JP2004093750A

JP2004093750A - Optical switch

Info

Publication number: JP2004093750A
Application number: JP2002252990A
Authority: JP
Inventors: Toshiharu Nishino; 西野　利晴; Kunpei Kobayashi; 小林　君平; Takeshi Suzuki; 鈴木　剛; Norihiro Arai; 荒井　則博; Masayuki Takahashi; 高橋　政之
Original assignee: Casio Computer Co Ltd
Current assignee: Casio Computer Co Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-25
Anticipated expiration: 2022-08-30
Also published as: JP4092986B2

Abstract

PROBLEM TO BE SOLVED: To provide an optical switch with which a traveling route of an optical signal is accurately and stably switched just as it is with a simple structure without converting the optical signal into an electric signal. SOLUTION: A first liquid crystal device LA1 which is constructed by arranging a homogeneous type first liquid crystal element 1 and a second liquid crystal element 2 with respective alignment directions of liquid crystal molecules mutually perpendicularly intersecting and which imparts definite retardation to transmitted light irrespective of temperature and a second liquid crystal device LA2 which is constructed by arranging a similarly homogeneous type first liquid crystal element 3 and a second liquid crystal element 4 similarly with respective alignment directions of liquid crystal molecules mutually perpendicularly intersecting are arranged in parallel. A first beam splitter 5 to split incident light Ri into polarized light components R1, R2 with their plane of polarization mutually perpendicularly intersecting and a first reflection mirror 6 are arranged on the incident side of the incident light Ri. A second beam splitter 7 to combine the polarized light components R1, R2, forming outgoing light Ro and emit it to a specified direction and a second reflection mirror 8 are arranged on the outgoing side emitting the outgoing light Ro. COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
この発明は、光通信ネットワークやその他の光信号処理において伝搬する光信号の進行ルートを空間的に切り換える光スイッチに関する。
【０００２】
【従来の技術】
今日、光通信ネットワークの発展に伴い、光信号を伝搬するための光ファイバが広く使用されている。しかし、光ファイバにより光信号を伝送するためには、光ファイバ間で光信号の進行ルートを切り換える必要がある。
【０００３】
このような切換えを行う一つの方法として、光信号を通常の光電変換用電子デバイスで電気信号に変換し、変換された電気信号に応じて異なる進行ルートに配設した光源を点滅させることにより光信号の進行ルートの切換を行うものがある。
【０００４】
【発明が解決しようとする課題】
しかるに、情報データの伝送レートは上昇し続けているので、光ファイバにより伝送される光信号の広いデータ帯域を処理するのに通常の電子デバイスを用いることは益々困難になってきている。更に、光信号と電気信号の間で変換をする必要があるため、データフォーマットが制限されてしまうと共に装置が複雑且つ高価になるという問題があった。
【０００５】
この発明は、簡単な構造で光信号を電気信号に変換することなく光信号のまま正確に安定して進行ルートを切り換えることが可能な光スイッチを提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明の光スイッチは、入射光の互いに直交する偏光成分のうちの一方の第１偏光成分光を反射し、他方の第２偏光成分光を透過させる偏光分離手段と、前記偏光分離手段により反射された前記第１の偏光成分光の進行方向を前記第２偏光成分光と平行な方向に導く第１の導光手段と、前記偏光分離手段により分離された第２の偏光成分光と、前記偏光分離手段により分離され、前記第１の導光手段により導かれた前記第１の偏光成分光が入射され、電界の印加に応じてリタデーションの値が透過光の波長の実質的に１／２の奇数倍だけ互いに異なる第１の配向状態と第２の配向状態とに切り替え可能な液晶素子と、前記液晶素子の前記リタデーションの温度依存性を補償する補償用液晶素子とからなる液晶装置と、前記液晶装置の光出射側に配置され、前記偏光分離手段により分離された第２の偏光成分光の前記液晶装置を透過した光を、前記第１の偏光成分光の前記液晶装置を透過した光の進行方向と交差する方向に導く第２の導光手段と、前記第１の偏光成分光の前記電気光手段を透過した光と、第２の偏光成分光の前記電気光手段を透過して前記第２の導光板により導かれた光とが入力され、前記２つの光を同一の光路に出射させる偏光合成手段とからなり、入射光を前記電気光学手段に印加される電界に応じてそれぞれ異なる方向へ出射することを特徴とするものである。
【０００７】
この光スイッチにおいては、液晶装置の配向状態が入力信号に応じて透過光の旋光量が温度に拘わらず互いに９０°だけ異なる第１の液晶配向状態と第２の液晶配向状態に切り換えられ、この液晶装置に光スイッチの入射光が互いに偏光面の方向が直交するＳ波とＰ波の偏光成分光に分離されて入射し、液晶装置を透過する際に、各偏光成分光が温度に拘わらず第１と第２の各液晶配向状態に応じて一定量だけ旋光され、この後、液晶装置を出射した各偏光成分光は合成されて出射光となり所定方向に出射される。従って、本光スイッチによれば、温度に拘わらず常に安定して光信号を電気信号に変換することなく光信号のままその進行ルートを切り換えることができる。その結果、広いデータ帯域の光信号の進行ルートを光信号のままロスなく安定して正確に切り換えることができる安価な光スイッチを提供することが可能となる。
【０００８】
上述の光スイッチにおいて、前記液晶装置の前記液晶素子と前記補償用液晶素子は、それぞれ液晶分子を基板に平行に配向させた２個のホモジニアス型液晶素子であって、且つそれぞれの液晶分子の配向方向が互いに直交する配置で設置してなり、前記液晶素子と前記補償用液晶素子はそれぞれ、印加電圧に応じて液晶の配向状態を液晶分子が基板に平行に配向した第１の配向状態と液晶分子が立ち上がり配向した第２の配向状態との間で切り換えることにより、前記液晶装置を透過する光の偏光面を互いにほぼ９０゜異ならせた光を出射するようにするのが好ましい。
【０００９】
その場合、液晶装置を、前記第１偏光成分光の光路中に配置された第１液晶装置と、前記第２偏光成分光の光路中に配設された第２液晶装置とで構成するのがよい。
【００１０】
また、液晶装置を第１液晶装置と第２液晶装置とで構成した場合、前記偏光分離手段と前記偏光合成手段を、互いに直交する方向に反射軸と透過軸とを有して入射光のうちの偏光面が前記反射軸に沿った偏光成分光を反射し偏光面が前記透過軸に沿った偏光成分光を透過させる１個の反射偏光板とし、この反射偏光板を前記第１液晶装置と前記第２液晶装置間を通して斜めに配置しても良く、これにより、構成部材数が減って構造がより簡素化される。
【００１１】
【発明の実施の形態】
図１（ａ）、図１（ｂ）は、この発明の第１実施形態例としての光スイッチの構成を示す模式的構成図であり、それぞれ、光の進行方向を変えずに出射させる状態と光の進行方向を９０°変化させて出射させる状態を示している。
【００１２】
この実施形態例の光スイッチは、２個の第１液晶素子１，３と、２個の温度補償用の第２液晶素子２，４からなる液晶装置ＬＡを用い、その入射光Ｒｉが入射する光入射側に偏光分離手段としての第１ビームスプリッタ５と第１の導光手段としての第１反射鏡６を配置し、出射光Ｒｏを出射させる光出射側に偏光合成手段としての第２ビームスプリッタ７と第２の導光手段としての第２反射鏡８を配置した構成となっている。なお、本例における入射光Ｒｉは、波長が１６２０ｎｍのレーザー光である。
【００１３】
本例の液晶装置ＬＡは、第１液晶素子１と第２液晶素子２をそれぞれの入、出射面を平行に並列配置してなる第１の液晶装置ＬＡ１と、第１液晶素子３と第２液晶素子４をそれぞれの入、出射面を平行に並列配置してなる第２の液晶装置ＬＡ２とで、構成してある。また、異なる液晶装置同士の第１液晶素子１と第１液晶素子３及び第２液晶素子２と第２液晶素子４も、それらの各入、出射面が互いに平行となるように配置してある。本例の４個の液晶素子１乃至４は、それぞれ、電極が形成された一対の電極基板１ａ，１ｂ、２ａ，２ｂ、３ａ，３ｂ及び４ａ，４ｂ間に液晶分子を各電極基板に対して平行に配向させて挟持したホモジニアス型液晶素子である。
【００１４】
第１の液晶装置ＬＡ１においては、ホモジニアス型の第１、第２液晶素子１、２を、それぞれの液晶分子の配向方向が互いに直交するように配置してある。即ち、図２の透過光の偏光方向と各液晶素子における液晶分子の配向方向との関係を示す説明図にも示されているように、第１液晶素子１の一対の電極基板１ａ，１ｂ近傍の液晶分子の各配向方向つまりそれぞれの電極上に被着してある各配向膜（不図示）に施したラビング等の各配向処理方向ｄ１、ｄ１と、第２液晶素子２の一対の電極基板２ａ，２ｂにおけるそれぞれの同配向処理方向ｄ２、ｄ２とを、直交させてある。
【００１５】
そして、第２の液晶装置ＬＡ２においても、同様に、ホモジニアス型の第１、第２液晶素子３、４を、それぞれの液晶分子の配向方向が互いに直交するように、各液晶素子３、４に施した各配向処理方向ｄ３、ｄ４を直交させて、配置してある。なお、本例の第１の液晶装置ＬＡ１と第２の液晶装置ＬＡ２における対応する液晶素子１、３及び２、４同士の各配向処理ｄ１とｄ３及びｄ２とｄ４は、互いに直交させてあるが、互いに平行させてもよい。
【００１６】
上述のように構成された液晶素子ＬＡの各液晶素子１〜４においては、液晶を介して対向する一対の電極基板１ａ，１ｂ、２ａ，２ｂ、３ａ，３ｂ及び４ａ，４ｂに入力信号に応じて電圧が印加され、図１（ａ）に示すように電圧が印加されず（オフ時）液晶分子ｍＬが電極基板に平行に配向した第１の液晶配向状態と、図１（ｂ）に示すように電圧が印加されて（オン時）液晶分子が電極基板に対してほぼ垂直な姿勢に立ち上がり配向した第２の液晶配向状態とが、切り換えられる。ここで、上記第１の液晶配向状態においては、第１及び第２の液晶装置ＬＡ１、ＬＡ２に入射する各直線偏光は、それぞれ、第１液晶素子１から第２液晶素子２及び第１液晶素子３から第２液晶素子４を透過する間に、各液晶装置ＬＡ１、ＬＡ２による複屈折作用を受け、各液晶素子の温度に拘わらず、常に透過光の波長λの１／２の位相差が付与される。この理由は、以下の通りである。
【００１７】
即ち、第１及び第２の各液晶装置ＬＡ１、ＬＡ２における各第１液晶素子１、３は、図３の各液晶素子のリタデーション値Ｒｅ（Δｎｄ）の温度依存性図に示されるように、実線の曲線αで示されるリタデーションの温度依存性を示す。一方、温度補償用としての各第２液晶素子２、４は、破線の曲線βで示されるリタデーションの温度依存性を示す。ここで、第１の液晶装置ＬＡ１は上述したようにホモジニアス型液晶素子である第１液晶素子１と第２液晶素子２を互いに液晶分子の配向が直交するように配置してなるから、第１の液晶配向状態（オフ状態）にある第１の液晶装置ＬＡ１を透過する光に付与される位相差つまり第１の液晶装置ＬＡ１全体を通してのリタデーション値Ｒｅは、各液晶素子１、２の個々のリタデーションの差となる。この各液晶素子１、２の個々のリタデーションの差は、図３において二点鎖線γで示すように、−１０℃〜８０℃の温度範囲において約８１０ｎｍで略一定である。この温度に拘わらず一定なリタデーションの差は、レーザー光である透過光の波長λ＝１６２０ｎｍの１／２となっている。
【００１８】
第２の液晶装置ＬＡ２についても、上述とまったく同じ理論が成立し，第１の液晶配向状態（オフ状態）における全体を通してのリタデーション値Ｒｅは、−１０℃〜８０℃の温度範囲において約８１０ｎｍで略一定である。
【００１９】
以上のようにして、各液晶装置ＬＡ１、ＬＡ２を透過する各レーザー光は、各液晶装置の複屈折作用を受けて波長λの１／２の位相差が付与されるから、それぞれの偏光面が各液晶素子の温度に拘わらず常に９０°だけ回転されて出射される。第１の液晶装置ＬＡ１の光入射側には、偏光分離手段としての第１ビームスプリッタ５を対向配置してある。この第１ビームスプリッタ５はその偏光分離面５ａを第１液晶素子１の光入射面に対し４５°に傾斜させて設置してある。
【００２０】
上述の第１ビームスプリッタ５は、入射光を偏光分離面５ａにおいて互いに偏光面が直交する一対の偏光成分光（Ｓ波とＰ波）に分離し、それらを互いに直角方向に出射させるものである。本例では、第１ビームスプリッタ５に入射する入射光Ｒｉを、図中｜で示す紙面に対して平行方向の偏光面を有する第１偏光成分光Ｒ１と、図中●で示す紙面に対して直角方向の偏光面を有する第２偏光成分光Ｒ２とに分離し、第２偏光成分光Ｒ２を第１液晶素子１の光入射面に平行な方向へ反射させ、第１偏光成分光Ｒ１を第１液晶素子１の光入射面に直角に入射する方向に透過させる。
【００２１】
第２の液晶装置ＬＡ２の光入射側には、第１の導光手段としての第１反射鏡６を、第１液晶素子３の光入射面に対し４５°に傾斜させた姿勢で、前記第１ビームスプリッタ５から出射される第２偏光成分光Ｒ２を反射させて第１液晶素子３に対し直角に入射させることが可能な位置に配置してある。
【００２２】
一方、液晶装置ＬＡの光出射側においては、第２の液晶装置ＬＡ２の第２液晶素子４に対向する位置には偏光合成手段としての第２ビームスプリッタ７を、第１の液晶装置ＬＡ１の第２液晶素子２に対向する位置には第２の導光手段としての第２反射鏡８を、それぞれ配置してある。ここで、第２ビームスプリッタ７は、その偏光分離面７ａを対向する第２液晶素子４の光出射面に対し４５°に傾斜させた配置で設置してあり、第２反射鏡８はその反射面を対向する第２液晶素子２の光出射面に対し４５°に傾斜させた配置で設置してある。
【００２３】
第２反射鏡８は、第２液晶素子２を透過してくる第１偏光成分光Ｒ１を第２ビームスプリッタ７に向けて反射させるものである。本例では、第２液晶素子２の光出射面に直角に出射する第１偏光成分光Ｒ１を直角方向に反射させて第２ビームスプリッタ７の偏光分離面７ａに４５°の入射角で入射させる。
【００２４】
第２ビームスプリッタ７は、前述した第１ビームスプリッタ５と同じ部材で同じ機能を備えたものであり、第２液晶素子４から出射する第２偏光成分光Ｒ２と第２反射鏡８により反射された第１偏光成分光Ｒ１とが直交する位置に、偏光分離面７ａを第１、第２偏光成分光Ｒ１、Ｒ２の各進行方向に対し４５°に交差させて配置してある。
【００２５】
これにより、この第２ビームスプリッタ７における偏光分離面７ａに対し、第２液晶素子４に対向する側（以下、表側という）から入射する第２偏光成分光Ｒ２とその裏側から入射する第１偏光成分光Ｒ１とが合成され、出射光Ｒｏとして所定方向に出射される。
【００２６】
次に、本実施形態例の光スイッチの動作について説明する。
まず、図１（ａ）に示す４個の液晶素子１〜４全てに電圧が印加されていないオフ時においては、各液晶素子１〜４の液晶分子ｍＬが、それぞれの電極基板に平行に配向している。即ち、各液晶装置ＬＡ１、ＬＡ２は、入射する偏光成分光の偏光面を９０°回転させることが可能な第１の液晶配向状態をとっている。
【００２７】
このような状態下で、本光スイッチに対する入射光Ｒｉが第１ビームスプリッタ５に入射すると、そのうちの偏光面の振動方向が偏光分離面５ａに沿った第２偏光成分光Ｒ２（図中●印で示す）は入射方向に対して直角方向に反射され、偏光面の振動方向が偏光分離面５ａに交差する第１偏光成分光Ｒ１（｜印で示す）は入射方向に沿って同方向にそのまま第１ビームスプリッタ５を透過する。
【００２８】
第１ビームスプリッタ５の偏光分離面５ａで反射された第２偏光成分光Ｒ２は、第１反射鏡６に４５°の入射角で入射して直角に反射され第１液晶素子３の入射面に対し直角に入射する。この過程において、第２偏光成分光Ｒ２の偏光面の振動方向は変わらず、紙面直角方向のままである。従って、第２偏光成分光Ｒ２は、その偏光面の振動方向が図２に示すように第１液晶素子３の液晶分子配向方向ｄ３に対して４５°に交差する方向となった状態でオフ状態の第１液晶素子３に入射する。
【００２９】
上述の偏光状態で第１液晶素子３に入射した第２偏光成分光Ｒ２は、共にオフ状態で互いに液晶分子の配向方向が直交するように配置された第１液晶素子３と第２液晶素子４を透過する間に、この第２偏光成分光Ｒ２の波長の１／２相当分の位相差が付与されるために偏光面が９０°回転される。従って、第２偏光成分光Ｒ２は、その偏光面の振動方向が紙面平行方向となった状態に旋光されて、第２液晶素子４の光出射面からその直角方向に出射される。第２液晶素子４を出射した第２偏光成分光Ｒ２は、第２ビームスプリッタ７に直角に入射し、その偏光分離面７ａに対し表側から４５°の入射角で入射する。
【００３０】
一方、第１ビームスプリッタ５の偏光分離面５ａを透過した第１偏光成分光Ｒ１は、オフ状態の第１液晶素子１の入射面に対し直角に入射する。この第１偏光成分光Ｒ１も、オフ状態の第１の液晶装置Ｌａ１を透過する間に、第２偏光成分光Ｒ２と同様に偏光面を９０°回転される。
【００３１】
即ち、偏光面の振動方向が紙面平行方向の第１偏光成分光Ｒ１は、図２に示すように、その偏光面の振動方向が第１液晶素子１の液晶分子配向方向ｄ１に対して４５°に交差する方向となった状態でオフ状態の第１液晶素子１に入射する。そして、共にオフ状態で互いに液晶分子の配向方向が直交するように配置された第１液晶素子１と第２液晶素子２を透過する間に、この第１偏光成分光Ｒ１の波長の１／２相当分の位相差が付与されるために偏光面が９０°回転される。従って、第２液晶素子２を出射する第１偏光成分光Ｒ１の偏光面の振動方向は、紙面垂直方向となっている。
【００３２】
第２液晶素子２からその光出射面に対し直角方向に出射した第１偏光成分光Ｒ１は、第２反射鏡８により直角に反射され、第２ビームスプリッタ７の偏光分離面７ａにその裏側から偏光面が紙面に直角な状態のまま４５°の入射角で入射する。
【００３３】
第２ビームスプリッタ７の偏光分離面７ａに対してその表裏両側から入射した第１、第２偏光成分光Ｒ１、Ｒ２は、同方向に重畳して出射されるために合成され、偏光分離される前の入射光Ｒｉと同じ構成の出射光Ｒｏとなって入射光Ｒｉの入射方向に沿った同方向に出射される。即ち、第２ビームスプリッタ７の偏光分離面７ａにその一方の表側から入射する第２偏光成分光Ｒ２は、偏光面の振動方向が偏光分離面７ａに対して交差する方向であるからそのまま透過して入射方向と同方向に出射し、偏光分離面７ａの裏側から入射した第１偏光成分光Ｒ１は、偏光面の振動方向が偏光分離面７ａに沿った方向であるから直角方向に反射されて第２偏光成分光Ｒ２と同方向に出射され、出射光Ｒｏに合成される。
【００３４】
次に、本光スイッチに光の進行方向を切り換える旨の信号が入力されると、４個の液晶素子１〜４全てに電圧が印加され（オン時）、各液晶素子１〜４の液晶分子ｍＬが図１（ｂ）に示すようにそれぞれの電極基板１ａ〜４ｂに対して略直角方向に立ち上がった状態に配向する。即ち、液晶装置ＬＡは、入射光の偏光面を回転させずにそのまま出射させる第２の液晶配向状態となる。
【００３５】
このような状態下では、液晶装置ＬＡに入射する第１、第２偏光成分光Ｒ１、Ｒ２は、偏光面が回転されることなくそのまま液晶装置ＬＡを透過し出射する。すなわち、上述のオフ時と同様に第１ビームスプリッタ５の偏光分離面５ａで反射され第１反射鏡６で反射されて第１液晶素子３に入射する偏光面の振動方向が紙面直角方向に沿った第２偏光成分光Ｒ２は、偏光面の振動方向が同じ方向のまま第１液晶素子３と第２液晶素子４の各液晶層を透過して出射し、第２ビームスプリッタ７の偏光分離面７ａに表側から入射する。また、第１ビームスプリッタ５の偏光分離面５ａを透過した第１偏光成分光Ｒ１も、偏光面の振動方向が同じ方向のまま、第１液晶素子１と第２液晶素子２の各液晶層を透過して出射し、第２反射鏡８で直角に反射されて第２ビームスプリッタ７の偏光分離面７ａに裏側から入射する。
【００３６】
そして、第２ビームスプリッタ７の偏光分離面７ａに表側から入射した第２偏光成分光Ｒ２は、偏光面の振動方向が偏光分離面７ａに平行であるために、直角に反射される。一方、偏光分離面７ａに裏側から入射した第１偏光成分光Ｒ１は、偏光面の振動方向がその偏光分離面７ａに交差するために透過し、入射方向と同方向、つまり第２偏光成分光Ｒ２の出射方向と同方向に重畳して出射される。このため、第２偏光成分光Ｒ２と第１偏光成分光Ｒ１とが合成され、偏光分離される前の入射光Ｒｉと同じ構成の出射光Ｒｏとなって入射光Ｒｉに対して直角方向に出射される。
【００３７】
以上のように、本実施形態例の光スイッチは、液晶装置ＬＡを構成する各液晶素子１〜４に印加する電圧を入力信号に応じて一律に切り換えるだけの簡単な操作で、光信号を電気信号に変換することなく光信号のままその進行方向を９０°異なる方向に切り換えることができる。そして、この光スイッチ効果は、旋光手段としての液晶装置を複数の液晶素子で構成し、それら液晶素子を個々のリタデーションの温度依存性が互いに補償し合うように組み合わせてあるから、温度に拘わらず安定的に奏される。
【００３８】
次に、本発明の第２実施形態例について、図４（ａ）と図４（ｂ）の模式的構成図に基づき説明する。図４（ａ）と図４（ｂ）は、それぞれ、光の進行方向を変えずに出射させる状態と光の進行方向を９０°変化させて出射させる状態を示している。なお、上述の第１実施形態例と同一の構成要素は、同じ符号を付してその説明を省略する。
【００３９】
本例の光スイッチは、旋光手段としての液晶装置ＬＡを２個の第１液晶素子１０と第２液晶素子１１とで構成し、偏光分離手段及び偏光合成手段として第１、第２反射偏光板１２、１４を用いたものである。
【００４０】
第１液晶素子１０と第２液晶素子１１は、共に液晶分子ｍＬをそれぞれの基板１０ａ，１０ｂ及び１１ａ，１１ｂに平行な所定方向に配向させたホモジニアス型液晶素子であり、それぞれの液晶分子配向方向が互いに直交する配置で並列に配置してある。そして、第１液晶素子１０と第２液晶素子１１のそれぞれのリタデーションの温度依存性を、前述の実施形態例と同様に、液晶装置ＬＡが温度に拘わらず一定のリタデーションが得られるように互いに補償し合う構成としてある。即ち、本例の第１液晶素子１０と第２液晶素子１１からなる液晶装置ＬＡは、前述した第１実施形態例における第１液晶素子１と第２液晶素子２からなる第１の液晶装置ＬＡ１或いは第１液晶素子３と第２液晶素子４からなる第２の液晶装置ＬＡ２と同一の構成である。液晶装置ＬＡの光入射側には、偏光分離手段としての第１反射偏光板１２と第１の導光手段としての第１反射鏡１３を、第１液晶素子１０の光入射面の所定の領域に対向させるとともに、その光入射面に対し４５°に傾斜させた姿勢で互いに平行に配置してある。
【００４１】
第１反射偏光板１２は、光学軸として互いに直交する方向に反射軸１２ａと透過軸１２ｂとを有するものであり、それら光学軸１２ａ、１２ｂを第１液晶素子１０の液晶分子の配向方向ｄ１に対して４５°で交差させた配置で、設置してある。
【００４２】
液晶装置ＬＡを介してその光出射側には、前記第１反射鏡１３に対向する位置に偏光合成手段としての第２反射偏光板１４を、前記第１反射偏光板１２に対向する位置には第２の導光手段としての第２反射鏡１５を、それぞれ配設してある。これら第２反射偏光板１４と第２反射鏡１５は、第２液晶素子１１の光入射面に対し共に４５°に傾斜させた姿勢で互いに平行に配置してある。
【００４３】
ここで、第２反射偏光板１４は、第２液晶素子１１から出射する第２偏光成分光Ｒ２と第２液晶素子１１から出射し第２反射鏡１５により反射された第１偏光成分光Ｒ１とが直交する位置に、それぞれの偏光成分光Ｒ１、Ｒ２の各進行方向に対し４５°で交差する姿勢で配置してある。これにより、この第２反射偏光板１４の第２液晶素子１１に対向する面（以下、表面という）に入射する第２偏光成分光Ｒ２とその裏面に入射する第１偏光成分光Ｒ１とが合成され、出射光Ｒｏとして所定方向に出射される。
【００４４】
以上のように構成された本例の光スイッチによる場合も、前述した第１実施形態例と同様に、図４（ａ）に示す第１、第２液晶素子１０、１１に電圧が印加されていないオフ時においては入射光Ｒｉと同方向に出射光Ｒｏが出射され、図４（ｂ）に示す第１、第２液晶素子１０、１１に電圧が印加されたオン時においては、出射光Ｒｏの出射方向が入射光Ｒｉに沿った方向に対して直角の方向に切り換えられる。そして、この光スイッチ効果は、第１、第２液晶素子１０、１１の温度に拘わらず、常に安定して奏される。
【００４５】
なお、本発明は、上記実施形態例等に限定されるものではなく、本発明の技術的範囲において種々の変形が可能であることは勿論である。
【００４６】
例えば、図４に示した実施形態の変形例として、第１反射偏光板と第２反射偏光板を、図６に示すように部品として１個にまとめることも可能である。この変形例においては、図１に示す第１実施形態例と同様に液晶装置ＬＡを第１の液晶装置ＬＡ１と第２の液晶装置ＬＡ２に分け、これらの間に１個の反射偏光部材１６を各液晶素子１〜４の入、出射面に対し４５°に傾斜させた配置で設けてある。これにより、反射偏光部材１６の第１液晶素子１の入射面に対向する部分が第１反射偏光板１２と同じ機能を果たす第１反射偏光部となり、反射偏光部材１６の第２液晶素子４の出射面に対向する部分が第２反射偏光板１４と同じ機能を果たす第２反射偏光部となる。
【００４７】
上述のように構成された本変形例の光スイッチによれば、部品数が少なくなって構造がより簡素化されるとともに、第１乃至第２実施形態例と同様に温度に拘わらず常に安定して所望の光スイッチ効果が奏される。
【００４８】
また、図７に示すように、液晶装置ＬＡに対する入射光Ｒｉの入射方向を、第１液晶素子１の入射面に対して平行とし、偏光分離手段としての第１ビームスプリッタ５と偏光合成手段としての第２ビームスプリッタ７を第１液晶装置ＬＡ１を介して対向配置してもよい。この場合、液晶装置ＬＡのオフ時には、出射光Ｒｏが入射光Ｒｉに対して直角方向に出射され、オン時には出射光Ｒｏが入射光Ｒｉに対して逆方向に出射される。このように、本発明によれば、入射光に対する出射光の相対方向が異なる種々の光スイッチを実現することができる。
【００４９】
更に、複数の液晶素子からなる液晶装置の透過光に付与する位相差は、透過光の波長の１／２に限らず、透過光の波長の１／２の奇数倍であればよい。
【００５０】
また更に、本発明の液晶装置を構成する液晶素子としては、ホモジニアス型液晶素子に限らず、ツイストネマチック型液晶素子等の他の種々の液晶素子を用いることが可能である。この場合、透過光に温度に拘わらず波長の１／２の奇数倍相当分の位相差が付与されるように、液晶装置を構成する複数の液晶素子におけるそれぞれのリタデーションの温度依存性や配向処理方向の配置を設定すればよい。
【００５１】
更にまた、液晶装置の第１の液晶配向状態と第２の液晶配向状態における入射光の偏光面の各回転量は、上述の実施形態例等では９０°と０°に設定してあるが、これに限らず、１８０°と９０度或いは−４５度と４５°等、互いに９０°だけ異なる種々の組合せが可能である。
【００５２】
また更に、複数の液晶素子を組み合わせるだけで液晶装置のリタデーションを温度に拘わらず一定にすることが困難な場合は、一つの液晶素子に印加する電圧を液晶装置のリタデーションが一定になるように温度に応じて調整するようにしても良い。
【００５３】
加えて、第１と第２の導光手段は、それぞれ、１個の反射鏡に限らず、複数の反射鏡を組み合わせて構成してもよい。
【００５４】
【発明の効果】
この発明の光スイッチは、入射光の互いに直交する偏光成分のうちの一方の第１偏光成分光を反射し、他方の第２偏光成分光を透過させる偏光分離手段と、前記偏光分離手段により反射された前記第１の偏光成分光の進行方向を前記第２偏光成分光と平行な方向に導く第１の導光手段と、前記偏光分離手段により分離された第２の偏光成分光と、前記偏光分離手段により分離され、前記第１の導光手段により導かれた前記第１の偏光成分光が入射され、電界の印加に応じてリタデーションの値が透過光の波長の実質的に１／２の奇数倍だけ互いに異なる第１の配向状態と第２の配向状態とに切り替え可能な液晶素子と、前記液晶素子の前記リタデーションの温度依存性を補償する補償用液晶素子とからなる液晶装置と、前記液晶装置の光出射側に配置され、前記偏光分離手段により分離された第２の偏光成分光の前記液晶装置を透過した光を、前記第１の偏光成分光の前記液晶装置を透過した光の進行方向と交差する方向に導く第２の導光手段と、前記第１の偏光成分光の前記電気光手段を透過した光と、第２の偏光成分光の前記電気光手段を透過して前記第２の導光板により導かれた光とが入力され、前記２つの光を同一の光路に出射させる偏光合成手段とからなり、入射光を互いに偏光方向が直交するＳ波とＰ波の偏光成分光に分離して液晶装置に入射させ、液晶装置を透過させる際に、その旋光作用により各偏光成分光を温度に拘わらず一定量旋光させ、この後、液晶装置を出射した各偏光成分光を合成するものであり、液晶装置に入力される信号に応じて透過光の旋光量が互いに９０°だけ異なる第１の液晶配向状態と第２の液晶配向状態に切り換えるものであるから、温度に拘わらず常に安定して光信号を電気信号に変換することなく光信号のままその進行ルートを切り換えることができる。その結果、広いデータ帯域の光信号の進行ルートを光のロス無く安定して正確に切り換えることができる安価な光スイッチを提供することが可能となる。
【００５５】
この光スイッチにおいては、前記液晶装置を構成する前記液晶素子と前記補償用液晶素子はそれぞれ、液晶分子が基板に対して平行に配向したホモジニアス型液晶素子を各液晶素子の液晶分子の配向方向が互いに直交する配置で設置して構成することが好ましく、これにより、温度に拘わらず安定的に光信号を光信号のままその進行方向を切り換えることができる光スイッチを簡素に構成することができる。
【００５６】
そして、複数のホモジニアス型液晶素子からなる液晶装置を、分離された各偏光成分光の光路中にそれぞれ配置するのがよく、これにより、温度変化に対しより安定して光のロスの少ない鋭敏な光スイッチ効果を得ることができる。
【００５７】
また、上述のように液晶装置を２個の液晶装置で構成した場合、１個の反射偏光板を偏光分離手段と偏光合成手段を兼用する部材とし、この反射偏光板を２個の液晶装置の間を通して斜めに配置してもよく、これにより、構成部材数が少なくなり、本発明の光スイッチの構造がより簡素化される。
【図面の簡単な説明】
【図１】この発明の第１実施形態例としての光スイッチを示す模式的構成図で、（ａ）はその光スイッチがオフされた状態を示し、（ｂ）はオンされた状態を示す。
【図２】上記第１実施形態例における透過光の偏光面の方向と液晶分子の配向方向との関係を示す説明図。
【図３】上記第１実施形態における液晶素子のリタデーション値の温度依存性を示すグラフ図。
【図４】この発明の第２実施形態例としての光スイッチを示す模式的構成図で、（ａ）はその光スイッチがオフされた状態を示し、（ｂ）はオンされた状態を示す。
【図５】上記第２実施形態例におけるおける透過光の偏光面の方向と液晶分子の配向方向との関係を示す説明図。
【図６】この発明の上記実施形態例の変形例を示す模式的構成図。
【図７】この発明の上記実施形態例の他の変形例を示す模式的構成図。
【符号の説明】
１，３，１０…第１液晶素子
２，４，１１…第２液晶素子
ＬＡ　…液晶装置
ＬＡ１…第１の液晶装置
ＬＡ２…第２の液晶装置
５…第１ビームスプリッタ
６，１３…第１反射鏡
７…第２ビームスプリッタ
８，１５…第２反射鏡
１２…第１反射偏光板
１４…第２反射偏光板
１６…反射偏光部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical switch for spatially switching a traveling route of an optical signal propagating in an optical communication network or other optical signal processing.
[0002]
[Prior art]
Today, with the development of optical communication networks, optical fibers for propagating optical signals are widely used. However, in order to transmit an optical signal through an optical fiber, it is necessary to switch the traveling route of the optical signal between the optical fibers.
[0003]
One method of performing such switching is to convert a light signal into an electric signal using a normal electronic device for photoelectric conversion, and blink a light source disposed on a different traveling route according to the converted electric signal. In some cases, the route of a signal is switched.
[0004]
[Problems to be solved by the invention]
However, as the transmission rate of information data continues to increase, it becomes increasingly difficult to use ordinary electronic devices to process a wide data band of an optical signal transmitted by an optical fiber. Further, since it is necessary to convert between an optical signal and an electric signal, there are problems that the data format is restricted and the device becomes complicated and expensive.
[0005]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical switch which can switch a traveling route accurately and stably with an optical signal without converting an optical signal into an electric signal with a simple structure.
[0006]
[Means for Solving the Problems]
The optical switch according to the present invention includes: a polarization separation unit that reflects one of the first polarization component lights of the polarization components of the incident light that are orthogonal to each other and transmits the other second polarization component light; A first light guiding unit for guiding a traveling direction of the first polarized component light in a direction parallel to the second polarized component light; a second polarized component light separated by the polarization separating unit; The first polarized component light separated by the polarized light separating means and guided by the first light guiding means is incident, and the retardation value is substantially の of the wavelength of the transmitted light in response to the application of an electric field. A liquid crystal device that can be switched between a first alignment state and a second alignment state that are different from each other by an odd number of times, and a liquid crystal device that includes a compensation liquid crystal element that compensates for the temperature dependence of the retardation of the liquid crystal element; Light output side of the liquid crystal device The second polarized component light, which is disposed and separated by the polarization splitting means, is transmitted through the liquid crystal device in a direction crossing the traveling direction of the first polarized component light transmitted through the liquid crystal device. Second light guiding means for guiding, light of the first polarized light component transmitted through the electric light means, and light of the second polarized light component transmitted through the electric light means and guided by the second light guide plate. And polarized light combining means for receiving the input light and emitting the two lights to the same optical path, and emitting the incident light in different directions according to the electric field applied to the electro-optical means. It is assumed that.
[0007]
In this optical switch, the alignment state of the liquid crystal device is switched between a first liquid crystal alignment state and a second liquid crystal alignment state in which the amount of rotation of transmitted light differs by 90 ° regardless of the temperature in accordance with an input signal. When the incident light of the optical switch is separated into the S-wave and the P-wave polarization component light whose polarization planes are orthogonal to each other and is incident on the liquid crystal device, and is transmitted through the liquid crystal device, each polarization component light is transmitted regardless of the temperature. The light is rotated by a certain amount according to the first and second liquid crystal alignment states, and thereafter, the respective polarized component lights emitted from the liquid crystal device are combined to be emitted light and emitted in a predetermined direction. Therefore, according to the present optical switch, it is possible to always stably switch the traveling route of the optical signal without converting the optical signal into an electric signal regardless of the temperature. As a result, it is possible to provide an inexpensive optical switch that can stably and accurately switch a traveling route of an optical signal in a wide data band without loss as an optical signal.
[0008]
In the above optical switch, the liquid crystal element and the compensating liquid crystal element of the liquid crystal device are two homogeneous liquid crystal elements each having liquid crystal molecules aligned in parallel with a substrate, and the alignment of each liquid crystal molecule. The liquid crystal element and the compensating liquid crystal element are arranged in directions perpendicular to each other, and the liquid crystal element and the compensation liquid crystal element are respectively arranged in a first alignment state in which liquid crystal molecules are aligned in parallel with a substrate according to an applied voltage. It is preferable to switch between the second alignment state in which the molecules rise and align so as to emit light whose polarization planes of light transmitted through the liquid crystal device are different from each other by approximately 90 °.
[0009]
In this case, the liquid crystal device is constituted by a first liquid crystal device disposed in the optical path of the first polarized light component and a second liquid crystal device disposed in the optical path of the second polarized light component. Good.
[0010]
When the liquid crystal device is composed of a first liquid crystal device and a second liquid crystal device, the polarization splitting means and the polarization synthesizing means have a reflection axis and a transmission axis in directions orthogonal to each other, and Is a single reflective polarizer that reflects polarized component light along the reflection axis and transmits polarized component light along the transmission axis, and the reflective polarizer is the same as the first liquid crystal device. The second liquid crystal devices may be arranged obliquely through the second liquid crystal devices, thereby reducing the number of constituent members and simplifying the structure.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIGS. 1A and 1B are schematic configuration diagrams showing the configuration of an optical switch according to a first embodiment of the present invention, in which a light is emitted without changing the traveling direction of light. The state in which the traveling direction of light is changed by 90 ° and emitted is shown.
[0012]
The optical switch of this embodiment uses a liquid crystal device LA including two first liquid crystal elements 1 and 3 and two second liquid crystal elements 2 and 4 for temperature compensation, and the incident light Ri is incident thereon. A first beam splitter 5 as polarization splitting means and a first reflecting mirror 6 as first light guiding means are arranged on the light incident side, and a second beam as polarization combining means is provided on the light emitting side for emitting the emitted light Ro. The configuration is such that a splitter 7 and a second reflecting mirror 8 as a second light guiding means are arranged. Note that the incident light Ri in this example is a laser light having a wavelength of 1620 nm.
[0013]
The liquid crystal device LA of the present example includes a first liquid crystal device LA1 in which a first liquid crystal element 1 and a second liquid crystal element 2 are arranged in parallel with their input and output surfaces parallel to each other, a first liquid crystal element 3 and a second liquid crystal element 3, respectively. The liquid crystal element 4 is constituted by a second liquid crystal device LA2 in which respective input and output surfaces are arranged in parallel in parallel. Further, the first liquid crystal element 1 and the first liquid crystal element 3 and the second liquid crystal element 2 and the second liquid crystal element 4 of different liquid crystal devices are also arranged such that their respective input and output surfaces are parallel to each other. . The four liquid crystal elements 1 to 4 of the present example respectively apply liquid crystal molecules to a pair of electrode substrates 1a, 1b, 2a, 2b, 3a, 3b and 4a, 4b on which electrodes are formed. It is a homogeneous liquid crystal element that is held while being oriented in parallel.
[0014]
In the first liquid crystal device LA1, the first and second homogeneous liquid crystal elements 1 and 2 are arranged so that the alignment directions of the liquid crystal molecules are orthogonal to each other. That is, as shown in FIG. 2 showing the relationship between the polarization direction of the transmitted light and the orientation direction of the liquid crystal molecules in each liquid crystal element, the vicinity of the pair of electrode substrates 1a and 1b of the first liquid crystal element 1 is also shown. Alignment directions d1 and d1 such as rubbing applied to the respective alignment directions of the liquid crystal molecules, that is, the respective alignment films (not shown) deposited on the respective electrodes, and a pair of electrode substrates of the second liquid crystal element 2. The same orientation processing directions d2 and d2 in 2a and 2b are orthogonal to each other.
[0015]
Similarly, in the second liquid crystal device LA2, the first and second liquid crystal elements 3 and 4 of the homogeneous type are similarly connected to the respective liquid crystal elements 3 and 4 so that the alignment directions of the liquid crystal molecules are orthogonal to each other. The applied orientation directions d3 and d4 are orthogonal to each other. Although the respective alignment treatments d1 and d3 of the corresponding liquid crystal elements 1, 3, 2 and 4 in the first liquid crystal device LA1 and the second liquid crystal device LA2 in this example are orthogonal to each other, , May be parallel to each other.
[0016]
In each of the liquid crystal elements 1 to 4 of the liquid crystal element LA configured as described above, a pair of electrode substrates 1a, 1b, 2a, 2b, 3a, 3b and 4a, 4b facing each other via a liquid crystal according to an input signal. 1 (a), no voltage is applied (at the time of OFF), and the liquid crystal molecules mL are oriented in parallel to the electrode substrate, as shown in FIG. 1 (a). In this manner, the voltage is applied (at the time of ON), and the liquid crystal molecules are switched to the second liquid crystal alignment state in which the liquid crystal molecules rise and are oriented substantially perpendicular to the electrode substrate. Here, in the first liquid crystal alignment state, the respective linearly polarized lights incident on the first and second liquid crystal devices LA1 and LA2 are respectively converted from the first liquid crystal element 1 to the second liquid crystal element 2 and the first liquid crystal element. During the transmission from the third liquid crystal element 4 to the second liquid crystal element 4, the liquid crystal devices LA1 and LA2 perform a birefringent action, and a phase difference of 1/2 of the wavelength λ of the transmitted light is always applied regardless of the temperature of each liquid crystal element. Is done. The reason is as follows.
[0017]
That is, the first liquid crystal elements 1 and 3 in the first and second liquid crystal devices LA1 and LA2 have solid lines as shown in the temperature dependence diagram of the retardation value Re (Δnd) of each liquid crystal element in FIG. Shows the temperature dependence of the retardation indicated by curve α. On the other hand, each of the second liquid crystal elements 2 and 4 for temperature compensation shows the temperature dependence of the retardation indicated by the dashed curve β. Here, the first liquid crystal device LA1 has the first liquid crystal element 1 and the second liquid crystal element 2 which are homogeneous liquid crystal elements arranged as described above so that the liquid crystal molecules are orthogonal to each other. The phase difference given to the light transmitted through the first liquid crystal device LA1 in the liquid crystal alignment state (off state), that is, the retardation value Re throughout the entire first liquid crystal device LA1 is the individual value of each of the liquid crystal elements 1 and 2. The difference in retardation. The difference between the individual retardations of the liquid crystal elements 1 and 2 is substantially constant at about 810 nm in a temperature range of -10 ° C. to 80 ° C. as shown by a two-dot chain line γ in FIG. The constant retardation difference irrespective of the temperature is の of the wavelength λ = 1620 nm of the transmitted light which is the laser light.
[0018]
The same theory as described above holds true for the second liquid crystal device LA2, and the entire retardation value Re in the first liquid crystal alignment state (off state) is about 810 nm in a temperature range of −10 ° C. to 80 ° C. It is almost constant.
[0019]
As described above, each laser beam transmitted through each of the liquid crystal devices LA1 and LA2 is given a phase difference of の of the wavelength λ due to the birefringence action of each liquid crystal device. The light is always rotated by 90 ° and emitted regardless of the temperature of each liquid crystal element. On the light incident side of the first liquid crystal device LA1, a first beam splitter 5 as a polarization splitting means is disposed to face. The first beam splitter 5 is installed with its polarization splitting surface 5a inclined at 45 ° with respect to the light incident surface of the first liquid crystal element 1.
[0020]
The above-described first beam splitter 5 separates incident light into a pair of polarization component lights (S-wave and P-wave) whose polarization planes are orthogonal to each other on the polarization separation plane 5a, and emits them in a direction perpendicular to each other. . In this example, the incident light Ri incident on the first beam splitter 5 is converted into a first polarized component light R1 having a polarization plane parallel to the paper surface indicated by | in the drawing and a paper surface indicated by ● in the drawing. The light is separated into a second polarized light component R2 having a plane of polarization in a perpendicular direction, the second polarized light component R2 is reflected in a direction parallel to the light incident surface of the first liquid crystal element 1, and the first polarized light component R1 is converted to the second polarized light component R1. The light is transmitted in a direction perpendicular to the light incident surface of one liquid crystal element 1.
[0021]
On the light incident side of the second liquid crystal device LA2, the first reflecting mirror 6 as the first light guiding means is tilted at 45 ° with respect to the light incident surface of the first liquid crystal element 3, and The second polarization component light R 2 emitted from the one beam splitter 5 is arranged at a position where the second polarization component light R 2 can be reflected and incident on the first liquid crystal element 3 at right angles.
[0022]
On the other hand, on the light emission side of the liquid crystal device LA, a second beam splitter 7 as a polarization combining means is provided at a position facing the second liquid crystal element 4 of the second liquid crystal device LA2, and a second beam splitter 7 of the first liquid crystal device LA1. At positions facing the two liquid crystal elements 2, second reflecting mirrors 8 as second light guide means are arranged. Here, the second beam splitter 7 is installed so that its polarization splitting surface 7a is inclined at 45 ° with respect to the light emitting surface of the second liquid crystal element 4 facing the second beam splitter 7, and the second reflecting mirror 8 reflects the reflected light. The second liquid crystal element 2 is disposed so that its surface is inclined at 45 ° with respect to the light emitting surface of the second liquid crystal element 2 facing the second liquid crystal element 2.
[0023]
The second reflecting mirror 8 reflects the first polarized component light R1 transmitted through the second liquid crystal element 2 toward the second beam splitter 7. In this example, the first polarization component light R1 emitted at a right angle to the light emission surface of the second liquid crystal element 2 is reflected in the right angle direction and is incident on the polarization splitting surface 7a of the second beam splitter 7 at an incident angle of 45 °. .
[0024]
The second beam splitter 7 has the same function as the first beam splitter 5 and has the same function. The second beam splitter 7 is reflected by the second reflecting mirror 8 and the second polarization component light R2 emitted from the second liquid crystal element 4. The polarized light separating surface 7a is disposed at a position orthogonal to the first polarized light component R1 so as to intersect at 45 ° with each traveling direction of the first and second polarized light components R1 and R2.
[0025]
As a result, the second polarization component light R2 incident on the polarization separation surface 7a of the second beam splitter 7 from the side facing the second liquid crystal element 4 (hereinafter, referred to as the front side) and the first polarization incident from the back side. The component light R1 is combined and emitted in a predetermined direction as emission light Ro.
[0026]
Next, the operation of the optical switch according to the present embodiment will be described.
First, when no voltage is applied to all of the four liquid crystal elements 1 to 4 shown in FIG. 1A, the liquid crystal molecules mL of each of the liquid crystal elements 1 to 4 are aligned in parallel to the respective electrode substrates. are doing. That is, each of the liquid crystal devices LA1 and LA2 has the first liquid crystal alignment state in which the polarization plane of the incident polarization component light can be rotated by 90 °.
[0027]
In this state, when the incident light Ri to the present optical switch enters the first beam splitter 5, the vibration direction of the polarization plane is changed to the second polarization component light R2 along the polarization separation plane 5a (indicated by a black circle in the figure). ) Is reflected in a direction perpendicular to the incident direction, and the first polarized light component R1 (indicated by |) in which the vibration direction of the polarization plane intersects with the polarization splitting surface 5a remains in the same direction along the incident direction. The light passes through the first beam splitter 5.
[0028]
The second polarization component light R2 reflected by the polarization splitting surface 5a of the first beam splitter 5 is incident on the first reflecting mirror 6 at an incident angle of 45 °, is reflected at a right angle, and is incident on the incident surface of the first liquid crystal element 3. Incident at right angles to the plane. In this process, the vibration direction of the polarization plane of the second polarization component light R2 does not change and remains in the direction perpendicular to the plane of the paper. Accordingly, the second polarization component light R2 is turned off in a state where the vibration direction of the polarization plane thereof intersects the liquid crystal molecule alignment direction d3 of the first liquid crystal element 3 at 45 ° as shown in FIG. To the first liquid crystal element 3.
[0029]
The second polarization component light R2 incident on the first liquid crystal element 3 in the above-mentioned polarization state is composed of the first liquid crystal element 3 and the second liquid crystal element 4 which are both turned off and arranged so that the orientation directions of the liquid crystal molecules are orthogonal to each other. During the transmission of the second polarized component light R2, the polarization plane is rotated by 90 ° because a phase difference corresponding to 波長 of the wavelength of the second polarized light component R2 is provided. Therefore, the second polarization component light R2 is rotated in a state where the oscillation direction of the polarization plane is parallel to the plane of the paper, and is emitted from the light emission surface of the second liquid crystal element 4 in the direction perpendicular thereto. The second polarization component light R2 emitted from the second liquid crystal element 4 enters the second beam splitter 7 at a right angle, and enters the polarization splitting surface 7a at an incident angle of 45 ° from the front side.
[0030]
On the other hand, the first polarization component light R1 transmitted through the polarization splitting surface 5a of the first beam splitter 5 is incident at right angles to the incident surface of the first liquid crystal element 1 in the off state. The first polarization component light R1 is also rotated by 90 ° in the polarization plane, similarly to the second polarization component light R2, while transmitting through the first liquid crystal device La1 in the off state.
[0031]
That is, as shown in FIG. 2, the first polarization component light R1 whose polarization plane vibrates in a direction parallel to the paper plane has a vibration direction of the polarization plane of 45 ° with respect to the liquid crystal molecule alignment direction d1 of the first liquid crystal element 1. And enters the first liquid crystal element 1 in the off state in a direction intersecting with. Then, while transmitting through the first liquid crystal element 1 and the second liquid crystal element 2 arranged so that the alignment directions of the liquid crystal molecules are orthogonal to each other in the off state, the wavelength of the first polarization component light R1 is １／. The polarization plane is rotated by 90 ° to provide a considerable phase difference. Therefore, the oscillation direction of the polarization plane of the first polarization component light R1 emitted from the second liquid crystal element 2 is perpendicular to the paper.
[0032]
The first polarization component light R1 emitted from the second liquid crystal element 2 in the direction perpendicular to the light exit surface is reflected at right angles by the second reflecting mirror 8, and is reflected from the back side to the polarization separation surface 7a of the second beam splitter 7. Light is incident at an incident angle of 45 ° while the polarization plane is perpendicular to the paper surface.
[0033]
The first and second polarized light components R1 and R2 incident on the polarization splitting surface 7a of the second beam splitter 7 from both front and back sides are superimposed and emitted in the same direction and are combined and polarized and separated. The emitted light Ro has the same configuration as the previous incident light Ri, and is emitted in the same direction along the incident direction of the incident light Ri. That is, the second polarization component light R2 incident on the polarization separation surface 7a of the second beam splitter 7 from one of its front sides is transmitted as it is because the vibration direction of the polarization surface is a direction intersecting the polarization separation surface 7a. The first polarization component light R1 emitted in the same direction as the incident direction and incident from the back side of the polarization separation surface 7a is reflected in a right angle direction because the oscillation direction of the polarization surface is the direction along the polarization separation surface 7a. The light is emitted in the same direction as the second polarization component light R2 and is combined with the emitted light Ro.
[0034]
Next, when a signal for switching the traveling direction of light is input to the optical switch, a voltage is applied to all four liquid crystal elements 1 to 4 (when turned on), and the liquid crystal molecules of each of the liquid crystal elements 1 to 4 are turned on. As shown in FIG. 1B, the mL is oriented in a state of rising in a direction substantially perpendicular to each of the electrode substrates 1a to 4b. That is, the liquid crystal device LA is in the second liquid crystal alignment state in which the incident light is emitted without rotating the polarization plane.
[0035]
In such a state, the first and second polarized light components R1 and R2 incident on the liquid crystal device LA pass through the liquid crystal device LA and exit without being rotated in the polarization plane. That is, as in the case of the above-described OFF state, the vibration direction of the polarization plane reflected by the polarization splitting surface 5a of the first beam splitter 5, reflected by the first reflecting mirror 6, and incident on the first liquid crystal element 3 is along the direction perpendicular to the plane of the paper. The second polarized component light R2 passes through the respective liquid crystal layers of the first liquid crystal element 3 and the second liquid crystal element 4 and exits while the vibration direction of the polarization plane is the same, and the polarization separation plane of the second beam splitter 7 is emitted. 7a is incident from the front side. Also, the first polarization component light R1 transmitted through the polarization splitting surface 5a of the first beam splitter 5 also divides the liquid crystal layers of the first liquid crystal element 1 and the second liquid crystal element 2 while maintaining the same vibration direction of the polarization plane. The light is transmitted and emitted, is reflected at a right angle by the second reflecting mirror 8, and is incident on the polarization splitting surface 7a of the second beam splitter 7 from the back side.
[0036]
Then, the second polarization component light R2 incident on the polarization separation surface 7a of the second beam splitter 7 from the front side is reflected at a right angle because the oscillation direction of the polarization surface is parallel to the polarization separation surface 7a. On the other hand, the first polarization component light R1 incident on the polarization separation surface 7a from the back side is transmitted because the vibration direction of the polarization surface crosses the polarization separation surface 7a, and is transmitted in the same direction as the incident direction, that is, the second polarization component light. The light is emitted while being superimposed in the same direction as the emission direction of R2. For this reason, the second polarization component light R2 and the first polarization component light R1 are combined, and the emitted light Ro has the same configuration as the incident light Ri before being polarized and separated, and is emitted in a direction perpendicular to the incident light Ri. Is done.
[0037]
As described above, the optical switch of this embodiment converts an optical signal into an electrical signal by a simple operation of uniformly switching the voltage applied to each of the liquid crystal elements 1 to 4 constituting the liquid crystal device LA according to the input signal. It is possible to switch the traveling direction of the optical signal to a direction different by 90 ° without converting the signal into a signal. This optical switch effect is achieved by irrespective of the temperature because the liquid crystal device as the optical rotation means is composed of a plurality of liquid crystal elements, and the liquid crystal elements are combined so that the temperature dependence of the individual retardations compensate each other. Played stably.
[0038]
Next, a second embodiment of the present invention will be described based on the schematic configuration diagrams of FIGS. 4A and 4B. FIGS. 4A and 4B show a state where light is emitted without changing the traveling direction and a state where light is emitted while changing the traveling direction by 90 °, respectively. The same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0039]
In the optical switch of the present example, a liquid crystal device LA as an optical rotation unit is composed of two first liquid crystal elements 10 and a second liquid crystal element 11, and a first and a second reflective polarizer as a polarization separating unit and a polarization combining unit. 12 and 14.
[0040]
Each of the first liquid crystal element 10 and the second liquid crystal element 11 is a homogeneous liquid crystal element in which liquid crystal molecules mL are aligned in a predetermined direction parallel to the respective substrates 10a, 10b and 11a, 11b. Are arranged in parallel at right angles to each other. The temperature dependence of the retardation of each of the first liquid crystal element 10 and the second liquid crystal element 11 is compensated for each other so that the liquid crystal device LA can obtain a constant retardation irrespective of the temperature, as in the above-described embodiment. There is a configuration that works together. That is, the liquid crystal device LA including the first liquid crystal element 10 and the second liquid crystal element 11 in the present embodiment is the same as the first liquid crystal device LA1 including the first liquid crystal element 1 and the second liquid crystal element 2 in the first embodiment described above. Alternatively, it has the same configuration as the second liquid crystal device LA2 including the first liquid crystal element 3 and the second liquid crystal element 4. On the light incident side of the liquid crystal device LA, a first reflective polarizing plate 12 as a polarization splitting unit and a first reflecting mirror 13 as a first light guiding unit are provided in a predetermined region of a light incident surface of the first liquid crystal element 10. And are arranged in parallel with each other in a posture inclined at 45 ° to the light incident surface.
[0041]
The first reflective polarizing plate 12 has a reflection axis 12a and a transmission axis 12b in directions orthogonal to each other as optical axes, and the optical axes 12a and 12b are aligned with the alignment direction d1 of the liquid crystal molecules of the first liquid crystal element 10. It is installed in an arrangement where it intersects at an angle of 45 °.
[0042]
On the light exit side through the liquid crystal device LA, a second reflective polarizing plate 14 as a polarization combining means is provided at a position facing the first reflecting mirror 13 and at a position facing the first reflecting polarizing plate 12. Second reflecting mirrors 15 as second light guiding means are provided respectively. The second reflective polarizer 14 and the second reflective mirror 15 are arranged in parallel with each other in a posture inclined at 45 ° to the light incident surface of the second liquid crystal element 11.
[0043]
Here, the second reflective polarizing plate 14 is configured to generate a second polarized component light R2 emitted from the second liquid crystal element 11 and a first polarized component light R1 emitted from the second liquid crystal element 11 and reflected by the second reflecting mirror 15. Are arranged at a position orthogonal to each other at an angle of 45 ° with respect to each traveling direction of the respective polarized light components R1 and R2. As a result, the second polarization component light R2 incident on the surface (hereinafter, referred to as the front surface) of the second reflective polarizing plate 14 facing the second liquid crystal element 11 and the first polarization component light R1 incident on the back surface thereof are combined. Then, the light is emitted in a predetermined direction as emitted light Ro.
[0044]
In the case of the optical switch of the present example configured as described above, similarly to the above-described first embodiment, the voltage is applied to the first and second liquid crystal elements 10 and 11 shown in FIG. In the off state, the outgoing light Ro is emitted in the same direction as the incident light Ri. In the on state in which a voltage is applied to the first and second liquid crystal elements 10 and 11 shown in FIG. Is switched to a direction perpendicular to the direction along the incident light Ri. This optical switch effect is always stably performed regardless of the temperatures of the first and second liquid crystal elements 10 and 11.
[0045]
It should be noted that the present invention is not limited to the above embodiments and the like, and it is needless to say that various modifications can be made within the technical scope of the present invention.
[0046]
For example, as a modification of the embodiment shown in FIG. 4, the first reflective polarizer and the second reflective polarizer can be integrated as one component as shown in FIG. In this modification, the liquid crystal device LA is divided into a first liquid crystal device LA1 and a second liquid crystal device LA2, as in the first embodiment shown in FIG. 1, and one reflective polarizing member 16 is provided therebetween. Each of the liquid crystal elements 1 to 4 is provided so as to be inclined at 45 ° with respect to the entrance and exit surfaces. As a result, the portion of the reflective polarizing member 16 facing the incident surface of the first liquid crystal element 1 becomes the first reflective polarizing section that performs the same function as the first reflective polarizing plate 12, and the second liquid crystal element 4 of the reflective polarizing member 16 The portion facing the emission surface is a second reflective polarizing section that performs the same function as the second reflective polarizing plate 14.
[0047]
According to the optical switch of the present modification configured as described above, the number of components is reduced, the structure is simplified, and the optical switch is always stable regardless of the temperature as in the first and second embodiments. Thus, a desired optical switch effect is achieved.
[0048]
Further, as shown in FIG. 7, the incident direction of the incident light Ri on the liquid crystal device LA is made parallel to the incident surface of the first liquid crystal element 1, and the first beam splitter 5 as the polarization separating means and the polarization combining means as the polarization separating means. May be arranged to face each other with the first liquid crystal device LA1 interposed therebetween. In this case, when the liquid crystal device LA is off, the outgoing light Ro is emitted in a direction perpendicular to the incident light Ri, and when the liquid crystal device LA is on, the outgoing light Ro is emitted in the opposite direction to the incident light Ri. As described above, according to the present invention, it is possible to realize various optical switches in which the relative direction of the outgoing light with respect to the incident light is different.
[0049]
Further, the phase difference given to the transmitted light of the liquid crystal device including a plurality of liquid crystal elements is not limited to １／ of the wavelength of the transmitted light, but may be an odd multiple of 波長 of the wavelength of the transmitted light.
[0050]
Furthermore, the liquid crystal element constituting the liquid crystal device of the present invention is not limited to a homogeneous liquid crystal element, and various other liquid crystal elements such as a twisted nematic liquid crystal element can be used. In this case, the temperature dependence of the retardation of each of the plurality of liquid crystal elements constituting the liquid crystal device and the alignment treatment are performed so that the transmitted light has a phase difference equivalent to an odd multiple of 波長 of the wavelength regardless of the temperature. What is necessary is just to set the arrangement of directions.
[0051]
Furthermore, the respective rotation amounts of the polarization plane of the incident light in the first liquid crystal alignment state and the second liquid crystal alignment state of the liquid crystal device are set to 90 ° and 0 ° in the above-described embodiment and the like, The present invention is not limited to this, and various combinations that differ from each other by 90 °, such as 180 ° and 90 ° or −45 ° and 45 °, are possible.
[0052]
Furthermore, if it is difficult to keep the retardation of the liquid crystal device constant regardless of the temperature simply by combining a plurality of liquid crystal elements, the voltage applied to one liquid crystal element is adjusted so that the retardation of the liquid crystal device becomes constant. May be adjusted according to the conditions.
[0053]
In addition, each of the first and second light guide means is not limited to one reflecting mirror, and may be configured by combining a plurality of reflecting mirrors.
[0054]
【The invention's effect】
An optical switch according to the present invention includes: a polarization separating unit that reflects one of the first polarization component lights of the polarization components of the incident light that are orthogonal to each other and transmits the other second polarization component light; A first light guiding unit for guiding a traveling direction of the first polarized component light in a direction parallel to the second polarized component light; a second polarized component light separated by the polarization separating unit; The first polarized component light separated by the polarized light separating means and guided by the first light guiding means is incident, and the retardation value is substantially の of the wavelength of the transmitted light in response to the application of an electric field. A liquid crystal device that can be switched between a first alignment state and a second alignment state that are different from each other by an odd number of times, and a liquid crystal device that includes a compensation liquid crystal element that compensates for the temperature dependence of the retardation of the liquid crystal element; Light emission of the liquid crystal device And the direction in which the light of the second polarization component light transmitted through the liquid crystal device separated by the polarization splitting means intersects with the traveling direction of the light of the first polarization component light transmitted through the liquid crystal device. A second light guiding means, a light of the first polarized component light transmitted through the electric light means, and a second polarized light component transmitted by the electric light means and the second light guide plate. And a polarization combining unit that receives the guided light and emits the two lights to the same optical path, separates the incident light into S-wave and P-wave polarization component lights whose polarization directions are orthogonal to each other, and forms a liquid crystal. When the light is incident on the device and passes through the liquid crystal device, a rotation of each polarized component light is performed by a certain amount regardless of the temperature due to the optical rotation, and thereafter, each polarized component light emitted from the liquid crystal device is synthesized. The amount of rotation of the transmitted light depends on the signal input to the liquid crystal device. Since the first liquid crystal alignment state and the second liquid crystal alignment state which are different from each other by 90 ° are switched, the optical signal does not convert into an electric signal stably at all times regardless of the temperature. You can switch routes. As a result, it is possible to provide an inexpensive optical switch that can stably and accurately switch the traveling route of an optical signal in a wide data band without loss of light.
[0055]
In this optical switch, each of the liquid crystal element and the compensating liquid crystal element constituting the liquid crystal device is a homogeneous liquid crystal element in which liquid crystal molecules are aligned parallel to a substrate. It is preferable that the optical switches are installed and arranged in a mutually orthogonal arrangement, so that an optical switch that can stably switch the traveling direction of the optical signal without changing the optical signal regardless of the temperature can be simply configured.
[0056]
A liquid crystal device composed of a plurality of homogeneous liquid crystal elements is preferably disposed in the optical path of each of the separated polarized light components, whereby the liquid crystal device is more stable and sensitive to temperature changes and has less light loss. An optical switch effect can be obtained.
[0057]
In addition, when the liquid crystal device is composed of two liquid crystal devices as described above, one reflective polarizing plate is a member that also serves as a polarization separating unit and a polarization combining unit, and this reflective polarizing plate is used for the two liquid crystal devices. It may be arranged obliquely through the gap, thereby reducing the number of components and simplifying the structure of the optical switch of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an optical switch as a first embodiment of the present invention, where (a) shows a state where the optical switch is turned off, and (b) shows a state where it is turned on.
FIG. 2 is an explanatory diagram showing a relationship between a direction of a polarization plane of transmitted light and an alignment direction of liquid crystal molecules in the first embodiment.
FIG. 3 is a graph showing the temperature dependence of a retardation value of the liquid crystal element according to the first embodiment.
FIGS. 4A and 4B are schematic diagrams showing an optical switch as a second embodiment of the present invention, wherein FIG. 4A shows a state where the optical switch is turned off, and FIG. 4B shows a state where the optical switch is turned on.
FIG. 5 is an explanatory diagram showing the relationship between the direction of the polarization plane of transmitted light and the orientation direction of liquid crystal molecules in the second embodiment.
FIG. 6 is a schematic configuration diagram showing a modification of the embodiment of the present invention.
FIG. 7 is a schematic configuration diagram showing another modified example of the embodiment of the present invention.
[Explanation of symbols]
1,3,10 ... first liquid crystal element
2, 4, 11 ... second liquid crystal element
LA: Liquid crystal device
LA1: First liquid crystal device
LA2: second liquid crystal device
5. First beam splitter
6,13 ... First reflector
7 Second beam splitter
8, 15 ... second reflecting mirror
12: First reflective polarizing plate
14: Second reflective polarizing plate
16 Reflective polarizing member

Claims

Polarization splitting means for reflecting one first polarization component light of the polarization components orthogonal to each other of the incident light and transmitting the other second polarization component light;
First light guide means for guiding the traveling direction of the first polarized light component reflected by the polarized light separating means in a direction parallel to the second polarized light component;
The second polarized light component separated by the polarized light separating means and the first polarized light component separated by the polarized light separating means and guided by the first light guiding means are incident and applied to an electric field. A liquid crystal element whose value of the retardation can be switched between a first alignment state and a second alignment state that are different from each other by an odd multiple of substantially half of the wavelength of the transmitted light, and the retardation of the liquid crystal element. A liquid crystal device comprising a compensating liquid crystal element for compensating for temperature dependence;
The second polarization component light, which is disposed on the light emission side of the liquid crystal device and is separated by the polarization splitting means, is transmitted through the liquid crystal device, and the first polarization component light is transmitted through the liquid crystal device. Second light guiding means for guiding in a direction intersecting with the traveling direction of
The first polarized component light transmitted through the liquid crystal device and the second polarized component light transmitted through the liquid crystal device and guided by the second light guiding unit are input, and Polarization combining means for emitting two lights to the same optical path,
An optical switch for emitting incident light in different directions according to an electric field applied to the liquid crystal device.

The liquid crystal element and the compensating liquid crystal element of the liquid crystal device are two homogeneous liquid crystal elements in which liquid crystal molecules are aligned in parallel with a substrate, and the alignment directions of the liquid crystal molecules are orthogonal to each other. The liquid crystal element and the compensating liquid crystal element are arranged in a first alignment state in which liquid crystal molecules are aligned in parallel with a substrate according to an applied voltage, and the liquid crystal molecules are aligned substantially perpendicularly to the substrate. 2. The optical switch according to claim 1, wherein by switching between the second alignment state and the second alignment state, light whose polarization planes of light transmitted through the liquid crystal device are different from each other by approximately 90 ° is emitted. 3.

3. The liquid crystal device according to claim 2, comprising: a first liquid crystal device arranged in an optical path of the first polarized light component; and a second liquid crystal device arranged in an optical path of the second polarized light component. An optical switch according to claim 1.

The polarized light separating means and the polarized light synthesizing means have a reflection axis and a transmission axis in directions orthogonal to each other, and the polarization plane of the incident light reflects the polarization component light along the reflection axis, and the polarization plane is the polarization plane. 10. A liquid crystal display comprising: one reflective polarizer that transmits polarized component light along a transmission axis; and wherein the reflective polarizer is obliquely disposed between the first liquid crystal element and the second liquid crystal element. Item 4. The optical switch according to item 3.