with the axial through hole in the radial direction. The second air hole 324 communicates with the air cavity 323 . Wherein, the diameter of the second air hole 324 can be set according to the cavity length of the air cavity 323 , for example, the diameter of the second air hole 324 can be greater than or equal to 5 μm and less than or equal to 20 μm. The diameter of the second air hole 324 may be the same as that of the first air hole 321 or may be different, which is not limited in this embodiment of the present application.

The second air hole 324 is arranged between the first end and the second end of the hollow-core optical fiber 32, and communicates with the air cavity 323. On the one hand, when injecting PDMS33 from the second end of the hollow-core optical fiber 32, the first end and the second end Part of the air between the two ends will be exhausted from the second air hole 324 , so as to facilitate the injection of PDMS 33 . On the other hand, discharging part of the air between the first end and the second end from the second air hole 324 can reduce the cavity length of the air cavity 323 . When the cavity length of the air cavity 323 needs to be increased, air can also be injected into the air cavity 323 from the second air hole 324 . That is to say, the cavity length of the air cavity 323 can be easily adjusted by exhausting or injecting gas from the second air hole 324 .

When preparing the sensor 3 provided by the embodiment of the present application, the second end of the single-mode optical fiber 31 can be fused with the first end of the hollow-core optical fiber 32 to form the first reflection interface M1, and then the hollow-core optical fiber 32 can be cut to make the hollow-core optical fiber 32 The cavity length of the core fiber 32 reaches the first preset cavity length, and makes an angle α 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 drill a first air hole 321 in the radial direction at the first end of the hollow-core optical fiber 32 , so that the first air hole 321 communicates with the axial through hole of the hollow-core optical fiber 32 . A second air hole 324 is drilled radially between the first end and the second end of the hollow-core optical fiber 32 by using a femtosecond laser, so that the second air hole 324 communicates with the axial through hole of the hollow-core optical fiber 32 . Afterwards, using capillarity, the liquid PDMS33 is injected into the first end of the hollow-core optical fiber 32 from the first air hole 321, and the injection process ensures that there is no bubble generation near the end of the single-mode optical fiber 31, thereby forming a PDMS cavity 322 with a certain cavity length (the first Section PDMS33). Using the capillary phenomenon, the liquid PDMS33 is slowly injected from the second end of the hollow-core optical fiber 32 to form a second section of PDMS33, and an air cavity 323 with a certain cavity length is formed between the first end and the second end of the hollow-core optical fiber 32 . Finally, heat the PDMS33 to cure it.

Wherein, the length of the first preset cavity may be 1 to 2 mm (millimeter). In addition, the cavity length of the PDMS cavity 322 can be 100 to 150 μm, and the cavity length of the air cavity 323 can be a preset multiple of the cavity length of the PDMS cavity 322. 1.4 times, like this, it can be guaranteed that the optical path of the air cavity 323 is a preset multiple of the optical path of the PDMS cavity 322, thereby ensuring that the free spectral range of the PDMS cavity 322 is a preset multiple of the free spectral range of the air cavity 323, and the PDMS cavity The free spectral range of 322 and the free spectral range of the air cavity 323 are close to but not equal, so that there is an enhanced vernier effect. Exemplarily, 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 this embodiment 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 (that is, the interference spectrum of a single PDMS cavity 322) can be monitored in real time by the spectrometer 4 (as shown in the curve in Figure 2(a)) According to the first interference spectrum P1, it can be determined how much the cavity length of the current PDMS cavity 322 has reached, and when it is determined that the cavity length of the PDMS cavity 322 reaches 100 to 150 μm, stop injecting PDMS 33 into the first end. In the same way, when the liquid PDMS33 is injected into the second end of the hollow-core optical fiber 32, the second interference spectrum P2 (that is, the interference spectrum of a single air cavity 323) can be monitored in real time by the spectrometer 4 (as shown in the curve in Figure 2 (b) ), according to the second interference spectrum P2, it can be determined how much the cavity length of the current air cavity 323 has reached, 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, stop injecting PDMS33 into the second end.

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 the refractive index of PDMS33, about 1.4, n ₂ is the refractive index of air, about 1.0, L ₁ is the cavity length of the PDMS cavity 322, L ₂ is the air cavity 323 The cavity length, λ is the wavelength of the incident light R.

After measuring the first interference spectrum P1 and the second interference spectrum P2, the spectrometer 4 can superimpose the first interference spectrum P1 and the second interference spectrum P2 to form a parallel interference spectrum P3 (that is, the air cavity 323 and the PDMS cavity 322 constitute The parallel interference spectrum P3) generated after the parallel structure (as shown in the upper part of the curve in Figure 4). Among them, the parallel interference spectrum P3 can be expressed by the following second expression:

I _all (λ)＝I ₁ (λ)+I ₂ (λ)

Among them, 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, that is, 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, so the air cavity 323 and the PDMS The interference spectrum (ie, the parallel interference spectrum P3 ) produced by the parallel double cavities formed by the cavities 322 will produce an envelope phenomenon (ie, the vernier effect). The curve in the lower part of Fig. 4 is the envelope spectrum P4 (that is, the connection of each trough of the parallel interference spectrum P3) that the parallel interference spectrum P3 produces, and the envelope spectrum P4 can be represented by the third expression as follows:

Among them, 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 PDMS 33 changes, and the cavity length of the PDMS cavity 322 also changes. Based on this, the sensitivity of the PDMS cavity 322 can be determined according to the following formula 1:

Among them, S ₁ is the sensitivity of the PDMS cavity 322, α is the thermo-optic coefficient of PDMS33, its value is about -5.0×10 ^-4 /℃, β is the thermal expansion coefficient of PDMS33, its value is about 9.6×10 ^-4 /℃ , λ _m1 is the wavelength corresponding to the m1th peak in the first interference spectrum P1. It should be noted 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 rises, the first section of PDMS33 and the second section of PDMS33 will expand, thereby squeezing the air cavity 323 to shorten the cavity length of the air cavity 323. When the temperature decreases, the first section of PDMS33 and the second section of PDMS33 will expand. The PDMS 33 shrinks, so that the cavity length of the air cavity 323 becomes longer. Based on this, the sensitivity of the air cavity 323 can be determined according to the following formula two:

Wherein, S ₂ is the sensitivity of the air cavity 323, L ₁ is the cavity length of the PDMS cavity 322, L ₂ is the cavity length of the air cavity 323, L ₃ is the length of the second section of PDMS 33, λ _m2 is the second interference spectrum P2 The wavelength corresponding to the m2th peak. It should be noted 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. It should be noted that λ _m1 and λ _m2 can be equal or unequal, and when they are not equal, in order to make the sensitivity of the PDMS cavity 322 comparable to that of the air cavity 323, the difference between the two can be as much as possible small.

It can be known from formula 2 that increasing the cavity length of the PDMS cavity 322 and the length of the second section of PDMS 33 will both increase the sensitivity of the air cavity 323 . However, due to increasing the cavity length of the PDMS cavity 322, the loss caused by the transmission of light in the PDMS cavity 322 will be increased, thereby reducing the intensity of reflected light and affecting the intensity of the first interference spectrum P1, so the cavity length of the PDMS cavity 322 is not suitable. is too big. And increasing the length of the second section of PDMS33 can prevent light from being reflected back from the end face of the second end of the hollow-core optical fiber 32, and will not affect the transmission of effective reflected light. Therefore, the length of the second section of PDMS33 can be appropriately increased. The sensitivity of the air cavity 323 is increased.

From Formula 1 and Formula 2, it can be seen that S ₁ >0, S ₂ <0, which further shows that when the temperature changes, the frequency shift directions of the first interference spectrum P1 and the second interference spectrum P2 are opposite, and the PDMS cavity 322 and the air cavity 323 are opposite to each other. Temperature has an inverse temperature response.

Finally, the sensitivity of the temperature sensor 3 can be determined by the following formula three:

Wherein, M ₁ ′ is the magnification of the sensitivity of the temperature sensor 3 relative to the sensitivity of a single PDMS cavity 322 , and M ₂ ′ is the magnification of the sensitivity of the temperature sensor 3 relative to the sensitivity of a single air cavity 323 . M ₁ ' and M ₂ ' can be expressed by the following formula 4:

Where M is the magnification of the conventional vernier effect of the temperature sensor 3 .

According to formula three and four, it can be seen that relative to a single PDMS cavity 322 and a single air cavity 323, the magnifications of the temperature sensor 3 are M ₁ ' and M ₂ ' respectively, and M ₁ ' and M ₂ ' are significantly greater than the temperature The conventional magnification M of the sensor 3 , therefore, the sensitivity of the temperature sensor 3 provided by the embodiment of the present application is obviously greater than the sensitivity of a single PDMS cavity 322 and a 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. Combining Figure 2 and Figure 5, it can be seen that when the temperature changes from 30°C to 31°C, the shifts of the first interference spectrum P1 and the second interference spectrum P2 are small, while the shift of the envelope spectrum P4 is large. That is, the translation amount of the envelope spectrum P4 is much larger than the translation amounts of the first interference spectrum P1 and the second interference spectrum P2.

In some embodiments, the present application also provides a device, which includes the temperature sensing system of the foregoing embodiments, wherein the sensor 3 is used for temperature measurement.

To sum up, in the embodiment of the present application, the sensor 3 includes a first sensing interferometer 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 temperature, the first sensing interferometer and the second sensing interferometer can produce an enhanced vernier effect, effectively improving the sensor 3 The magnification ratio increases the sensitivity of the sensor 3.

Those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the application and form different examples. For example, in the claims, any one of the claimed embodiments can be used in any combination.

As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still understand the foregoing The technical solutions described in each embodiment are modified, or some of the technical features are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the application.

Claims (10)

1. A temperature sensing system, characterized in that, the temperature sensing 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 to the fiber optic connector, the sensor includes a first sensing interferometer and a second sensing interferometer interconnected, the first sensing interferometer and said second sensing interferometer having an opposite temperature response to temperature, said sensor sensing temperature based on a vernier effect produced by said first sensing interferometer and said second sensing interferometer, said first The sensing interferometer and the second sensing interferometer have opposite temperature responses to temperature, which means that the first interference spectrum and the second interference spectrum shift in opposite directions as the temperature changes; wherein, the first interference spectrum The spectrum is the interference spectrum formed by the reflected light returned by the first sensing interferometer, and the second interference spectrum is the interference spectrum formed by the reflected light returned by the second sensing interferometer. 2. The temperature sensing system according to claim 1, wherein the sensor comprises: a single-mode optical fiber, a hollow-core optical fiber and PDMS; The first end of the single-mode optical fiber is connected to the optical fiber connector, and the second end of the single-mode optical fiber is connected to the first end of the hollow-core optical fiber; The first end of the hollow-core optical fiber is radially provided with a first air hole communicating with the axial through hole of the hollow-core optical fiber, and the PDMS is injected into the hollow-core optical fiber through the first air hole. a first end of a hollow core fiber forms said first sensing interferometer; The PDMS is injected into the hollow-core fiber from the second end of the hollow-core fiber, the second sensing interferometer is formed between the first end and the second end of the hollow-core fiber, and the first The free spectral range of the sensing interferometer is a preset multiple of the free spectral range of the second sensing interferometer. 3. The temperature sensing system according to claim 2, wherein the preset multiple is greater than or equal to 0.9 and less than or equal to 0.99. 4. The temperature sensing system according to claim 2, wherein the preset multiple is greater than or equal to 1.01 and less than or equal to 1.10. 5. The temperature sensing system according to claim 2, wherein there is an included angle between the end face 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 greater than is equal to zero. 6 . The temperature sensing system according to claim 5 , wherein the degree of the included angle is greater than or equal to 7 degrees. 7. The temperature sensing system according to claim 2, characterized in that, the hollow-core optical fiber is further provided with a second air hole communicating with the axial through hole in the radial direction, and the second air hole is connected to the The second sensing interferometer is connected. 8. The temperature sensing system according to claim 2, wherein the 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 according to any one of claims 1-8, wherein the optical fiber connector comprises an optical fiber circulator or an optical fiber coupler. 10. A temperature sensing device, characterized in that the temperature sensing device comprises the temperature sensing system according to any one of claims 1-9.

Images