JPS6252437A - Method and apparatus for measuring refractive index of reflective type anisotropic medium - Google Patents

Abstract

PURPOSE:To make it possible to measure the refractive index distribution on the surface of an anisotropic medium, by irradiating a medium to be measured with linear polarized light and measured the intensity of reflected light on the basis of the refractive index in a polarizing axis direction. CONSTITUTION:The linear polarized light 2 from a light source 1 is guided to a directional photocoupling element 3 but, because the main axes X, Y of the directional photocoupling element 3 coincide with the polarizing axis of the light source 1, said light passes in a low loss state. The linear polarizing light 2 irradiates a medium 7 to be measured while the polarizing axis thereof is rotated by 45 deg. by a Faraday rotary element 14. The reflected light 12 passes through the Faraday rotation element 14 while the polarizing axis thereof is rotated by 45 deg. and, therefore, said polarizing axis becomes vertical to that of the light source 1. When the directional photocoupling element 3 advances to the direction opposite to that of the polarized light 2, the polarized component in the X-axis direction is changed in its light path with good efficiency and measured by an optical detector 10.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method and apparatus for measuring the refractive index of a medium by shining light onto a medium and measuring the intensity of reflected light.

"Prior Art" FIG. 4 shows the principle of a conventional reflective layer refractive index measuring device. 1 is a light source that outputs linearly polarized light, and light 2 from the light source 1 is first guided to a directional optical coupling element 3.

Since the main axis of the directional optical coupling element 3 is fixed so as to narrowly coincide with the light beam of the light source 1, the light 2 from the light source passes through with low loss. Thereafter, the light passes through a four-wavelength plate 4 and is irradiated onto a medium 7 to be measured through a lens 6. Here, since the principal axis of the wave plate is inclined at 45 degrees with respect to the polarization axis of the light source, the light 5 passing through the wave plate 4 becomes circularly polarized. Fifth
It is shown as a vector in the figure. The vector numbers in FIG. 5 correspond to the respective numbers of the lights in FIG.

The original light going from the light source to the medium is shown by a solid line, and the reflected light is shown by a broken line.
It is the main axis of x, y &! /4 This is the main axis of the wave plate 4. Therefore, the light 8 reflected by the medium 7 also becomes circularly polarized light as shown in FIG. and.

Once again, when passing through the wavelength plate 4, the reflected light 8 changes into directly #JI polarized light 9 parallel to the X axis. The reflected light 9, which has become linearly polarized light perpendicular to the reflected light, is separated by the directional optical coupling element 3 and measured by the photodetector 10.

[Problems to be Solved by the Invention] As is clear from the above explanation, in the conventional method, the medium to be measured 7 was irradiated with circularly polarized light and measured, so the polarization of the irradiated light was It was not possible to make detailed measurements of anisotropic media, which have different refractive indices in different directions. Therefore, refractive index measurements of anisotropic media are mainly performed in transmission mode.
It had the disadvantage that it had to be processed into a state suitable for passing through the measurement sample.

Is the non-invention a one-dimensional irradiation state in which the refractive index of an anisotropic medium is measured by a reflection method? Problem with polarization axis control for detecting reflected light? The purpose of item 7 is to measure a medium to be measured in which stress is applied non-uniformly, a medium that cannot be processed for a light transmission method, or a medium whose refractive index changes when processed. Preferred method and equipment?
It is about providing.

"Means for Solving the Problems" The method of the present invention irradiates the medium to be measured with ti[l/iA polarized light, and determines the surface of the anisotropic medium from the intensity of the reflected light according to the refractive index in the direction of the polarization axis. It measures the refractive index distribution, and in detecting reflected light, the polarization axis is rotated perpendicular to the axis of the irradiated light before the reflected light reaches the directional optical coupler, increasing the efficiency. This method is fundamentally different from the conventional technique in which the measurement medium is irradiated with circularly polarized light and the refraction is measured assuming that the medium is all 7 isotropic. be.

The uninvented device is a light source capable of outputting A-line polarized light.

A directional optical coupling element, a Faraday rotation element, an optical lens, and a photodetector are each arranged on the optical path.

"Actual Example" Figure 1 is a diagram showing an example of non-invention, 1
is a light source that outputs linearly polarized light, 2 is the irradiation light of 1 IL light, 3 is the directional optical coupling element, 6 is the lens for the conduit (parallel to the reflected light), 7 is the medium to be measured, 14 is the Faraday ig1 11 is the irradiated light that has passed through the Faraday rotary element 14, 12 is the reflected light from the medium to be measured, and 13 is the reflected light that has passed through the Faraday rotary element 14. Figure 2 shows the propagation in Figure 1. The polarization direction of light is represented by seven vectors, and the vector number in one figure corresponds to the bud number of each propagating light.

In Figures 1 and 42, linearly polarized light 2 emitted from light source 1
is guided to the directional optical coupling element 3.

The main axes X, Y of the directional optical coupling device 3 are as shown in the figure.
Since the light coincides with the polarization axis of the light source, it passes through the directional optical coupling element 3 with low loss. It becomes an irradiation light for an arrow! ! Polarized light 2 passes through Faraday rotation element 142, and the polarization axis is rotated by 45 degrees as shown in FIG. Therefore, the medium to be measured 7 must always be irradiated with linearly polarized light in the direction 45 with respect to the Y axis, and the refractive index in this direction is 1.
The reflected light 12 will return due to the reflectance. And the reflected light 12 is Faraday! 21-turn element 14'! Since the polarization axis rotates by 45 degrees when passing through ', the polarization axis becomes perpendicular to the polarization axis of f[, as shown in FIG. When the directional optical coupling element 3 travels in the opposite direction to the irradiation source, the polarized light component in the X-axis direction efficiently passes through the optical path. be changed and measured with a photodetector 10. As is clear from the above description, in the present invention, it is possible to measure the refractive index in a certain direction, and it is possible to measure the surface condition (for example, stress distribution) of an anisotropic medium without processing the medium. Special *’t”
Pi. As an example, FIG. 3 shows the breakage Ifi of a polarization-maintaining optical fiber that is subjected to stress application of S times M. fiber 1
Stress is applied to the inside of ff1116. Core 17. There is a land 18, and due to the difference in coefficient of thermal expansion, a stress shown by a broken principal stress line 19 is generated.

The birefringence distribution state caused by this stress cannot be measured using conventional reflection methods. but.

If the uninvented method is applied, it is possible to clearly separate and measure the refractive index in the X-axis sidewave direction and the y-axis sidewave direction.In addition, the refractive index distribution of the optical fiber shown in FIG. The state can be measured.

"The Young Fruit of the Invention" As explained above, the uninvented method and device can measure the refraction double distribution in a certain polarization direction of the medium to be measured. refraction weight i about the axis
By determining 'k111I, it is possible to measure the stress distribution on the surface of the medium.

Especially the irradiation light? Because the light is focused with a lens etc. and the measurement is 0T,
It is possible to measure the anisotropic refractive index and stress state in extremely minute regions of the order of several μm.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is an explanatory diagram showing the polarization states of irradiated light and reflected light in the present invention, @3
4 is a principle diagram of a conventional measuring device, and FIG. 5 is an explanatory diagram showing the polarization states of irradiated light and reflected light in the conventional device. 1... Light source, 2... [ls polarized irradiation light, 3...
Directional optical coupling element, 6... condensing lens, 7... medium to be measured. 8... Reflected light, 10... Photodetector, 11... Faraday rotation element 2 appropriate irradiation light, 12... Reflected light,
13...Reflected light that passed through the Faraday rotation element. 14...Faraday rotation element. Applicant Nippon Electric @ Telephone Co., Ltd. Figure 1 ÷ [ ) 10 Figure 2 I: Bald head Y3: Force direction 1 unit light coupling element

Claims (2)

[Claims] (1) In a method of measuring the refractive index of a medium by shining light onto a medium and measuring the intensity of reflected light, linearly polarized light from a light source is passed through a directional optical coupling element, and then passed through a Faraday rotation element. 4 with respect to the polarization axis of the light source
Rotate the light by 5 degrees, apply it to a medium through an optical lens in a linearly polarized state, and guide the reflected light from the medium again to the Faraday rotator and pass it through, thereby rotating the polarization axis of the reflected light by 45 degrees. , followed by a directional optical coupling element, and the coupling element separates and detects a polarized light component perpendicular to the polarization axis of the light source. Method. (2) The light source outputs a light source capable of outputting linearly polarized light, a directional optical coupling element, a Faraday rotation element that rotates the polarization axis of the linearly polarized light passing through it by 45 degrees, an optical lens, and a photodetector. A refractive index measuring device for a reflective anisotropic medium characterized by a configuration in which it is placed on the optical path of light.