JPS62150170A - Optical fiber applied sensor - Google Patents

Abstract

PURPOSE:To measure value of voltage to be measured accurately, by a method wherein an optical fiber phase modulated according to a change in the physical quantity to be measured is received, converted into an electrical signal with an electrooptic element and respective frequencies are separated with an electrical signal processing section to pick up the frequency component of a voltage to be measured. CONSTITUTION:Light emitted from a light source 12 is turned to a linearly polarized light with a polarizer 14, focused and propagated to a polarization maintaining optical fiber 15 with a lens 13 and made a parallel light with a lens 16 to be transmitted through an electrooptic element 17. At this point, this linearly polarized light is subjected to a phase modulation by a voltage V to be measured to be changed to an elliptically polarized light which is focused and propagated with a lens 18 to a polarization maintaining optical fiber 19 to be transmitted through a polarization beam splitter 21. With such an arrangement, intensity of the light become proportional to the voltage being measured and light is focused with a light receiving element 22 and converted to an electrical signal with an electrical signal processing section 23. Then, after conversion to the electrical signal respective frequencies are separated with an electrical signal processing section 23 to extract only the frequency component of the voltage to be measured thereby detecting a correct value of the voltage being measured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical fiber applied sensor that detects a physical quantity to be measured using optical means.

2. Prior Art A conventional optical fiber applied sensor using a polarization maintaining optical fiber has a configuration as shown in Fig. 2, as shown in "Optronics, January 1983 issue, P31, Fig. In this case, the physical quantity to be measured is electric current.

That is, the light 1 emitted from the light source section becomes linearly polarized light by the polarizer 2, and is focused by the lens 2 onto the polarization-maintaining optical fiber 3. At this time, the polarization eigenaxis of the polarization-maintaining optical fiber 3 is made to coincide with the linear polarization axis.

The linearly polarized light propagated along the polarization eigenaxis of the polarization-maintaining optical fiber 3 is turned into parallel light by the lens 4 and transmitted 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 it becomes elliptically polarized light, and the lens 6
and enters the polarization maintaining optical fiber 7. Here, the linear polarization direction when the magnetic field H is 0 is incident at an angle of 45° with respect to the polarization eigenaxis of the polarization maintaining optical fiber. After propagating through the polarization-maintaining optical fiber 7, this elliptically polarized light is split into vector lights of two orthogonal components by the polarization beam splitter 9, each of which is received by the light receiving section 10, and electrically processed to obtain the measured current value. This is what we seek.

Problems to be Solved by the Invention In general, polarization-maintaining optical fibers have differences in the temperature characteristics of the transfer constant in each direction of their mutually orthogonal eigenaxes, or in the phase change due to external pressure such as fiber fluctuation. Therefore, in the case of light having polarization components on both orthogonal eigenaxes, such as elliptically polarized light, the phase changes due to changes in external pressure such as changes in ambient temperature and fiber fluctuations.

Therefore, in the method described above, the light propagating through the polarization-maintaining optical fiber 7 is elliptically polarized light that has been phase-modulated by the magnetic field, and during propagation it is also subject to phase changes due to changes in ambient temperature, etc. , it becomes difficult to accurately detect current information.

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 transmitted through a polarization-maintaining optical fiber is modulated by a change in a physical quantity other than the physical quantity to be measured. It has an optical element that has the function of modulating the phase of transmitted light according to changes in the physical quantity to be measured, which has different frequency ranges, and a polarization-maintaining optical fiber. A light receiving section converts the optical signal into an electrical signal, and electrically separates and extracts only the frequency range of the change in the physical quantity to be measured.

Operation The present invention uses the method described above to accurately detect a physical quantity to be measured without being affected by changes in the surrounding environment such as temperature changes.

Embodiment FIG. 1 shows an optical fiber applied voltage sensor for detecting voltage having a commercial frequency (60H2, 60H2) as an embodiment of the optical fiber applied sensor of the present invention.

The light emitted from the light source 12 becomes linearly polarized light by the polarizer 14, is condensed into the polarization-maintaining optical fiber 15 by the lens 13, and propagated, becomes parallel light by the lens 1θ, and is transmitted through the electro-optical element 17. At this time, the linearly polarized light undergoes phase modulation by the voltage to be measured V, and becomes elliptically polarized light, which is focused by the lens 18 onto the polarization-maintaining optical fiber 19 and propagated, and is transmitted through the polarizing beam splitter 21, which is proportional to the voltage to be measured. The light intensity signal is focused on the light receiving element 22 by the lens 2o, and converted into an electric signal by the electric signal processing section 23. Here, the light propagating through the polarization beam splitter 19 is elliptically polarized light having polarization components on both orthogonal eigenaxes of the polarization-maintaining optical fiber, and a change in phase occurs due to a change in ambient temperature; The frequency range of is usually about several Hz, and it is possible to electrically separate it from the frequency of the voltage to be measured (50Hz or 60Hz), and after converting it to an electrical signal, the electrical signal processing section 23・The frequency of the voltage to be measured is separated, and only the frequency component of the voltage to be measured is extracted to detect the accurate value of the voltage to be measured.

Effects of the Invention As described above, according to the present invention, after converting an optical signal that is phase-modulated in accordance with changes in the physical quantity to be measured into an electrical signal in the light receiving section, the plane of polarization is preserved due to changes in ambient temperature, etc. By electrically separating the phase change component received by the optical fiber and extracting only the change component of the physical quantity to be measured, accurate values can be detected.

[Brief explanation 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. Old...Light source section, 13.
1θ, 18.2o...Lens, 14.21...
...Polarizing beam splitter, 15.19...
- Polarization maintaining optical fiber, 17... Electro-optical element, 22... Light receiving section, 23... Electric signal processing section.

Claims (1)

[Claims] Modulates the phase of light passing through a polarization-maintaining optical fiber according to changes in a physical quantity to be measured, which has a frequency range that is different from the 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 physical quantity to be measured. and a polarization-maintaining optical fiber, which converts an optical signal that is phase-modulated according to the change in the physical quantity to be measured into an electrical signal in a light receiving section, and calculates the frequency of the change in the physical quantity to be measured. Optical fiber applied sensor configured to electrically isolate and extract only the range.