JP4456223B2 - Optical isolator - Google Patents

Description

【００４０】
表１から明らかなように、ファラデー回転子の対基板接合面と基板表面との間に接合回避手段を設けて接合・固定した光アイソレータが、接合歪みを回避して光学特性に優れ、接合強度も充分満足することができるものであることがわかる。
【００４１】
なお、本発明は、上記実施形態に限定されるものではない。上記実施形態は、例示であり、本発明の特許請求の範囲に記載された技術的思想と実質的に同一な構成を有し、同様な作用効果を奏するものは、いかなるものであっても本発明の技術的範囲に包含される。
【００４２】
【発明の効果】
以上詳細に説明したように、本発明の光アイソレータは、小型化されてＬＤモジュール内に組み込むのに適しており、光学素子を良好な光学特性となる最適位置に偏光面を調整することが極めて容易で、かつ光学素子の対基板接合強度が極めて高く、さらに接合応力を受けることがなく、そのため大きな逆方向挿入損失を有する信頼性の高い光アイソレータを低コストで提供することができる。
【図面の簡単な説明】
【図１】本発明の光アイソレータの構成例を示す説明図である。
（ａ）斜視図、（ｂ）光学素子および磁石と基板との接合面の状態を表す断面図。
【図２】本発明の光アイソレータのファラデー回転子の対基板接合面または基板表面に設けられる接合回避手段を表す説明図である。
（ａ）凹状の段差による間隙を接合回避手段とした、（ｂ）凸状の段差による間隙を接合回避手段とした、（ｃ）ファラデー回転子の光透過面面積を縮小してできた間隙を接合回避手段とした。
【図３】従来の光アイソレータの構成例を示す説明図である。
（ａ）斜視図、（ｂ）光学素子および磁石と基板との接合面の状態を表す断面図。
【符号の説明】
１、２０…光アイソレータ、
２Ａ、２Ｂ、２２Ａ、２２Ｂ、５２Ａ、５２Ｂ…偏光子（偏光ガラス）、
３、２３、５３…ファラデー回転子、 ４、２４、…平板状基板、
３４、４４…段差を有する基板、 ５１…光学素子、
５Ａ、５Ｂ、２５Ａ、２５Ｂ…永久磁石、
２ｄ、２２ｄ、３２ｄ、４２ｄ、…基板の偏光子接合面、
５２ｄ…偏光子の基板接合面、
３ｃ…ファラデー回転子の接合回避手段を設ける部分、
３３ｃ、４３ｃ、５３ｃ…間隙、 ２３ｄ…基板のファラデー回転子接合面、
５ｄ、２５ｄ…基板の永久磁石接合面。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical isolator used for optical communication, optical information processing, optical measurement, and the like.
[0002]
[Prior art]
Optical isolators are used in optical amplifiers, semiconductor laser devices, and the like.
In this optical isolator, the relative angle between two polarizers is set to about 45 °, and a Faraday rotator with a Faraday rotation angle of about 45 ° is inserted between them to fix them together. It has a function of transmitting light and blocking light in the reverse direction.
[0003]
In recent years, there has been a strong demand for miniaturization, mass production, and cost reduction for this optical isolator. For example, the optical isolator disclosed in Japanese Patent Laid-Open No. 10-227996 has been developed and utilized. It has become.
As shown in FIG. 3 (a), this optical isolator 20 includes a rectangular parallelepiped optical element composed of polarizers 22A and 22B and a Faraday rotator 23 and a rectangular parallelepiped magnet 25A and 25B, which are alloyed or synthesized on a flat substrate 24. It has a structure that is bonded and fixed with a resin adhesive. FIG. 3B shows that the bonding surface by the bonding agent when the optical element and the magnet are bonded to the substrate is the entire surface of the substrate surface. 22d represents a bonding surface of the polarizer, 23d represents a bonding surface of the Faraday rotator, and 25d represents a bonding surface of the magnet.
[0004]
The optical isolator having such a configuration can be easily mounted on a TEC (Thermo Electric Cooler), easily aligned in the LD (laser diode) module, and can be easily miniaturized. It is believed that there is an advantage.
[0005]
However, when a rectangular parallelepiped optical element in which individual optical elements are bonded to a flat substrate is bonded to the flat substrate, there arises a problem that desired optical characteristics cannot be obtained due to distortion during bonding.
[0006]
It is also known that distortion can be mitigated by previously bonding the optical element with a synthetic resin adhesive, particularly a silicone adhesive, in order to avoid bonding distortion of the optical element. However, in this case, sufficient strength cannot be obtained for bonding between the substrate and the optical element, and the optical isolator may be damaged during handling.
[0007]
[Problems to be solved by the invention]
Accordingly, the present invention has been made in view of the above problems. The optical isolator element is bonded and integrated on the substrate, the assembly position can be adjusted with high accuracy, the bonding strength is high, and the bonding distortion of the optical element is avoided. An object of the present invention is to provide a reliable and low-cost optical isolator having excellent optical characteristics.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, an optical isolator according to the present invention includes at least one polarizer and at least one Faraday rotator, and a rectangular parallelepiped optical element bonded with a light transmission surface to a substrate with a bonding agent. In the bonded / fixed optical isolator, the Faraday rotator in the optical element is not bonded to the substrate .
[0009]
In this way, if only the surface of the Faraday rotator in the rectangular parallelepiped optical element facing the substrate is not bonded to the substrate, distortion of the optical element after bonding can be eliminated, and desired optical characteristics can be obtained. It will be obtained. Furthermore, the optical element can be easily aligned with high accuracy, and the optical element can be bonded and fixed with sufficiently strong adhesive strength, and a highly reliable and low-cost optical isolator is provided. Can do.
[0010]
In this case, since the Faraday rotator in the optical element is not bonded to the substrate, a bonding avoiding means can be provided .
In this way, if a means for avoiding bonding is provided so that the Faraday rotator in the optical element is not bonded to the substrate, the distortion of the optical element after bonding is eliminated without reliably bonding the Faraday rotator to the substrate. In addition, desired optical characteristics can be obtained, and alignment of the optical element can be strongly bonded and fixed with high accuracy.
[0011]
In this case, the joining avoiding means can be a material that repels the joining agent .
As described above, if a material that repels the bonding agent is previously attached to the surface of the Faraday rotator as a bonding avoidance means, a bonding agent such as solder or synthetic resin adhesive is attached to the surface of the optical element. However, the bonding agent is repelled only on the surface of the Faraday rotator facing the substrate, and the bonding surface with another bonding agent can be firmly bonded to the substrate and the distortion of the optical element after bonding is eliminated. And deterioration of the optical characteristics can be avoided.
[0012]
In this case, the bonding avoiding means can be a gap provided between the bonding surface of the substrate and the Faraday rotator .
As described above, the same effect as described above can be obtained even if a gap is provided between the bonding surface of the substrate and the Faraday rotator as the bonding avoidance means.
[0013]
Further, in this case, the joining avoiding means may be formed by bonding the light transmitting surface area of the Faraday rotator constituting the optical element smaller than the light transmitting surface area of the polarizer .
[0014]
As described above, even if the joining avoiding means is formed by bonding the light transmitting surface area of the Faraday rotator constituting the optical element to be smaller than the light transmitting surface area of the polarizer, there is nothing for transmitting light such as a laser. Since a gap can be formed on the Faraday rotator-to-substrate bonding surface without affecting the bonding, it is possible to avoid bonding distortion after bonding of the optical element while maintaining bonding strength on the other surface. Can be obtained.
[0015]
In addition, the bonding avoiding means may be configured by forming solder bonding metallization on the side surface portion of the optical element other than the Faraday rotator and soldering to the substrate .
As described above, when solder is used for bonding to the substrate, the Faraday rotator is not subjected to metallization when soldering metallization is formed on the side surface portion of the optical element as a bonding avoidance means. Thus, it is possible to avoid joining the Faraday rotator to the substrate.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
In order to prevent mechanical damage and destruction due to impact, drop, etc. when handling the optical isolator, the present inventors use the bonding agent having a high bonding strength to cause distortion in the optical element, resulting in desired optical characteristics. As a remedy, it was found that a silicone resin adhesive is effective as an adhesive that can alleviate joint distortion, and deterioration of optical properties can be avoided. However, the silicone resin adhesive does not provide high bonding strength, and there is a risk that the optical element may be damaged when the optical isolator is handled.
[0017]
Thus, as a result of various investigations on the cause of the joint distortion, it was found that this distortion was mainly caused by the Faraday rotator. For this reason, it was conceived that optical property deterioration due to bonding distortion can be avoided by providing bonding avoidance means on the surface of the Faraday rotator to the substrate bonding surface in the optical element of the optical isolator. Was completed.
[0018]
FIG. 1A is an explanatory diagram showing an example of the configuration of the optical isolator of the present invention.
This optical isolator 1 is formed by setting a relative angle between two polarizers 2A and 2B to about 45 °, and inserting a Faraday rotator 3 having a Faraday rotation angle of about 45 ° between them to fix them. It is a rectangular parallelepiped optical element, and has a function of transmitting light in the forward direction and blocking light in the reverse direction.
[0019]
As shown in FIG. 1B, the optical element is formed on the optical element bonding surface (polarizer bonding surface 2d, Faraday rotator bonding surface 3c) of the substrate 4, and the rectangular parallelepiped shape is formed on the magnet bonding surface 5d. The permanent magnets 5A and 5B are joined and fixed.
[0020]
In this case, the cross sections of the polarizers 2A and 2B and the Faraday rotator 3 are both rectangular, particularly preferably square, and an optical element is formed by sandwiching the 45 ° Faraday rotator 3 between the two polarizers 2A and 2B. It is preferable to bond and fix to the center of the substrate with a synthetic resin adhesive such as an epoxy resin adhesive. In addition, when heat resistance is required, it is preferable to use solder or low melting point glass for bonding. As the Faraday rotator 3, a single crystal plate such as bismuth-substituted rare earth iron garnet is often used.
[0021]
The magnets 5A and 5B are made of, for example, Sm-Co permanent magnets. The magnets sintered and molded in a rectangular parallelepiped are magnetized in parallel to the optical axis, and are arranged next to the Faraday rotator 3 in parallel to the optical axis. A desired optical isolator 1 is configured by fixing. It is preferable to use a synthetic resin adhesive such as an epoxy resin for joining and fixing the magnet.
Further, a substrate obtained by machining a stainless steel plate (SUS304) with high accuracy is used. When transparency is required, quartz glass, GGG, or the like is used.
[0022]
Here, the maximum structural features of the optical isolator of the present invention will be described.
The feature is that, as shown in FIG. 1B, the Faraday rotator 3 in the optical element is provided with a joining avoiding means 3c so as not to be joined to the substrate 1.
[0023]
As a specific example of the bonding avoiding means, first, a material that repels a bonding agent is applied in advance to the Faraday rotator bonding surface or the Faraday rotator bonding surface of the substrate, and the optical element is bonded to the substrate. -It is intended to avoid the occurrence of joint distortion at the joint surface of the Faraday rotator when fixed.
[0024]
As described above, if a material that repels the bonding agent is previously attached to the surface of the Faraday rotator as a bonding avoidance means, a bonding agent such as solder or synthetic resin adhesive is attached to the surface of the optical element. However, only the surface of the Faraday rotator facing the substrate is not repelled and bonded, and the other surface can be firmly bonded to the substrate, and the distortion of the optical element after bonding can be eliminated. And deterioration of optical characteristics can be prevented.
[0025]
As a material for repelling the bonding agent, specifically, in the case of alloy solder, a non-metallized layer is formed on the side surface of the optical element, and in the case of an epoxy resin adhesive, a fluorine resin coating or the like is preferable.
[0026]
Secondly, the bonding avoiding means can be a gap provided between the bonding surface of the substrate and the Faraday rotator.
For example, as shown in FIG. 2A, the substrate 34 with a concave step is formed by engraving the anti-Faraday rotator bonding surface of the substrate to form a concave step, and is formed when optical elements are bonded. The gap 33c is used as the joining avoiding means 3c. In this case, the bonding surface of the optical element by the bonding agent is the polarizer bonding surface 32d.
[0027]
Further, as shown in FIG. 2B, the substrate 44 with a convex step is formed such that the joining surface 42d of the two polarizers forming the optical element is formed as a convex step from the surface of the flat substrate. In this case, the gap 43c formed between the Faraday rotator and the surface to be bonded to the substrate is used as the bonding avoiding means 3c.
[0028]
Third, as shown in FIG. 2 (c), the bonding avoiding means 3c is optically bonded by forming the light transmitting surface area of the Faraday rotator 53 smaller than the light transmitting surface areas of the polarizers 52A and 52B. When the element 51 is configured and bonded to the substrate, the gap 53c formed between the substrate-to-substrate bonding surface of the Faraday rotator and the substrate serves as the bonding avoiding means 3c. In this case, the bonding surface of the optical element with the bonding agent is the polarizer-to-substrate bonding surface 52d.
[0029]
With this configuration, the Faraday rotator can be directly joined by forming a gap between the Faraday rotator-to-substrate bonding surface and the substrate without any effect on the transmission of light from a laser or the like. Can be prevented. Therefore, while maintaining the bonding strength at the bonding surface 52d of the other polarizer, it is possible to eliminate the bonding distortion generated after the bonding of the optical element and to avoid the deterioration of the optical characteristics.
[0030]
By configuring the optical isolator of the present invention as described above, the following operations and effects can be obtained.
If a means for avoiding bonding to the substrate is provided only on the Faraday rotator-to-substrate bonding surface in the rectangular parallelepiped optical element, distortion of the optical element after bonding can be eliminated and desired optical characteristics can be eliminated. Can be obtained. Furthermore, the optical elements can be easily aligned with high accuracy, and the optical elements can be bonded and fixed with sufficient bonding strength on other bonding surfaces, and a highly reliable and low-cost optical isolator. Can be provided.
[0031]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.
(Examples 1 to 3, Comparative Example 1)
First, an optical element was produced. Two polarizing glasses with anti-reflective coating for air on one side and anti-reflective coating for adhesive on the other side, and a Faraday rotator with anti-reflective coating for adhesive on both sides via adhesive Then, the surfaces coated with the anti-reflection coating for each adhesive are bonded face to face. At this time, polarized light is incident from the forward direction and the reverse direction on the optical element laminated with the polarizing glass / Faraday rotator / polarizing glass, respectively, and the forward insertion loss is minimized in the magnetic field. Are overlapped so that the maximum is possible, and bonding and solidification are performed while adjusting the angle. The superposed optical element is cut into a predetermined size to form a bonded optical element.
[0032]
Using this optical element, the following optical isolators were fabricated and optical characteristics were determined.
Experiments were conducted using a transparent substrate (quartz, GGG) as a substrate for bonding the optical element and the magnet in order to confirm the bonding location. As the magnet, two Sm-Co permanent magnets were used.
[0033]
In Example 1, an adhesive repellent material was applied to the surface of the Faraday rotator which was to be bonded to the substrate, thereby providing a bonding avoidance means. A fluorine resin was used as the repellent material.
[0034]
In Example 2, a gap is provided between the Faraday rotator-to-substrate bonding surface and the substrate. In Example 2-1, the Faraday rotator bonding surface on the substrate surface has a depth of 0.3 mm due to a concave step. A substrate in which a gap was formed was used. In Example 2-2, a substrate in which a gap of 0.3 mm depth was formed by a convex step with the two polarizer bonding surfaces on the substrate surface being raised was used. In Example 2-3, an optical element in which the light transmission surface area of the Faraday rotator was smaller than the light transmission surface area of the polarizer was bonded to a flat substrate to form a gap having a depth of 0.1 mm.
[0035]
In Example 3, a gap was formed without applying any synthetic resin adhesive to the Faraday rotator joint surface of the substrate surface. In Example 3, a gap corresponding to the film thickness of the epoxy resin adhesive is generated.
[0036]
Comparative Example 1-1 was obtained by applying an epoxy resin adhesive to the entire surface including the surface to be bonded to the substrate of the optical element, that is, the surface to be bonded to the Faraday rotator, and Comparative Example 1-2 was also a silicone resin adhesive. Is applied.
[0037]
As shown in FIG. 2A of Example 2-1, a substrate having a concave step as a gap is 1.2 mm wide × 0 at the center of a 2.3 mm wide × 1.5 mm deep × 0.5 mm thick flat plate. A step of 5 mm depth × 0.3 mm depth is provided. Further, as shown in FIG. 2B of Example 2-2, the gap provided between the convex steps is two 1.2 mm width × 0.5 mm depth × 0.3 mm height. It is formed by making a rectangular parallelepiped according to the position of the polarizer, and is 1.2 mm wide × 0.5 mm deep. The light transmission surface area of the Faraday rotator of Example 2-3 was 8.5% smaller than that of the polarizer.
[0038]
For each example, ten samples were prepared, the reverse insertion loss was measured, an impact fracture test was performed, and a comprehensive judgment was made. The results are summarized in Table 1. Each test method and criteria are as follows.
(A) The criterion for the reverse insertion loss was ≧ 38 dB.
(B) Impact fracture test: After measuring the optical properties, five 2000G impact tests were performed for each of the six directions. By this test, an optical element or a magnet that does not peel off is accepted.
[0039]
[Table 1]

[0040]
As is clear from Table 1, the optical isolator, which is bonded and fixed by providing a bonding avoidance means between the Faraday rotator's surface to substrate bonding surface and the substrate surface, avoids bonding distortion and has excellent optical characteristics and bonding strength. It can be seen that it can be fully satisfied.
[0041]
The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
[0042]
【The invention's effect】
As described above in detail, the optical isolator of the present invention is suitable for being miniaturized and incorporated in an LD module, and it is extremely important to adjust the plane of polarization of the optical element to an optimal position that provides good optical characteristics. An optical isolator that is easy and has a very high bonding strength with respect to the substrate and is not subjected to bonding stress, and thus has a large reverse insertion loss and can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration example of an optical isolator according to the present invention.
(A) Perspective view, (b) Sectional drawing showing the state of the joint surface of an optical element and a magnet, and a board | substrate.
FIG. 2 is an explanatory view showing a bonding avoiding means provided on the surface to be bonded to the substrate of the Faraday rotator or the substrate surface of the optical isolator of the present invention.
(A) A gap formed by a concave step was used as a joining avoiding means, (b) a gap formed by a convex step was used as a joining avoiding means, and (c) a gap formed by reducing the light transmission surface area of the Faraday rotator. The joining avoidance means was used.
FIG. 3 is an explanatory diagram showing a configuration example of a conventional optical isolator.
(A) Perspective view, (b) Sectional drawing showing the state of the joint surface of an optical element and a magnet, and a board | substrate.
[Explanation of symbols]
1, 20 ... optical isolator,
2A, 2B, 22A, 22B, 52A, 52B ... Polarizer (polarizing glass),
3, 23, 53 ... Faraday rotator, 4, 24, ... flat substrate,
34, 44 ... Substrate having a step, 51 ... Optical element,
5A, 5B, 25A, 25B ... permanent magnets ,
2d, 22d, 32d, 42d,...
52d ... substrate bonding surface of the polarizer,
3c: A portion for providing a Faraday rotator joint avoiding means,
33c, 43c, 53c ... gap, 23d ... Faraday rotator joint surface of the substrate,
5d, 25d ... permanent magnet joint surfaces of the substrate.

Claims (5)

In an optical isolator comprising at least one polarizer and at least one Faraday rotator , wherein a substrate is bonded and fixed to at least one side surface other than the light transmission surface of a rectangular parallelepiped optical element bonded with each other by a light transmission surface . The optical isolator is characterized in that the Faraday rotator in the optical element is not bonded to the substrate. 2. The optical isolator according to claim 1 , wherein the Faraday rotator has a material that repels a bonding agent as a bonding avoidance means for preventing the Faraday rotator from being bonded to the substrate . As bonding avoidance means for the Faraday rotator from being bonded to the substrate, according to claim 1 or claim 2, characterized in that with a gap provided between the joining surfaces of the substrate and the Faraday rotator The optical isolator described in 1. As a means for avoiding the Faraday rotator from being bonded to the substrate, the light transmitting surface area of the Faraday rotator constituting the optical element is made smaller than the light transmitting surface area of the polarizer and bonded together. optical isolator set forth in any one of claims 1 to 3, characterized in that. As a means for avoiding the Faraday rotator from being bonded to the substrate, solder bonding metallization is formed on the side surface portion of the optical element other than the Faraday rotator, and the substrate is soldered to the substrate. optical isolator set forth in any one of claims 1 to 4, characterized in that.

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