JPH0156387B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber applied sensor for measuring various physical quantities such as voltage and current.

FIG. 1 shows a current (magnetic field) sensor as an example of an optical fiber applied sensor, where 1 is an optical transmitter, 2 is an optical receiver, 3a and 3b are optical fibers, and 4 is an optical fiber sensor.
a, 4b are gradient index lenses, 5 is a polarizer, 6
is an optical faraday element, and 7 is an analyzer.

Light from the optical transmitter 1 is guided to the optical sensor section by an optical fiber 3a. In the optical sensor section, the light from the optical fiber 3a is collimated by a refractive index gradient lens 4a, and then converted into linearly polarized light by a polarizer 5. ). Now, if a magnetic field is applied in parallel to the optical Faraday element 6, the plane of polarization of the linearly polarized light passing through the optical Faraday element 6 rotates in proportion to the strength of the magnetic field. The degree of this rotation is converted into light intensity by a polarizer 5 and an analyzer 7 whose optical axis is tilted by 45 degrees, and the light is focused by a gradient index lens 4b and sent to an optical receiver via an optical fiber 3b. Lead to 2. The optical receiver 2 performs an operation of converting an optical signal into an electrical signal and determining the strength of the magnetic field applied to the optical sensor section. If you know the strength of the magnetic field, you can immediately determine the magnitude of the current. As the polarizer 5 and analyzer 7, a Glan-Thompson prism or a polarizing beam splitter is used.

Since the conventional optical fiber applied sensor is configured as described above, the temperature dependence of the light emitting diode or semiconductor laser used as the light source causes errors. In other words, the emission spectra of light-emitting diodes and semiconductor lasers generally shift toward longer wavelengths as the temperature rises, and the extinction ratio of the Glan-Thompson prism and polarizer splitter used as the polarizer 5 and analyzer 7 changes slightly due to wavelength fluctuations. Yes, but it changes. Although this change is on the order of several percent, it causes an error in the optical sensor output, which is a problem when used as a voltage/current sensor that requires extremely high accuracy.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and uses a polarizing beam splitter as a polarizer and an analyzer, respectively, and one polarizing beam splitter uses transmitted light (P-polarized light). separation), and the other polarization beam splitter uses reflected light (S polarization separation).
It is an object of the present invention to provide an optical fiber applied sensor that can eliminate fluctuations in optical sensor output due to changes in the wavelength of a light source.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1 is an optical transmitter, 2 is an optical receiver, 3a and 3b are optical fibers, 4a and 4b are gradient index lenses, 6 is a Faraday element, and 8a and 8b are polarized beam splitters. 9 is a prism. One of the polarizing beam splitters of the polarizer 8a and the analyzer 8b is used for transmission (P polarization separation) and the other for reflection (S polarization separation).

According to experimental results, the extinction ratio (degree of polarization separation) of the Glan-Thompson prism and polarization beam splitter
was confirmed to change slightly due to changes in the spectrum of the light source. That is, if only transmission (P-polarized light separation) is used as a polarizer and analyzer, when the temperature of the light source (e.g., a light emitting diode) increases from 0°C to 70°C, the sensor output will increase by several percent, and the reflection ( If only S-polarization splitting is used, it decreases by several percent.

However, in this invention, the polarizing beam splitters of the polarizer 8a and the analyzer 8b use only the transmitted light as one polarizing beam splitter and only the reflected light as the other polarizing beam splitter, so they are separated by reflection. The S-polarized light that is transmitted decreases as the temperature of the light source increases, and conversely, the P-polarized light that is separated by transmission increases.As a whole, this change is canceled out, and the sensor output is not affected by the temperature change of the light source. do not have. According to experiments, it was found that while the output fluctuation due to temperature of conventional sensors using only P-polarized light or S-polarized light was several percent, the sensor of the present invention had fluctuations within 1%. .

Note that in the above embodiment, a current sensor has been described, but the present invention can be applied to any sensor as long as it uses a polarizer and an analyzer.

As described above, according to the present invention, as a polarizer and an analyzer, one uses the transmitted light (P polarization separation) from the polarization beam splitter, and the other uses the reflected light (S polarization separation) from the polarization beam splitter. Since the influence of fluctuations in the emission spectrum due to changes in the temperature of the light source is offset, the measurement accuracy is greatly improved and highly reliable results can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional optical fiber applied sensor, and FIG. 2 is a block diagram showing the configuration of an optical fiber applied sensor according to an embodiment of the present invention. 1... Optical transmitter, 2... Optical receiver, 3a, 3b
...Optical fiber, 4a, 4b... Gradient index lens, 6... Optical Faraday element, 8a... Polarizer, 8b... Analyzer, 9... Prism. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In an optical fiber applied sensor that measures various physical quantities by guiding light from an optical transmitter to an optical receiver via an optical fiber, a polarizer, an optical faraday element, an analyzer, and an optical fiber, the above polarizer and An optical fiber applied sensor characterized in that each of the analyzers uses a polarizing beam splitter, one polarizing beam splitter uses transmitted light, and the other polarizing beam splitter uses reflected light.