JPH11101952A - Element for optical isolator and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a small sized element for an optical isolator, which is excellent in the reliability of moisture resistance and light resistance, in an easy manufacturing process. SOLUTION: The element 1 for the optical isolator, which is in a nearly rectangular parallelepiped form, is constituted by laminating a Farady rotator 2 and a pair of polarizers 3, 4, which oppose each other via this Farady rotator 2, via joining members 5. The element 1 for the optical isolator, in which there is no possibility that the joining members 5 may be deteriorated even if used for a long period of time or in a high output laser beam, can be provided because the element 1 for the optical isolator is constituted of the polarizers 3, 4 and a pair of the joining members 5 opposing to the polarizers 3, 4. The joining members 5 are constituted of low-melting glass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for an optical isolator used for removing return light generated when light emitted from a light source is introduced into various optical elements or optical fibers.

[0002]

2. Description of the Related Art Conventionally, light emitted from a light source such as a laser light source is incident on various optical elements and optical fibers, and a part of the incident light is reflected on the end faces and inside of the various optical elements and optical fibers. Or scattered. Some of the reflected and scattered light tends to return to the light source as return light, and an optical isolator is used to prevent the return light. Conventionally, this type of optical isolator has a configuration in which a flat Faraday rotator is installed between two polarizers, and these three components are housed in a cylindrical magnet via a component holder. . Here, usually, the Faraday rotator changes the plane of polarization of light of a predetermined wavelength in a saturation magnetic field by 45 °.
The thickness is set to a rotating thickness, and the two polarizers are rotationally adjusted so that their transmission polarization directions are shifted by 45 ° in the rotation direction. In the optical isolator having the above structure,
The Faraday rotator and the two polarizers are separate parts, and each element requires a holder, which increases the number of parts and the number of assembly steps, making it impossible to reduce the size. Therefore, the operation becomes complicated. Therefore, as shown in FIG. 3, the present applicant bonded the polarizers 3 and 4 and the Faraday rotator 2 with an optical adhesive 22 and laminated and integrated them, thereby reducing the number of parts and increasing the productivity. An optical isolator 20 using an optical isolator element 21 has been proposed (JP-A-4-3389).
No. 16). When each optical element is bonded,
Since the adhesive is peeled off in a high-humidity environment, it has been proposed to provide a sealing material having a side surface coated with a metal thin film or a resin. This optical isolator element 21
In the case of manufacturing, a large polarizer substrate and a Faraday rotator substrate are alternately integrated with an optical adhesive, and this is cut to obtain a large number of optical isolator elements 21. There is an advantage that the performance and production amount can be increased, and the number of parts such as holders can be reduced.

[0003]

However, as described above, the element for an optical isolator in which a plate-like polarizer is adhered to both surfaces of a Faraday rotator with an optical adhesive and integrated has the following problems. .

Since the opening (portion through which light is transmitted) is fixed with an optical adhesive, it has poor moisture resistance, and its use under high-temperature, high-humidity conditions is particularly limited.

[0005] Since the opening is fixed with an optical adhesive, there is a possibility that the adhesive layer may be deteriorated when used for a long time or in a high-output laser beam, and there is a problem in reliability.

[0006] Outgas generated from the optical adhesive may adversely affect other components. In particular, installation in a semiconductor laser package cannot be installed in the package because the outgas adversely affects the emission characteristics of the semiconductor laser chip, leading to an increase in the size of the device. The present invention has been made in view of the above points, and its purpose is to provide excellent moisture resistance and light resistance, and can be installed in a semiconductor laser package without generating outgas.
An object of the present invention is to provide a highly reliable optical isolator element. It is still another object of the present invention to provide a method for manufacturing an optical isolator element having a small number of parts and a small number of assembling steps and high productivity.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and has a Faraday rotator for rotating the polarization direction of light in accordance with the direction of a magnetic field applied in the direction of a central axis. In an optical isolator element in which a pair of polarizers facing each other via the Faraday rotator are stacked via a bonding member, the optical isolator element has a substantially rectangular parallelepiped shape, and the polarizer and Provided is an optical isolator element in which the Faraday rotator is joined to a polarizer by a side wall portion formed of a pair of joining members facing each other, and the Faraday rotator is joined between wall surfaces of the pair of side wall portions.

As described above, in the optical isolator element of the present invention, since the optical element is arranged with a space on the optical path, there is no optical adhesive or the like in the opening. Therefore, there is no deterioration in the characteristics even under the condition of high temperature and high humidity, high output, and use in laser light for a long time. Further, since each optical element is integrated by a bonding material, the number of components such as a holder constituting the optical isolator can be reduced, and the size of the optical isolator can be reduced. In addition, since the optical isolator element is bonded only on two opposing side surfaces, and the other side surface is not bonded, it is possible to clean dirt on the surface of the internal optical element adhered at the time of manufacturing the optical isolator element,
Therefore, a low insertion loss is obtained. In addition, when the four sides are completely joined, the internal air expands and contracts due to changes in the external temperature and atmospheric pressure, and the element for the optical isolator is distorted. Therefore, there is a risk of deterioration in characteristics and damage to the joint or the optical element. However, according to the present invention, there is no problem of breakage because air flows in and out from an unjoined portion (open end). In addition, since optical adjustment and bonding are performed on a large-sized substrate, and then a large number of pieces are cut out, a large number of elements for optical isolators with uniform and excellent characteristics can be easily manufactured, and the number of assembly steps can be reduced. And is excellent in mass productivity. In addition, since an inorganic material such as low-melting glass or solder is used for the bonding material, no organic outgas is generated from the optical isolator element. Therefore, the element for the optical isolator can be installed in the semiconductor laser package, and the miniaturization of the device and the stabilization of the characteristics are realized.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a configuration of an optical isolator element 1 according to the present invention. As shown in FIG. 1, the optical isolator element 1 includes a flat Faraday rotator 2, flat flat polarizers 3 and 4 disposed on both sides of the flat Faraday rotator 2, and a low-melting glass as a bonding agent. 5 is comprised. Each of the optical elements (the Faraday rotator 2 and the polarizers 3 and 4) is bonded to two opposing side surfaces with a space t on the optical path at a portion other than the opening A which is a surface through which light is transmitted. ing.

The joining is performed by melting and solidifying the low melting point glass. Here, the Faraday rotator 2 is made of a bismuth-substituted garnet crystal or the like, and the thickness of the Faraday rotator 2 is the thickness of light incident on the Faraday rotator 2 when a saturation magnetic field in the optical axis L direction is applied to the Faraday rotator 2. The polarizing plane is configured to have a thickness necessary to rotate around the optical axis by 45 °. When used as an optical isolator, in order to apply a magnetic field to the Faraday rotator 2, it is necessary to arrange the optical isolator element 1 in a magnet. In the present embodiment, the magnet and the optical isolator element 1 are held. The configuration of the holder and the like is omitted. Also, if a self-biased Faraday rotator is used, an optical isolator can be configured without a magnet, and further miniaturization can be realized.

The two polarizers 3 and 4 are absorption polarizers having a function of absorbing a polarization component in one direction of light incident in the direction of the optical axis L, or a birefringent polarizer having a function of separating light. It is configured. Here, the transmission polarization directions of both polarizers are relatively shifted about the optical axis by 45 °.
The space t on the optical path of each of these optical elements is a low melting glass 5
Can be set accurately by the size, firing temperature, and firing time. Therefore, since the optical isolator element 1 of the present invention has no substance other than the air layer in the opening A between the optical elements, even if used for a long time or in a high-power laser beam, the characteristic due to the deterioration of the adhesive layer is obtained. It is possible to provide an optical isolator element with high reliability without a possibility of reduction.

[0012] Similarly, even under high temperature and high humidity conditions, excellent reliability is exhibited. Further, since an inorganic material such as low-melting glass or solder is used for the bonding material, no organic outgas is generated from the optical isolator element 1. In general, an oxide film is formed on the surface of a semiconductor laser chip made of GaAs or the like due to a slight amount of residual oxygen, and a decrease in oscillation efficiency is observed. Therefore, the package on which the semiconductor laser chip is installed is hermetically sealed with an inert gas such as nitrogen gas. Naturally, it is impossible to install components that generate outgas in the sealed package. Here, the outgas is mainly generated from an organic bonding material, and the optical isolator element of the present invention using a low melting point glass or an inorganic material of solder as the bonding material is:
As described above, since there is almost no outgassing and the size is small, it can be installed in a package like a semiconductor laser chip or a lens. Therefore, a very high performance and very small semiconductor laser module can be provided.

Further, since the optical isolator element of the present invention does not completely seal and has an open side surface, the internal optical element can be cleaned. The cleaning can be performed, for example, by ultrasonic cleaning using an alcohol solution such as ethanol, or cleaning using an air duster. Further, even when the temperature or the atmospheric pressure of the external atmosphere changes, the open end does not cause expansion or contraction of the air inside the optical isolator element, so that the characteristics are not deteriorated or damaged due to the distortion. Here, the low melting point glass used is made of a glass material that melts at about 450 ° C. or less, which is the heat resistant temperature of each optical element.

FIG. 2 is a view showing a manufacturing procedure of the element 1 for an optical isolator according to the present invention. First, as shown in FIG. 1A, plate-shaped polarizer substrates 13 and 14, a plurality of strip-shaped Faraday rotator substrates 12, and a plurality of column-shaped low-melting glass preforms 15 are prepared. . next,
As shown in FIG. 2B, a polarizer substrate 13, a Faraday rotator substrate 12, a low-melting glass preform 15, and a polarizer substrate 14 are laminated in this order. At this time, the Faraday rotator substrate 12 and the low-melting-point glass preform 15 are alternately placed between the polarizer substrates 13 and 14. Also,
In order to provide an air layer between the Faraday rotator substrate 12 and the polarizers 13 and 14, it is desirable to provide a spacer in advance.

Next, as shown in FIG. 2C, a laminate of a polarizer substrate 13, a plurality of Faraday rotator substrates 12, a low-melting glass preform 15, and a polarizer substrate 14 is replaced with a low-melting glass preform. The low-melting-point glass preform is melted in a high-temperature furnace 6 set to a melting operation temperature of 15 and is fired and integrated. The melting temperature of the low-melting glass should not exceed the heat-resistant temperature of each optical element and should be approximately 450 ° C. or less. After baking for several minutes, the temperature is returned to normal temperature, and the three optical element substrates are integrated by melting and solidifying the low-melting glass 15 to obtain the element substrate 11 for an optical isolator. At this time, the optical isolator element substrate 11 is
Accordingly, the polarizer substrates 13 and 14 and the plurality of Faraday rotator substrates 12 are joined and integrated.

Here, if the polarizer substrates 13 and 14 are those whose transmission polarization directions are precisely defined,
It is possible to join without optical adjustment. When high characteristics are required for the optical isolator, the polarizer substrate 13 and the polarizer substrate 14 can be adjusted around the optical axis while monitoring the light transmission power, and can be joined and integrated. The polarizer substrates 13 and 14 and the Faraday rotator substrate 1
It is desirable to apply an anti-reflection coat to 2 in advance. This is to prevent Fresnel reflection caused by the difference in the refractive index between each substrate, the low melting point glass layer, and the air layer. Next, the integrated optical isolator element substrate 1
1 (d), the center of the junction and a line perpendicular to the center of the junction are cut at a cutting width W leaving a junction width X, and an optical isolator element 1 as shown in FIG. It is possible to manufacture an optical isolator element having a uniform shape and characteristics by cutting a large number of pieces and cleaning them.
For cleaning, the inside of the optical isolator element 1 can be cleaned by immersing in, for example, an alcohol-based cleaning agent or an alkaline aqueous solution-based cleaning agent and performing ultrasonic cleaning.

As described above, according to the manufacturing method of the present invention, it is possible to manufacture a large number of optical isolator elements simultaneously in a short time with a small number of assembly adjustment steps. In addition, by using the low-melting glass preformed in a columnar shape, the size of the opening A, the optical element interval t, and the bonding width X can be manufactured with high precision and with good reproducibility. In the present embodiment, a method using a columnar preform of low melting point glass was described, but the present invention is not limited to this, and a bonding material is screen-printed directly on an optical element instead of a preform of metal solder, or a preform. It is sufficient if the thickness and width can be set as required in a straight line. Further, in the present embodiment, the configuration using two polarizers and one Faraday rotator was used, but the present invention is not limited to this, and the same manufacturing method is used by using a larger number of polarizers and Faraday rotators. It is also possible to manufacture an element for an optical isolator.

[0018]

As described above, the optical isolator element and the method of manufacturing the same according to the present invention have the following excellent effects.

Since each optical element is fixed in a portion other than the opening A, there is no possibility that the bonding material is deteriorated even when used for a long time or in a high-output laser beam, and the reliability is excellent.

Since each optical element is joined with an inorganic material such as low-melting glass or metal solder, no outgas is generated and the moisture resistance is excellent.

Since each optical element is directly integrated,
The number of components such as a holder constituting the optical isolator can be reduced, and the size of the optical isolator can be reduced.

Since the joint has an open side surface, the internal optical element can be cleaned. Further, even when a change in the temperature or the atmospheric pressure of the external atmosphere occurs, deterioration of the characteristics due to the distortion and damage due to the distortion due to the open end are eliminated.

In the method of manufacturing an element for an optical isolator, since it can be manufactured using a large optical element substrate, mass productivity can be improved and cost can be reduced. Further, the bonding interval t, the bonding width X, the opening A, and the size of each optical element can be manufactured with high accuracy and high reproducibility.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an optical isolator element of the present invention.

FIG. 2 is a diagram showing a method for manufacturing an optical isolator element of the present invention.

FIG. 3 is a perspective view showing a conventional optical isolator.

[Explanation of symbols]

 Reference Signs List 1 element for optical isolator 2 Faraday rotator 3, 4 polarizer 5 low melting glass 6 high temperature furnace 11 element substrate for optical isolator 12 Faraday rotator substrate 13, 14 polarizer substrate 15 low melting glass preform 20 optical isolator 21 optical isolator Element 22 optical adhesive 23 magnet

Claims (3)

[Claims] 1. A joining member comprising: a Faraday rotator for rotating the polarization direction of light corresponding to the direction of a magnetic field applied in the direction of a central axis; and a pair of polarizers opposed to each other via the Faraday rotator. In the element for optical isolator laminated via, the element for optical isolator has a substantially rectangular parallelepiped shape, and the polarizer and the polarizer are joined by a side wall portion composed of a pair of joining members opposed to each other. An optical isolator element, wherein the Faraday rotator is further joined between wall surfaces of the pair of side wall portions. 2. The element for an optical isolator according to claim 1, wherein a low melting point glass or metal solder is used for said joining member. 3. A step of alternately disposing a Faraday rotator substrate and substantially linear joining members on one surface of the polarizer substrate at equal intervals, and laminating a polarizer substrate on the Faraday rotator substrate and the joining member. A method for manufacturing an element for an optical isolator, comprising: a step of melting and solidifying the bonding member; and a step of cutting a laminated substrate into which the bonding member has been melted and solidified into a desired size.