JP2757045B2 - Manufacturing method of optical isolator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an optical isolator in which polarizers are arranged on both sides of a Faraday rotator. An optical isolator is a non-reciprocal optical device having a function of permitting light to pass in one direction but blocking light in the opposite direction, and is used in fields such as optical communication and optical measurement. The present invention is a method particularly suitable for mass production of small optical isolators.

[Prior art] As a typical structure of an optical isolator, a Faraday rotator in which a magneto-optical crystal is mounted in a permanent magnet is provided on both sides.
There is a prism holder in which a polarizer with a prism is arranged in a prism holder. The Faraday rotator changes the plane of polarization of the incident light.
The polarizers are rotated by 45 degrees, and the polarizers located on both sides of the polarizers are combined in directions in which the planes of polarization of polarization pass by 45 degrees.

As a Faraday rotator, a block of YIG (yttrium-iron garnet) single crystal is used.
A thick film of bismuth-substituted garnet single crystal by the LPE (liquid phase epitaxial) method has been put to practical use.

[Problems to be Solved by the Invention] In the related art, components such as a polarizer and a Faraday rotator are used.
Each of them is assembled while adjusting the relative angles and dimensions thereof, which has a drawback that production efficiency is very poor. In particular, with the miniaturization of devices incorporating the optical isolator, the optical isolator is required to be further miniaturized, but this has been difficult with the conventional structure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a manufacturing method that can efficiently and inexpensively mass-produce optical isolators and is particularly suitable for miniaturization.

Means for Solving the Problems According to the present invention, which can achieve the above object, a wafer-like polarizer is provided on both surfaces of a wafer-like Faraday rotator in which a magneto-optical crystal is formed on a substrate via an adhesive layer. Is placed in a magnetic field, a laser beam is input from one side, and the polarizer angle is adjusted so that the amount of transmitted light is minimized. To obtain a chip-shaped non-reciprocal element portion, and insert and fix each of the non-reciprocal element portions into a cylindrical permanent magnet.

Examples of the magneto-optical crystal include a bismuth-substituted garnet thick film. A metal grating polarizer or the like can be used as the polarizer.

[Operation] In the present invention, a wafer-like Faraday rotator and a polarizer are used, and the angle of the polarizer is adjusted by combining them.
For this reason, after the angle adjustment is completed and fixed, the individual non-reciprocal element portions obtained by cutting the wafer assembly have already completed the angle adjustment. In other words, according to the present invention, it is possible to adjust the angle without individually adjusting the non-reciprocal element portions, so that the angle can be adjusted only once per wafer, and the process can be greatly simplified. Accordingly, an optical isolator having good isolation characteristics can be obtained only by inserting and fixing the chip-shaped non-reciprocal element portion obtained by cutting into the permanent magnet.

Embodiment FIGS. 1A to 1G show an embodiment of a manufacturing process of an optical isolator according to the present invention. First, as shown in FIG. 1A, a wafer-like Faraday rotator 10 having a magneto-optical crystal formed on a substrate, and wafer-like polarizers 12 and 14 are prepared. They are arranged with polarizers 12, 14 on both sides of the Faraday rotator 10 so that a layer of adhesive is interposed therebetween (FIG.
reference). Here, the magneto-optical crystal formed on the substrate as the Faraday rotator 10 is a bismuth-substituted garnet single crystal thick film obtained by the LPE method. Recently, wafers of this type have become readily available in the size of several inches in diameter. As the polarizers 12 and 14, metal lattice polarizers having a diameter of several inches are used. This metal grating polarizer has an extinction ratio of about 40 dB at a plate thickness of several hundred μm, and can be sufficiently used as an optical isolator. The adhesive forms a layer by any method such as coating. In this state, the adhesive layer has not yet been cured.

The members combined in this manner are arranged in the coil 16 as shown in FIG. Then, as shown in FIG. 4D, a current I is applied to the coil 16 to apply a magnetic field, a laser beam is input from one side, and the transmitted light is detected. Then, the relative angles of the polarizers 12 and 14 are adjusted so that the amount of transmitted light is minimized. The adhesive is cured and integrated in a state where the amount of transmitted light is minimized.

Next, as shown in FIG. 8E, the combined body is cut into a dice shape at a predetermined size to obtain a chip-shaped non-reciprocal element portion 18. Finally, as shown in FIGS. F and G, the non-reciprocal element portion 18 is inserted into the cylindrical permanent magnet 20 and fixed with an adhesive. For this reason, a square hole 22 is provided in the permanent magnet 20 so that the non-reciprocal element portion 18 just fits therein. Thus, the optical isolator is completed.

The magneto-optical crystal and the wafer-shaped polarizer constituting the Faraday rotator are not limited to the above materials. For example, a rutile crystal plate or the like can be used instead of the metal lattice polarizer.

[Effects of the Invention] The present invention relates to a wafer assembly capable of cutting out a large number of non-reciprocal element portions as described above. There is no need to make adjustments, so that the production efficiency is extremely high and it is possible to manufacture in large quantities and at low cost. Also, the production equipment and the number of man-hours do not increase more than necessary.

Furthermore, since the non-reciprocal element portion whose angle has been adjusted is obtained by cutting, its size can be reduced, and a small optical isolator can be easily manufactured.

[Brief description of the drawings]

1A to 1G are process explanatory views of one embodiment of a method for manufacturing an optical isolator according to the present invention. 10: Wafer-shaped Faraday rotator, 12, 14: Wafer-shaped polarizer, 16: Coil, 18: Chip-shaped non-reciprocal element, 20
... A cylindrical permanent magnet.

Claims (1)

(57) [Claims] 1. A wafer-like polarizer is disposed on both sides of a wafer-like Faraday rotator having a magneto-optical crystal formed on a substrate via an adhesive layer, placed in a magnetic field, and placed on one side. Laser light is input and combined with the adhesive in a state where the polarizer angle is adjusted so that the amount of transmitted light is minimized, and then the combined body is cut to obtain a chip-shaped non-reciprocal element portion. A method for manufacturing an optical isolator, wherein the non-reciprocal element portions are inserted and fixed in respective cylindrical permanent magnets.