Average temperature sensor based on birefringence thermo-optic effect of polarization maintaining fiber

Abstract

The invention discloses an average temperature sensor based on a birefringence thermo-optic effect of a polarization-maintaining optical fiber. The average temperature sensor comprises a wide-spectrum light source, an optical fiber polarization beam splitter, an optical detector, a compensation optical fiber, a titanium diffusion waveguide, a temperature-sensitive optical fiber and a polarization-maintaining reflector, the broadband light source is connected with one optical fiber in double ports of the optical fiber polarization beam splitter, the optical detector is connected with the other optical fiber in the double ports of the optical fiber polarization beam splitter, the single end of the optical fiber polarization beam splitter is in 45-degree countershaft connection with the compensation optical fiber, and the slow axis of the compensation optical fiber is connected with the input end of the titanium diffusion waveguide. The output end of the titanium diffusion waveguide is connected with a temperature-sensitive optical fiber fast axis, and the temperature-sensitive optical fiber is connected with a polarization-maintaining reflector; the average temperature of the measured environment is obtained by detecting the sensitive optical fiber, the average temperature can be provided for an optical fiber sensor and other applications needing the temperature comprehensive effect, and the method has important significance for a sensor with a certain sensitive space or needing the temperature comprehensive effect measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, in particular to an average temperature sensor based on the birefringence thermo-optical effect of polarization-maintaining optical fiber. Background Art

[0002] Fiber optic sensing boasts high measurement sensitivity, a wide range of measurable quantities, compact size, and flexible use. Related technologies are widely used in aerospace, mining and energy, industrial control, healthcare, bridge construction, and other fields. However, fiber optic sensing also has a natural disadvantage: the sheer number of physical quantities it can measure. In typical testing environments, environmental influences on sensors cannot be completely avoided, becoming a key factor impacting the expansion of fiber optic sensing applications. Examples include fiber optic displacement sensors and fiber optic gyroscopes.

[0003] Temperature can affect the geometric dimensions, internal stress, and material properties of optical fibers, thereby causing changes in multiple parameters such as the polarization state, phase, intensity, and scattering of light transmitted through the fiber. Sensors using polarization-maintaining fiber can reduce some temperature noise. For example, fiber optic gyros use polarization-maintaining fiber to form a reciprocal optical path, which greatly reduces the impact of temperature on gyro performance. However, this still cannot completely solve the problem of fiber temperature sensitivity. Fiber optic sensors typically suppress temperature noise by adding temperature-sensitive units for temperature compensation. However, for high-precision sensing, suppressing errors caused by temperature cross-sensitivity is key to improving sensor accuracy.

[0004] For example, fiber optic gyroscopes and fiber optic displacement sensors require monitoring the temperature of the sensitive optical fiber and compensating for the sensor's temperature effects based on the temperature change and rate of change. However, in practice, the optical fiber sensing unit has a certain spatial volume, and the ultimate noise is determined by the combined temperature effects of the entire space. A single point test cannot fully demonstrate the impact of temperature on the sensitive fiber. Summary of the Invention

[0005] In order to address the shortcomings of the above-mentioned existing technologies, the purpose of the present invention is to provide an average temperature sensor solution based on the thermo-optical effect of birefringence of polarization-maintaining fiber. This solution measures the average temperature of the environment in which the entire temperature-sensitive fiber is located by measuring the influence of temperature on the birefringence of polarization-maintaining fiber.

[0006] The purpose of the present invention is achieved through the following technical means:

[0007] The invention discloses an average temperature sensor based on the polarization-maintaining optical fiber birefringence thermo-optical effect, comprising a broadband light source, an optical fiber polarization beam splitter, an optical detector, a compensation optical fiber, a titanium diffused waveguide, a temperature-sensitive optical fiber, and a polarization-maintaining reflector.

[0008] The broadband light source is connected to one of the optical fibers in the dual ports of the optical fiber polarization beam splitter.

[0009] the other optical fiber in the two-port of the optical fiber polarization beam splitter is connected with the optical detector,

[0010] the single end of the optical fiber polarization beam splitter is connected with the 45° axis of the compensating optical fiber,

[0011] the slow axis of the compensating optical fiber is connected with the input end of the titanium diffusion waveguide,

[0012] the output end of the titanium diffusion waveguide is connected with the fast axis of the temperature sensitive optical fiber,

[0013] the temperature sensitive optical fiber is connected with the polarization maintaining mirror.

[0014] the titanium diffusion waveguide is connected with the driving and solving circuit.

[0015] Further, the output broadband light of the broadband light source is non-polarized light, and only light with one polarization direction passes through the beam splitter after passing through the optical fiber polarization beam splitter.

[0016] Further, the light with only one polarization direction passing through the beam splitter is power-equally divided into two polarization states of light after passing through the 45° fusion point and is transmitted in the compensating optical fiber, the titanium diffusion waveguide and the sensitive optical fiber.

[0017] Further, the change of temperature causes the change of birefringence and geometric length of the sensitive optical fiber, thereby causing the change of optical path, and the two polarization states of light transmitted in the compensating optical fiber, the titanium diffusion waveguide and the sensitive optical fiber carry phase difference, return to the 45° fusion point after modulation by the titanium diffusion waveguide, the two polarization states are again equally allocated to two axes and interfere, and only the interference light signal on one axis is reserved after passing through the optical fiber polarization beam splitter and is detected by the detector.

[0018] Further, the driving and solving circuit obtains the phase difference information by demodulation, thereby obtaining the temperature information of the temperature measuring optical fiber.

[0019] Further, the phase is determined by the temperature of each position of the optical fiber, and the temperature information obtained by solving is average temperature information.

[0020] Further, the solving mode of the driving and solving circuit is:

[0021] the system modulation depth is set to π / 2, at this time the peak-to-peak value of the modulation square wave voltage is half the wave voltage of the waveguide; the initial temperature of the optical fiber is T0, the test system is calibrated, the maximum output of the modulation wavelength phase is 1; the sensitive optical fiber is arranged in the measured sample according to the measurement requirement, the length of the arranged optical fiber is L, and the change of temperature causes the change of birefringence of the optical fiber, thereby causing the phase difference of the light transmitted by the fast and slow axes;

[0022] After the phase difference is generated, the light intensity is different. The output square wave is modulated in the order of "high value" minus "low value" to obtain the output value m. In the process, the peak value reaches 1 and then decreases, and the result is:

[0023]

[0024] By calculation, we get:

[0025]

[0026] The temperature increase at this time is obtained:

[0027]

[0028] The measured temperature is:

[0029] T=T0+ΔT.

[0030] The present invention arranges temperature-sensitive optical fibers and sensing optical fibers in the same batch and in the same space, that is, optical fibers of the same type are used as temperature-sensitive optical fibers and laid out in the same manner as sensor-sensitive optical fibers. By integrating the temperature-sensitive optical fibers' transmission characteristics and detecting the sensitive optical fibers, the "average temperature" of the measured environment is obtained. This can provide the "average temperature" for optical fiber sensors and other applications requiring a comprehensive temperature effect. Therefore, it is of great significance for sensors with a certain sensitive space or that need to measure the comprehensive temperature effect.

[0031] Specifically, compared with the prior art, the beneficial effects of the present invention include:

[0032] 1. The present invention can detect the average temperature of the space where the temperature-sensitive optical fiber is located in real time.

[0033] 2. The present invention adopts common optical devices, which are low-cost, convenient and efficient.

[0034] 3. The present invention can select the same type of polarization-maintaining optical fiber as the measured environment as the temperature-sensitive optical fiber, thereby directly obtaining the comprehensive impact of temperature on the optical fiber.

[0035] 4. This method is easy to implement and has strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. By referring to the drawings, the features and advantages of the present invention will be more clearly understood. The drawings are schematic and should not be understood as limiting the present invention in any way. Those skilled in the art can derive other drawings based on these drawings without inventive effort. Among them:

[0037] Figure 1This is a schematic diagram of an average temperature sensor based on the polarization-maintaining optical fiber birefringence thermo-optical effect of the present invention.

[0038] Figure 2 It is a principle diagram of the sensor birefringence phase resolution method of the present invention.

[0039] In the figure: 1-broad-spectrum light source; 2-fiber polarization beam splitter; 3-photodetector; 4-45° melting point; 5-compensation fiber; 6-titanium diffused waveguide; 7-temperature-sensitive fiber; 8-polarization-maintaining mirror; 9-drive solution circuit; 10-interference signal; 11-modulation signal; 12-detection signal. DETAILED DESCRIPTION

[0040] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features therein can be combined with each other without conflict.

[0041] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0042] like Figure 1 As shown, the average temperature sensor solution based on the polarization-maintaining fiber birefringence thermo-optical effect of the present invention includes a broadband light source 1, a fiber polarization beam splitter 2, a light detector 3, a 45° melting point 4, a compensation fiber 5, a titanium diffused waveguide 6, a temperature-sensitive fiber 7, a polarization-maintaining reflector 8, and a driving and solving circuit 9, which are connected by optical fiber fusion splicing.

[0043] The broadband light source 1 is connected to one of the optical fibers in the dual ports of the optical fiber polarization beam splitter 2.

[0044] The optical detector 3 is connected to the other optical fiber in the dual port of the optical fiber polarization beam splitter 2.

[0045] The single end of the optical fiber polarization beam splitter 2 is connected to the 45° melting point 4 of the compensation optical fiber 5.

[0046] The slow axis of the compensation fiber 5 is connected to the input end of the titanium diffused waveguide 6.

[0047] The output end of the titanium diffused waveguide 6 is connected to the fast axis of the temperature sensitive optical fiber 7.

[0048] The temperature sensitive optical fiber 7 is connected to the polarization maintaining mirror 8 .

[0049] The broadband light source 1 outputs unpolarized broadband light. After passing through the fiber polarization beam splitter 2, only light with one polarization direction passes through the beam splitter, assuming this polarization state is the x polarization state. After passing through the 45° melting point, the power is equally divided into the x and y polarization states, which are transmitted through the compensation fiber 5, titanium diffused waveguide 6, and sensitive fiber 7. Temperature changes will cause changes in the birefringence and geometric length of the sensitive fiber 7, thereby causing changes in the optical path. The two polarized light beams carrying phase differences are modulated by the waveguide and return to the 45° melting point 5. The two polarization states are again equally distributed to the two axes and interfere with each other. After passing through the fiber polarization beam splitter 2, only the interference light signal on one axis remains and is detected by the detector 3. Phase difference information is obtained through demodulation, thereby obtaining the temperature information of the temperature-measuring fiber. Since the phase is determined by the temperature at each position of the fiber, the average temperature information is calculated.

[0050] The system measurement method is as follows. The change of birefringence Δn with temperature is as follows:

[0051]

[0052] The thermal expansion effect of optical fiber is related to the quartz glass and coating layer. The thermal expansion coefficient of the polarization-maintaining fiber is approximately α(L)≈3ppm / °C. Assuming the length of the sensitive fiber is L, the phase difference Δφ between the two polarization states transmitted back and forth through the sensitive fiber is:

[0053]

[0054] At room temperature, the birefringence of polarization-maintaining fiber is about 5×10 -4 , then the phase difference change caused by temperature is:

[0055]

[0056] The initial phase difference is offset by the compensation optical fiber, so that the phase difference of the system is zero under normal temperature conditions.

[0057] like Figure 2 The figure shows the method for calculating the birefringence phase difference caused by the optical fiber temperature, including the interference signal 10, the modulation signal 11, and the detection signal 12. Assuming that the light source power is I0 and the splicing loss is ignored, the coherent intensity I of the return light is

[0058]

[0059] in To detect the phase of the applied modulation signal, is the residual initial phase difference.

[0060] When the temperature change produces a phase difference of Δφ, the modulated square wave signal with a fixed amplitude generates a square wave output signal, whose amplitude is determined by the phase difference between the two beams of light. The phase difference is obtained by the amplitude intensity, and the measured average temperature value is obtained.

[0061] An offset can also be added to the modulated signal to lock the system output at a fixed phase difference position. The added offset signal reflects the phase difference caused by temperature in the system, thereby improving the stability and sensitivity of the system and linearizing the relationship between output and input.

[0062] For example, if the system modulation depth is set to π / 2, the peak-to-peak value of the modulated square wave voltage is the half-wave voltage of the waveguide. The initial temperature of the optical fiber is 20°C. At this time, the test system is zero-calibrated, that is, the output is 0, and the maximum output of the phase of the entire wavelength is modulated to 1. The sensitive optical fiber is arranged in the sample to be tested according to the measurement requirements. Assume that the length of the arranged optical fiber is 10cm. At this time, the temperature causes the birefringence of the optical fiber to change, thereby causing a phase difference between the light transmitted by the fast and slow axes. If the light intensity is different after the phase difference occurs, if the output square wave is "high value" minus "low value" in the order of the modulated square wave, the output is -0.35, and the peak value reaches 1 and then decreases during the process (if it occurs, the phase increases or decreases by 2π according to the sign), then:

[0063]

[0064] By calculation, we can get:

[0065]

[0066] The temperature increase at this time is:

[0067]

[0068] The measured temperature is 20.44°C.

[0069] An offset can also be added to the modulated signal to lock the system output at a fixed phase difference position. The added offset signal reflects the phase difference caused by temperature in the system, thereby improving the stability and sensitivity of the system and linearizing the relationship between output and input.

[0070] The present invention utilizes the temperature effect of the birefringence of polarization-maintaining optical fiber to achieve temperature measurement, and utilizes polarization-maintaining optical fiber to realize the detection of spatial average temperature. In combination with the modulation and demodulation algorithm, signal detection is made more convenient, and large phase differences can be compensated by compensating optical fiber or spatial compensation optical path, thereby realizing accurate measurement of average temperature in a wide temperature range and a wide spatial range. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An average temperature sensor based on the thermo-optical effect of polarization-maintaining fiber birefringence, characterized in that: It includes a broadband light source, a fiber polarization beam splitter, a light detector, a compensation fiber, a titanium diffused waveguide, a temperature-sensitive fiber, a polarization-maintaining reflector, and a driving and solving circuit; Among them, the broadband light source is connected to one optical fiber in the dual port of the optical fiber polarization beam splitter, the light detector is connected to the other optical fiber in the dual port of the optical fiber polarization beam splitter, and the single end of the optical fiber polarization beam splitter is connected to the 45° melting point axis of the compensation optical fiber. The slow axis of the compensation fiber is connected to the input end of the titanium diffused waveguide. The output end of the titanium diffused waveguide is connected to the temperature sensitive optical fiber fast axis. The temperature sensitive optical fiber is connected to the polarization maintaining mirror. Titanium diffused waveguide connected to the driver solver circuit.

2. The average temperature sensor based on the polarization-maintaining fiber birefringence thermo-optical effect according to claim 1, characterized in that: The output broadband light of the broadband light source is non-polarized light, and after passing through the optical fiber polarization beam splitter, only light with one polarization direction passes through the beam splitter.

3. The average temperature sensor based on the polarization-maintaining fiber birefringence thermo-optical effect according to claim 2, characterized in that: The light having only one polarization direction passing through the beam splitter is equally split into two polarization states after passing through a 45° melting point and is transmitted in the compensation optical fiber, the titanium diffused waveguide and the sensitive optical fiber.

4. The average temperature sensor based on the polarization-maintaining fiber birefringence thermo-optical effect according to claim 3, characterized in that: Temperature changes cause changes in the birefringence and geometric length of the sensitive optical fiber, thereby causing changes in the optical path. The two polarization states of light transmitted in the compensating optical fiber, titanium diffused waveguide, and sensitive optical fiber carry a phase difference. After being modulated by the titanium diffused waveguide, it returns to the 45° melting point. The two polarization states are again equally distributed to the two axes and interfere with each other. After passing through the optical fiber polarization beam splitter, only the interference light signal on one axis is retained and detected by the detector.

5. The average temperature sensor based on polarization-maintaining fiber birefringence thermo-optical effect according to claim 4, characterized in that: The driving and solving circuit obtains phase difference information through demodulation, thereby obtaining the temperature information of the temperature measuring optical fiber.

6. The average temperature sensor based on polarization-maintaining fiber birefringence thermo-optical effect according to claim 5, characterized in that: The phase is determined by the temperature at each position of the optical fiber, and the temperature information obtained by calculation is the average temperature information.

7. The average temperature sensor based on the polarization-maintaining fiber birefringence thermo-optical effect according to claim 6, characterized in that: The solution method of the driving solution circuit is: Set the system modulation depth to π / 2, at which point the peak-to-peak value of the modulated square wave voltage is equal to the half-wave voltage of the waveguide; the initial temperature of the optical fiber is T0, and the test system is zero-calibrated, with the maximum output of the phase modulation of the entire wavelength being 1; The sensitive optical fiber is placed in the sample to be measured according to the measurement requirements. The length of the placed optical fiber is L. Temperature changes cause changes in the optical fiber birefringence, which causes a phase difference between the light transmitted on the fast and slow axes. After the phase difference is generated, the light intensity is different. The output square wave is obtained by subtracting the "low value" from the "high value" in the order of the modulated square wave, and the output value m is obtained. In the process, the peak value reaches 1 and then decreases. The result is: By calculation, we get: The temperature increase at this time is obtained: The measured temperature is: T=T0+ΔT.

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