JPS61270632A - Optical fiber type measuring instrument for temperature distribution - Google Patents

Abstract

PURPOSE:To measure the lengthwise temperature distribution of an optical fiber continuously and precisely by utilizing a temperature function of the intensity ratio of Stokes light and anti-Stokes light based upon the Raman scatter of the optical fiber itself. CONSTITUTION:Rayleigh scattered light and Raman scattered light generated in the optical fiber 7 return partially in the optical fiber 7 as back scattered light and are projected from an incidence end, and they are passed through a condenser lens 6, separated by a directional coupler 5, and sent to a detection system 13. The detection system 13 consists of a guide-in fiber 14, a half-mirror 15, optical filters 16 and 17, photodetecting elements 18 and 19, and an amplifier 21. Then, the intensity values of the Stokes light and anti-Stokes light inputted to a signal processing circuit 22 through the detection system 13 is corrected in consideration of wavelength characteristics of the loss of the optical fiber 7, transmission characteristics of the filters 16 and 17, gains of the photodetecting elements 18 and 19, etc., to obtain electric outputs. The ratio of them is calculated to find the temperature of the fiber 7 at a point (x) and the continuous lengthwise temperature distribution of the fiber 7 is obtained.

Description

Detailed Description of the Invention [Industrial Application Field 1] This invention is a temperature measuring device that utilizes the fact that the intensity ratio of Stokes light and anti-Stokes light due to Raman scattering is a function of temperature. The present invention relates to an optical fiber type temperature distribution 31 measuring device that can continuously measure the temperature distribution in the transverse direction with high accuracy every month.

[Prior Art] FIG. 5 shows a temperature measuring device using a conventional optical fiber.

A pulse signal from the pulse generator 1 is inputted to a light source driving device 3 via a pulse delay circuit 2, and pulsed light is emitted from a light source 4 by driving the light source driving device 3 in accordance with the pulse signal. The pulsed light emitted from the light source 4 is sent to the directional coupler 5
, passes through the condenser lens 6 and enters the optical fiber 7. This incident light causes Rayleigh scattering in the optical fiber 7, and the back scattered light travels backward through the optical fiber 7, passes through the condensing lens 6, is separated by the directional coupler 5, is photoelectrically converted by the light receiving element 8, and is further The signal is amplified by an amplifier 9 and input to a signal processing circuit 10 . Further, a pulse signal from the pulse generator 1 is input to the signal processing circuit 10, and a display 11 for displaying the result is connected to the signal processing circuit 10.

Points a, h, and c along the axial direction of the optical noah/river 7.

... is equipped with a temperature converter 12. The temperature converter 12 is an optical one. Both m1i-n and m1i-n increase the microphone bend loss of the optical fiber 7. Therefore, the intensity signal of the backscattered light from the optical fiber 7 input to the signal processing circuit 10 is as follows:
At J shown in FIG. 6, a decrease due to microvent loss appears corresponding to each point a, b, and c where the temperature converter 12 is installed. From the amount of decrease in the backscattered light intensity, the temperatures at each point a, b, and c can be determined as shown in FIG.

The time 1r required for the pulsed light emitted from the light source 4 to reach the light receiving element 8 is tr= 2 R(X ) /
c (where (x) is the length of the optical fiber 7 from the input end of the optical fiber 7 to the point where 1j scattering occurs, and C is the speed of light in the optical fiber 7). So,
In the signal processing circuit 10, the pulse signal from the device 1 and the detection signal from the light-receiving element 8 are determined from which time difference to the time 1.
By measuring r by h1, it is possible to locate the position based on the backscattered light.

[Problem to be Solved by the Invention 1] However, the temperature is measured at multiple points along the optical fiber 7 from the amount of decrease in the backscattered light intensity using the temperature converter 12.
In the second method, the number of temperature measurement points is limited because the light intensity is attenuated each time it passes through the temperature converter 12. Furthermore, if an attempt is made to measure the temperature h1 at multiple points with L to reduce the loss of the temperature converter 12 due to temperature changes, there is a problem in that the accuracy of the measured temperature deteriorates.

[Object of the Invention] This invention was devised to solve the problem of the prior art described in -1 below, and the present invention is to continuously and accurately measure g1 of the temperature distribution in the longitudinal direction of an optical fiber. The purpose of the present invention is to provide an optical fiber type temperature distribution measurement device that can measure temperature distribution.

[Summary of the Invention 1 This invention provides an optical fiber disposed in a measurement temperature region;
A light source for inputting pulsed light into an optical fiber from its input end, and the intensity of Stokes light and anti-Stokes light due to Raman scattering of the backscattered light of the 11th pulse emitted from the input end of the optical fiber. and the intensity ratio J of the Stokes light and anti-Stokes light detected by the detection system.
When determining the temperature of the optical fiber, the pulsed light is emitted from the light source and a signal processing circuit is provided to determine the temperature measurement position of the optical fiber from the time from when the detection system detects the Raman scattered light. That's what happens.

This invention is characterized by performing temperature S1 measurement by utilizing the fact that the intensity ratio of Stokes light and anti-Stokes light due to Raman scattering (including stimulated Raman scattering) of backscattered light is a function of temperature. do.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, 7 is an optical fiber, and the optical fiber 7
is placed in the temperature range to be measured. A directional coupler 5 is provided on the incident end side of the optical fiber 7 through a condensing lens 6, and a light source 4 is provided in one port of the directional coupler 5, and a backscattering source 4 is provided in the other port of the directional coupler 5. Light detection system 1
3 is provided. The light source 4 is connected to a light source driver @3, a pulse dino circuit 2, and a pulse generator 1. The signal output from the pulse generator 1 is input as is to the signal processing circuit 22, while the pulse signal delayed by a predetermined time by the pulse delay circuit 2 is input to the light source driving device 3. The light source driving device 3 drives the light source 4 according to the input pulse signal, and the light source 4 emits pulsed light. The pulsed light from the light source 4 is passed through the directional coupler 5
, passes through the condenser lens 6 and enters the optical fiber 7. The energy of the pulsed light incident on the optical fiber 7 is 106
If the optical fiber 7 is covered with W/C1112 or more to an extent that does not cause optical damage, Raman scattering will occur in the optical fiber 7 in addition to Rayleigh scattering, and Stokes light and anti-Stokes light will be generated (see Figure 2). ).

Now, let us assume that the frequency of the incident pulsed light is ωo1, and the unique frequency of the substance determined by the core material of the optical fiber 7 is ωf.
Stokes light is emitted during the transition of matter from the ground state to the excited state by the incident pulsed light (), and its frequency ωS is θ)S-ω0-ω[, , l-1 near and opposite. (1ε) When pulsed light illuminates a substance in an excited state, it transitions to the υ ground state.
4 filter process rli+;, its frequency (1) a is ωa-ω
o 1ωt. (In general, n-order light is generated in Stokes light and anti-Stokes light16, but l
In ii+, only the first-order light was described. ) The light is buffed with an antler (1 moment, then a part of the Raman scattered light is backscattered light as light 7), returns to the fiber 7, is emitted from the input end, and passes through the condenser lens 6. Afterwards h direction If
It is separated by the coupler 5 and cannot be sent to the detection thread 133. The detection system 13 detects the direction tIItI! 1 combiner 51, an introduction horn 14 that guides the extracted backscattered light, and an introduction
The light emitted from Noah Iba 14 is 25") - J half mirror 15, 69 on the transmission side of half mirror 15.
[Nore 7. T optics - Noirta 16, light receiving element 1B and amplification j? li 20, an optical filter 17 provided on the reflection side of the half mirror 15, a light receiving element 19, an amplifier 21, etc. The optical filter 16 has a frequency θ)
A filter that transmits only the first-order Stokes light of 0-ωt is used, -h, and the optical filter 17 has a frequency θ)a+ω
A device is used that transmits only the first order light (-1). Therefore, in the light receiving element 118, the intensity of the first order light (1 - -1) of the backscattered light from the optical fiber 7 is used. is detected, and one light receiving element detects the intensity of the first-order anti-Stokes light.The outputs of the light receiving elements 18 and 19 are sent to the amplifier 20°2.
After each signal is multiplied by 11 by 1, it is input to the signal processing circuit 22. In addition, 23 is a display device.

At temperature T (K), the ratio of the number of substances in the excited state to the number of substances in the ground state is exp(-hωr7'2
πkT). Here, h is a blank constant, k
i, L Boltzmann's constant r. Therefore, the ratio of the intensity 1s of the S I -us light to the intensity Ia of the anti-Stokes light is Ia
/Is =exp (-h tof /2π to)
Once the core material is determined, it becomes a function only of temperature.

At this point, light is emitted from light source 4 (-7, light - Noa buff input t
It is generated at a point distance x from the A end, enters the light receiving elements 18 and 19 after fir (X) time, and is further amplified i! !
The intensities of the Stokes light and the anti-Stokes light that have not been amplified by i20.21 and are input to the August processing circuit 22 are determined by the wavelength characteristics of the loss of the optical fiber 7, and the optical filter 16.17.
Electrical output ES is calculated by making corrections taking into consideration the transmission characteristics of , the gain of the light receiving elements 18 and 19, etc.

['Ta 4η and take these ratios, [a/[S,
Zu exp (-hωt/2π ni) roars. From this, the temperature T at point X of the optical fiber 7 can be determined, and a continuous temperature distribution along the length of the optical fiber 7 can be obtained as shown in FIG. 3. Note that the distance x is determined based on the time difference between the pulse offset of the pulse generator 1h'l) input to the signal processing circuit 22 and the detection signal of the Raman scattered light from the light receiving element 18.10.

Temperature converter 12 installed at conventional temperature H1 measuring point-J'1
From the change in the intensity of backscattered light due to Rayleigh scattering of human light, i [ii! In the measuring method, it is difficult to measure one multi-point piece because the light propagating through the optical fiber 7 is attenuated each time it passes through the temperature h11. However, in the present invention, in which the temperature is measured from Raman scattering of the optical fiber 7 itself without providing the temperature converter 12 or the like in the optical fiber 7, the incident light is attenuated due to causes other than the inherent transmission loss of the optical fiber 7. Multi-point measurement, which is close to continuous measurement, is possible. Furthermore, since the temperature is determined from the ratio of the intensity of the Stokes light and the anti-Stokes light at two wavelengths, the temperature g1 can be measured with high precision without being affected by variations in the intensity of the light source 4.

In order to prevent excessive backscattered light from entering the light receiving element 18.19 from the input end of the optical fiber 7, as shown in FIG. 4, the directional coupler 5 of FIG. Instead, an acousto-optic element 24 is provided, and the acousto-optic element driving device 2 is controlled by a pulse controller 251.
6 may be used. Acousto-optic element 2
4, a phase grating is formed by ultrasonic waves by driving the acousto-optic element driving device 26, and backscattering from the optical fiber 7 is diffracted and intensity-modulated by this phase grating. The backscattered light diffracted by the acousto-optic element 24 is guided to the half mirror 15 by the introduction fiber 14. The acousto-optic element 24 is driven by a pulse drive circuit of the light source 4, which is composed of a pulse generator 1 and a pulse delay circuit 2. In addition, if the backscattered light is weak, it is best to average it using a boxcar j′ veraget.
゜ 'J, as an optical fiber 7 for measuring 1 of the above -mentioned embodiment, you may use a normal glass fiber, a plus Futsukufibar pond, and a liquid eni 11 fiber. . Furthermore, by using polarization-maintaining fibers between the optical fibers 7 and using a wavefront with a width of A, J, the efficiency of 4L! 1. Also, the diameter of the optical fiber 7 allows Raman scattering to be @I! II! It is better to make it as small as possible to make it more appealing to the target. In addition,"
- In the above embodiment, the half mirror 15) and the optical filter 1
Although the detection system 13 was constructed using 6.17, it could also be constructed using a spectrometer or the like.

[Effects of the Invention] In summary, according to the present invention, the intensity of the S1~-x light and the anti-Sx light due to Raman scattering of the optical fiber itself is a function of temperature 1m (- 1α measurement is carried out using The advantage of bamboo is that it is not only possible to carry out continuous <r multiplicity measurements, but also to be affected by changes in the light source, etc. It is possible to demonstrate the following.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of an ill measuring device according to the present invention 4.
Fig. 2 shows an example of the Simann scattering that occurs during light production, and Fig. 33 shows the results of the first measurement of the distribution of wetness obtained in accordance with the present invention. Figure 4 shows a configuration diagram of another embodiment of the 1yyi according to the present invention, Figure 5 shows a conventional thirst measuring device, Figure 6 shows the same diagram. Figure 7 is a graph showing the change in the intensity of the backscattered light detected by the measured Kl, and Figure 7 is a graph showing the temperature distribution determined from the intensity change of the backscattered light in Figure 6. , 1 is a pulse generator (1-device, 2 is a pulse delay circuit, 3 is a light source driver, 4 is a light source, 5 is a directional coupler, 6
(1 condenser lens, 7 optical fiber, 8 light receiving element f, 1)
is the amplifier, 10 is the Hakugo I11 circuit, '11 is the display,
12 is a temperature converter, 13 is a detection system, 11 is an introduction Noah bar, 15 is a half mirror 116° 17LU optical filter,
18.19 is the photodetector f, 2 (1, 21i amplifier, 22
is the circuit, 23 is the display, 24 tJ
The acousto-optic element 25 is a pulse control device (1-car, 26 is a synphonic optical cable driving) device. Patent Applicant Roi1'l\i-sen Co., Ltd.'s 1st generation patent attorney Nobuo Kinuya = 13- Four people are angry ≦ Small R setting

Claims (1)

[Claims] An optical fiber disposed in the measurement temperature region, a light source for inputting pulsed light into the optical fiber from its input end, and a light source for transmitting backscattered light of the pulsed light emitted from the input end of the optical fiber due to Raman scattering. A detection system that detects the intensity of Stokes light and anti-Stokes light, and a detection system that determines the temperature of the optical fiber from the intensity ratio of the Stokes light and anti-Stokes light detected by the detection system, and detects the temperature of the optical fiber after pulsed light is emitted from the light source. 1. An optical fiber type temperature distribution measuring device, comprising: a signal processing circuit that determines a temperature measurement position of an optical fiber from the time it takes for the optical fiber to detect Raman scattered light.