JPH01219816A - Aligning method for axis of polarization of optical isolator element - Google Patents

Abstract

PURPOSE:To form the optical isolator element of high quality with stability and productivity by passing the laser light from a laser from the side of an analyzer, and aligning the axes of polarization of a polarizer and the analyzer with each other by rotating the both so that the cutoff rate of ordinary light from the side of the polarizer is minimum. CONSTITUTION:A Faraday rotation element 2 is applied with a saturation magnetic field during an assembling and adhering process, and the laser light from the semiconductor laser device is made incident vertically from the side of the analyzer 3; and the polarizer 1 and analyzer 3 are rotated mutually and the light power intensity of the ordinary light component of the laser light emitted from the side of the polarizer 1 is measured. Then the axes of polarization of the polarizer 1 and analyzer 3 are aligned with each other at the position where the light power intensity is minimum and they are fixed and adhered with an epoxy adhesive. Further, when the position where the light power intensity of return light is found, the laser light is made incident vertically from the side of the analyzer 3, the power intensity of the light passed through the polarizer 1 is measured by a light power meter, and the polarizer 1 is rotated finely and adjusted so that the cutoff rate is optimum. Consequently, the superior performanceis obtained with the good reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention relates to a polarizer used in manufacturing an optical inlator element,
The present invention relates to a method of adjusting the angle of the polarization axis of an optical isolator element in order to obtain an optimal amount of light attenuation when bonding an analyzer and a garnet thick film plate that is a Faraday rotation element.

[Prior Art] FIG. 1 is a diagram showing the structure and operating principle of an optical isolator element.

In Fig. 1(,), the incident light 4 entering from the left side is.

Polarizer 1. Faraday rotator 2. Go through Analyzer 3 to the right. At this time, since the polarization axis 11 of the polarizer 1 is formed in the vertical direction, the vertical component of the light is polarized as ordinary light. The plane of polarization of the light 42 polarized by the polarizer 1 is
When the light passes through the Faraday rotation element 2 to which the magnetic field H is applied in the same direction as the direction in which the light travels, it rotates approximately 45 degrees while passing through the Faraday rotation element 2. On the other hand, the analyzer 3 is made so that its polarization axis 31 has an angle of 45 degrees with respect to the polarization axis 11 of the polarizer 1. Therefore, the light 44 that passes through the analyzer 3 becomes only light that is polarized at 45 degrees.

On the other hand, FIG. 1(b) is a diagram showing the operation of the returning light.

Even if the returned light 5 contains light polarized in each direction with respect to the direction of travel of the light, when it passes through the analyzer 3 which has the polarization axis 31 in the 45-degree direction, the plane of polarization in the 45-degree direction is Only the light that has this light passes through the analyzer 3 as ordinary light 52, and when these lights 52 pass through the Faraday rotator 2 to which a magnetic field in the opposite direction to that of the returning light is applied, the Faraday rotator 2 changes the polarization of this ordinary light 52. Rotate the wavefront 45 degrees. Therefore, the light 53 exiting the Faraday rotation element 2 is highly attenuated in the polarizer 1 because its plane of polarization is perpendicular to the polarization axis 11 of the polarizer 1.

The optical inulator element configured in this way is as follows.

Currently, it is an indispensable component for stable transmission in the optical oscillation part of optical communication equipment that transmits data at speeds of 1.1 gigapits/second or more.

Assembling and adhering the polarizing crystal plates (polarizer 1 and analyzer 3) and garnet thick film plate (Faraday rotation element 2), which is the manufacturing process of the optical isolator element, involves sandwiching the garnet thick film plate between two polarizing crystal plates. ◇At this time, the analyzer 3 is aligned so that the polarization axis 31 of the analyzer 3 is at an angle of 45 degrees with respect to the polarization axis 11 of the polarizer 1.

[Problems to be Solved by the Invention] However, with this method, when an optical isolator element is actually used, variations occur in isolation, which is the main characteristic of the optical isolator element. This is due to errors in the Faraday rotation angle due to variations in the thickness of the Faraday rotation element 2 used, deviations in the polarization axis of the polarizing crystal plate, etc., resulting in a small isolation value indicating the blocking rate of the returned light. As a result, there was a drawback that the performance of the optical inlator element could not be fully utilized.

[Means for Solving the Problems] In order to eliminate these drawbacks, the present invention fixes a polarizer and an analyzer in advance, and sandwiches a garnet thick film, which is a Faraday rotation element, during assembly and bonding. Applying a magnetic field to a garnet thick film plate, passing laser light from a semiconductor radar from the analyzer side, and trying to manufacture a shim so that the light/power intensity of the ordinary light component of the light that exits the polarizer is minimized. To achieve the best isolation of the element, while rotating the polarizing crystal plate (polarizer and analyzer), search for a position that exhibits the optimal isolation characteristics and align the polarization axis.

By fixing, an optical isolator element of high quality and stable productivity is provided.

[Operations] At present, although Faraday rotation elements are used, it is difficult to accurately set the Faraday rotation angle of a net thick film to 45 degrees. This variation in the Faraday rotation angle of the Faraday rotation element has a strong effect on the inlation, which is the main characteristic of optical isolation.

As a solution to this problem, a polarizer and an analyzer are used when assembling and bonding the optical isolator element so that the plane of polarization of the returned light is 90 degrees to the polarization axis of the polarizer.

Rotate each to align the polarization axis.

By using a fixing method, it is possible to further improve the isolation, that is, the blocking rate of the returning light with respect to the forward light, and to provide a method of manufacturing an optical inulator element having stable characteristics.

[Example] In an example of the present invention, the material of the optical inulator element is polarizer 1. A square rutile polarizing crystal plate was made as the analyzer 3, and a Faraday rotator 2 was made by a liquid phase epitaxial growth method. Part of the iron in gadolinium, bismuth, iron, and garnet was directly replaced with aluminum and gallium.

A thick garnet film, which is a material with a large Faraday effect and has the same square angle as the polarizing crystal plate and a Faraday rotation angle of 43.5±0.1 degrees, was used, and each material was coated with an anti-reflection coating.

First, as a conventional method for comparison, assuming that the Faraday rotation angle of Faraday rotation element 2 is 45 degrees, polarizer 1. Align the polarization axis of analyzer 3 with 45 degrees and insert polarizer 1.
Faraday element 2. Polarizer 3 was adhered in this order with an epoxy adhesive.

Next, as a method according to the present invention, a saturation magnetic field is applied to the Faraday rotation element 2 during the assembly and bonding steps.

Rede light from a semiconductor laser device (not shown) is vertically incident on the analyzer 3 side, and the polarizer 1. The optical power intensity of the ordinary light component of the Rede light emitted from the polarizer 1 side is measured by rotating the analyzers 3 with respect to each other, and the polarization axes of the polarizer 1 and the analyzer 3 are set at the position where this optical power intensity is the minimum. I fixed them together and glued them together with epoxy adhesive.

In addition, in the method of the present invention, in order to find the minimum position of the light beam intensity of the returned light, the wavelength of 1.3
1 TTM semiconductor laser light is vertically incident from the analyzer 3 side, the power intensity of the light that has passed through the polarizer 1 is measured with an optical power meter, and the polarizer l is slightly rotated so that the blocking rate is optimized. ,It was adjusted.

In this way, the insertion loss and isolation were measured for each of the optical inulator elements manufactured using the two methods according to the conventional method and the method according to the present invention.

As a result, in the optical isolator element manufactured using the conventional method, the insertion loss was 05 ± 0.02 dB and the isolation was 25.8 ± 0.3 dB. In the optical inlator element manufactured using the above method, the insertion loss was 0.6±0.02 dB and the isolation was 360±1.0 dB.

[Effects of the Invention] As described above, two optical isolator elements whose axes were aligned during adhesive assembly using the present invention were obtained.

It is not just a matter of making it possible to manufacture a compensator element in addition to the optical isolator element manufactured by the conventional method.

Since reproducibility can be easily obtained, there is no need to limit the number of people involved in manufacturing, and there is no variation in characteristics due to errors in the Faraday rotation angle of the Faraday rotation element or the polarization axis of the polarizing crystal plate.9 Product quality performance It is now possible to provide an excellent optical inlator element.

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[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of an optical isolator element, and FIG. 1 (,) shows a polarizer for incident light. The operation of the Faraday rotation element and analyzer is shown in Figure 1 (b).
) shows the operation of the polarizer, Faraday rotator, and analyzer with respect to the returned light. 1°゛° polarizer, 2... Faraday rotation element, 3...
・Analyzer, 4...Incoming light, 5...Returning light, 21...
・Direction of magnetic field applied to Faraday rotation element, 41, 42
゜43.44...Polarized light in the incident light, 51,52゜53...-Polarized light in the returned light.

Claims (1)

[Claims] 1. A polarizer whose polarization axis has a specific angle with respect to one specific side, and an analyzer whose polarization axis has an angle of 45 degrees with respect to the polarization axis of the polarizer; A method for aligning the polarization axis when manufacturing an optical isolator element in which a garnet thick film with a Faraday rotation angle of approximately 45 degrees is sandwiched between these polarizers and analyzers, and a magnetic field is applied to the garnet thick film. In this step, the polarizer and the analyzer are rotated with respect to each other to align the polarization axes so that the laser beam from the laser passes through the analyzer side and the blocking rate of ordinary light coming out from the polarizer side is minimized. A method for aligning polarization axes of an optical isolator element, characterized by: