JP3688865B2 - Method for manufacturing device for optical isolator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical isolator element used for removing return light generated when various kinds of optical elements and optical fibers are introduced from light emitted from a light source.
[0002]
[Prior 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 or scattered on end surfaces or inside of the various optical elements or optical fibers. To do. A part of the reflected and scattered light tries 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 is configured by installing a flat Faraday rotator between two polarizers, and housing these three components in a cylindrical magnet via a component holder. . Here, normally, the Faraday rotator is set to a thickness that rotates the polarization plane of light of a predetermined wavelength in the saturation magnetic field by 45 °, and the two polarizers have their transmission polarization directions shifted in the 45 ° rotation direction. The rotation is adjusted. In the optical isolator having the above structure, the Faraday rotator and the two polarizers are separate parts, and a holder is required for each element. Therefore, the number of parts increases, the number of assembly steps increases, and the size cannot be reduced. The assembly adjustment of the micro optical element is necessary, and the work becomes complicated. Therefore, as shown in FIG. 3, the applicant reduced the number of parts and increased productivity by laminating and integrating the polarizers 3 and 4 and the Faraday rotator 2 with an optical adhesive 22. An optical isolator 20 using the optical isolator element 21 has been proposed (see Japanese Patent Application Laid-Open No. 4-338916). In addition, when each optical element is bonded, the adhesive is peeled off in a high humidity environment. Therefore, it has been proposed to provide a sealing material with a metal thin film or resin coated on the side surface. In the case of producing the optical isolator element 21, a method of obtaining a large number of optical isolator elements 21 by alternately integrating a large polarizer substrate and a Faraday rotator substrate with an optical adhesive. By using, there is an advantage that workability and production volume can be increased and the number of parts such as holders can be reduced.
[0003]
[Problems to be solved by the invention]
However, as described above, the optical isolator element in which plate-like polarizers are bonded and integrated on both surfaces of the Faraday rotator with an optical adhesive has the following problems.
[0004]
(1) Since the opening (the portion through which light is transmitted) is fixed with an optical adhesive, it is inferior in moisture resistance, and its use under high temperature and high humidity conditions is particularly limited.
[0005]
{Circle around (2)} Since the opening is fixed with an optical adhesive, there is a possibility of deterioration of the adhesive layer when used for a long time or in a high-power laser beam, and there is a problem in reliability.
[0006]
(3) The outgas generated from the optical adhesive may adversely affect other parts. In particular, the installation in the semiconductor laser package has an adverse effect on the light emission characteristics of the semiconductor laser chip, so that it cannot be installed in the package, leading to an increase in the size of the apparatus. The present invention has been made in view of the above points, and its purpose is to provide a highly reliable optical isolator element that is excellent in moisture resistance and light resistance and that can be installed in a semiconductor laser package without generation of outgas. It is to provide. It is another object of the present invention to provide a method for manufacturing an optical isolator element having a small number of parts and an assembling man-hour and high productivity.
[0007]
[Means for Solving the Problems]
The method for manufacturing an optical isolator element of the present invention includes a step of alternately arranging a plurality of strip-shaped Faraday rotator substrates and a plurality of joining members formed in a columnar shape at regular intervals between the plurality of polarizer substrates. And a step of melting and solidifying the joining member to form a laminated substrate in which the plurality of polarizer substrates and a plurality of Faraday rotator substrates are integrated, and a step of cutting the laminated substrate to a desired size. It is characterized by.
[0008]
As described above, since the optical isolator element of the present invention has the optical element arranged with a space on the optical path, there is no optical adhesive or the like in the opening. For this reason, there is no deterioration in characteristics even under high temperature and high humidity conditions, high power, and long-time use in laser light. Moreover, since each optical element is integrated by the bonding material, the number of parts such as a holder constituting the optical isolator can be reduced, and the optical isolator can be downsized. Moreover, since the optical isolator element is bonded only at the two opposite side surfaces and the other side surfaces are not bonded, the surface of the internal optical element attached when the optical isolator element is made can be cleaned. Therefore, a low insertion loss can be obtained. In addition, when the four side surfaces are completely joined, the internal air expands and contracts due to changes in the external temperature and pressure, and the optical isolator element is distorted, which may result in property deterioration and damage to the joint or optical element. However, according to the present invention, there is no problem of breakage because air enters and exits from the unjoined portion (open end). In addition, a large number of substrates are used for optical adjustment and bonding, and then a large number of pieces are cut out. Therefore, a large number of uniform and excellent optical isolator elements can be easily produced, reducing the number of assembly steps. And excellent in mass productivity. Further, since an inorganic material such as low-melting glass or solder is used as the bonding material, no organic outgas is generated from the optical isolator element. Therefore, an optical isolator element can be installed in the semiconductor laser package, and the device can be downsized and the characteristics can be stabilized.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
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 the figure, this optical isolator element 1 includes a flat Faraday rotator 2, flat polarizers 3 and 4 arranged with spaces on both sides thereof, and a low melting point glass as a bonding agent. It is composed of five. Each optical element (the Faraday rotator 2 and the polarizers 3 and 4) is a portion other than the opening A which is a surface through which light is transmitted, and has two spaces facing each other with a space t on the optical path. ing.
[0010]
Joining is performed by melting and solidifying low-melting glass. Here, the Faraday rotator 2 is composed of a bismuth-substituted garnet crystal or the like, and the thickness of the Faraday rotator 2 is that of light incident on the Faraday rotator 2 when a saturation magnetic field in the direction of the optical axis L is applied to the Faraday rotator 2. The polarization plane has a thickness required to rotate around the 45 ° optical axis. In order to apply a magnetic field to the Faraday rotator 2 when used as an optical isolator, it is necessary to arrange the optical isolator element 1 in the magnet. In this embodiment, the magnet and the optical isolator element 1 are held. The configuration of the holder and the like to be omitted is omitted. If a self-biased Faraday rotator is used, an optical isolator can be formed without a magnet, and further miniaturization can be realized.
[0011]
The two polarizers 3 and 4 are composed of 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 birefringent polarizers having a function of separating the polarizers. Yes. Here, the transmission polarization directions of both polarizers are relatively shifted around the 45 ° optical axis. The space t on the optical path of each optical element can be accurately set according to the size, firing temperature, and firing time of the low-melting glass 5. 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, the characteristics due to the alteration of the adhesive layer can be used for a long time or in a high-power laser beam. There is no possibility of reduction, and an optical isolator element having excellent reliability can be provided.
[0012]
It shows excellent reliability even under high temperature and high humidity conditions. Further, since an inorganic material such as low-melting glass or solder is used as the bonding material, no organic outgas is generated from the optical isolator element 1. In general, a semiconductor laser chip made of GaAs or the like has an oxide film formed on its surface by a slight residual oxygen, and a decrease in oscillation efficiency is observed. Therefore, the package in which the semiconductor laser chip is installed is hermetically sealed with an inert gas such as nitrogen gas. Naturally, it is impossible to install a component that generates outgas in the sealed package. Here, outgas is mainly generated from an organic bonding material, and the optical isolator element of the present invention using an inorganic material such as low melting glass or solder as the bonding material has almost no outgassing as described above. Moreover, since it is small in size, it can be installed in a package like a semiconductor laser chip or a lens. Therefore, a high performance and very small semiconductor laser module can be provided.
[0013]
Furthermore, 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. For example, ultrasonic cleaning with an alcohol solution such as ethanol or cleaning with an air duster is possible. Further, even when a change in temperature or pressure of the external atmosphere occurs, the open end does not cause expansion or contraction of air inside the optical isolator element, and therefore, deterioration of characteristics due to strain or breakage is eliminated. Here, the low melting point glass used is composed of a glass material that melts at about 450 ° C. or less, which is the heat resistant temperature of each optical element.
[0014]
FIG. 2 is a diagram showing a manufacturing procedure of the optical isolator element 1 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 low-melting glass preforms 15 formed in a columnar shape are prepared. . Next, as illustrated in FIG. 2B, the polarizer substrate 13, the Faraday rotator substrate 12, the low melting point glass preform 15, and the 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 placed in close contact with each other between the polarizer substrates 13 and 14. In order to provide an air layer between the Faraday rotator substrate 12 and the polarizers 13 and 14, it is desirable to place a spacer in advance.
[0015]
Next, as shown in FIG. 2C, a laminate of the polarizer substrate 13, the plurality of Faraday rotator substrates 12, the low melting glass preform 15, and the polarizer substrate 14 is melted into the low melting glass preform 15. A low-melting glass preform is melted in a high-temperature furnace 6 set at a working temperature and fired and integrated. The melting temperature of the low melting point glass is a temperature that does not exceed the heat resistance temperature of each optical element and is about 450 ° C. or lower. After baking for several minutes, the temperature is returned to room temperature, and the three optical element substrates are integrated by melting and solidifying the low-melting glass 15 to obtain an element substrate 11 for an optical isolator. At this time, in the optical isolator element substrate 11, the polarizer substrates 13 and 14 and the plurality of Faraday rotator substrates 12 are joined and integrated by the low melting point glass 15.
[0016]
Here, the polarizer substrates 13 and 14 can be joined without optical adjustment if their transmission polarization directions are precisely defined. When the optical isolator is required to have high characteristics, the polarizer substrate 13 and the polarizer substrate 14 can be joined and integrated by adjusting around the optical axis while monitoring the light transmission power. The polarizer substrates 13 and 14 and the Faraday rotator substrate 12 are preferably provided with an antireflection coating in advance. This is to prevent Fresnel reflection caused by the difference in refractive index between each substrate, the low-melting glass layer and the air layer. Next, the integrated optical isolator element substrate 11 is cut at the cutting width W leaving the bonding width X at the center of the bonding portion and the line perpendicular thereto, as shown in FIG. A large number of optical isolator elements 1 as shown in (e) are cut and washed to produce an optical isolator element having a uniform shape and characteristics. For example, the interior of the optical isolator element 1 can be cleaned by immersing it in an alcohol-based cleaning agent or an alkaline aqueous cleaning agent and performing ultrasonic cleaning.
[0017]
Thus, 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. Further, by using a low melting point 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 accuracy and with good reproducibility. In this embodiment, the method of using a low-melting-point glass columnar preform has been described. However, the present invention is not limited to this, and a metal solder preform or screen printing of a bonding material directly on an optical element instead of a preform. As long as it is linear, its thickness and width can be set as required. In the present embodiment, a configuration with two polarizers and one Faraday rotator was used. However, the present invention is not limited to this, and a similar manufacturing method using a larger number of polarizers and Faraday rotators is used. It is also possible to produce an optical isolator element.
[0018]
【The invention's effect】
As described above, the optical isolator element and the manufacturing method thereof according to the present invention have the following excellent effects.
[0019]
{Circle around (1)} Since each optical element is fixed at a portion other than the opening A, there is no possibility of deterioration of the bonding material even if it is used for a long time or in a high-power laser beam, and it is excellent in reliability.
[0020]
(2) Since each optical element is bonded with an inorganic material such as low melting point glass or metal solder, no outgas is generated and the moisture resistance is excellent.
[0021]
(3) Since each optical element is directly integrated, the number of parts such as a holder constituting the optical isolator can be reduced, and the optical isolator can be miniaturized.
[0022]
{Circle around (4)} Since the joint has an open side surface, the internal optical element can be cleaned. In addition, even when a change in the temperature or pressure of the external atmosphere occurs, the open end eliminates deterioration in characteristics due to distortion and breakage.
[0023]
(5) In the method of manufacturing an optical isolator element, since it can be manufactured with a large optical element substrate, mass productivity is improved and cost can be reduced. In addition, 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 good 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 view 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]
DESCRIPTION OF SYMBOLS 1 Optical isolator element 2 Faraday rotator 3, 4 Polarizer 5 Low melting glass 6 High temperature furnace 11 Optical isolator element substrate 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 (2)

A step of alternately arranging a plurality of strip-shaped Faraday rotator substrates and a plurality of columnar joining members at regular intervals between the plurality of polarizer substrates ;
A step of melting and solidifying the joining member to form a laminated substrate in which the plurality of polarizer substrates and the plurality of Faraday rotator substrates are integrated ;
The method of manufacturing an optical isolator element characterized Rukoto to have a the step of cutting the stacked substrate into a desired size. In the step of disposing the plurality of Faraday rotator substrates and the plurality of bonding members between the plurality of polarizer substrates,
  2. The method for manufacturing an optical isolator element according to claim 1, wherein a spacer is provided in advance to provide an air layer between the plurality of Faraday rotator substrates and the plurality of polarizer substrates.

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