JPH08262372A - Optical isolator - Google Patents

Abstract

PURPOSE: To prevent the deterioration in quenching characteristics by lessening the application of the external stress applied thereon at the time of assembling and packaging and the internal stress generated by a difference in the coefft. of thermal expansion between members and joining materials and shrinkage by drying and expansion by moisture absorption, etc., on a Faraday rotating element. CONSTITUTION: Polarizer holders 14 respectively internally mounted with polarizers 16 are arranged on both sides of a hollow permanent magnet 10 internally mounted with the Faraday rotating element 12 and a cylindrical metallic pipe 18 is put and fixed on their outer peripheries. The Faraday rotating element 12 is directly fixed to the inside wall of the hollow permanent magnet 10 and is integrated thereto by coupling the permanent magnet 10 and the polarizer holders 14 on both sides thereof. The integrated member is fixed to the inner peripheral surface of the metallic pipe 18 only at the outer peripheral part of the polarizer holders 14, by which a spacing is formed between the permanent magnet 10 and the metallic pipe 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator used in an optical communication system, an optical measuring system, etc., and more specifically, a hollow permanent magnet in which a Faraday rotator is mounted and a position outside thereof. The present invention relates to an optical isolator in which a gap is formed between a metal pipe and a metal pipe to prevent deterioration of extinction characteristics due to external and internal stress.

[0002]

2. Description of the Related Art An optical isolator is a nonreciprocal optical device that allows the passage of light in one direction but blocks the passage of light in the opposite direction. For example, laser light is used in an optical communication system using a semiconductor laser as a light source. Is used to prevent returning to the light source side by reflection. This type of optical isolator has a structure in which polarizer holders with polarizers are arranged on both sides of a hollow permanent magnet with a Faraday rotator inside, and a metal pipe is attached to the outer circumference of the holders to fix them. Has been adopted. Here, the metal pipe has a function of holding and fixing the polarizer holder and the permanent magnet, and a function of reinforcing / protecting the whole and attaching it to an external device (a substrate or the like).

The Faraday rotator is made of various magneto-optical crystals and is set to have a thickness such that the plane of polarization of incident light is internally rotated by 45 degrees by a magnetic field generated by a permanent magnet. This type of magneto-optical crystal has an external stress (a stress received during the assembly of an optical isolator or a mounting on an external device) and an internal stress (a difference in thermal expansion coefficient between optical isolator constituent members and a bonding material, and drying shrinkage / contraction). If stress due to hygroscopic expansion is applied, the crystal is distorted and the extinction characteristic of the crystal deteriorates. Therefore, the following measures have been taken in order to prevent the extinction characteristic of the crystal from deteriorating. By inserting the Faraday rotator fixed to the Faraday rotator holder into the hollow permanent magnet, the Faraday rotator and permanent magnet do not come into direct contact, and stress is transmitted to the Faraday rotator. Block. Aligning the thermal expansion coefficients of the permanent magnet and the metal pipe, or the bonding material used to fix them together, prevents stress generation due to temperature fluctuations. By using a soft material (soft adhesive) as the bonding material used for fixing the permanent magnet and the metal pipe, it becomes difficult for stress to be transmitted to the Faraday rotator through the permanent magnet.

As a concrete example of the above, Japanese Patent Laid-Open No. 5-173
091 discloses Cd _1-X Mn _X Te (0 <X ≦ 0.
7) Regarding an optical isolator using a Faraday rotator made of a single crystal, a Faraday rotator is attached to the tip of a Faraday rotator holder arranged outside a hollow permanent magnet, and inserted into the hollow permanent magnet. A technique has been proposed in which the Faraday rotator is prevented from coming into contact with the inner wall surface of the permanent magnet so as not to receive the stress of the adhesive and prevents the deterioration of the extinction characteristic.

[0005]

As described above, the structure using the Faraday rotator element holder requires a separate part called the Faraday rotator element holder, which increases the number of parts. Further, in the structure in which a flange is provided on the Faraday rotator holder and arranged outside the hollow permanent magnet, not only the axial length becomes longer, but also the flange becomes an obstacle when arranging the polarizer holders on both sides. . In the case of the above structure, it is actually difficult to make the thermal expansion coefficients of the respective members equal. Furthermore, when a soft adhesive or the like is used as the joining material, the reliability is poor and the feasibility is poor.

An object of the present invention is that external stress applied during assembly and mounting, and internal stress generated due to difference in thermal expansion coefficient between members and bonding materials, dry shrinkage, hygroscopic expansion, etc. are applied to the Faraday rotator. It is to provide an optical isolator having a structure in which the deterioration of the extinction characteristic is prevented by reducing the above, and thereby the manufacturing yield can be improved.

[0007]

According to the present invention, a polarizer holder having a polarizer installed therein is arranged on each side of a hollow permanent magnet having a Faraday rotation element installed therein.
It is an optical isolator having a structure in which a cylindrical metal pipe is covered on and fixed to the outer circumference thereof. In the present invention, the Faraday rotator is directly fixed to the inner wall of the hollow permanent magnet, and the permanent magnet and the polarizer holders on both sides thereof are integrally coupled,
This integrated member is fixed to the inner peripheral surface of the metal pipe only by the outer peripheral portion of the polarizer holder, and a gap is provided between the permanent magnet and the metal pipe, which is a feature of this point.

For that purpose, for example, the outer diameter of the permanent magnet is made smaller than the outer diameter of the polarizer holder so that a noticeable gap is formed between the outer peripheral surface of the permanent magnet and the inner peripheral surface of the metal pipe. To do. Conversely, a part of the inner peripheral surface of the metal pipe may have a large diameter. Alternatively, the outer diameter of the permanent magnet and the outer diameter of both the polarizer holders should be the same, and the outer peripheral surface of the permanent magnet or the surface of the metal pipe facing the permanent magnet should be a surface on which solder does not adhere (for example, a non-plated surface). You may solder to the inner peripheral surface of a metal pipe only with the outer peripheral part of a child holder. This soldering can be easily performed by inserting a sheet-shaped solder into the soldering place. Instead of soldering, it is possible to use adhesive bonding or welding. Both polarizer holders may be fixed to the metal pipes, but fixing only one of the polarizer holders to the metal pipe reduces the stress applied to the permanent magnet.

[0009]

[Function] Since a gap is formed between the hollow permanent magnet and the metal pipe located outside the hollow magnet, and the structure is not fixed directly, when assembling the optical isolator or mounting it on an external device (board) The external stress applied, and the internal stress generated due to the difference in thermal expansion coefficient between the constituent members and the bonding material, dry shrinkage, and hygroscopic expansion, are difficult to be transmitted to the Faraday rotator through the permanent magnet, and the extinction characteristics of the extinction characteristic due to stress application Deterioration is suppressed. The reduction of the deterioration factor of the extinction characteristic contributes to the improvement of manufacturing yield.

[0010]

1 is an assembly explanatory view showing an embodiment of an optical isolator according to the present invention, and FIG. 2 is a sectional view after the assembly. The Faraday rotation element 12 is mounted inside the hollow permanent magnet 10, and the polarizer 1 is installed inside the polarizer holder 14.
Wear 6. The Faraday rotation element 12 is composed of a magneto-optical crystal (for example, a non-magnetic garnet substrate on which a Bi-substituted iron garnet single crystal film is grown by the LPE method), and is attached to the inner wall surface of the hollow permanent magnet 10 by adhesion or glass fusion. It is fixed directly (without using another member such as a holder). The polarizer holder 14 has a shape similar to that of the permanent magnet 10 and is made of ceramics or the like. Then, the polarizer (for example, polarizing glass) 16 is fixed inside the polarizer holder 14 with an adhesive. Such a polarizer 16
Two polarizer holders 14 each having a built-in are used and are arranged on both sides of the permanent magnet 10.

In this embodiment, the outer diameter of the permanent magnet 10 is designed to be slightly smaller than the outer diameter of the polarizer holders 14 on both sides. Next, the polarizer 16 and the Faraday rotator 1
2. The angle is adjusted so that the rows of the polarizer 16 have desired characteristics, and the polarizer holder 14, the permanent magnet 10, and the polarizer holder 14 are bonded together at their end faces to be integrated. This integrated member is inserted and fixed in the cylindrical metal pipe 18. The metal pipe 18 is usually a stainless steel cylinder whose surface is plated with gold. Since the outer diameter of the permanent magnet 10 is smaller than the outer diameter of the polarizer holder 14, a noticeable gap is generated between the permanent magnet 10 and the inner peripheral surface of the metal pipe 18. It is fixed to the metal pipe 18 only by itself, and the permanent magnet 10 is not directly fixed to the metal pipe 18. The metal pipe 18 and the polarizer holder 14 may be fixed by adhesion or soldering. In this embodiment, only one of the polarizer holders (the right polarizer holder in FIG. 2) is soldered to the metal pipe, and the solder material is indicated by reference numeral 19.

In this embodiment, since a large gap is formed between the permanent magnet 10 and the metal pipe 18 and is not directly fixed, external stress is applied to the permanent magnet when the optical isolator is mounted on an external device. It's hard to join in 10. Further, the stress inside the optical isolator caused by the difference in the coefficient of thermal expansion between the constituent members and the bonding material, the drying shrinkage and the hygroscopic expansion of the adhesive, and the like is not easily applied to the permanent magnet 10. Those results,
The external / internal stress applied to the Faraday rotation element 12 will be reduced.

Further, in the case of this embodiment, the spacer tube may be loosely fitted on the outer side of the permanent magnet 10. This spacer tube includes a first polarizer holder, a permanent magnet and a second polarizer holder.
This is for making the outer diameters of the polarizer holders uniform and facilitating the characteristic adjustment and the joining work. By loosely fitting the spacer tube, stress is reduced from the metal pipe through the permanent magnet.

3 to 7 show another embodiment of the optical isolator according to the present invention. The members corresponding to those in FIGS. 1 and 2 are designated by the same reference numerals to simplify the description.

In the example shown in FIG. 3, contrary to the above embodiment, the permanent magnet 20 has the same outer diameter as the polarizer holder 14, but the inner diameter of the inner peripheral portion of the metal pipe 22 facing the permanent magnet 20 is changed. This is a configuration in which the depressions 23 are enlarged and formed in a circumferential shape.
Thereby, the outer peripheral surface of the permanent magnet 20 and the metal pipe 22
There is a noticeable gap between and. Also in this embodiment, only one of the polarizer holders is soldered to the metal pipe.

In the example shown in FIG. 4, the outer diameter of the permanent magnet 20 is the same as the outer diameter of the polarizer holder 14, and is housed in the metal pipe 18. In the case of such a structure, particularly, the polarizer holder 14 and the metal pipe 18 are fixed only to each other so that a slight gap is formed between the permanent magnet 20 and the metal pipe 18. For that purpose, it is necessary to secure an appropriate clearance between the permanent magnet 20 and the metal pipe 18. For example, when the solder material 19 is used, the outer periphery of the permanent magnet 20 should not be gold-plated, or conversely, the portion of the inner peripheral surface of the metal pipe 18 facing the permanent magnet should not be gold-plated. Masking may be performed so that the soldering area is limited to only the polarizer holder portion. An adhesive may be used instead of soldering, but it is necessary to limit the application area to the portion of the polarizer holder.

In the example shown in FIG. 5, the inner peripheral shape of the metal pipe 26 has a small diameter only in the vicinity of one end so that it can be fitted only to one of the polarizer holders 14, and after the fitting, the welding is performed at the end (welding part). (Indicated by reference numeral 27). In this case, at least one of the polarizer holders is made of weldable stainless steel or the like.

In the example shown in FIG. 6, the metal pipe 28 has a bottomed shape and is soldered to the end face of one of the polarizer holders 14 (solder material is indicated by reference numeral 19) only at the bottom. Adhesion may be used instead of soldering. As in the other embodiments, there is a slight gap between the permanent magnet 20 and the metal pipe 28.

In the example shown in FIG. 7, the metal pipe 30 has a bottomed shape, and the inner peripheral surface of the bottom portion and the end surface of one of the polarizer holders 14 are welded and fixed (the welded portion is denoted by reference numeral 27).
Also in this embodiment, as in the other embodiments, there is a slight gap between the permanent magnet 20 and the metal pipe 30.

[0020]

As described above, according to the present invention, since the permanent magnet and the metal pipe are not directly fixed but are fixed only by the polarizer holder portion, the external stress (of the optical isolator) is fixed. The stress received during assembly or mounting on external equipment) and internal stress (differences in thermal expansion coefficient of optical isolator components and bonding materials, stress due to dry shrinkage / hygroscopic expansion) become permanent Faraday rotator elements through permanent magnets. It becomes difficult for the light to be transmitted, and as a result, deterioration of the extinction characteristic can be prevented. Then, the factor of deterioration of the extinction characteristic is reduced, so that the manufacturing yield is improved.

[Brief description of drawings]

FIG. 1 is an assembly process diagram showing an embodiment of an optical isolator according to the present invention.

FIG. 2 is a sectional view of the assembled state.

FIG. 3 is a sectional view showing another embodiment of the optical isolator according to the present invention.

FIG. 4 is a sectional view showing another embodiment of the optical isolator according to the present invention.

FIG. 5 is a sectional view showing another embodiment of the optical isolator according to the present invention.

FIG. 6 is a sectional view showing another embodiment of the optical isolator according to the present invention.

FIG. 7 is a sectional view showing another embodiment of the optical isolator according to the present invention.

[Explanation of symbols]

 10, 20 Permanent magnet 12 Faraday rotation element 14 Polarizer holder 16 Polarizer 18, 22, 26 Metal pipe 19 Bonding material

Claims (3)

[Claims] 1. A polarizer holder having a polarizer inside is arranged on each side of a hollow permanent magnet having a Faraday rotator inside, and is fixed by covering a cylindrical metal pipe on the outer periphery thereof. In the optical isolator, the Faraday rotator is directly fixed to the inner wall of the hollow permanent magnet, and the permanent magnet and the polarizer holders on both sides of the permanent magnet are combined and integrated, and this integrated member is attached to the polarizer holder. An optical isolator, wherein the optical isolator is fixed to the inner peripheral surface of the metal pipe only at the outer peripheral portion, and a gap is provided between the permanent magnet and the metal pipe. 2. The optical isolator according to claim 1, wherein only the outer peripheral portion of one of the polarizer holders is bonded to the inner peripheral surface of the metal pipe. 3. The optical isolator according to claim 2, wherein the inner diameter of a portion near one end of the metal pipe is reduced so that one of the polarizer holders is fitted, and the outer end face of the fitting portion is fixed by welding.