The core mismatch is the mismatch of the core during fiber fusion. According to the core mismatch principle, the core mismatch interference structure is a special Mach-Zehnder interferometer. In the single mode-multimode-single mode (Single mode-Multi mode-Singlemode, SMS) structure (such as figure 1 (Shown), the input end single-mode fiber couples the incident light into the single-mode fiber with the core misaligned, the multi-mode fiber modulates the incident light through the output end single-mode fiber, and the light wave mode is transmitted along the optical fiber in the transmission direction There will be a phenomenon that the light intensity changes periodically with the length of the multi-mode fiber, and even the light field distribution in the multi-mode fiber is almost the same as the incident light field. This is the mode interference effect in the multi-mode fiber, also called mode Interference, because the interference between multiple modes can be realized in one fiber, the optical path is simplified, the structure is more compact, and the loss is low, and it is free from external interference, which has a good development prospect.
 figure 2 Shows a schematic diagram of the structure of a core mismatch interferometer that uses a core mismatch interferometer structure to measure temperature according to the present invention. figure 2 The shown core mismatch interference structure includes a pump source 201, a wavelength division multiplexer (WDM) 202, a gain fiber 203, a first single-mode fiber (SMF) 204, and a second single-mode fiber 205 connected in sequence. The third single-mode fiber 206 and the optical spectrum analyzer 207. The output end of the pump source 201 is sequentially connected to a wavelength division multiplexer (WDM) 202 and a gain fiber 203. The gain fiber 203 is connected to the input end of the first single-mode fiber 204, and the output end of the first single-mode fiber 204 is connected to the second The input end of the single-mode fiber 205 is connected by a staggered fusion splicing structure, the output end of the second single-mode fiber 205 and the input end of the third single-mode fiber 206 are connected by a staggered fusion splicing structure, and the output end of the third single-mode fiber 206 is connected with the spectrum analysis Instrument 207 is connected.
 The working principle of the core mismatch interference structure for measuring temperature by using the core mismatch interference structure according to the present invention is as follows:
 First, the first single-mode optical fiber 204, the second single-mode optical fiber 205, and the third single-mode optical fiber 206 are subjected to fiber misalignment welding. image 3 It is the image diagram of single-mode fiber dislocation splicing. When fiber dislocation splicing, the amount of dislocation is gradually adjusted from small to large. Figure 4 It is the transmission spectrum of different dislocation amount. Observing the transmission spectrum, it is found that when the dislocation amount is too small, no obvious inter-mode interference phenomenon occurs, such as Figure 4 As shown in a, this is because when the transmitted light is coupled from the first single-mode fiber into the second single-mode fiber (length is 9cm), most of the light propagates through the core, and only a small part is coupled into the cladding. When the three single-mode fibers meet, the interference effect is not obvious; when the amount of misalignment is appropriate, the mode in the fiber will change, and the mode change will cause different interference results. With the increase of the amount of misalignment, the interference phenomenon becomes more obvious; When the amount is too large, due to the large loss at the fiber fusion splice, the inter-mode interference phenomenon is also not obvious, such as Figure 4 c is shown. The size of the core/cladding of the optical fiber used in the present invention is 10/125μm. When the misalignment is small, the light injected from the front core core into the back cladding is weak and the interference phenomenon is not obvious; when the misalignment is large, The front-end core is injected into the back-end cladding with stronger light, but the light in the core is weak, and the interference phenomenon is affected; when the radial misalignment distance is 3~4μm, the front-end core is injected into the back-end cladding and the core The light intensity is similar, so there is the best effect, as shown in Figure 4b. The best experimental results are obtained when the distance between the first single-mode fiber and the second single-mode fiber is the same as the distance between the second single-mode fiber and the third single-mode fiber.
 Secondly, perform temperature calibration on the core mismatch interference structure. The calibration process is as follows: Combine the first single-mode fiber, the second single-mode fiber, and the third single-mode fiber with the temperature control device as a whole. The sensor undergoes corresponding changes in expansion or contraction, resulting in a red or blue shift of the comb spectrum (such as Figure 5 As shown), according to the change of the wavelength value at the trough at different temperatures, the sensitivity of the sensor to changes in external temperature conditions can be obtained,
 As the temperature increases, the transmission spectrum of the comb filter moves to the shortwave direction. By gradually increasing the temperature and recording the length of the comb spectrum movement, the curve of the comb spectrum change with temperature is obtained. The schematic diagram is as follows Image 6 Shown. Select the wavelength of the measurement point. At this time, the spectral wavelength curve drifts. According to the drift amount, the outside temperature can be inferred by the following formula:
 Where X is the temperature, Y is the changing wavelength, and a and b are constants.
 Finally, the external temperature is measured through the relationship curve between spectral line drift and temperature. Use the temperature calibration curve to determine the temperature experienced by the sensor.
 In combination with the description and practice of the present invention disclosed herein, other embodiments of the present invention are easily thought of and understood by those skilled in the art. The description and embodiments are only considered to be exemplary, and the true scope and spirit of the present invention are defined by the claims.