JP2004061997A

JP2004061997A - Optical isolator

Info

Publication number: JP2004061997A
Application number: JP2002222439A
Authority: JP
Inventors: Masaki Michiwaki; 道脇　正樹
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2002-07-31
Filing date: 2002-07-31
Publication date: 2004-02-26

Abstract

<P>PROBLEM TO BE SOLVED: To achieve downsizing of an optical isolator as the sectional shapes of respective optical elements are elliptic nearly similar to the shape of a transmitted light beam in section and is so sized as to eliminate nearly useless portions with respect to the transmitted light beam; further, the shape and size of the through-hole of a permanent magnet internally holding the respective optical elements are nearly similar to those of the respective optical elements and therefore the through-hole size of the permanent magnet is diminished nearly down to the threshold and the external shape size of the permanent magnet for obtaining the magnetic field intensity necessary for magnetically saturating a Faraday rotator can be made smaller. <P>SOLUTION: The optical isolator comprises the respective optical elements; the flat planar Faraday rotator 3, a polarizer 1, and an analyzer 2, and the permanent magnet for applying the magnification to the Faraday rotator 3, in which the respective optical elements are sectionally elliptic; the permanent magnet 4 has the through-hole coincident with the shapes of the respective optical elements; the respective optical elements are inserted and fixed into the through-hole and a plane section 6 parallel to the transmitted polarized wave direction of the polarizer is formed in part of the outer periphery of the permanent magnet. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、光源から出射された光を各種光学素子や光ファイバに導入する際に生じる戻り光を除去するために用いられる光アイソレータに関する。
【０００２】
【従来の技術】
従来の光アイソレータにおいて、レーザー等の光源から出射した光は、各種光学素子や光ファイバに入射されるが、入射光の一部は各種光学素子、光ファイバを透過する際、反射や散乱を起こす。反射や散乱した光の一部は光源側に戻るが、この戻り光を遮断するため、光アイソレータが用いられる。
【０００３】
この種の光アイソレータは、図３に示すように、断面形状が正方形もしくは長方形の偏光子１、検光子２及びファラデー回転子３をそれぞれ部品ホルダ７，８，９に固定し、円形の貫通孔５を有する円柱状の永久磁石４内にファラデー回転子３が配置される様に構成されている。ファラデー回転子３は飽和磁界強度において所定の波長を持つ光の偏光面を４５゜回転する厚みを持ち、偏光子１と検光子２はそれぞれの透過偏波方向が４５゜回転方向にずれるように回転調整されて構成されている。
【０００４】
この様な光アイソレータにおいては、断面形状が正方形もしくは長方形のファラデー回転子３の周囲に丸い貫通孔５を有する永久磁石４を配設する構造となっている為、永久磁石４の貫通孔５の直径はファラデー回転子３の対角線よりも大きくする必要があり、さらにファラデー回転子３を磁気的に飽和する為に十分な磁界を印加するには永久磁石４の肉厚を確保する必要があり、必然的に外径が大きくなり、光アイソレータの小型化が難しかった。この課題を解決するために、図４に示す様に、光学素子が多角形であり、永久磁石４の貫通孔５をファラデー回転子３の形状に合わせた形状とし、従来存在していた永久磁石４と光学素子間の空隙１０を磁界印加に寄与するように利用し、永久磁石４の外径寸法を減少することが可能な光アイソレータが提案されていた（特開２００２−８２３０９公報参照）。
【０００５】
さらに、光アイソレータを半導体レーザーモジュールに組み込む際には、レーザー光の損失を最小にするために、半導体レーザーからの出射光の偏波面と光アイソレータの偏光子１の偏波面を一致させる必要があるが、従来の光アイソレータは円筒形状であるため、光を通しながら回転調整する必要があり、光アイソレータの組み込み工数が多くかかっていた。この課題を解決するために、図５に示す様に、平板状の取り付け基板１１上に四角形の偏光子１，検光子２，ファラデー回転子３と直方体の永久磁石４を設置し、偏光子１の透過偏波方向と基板１１を平行にすることにより、偏波面の調整を行うこと無しに半導体レーザーモジュールに組み込める光アイソレータが提案されていた（特開平１０−２２７９９６号公報参照）。
【０００６】
【発明が解決しようとする課題】
しかしながら、図４に示す従来の構成では、多角形の光学素子であるため、一般に楕円形状である透過光ビームの透過領域に対して、光学素子上にビームが透過しない無駄な部分が存在していた。その為、光アイソレータの小型化に支障を来していた。
【０００７】
さらに、図５に示す従来の構造では、四角形の光学素子の両側に直方体の永久磁石を配置する構造であるため、上記と同様光学素子上にビームが透過しない無駄な部分が存在していた。さらに直方体の磁石を二つ使用し、且つ構成部品保持のための平板状基板が存在するため、寸法が大きく、且つ部品点数が多くなり、光アイソレータの小型化に支障を来していた。
【０００８】
【課題を解決するための手段】
そこで、本発明は、上記問題点に鑑みてなされたものであり、平板状のファラデー回転子、偏光子、検光子の各光学素子と、ファラデー回転子に磁界を印加する永久磁石から構成されている光アイソレータにおいて、各光学素子は断面が楕円状であり、上記永久磁石は各光学素子の形状に合致した貫通孔を備え、該貫通孔に各光学素子を挿入固定するとともに、上記永久磁石の外周の一部に、上記偏光子の透過偏波方向と平行な平面部を形成したことを特徴とする。
【０００９】
また、上記偏光子の楕円の長軸方向が透過偏波方向と一致していることを特徴とする。
【００１０】
すなわち、本発明によれば、各光学素子の断面形状は断面が透過光ビームの形状とほぼ同様の楕円であり、透過光ビームに対してほぼ無駄な部分が無い大きさとなっており、さらに各光学素子を内部に保持する永久磁石の貫通孔の形状及び寸法が各光学素子とほぼ同様であるため、永久磁石の貫通孔寸法が限界近くまで小さくなっており、ファラデー回転子を磁気的に飽和させるために必要な磁界強度を得るための永久磁石の外形寸法を小さくすることができ、光アイソレータの小型化を実現できる。
【００１１】
さらに、永久磁石の外周面に設けた平面部を底面として利用することで、各光学素子と永久磁石を保持する平板状の基板を必要とすることなく偏光子の偏波面と底面を一致することが可能となり、光アイソレータを半導体レーザーモジュールに組み込む際には、光アイソレータを回転調整することが不要となる。
【００１２】
【発明の実施の形態】
以下、本発明の実施の形態を図を用いて説明する。
【００１３】
図１は本発明の光アイソレータの外観を示す斜視図、図２はその断面図である。
【００１４】
偏光子１、検光子２、ファラデー回転子３の各光学素子は断面が楕円の平板状であり、永久磁石４に各光学素子に合致した貫通孔５を備え、この貫通孔５内に各光学素子を固定して構成されている。ファラデー回転子３は飽和磁界強度において所定の波長を持つ光の偏光面を４５゜回転する厚みを持ち、偏光子１と検光子２はそれぞれの透過偏波方向が４５゜回転方向にずれるように構成されている。
偏光子１、検光子２としては、通常赤外偏光ガラス（例：コーニング社製ポーラコア）を用いる。
【００１５】
ファラデー回転子３としては希土類鉄ガーネット単結晶、例えば（ＨｏＴｂＢｉ）_３Ｆｅ_５Ｏ_１２や、（ＬｕＴｂＢｉ）_３（ＦｅＡｌ）_５Ｏ_１２等を使用する。
【００１６】
永久磁石４は円柱状であり、その外周面の一部が削除されて平面部６を形成しており、中央に各光学素子を挿入固定する為の貫通孔５を有し、貫通孔５は各光学素子とほぼ同形状且つ同寸法の楕円形であり、永久磁石４の外周面の平面部６と貫通孔５の楕円の長軸が平行となるようにする。
【００１７】
外周の平面部６の幅は外周の直径の約５０％程度にすれば、平面部６を底面にして光アイソレータを設置したときの安定性にも問題が無い。
【００１８】
永久磁石４の材質としては、サマリウム・コバルト系磁石や、ネオジウム・鉄・ボロン系磁石等を使用する。
【００１９】
偏光子１、検光子２及びファラデー回転子３と永久磁石４との接合は、接合材１２として接着剤、半田、低融点ガラス等を用いる。それぞれの材質固有の熱膨張係数に合わせて接合材を選定する必要がある。熱膨張係数が大きく異なると、固定後に各部品に残留応力が発生し、光学特性を満たさないばかりか製品の信頼性を損なってしまう可能性がある為である。光学素子を永久磁石４の貫通孔５に挿入する前に、貫通孔５の内径に接合剤１２をあらかじめ塗布しておく。その後、光学素子を挿入し、光学素子の外周と貫通孔５の内径が接合剤１２を介して接合されるようにする。
【００２０】
光学素子と永久磁石４の貫通孔５の間の隙間はできるだけ小さい方が光アイソレータの小型化に寄与するため望ましい。理想的には隙間が存在せず、光学素子と貫通孔５の内径が接触していることが望ましいが、接合材１２が存在するため、少なくともその厚み分、すなわち約１０μｍ〜１００μｍ程度は隙間が存在することになる。
【００２１】
光学素子の加工は、一般に大板状の光学素子基板をダイシングソー等により加工するが、この方法では楕円への加工は困難であるため、楕円形状の型を配列した金型と、シリコンカーバイド等の研削剤を用いた超音波加工で行う。
【００２２】
偏光子１を加工する際、偏光子１の透過偏波方向と楕円の長軸が一致するように加工することが好ましい。また、検光子２を加工する際は、検光子２の透過偏波方向と楕円の長軸が４５°の角度をなすように加工する。このように加工することで、偏光子１と検光子２をそれぞれの楕円長軸が一致するように永久磁石４の貫通穴５内に挿入固定すれば、光を通しながらの回転調整をすることなく光アイソレータの組立が可能となり、光アイソレータの組立時間削減が可能となる。
【００２３】
各光学素子形状は、光アイソレータを透過するビームの形状にできるだけ近づけることが光アイソレータの小型化につながり、望ましい。厳密には超音波加工の際、光学素子の外周部に微少なチッピングが発生するため、その分を透過光ビームより大きくして加工する必要があるが、チッピングを撲滅することが可能であれば透過光ビームと全く同形状、同寸法に加工すればよい。また、必ずしも完全な楕円ではなくともよく、比較的楕円に近い形で、その長軸、短軸が外観上明らかに確認できるようであればよい。また、例えば断面が長方形であっても構わない。その際は長方形の長辺が偏光子１の透過偏波方向と一致するように加工し、永久磁石４の貫通孔５の形状も長方形にすればよい。
【００２４】
一般に光アイソレータを透過するビームの形状は、長軸／短軸の比が１．５〜３．０の楕円状であるため、光学素子の形状もこの比の範囲になるような楕円状に加工することが好ましい。
【００２５】
【実施例】
ここで、以下に示す方法で実験を行った。
【００２６】
本発明の光アイソレータと、従来の光アイソレータをそれぞれ５個作製し、その光学特性及び外径寸法の確認を行った。試作は波長１５５０ｎｍについて実施した。
【００２７】
まず、本発明の光アイソレータについては、偏光子１、検光子２にはコーニング社製の偏光ガラス（商品名ポーラコア１５５０Ｈ）を用い、ファラデー回転子３には希土類鉄ガーネット単結晶を使用した。
【００２８】
光学素子の寸法は、楕円の長軸を１．０ｍｍ，短軸を０．６ｍｍとした。偏光子１の透過偏波方向が楕円の長軸と平行になるように超音波加工にて加工を行った。また、検光子２の透過偏波方向が楕円の長軸と４５°の角度をなすように超音波加工にて加工を行った。
【００２９】
永久磁石４は材質としてサマリウム・コバルト系磁石を使用した。楕円の貫通孔５の寸法は、長軸１．０５ｍｍ，短軸０．６５ｍｍ、厚み１．５ｍｍとした。外周は直径１．６５ｍｍ、外周の平面部６の幅を０．９ｍｍとした。この時永久磁石４の中心軸状の磁界強度は、磁石内部で約１２００Ｇとなり、ファラデー回転子３を磁気的に飽和させるには十分な磁界強度が得られる。
【００３０】
光学素子と永久磁石４との固定はエポキシ系熱硬化型接着剤を使用し、光学素子の外周部と永久磁石４の貫通孔５の内壁とで接着固定される様にし、光アイソレータの光路上には接着剤が存在しない構造とした。
【００３１】
従来の光アイソレータについては、図３に示す構造のものを作製した。偏光子１、検光子２、ファラデー回転子３はダイシングソーによって１．０ｍｍ角の正方形のチップに加工した。
【００３２】
これらの光学素子をＳＵＳ３０４製の部品ホルダ７，８，９にエポキシ系熱硬化型接着剤を用いて固定した。ファラデー回転子３に磁界を印加する永久磁石４としてはサマリウム・コバルト系磁石を使用した。永久磁石４はリング状になっており、ファラデー回転子３がその内径部の中央にくるように固定する。永久磁石４の内径は１．８ｍｍ，外径は２．６ｍｍ、厚みは１．１ｍｍとした。そうすることでファラデー回転子３に１２００Ｇ以上の磁界が印加され、ファラデー回転子３が磁気的に飽和されて、光アイソレータに必要な機能を果たすようになる。
【００３３】
それぞれの光学素子を固定した部品ホルダ７，８，９を光学的に調整し、偏光子１と検光子２が４５°の角度をなす様に調整し、それぞれの部品ホルダをＹＡＧ溶接にて固定して従来の光アイソレータを完成させた。
【００３４】
以上の様にして作製した本発明の光アイソレータと従来の光アイソレータの光学特性と外径寸法の比較を表１に示す。
【００３５】
【表１】

【００３６】
【表２】

【００３７】
表１より、本発明の光アイソレータは、従来の光アイソレータと同等の光学特性を持つことが確認できた。更に表２より、本発明の光アイソレータは、外径寸法を従来の２．６ｍｍから１．６５ｍｍにすることができ、約３６．５％の小型化が実現できた。
【００３８】
【発明の効果】
以上の様に本発明によれば、光学素子の形状及び寸法が透過光ビームとほぼ同形状、且つ同寸法の為、光アイソレータの小型化が実現できる。また、永久磁石外周部の平面部と偏光子の透過偏波方向を一致させることで、光アイソレータを半導体レーザーモジュールに組み込む際の回転調整を省くことができ、組立工数の削減が実現できる。
【図面の簡単な説明】
【図１】本発明の光アイソレータを示す斜視図である。
【図２】本発明の光アイソレータを示す断面図である。
【図３】従来の光アイソレータを示す断面図である。
【図４】従来の光アイソレータを示す斜視図である。
【図５】従来の光アイソレータを示す斜視図である。
【符号の説明】
１：偏光子
２：検光子
３：ファラデー回転子
４：永久磁石
５：貫通孔
６：平面部
７：部品ホルダ
８：部品ホルダ
９：部品ホルダ
１０：空隙
１１：平板状基板
１２：接合材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical isolator used for removing return light generated when light emitted from a light source is introduced into various optical elements and optical fibers.
[0002]
[Prior art]
In a conventional optical isolator, light emitted from a light source such as a laser is incident on various optical elements and optical fibers, but a part of the incident light causes reflection and scattering when transmitting through various optical elements and optical fibers. . A part of the reflected or scattered light returns to the light source side, and an optical isolator is used to block the returned light.
[0003]
As shown in FIG. 3, this type of optical isolator fixes a polarizer 1, an analyzer 2, and a Faraday rotator 3 having a square or rectangular cross section to component holders 7, 8, and 9, respectively, and forms a circular through hole. The Faraday rotator 3 is arranged in a columnar permanent magnet 4 having the same. The Faraday rotator 3 has a thickness that rotates the polarization plane of light having a predetermined wavelength by 45 degrees in the saturation magnetic field strength, and the polarizer 1 and the analyzer 2 are arranged such that their transmission polarization directions are shifted by 45 degrees. The rotation is adjusted.
[0004]
In such an optical isolator, the permanent magnet 4 having a round through hole 5 is provided around the Faraday rotator 3 having a square or rectangular cross section. The diameter needs to be larger than the diagonal line of the Faraday rotator 3, and it is necessary to secure the thickness of the permanent magnet 4 in order to apply a sufficient magnetic field to magnetically saturate the Faraday rotator 3, The outer diameter inevitably increased, making it difficult to miniaturize the optical isolator. In order to solve this problem, as shown in FIG. 4, the optical element has a polygonal shape, and the through-hole 5 of the permanent magnet 4 has a shape conforming to the shape of the Faraday rotator 3. There has been proposed an optical isolator capable of reducing the outer diameter of the permanent magnet 4 by utilizing the gap 10 between the optical element 4 and the optical element so as to contribute to the application of a magnetic field (see JP-A-2002-82309).
[0005]
Furthermore, when incorporating the optical isolator into the semiconductor laser module, it is necessary to make the plane of polarization of the light emitted from the semiconductor laser coincide with the plane of polarization of the polarizer 1 of the optical isolator in order to minimize the loss of laser light. However, since the conventional optical isolator has a cylindrical shape, it is necessary to adjust the rotation while passing light, and the man-hour for assembling the optical isolator has increased. In order to solve this problem, as shown in FIG. 5, a rectangular polarizer 1, an analyzer 2, a Faraday rotator 3 and a rectangular parallelepiped permanent magnet 4 are provided on a flat mounting substrate 11, and the polarizer 1 An optical isolator that can be incorporated in a semiconductor laser module without adjusting the plane of polarization by making the transmission polarization direction of the substrate 11 parallel to the substrate 11 has been proposed (see Japanese Patent Application Laid-Open No. 10-227996).
[0006]
[Problems to be solved by the invention]
However, in the conventional configuration shown in FIG. 4, since the optical element is a polygonal optical element, there is a useless portion where the beam does not transmit on the optical element with respect to the transmission area of the transmitted light beam which is generally elliptical. Was. This has hindered miniaturization of the optical isolator.
[0007]
Further, the conventional structure shown in FIG. 5 has a structure in which rectangular parallelepiped permanent magnets are arranged on both sides of a rectangular optical element, so that there is a useless portion on the optical element similar to the above, in which a beam is not transmitted. Further, the use of two rectangular magnets and the presence of a flat substrate for holding the components, the size is large and the number of components is large, which hinders miniaturization of the optical isolator.
[0008]
[Means for Solving the Problems]
Therefore, the present invention has been made in view of the above problems, and is configured by a flat Faraday rotator, a polarizer, each optical element of an analyzer, and a permanent magnet that applies a magnetic field to the Faraday rotator. In an optical isolator, each optical element has an elliptical cross section, and the permanent magnet has a through-hole matching the shape of each optical element, and inserts and fixes each optical element in the through-hole. A flat portion parallel to the transmission polarization direction of the polarizer is formed on a part of the outer periphery.
[0009]
In addition, the major axis direction of the ellipse of the polarizer coincides with the transmission polarization direction.
[0010]
That is, according to the present invention, the cross-sectional shape of each optical element is an ellipse whose cross section is almost the same as the shape of the transmitted light beam, and has a size with almost no useless portion for the transmitted light beam. Since the shape and size of the through hole of the permanent magnet that holds the optical element inside is almost the same as each optical element, the size of the through hole of the permanent magnet is reduced to near the limit, and the Faraday rotator is magnetically saturated. The external dimensions of the permanent magnet for obtaining the required magnetic field strength can be reduced, and the size of the optical isolator can be reduced.
[0011]
Furthermore, by using the flat portion provided on the outer peripheral surface of the permanent magnet as a bottom surface, the polarization plane and the bottom surface of the polarizer can be matched without requiring a flat substrate holding each optical element and the permanent magnet. When an optical isolator is incorporated in a semiconductor laser module, it is not necessary to adjust the rotation of the optical isolator.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a perspective view showing an appearance of an optical isolator of the present invention, and FIG. 2 is a sectional view thereof.
[0014]
Each optical element of the polarizer 1, the analyzer 2, and the Faraday rotator 3 is a flat plate having an elliptical cross section. The permanent magnet 4 is provided with a through hole 5 corresponding to each optical element. It is configured with the element fixed. The Faraday rotator 3 has a thickness that rotates the polarization plane of light having a predetermined wavelength by 45 degrees in the saturation magnetic field strength, and the polarizer 1 and the analyzer 2 are arranged such that their transmission polarization directions are shifted by 45 degrees. It is configured.
As the polarizer 1 and the analyzer 2, an infrared polarizing glass (eg, a polar core manufactured by Corning Incorporated) is usually used.
[0015]
As the Faraday rotator 3, a rare earth iron garnet single crystal, for example, (HoTbBi) ₃ Fe ₅ O ₁₂ or (LuTbBi) ₃ (FeAl) ₅ O ₁₂ is used.
[0016]
The permanent magnet 4 has a columnar shape, a part of the outer peripheral surface thereof is removed to form a flat portion 6, and has a through hole 5 in the center for inserting and fixing each optical element. It is an ellipse having substantially the same shape and dimensions as each optical element, and the major axis of the ellipse of the through hole 5 is parallel to the plane portion 6 of the outer peripheral surface of the permanent magnet 4.
[0017]
If the width of the outer peripheral flat portion 6 is about 50% of the outer peripheral diameter, there is no problem in stability when the optical isolator is installed with the flat portion 6 as the bottom surface.
[0018]
As the material of the permanent magnet 4, a samarium / cobalt magnet, a neodymium / iron / boron magnet, or the like is used.
[0019]
The bonding between the polarizer 1, the analyzer 2, the Faraday rotator 3, and the permanent magnet 4 uses an adhesive, solder, low-melting glass, or the like as the bonding material 12. It is necessary to select a joining material according to the thermal expansion coefficient specific to each material. If the thermal expansion coefficients differ greatly, residual stress is generated in each component after fixing, which may not only satisfy the optical characteristics but also impair the reliability of the product. Before the optical element is inserted into the through hole 5 of the permanent magnet 4, a bonding agent 12 is applied to the inner diameter of the through hole 5 in advance. After that, the optical element is inserted so that the outer periphery of the optical element and the inner diameter of the through hole 5 are bonded via the bonding agent 12.
[0020]
It is desirable that the gap between the optical element and the through hole 5 of the permanent magnet 4 be as small as possible because it contributes to downsizing of the optical isolator. Ideally, there is no gap, and it is desirable that the optical element and the inner diameter of the through hole 5 are in contact with each other. However, since the bonding material 12 is present, the gap is at least as thick as the thickness, that is, about 10 μm to 100 μm. Will exist.
[0021]
The processing of an optical element is generally performed by processing a large plate-shaped optical element substrate with a dicing saw or the like. However, since processing into an ellipse is difficult with this method, a mold in which elliptical molds are arranged and a silicon carbide or the like are used. This is performed by ultrasonic processing using an abrasive.
[0022]
When processing the polarizer 1, it is preferable to process the polarizer 1 so that the transmission polarization direction of the polarizer 1 and the major axis of the ellipse coincide. When processing the analyzer 2, the processing is performed so that the transmission polarization direction of the analyzer 2 and the major axis of the ellipse form an angle of 45 °. By processing in this way, if the polarizer 1 and the analyzer 2 are inserted and fixed in the through-hole 5 of the permanent magnet 4 so that the respective elliptical major axes coincide, the rotation adjustment while passing light can be performed. As a result, the optical isolator can be assembled, and the assembling time of the optical isolator can be reduced.
[0023]
It is desirable that the shape of each optical element be as close as possible to the shape of the beam transmitted through the optical isolator, which leads to downsizing of the optical isolator. Strictly speaking, during ultrasonic processing, micro chipping occurs at the outer peripheral portion of the optical element, so it is necessary to process it by making it larger than the transmitted light beam, but if chipping can be eliminated What is necessary is just to process into the same shape and the same dimension as the transmitted light beam. Further, the shape is not necessarily a perfect ellipse, but may be any shape as long as its major axis and minor axis can be clearly confirmed in appearance in a relatively elliptical form. Also, for example, the cross section may be rectangular. In this case, the long side of the rectangle may be processed so as to match the transmission polarization direction of the polarizer 1, and the shape of the through hole 5 of the permanent magnet 4 may be rectangular.
[0024]
Generally, the shape of a beam transmitted through an optical isolator is an ellipse having a ratio of major axis / minor axis of 1.5 to 3.0, and the shape of an optical element is also processed into an elliptical shape within the range of this ratio. Is preferred.
[0025]
【Example】
Here, an experiment was performed by the following method.
[0026]
Five optical isolators of the present invention and five conventional optical isolators were manufactured, and their optical characteristics and outer diameter dimensions were confirmed. The trial production was performed at a wavelength of 1550 nm.
[0027]
First, as for the optical isolator of the present invention, a polarizing glass (trade name: Polar core 1550H) manufactured by Corning Co., Ltd. was used for the polarizer 1 and the analyzer 2, and a rare earth iron garnet single crystal was used for the Faraday rotator 3.
[0028]
The dimensions of the optical element were such that the major axis of the ellipse was 1.0 mm and the minor axis was 0.6 mm. Processing was performed by ultrasonic processing so that the transmission polarization direction of the polarizer 1 was parallel to the major axis of the ellipse. The processing was performed by ultrasonic processing so that the transmission polarization direction of the analyzer 2 was at an angle of 45 ° with the major axis of the ellipse.
[0029]
As the material of the permanent magnet 4, a samarium-cobalt magnet was used. The dimensions of the elliptical through-hole 5 were a major axis of 1.05 mm, a minor axis of 0.65 mm, and a thickness of 1.5 mm. The outer circumference had a diameter of 1.65 mm, and the width of the outer flat portion 6 was 0.9 mm. At this time, the magnetic field strength of the central axis of the permanent magnet 4 becomes about 1200 G inside the magnet, and a magnetic field strength sufficient to magnetically saturate the Faraday rotator 3 is obtained.
[0030]
The optical element and the permanent magnet 4 are fixed with an epoxy-based thermosetting adhesive at the outer peripheral portion of the optical element and the inner wall of the through hole 5 of the permanent magnet 4 so as to be fixed on the optical path of the optical isolator. Had no adhesive.
[0031]
A conventional optical isolator having the structure shown in FIG. 3 was manufactured. The polarizer 1, the analyzer 2, and the Faraday rotator 3 were processed into a square chip of 1.0 mm square by a dicing saw.
[0032]
These optical elements were fixed to SUS304 component holders 7, 8, and 9 using an epoxy-based thermosetting adhesive. As the permanent magnet 4 for applying a magnetic field to the Faraday rotator 3, a samarium-cobalt magnet was used. The permanent magnet 4 has a ring shape, and is fixed so that the Faraday rotator 3 is located at the center of the inner diameter. The inner diameter of the permanent magnet 4 was 1.8 mm, the outer diameter was 2.6 mm, and the thickness was 1.1 mm. By doing so, a magnetic field of 1200 G or more is applied to the Faraday rotator 3, and the Faraday rotator 3 is magnetically saturated, so that the function required for the optical isolator is achieved.
[0033]
The component holders 7, 8, 9 to which the respective optical elements are fixed are optically adjusted so that the polarizer 1 and the analyzer 2 form an angle of 45 °, and the respective component holders are fixed by YAG welding. Thus, a conventional optical isolator was completed.
[0034]
Table 1 shows a comparison of the optical characteristics and outer diameters of the optical isolator of the present invention and the conventional optical isolator manufactured as described above.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
From Table 1, it was confirmed that the optical isolator of the present invention has optical characteristics equivalent to those of the conventional optical isolator. Further, as shown in Table 2, the optical isolator of the present invention was able to reduce the outer diameter dimension from 2.6 mm to 1.65 mm, thereby achieving a reduction in size of about 36.5%.
[0038]
【The invention's effect】
As described above, according to the present invention, since the shape and dimensions of the optical element are substantially the same as and the same as those of the transmitted light beam, the size of the optical isolator can be reduced. Further, by making the plane of polarization of the outer peripheral portion of the permanent magnet coincide with the transmission polarization direction of the polarizer, rotation adjustment when the optical isolator is incorporated into the semiconductor laser module can be omitted, and the number of assembly steps can be reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an optical isolator of the present invention.
FIG. 2 is a sectional view showing an optical isolator of the present invention.
FIG. 3 is a sectional view showing a conventional optical isolator.
FIG. 4 is a perspective view showing a conventional optical isolator.
FIG. 5 is a perspective view showing a conventional optical isolator.
[Explanation of symbols]
1: Polarizer 2: Analyzer 3: Faraday rotator 4: Permanent magnet 5: Through hole 6: Flat part 7: Component holder 8: Component holder 9: Component holder 10: Air gap 11: Flat substrate 12: Bonding material

Claims

In an optical isolator composed of a flat Faraday rotator, a polarizer, and an analyzer, and a permanent magnet that applies a magnetic field to the Faraday rotator, each optical element has an elliptical cross section, and the permanent The magnet is provided with a through hole conforming to the shape of each optical element. Each of the optical elements is inserted and fixed in the through hole. An optical isolator characterized by forming a portion.

2. The optical isolator according to claim 1, wherein the major axis direction of the ellipse of the polarizer coincides with the transmission polarization direction.