Method of manufacturing an optical isolator

Metal fusion bonding – Process – With pretreating other than heating or cooling of work part...

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Details

2281221, 372703, B23K 120

Patent

active

056718810

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method of manufacturing an optical isolator which is for use in optical communication, optical measurement, and the like and which utilizes the Faraday effect and, in particular, to a method of manufacturing an optical isolator which is excellent in environment resistance.


BACKGROUND ART

Recently, an optical Communication system using a semiconductor laser as a light source and an optical apparatus employing a semiconductor laser have become widely used and are more and more expanding in scope and scale of applications.
In order to improve the accuracy and the stability of the optical communication system and the optical apparatus of the type described, an optical isolator is used for the purpose of removing a return light to the semiconductor laser.
The optical isolator comprises optical elements including a polarizer, an analyzer, and a Faraday rotator, a permanent magnet for generating a magnetic field, and a holder for fixing and protecting these components.
An organic adhesive has been used in a conventional method of fixing and adhering each optical element to the holder. However, the organic adhesive is poor in long-term stability of the adhesive strength and deteriorated in characteristic particularly due to the change in environmental condition such as the temperature and the humidity.
In view of the above, for the optical isolator used in, for example, an optical communication repeater, which is required to have a highly reliability over a long time period, it is proposed to manufacture the optical isolator by the use of a metal fusion-bonding method, instead of the conventional fixing method using the organic adhesive.
The adhering and fixing method using the metal fusion-bonding method is a technology brought into practical use and is used in wide applications such as a gas turbine blade, a vacuum window of a magnetron or a microwave electron tube, and a high-output high-frequency propagation transmitter tube. In the optical isolator, a metallized layer for fixation by metal fusion-bond is formed on at least a peripheral region except a light transmitting portion of the optical elements. The holder and each optical element are bonded together by soldering.
Those materials used in forming the metallized layer are different in dependence on materials to be adhered. Generally, in order to assure an adhesion strength, a layer consisting of Cr, Ta, W, Ti, Mo, Ni, or Pt, or a layer consisting of an alloy including at least one of the above-mentioned metals is formed as an underlying layer. Au, Ni, Pt or the like is used as a topmost layer. An intermediate layer of Ni or Pt may be formed between the underlying layer and the topmost layer.
As a fusion bonding metal, use is made of soldering materials such as Au--Sn alloy, Pb--Sn alloy, and Au--Ge alloy or various kinds of brazing materials. Among those, the Au--Sn alloy soldering material having a high adhesive strength and a relatively low fusion temperature is preferred for use in fixation by metal fusion bonding because it is excellent in adhesive strength and working efficiency.
As a method of forming the above-mentioned metallized layer, a wet process by plating and a dry process by vacuum deposition or sputtering are known. Among those, the dry process is often used in order to prevent the defect occurrence and the dust sticking on an optical surface of the optical element or an antireflection film.
However, when a metallized film is formed by the vacuum deposition or the sputtering, there is a serious problem in mass productivity. The conventional metallizing method comprises steps of forming the antireflection film on the surface of an optical material block; cutting it into pieces each having a size of a single optical element; masking a light transmitting portion of the optical element 5 by the metal mask 7 so that the metallized film is formed only on unmasked portions, as shown in FIG. 1, optical element 5 and a metal mask 7 being fixed mutually by a substrate holder 6 and a jig 8; and perform

REFERENCES:
patent: 5033052 (1991-07-01), Masuko et al.
patent: 5113404 (1992-05-01), Gaebe et al.
patent: 5128956 (1992-07-01), Aoki et al.
patent: 5329539 (1994-07-01), Pearson et al.

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