JPS5930032A - Optical fiber thermometer - Google Patents

Abstract

PURPOSE:To simplify the mechanism along with a higher accuracy in the temperature measurement by using a double refractive optical fiber as sensor while the phase of a signal based on the change in the double refraction property due to temperature is detected in a digital manner. CONSTITUTION:A thermometer is composed of a light source 1 of semiconductor laser, a linear polarizer 2, a double refractive optical fiber 3, a light beam splitter 4, a 1/4 wavelength plate 5, polarizers 6 and 8, a photodetectors 7 and 9 and a counter 10. As leaving the other end of an optical fiber 3 propagating therethrough, light from the light source 1 is divided into two with the splitter 4. One beam is shifted by 90 deg. in the phase difference passing through a 1/4 wavelength plate 5 and gives a signal of light intensity I1 received with the detector 7. The other beam passes through the polarizer 8 and gives an electrical signal of light intensity I2 received with the detector 9. Then, the counter 10 counts the light intensities I1 and I2 to calculate the temperature of the optical fiber 3 from the counts.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermometer using a single mode birefringent optical fiber.

Conventionally, relatively high-precision thermometers using optical fibers have been put into practical use, using special materials such as semiconductors or fluorescent materials as sensors, and using optical fibers simply as a light transmission medium. There is. However, such conventional thermometers have a problem in that the reliability of the connection between the sensor and the optical fiber is low, and since analog processing is performed, there is a limit to accuracy.

The present invention has been made to solve these conventional problems, and its purpose is to eliminate the coupling part between the sensor and the optical fiber rather than using the optical fiber itself as a sensor, and also to eliminate the coupling part between the sensor and the optical fiber. An object of the present invention is to provide an optical fiber thermometer that can easily obtain high accuracy and high stability through processing.

In order to achieve such an object, the present invention uses a birefringent optical fiber and digitally detects the phase of a signal even when the magnitude of birefringence changes due to temperature. .

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 1 is a configuration diagram of an embodiment of an optical fiber thermometer according to the present invention. In the figure, light emitted from a light source 1 consisting of a semiconductor laser, a light emitting diode, etc. is linearly polarized by a linear polarizer 2, and then connected to one end of a birefringent optical fiber 3 by a commonly known method such as using a condenser lens. is injected into. Here, the polarization axis of the birefringent optical fiber 3 is set at an angle of 45° with respect to the polarization direction of the incident light. The light propagating through the birefringent optical fiber 3 and exiting from the other end is split into two by a light beam splitter 4. One of the two divided light beams passes through a quarter-wave plate 5 to generate a 90° phase difference, passes through a polarizer 6, is received by a photodetector 7, and is processed by a light intensity filter. , is output as an electrical signal.

On the other hand, the other beam split into two by the optical beam splitter 4 is
It passes only through the polarizer 8 without passing through the quarter-wave plate and is received by the photodetector 9, and the light intensity is 1. is output as an electrical signal.

Here, the light intensity I,,1. is as follows.

II = Io (1+cosΔ) It=Ia C1+sinΔ) However, IO is a constant, and Δ is the magnitude of birefringence of the birefringent optical fiber 3. This Δ is a quantity that changes with temperature, as is well known. And the light intensity I,,I
- changes with temperature as shown in FIG. Light intensity 1. and 1 have a phase difference of 90° with respect to Δ.

In FIG. 1, 10 is a counter, which inputs I1 and I2 and digitally counts the magnitude including the sign of Δ. At this time, the count value is linearly proportional to the temperature of the optical fiber 3, for example, as shown in FIG.

Note that Δ also changes when the optical fiber 3 is subjected to mechanical vibration, but the signal generated from this is vibrational and is not counted by the counter 1o.

As described above, according to the optical fiber thermometer according to the present invention, since the optical fiber itself acts as a sensor, there is no problem of decreased reliability of the coupling part between the sensor and the optical fiber as in the past. Since temperature can be measured digitally, higher accuracy and stability can be easily obtained compared to conventional analog methods.

Moreover, not only the sensor structure is simplified, but also measurement errors due to mechanical vibrations are eliminated.

Additionally, since the sensor is made of flexible, highly insulated optical fiber, it is possible to remotely measure temperatures in environments where normal electrical measurements are difficult, such as inside high-voltage equipment or power engines. K so that it can be easily measured.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of an optical fiber thermometer according to the present invention, Fig. 2 is a graph showing the relationship between temperature and light intensity, and Fig. 3 is a graph showing the relationship between temperature and light intensity.
The figure is a graph showing the relationship between temperature and count value. 1......Light source 2...Linear polarizer 3...
...Birefringent optical fiber 4...
...Light beam splitter 5 ...... Quarter wavelength plate 6.8 ... Polarizer 7.9 ... Photodetector 10・・・・・・・・・Counter patent applicant Toshihiko Yoshino N' i3d SiWT, Steam (C)

Claims (1)

[Claims] A birefringent optical fiber, a light input means for inputting light from one end of the optical fiber, an optical end for splitting the output light from the other end of the optical fiber, and a 90° angle between the orthogonal polarizations of the split light. optical means for producing a phase difference of 100°, optical means for producing interference between the orthogonal polarized lights, detection means for detecting the respective light intensities, and absolute position resolution of the electrical signal output from the detection means. A fiber optic thermometer with means for digitally detecting.