CN204807233U - Temperature sensor of photonic crystal optic fibre michelson interferometer based on corrosion treatment - Google Patents

Abstract

The utility model provides a temperature sensor of a photonic crystal optical fiber Michelson interferometer based on corrosion treatment, which is characterized in that: a broadband light source 1, a transmission optical fiber 2, a circulator 3, a transmission optical fiber 4, a sensing head 5, and a temperature control Box 6, transmission optical fiber 7, and spectrometer 8; the photonic crystal optical fiber that has been corroded and coated with graphene film and gold film on the end surface constitutes the sensor head 5, and one end of the sensor head 5 passes through the transmission fiber 4 and the b end of the circulator 3 The sensor head 5 is placed in the temperature control box 6; the a end of the circulator is connected to the broadband light source 1 through the transmission fiber 2, and the c end of the circulator is connected to the spectrometer 8 through the transmission fiber 7. The utility model has the advantages of small volume, convenient use of the probe structure, anti-electromagnetic interference, corrosion resistance and high sensitivity.

Description

A Temperature Sensor Based on Corrosion Processed Photonic Crystal Fiber Michelson Interferometer

technical field

The utility model belongs to the technical field of optical fiber sensing, in particular to a temperature sensor of a photonic crystal optical fiber Michelson interferometer based on corrosion treatment.

Background technique

Optical fiber sensing technology developed rapidly with the development of optical fiber communication technology in the 1970s. It uses light waves as the carrier and optical fiber as the medium to perceive and transmit external measured signals. It is a new type of sensing technology for many economic and military The high and new technologies that the powerful countries are vying to research can be widely used in various fields of national economy and national defense and military fields, such as in aerospace (temperature measurement, gyroscope, etc.), power transmission (current measurement and voltage measurement of high-voltage transmission network), navigation (acoustic measurement, etc.) Sodium), petroleum exploration (liquid level height, flow measurement), scientific research and many other fields of application. The sensing sensitivity of fiber optic sensors is many times higher than that of traditional sensors, and has the advantages of high sensitivity, corrosion resistance, anti-interference, and small size.

Photonic crystal fiber (photonic crystal fiber, referred to as PCF) is composed of quartz material. It is a kind of optical fiber with periodic distribution of dielectric constant. The order of magnitude of its change period reaches the order of light wavelength. Compared with traditional optical fibers, photonic crystal fibers have the characteristics of unlimited single-mode transmission, adjustable dispersion, high birefringence, and polarization control. According to the light guiding principle, photonic crystal fiber can be divided into refractive index guided photonic crystal fiber and photonic bandgap photonic crystal fiber. The refractive index guided photonic crystal fiber is similar to the light guiding mechanism of the traditional total internal reflection fiber. The effective refractive index of the core is higher than that of the cladding, which meets the principle of total internal reflection light guiding. The photonic crystal fiber LMA-10 used in this patent is a refractive index guided photonic crystal fiber.

Introduction to Michelson interferometer: The traditional fiber optic Michelson interferometer is composed of a light source, a 3dB coupler, two optical fibers, a mirror, and a detector; one of the two optical fibers is used as a reference fiber, and the other is used as a signal fiber. After passing through the isolator, the light emitted by the light source enters the 3dB fiber optic coupler, and is divided into two paths of light with the same light intensity, which are respectively emitted from the a-end and b-end of the coupler, and all the way through the signal fiber, modulated by the external signal, and then reflected by the mirror , return from the original path and inject into port a. The other path is directly reflected back into port b after passing through the reference fiber. The two paths of light injected from ports a and b interfere when coupled in the coupler, and the phase change caused by the modulation signal will be reflected in the interference signal. After photoelectric conversion, the change of the phase can be accurately measured by using the change of light intensity, and the change of this phase can accurately record the external modulation signal, which is the basic principle of using Michelson interferometer for detection. In the improved fiber optic Michelson interferometer, by etching and splicing the optical fiber, the ordinary transmission optical fiber forms a specific structure, which can realize the function of the optical fiber coupler to split and combine light; at this time, when the light is transmitted to the coupler When , the light originally transmitted only in the core of the transmission fiber will be transmitted in the core and the cladding respectively, and when transmitted to the end face of the fiber, due to Fresnel reflection at the end face of the fiber, the light transmitted in the core and cladding will Reverse transmission, and achieve light combination at the fiber coupler. At this point, two paths of light propagation can be realized in the same optical fiber. By detecting the interference spectrum of the light transmitted by the two paths, the change of the external modulation signal can be obtained from the change of the interference signal. Coating gold on the end face of the optical fiber can greatly enhance the efficiency of light reflection, making the detection more accurate.

A temperature sensor based on corroded photonic crystal fiber Michelson interferometer. Fiber Optic Sensor.

Contents of the invention

The purpose of the utility model is to provide a technical scheme of a temperature sensor of a photonic crystal fiber Michelson interferometer based on corrosion treatment.

Described a kind of temperature sensor based on the photonic crystal fiber Michelson interferometer of corrosion treatment is characterized in that by broadband light source 1, transmission fiber 2, circulator 3, transmission fiber 4, sensing head 5, temperature control box 6, The transmission fiber 7 and the spectrometer 8 are composed; the photonic crystal fiber that has been corroded and coated with graphene film and gold film on the end face constitutes the sensing head 5, and one end of the sensing head 5 is connected to the b end of the circulator 3 through the transmission fiber 4, and the transmission The sensing head 5 is placed in the temperature control box 6; the a end of the circulator is connected to the broadband light source 1 through the transmission fiber 2, and the c end of the circulator is connected to the spectrometer 8 through the transmission fiber 7. The function of the circulator 3 is to separate the forward (input) optical signal and the reverse (output) optical signal transmitted in the optical fiber, and the circulator 3 is unidirectional along the optical path a→b→c.

The temperature sensor based on the corrosion-treated photonic crystal fiber Michelson interferometer is characterized in that the model of the photonic crystal fiber to be used when making the sensing head 5 is LMA-10.

The temperature sensor based on the corrosion-treated photonic crystal fiber Michelson interferometer is characterized in that the length of the sensing head 5 is 100 μm.

Described a kind of temperature sensor based on the photonic crystal fiber Michelson interferometer of corrosion treatment is characterized in that used single-mode fiber can adopt G.652, G.653 and G.655 single-mode fiber; Transmission fiber 2, The lengths of the transmission optical fiber 4 and the transmission optical fiber 7 are both 20-30 cm.

The utility model has the advantages that the sensor is small in size, easy to use with a probe structure, anti-electromagnetic interference, corrosion-resistant and high in sensitivity.

Description of drawings

Fig. 1 is the structural representation of the utility model

Figure 2 is a cross-sectional view of the untreated photonic crystal fiber used

Figure 3 is a cross-sectional view of a photonic crystal fiber after corrosion treatment

Figure 4 is a comparison diagram of the area of photonic crystal fiber before and after corrosion

Figure 5 is a schematic diagram of the structure of the sensor head and the interface between the sensor head and the transmission fiber

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described:

As shown in Figure 1, a temperature sensor of a photonic crystal fiber Michelson interferometer based on corrosion treatment consists of a broadband light source 1, a transmission fiber 2, a circulator 3, a transmission fiber 4, a sensing head 5, a temperature control box 6, a transmission Composed of optical fiber 7 and spectrometer 8. The fabrication of the sensing head 5 is as follows: one end of a section of photonic crystal fiber and the transmission fiber 4 are spliced without collapsing by a fusion splicer, and then the other end of the photonic crystal fiber is vertically immersed in HF acid solution for corrosion. Due to the capillary effect, the corrosive solution enters the air holes of the photonic crystal fiber. After 180 seconds, the wall of each circular air hole periodically arranged in the photonic crystal fiber is corroded and disappears, so that the hexagonal area originally arranged in the photonic crystal fiber is corroded into a hexagonal air hole. And due to corrosion, the solid portion surrounded by the air pores becomes thinner, forming a thin core portion with a diameter of about 2 μm. The photonic crystal fiber end face before etching is shown in Figure 2, where the white circular holes are air holes, and the gray part is quartz material. The corroded photonic crystal fiber is shown in Figure 3, the gray part is quartz material, the white part of the hexagon is the air hole formed after corrosion, and the solid part surrounded by periodically arranged air holes in the center becomes thin. The comparison diagram of the boundary before and after corrosion is shown in Figure 4. It can be seen from Figure 4 that after corrosion, the range of the hexagonal air cavity is slightly larger than the hexagonal area formed by the arrangement of uncorroded circular air holes, and the thin core The section is slightly smaller than the central section surrounded by the uncorroded circular air hole. The other end face of the processed photonic crystal fiber is coated with a thin graphene film, and then coated with a layer of gold film on the graphene film; The cavity, and the graphene film does not affect the transmission and distribution of light; the function of the gold film is to strengthen the reflection of light on the end face of the sensor head. The corroded and coated photonic crystal fiber constitutes the sensing head 5 . One end of the sensor head 5 is connected to the b end of the circulator 3 through the transmission fiber 4, and the sensor head 5 is placed in the temperature control box 6; the a end of the circulator is connected to the broadband light source 1 through the transmission fiber 2, and the c end of the circulator The end is connected to the spectrometer 8 through the transmission fiber 7.

The working mode of the device of the utility model is as follows: the fusion interface between the sensing head and the transmission fiber is shown in Figure 5, the transmission fiber is a single-mode fiber, the light mainly propagates in the fiber core, and the fiber core diameter is about 8 μm. The light emitted by the broadband light source enters the a-end of the circulator through the transmission fiber 2, and the circulator a→b makes the light unidirectionally transmitted to the b-end of the circulator, and enters the sensor head through the transmission fiber 4, where the sensor head and the transmission fiber are fused At the interface, the light will enter the air hole of the photonic crystal fiber due to the mismatch between the size of the transmission fiber core and the thin core in the middle of the sensor head. The light is transmitted along the thin core and the air cavity in the sensor head, and reflected at the gold film on the end face of the sensor; the reflected light is reversely transmitted along the thin core and the air cavity, and is fused at the interface between the sensor head and the transmission fiber Commonly enter the core of the transmission fiber and interfere due to a stable optical path difference. The signal of the interference light is reversely transmitted along the transmission fiber 4 to the port b of the circulator, and the circulator b→c makes the light unidirectionally transmitted to the end of the circulator c, and enters the spectrometer through the transmission fiber 7, and the interference spectrum is displayed on the spectrometer.

The phase formula of an optical signal can be expressed by the following formula:

$\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;nL</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}$

Where n is the refractive index of the medium through which the light is transmitted, L is the distance traveled by the light, and λ is the wavelength of the transmitted light.

For the fiber Michelson interferometer, due to the reflection at the end face, the light transmission distance is twice, and the phase difference of the interfering light can be expressed by the following formula:

$\mathrm{<span\; class="notranslate">\; \&Delta;\&psi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; cavity</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; core</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; L</span>}$

Where n _cavity and n _core are the refractive indices of the air cavity and the thin core, respectively, and n _cavity -n _core is the difference between the effective refractive indices of the air cavity and the thin core.

When the external temperature changes, the (n _cavity -n _core )L changes due to the different responses of the thin core and the air cavity to the temperature change, which shows the drift of the interference spectrum on the spectrometer. The drift of the spectrum is related to the temperature change, so the temperature sensitivity of the sensor can be further calculated by monitoring the change of the interference spectrum.

Claims (4)

1. A temperature sensor based on an corrosion-treated photonic crystal fiber Michelson interferometer, characterized in that it consists of a broadband light source (1), a transmission fiber (2), a circulator (3), a transmission fiber (4), and a sensing head (5), temperature control box (6), transmission optical fiber (7), and spectrometer (8); the photonic crystal optical fiber that has been corroded and coated with graphene film and gold film on the end surface constitutes the sensor head (5), the sensor head One end of (5) is connected to the b end of the circulator (3) through the transmission fiber (4), the sensor head (5) is placed in the temperature control box (6); the a end of the circulator is connected to the b end of the circulator through the transmission fiber (2) The broadband light source (1) is connected, and the c-end of the circulator is connected with the spectrometer (8) through the transmission fiber (7). 2. A temperature sensor based on an etching-treated photonic crystal fiber Michelson interferometer according to claim 1, characterized in that the model of the photonic crystal fiber to be used when making the sensing head (5) is LMA-10. 3. The temperature sensor based on the corrosion-treated photonic crystal fiber Michelson interferometer according to claim 1, characterized in that the length of the sensing head (5) is 100 μm. 4. the temperature sensor of a kind of photonic crystal fiber Michelson interferometer based on corrosion treatment according to claim 1, it is characterized in that used single-mode optical fiber can adopt G.652, G.653 and G.655 single-mode Optical fibers; the lengths of the transmission optical fibers (2), the transmission optical fibers (4), and the transmission optical fibers (7) are all 20-30 cm.