JPH06100619B2 - Optical fiber sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber application sensor for detecting a physical quantity to be measured by using an optical means.

2. Description of the Related Art An optical fiber application sensor using a conventional polarization-maintaining optical fiber is disclosed in, for example, "Opttronics, 1983, January issue, P3".
As shown in Fig. 1, Fig. 13 ", the physical quantity to be measured is a current.

That is, the light 1 emitted from the light source unit is linearly polarized by the polarizer 2 and is condensed by the lens 2 on the polarization-maintaining optical fiber 3. At this time, the polarization proper axis of the polarization-maintaining optical fiber 3 and the linear polarization axis are matched. The linearly polarized light propagating along the polarization proper axis of the polarization-maintaining optical fiber 3 becomes parallel light at the lens 4 and passes through the magneto-optical element 5. At this time, the polarization direction of the linearly polarized light is rotated by the magnetic field H generated by the current to be measured and becomes elliptically polarized light, which is incident on the polarization-maintaining optical fiber 7 by the lens 6. Here, the linear polarization direction when the magnetic field H is O is incident at an angle of 45 ° with respect to the polarization proper axis of the polarization maintaining optical fiber. This elliptically-polarized light propagates through the polarization-maintaining optical fiber 7 and is then passed through the polarization beam splitter 9 at a right angle of 2 degrees.
Received by each light receiving unit 10 which is split into vector light of the component,
This is to electrically calculate and obtain a measured current value.

Problems to be Solved by the Invention In general, a polarization-maintaining optical fiber has a difference in temperature characteristic of a propagation constant in each direction of eigen axes orthogonal to each other, or in a phase change due to external pressure such as fiber fluctuation. Therefore, in the case of light having polarization components on both orthogonal eigen axes, such as elliptically polarized light, the phase also changes due to changes in ambient temperature and changes in external pressure such as fiber fluctuations.

Therefore, in the method as described above, the light propagating through the polarization-maintaining optical fiber is elliptically polarized light that is phase-modulated by the magnetic field, and is also subjected to a phase change due to a change in ambient temperature during propagation, It becomes difficult to detect the current information accurately.

Means for Solving the Problems In order to solve the above problems, the present invention provides a frequency range in which the phase of light passing through a polarization-maintaining optical fiber is modulated by a change in a physical quantity other than the measured physical quantity. It has an optical element that has the function of modulating the phase of the transmitted light according to changes in the measured physical quantity having different frequency ranges, and a polarization-maintaining optical fiber, and is phase-modulated according to the change of the measured physical quantity. The optical signal is converted into an electric signal by the light receiving section, and only the frequency range of the change of the physical quantity to be measured is electrically separated and taken out.

Action The present invention accurately detects the physical quantity to be measured by the above method without being affected by changes in the surrounding environment such as temperature changes.

EXAMPLE FIG. 1 shows an optical fiber applied voltage sensor for detecting a voltage having a commercial frequency (50 Hz, 60 Hz) as an example of the optical fiber applied sensor of the present invention.

Light emitted from the light source 12 becomes linearly polarized light by the polarizer 14 and the lens
At 13, the light is condensed and propagated in the polarization-maintaining optical fiber 15,
The light becomes parallel light at 16 and passes through the electro-optical element 17. At this time, the linearly polarized light is phase-modulated by the voltage V to be measured, becomes elliptically polarized light, is condensed and propagated in the polarization-maintaining optical fiber 19 by the lens 18, and is transmitted through the polarization beam splitter 21 to be proportional to the voltage to be measured. Light intensity signal, lens 20
Then, the light is collected on the light receiving element 22 and converted into an electric signal by the electric signal processing unit 23. Here, the light propagating through the polarization beam splitter 19 is an elliptically polarized light having polarization components on both orthogonal eigen axes of the polarization-maintaining optical fiber, and a phase change occurs due to ambient temperature change. The frequency range of is usually several Hz, and the frequency of the measured voltage (50H
z or 60 Hz) can be electrically separated from each other, and after being converted into an electric signal, each frequency is separated by the electric signal processing unit 23, and only the frequency component of the measured voltage is taken out,
This is to detect an accurate value of the measured voltage.

EFFECTS OF THE INVENTION As described above, according to the present invention, after converting the optical signal phase-modulated according to the change of the physical quantity to be measured into the electric signal in the light receiving section, the polarization plane preserving light is changed due to the change of the ambient temperature. An accurate value can be detected by electrically separating the phase change component received by the fiber and extracting only the change component of the measured physical quantity.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical fiber applied sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional optical fiber applied sensor. 11 …… Polarizer, 12 …… Light source section, 13,16,18,20 …… Lens, 14,21 …… Polarizing beam splitter, 15,19 …… Polarization-maintaining optical fiber, 17 …… Electro-optical element, 22: Light receiving part, 23: Electric signal processing part.

Front page continuation (72) Inventor Kazuro Toda 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Koichi Kanayama, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A change in a physical quantity other than the measured physical quantity,
An optical element having a function of modulating the phase of transmitted light according to a change in a physical quantity to be measured having a frequency range different from the frequency range in which the phase of light transmitted through a polarization-maintaining optical fiber is modulated; A storage optical fiber is provided, and an optical signal phase-modulated in accordance with a change in the measured physical quantity is converted into an electric signal by a light receiving unit, and only a frequency range of the change in the measured physical quantity is electrically separated and taken out. Optical fiber applied sensor configured as above.