JPH10122993A - Photo-pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized lightweight photo-pressure sensor by using a nonmagnetic rare earth garnet monocrystal as photoelastic element. SOLUTION: As the photoelastic element of an optical pressure sensor formed of a polarizer, a photoelastic element, and an analyzer, nonmagnetic rare earth garnet monocrystal is used. The nonmagnetic rare earth garnet monocrystal is properly selected from those shown by the general formula (RC)3 A5 O12 (in the formula, R represents at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Td, Dy, Ho, Er, Tm, Yb and Lu, C represents at least one selected from the group consisting of Li and Ca by which R can be partially substituted, and A represents at least one selected from the group consisting of Ga, Sc, A, Zr, Si, In, and Mg). This photo-pressure sensor is formed of the polarizer, the nonmagnetic rare earth garnet monocrystal, and the analyzer in order from the light source side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pressure sensor using a non-magnetic rare earth garnet single crystal. More specifically, the present invention relates to a compact and lightweight optical pressure sensor using a highly sensitive nonmagnetic rare earth garnet single crystal.

[0002]

2. Description of the Related Art With the development of optical fiber communication, an optical fiber as an optical transmission line, a semiconductor laser or a light emitting diode as a light source, a photo diode as a light receiving element, and small optical components such as a cell hook lens or a glass polarizer. Many elemental technologies have been developed. In recent years, with the background of these technologies, there has been an increasing interest in optical applied measurement technology having excellent characteristics such as being unaffected by electromagnetic induction and free from danger of ignition or explosion.

[0003] As one field of optical applied measurement, there is a phenomenon in which a transparent elastic body behaves like a birefringent crystal due to strain when a pressure is applied in one direction of the transparent elastic body, that is, an optical pressure measurement applying a photoelastic effect. . One example is shown in FIG. In FIG. 1, reference numeral 1 denotes a polarizer made of rutile single crystal or the like,
Reference numeral 2 denotes a photoelastic element made of quartz glass or the like, and reference numeral 3 denotes an analyzer made of rutile single crystal or the like.

In FIG. 1, light transmitted through a polarizer 1 becomes linearly polarized light and enters a photoelastic element 2. When pressure is applied to the photoelastic element 2, light becomes elliptically polarized light due to the birefringence of the photoelastic element 2. Accordingly, the intensity (P1) of the light passing through the analyzer 3 changes according to the pressure. This is the basic principle. However, since quartz glass or the like conventionally used for a photoelastic element has a small photoelastic effect, the element itself must be enlarged, and it is difficult to reduce the size of the pressure detecting unit.

[0005]

Means for Solving the Problems The present inventors have intensively studied to develop a material having a large photoelastic effect in order to realize a compact optical pressure sensor. As a result, they have found that a nonmagnetic rare earth garnet single crystal has a large photoelastic effect, and have further studied and completed the present invention.
That is, the present invention is an optical pressure sensor comprising a polarizer, a photoelastic element, and an analyzer, wherein the photoelastic element is a nonmagnetic rare earth garnet single crystal.

In the present invention, the nonmagnetic rare earth garnet single crystal used as the photoelastic element is not particularly limited, and has the general formula: (RC) ₃ A ₅ O ₁₂ [where R is Y, La, Ce, Pr, Nd ,
At least one selected from the group consisting of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and C is at least one selected from the group consisting of Li and Ca which can partially substitute R , A
Is at least one selected from the group consisting of Ga, Sc, Al, Zr, Si, In, and Mg.] Is preferably selected from the rare earth iron garnet single crystals. In particular, a [Gd ₃ Ga ₅ O ₁₂ ] substrate or a [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate, which is a substrate for growing a bismuth-substituted rare earth iron garnet single crystal film widely used in a Faraday rotator for an optical isolator Is a particularly preferred material because it is easily available, relatively inexpensive, and excellent in transparency.

The present invention basically comprises a polarizer, a nonmagnetic rare earth garnet single crystal, and an analyzer from the light source side.
If the laser light is guided by the polarization maintaining optical fiber, the polarizer can be omitted. It is also possible to add a quarter-wave plate in order to make the pressure and the light intensity transmitted through the analyzer a linear relationship. In this case, a quarter-wave plate can be provided either between the polarizer and the non-magnetic rare-earth garnet single crystal or between the non-magnetic rare-earth garnet single crystal and the analyzer.

In practicing the present invention, there is no particular limitation on the wavelength of the light source, and a comprehensive consideration is given to the wavelength range in which the light transmittance of the nonmagnetic garnet single crystal is favorable, the availability of the laser light source, the price, and the like. , May be selected as appropriate. Actually, the laser light source and light receiving element are inexpensive and easy to obtain.
The wavelength region of the 8 μm band is most preferable. The next best thing is
1.31 μm and 1.55 μm long wavelength optical communication wavelengths can also be selected.

[0009]

EXAMPLES The present invention will be described in more detail with reference to examples, but the following examples are not intended to limit the embodiments and the scope of the present invention. Example 1 A 500 μm-thick Shin-Etsu Chemical Co., Ltd. lattice constant
A (111) garnet single crystal [Gd ₃ Ga ₅ O ₁₂ ] substrate of 1.2383 nm was cut into a size of 2 mm × 2 mm. Next, this 2mm x 2m
Gd ₃ Ga ₅ O ₁₂ having a size of m was set in the evaluation device shown in FIG. 2, and the relationship between the pressure applied to Gd ₃ Ga ₅ O ₁₂ and the intensity of light passing through the analyzer was examined. . The measurement results are shown in FIG. The pressure applied to Gd ₃ Ga ₅ O ₁₂ is 0 N / mm ² to 15 N / mm
^A linear relationship was obtained in the range of ² . The measurement error in this measurement range was ± 2%.

In FIG. 2, a semiconductor laser light source (10) having a wavelength of 0.78 μm, an optical fiber (11) for guiding laser light from the semiconductor laser light source 10, and a laser beam emitted from the optical fiber 11 are converted into a parallel beam. Gradient index lens (12), Glan-Thompson prism (polarizer) for making (13)
Gd ₃ Ga ₅ O ₁₂ of size 2 mm × 2 mm (14), Gd ₃ Ga ₅ O ₁₂
Metal holder for fixing (15), pressing a metal jig (16) for applying pressure to the Gd ₃ Ga ₅ O _12, made of quartz 0.78
μm quarter-wave plate (17), Glan-Thompson prism (analyzer) (18), optical power meter (1)
9).

Example 2 A (111) garnet single crystal [(CaGd) ₃ (ZrMgGa) having a thickness of 500 μm and a lattice constant of 1.2407 nm manufactured by Chrismatech Co., Ltd.
₅ O ₁₂ ] The substrate was cut into a size of 2 mm × 2 mm. Next, in the same manner as in Example 1, a (CaGd) ₃ (ZrMg
The relationship between the pressure applied to Ga) ₅ O ₁₂ and the intensity of light passing through the analyzer was examined. However, in FIG.
m laser light source (10), quarter wave plate for wavelength of 1.31 μm (17)
And As a result, as the pressure applied _{(CaGd) 3 (ZrMgGa) 5} O 12, a linear relationship was obtained in the range from 0N / mm ² of 18N / mm ^2. The measurement error in this measurement range was ± 2%.

[0012]

According to the present invention, a compact and lightweight optical pressure sensor can be manufactured and provided industrially very easily using a rare earth garnet single crystal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical pressure sensor using a photoelastic effect.

FIG. 2 is a schematic view showing a method for evaluating an optical pressure sensor according to the present invention.

FIG. 3 is a diagram showing measurement results in Example 1.

[Explanation of symbols]

1: Polarizer 2: Photoelastic element 3: Analyzer 10: Stabilized semiconductor laser light source 11: Optical fiber 12: Distributed index lens 13: Glan-Thompson prism (polarizer) 14: Gd ₃ Ga ₅ O ₁₂ 15: Metal Holder 16: Metal jig for pressurization 17: 1/4 wavelength plate 18: Glan-Thompson prism (analyzer) 19: Optical power meter

Claims (2)

[Claims] 1. An optical pressure sensor comprising a polarizer, a photoelastic element, and an analyzer, wherein the photoelastic element is a nonmagnetic rare earth garnet single crystal. 2. The method according to claim 1, further comprising the step of:
The optical pressure sensor according to claim 1, further comprising a quarter-wave plate.