JPH11125797A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diminish the difference in the coeffts. of thermal expansion between an optical element and a metallic holder and to suppress the generation of residual strains by a soldering stage by using a coefft. of thermal expansion value of a specific range for the metallic holder. SOLUTION: Polar cores 1 and 1a are fixed by soldering to the metallic holder 2. When the solder is melted at the time of soldering, strains are not generated in the polar cores 1 and 1a together with the metallic holder 2 but at the time of cooling, both shrink and the stress meeting the difference in the coeffts. of thermal expansion between both acts on both, respectively. From such condition, a metallic material having the specific coeffts. of thermal expansion is selected for the polar cores having the small coeffts. of thermal expansion. Further, a holder is desired not to disturb the magnetic field generated by a permanent magnet in view of the point that the polar cores are used in proximity to the permanent magnet. In such a case, the material used for the metallic holder 2 is austenitic and ferritic stainless steels which exhibit nonmagnetism and weak magnetism near ordinary temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component used in an optical communication system or an optical measuring instrument, and is used to prevent light emitted from a light source from being reflected by an end face of an optical element in the optical system and returning to the light source. The present invention relates to an optical isolator used for prevention.

[0002]

2. Description of the Related Art When light emitted from a light source is transmitted using an optical system, light reflected at an end face of an optical element in the optical system returns to the light source. For example, in optical communication, light emitted from a laser of a light source is converged by a coupling lens and collected on an end face of an optical fiber.

At this time, most of the light enters and propagates in the optical fiber, but a part of the light is reflected at the end face of the fiber and returns to the laser of the light source. The light that has returned into the laser generally differs from the light in the laser in both phase and polarization direction, which disturbs laser oscillation and causes laser light noise.

In order to prevent such noise, an optical isolator for blocking return light is used. Optical isolators have high blocking characteristics (isolation) of return light, low transmission loss (insertion loss) of incident light,
Is required.

As shown in FIG. 1, a typical structure of an optical isolator is such that a polarizer 1 and an analyzer 1a are arranged on both sides of a plate-like Faraday rotator 3, and a Faraday rotator 3 is provided.
Is provided around the periphery of the cylindrical permanent magnet 4 for magnetizing the element in one direction. These optical elements, magnets, and the like are fixed to the metal holder 2 by soldering or the like. The holders 2 are usually laser-welded after positioning.

At the time of soldering, the optical element, metal holder, etc. are uniformly heated to a high temperature, and when cooled to room temperature after soldering, the respective materials have different coefficients of thermal expansion. Residual distortion occurs.

[0007]

Due to the occurrence of the distortion, the optical uniformity of the optical element is reduced, the isolation characteristics are degraded, and the optical element is damaged such as cracks.
Normal transmission of light may be hindered.

Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to provide an optical isolator which does not deteriorate optical characteristics of an optical element or cause damage such as cracks. Aim.

[0009]

In order to achieve the above object, the present invention focuses on the value of the coefficient of thermal expansion of a metal holder and uses a value of the coefficient of thermal expansion in a specific range.
This is to reduce the difference in thermal expansion coefficient between the optical element and the metal holder, thereby suppressing the occurrence of residual distortion due to the soldering process.

FIG. 1 is an explanatory view of an optical isolator.
The present invention pays attention to the problem of cracking of a polar core used as a polarizing element (general term for the polarizer 1 and the analyzer 1a) which affects the yield in manufacturing, particularly.

In FIG. 1, polar cores 1 and 1a are:
It is fixed to the metal holder 2 by soldering. At the time of soldering, when the solder is molten, the polar cores 1 and 1
a is not distorted together with the metal holder 2,
At the time of cooling, both contract, and a stress corresponding to the difference between the thermal expansion coefficients of both acts on both.

In the vicinity of the interface where the two are connected via solder, substantially the same stress acts. However, since the stress leading to destruction is generally smaller in a ceramic such as a polar core than in a metal, the ceramic is First, destroy. Metal
Although the stress is easily relaxed by the elastic deformation and the plastic deformation, the ceramic is hardly plastically deformed and is broken. A feature of ceramic is that it is weaker to tensile stress than to compressive stress.

Under such circumstances, it is the starting point of the operation in the present invention to select a metal material holder having a specific range of thermal expansion coefficient for a polar core having a small thermal expansion coefficient. From the viewpoint of close use, it has been found that it is desirable that the holder is made of a non-magnetic or weak magnetic material and does not disturb the magnetic field generated by the permanent magnet.

That is, the present invention provides an optical isolator in which a ceramic polarizer and an analyzer arranged before and after a Faraday rotator to which a magnetic field generated by a permanent magnet is applied are held by soldering to a metal holder. In the above, the metal holder is an optical isolator made of austenitic ferritic stainless steel.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, the dimensions are 1.6 mm × 1.6 m.
m × 0.2 mm flat polar core (made of ceramic, coefficient of thermal expansion 6.5 × 10 ⁻⁶ / ° C.) 1 and 1a
It was bonded to a metal holder 2 having an outer diameter of 4.0 mm, an inner diameter of 1.4 mm, and a thickness of about 0.4 mm using gold-tin solder. In addition, in the adhesion part of the polar cores 1 and 1a and the metal holder 2,
It is coated with gold and held at 370 ° C. for adhesion.

Here, the material used for the metal holder 2 is as follows.
SUS-329J1 and A, austenitic ferritic stainless steels that exhibit non-magnetic and weak magnetic properties near room temperature
-SUS-329LJ2, which contains Fe, Cr and Ni as main components.

For each of these metal holders, 100
The pieces were bonded to each other, and the rate of occurrence of cracks in the polar core was determined. The results are shown in Table 1 in comparison with the case where SUS-304, which is commonly used as a nonmagnetic or weakly magnetic austenitic stainless steel, is used.

[0019]

From Table 1, it can be seen that, compared to SUS-304, which is an austenitic stainless steel, those using SUS-329J1 and A-SUS-329LJ2, which are austenitic / ferritic stainless steels, as metal holders have polar cores. The crack occurrence rate is remarkably reduced, which is industrially beneficial.

The TbBi-based garnet film and the TbBi-based garnet film were used as a Faraday rotator and combined with a Sm ₂ Co _17- based magnet to form an isolator. there were.

[0022]

According to the present invention, it is possible to provide an optical isolator which is free from deterioration of optical characteristics and reduces damage such as cracking of an optical element (polar core).

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical isolator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizer (polar core) 1a Analyzer (polar core) 2 Metal holder 3 Faraday rotation element 4 Permanent magnet 5 External holder

Claims (1)

[Claims] An optical isolator in which a ceramic polarizer and an analyzer disposed before and after a Faraday rotator to which a magnetic field generated by a permanent magnet is applied is held by soldering to a metal holder. Made holder,
An optical isolator characterized by being an austenitic ferritic stainless steel.