KR100525206B1 - Apparatus and method of measuring temperature and strain using a single Fiber Bragg Grating - Google Patents

Abstract

The present invention relates to a temperature and strain measurement system and method using an optical fiber grating that can calculate the temperature and strain around the optical fiber grating after analyzing the light after reacting with the optical fiber grating and transmits light to the optical fiber grating and the optical fiber grating. And a temperature / strain calculator for analyzing the polarization dependent loss and the resonant wavelength shift by the optical fiber grating of the transmitted light to calculate the temperature and strain of the optical fiber grating. The temperature / strain measurement system using the optical fiber grating provides the advantage of using a single optical fiber grating.

Description

Apparatus and method of measuring temperature and strain using a single Fiber Bragg Grating}

The present invention relates to a temperature and strain measuring system and method using an optical fiber grating, and more particularly, to a temperature using an optical fiber grating capable of calculating a temperature and strain around an optical fiber grating by analyzing light after reacting with the optical fiber grating. Strain measurement systems and methods.

As the optical fiber grating changes in temperature or strain, the wavelength of the optical signal reflected from the optical fiber grating changes. Therefore, the wavelength change of the light reflected from the optical fiber grating can be measured and used to determine what size of external temperature, strain, pressure, etc., is applied from the amount of change in the wavelength.

However, when two physical quantities of temperature and strain are applied at the same time, it is not known how much the temperature and strain have been changed by measuring only the amount of change in the reflected wavelength because the optical fiber reacts to both physical quantities simultaneously.

In order to solve this problem, Korean Laid-Open Patent Publication No. 1998-0082465 discloses a method for calculating temperature and strain using a pair of optical fiber grids in which two optical fiber grids having different outer diameters are bonded in series.

However, the disclosed temperature / strain measuring method has difficulty in manufacturing because it is necessary to manufacture and use a pair of optical fiber grids with different outer diameters for the same base material.

The present invention was devised to improve the above problems, and an object thereof is to provide a temperature and strain measurement system and method using an optical fiber grating capable of measuring temperature and strain using a single optical fiber grating.

In order to achieve the above object, a temperature and strain measurement system using an optical fiber grating according to the present invention comprises: an optical fiber grating; And a temperature / strain calculator configured to output light to the optical fiber grating and analyze the polarization dependent loss amount and the resonance wavelength shift amount of the transmitted light by the optical fiber grating to calculate the temperature and strain of the optical fiber grating. '

Preferably, the temperature / strain calculator is installed to detect light reflected from the optical fiber grating, and the optical fiber grating is applied with a short period optical fiber grating.

The temperature / strain calculator may include: a light source emitting light of which wavelength is changed according to a control signal; A polarization adjuster for adjusting a polarization state of light emitted from the light source; An optical splitter configured to transmit input light passing through the polarization adjuster to the optical fiber grating, and output light reflected from the optical fiber grid to be separated from the input light; A temperature / strain calculator configured to control the light source and the polarization adjuster and obtain a temperature and strain of the optical fiber grating by analyzing resonance wavelengths and polarization dependent loss of reflected light reflected from the optical fiber grating and output through the optical splitter; Equipped.

Preferably, the light splitter is a circulator is applied.

In addition, the temperature / strain measuring method using the optical fiber grating according to the present invention to achieve the above object comprises the steps of: transmitting the light generated in accordance with the polarization generation pattern is set to the optical fiber grating; And calculating the temperature and strain of the optical fiber grating by receiving the light reflected from the optical fiber grating and calculating the resonance wavelength and the polarization dependent loss amount, wherein the optical fiber grating is applied with a short period optical fiber grating.

According to another aspect of the present invention, there is provided a temperature / strain measuring method using an optical fiber grating, comprising: transmitting light generated according to a set polarization generation pattern to the optical fiber grating; And calculating the temperature and strain of the optical fiber grating by receiving the light transmitted through the optical fiber grating and calculating the resonance wavelength and the polarization dependent loss amount, wherein the optical fiber grating is applied with a long period optical fiber grating.

Hereinafter, a temperature and strain measuring system and method using an optical fiber grating according to a preferred embodiment of the present invention with reference to the accompanying drawings will be described in more detail.

1 is a view schematically showing a temperature and strain measurement system using an optical fiber grating according to an embodiment of the present invention.

Referring to the drawings, the temperature and strain measurement system 100 includes an optical fiber grating 160 and a temperature / strain calculator 110.

The optical fiber grid 160 has a grid 161 formed at a predetermined interval on the optical fiber.

Preferably, the grating 161 is applied to one side of the optical fiber formed by irradiating ultraviolet light at a predetermined interval. In the drawings, the grid 161 is illustrated vertically to aid visual understanding.

As shown in FIG. 2, the optical fiber grating 160 may be manufactured using the laser light source 210, the focusing lens 220, and the amplitude mask 230.

That is, when the optical fiber 260 to form a grating is mounted on the holder 240 and then the light is emitted from the laser light source 210 that emits ultraviolet light, the focusing lens 220 and the light at a predetermined interval selectively transmit the light. Ultraviolet laser is irradiated to the optical fiber 260 at a predetermined interval through the amplitude mask 230 formed so as to be made, so that the light irradiation site is a grating.

The optical fiber 260 irradiated with ultraviolet rays in this manner has a combination of geometric asymmetry in which the ultraviolet laser is irradiated only on one side and the polarization state of the ultraviolet laser act as anisotropy. ), Which causes birefringence in the optical fiber 260. The birefringence generation due to the polarization of the ultraviolet laser or the like is disclosed in detail in a paper published by T. Erdogan (p2100 to p2105 of the 1994 journal of the Optical Society of America B).

The optical fiber grating 161 produced through such a manufacturing process has a severe polarization dependency, and this polarization dependence causes polarization dependency loss (PDS), which is a loss factor of the device.

In addition, in order to deepen the refractive index anisotropy in the cross section of the optical fiber 260 core, an appropriately adjusted doping ratio of a material, for example, germanium (Ge), which is doped into the core layer of the optical fiber 260 is used. It is preferable to apply the light irradiation time for lattice formation sufficiently shorter than the saturation time corresponding to refractive index isotropy.

Preferably, the optical fiber grating 160 is a short period optical fiber grating is applied. The short-period optical fiber grating 160 is formed by forming the interval between the gratings 161 about several hundred nanometers (nm), and has a large polarization dependency characteristic.

Alternatively, a long period optical fiber grating (see FIG. 3: 460) having a lattice spacing of several hundred micrometers may be applied.

In the present invention, temperature and strain are measured using the polarization dependence of the optical fiber grating 161.

Therefore, when the optical fiber grating 160 is manufactured, an appropriate irradiation of the time for exposing ultraviolet rays to the optical fiber 260 is applied so that the degree of difference in refractive index becomes large depending on the light irradiation direction.

The temperature / strain calculator 110 includes a temperature / strain calculator 120, a light source 130, a polarization controller 140, and a circulator 150.

The light source 130 is preferably a tunable laser diode (tunable laser diode) that can vary the wavelength of the emitted light according to the control signal of the temperature / strain calculation unit 120.

The polarization controller 140 adjusts the polarization state of the light emitted from the light source 130 according to the control signal of the temperature / strain calculation unit 120 and outputs it to the circulator 150.

Here, the adjustment of the polarization state is appropriately applied according to the method of measuring the polarization dependent loss (PDL). Known polarization dependent loss measurement methods include an all state scanning method, a Mueller matrix method, a Jones matrix method, and the like.

When the all state scanning method is applied to the measurement of the polarization dependence loss, a polarization adjuster capable of making the light emitted from the light source 130 into the all-state polarization state may be applied. Such a polarization adjuster is generally referred to as a polarization scrambler. do.

Meanwhile, when the Mueller matrix method and the Jones matrix method are applied, a polarization regulator capable of generating at least three different input polarization states may be applied.

Here, the different input polarization states form polarization directions differently such as linear horizontal, linear vertical, linear diagonal, and rigid-hand circular. Say that.

The polarization controller 140 is configured to generate a desired polarization state by combining a half plate, a quarter plate, and the like. The structure of the polarization controller 140 is variously known, and a detailed description thereof will be omitted.

The circulator 150 is applied as an optical splitter so that the path of the light reflected from the optical fiber grating 160 with respect to the light incident on the optical fiber grating 161 may be output by a path different from the light incident path.

Of course, the optical fiber coupler (not shown) may be applied instead of the circulator 150.

The temperature / strain calculation unit 120 controls the light source 130 and the polarization adjuster 140 according to a control pattern set to generate light of a set wavelength and polarization state, and the optical fiber grid 160 through the circulator 150. Receiving the light reflected from the to calculate the resonant wavelength and PDL value, using the calculated value to calculate the temperature and strain of the optical fiber grid 160 or its surroundings.

The temperature / strain calculation unit 120 includes a light receiving unit (not shown), a control unit (not shown) for processing signals output from the light receiving unit, an input unit (not shown) for outputting user input signals to the control unit, and a storage device used by the control unit. (Not shown) can be provided.

Meanwhile, when the long period optical fiber grating is applied, the circulator 150 may be omitted, and as shown in FIG. 3, the long period optical fiber grating 460 for the light emitted from the light source 430 through the polarization regulator 440. What is necessary is just to construct the temperature / strain calculation part 420 so that temperature / strain may be calculated from the light which permeate | transmitted.

The method of using the light reflected from the short period optical fiber grating 160 and the method of using the light transmitted from the long period optical fiber grating 460 have the same principle of calculating the temperature / strain in consideration of the correlation between the reflected light and the transmitted light. In the following, the case of using the short period optical fiber grating 160 will be described.

First, two independent variables are required in order to separately distinguish and calculate the influences of the two measurement target physical quantities, temperature (T) and strain (ε). When such a relationship is expressed, it can be expressed as Equation 1 below.

Where ΔT and Δε are changes in temperature and strain, Δx ₁ and Δx ₂ are two independent variables to be applied, and K _i T and K _i ε (i = 1,2) are independent variables (x _i ), respectively Is a relational constant related to temperature and strain response to.

Therefore, if the resonant wavelength λB and the polarization dependence loss PDL of the optical fiber grating 160 are applied to the independent variables x ₁ and x ₂ , and the corresponding relation constant is obtained, the temperature is obtained from Equation 2 below. And the amount of change in strain can be obtained.

Experimental results performed to determine the suitability of the temperature / strain calculation method will be described below with reference to FIGS. 4 to 8.

First, the optical fiber grid 160 is connected to the experimental apparatus as shown in FIG. 4, and then the resonance wavelength and PDL change according to the temperature and strain variation were measured by the Muller matrix method. The experimental apparatus was applied to the light source 330, the polarization controller 340, the measuring device 320, the holder 370, the oven 310 and the computer 350.

As for the applied optical fiber grating 160, an argon-ion laser light having a center wavelength of 244 nm was applied to the optical fiber for about 1 minute using an amplitude mask having a 1060 nm period of 10 nm for the optical fiber.

The holder 370 is installed to move the strain to the optical fiber grid 160. That is, when applying strain, the first holder 270a may be moved by a distance set in the direction of the arrow.

The measuring unit 320 may be a device capable of measuring the polarization dependent loss and the power, and as an example, an Expo PDL / OL meter, a Donam system PDL meter, and the like may be used.

The computer 350 controls the light source 330 and the polarization regulator 340 so that light having a predetermined wavelength and polarization state is applied to the optical fiber grid 160 according to the set light generation pattern, and is detected through the measuring unit 320. It is constructed to calculate, record and display temperature / strain using resonant wavelength and PDL value.

Here, the measuring unit 320 and the computer 350 play a role corresponding to the temperature / strain calculation unit 120 and 420.

Referring to FIG. 5, which shows an experimental result at room temperature without applying temperature and strain using the experimental apparatus, the peak depth is 31 dB and the maximum PDL is about 8 dB in the wavelength region of 1537.2 nm. Shows.

The result of the transmission spectrum when the strain is forcibly varied from 0 to 0.438% ε by applying a strain increment of 0.063% ε to the optical fiber grating 160 is shown in FIG. 6. As can be seen from FIG. 6, the resonant wavelength is linearly shifted with respect to the increase rate of the applied strain, and the change in the peak depth is negligible. Even when the temperature of the oven 310 was varied, the change in spectrum provided a linearity similar to that of applying the strain variable.

These results show that the wavelength change alone cannot calculate the change of temperature and strain independently.

On the other hand, the result of measuring the change in the resonance wavelength and the change in the maximum PDL while varying the strain while keeping the temperature at room temperature (22 degrees) is shown in FIG. For reference, the line connected with the square mark is the maximum PDL value, and the line connected with the circular mark is the resonance wavelength value.

As can be seen from FIG. 7, the period of the lattice becomes longer as the strain is increased, and as a result, the resonance wavelength is gradually increased. In addition, as the strain increases, the maximum PDL value also increases, which can be seen that the non-uniform distribution of strain in the core layer of the optical fiber grating.

As a result, the birefringence and the maximum PDL of the optical fiber grating increase with strain.

On the other hand, the results of measuring the maximum PDL value and the resonance wavelength when the temperature is varied from 30 degrees to 70 degrees in the optical fiber grid 160 is shown in FIG. As can be seen from FIG. 8, it can be seen that the resonance wavelength and the maximum PDL value increase linearly with respect to the change in temperature.

Therefore, the known temperature and strain are applied to the optical fiber grating 160 from the experimental results, and the relation constant is obtained from the known temperature and strain value, the measured maximum PDL value and the resonant wavelength, and the optical fiber is obtained using the obtained relation constant. By analyzing the light reflected from the grating and applying the resonance wavelength and the maximum PDL value to Equation 2, the temperature and the degree of tension can be calculated.

As described so far, the temperature / strain measurement system and method using the optical fiber grating according to the present invention provides the advantage of using a single optical fiber grating.

1 is a view schematically showing a temperature and strain measurement system using a short-period optical fiber grating according to an embodiment of the present invention,

2 is a view for explaining a process of manufacturing the optical fiber grating applied to FIG.

3 is a view schematically showing a temperature and strain measurement system using a long period optical fiber grating according to another embodiment of the present invention,

FIG. 4 is a diagram for explaining a process of obtaining coefficient values for calculating temperature and strain for an applied optical fiber grid;

5 is a graph showing the transmission spectrum and polarization dependent loss of each wavelength measured for the optical fiber grating using the experimental apparatus of FIG.

FIG. 6 is a graph showing transmittance for each wavelength measured while gradually increasing strain on an optical fiber grid using the experimental apparatus of FIG. 4.

7 is a graph showing the change in resonance wavelength shift and maximum polarization dependent loss rate according to the variation of strain,

8 is a graph showing a change in resonant wavelength shift and maximum polarization dependent loss rate according to temperature variation.

<Description of Symbols for Major Parts of Drawings>

110: temperature / strain calculator 120: temperature / strain calculator

130: light source 140: polarization regulator

150: circulator 160: optical fiber grid

Claims (9)

delete delete An optical fiber grating; And a temperature / strain calculator configured to output light to the optical fiber grating and analyze the polarization dependent loss amount and the resonance wavelength shift amount of the transmitted light by the optical fiber grating to calculate the temperature and strain of the optical fiber grating. The optical fiber grating is a short cycle optical fiber grating temperature / strain measurement system using an optical fiber grating. The method of claim 3, wherein the temperature / strain calculator A light source for emitting light whose wavelength is changed according to a control signal; A polarization adjuster for adjusting a polarization state of light emitted from the light source; An optical splitter configured to transmit input light passing through the polarization adjuster to the optical fiber grating, and output light reflected from the optical fiber grid to be separated from the input light; A temperature / strain calculator configured to control the light source and the polarization adjuster and obtain a temperature and strain of the optical fiber grating by analyzing resonance wavelengths and polarization dependent loss of reflected light reflected from the optical fiber grating and output through the optical splitter; Temperature / strain measurement system using an optical fiber grating characterized in that it comprises. 5. The temperature / strain measuring system according to claim 4, wherein the optical splitter is a circulator. In the temperature / strain measurement method using an optical fiber grating, end. Transmitting the light generated according to the set polarization pattern to the optical fiber grid; I. And calculating the temperature and strain of the optical fiber grating by receiving the light reflected from the optical fiber grating and calculating the resonance wavelength and the polarization-dependent loss amount of the optical fiber grating. 7. The method of claim 6, wherein the optical fiber grating is a short period optical fiber grating. In the temperature / tensileness measurement method using an optical fiber grating, end. Transmitting the light generated according to the set polarization pattern to the optical fiber grid; I. And calculating the resonance wavelength and the polarization dependent loss amount by receiving the light transmitted through the optical fiber grid to calculate the temperature and strain of the optical fiber grid. 10. The method of claim 8, wherein the optical fiber grating is a long period optical fiber grating.