JPS58160848A - Photointerferometer - Google Patents

Abstract

PURPOSE:To obtain a photointerferometer capable of varying the length of light passages of two light waves with high accuracy, by using an optical fiber and varying the temperature of an atmosphere of this optical fiber. CONSTITUTION:A light wave 31 is split to two waves by a beam splitter 32 and is separated into a light wave 33 and a light wave 34. These two light waves are turned to a linear polarized light wave crossing at right angles each other by a half-wavelength plate when each light wave is the linear polarized light wave or by polarized light elements 35, 36 and half-wavelength plases 38, 29 each light wave is not the linear polarized light wave and it is synthesized again by a beam splitter 37. A synthesized wave 316 of two light waves crossed at right angles is aligned to perpendicularly intersecting two axes of a polarized wave picture preserving optical fiber 312 by a half-wavelength plate 310 and the fiber 312 is propagated. Only an axis direction component of a photodetection element 313 of perpendicularly intersecting two light waves is outputted by the element 313. A delay passage of this interferometer is made by varying the temperature of the fiber 312 to the temperature of an atmosphere of a thermostat 311 capable of setting the temperature.

Description

[Detailed description of the invention] The present invention relates to an optical interferometer.

Conventionally, an optical interferometer as shown in FIG. 1 has been used. The interferometer shown in the figure is commonly called a Matsuha-Zenda interferometer. In the figure, a light wave 11 is split into two by a beam splitter 12 and separated into a light wave 13 and a light wave 14. These two light waves are turned back by the mirror 15, the optical delay path 191, and the mirror 16, and are combined again by the beam splitter 17 to become a composite wave 18. In this interferometer, one side is used as a test optical path and the other side is used as a reference optical path. In this case, since the delay time of the optical delay path 19 is mechanically adjusted, highly accurate measurement is not possible.

The present invention provides an optical interferometer that can change the optical path length of two light waves with high precision by using an optical fiber and changing the ambient temperature of the optical fiber.

The present invention will be described in detail below using the drawings.

FIG. 2 shows the basic configuration of the present invention. In the figure, a light wave 22 that has been linearly polarized by a polarizer 21 is polarized by a half-wave plate 2.
3, it is rotated so that it is located between the two orthogonal optical axes 25° and 26 of the polarization-preserving optical fiber 9, which transmits light while preserving the polarization plane on the two orthogonal optical axes in a linearly polarized state. Ru. The polarization-maintaining optical fiber 29 is an optical fiber that is made so that two orthogonal linearly polarized waves 27 and 28 propagate independently without mode coupling with each other. It can be considered that two leading wavepaths are made of one optical fiber. The light wave 24 rotated by the half-wave plate 23 so as to fall between the two optical axes 25 and 26 enters the polarization-maintaining optical fiber 29 and is separated into a light wave 27 and a light wave 28, each of which propagates independently. On the output side, the light wave 27 and a portion of the light wave portion are combined by the analyzer 210 to form a light wave 211 .

On the other hand, since the two orthogonal optical waveguides of the polarization maintaining optical fiber 29 have different refractive indices, the two optical waves 27,
28 will propagate at different speeds from each other. Therefore, on the output side of the polarization maintaining optical fiber 29, the light wave 27
A phase difference ψ occurs between the light wave 28 and the light wave 28 . This phase difference ψ is given by the following equation.

2π ψ=−−L−Cp −a ・(To−T) (1)
λ Here, λ is the wavelength of the light wave 24, L is the length of the polarization-maintaining optical fiber 29, Cp is the photoelastic constant of the polarization-maintaining optical fiber 29, a is the Young's modulus and Poisson's ratio of the polarization-maintaining optical fiber 29, and A proportionality coefficient related to the coefficient of thermal expansion, To, is the softening temperature of silica glass containing a dopant, which is approximately 1000° C., and T is the ambient temperature in which the polarization maintaining optical fiber 29 is placed. From equation (1), it can be seen that the phase difference ψ between the light waves 27 and 28 has a linear relationship with the temperature change. This means that the temperature change corresponds to the movement of the optical delay path 19 of the interferometer in FIG. Beam splitter 12 and beam splitter 1 in FIG.
7 corresponds to the input side end face 212 of the polarization maintaining optical fiber 29 and the analyzer 210 in FIG. Here, the polarization-maintaining optical fiber 29 is housed in a thermostatic oven that can be set to any temperature. Figure 5 shows an example of the actual measurement results of the analyzer output change with respect to the ambient temperature change of the polarization preserving optical fiber.
Shown below. It can be seen that the optical output changes sinusoidally in response to temperature changes.

An embodiment of the invention is shown in FIG. In the figure, light wave 3
1 is split into two by a beam sgelitter 32, and a light wave 33. Separate to 34 light waves. When these two light waves are linearly polarized waves, they are turned into mutually orthogonal linearly polarized waves by a half-wave plate. Otherwise, they are turned into mutually orthogonal linearly polarized waves by polarizers 35 and 36 and half-wave plates 38 and 39.
is synthesized again by Synthetic wave 31 of two orthogonal light waves
6 is a polarization-maintaining optical fiber 31 using a half-wave plate 310.
A polarization-maintaining optical fiber 3 aligned with two orthogonal axes 2
Propagate 12. The analyzer 313 outputs only the axial component of the two orthogonal light waves. As the delay path of this interferometer, as mentioned earlier, the temperature of the polarization preserving optical fiber 312 is set using a constant temperature bath 311 whose temperature is variable.
produced by changing the atmospheric temperature. This amount of change is
A He-Ne laser (wavelength 0.6328, 4 m) produces 31 light waves per unit length and unit temperature change of polarization-maintaining optical fiber.
), it is easy to reduce the value to 0.1 μITI/° C.m or less and it can be changed continuously.

In the above explanation, only the combination of a polarization-maintaining optical fiber and a pine-Zehnder interferometer was discussed, but other interferometers and polarization-maintaining optical fibers may be combined. It is possible to make an interferometer similar to the one used in this study. In this interferometer, one side is the test optical path,
If the other path is used as a reference optical path, it is possible to measure the refractive index of a substance or the coherence of a light source with high precision.

For this measurement, there are methods such as using the light receiver 314 to find out from changes in coherence, or placing a screen in place of the light receiver 314 and finding from the amount of displacement of interference fringes.

A part of the interferometer constructed between the beam splitter 32 and the beam splitter 37 in FIG. 3 can also be constructed as shown in FIG. 4. In Figure 4, 4
1 and 42 are a combination of a polarizer and a half-wave plate, or a polarizer and a quarter-wave plate; in the former case, the half-wave plate 42
The output light of is adjusted to be inclined at 45° with respect to the optical axis of the polarizing beam splitter 43, and in the latter case, the output of the 174-wave plate 42 is adjusted to be circularly polarized. 44 and 45 are mirrors, and 46 is a polarizing beam splitter.

As described above, the present invention uses two orthogonal transmission lines of a polarization-maintaining optical fiber as two optical paths or a part of the optical path of an interferometer, and the difference in the length of these two optical paths can be changed with high precision depending on the temperature. This is to realize an optical fiber interferometer with an optical delay path that moves with high precision.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a conventional optical interferometer.
The figure is a perspective view showing the basic structure of the present invention, FIG. 3 is a structural system diagram showing an embodiment of the present invention, FIG. FIG. 5 is a characteristic side view showing changes in the output of the analyzer with respect to changes in ambient temperature of the polarization-maintaining optical fiber used in the present invention. 11, 13, 14... light waves, 12, 17...
Beam splitter, 15.16...Mira, 18...
・Synthetic wave, 19... Optical delay path, 21... Polarizer, 2
2 , 24 , 27 , 28 ... light wave, 23 ... half-wave plate, 25 , 26 ... optical axis, 29 ... polarization preserving light 7 eyeper, 210 ... analyzer, 211 ...・Light wave, 212...Input side end face, 31, 33, 34...
・Light wave, 32, 37...Beam splitter, 35
, 36... polarizer, 38, 39, 310...
Half-wave plate, 311... Constant temperature bath, 312... Polarization preserving optical fiber (, 313... Analyzer, 314... Light receiver, 316... Combined wave, 41... Polarizer, 42・
... Half-wave plate or quarter-wave plate, 43... Polarizing beam splitter, 44, 45... Mira, 46... Beam souffle ivy. Patent applicant International Telegraph and Telephone Corporation Representative Person Inuzuka 1 person from outside the university 3132333835 3637 11

Claims (1)

[Claims] a polarization-maintaining optical fiber that transmits incident light while preserving the polarization plane on two optical axes orthogonal to each other; a constant temperature chamber that maintains the polarization-maintaining optical fiber at any desired temperature; a synthesizing means for inputting the emitted light and synthesizing the components along the two orthogonal optical axes, and using the 2' optical waveguides along the two orthogonal optical axes as two independent optical paths in the thermostatic chamber; An optical interferometer characterized in that an optical path length difference between the optical paths is changed according to a change in ambient temperature.