CN106248248A - A kind of thermometry based on thin-core fibers Mach-Zehnder interferometer - Google Patents

Abstract

The invention provides a temperature measurement method based on a thin-core optical fiber Mach-Zehnder interferometer, said measuring method comprising the following steps: a) building a thin-core optical fiber Mach-Zehnder interferometer, and thin-core optical fiber Mach-Zehnder interferometer The instrument is sequentially connected with a pump source, a wavelength division multiplexer and a thin-core fiber Mach-Zehnder structure; the thin-core fiber Mach-Zehnder structure includes a thin-core fiber, a first doped rare-earth fiber and a second doped rare-earth fiber Optical fiber, the thin-core fiber is fused between the first doped rare-earth fiber and the second doped rare-earth fiber, the first doped rare-earth fiber and the second doped rare-earth fiber are used as the gain medium of the fiber laser; b) the thin-core The Mach-Zehnder structure of the optical fiber is fixed to the matrix material; c) gradually changing the temperature, recording the length of the comb spectrum movement, and drawing the change curve of the comb spectrum movement length and temperature; d) passing the comb spectrum movement length and The change curve of the temperature magnitude is measured for the applied temperature.

Description

A temperature measurement method based on thin-core fiber Mach-Zehnder interferometer

Patent cross-reference

This application claims the priority right of the Chinese invention patent application with application number CN201510670316.6 submitted on October 13, 2015.

technical field

The invention relates to the field of optical fiber interferometers, in particular to a temperature measurement method based on a thin-core optical fiber Mach-Zehnder interferometer.

Background technique

Generally, all-fiber sensors have the advantages of compact structure, long service life, sensitivity to test volume, and multiple transmission channels, and are widely used in optical fiber sensing, optical fiber communication, optical processing and other fields. Through the micro-machining technology of the fiber end face or building an all-fiber sensor with an interference structure, under the action of the pump source, an interference spectrum curve with a comb-like spectrum pattern is output. In the prior art, a Mach-Zehnder interferometer based on a dual-core optical fiber has an interference fringe-to-surface ratio of about 10 dBm, and a fringe interval of about 2 nm. Two 3dB couplers are made into a Mach-Zehnder interferometer system, combined with a double-core optical fiber to form a Mach-Zehnder interferometer with a double-stage structure, and the fringe-to-width ratio is about 30dBm.

The thin-core fiber Mach-Zehnder fiber sensor has a simple structure and is easy to realize. This structure consists of a thin-core fiber fusion spliced into two relatively thick core-diameter doped rare-earth fiber optics, which can effectively and accurately obtain the interference of the comb spectrum pattern. Spectral curves, therefore, require precise and efficient temperature measurements by means of a thin-core fiber-based Mach-Zehnder interferometer.

Contents of the invention

Provided according to the present invention is a kind of temperature measurement method based on thin-core optical fiber Mach-Zehnder interferometer, and described measurement method comprises the following steps:

b) Build the thin-core fiber Mach-Zehnder interferometer, the thin-core fiber Mach-Zehnder interferometer is sequentially connected to the pump source, a wavelength division multiplexer and the thin-core fiber Mach-Zehnder through the grating fiber structure; the thin-core optical fiber Mach-Zehnder structure includes a section of thin-core optical fiber, a first doped rare-earth optical fiber and a second doped rare-earth optical fiber, and the thin-core optical fiber is welded on the first doped rare-earth optical fiber and the second doped rare-earth optical fiber Between the rare earth fibers, the first doped rare earth fiber and the second doped rare earth fiber serve as the gain medium of the fiber laser;

b) Fix the Mach-Zehnder structure of the thin-core optical fiber with the matrix material, and place the

in a controlled environment;

c) Gradually change the temperature, record the length of the comb spectrum movement, and draw the change curve of the comb spectrum movement length and temperature;

d) Measure the temperature through the change curve of the shift length of the comb spectrum and the magnitude of the temperature.

Preferably, the pumping source uses a laser diode as a fiber laser.

Preferably, the first rare-earth-doped fiber and the second rare-earth-doped fiber are doped fibers doped with rare-earth elements, and are used for gaining a fiber laser.

Preferably, the wavelength division multiplexer is used to couple the pump light into the first rare earth-doped optical fiber.

Preferably, the fixing method described in step b) is to combine the thin-core optical fiber, the first doped rare earth optical fiber and the second doped rare earth optical fiber with a matrix material, and place them in an environment with controllable temperature changes. A temperature calibration using one of a continuous increase or decrease of the controlled temperature.

Preferably, the change curve of the shift length of the comb spectrum and the temperature is fitted by linear fitting or least square method.

Preferably, the first rare-earth-doped fiber and the second rare-earth-doped fiber are selected from one of erbium-doped fiber, ytterbium-doped fiber, or erbium-ytterbium co-doped fiber. The temperature measurement method based on the thin-core optical fiber Mach-Zehnder interferometer provided by the present invention is accurate and efficient in measurement, easy to operate, and suitable for application in various occasions.

It should be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on the claimed content of the present invention.

Description of drawings

With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

Fig. 1 schematically shows a schematic diagram of the temperature measurement structure of the fine-core fiber Mach-Zehnder interferometer of the present invention;

Fig. 2 shows the fusion splice schematic diagram of thin-core optical fiber and grating optical fiber of the present invention;

Fig. 3 shows the flow chart of the temperature measurement method based on the thin-core fiber Mach-Zehnder interferometer of the present invention;

Fig. 4 shows the curve of comb spectrum changing with temperature in one embodiment of the present invention.

detailed description

The objects and functions of the present invention and methods for achieving the objects and functions will be clarified by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in various forms. The essence of the description is only to help those skilled in the relevant art comprehensively understand the specific details of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

In this embodiment, a temperature measurement method based on a thin-core fiber Mach-Zehnder interferometer is described in detail. As shown in FIG. The Mach-Zehnder interferometer includes a laser diode as the pump source 101 of the fiber laser, a wavelength division multiplexer (WDM) 102 and a thin-core fiber Mach-Zehnder structure, and the thin-core fiber Mach-Zehnder The structure includes a section of thin-core optical fiber 104 , a first rare-earth-doped optical fiber 103 and a second rare-earth optical fiber 105 , and the thin-core optical fiber 104 is fused between the first rare-earth-doped optical fiber 103 and the second rare-earth-doped optical fiber 105 . The first doped rare earth fiber 103 and the second doped rare earth fiber adopt the doped fiber doped with rare earth elements as the gain medium of the fiber laser, and the first doped rare earth fiber 103 and the second doped rare earth fiber 105 are selected from erbium doped fiber One of optical fiber, ytterbium-doped optical fiber or erbium-ytterbium co-doped optical fiber, the wavelength division multiplexer 102 is used to couple the pump light into the first rare-earth-doped optical fiber 103 .

The thin-core optical fiber Mach-Zehnder structure is fixedly combined with the matrix material 107, and placed in an environment 106 with controlled temperature changes. In some embodiments, the temperature can be continuously increased, and in other embodiments, it can be continuous decrease in temperature. In this embodiment, the temperature-changing environment 106 is controlled by a temperature controller 108 to continuously increase the temperature.

In this embodiment, the thin-core optical fiber 104, the first doped rare-earth optical fiber 103 and the second doped rare-earth optical fiber 105 are connected in series through the grating optical fiber, as shown in FIG. The grating fiber with the core fiber 202 fused to each other is divided into a first grating fiber 201 and a second grating fiber 203, and the thin core fiber 202, the first grating fiber 201 and the second grating fiber 203 are all made of fiber coating, fiber cladding and fiber core Composition, FIG. 2 of this embodiment exemplarily shows the fiber coating 205 , the fiber cladding 206 and the fiber core 207 of the second grating fiber 203 .

It should be noted that the core diameter of the first doped rare earth fiber 103, the second doped rare earth fiber 105, the first grating fiber 201 and the second grating fiber 203 should be greater than the core diameter of the thin core fiber 104 (202) size.

The following is a specific description of the optical path and the change of the comb spectrum length in the temperature measurement method based on the thin-core fiber Mach-Zehnder interferometer in an embodiment of the present invention:

The total light intensity I is

where I ₁ , I ₂ and are the optical intensity and phase shift difference of the core and cladding in the thin-core fiber, respectively, and

Among them, n ₁ and n ₂ are the effective refractive indices of the core and cladding, respectively, and L ₁ and L ₂ are the lengths of the light beam traveling in the core and cladding, respectively. Since the lengths of the interference arms are equal and there is a refractive index difference Δn, then

It can be seen from formula 1 and formula 3 that the peak in the transmission spectrum occurs at the wavelength satisfying the following formula, where m is an integer

2πLΔn/λ=2mπ (4)

After simplification, Equation 4 is expressed as

m=LΔn/λ (5)

Derivation of λ in Equation 5 gives

Δm/Δλ=-LΔn/λ ² (6)

Taking Δm=1, the wavelength interval between adjacent peaks in the transmission spectrum at wavelength λ is

|Δλ|=λ ² /LΔn (7)

It can be seen from formula 7 that in the comb spectrum of the fine-core fiber Mach-Zehnder comb interferometer of the present invention, the wavelength interval between adjacent peaks is related to the central wavelength, the length of the thin-core fiber, and the difference in refractive index between the core and the cladding. When the central wavelength is constant, the wavelength interval between adjacent peaks is a function of the length of the thin-core fiber and the refractive index difference between the core and the cladding.

The comb spectrum is used for sensing test. When the interferometer is affected by the temperature and the substrate material is deformed, which causes the optical path difference between the two arms to change, the interference comb spectrum changes and the interference fringes move.

In order to more clearly illustrate the temperature measurement method of the present invention based on the thin-core optical fiber Mach-Zehnder interferometer, this embodiment is described in conjunction with the flow process of the specific temperature measurement method. As shown in Figure 3, the present invention is based on the thin-core optical fiber Mach-Zehnder The flow chart of the temperature measurement method of interferometer; The temperature measurement method based on thin-core fiber Mach-Zehnder interferometer comprises the steps:

Step 301, build a fine-core optical fiber Mach-Zehnder interferometer, and weld the Mach-Zehnder structure;

Step 302, fixing the fine-core Mach-Zehnder structure and the base material, and placing them in an environment with controllable temperature changes;

Step 303: Control the temperature through the temperature controller, gradually increase the temperature, record the length of the comb spectrum movement, and draw the change curve of the comb spectrum movement length and temperature; wherein the change curve of the comb spectrum movement length and temperature Carry out fitting by linear fitting or least square method, the fitting process of curve adopts least square fitting in the present embodiment, by equation

$\frac{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; S</span>}}{<span\; class="notranslate">\; \&part;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

$\frac{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; S</span>}}{<span\; class="notranslate">\; \&part;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Combine formula (8) and formula (9) to solve a ₀ and a ₁ , and construct an approximation function that satisfies the square approximation condition.

f(x)＝a ₀ +a ₁ x (10)

Step 304 , measure the applied temperature through the change curve of comb spectrum moving length and temperature, as shown in FIG. 4 , the curve of comb spectrum changing with temperature in one embodiment of the present invention.

According to the present invention, it is necessary to perform parameter matching on relevant optical fibers, and specific parameters include but not limited to matching of pump wavelength, wavelength division multiplexer, laser output wavelength and optical fiber parameters. Parameters in this embodiment are as shown in table 1:

Table 1 is based on the fiber parameters of the thin-core fiber Mach-Zehnder interferometer according to the present invention

According to the present invention, the core diameter of the rare earth-doped optical fiber is determined by the active optical fiber used. The core diameter of the cladding is preferably 125 μm, and the core diameter of the fiber core can be 4 μm, 8 μm or 10 μm, preferably 10/125 μm. Select the matching FLM, WDM, LD pigtail core diameter according to the selected core diameter. The pumping wavelength of the erbium-doped fiber can be 980nm or 1480nm, the pumping wavelength of the ytterbium-doped fiber can be 976nm or 915nm, the pumping wavelength of the erbium-ytterbium co-doped fiber can be 976nm, further determine the FLM according to the wavelength and core diameter parameters , WDM parameters. The final emitted laser wavelength is determined by the reflection wavelength of the Bragg fiber grating within a certain gain range of the active fiber (such as 1530-1560nm). The typical emission wavelength of ytterbium-doped fiber is 1535nm, the typical emission wavelength of erbium-doped fiber is 1064nm, and the typical emission wavelength of erbium-ytterbium co-doped fiber is 1550nm.

For example, in this embodiment, if an erbium-doped fiber with a core diameter of 10/125 μm is selected as the gain medium, the LD pigtail, WDM and FLM need to select the same type of core diameter. The output wavelength of LD is 976nm, the working wavelength of WDM is 976/1550nm, the working wavelength of FLM is 1550nm, and the selection range of FBG is 1530nm-1560nm, and the laser output can be obtained within this range. If the ytterbium-doped fiber with a core diameter of 10/125 μm is used as the gain medium in the experiment, the same type of core diameter should be selected for the LD pigtail, WDM and FLM. LD is 915nm single-mode output, WDM operating wavelength is 915/1064nm, FLM operating wavelength is 1064nm, FBG is selected near 1064nm, and laser output can be obtained within this range.

According to the temperature measurement method based on the fine-core fiber Mach-Zehnder interferometer of the present invention, the measurement is accurate and efficient, easy to operate, and suitable for application in various occasions.

Other embodiments of the invention will be apparent to and understood by those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (7)

1. A temperature measurement method based on thin-core fiber Mach-Zehnder interferometer, characterized in that said measurement method may further comprise the steps: a) Build the thin-core fiber Mach-Zehnder interferometer, the thin-core fiber Mach-Zehnder interferometer is sequentially connected to the pump source, a wavelength division multiplexer and the thin-core fiber Mach-Zehnder through the grating fiber structure; the thin-core optical fiber Mach-Zehnder structure includes a section of thin-core optical fiber, a first doped rare-earth optical fiber and a second doped rare-earth optical fiber, and the thin-core optical fiber is welded on the first doped rare-earth optical fiber and the second doped rare-earth optical fiber Between the rare earth fibers, the first doped rare earth fiber and the second doped rare earth fiber serve as the gain medium of the fiber laser; b) fixing the Mach-Zehnder structure of the fine-core optical fiber with the matrix material, and placing it in an environment with controllable temperature changes; c) Gradually change the temperature, record the length of the comb spectrum movement, and draw the change curve of the comb spectrum movement length and temperature; d) Measure the temperature through the change curve of the shift length of the comb spectrum and the magnitude of the temperature. 2. The temperature measurement method according to claim 1, wherein the pumping source is used as a fiber laser through a laser diode. 3. The temperature measuring method according to claim 1, characterized in that, the first rare-earth-doped optical fiber and the second rare-earth-doped optical fiber are doped optical fibers doped with rare-earth elements, which are used for the gain of fiber lasers. 4. The temperature measurement method according to claim 1, wherein the wavelength division multiplexer is used to couple the pump light into the first rare earth-doped optical fiber. 5. temperature measuring method according to claim 1, is characterized in that, the fixed method described in step b) is described thin-core fiber, the first doped rare-earth fiber and the second doped rare-earth fiber and substrate The materials are combined into one body, placed in an environment with controlled temperature changes for temperature calibration, and the calibration process adopts one of the continuous increase or continuous decrease of the controlled temperature. 6. The temperature measuring method according to claim 1, characterized in that, the change curve of the comb spectrum moving length and temperature is fitted by linear fitting or least square method. 7. The temperature measurement method according to claim 3, wherein the first rare earth-doped optical fiber and the second rare-earth element-doped optical fiber are selected from one of erbium-doped optical fiber, ytterbium-doped optical fiber or erbium-ytterbium co-doped optical fiber kind.