JPS60135732A - Temperature measuring device - Google Patents

Abstract

PURPOSE:To measure temperature easily with high sensitivity by causing linear polarized light to strike a polarization maintaining optical fiber in its main-axis direction through a polarizer, and photodetecting light passed through an analyzer which has the direction of polarization at right angles to the main axis by a photodetector. CONSTITUTION:Light from a light source 1 is made into linear polarized light by the polarizer installed at the incidence terminal of the polarization maintaining optical fiber 10 and the polarized light is made incident while aligned to the principal axis of the fiber 10; and the direction of polarization of the analyzer 9' is set at right angles to the principal axis and the projection light is photodetected by a photodetector 5 to display the result on a display device 8. Strain inducing parts A and A are set asymmetrically to increase the temperature dependency of the quenching ratio of the fiber 10 as a detection part, and light power due to the rotation of the principal axis accompanying temperature variation to calculate the temperature variation. Consequently, the need for a frequency stabilized laser and an interferometer is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a small, simple, and highly accurate temperature measuring device that utilizes the fact that *i*hi wave curved light 77' has a 1 degree dependence on extinction ratio.

Conventionally, there are many temperature measurement methods using a light beam.

For example, ■ A method for determining the temperature value of the amount of light emitted by a thermal radiator and measuring temperature changes; ■ A method for connecting an optical fiber to a mercury thermometer, and as the temperature rises, the mercury crosses the light beam, blocking the beam. There is a method of measuring temperature, and a method of assembling an Ikelson interferometer and measuring changes in interference fringes due to temperature changes in the refractive index or length of the core portion of the optical fiber (temperature 1 dependence of optical length). However, regarding (2), optical fibers are simply for transmitting heat, and temperatures between 500 degrees and 1000 degrees
Although it is suitable for radiators at high temperatures, it is not very versatile at room temperatures. ■ is from the position of the mercury column through which the light beam passes.

I can see the temperature, but I can't measure other temperatures. Therefore, it is common; it cannot be called a thermometer, but a VC for temperature monitoring system.
Are suitable. A common method for measuring temperature is ■. Its configuration diagram is shown in FIG.

The optical output from the frequency stabilized laser 1 is separated by a beam splitter 2, one passes through a single mode optical fiber 3, the other propagates in space, and is combined on the beam splitter 2' to form interference fringes. . The interference fringes are divided by the algorithm 4, and the interference fringes are detected by the detectors 5 and 5' at different positions and recorded in the Id data recorder 6. Both values are calculated by calculating pA7 and taking Arctan, converting the temperature change from the phase change and showing it on the display 8.

However, although this method has a measurement accuracy of about 1 mdθg, the equipment is complex and expensive, as it requires a frequency stabilized laser, a beam splitter, two photodetectors, and a computer, and it also requires real-time processing. Temperature measurement was difficult. Another disadvantage is that two optical paths are always required in order to use the interferometry method. .

In order to eliminate these drawbacks, the present invention takes advantage of the temperature dependence of the extinction ratio of polarization-maintaining optical fibers and uses this as a sensor to measure temperature from changes in the extinction ratio. By setting the stress applying part asymmetrically,
This method increases the temperature dependence of the extinction ratio and measures the temperature from the amount of change in the extinction ratio.It is simple and highly sensitive to VC temperature without the need for frequency-stabilized lasers, interferometer installation, data processing, etc. This is for measurement, and the details of the drawings are below□
Explanation to dry.

' Figure 2 shows an embodiment of the present invention, in which 1 light source (semiconductor laser, solid state laser, gas laser, old etc.), 9 and q are polarizers and analyzers, and 10 is an asymmetric stress applying device. polarization-maintaining optical fiber with a 5Fi photodetector, 8
It is an Fi display device. To operate this, the light from the light source 1 is made into linearly polarized light by the polarizer 9 and is incident on the main axis (X-axis) of the polarization-maintaining optical fiber 10, and further,
The polarization direction of the analyzer 9' is in the direction of the main axis of incidence and in the orthogonal direction CY.
axis). This is said to be set to crossed nicols.

Now, as shown in FIG. 3 (&), if the stress applying part is symmetrical, the intensity of the input light to the polarization maintaining optical fiber 10 and the intensity of the light passing through the analyzer 9' are detected by the photodetector 5. Since the extinction ratio, which is the ratio of the output light intensity, is as high as -60 to -40 dBAan, the output of analyzer q is extremely small, and even with temperature fluctuations, the single polarization structure has two main axes. (X axis, Y+M)
Since it is symmetrical with respect to ', the change in extinction ratio due to mode coupling is small. However, here in Figure 3 (1)), (Q),
When a polarization-maintaining optical fiber having 1 part of asymmetric stress as shown in (d) is used as a temperature sensor, the extinction ratio deteriorates and the optical output is received by the detector 5. [An important factor is that the stress distribution inside the core is not symmetrical with respect to the changes. This amount of change corresponds to the amount of change in temperature i, so it is necessary to calculate it backwards; the change can be known once.

Figure 4 shows the spindle rotation due to temperature fluctuations. First, the field vibration is 1fiiEo in the Y-axis direction of the wound fiber 0.

of light is incident. The amount of rotation of the main shaft when the temperature uniformly changes by T is △θ, which is infinitesimal.
a.

It can be written as △θ=(□)△'r...fl)a'r. After propagating through the optical fiber 0 of length e, the amount of change of light from the r-axis direction ``''''7 axis accompanied by 0 principal rotation is as follows.

B(g+5(-E--Δθ1. e-5Kxram θ-
F: OCom θe-1 to 7/π ゛... I; O5'(-1 △θ) ・・・・・・(2)
Equation (2) can be simplified as follows under the condition of Δθ<1.

-1Kxe-'1Kyd However, cos (-'-△'l" l2△θ, cos
△City 1 was used.

On the other hand, the fluctuation in the longitudinal direction of the unpaired element of the permittivity tensor, the mozu coupling @ (coupling from the Y' axis to the X direction) amc (1) is a m c (1)
= hand, /'eXp[-i (Kx-Ky' of embryo εxY'
) Z ] aZ...(4) It is given by. Here, 2 is the characteristic of 7 eyes.

-dance, ω is the angular frequency of light -Kx and the propagation constant in the X-axis and Y-axis principal axis directions.

The COSΔθ component of a m cfl) enters the detector 5, and since cosΔθ: 1, the mode coupling due to refractive index fluctuations is eventually caused by mode coupling@amc(A')Bo exp (-1Kxll ”-(
It can be expressed as 51. Since we observe σ], light is <war, so it is proportional to the square of the absolute value of the electric field. On the other hand, a
Since mc is a function of location, it is necessary to take a set average. Therefore, the detected light power pobs &
obs=, /':, /::7Σ<IEo△θ(e-■x
7 e-1 to 744-am c (JR'o ×e-i
K"f) dxay...(61. Here, <1B o Δθ(e-1Kxl-e-iKyri+am
C(1) Eoe-1Kx112〉=2BO”△θ2(1
-ay gu1+<i amdgM2> E, o ”-+7
1, so P ob s 4(21J 2 (1-ωs composition) + b
4) Pin・−+・f13). However, here P1n=j:), l-: Pot E02dxdyhl! '＝
(1amc(12> −...=+91Δ= KX
− is 'y. If we introduce the coherence range, or coherence, of the light source and set this function as γ, then equation (8) is modified as
+hg) Pin −・−an and the final expression is obtained.

When a semiconductor laser or an LED superluminescent diode with a multi-mode longitudinal mode is used, the term γ20 disappears, and the interference fringe term disappears. On the other hand, He-Ne laser, Y
When an AG laser or a semiconductor laser operating in a single mode is used, γ21 is obtained, and Potl exhibits oscillatory behavior due to the effects of ωSΔ and Re. In this temperature measuring device, stable measurement is possible when γ=0, so it is preferable to use a multimode semiconductor laser, an I, ED, or a superluminescent diode as the light source. Input power P in one set
Since 1n is constant, aθ hl is a constant, and 80=(ar), the output p
obs is expressed as follows.

POb8=(2△θ2+he) P 1noc(△T)
2 ・・・・・・αΩ Actually, when an LED with a wavelength of 1.3 μm is used as a light source, the length is 1
Figure 5 shows the results of an experiment using a 00m polarization-maintaining optical fiber as a sensor. The horizontal axis shows the temperature change △T with the set temperature T-20°, and the vertical axis shows kA Pobe/Pi
It takes the value of n. In order to make the expression easier to read, it was logarithmically transformed and shown on a logarithmic graph.

Note that the extinction ratio at room temperature was about 30 dB.

According to this, a clear straight line is shown over a range of 0.8 to several tens of degrees, and its slope is 2, indicating that it matches well with the formula alHc.

The above is an example in which a polarization-maintaining optical fiber with a symmetrical stress applying part is used as a sensor, but if a fiber with an asymmetrical stress applying part is used, it will depend on the degree of coefficient symmetry and will depend on the temperature range to be measured. can be designed. In order to further improve the detection sensitivity, there is a synchronous detection method in which an optical chopper 11 and a lock-in amplifier 12 are added as shown in FIG. "On the other hand, if a light source having γ and 1 is used, it is possible to simultaneously measure the simple birefringence of polarization-maintaining optical fibers. In that case, a light source with a good coherence range is used. For example, a He''Ne laser or a single mode oscillation semiconductor laser is optimal.

In this case, formula a1 contains the COS△Ke component, so it exhibits an oscillatory sugar content (1) as the temperature changes. This birefringence measurement method is shown in Figure 7.
and a temperature controller 14 are added, and these provide temperature fluctuations that vary depending on the stomach temperature control device. In this case, it is difficult to convert the box △Ke to i, since this is the case with a general polarization-maintaining fiber. Here, e is the original optical fiber length and ΔTd is the temperature dependence of refraction. One period of cos△Kl is given by 2π, so if the temperature change required for that change is ∆T transport, ∆noKoeα△'lzπ=2yr... Song I Therefore,
The stretching/refraction Δno is determined by

FIG. 8 shows actual measurement results for a fiber length of 10 m using a 1.52 μm He-Ne laser as a light source.

The horizontal axis shows the temperature T1, and the vertical axis shows the extinction ratio. This shows a sinusoidal variation as expected. In formula +1!9, R8=2π/1, 52×10, e-10m1AT
2 π = 1°C, a is given by α-1 (a = 5.2X10-) in a normal polarization-maintaining optical fiber, △n0 8T, so △noVi, = 2.9X1[,”” It is calculated as follows. This value is the value 3 determined by another method.
×10'''4.This method has the advantage of being non-destructive and fast, unlike the conventional method of cutting optical fibers.

As explained above, according to the present invention, whereas conventionally the temperature was detected by interferometry using the difference between two optical paths, the temperature detection method uses the temperature dependence of the extinction ratio of the polarization fiber. This eliminates disadvantages such as complication and high cost of the device due to frequency stabilization of the light source, light beam separation, etc., and has the advantage of providing a simple and highly sensitive temperature measuring instrument. In order to use the present invention as a temperature measuring device, it is necessary to use the device under conditions such that no external stress is applied to the polarization-maintaining optical fiber serving as the sensor. This is because the extinction ratio of a polarization maintaining optical fiber also changes depending on the strain of the fiber. Conversely, considering the use of this property, for example, if this device N is operated at a constant temperature and under stress, it will become a highly sensitive strain measuring device. It has the advantage of being able to measure the birefringence of polarization-maintaining optical fibers as well.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a temperature measurement device using conventional optical interferometry.
Figure 1@2 is a schematic configuration diagram showing an embodiment of the present invention, and Figure 3 (
a) to (d) are cross-sectional views of polarization-maintaining optical fibers used for measurements, FIG. 4 is a diagram for explaining the measurement principle of the measuring device of the present invention, and FIG. 5 is a measurement experiment using the device of the present invention. Figure 6 is a diagram showing the results, and Figure 6 is a schematic diagram of an example of a high-sensitivity device of the present invention. Figure 7 is an example of an application of the present invention, showing a method for measuring birefringence of a polarization-maintaining optical fiber. 8 are diagrams showing the measurement results.・1... light source, 2.2'... beam splitter,
3... Single mode fiber, 4... Prism, 5.5'... Light detection 286... Data recorder, 7... Calculator, 8... Level indicator, 9... Polarizer, q... Analyzer,
1o...Polarization maintaining optical fiber, 11...Optical chopper', 12...Lock-in amplifier, 13
...Temperature rise/decrease compensation, 14...Temperature controller. "°Mivida・' Figure 1 Figure 2 Figure 5 Figure 5 0.1 1 IQ 100 20c'ch-ud) 18 vs. temperature/firEΔT ('
C) Figure 8 Excess ('C) Figure 6 Figure 7

Claims (1)

[Claims] 0) A detection section made of a polarization-maintaining optical fiber;
a light source for inputting linearly polarized light so as to coincide with the main axis direction of the polarization maintaining optical fiber; and a polarizer installed at the input end of the polarization maintaining optical fiber; A temperature measuring device comprising: an analyzer whose polarization direction is aligned with another principal axis direction; a photodetector that receives emitted light that has passed through the analyzer; and a display device. (2) The temperature measuring device according to claim (1), characterized in that a single-longitudinal mode laser is used as the light source. (3) Claim (1) or (3) characterized in that an optical chopper that intermittents the light source and a lock-in amplifier synchronized with the optical chopper are added between the photodetector and the display device. 2) The temperature measuring device described in section 2). :4) Claim 0) characterized in that the detection part is a polarization-maintaining optical fiber having an asymmetrical stress applying part.
The temperature measuring device according to any one of Items to Items (3).