JPS61213611A - Polishing method for crystal - Google Patents

Abstract

PURPOSE:To make possible the polishing of a crystal while measuring exactly the thickness thereof by making incident light to the crystal from the polished surface thereof, taking the reflected light from a reflection film again out of the polished surface and measuring the rotating angle of the plane of polarization with respect to the plane of polarization of the incident light. CONSTITUTION:The crystal 3 of the thick liquid phase epitaxial garnet film is adhered by using an adhesive agent 5 onto a polishing jig 7 as the reflection film 6 and the surface of the crystal 3 is polished, by which the adjustment of the crystal 3 is executed. Laser light 11 which is made to the linearly polar ized light by passing through a polarizing plate 21 is made incident at proper times to the crystal 3 from the polished surface thereof during the polishing and is passed through the crystal 3, the non-magnetic garnet substrate 4 and the adhesive agent 5 so as to be reflected on the surface of the chromium reflec tion film 6. The reflected light is again passed through the agent 5, the substrate 4 and the crystal 3 and is then taken out as exit light 12. The rotating angle of the plane of polarization of such exit light 12 with respect to the plane of polarization of the incident light is read with an analyzer 22 and the polishing is executed while the film thickness of the crystal 3 is monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crystal polishing method, and more particularly to a crystal polishing method in which polishing is performed while monitoring the thickness of a crystal.

[Prior art and its problems]

Magnetic garnet liquid phase epitaxial (LPE) grown by liquid phase epitaxial method on a non-magnetic garnet substrate
Films are important as materials for magneto-optical devices. For example, Japanese Patent Application No. 55-93449 or Japanese Patent Application No. 55-126
As disclosed in the specification of No. 239, the use of a garnet LPE thick film crystal grown by liquid phase epitaxial growth on a non-magnetic garnet single crystal substrate as a material for a Faraday rotator makes it possible to use a yttrium-iron-garnet bulk single crystal. Compared to using it as a material for a Faraday rotator, it has a significant cost advantage.

When a Faraday rotator made of such a garnet thick film crystal is used, for example, in an optical isolator, when the incident light passes through the garnet thick film, the incident polarization plane is accurately set to 4
In order to rotate the crystal by 5°, it is necessary to adjust the thickness and length of the crystal by polishing, depending on the Faraday rotation coefficient of the crystal material.

In this 6N polishing, in the conventional method, the Faraday rotation coefficient of the crystal material is measured before polishing, and the Faraday rotation angle is set to 45° according to this Faraday rotation coefficient.
The target thickness for polishing is determined, the crystal is fixed to a polishing jig using adhesive, and the crystal is polished to the target thickness. During the polishing process, the thickness of the crystal was adjusted by measuring it with a micrometer or the like. However, in this method, since the crystal is fixed to the polishing jig using an adhesive, the thickness of the adhesive causes an error in measuring the thickness of the crystal, for example, an error of ±5 μm. Therefore, if the target thickness of the crystal to be polished is set to 70 μm, a variation in the crystal thickness of ±7% will occur. In this case, if the incident polarization plane is rotated by 45° when the incident light passes through the crystal by 70 μm, the variation in polishing thickness of ±7% corresponds to ±3.15% as a Faraday rotation angle. Therefore, when a Faraday rotator made of garnet thick film crystal is used as an optical isolator, isolation is obtained by the deviation Δθ of the Faraday rotation plane from 45°, as isolation = 10 log 5 in 2θ, so ±3.15 A variation in the Faraday rotation angle of .degree., that is, a variation in film thickness of 7%, causes a problem in that the isolation deteriorates to 25 dB.

[Purpose of the invention]

An object of the present invention is to provide a method of polishing a transparent crystal that causes a Faraday effect, such as an oxide magnetic material, while accurately measuring the thickness of the crystal, in order to solve the above-mentioned problems. It is in.

[Structure of the invention]

When polishing a transparent crystal that produces a Faraday effect, the present invention provides a reflective film between the crystal and a jig to which the crystal is attached, and allows light to shine through the polished surface of the crystal, which is the surface opposite to the reflective film. The polishing process is performed while monitoring the film thickness of the crystal by making the reflected light from the reflective film incident on the polishing surface and measuring the rotation angle of the polarization plane with respect to the polarization plane of the incident light on the extracted reflective film. It is a feature.

〔Example〕

Example 1 FIG. 1 is a diagram showing an example of the present invention, and in this example, an LPE garnet thick film crystal is polished.

A magneto-optical LPE Garnef thick film crystal grown on a non-magnetic garnet substrate 4 is attached using an adhesive 5 to a polishing jig 7 on which metallic chromium has been deposited as a reflective film 6. The thick film crystal 3 is adjusted by polishing the surface with diamond paste. At any time during the polishing process,
Laser light 11 with a wavelength of 1.30 μm, which has become linearly polarized light after passing through the polarizing plate 21, is incident from the polished surface of the thick film crystal 3 at a slight angle from the normal to the crystal plane, and a permanent magnet attached to the surface of the thick film crystal 3 is used. 8 through the garnet thick film crystal, the non-magnetic garnet substrate 4 and the adhesive 5, and is reflected by the surface of the chrome reflective film 6, and then the adhesive 6.
After passing through the non-magnetic garnet substrate 4 and the garnet thick film crystal 3, it is extracted as an emitted light 12, and the rotation angle of the polarization plane of the emitted light 12 with respect to the polarization plane of the incident light is measured using an analyzer 22.
The angle 2θF is twice the Faraday rotation angle of the material (garnet thick film crystal).

Although 2θp = 110° before the start of polishing, the polishing operation was stopped when the angle 20F was measured by interrupting the polishing at an appropriate time during the polishing, and the polishing operation was stopped when 2θp = 90.1°. As a result, it was possible to polish the garnet thick film crystal 3 with an accuracy of ±0.05° (±0.1%) for the Faraday rotation angle of 45° required for an optical isolator.

The isolation margin of the optical isolator using this material was 40 dB, and defects in film thickness did not contribute to deterioration of isolation (defects in thickness determine the upper limit of isolation).

Example 2 FIG. 2 is a diagram showing another example of the present invention, in which an LPE garnet thick film crystal is polished in the same manner as in Example 1.

The substrate crystal of the magneto-optical LPE garnet thick film crystal 3 grown on a non-magnetic garnet substrate (not shown) is removed by polishing in advance, and gold is deposited as a reflective film 13 on the surface from which the substrate has been removed by sputtering. The thick film crystal 3 is attached onto a polishing jig 7 using an adhesive 5 and polished to adjust the thickness of the thick film crystal 3 using colloidal silica dispersed in caustic soda as a polishing agent.

During the polishing process, the polarizing plate 2 is removed from the surface of the thick film crystal 3 at any time.
A laser beam 11 of 0.78 μm is incident on the linearly polarized wave 1 through the garnet thick film 3 magnetized by a permanent magnet 8 attached to the thick film surface. It is reflected by the surface of the reflective film 13, passed through the thick film crystal 3 again, and then reflected by a half mirror or 45°
The output light 12 is extracted through the prism 9, and the rotation angle of the polarization plane of the output light with respect to the polarization plane of the incident light is measured using an analyzer 2.
2 and read as an angle 20F, which is twice the Faraday rotation angle of the material (garnet thick film crystal).

2θ = 320° before the start of polishing, but by interrupting polishing at any time during the polishing process and measuring 20F,
The polishing operation was stopped when θp=88.8°. As a result, it was possible to polish the garnet thick film crystal with an accuracy of ±0°6° (±1.3%) for the Faraday rotation angle of 45° required for an optical isolator. The isolation of the optical isolator using this crystal was 36 dB, and there was no deterioration of the isolation (39.6 dB if it occurred) due to the thickness defect.

The two embodiments of the present invention have been described above, but the crystal to be polished is not limited to magnetic garnet, but may be any transparent material that produces Faraday rotation when a magnetic field is applied, or may be a ferromagnetic or paramagnetic material. It can be applied regardless of the

〔Effect of the invention〕

As described above, by using the present invention, when polishing to adjust the thickness and length of a crystal provided to a Faraday rotator, polishing can be performed while performing mechanical film thickness measurement, where the thickness of the adhesive deteriorates measurement accuracy. In contrast, by polishing while measuring the physical constant (Faraday rotation angle) required for the crystal, it is possible to adjust the thickness of the crystal with precision (by polishing).

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing embodiments of the present invention, respectively. 3... Garnet LPE thick film crystal 4... Non-magnetic garnet substrate 5... Adhesive 6.13... Reflective film 7... Polishing jig 8...・Permanent magnet 9...45° prism 11...Incoming light 12...Outgoing light 21...Polarizing plate 22...Analyzer

Claims (1)

[Claims] (1) When polishing a transparent crystal that produces a Faraday effect, a reflective film is provided between the crystal and the jig to which the crystal is attached, and light is emitted from the polished surface of the crystal, which is the surface opposite to the reflective film. It is characterized by polishing while monitoring the film thickness of the crystal by taking out the incident light reflected from the reflective film again from the polishing surface and measuring the rotation angle of the polarization plane with respect to the polarization plane of the incident light on the taken out reflective film. A method of polishing crystals.