JP4316088B2 - Arrayed waveguide grating - Google Patents

Description

【００１８】
ここで、従来の一般的なアレイ導波路型回折格子において、（数１）から前記光透過中心波長の温度依存性を求めてみる。従来の一般的なアレイ導波路型回折格子においては、ｄｎ_ｃ／ｄＴ＝１×１０^−５（℃^−１）、α_ｓ＝３．０×１０^−６（℃^−１）、ｎ_ｃ＝１．４５１（波長１．５５μｍにおける値）であるから、これらの値を（数１）に代入する。
【００１９】
また、波長λは、各光出力導波路６についてそれぞれ異なるが、各波長λの温度依存性は等しい。そして、現在用いられているアレイ導波路型回折格子は、波長１５５０ｎｍを中心とする波長帯の波長多重光を分波したり合波したりするために用いられることが多いので、ここでは、λ＝１５５０ｎｍを（数１）に代入する。そうすると、従来の一般的なアレイ導波路型回折格子の前記光透過中心波長の温度依存性は、（数２）に示す値となる。
【００２０】
【数２】

【００２１】
なお、ｄλ／ｄＴの単位は、ｎｍ／℃である。例えばアレイ導波路型回折格子の使用環境温度が２０℃変化したとすると、各光出力導波路６から出力される光透過中心波長は０．３０ｎｍシフトするものであり、前記使用環境温度変化が７０℃以上になると、前記光透過中心波長のシフト量が１ｎｍ以上になってしまう。
【００２２】
アレイ導波路型回折格子は１ｎｍ以下の非常に狭い間隔で波長を分波または合波できることが特徴であり、この特長を生かして波長多重光通信用に適用されるものであるため、上記のように、使用環境温度変化によって光透過中心波長が上記シフト量だけ変化することは致命的である。
【００２３】
そこで、従来から温度により光透過中心波長が変化しないように、図９に示したように、サーミスタ３１の検出温度に基づき、アレイ導波路型回折格子の温度を一定に保つペルチェ素子３０等の温度調節手段を設けたアレイ導波路型回折格子が提案されているが、上記温度調節手段を用いてアレイ導波路型回折格子の温度を一定に保つためには、ペルチェ素子等に例えば１Ｗといった通電を常時行なわなければならず、コストがかかり、しかも、ペルチェ素子やその制御機構を形成する部品の組立ずれ等に起因して、光透過中心波長シフトを正確に抑制できないことがあった。
【００２４】
そこで、上記課題を解決するために、本発明者は、図７に示すような構成のアレイ導波路型回折格子を提案した（特願平１１−２７０２０１号、特願２０００−０２１５３３に提案されているものであり、未だ公開になっていない）。
【００２５】
同図に示すアレイ導波路回折格子は、基板１上に石英系ガラスによって形成された導波路形成領域１０を形成している。導波路形成領域１０には従来例と同様に、１本の光入力導波路２、第１のスラブ導波路３、複数のアレイ導波路４、第２のスラブ導波路５、複数の光出力導波路６が設けられており、前記アレイ導波路４、光出力導波路６は、それぞれ予め定められた導波路間隔を介して並設されているが、同図に示すアレイ導波路回折格子においては、第１のスラブ導波路３が、第１のスラブ導波路３を通る光の経路と交わる切断面８で切断分離されている。
【００２６】
なお、同図では、切断面８は、図のＸ方向と成しており、切断面８によって、前記導波路形成領域１０は、導波路形成領域１０ａと導波路形成領域１０ｂとに切断分離されている。
【００２７】
図７に示すアレイ導波路回折格子の特徴的なことは、前記の如く、第１のスラブ導波路３が第１のスラブ導波路３を通る光の経路と交わる切断面８で分離スラブ導波路３ａ，３ｂに切断分離されており、この分離された分離スラブ導波路３ａ側を前記切断面８に沿ってスライド移動させることにより前記光透過中心波長をシフトさせるようにしたことであり、図７のアレイ導波路型回折格子には、上記スライド移動を行なうスライド移動機構が設けられている。
【００２８】
このスライド移動機構は、アレイ導波路回折格子の各光透過中心波長の温度依存変動を低減する方向に、分離スラブ導波路３ａ側を切断面８に沿ってスライド移動させる機構であり、同図に示す構成においては、高熱膨張係数部材７、ベース９、係止部材１４を設けて上記スライド移動機構を構成している。
【００２９】
分離スラブ導波路３ｂとアレイ導波路４と第２のスラブ導波路５と光出力導波路６が形成されている側の導波路形成領域１０ｂおよびその下の基板１は、石英ガラスやＩｎｖａｒロットなどの低熱膨張率の材料により形成されたベース９に固定されている。
【００３０】
また、分離スラブ導波路３ａと光入力導波路２が形成されている側の導波路形成領域１０ａおよびその下の基板１は、前記ベース９に対してスライド移動自在に設けられている。導波路形成領域１０ａの一端側は接着剤１３を介して高熱膨張係数部材７に固定されており、他端側は係止部材１４に係止されている。
【００３１】
高熱膨張係数部材７は、導波路形成領域１０ａの上面に沿って設けられた上板部７ａと導波路形成領域１０ａの側面に沿って設けられた側板部（図示されていない）とを有するＬ字形状の部材であり、側板部が固定部１１でベース９に固定されている。高熱膨張係数部材７は、例えば熱膨張係数が２．３１×１０^−５（１／Ｋ）のＡｌ（アルミニウム）により形成されている。
【００３２】
前記係止部材１４は、導波路形成領域１０ａの上面に沿って設けられた上板部１４ａと導波路形成領域１０ａの側面に沿って設けられた側板部（図示されていない）とを有するＬ字形状の部材であり、側板部が固定部１２でベース９に固定されている。係止部材１４の上板部の内壁と導波路形成領域１０ａの上面とは当接しており、導波路形成領域１０ａのスライド移動時に、導波路形成領域１０ａがベース９に対して上方側（ＸＹ平面に垂直なＺ軸方向）に変位しないようになっている。また、側板部の内壁と導波路形成領域１０ａの側面とは間隔を介しており、導波路形成領域１０ａのスライド移動が支障なく行なえるようになっている。
【００３３】
同図に示すアレイ導波路回折格子において、アレイ導波路回折格子の使用環境温度が変化すると、高熱膨張部材７が導波路形成領域１０よりも大きく膨張または収縮するので、ベースに固定されていない側の導波路形成領域１０ａおよびその基板１が、前記切断面８に沿って、図の矢印Ａ方向または矢印Ｂ方向にスライド移動し、それにより、分離スラブ導波路３ａ及び光入力導波路２がスライド移動する。
【００３４】
そして、前記切断面８に沿っての移動は、アレイ導波路回折格子の各光透過中心波長の温度依存変動を低減する方向に行われるため、この提案のアレイ導波路回折格子においては、アレイ導波路回折格子の使用環境温度変化に伴う各光透過中心波長の温度依存性が補償される。
【００３５】
なお、上記提案は、アレイ導波路型回折格子の線分散特性に着目して成されたものであり、以下、上記提案における光透過中心波長の温度依存性補償原理について、図８に基づいて述べる。
【００３６】
アレイ導波路型回折格子において光入力導波路２から入射された光は、第１のスラブ導波路（入力側スラブ導波路）３で回折し、アレイ導波路４を励振する。なお、前記の如く、隣接するアレイ導波路４の長さは互いにΔＬずつ異なっている。そこで、アレイ導波路４を伝搬した光は、（数３）を満たし、第２のスラブ導波路（出力側スラブ導波路）５の出力端に集光される。
【００３７】
【数３】

【００３８】
（数３）において、ｎ_sは第１のスラブ導波路３および第２のスラブ導波路５の等価屈折率、ｎ_cはアレイ導波路４の等価屈折率、φは回折角、ｍは回折次数、ｄは隣り合うアレイ導波路４同士の間隔であり、λは、前記の如く、各光出力導波路６から出力される光の透過中心波長である。
【００３９】
ここで、回折角φ=０となるところの光透過中心波長をλ_０とすると、λ_０は（数４）で表される。なお、波長λ_０は、一般に、アレイ導波路型回折格子の中心波長と呼ばれる。
【００４０】
【数４】

【００４１】
ところで、図８において、回折角φ=０となるアレイ導波路型回折格子の集光位置を点Ｏとすると、回折角φ＝φ_pを有する光の集光位置（第２のスラブ導波路５の出力端における位置）は、例えば点Ｐの位置（点ＯからＸ方向にずれた位置）となる。ここで、Ｏ−Ｐ間のＸ方向の距離をｘとすると波長λとの間に（数５）が成立する。
【００４２】
【数５】

【００４３】
（数５）において、Ｌ_fは第２のスラブ導波路５の焦点距離であり、ｎ_gはアレイ導波路４の群屈折率である。なお、アレイ導波路４の群屈折率ｎ_gは、アレイ導波路４の等価屈折率ｎ_cにより、（数６）で与えられる。
【００４４】
【数６】

【００４５】
前記（数５）は、第２のスラブ導波路５の焦点ＯからＸ方向の距離ｄｘ離れた位置に光出力導波路６の入力端を配置形成することにより、ｄλだけ波長の異なった光を取り出すことが可能であることを意味する。
【００４６】
また、（数５）の関係は、第１のスラブ導波路３に関しても同様に成立する。すなわち、例えば第１のスラブ導波路３の焦点中心を点Ｏ’とし、この点Ｏ’からＸ方向に距離ｄｘ’ずれた位置にある点を点Ｐ’とすると、この点Ｐ’に光を入射した場合に、出力の波長がｄλ’ずれることになる。この関係を式により表わすと、（数７）のようになる。
【００４７】
【数７】

【００４８】
なお、（数７）において、Ｌ_ｆ’は第１のスラブ導波路３の焦点距離である。この（数７）は、第１のスラブ導波路３の焦点Ｏ’とＸ方向の距離ｄｘ’離れた位置に光入力導波路２の出力端を配置形成することにより、前記焦点Ｏに形成した光出力導波路に６おいてｄλ’だけ波長の異なった光を取り出すことが可能であることを意味する。
【００４９】
したがって、アレイ導波路型回折格子の使用環境温度変動によってアレイ導波路型回折格子の光出力導波路から出力される光透過中心波長がΔλずれたときに、ｄλ’＝Δλとなるように、光入力導波路６の出力端位置を前記Ｘ方向に距離ｄｘ’だけずらせば、例えば焦点Oに形成した光出力導波路６において、波長ずれのない光を取り出すことができ、他の光出力導波路６に関しても同様の作用が生じるため、前記光透過中心波長ずれΔλを補正（解消）できることになる。
【００５０】
前記提案例は、第１のスラブ導波路３と第２のスラブ導波路５の少なくとも一方がスラブ導波路５を通る光の経路と交わる切断面８で切断分離したものであり、図７に示したように、第１のスラブ導波路３が切断分離されていると仮定して議論すると、この分離された第１のスラブ導波路のうち、例えば光入力導波路２に接続されている分離スラブ導波路３ａ側（光入力導波路２も含む）を、スライド移動機構によって前記切断面に沿ってスライド移動させれば、前記各光透過中心波長をシフトさせることが可能となる。
【００５１】
また、前記スライド移動機構によって、前記各光透過中心波長の温度依存変動（波長ずれ）Δλがｄλと等しくなるようにして、前記各光透過中心波長の温度依存変動を低減する方向に分離スラブ導波路３ａ及び光入力導波路２を前記切断面８に沿って移動させれば、前記光透過中心波長ずれを解消することが可能となる。
【００５２】
また、温度変化量と光入力導波路２の位置補正量の関係は以下のようにして導かれる。前記光透過中心波長の温度依存性（温度による光透過中心波長のずれ量）は、前記（数２）で表されるので、温度変化量Ｔを用いて光透過中心波長ずれ量Δλを（数８）により表わすことができる。
【００５３】
【数８】

【００５４】
（数７）、（数８）から、温度変化量Ｔと光入力導波路の位置補正量ｄｘ’を求めると、（数９）が導かれる。
【００５５】
【数９】

【００５６】
したがって、図７に示した構成において、（数９）により示される位置補正量ｄｘ’だけ、前記スライド移動機構によって切断面８に沿って第１のスラブ導波路３の分離スラブ導波路３ａ及び光入力導波路２をスライド移動させることにより、前記光透過中心波長ずれを解消することが可能となる。
【００５７】
例えば、従来の一般的なアレイ導波路型回折格子の導波路構成の各パラメータと（数９）に基づき、アレイ導波路型回折格子の使用環境温度の変化量Ｔと光入力導波路２の位置補正量ｄｘ’の関係を求めると、（数１０）に示す関係となる。この場合、アレイ導波路型回折格子の使用環境温度が１０℃変化した際、光入力導波路２の出力端の位置をＸ方向に約３．８３μｍ補正（移動）すれば、温度による中心波長すれが補正できる計算になる。
【００５８】
【数１０】

【００５９】
なお、前記の如く、アレイ導波路型回折格子は光の相反性を利用して形成されているものであり、第２のスラブ導波路５側を切断分離して、分離された分離スラブ導波路の少なくとも一方側を、スライド移動機構によって前記切断面に沿って前記各光透過中心波長の温度依存変動を低減する方向にスライド移動させれば、同様の効果が得られ、前記各光透過中心波長の温度依存変動を解消することが可能となる。
【００６０】
しかしながら、図７に示したような構成のアレイ導波路回折格子を多数作製し、それぞれのアレイ導波路型回折格子において、前記スライド移動機構によって分離導波路３ａ側を図７の矢印Ａ，Ｂ方向にスライド移動させてアレイ導波路型回折格子の光透過中心波長の温度依存性低減効果を調べたところ、十分な効果を発揮できないものが存在することが分かった。
【００６１】
本発明は上記課題を解決するために成されたものであり、その目的は、光透過中心波長の温度依存性を正確に抑制することができる安価なアレイ導波路型回折格子を提供することにある。
【００６２】
【課題を解決するための手段】
上記目的を達成するために、本発明は次のような構成をもって課題を解決するための手段としている。すなわち、第１の発明は、１本以上の並設された光入力導波路の出射側に第１のスラブ導波路が接続され、該第１のスラブ導波路の出射側には該第１のスラブ導波路から導出された光を伝搬する互いに異なる長さの複数の並設されたアレイ導波路が接続され、該複数のアレイ導波路の出射側には第２のスラブ導波路が接続され、該第２のスラブ導波路の出射側には複数の並設された光出力導波路が接続されて成る導波路構成を有し、前記光入力導波路から入力される互いに異なる複数の波長をもった光から１つ以上の波長の光を分波して各光出力導波路から出力する光分波機能を有し、前記各光出力導波路から出力される各光の光透過率が少なくとも予め定められた波長領域においては分波光の互いに異なる光透過中心波長を中心としてそれぞれ対応する光透過中心波長から波長がずれるにしたがって小さくなるアレイ導波路回折格子において、前記第１のスラブ導波路が該スラブ導波路を通る光の経路と交わる切断面で切断分離されており、この分離された分離スラブ導波路の少なくとも一方側を前記切断面に沿ってスライド移動させるスライド移動機構が設けられ、当該スライド移動機構により前記分離スラブ導波路の少なくとも一方側を前記切断面に沿ってスライド移動させることにより前記光透過中心波長をシフトさせる構成と成し、前記切断面はスラブ導波路内を通る光の経路の長手方向中心位置よりもアレイ導波路側の位置において前記光の経路と交わる面とし、前記アレイ導波路回折格子の導波路は基板上に形成されており、第１のスラブ導波路は前記基板と一体的に切断面で切断分離されていて、分離された一方側の分離スラブ導波路は当該分離された一方側の基板と一体的に前記切断面に沿ってスライド移動する構成と成しており、スライド移動機構は温度変化に応じて伸縮する高熱膨張係数部材を備えており、前記スライド移動させる側の分離スラブ導波路側の前記分離された基板には前記高熱膨張係数部材の一端側が固定されており、前記高熱膨張係数部材の他端側は該高熱膨張係数部材よりも熱膨張係数が低い低熱膨張率の材料によって形成された固定側となるベースに固定され、前記高熱膨張係数部材が使用環境の温度変化に応じて伸縮することによって、前記分離スラブ導波路の一方側が前記切断面に沿って、アレイ導波路回折格子の各光出力導波路から出力する光の光透過中心波長の温度依存変動を低減する方向にスライド移動する構成とした構成をもって課題を解決する手段としている。
【００６５】
本発明者が、図７に示したような上記提案のアレイ導波路回折格子の構成を有していながら、光透過中心波長の温度依存性低減効果を十分に発揮できないものが存在する原因を解明するために、アレイ導波路型回折格子を解体してみたところ、上記温度依存性低減効果を十分に発揮できないものは、図２に示すように、切断面８における切断部分で導波路形成領域１０ａの端面（切断面８ａ）と導波路形成領域１０ｂの端面（切断面８ｂ）との角度θが生じている（切断面８ａと切断面８ｂとが完全に一致した状態で上記スライド移動が行なわれない）ことが分かった。なお、図２には、図の簡略化のために、アレイ導波路型回折格子の導波路構成のうち、光入力導波路２と第１のスラブ導波路３のみが示されている。
【００６６】
したがって、この角度θを零に近づけるようにすることが重要であるが、角度θは、実際には図２に示すような大きなものではなく、せいぜい０．５度程度であり（図２においては説明を分かりやすくするためにθを大きく示した）、アレイ導波路型回折格子の作製上の誤差によってこの程度の大きさの角度θが生じてしまうことは避けられない。
【００６７】
そこで、本発明者は、前記切断面８の形成位置に着目した。その結果、第１のスラブ導波路３内を通る光の経路の長手方向中心位置よりも光入力導波路２側の位置において、前記光の経路と交わる切断面８で第１のスラブ導波路３を切断したときに、上記角度θとの兼ね合いによって上記アレイ導波路型回折格子における各光透過中心波長の温度依存変動低減効果を十分に発揮できないことが分かった。
【００６８】
そこで、本発明者は、上記角度θと、アレイ導波路型回折格子における光透過中心波長シフト量との関係を以下のように考察した。
【００６９】
すなわち、図２に示すように、アレイ導波路型回折格子における光入力導波路２の出力端２０が、第１のスラブ導波路３の幅方向の中心に形成されている（Ｗ１＝Ｗ２である）とする。光入力導波路２の出力端２０から第１のスラブ導波路３に入力された光は、アレイ導波路４側に向かって広がりながら第１のスラブ導波路３を伝搬するが、光入力導波路２の出力端２０（同図におけるＣ）から、第１のスラブ導波路３の出力端における幅方向の中心位置（Ｗ１＝Ｗ２となる位置）Ｂに向かって直進する光の強度が最も大きい。
【００７０】
そのため、切断面８によって切断された導波路形成領域１０ａの端面（切断面８ａ）と導波路形成領域１０ｂの端面（切断面８ｂ）との角度θが０の場合、すなわち、切断面８ａと切断面８ｂの角度ずれが生じていない理想的な場合には、第１のスラブ導波路３を伝搬する光の強度中心は、前記位置Ｂに向かう。
【００７１】
ここで、導波路形成領域１０ａの端面（切断面８ａ）と導波路形成領域１０ｂの端面（切断面８ｂ）との角度が、切断面８（８ａ，８ｂ）の端部Ａを支点として角度θずれた場合を考える。
【００７２】
なお、分離スラブ導波路３ａの長さ（光の経路方向の長さ）をＬ_ｆ１とし、分離スラブ導波路３ｂの長さ（光の経路方向の長さ）をＬ_ｆ２とし、アレイ導波路型回折格子の端面Ｅから光入力導波路２の出力端２０（同図におけるＣ）までの長さをＬ_０とする。また、切断面８ａと切断面８ｂとの間には屈折率整合剤が塗布されているので、切断面８ａ，８ｂの間の隙間によって光の反射が生じないものとする。
【００７３】
切断面８ａと切断面８ｂの角度がθの場合、図のＣの位置から入力された光強度の中心は、第１のスラブ導波路３内を、図のＢの位置から上方側にｄｘｇだけずれた点に向かって直進するので、この光の焦点距離Ｌ_ｆｇ’は、ＣＢ間の距離で近似できるものである。なお、同図において、点Ａと点Ｃ、点Ａと点Ｂをそれぞれ接続し、γ_１＝ｔａｎ^−１（Ｌ_ｆ１／Ｌ_０）、γ_２＝ｔａｎ^−１（Ｌ_ｆ２／Ｌ_０）を考えると、Ｌ_ＡＢ＝（Ｌ_０ ^２＋Ｌ_ｆ２ ^２）^１／２、Ｌ_ＡＤ＝（Ｌ_０ ^２＋Ｌ_ｆ２ ^２）^１／２・ｃｏｓ（θ＋γ_２）となり、ｄｘｇは、（数１１）で表わされる。また、Ｌ_ＢＤ＝（Ｌ_０ ^２＋Ｌ_ｆ２ ^２）^１／２・ｓｉｎ（θ＋γ_２）となり、前記焦点距離Ｌ_ｆｇ’は、（数１２）により近似できる。
【００７４】
【数１１】

【００７５】
【数１２】

【００７６】
また、図２において、角度θは大きく示してあるが、前記の如く、θは、実際には非常に小さい値なので、アレイ導波路型回折格子の線分散特性が成り立つと仮定してもなんら差し障りが無く、したがって、以下の式（数１３）が成り立つ。
【００７７】
【数１３】

【００７８】
ここで、ΔＬは、アレイ導波路の光路長差、ｎ_ｓは第１のスラブ導波路３の等価屈折率、ｄは隣り合うアレイ導波路４同士の間隔、λ_０はアレイ導波路型回折格子の回折角φ＝０となるところの光透過中心波長（一般に、アレイ導波路型回折格子の中心波長と呼ぶことがある）、ｎ_ｇはアレイ導波路４の群屈折率である。また、波長λ_０は、前記（数４）により表わされるものであり、アレイ導波路４の群屈折率ｎ_ｇは、前記（数６）により表わされるものである。
【００７９】
そこで、第１のスラブ導波路３を通る光の経路と交わるように形成する切断面８を、光入力導波路２に近い側に形成した場合とアレイ導波路４に近い側に形成した場合の両方において、上記（数４）、（数６）、（数１１）、（数１２）、（数１３）を用いて、アレイ導波路型回折格子における角度θと前記光透過中心波長シフト量との関係をそれぞれ算出した。この算出結果が、図３、４に示されている。
【００８０】
なお、上記算出結果は、上記第１実施形態例と同様の、以下のパラメータに基づいて算出した。すなわち、回折次数ｍは６１、隣り合うアレイ導波路４同士の長さの差ΔＬは６５．２μｍ、アレイ導波路４のピッチｄは１５μｍ、アレイ導波路４の等価屈折率ｎ_ｃは１．４５１、アレイ導波路群屈折率ｎ_ｇは１．４７５、第１、第２のスラブ導波路３，５の等価屈折率ｎ_ｓはそれぞれ１．４５３とした。なお、これらの等価屈折率値は、波長１．５５μｍの光に対する値であり、２５℃における値である。
【００８１】
また、上記切断面８を光入力導波路２に近い側に形成した場合（図３に示す算出結果）は、Ｌ_ｆ１＝１０００μｍ、Ｌ_ｆ２＝８０００μｍとし、上記切断面８をアレイ導波路４に近い側に形成した場合（図４に示す算出結果）は、Ｌ_ｆ１＝８０００μｍ、Ｌ_ｆ２＝１０００μｍとして求めた。
【００８２】
図３、４から明らかなように、角度θが大きくなるほど光透過中心波長シフト量も大きくなり、光透過中心波長シフト量は角度θにほぼ比例している。このことは、前記スライド移動機構によって分離スラブ導波路３ａ側を切断面８に沿ってスライド移動させたときに、このスライド移動によってシフトさせる適切な光透過中心波長シフト量（光透過中心波長シフト量の設計値）に加えて、角度θに対応する大きさだけアレイ導波路型回折格子の光透過中心波長が余分にシフトすることを意味する。
【００８３】
したがって、角度θが大きくなると、設計通り前記光透過中心波長をシフトさせることができなくなる。例えば、図３に示すように、切断面８を光入力導波路２に近い側に形成した場合は、角度θが０．１度のときに光透過中心波長シフト量が０．５ｎｍになっているので、光透過中心波長が０．５ｎｍ余分にシフトしてしまうことになり、アレイ導波路型回折格子によって、波長多重光を波長０．８ｎｍ間隔で分離しようとする場合には問題である。
【００８４】
一方、切断面８をアレイ導波路４に近い側に形成した場合は、図４に示すように、角度θが０．１度のときに光透過中心波長シフト量が０．１ｎｍになっており、アレイ導波路４に近い側に切断面８を形成することで、角度θに依存する光透過中心波長シフト量を５分の１程度に小さくできることが分かった。なお、この光透過中心波長シフト量（設計値からのずれ量）が０．１ｎｍであることは許容範囲である。
【００８６】
本発明は、上記考察結果に基づいて、第１のスラブ導波路を切断する切断面を、アレイ導波路側に近い側で切断する切断面とし、かつ、図７に示したような提案例の構成と同様のスライド機構を設けてアレイ導波路型回折格子を構成したために、光透過中心波長の温度依存性を正確に抑制することができる安価なアレイ導波路型回折格子とすることが可能となる。
【００８７】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて説明する。なお、本実施形態例の説明において、従来例と同一名称部分には同一符号を付し、その重複説明は省略する。図１には、本発明に係るアレイ導波路型回折格子の一実施形態例の概略図が平面図により示されている。本実施形態例は図７に示した上記提案例とほぼ同様に構成されており、本実施形態例が上記提案例と異なる特徴的なことは、切断面８を、第１のスラブ導波路３内を通る光の経路の長手方向中心位置よりもアレイ導波路４側の位置（アレイ導波路寄りの位置）において前記光の経路と交わる面としたことである。
【００８８】
すなわち、本実施形態例において、切断面８は、第１のスラブ導波路３を、光入力導波路２側よりもアレイ導波路４側に近い側で切断する面と成しており、具体的には、同図における長さＬ_ｆ１＝８０００μｍ、Ｌ_ｆ２＝１０００μｍと成している。
【００８９】
前記の如く、図７に示した提案例のアレイ導波路型回折格子において、各光透過中心波長の温度依存変動低減効果を十分に発揮できないものは、第１のスラブ導波路３内を通る光の経路の長手方向中心位置よりも光入力導波路２側の位置において、前記光の経路と交わる切断面８で第１のスラブ導波路３を切断し、かつ、図２に示した、切断面８における切断部分で導波路形成領域１０ａの端面（切断面８ａ）と導波路形成領域１０ｂの端面（切断面８ｂ）との角度θが比較的大きいことが分かった。
【００９０】
そして、本発明者は、上記角度θと、アレイ導波路型回折格子における光透過中心波長シフト量との関係を前記のように考察し、この考察結果に基づき、前記の如く、第１のスラブ導波路３を、光入力導波路２側よりもアレイ導波路４側に近い側に切断面８を形成して本実施形態例のアレイ導波路型回折格子を形成した。
【００９１】
本実施形態例は以上のように構成されており、本実施形態例のアレイ導波路型回折格子において、前記角度θを実際に測定したところ、θ＝約０．０５度であり、図６に示すように、アレイ導波路型回折格子の使用環境温度０℃〜８０℃において、光透過中心波長が殆ど変動しないアレイ導波路型回折格子となることが分かった。
【００９２】
なお、図５には、本実施形態例のアレイ導波路型回折格子において、前記角度θを故意に大きくして、角度θに対するアレイ導波路型回折格子の光透過中心波長シフト量を測定した実測結果が、図４に示した光透過中心波長シフト量の計算値と共に示されており、図５からも明らかなように、本実施形態例のように、第１のスラブ導波路３に形成する切断面８をアレイ導波路４に近い側に形成することにより、たとえ切断面８における前記角度θが多少大きくても、光透過中心波長を設計通りシフトすることができ、アレイ導波路型回折格子における光透過中心波長の温度依存性を効率的に低減できることが分かった。
【００９３】
なお、図５において、○が実測値、特性線が計算値であり、計算値と実測値はほぼ一致した。
【００９４】
本実施形態例によれば、アレイ導波路型回折格子の光透過中心波長の温度依存性を低減できるように図７に示した提案例とほぼ同様の構成とし、ただし、前記考察に基づき、図１に示すように、第１のスラブ導波路３を、光入力導波路２側よりもアレイ導波路４側に近い側に切断面８を形成して本実施形態例のアレイ導波路型回折格子を形成したので、光透過中心波長の温度依存性をほぼ設計通り正確に抑制することができるアレイ導波路型回折格子とすることができる。
【００９５】
また、本実施形態例によれば、図７に示した提案例と同様に、高熱膨張係数部材７、ベース９、係止部材１４を有して構成される簡単な構成のスライド移動機構を設けることによりアレイ導波路型回折格子の各光透過中心波長の温度依存性を効率的に低減できるものであり、アレイ導波路型回折格子の構成の複雑化を避けることができ、作製も容易にできる。
【００９６】
さらに、本実施形態例によれば、第１のスラブ導波路３を切断面８で切断しているために、例えばアレイ導波路型回折格子を構成するアレイ導波路部の作製誤差に起因して、前記光透過中心波長がＩＴＵグリッド波長等の設定波長からずれている場合には、その分だけ分離スラブ導波路３ａと分離スラブ導波路３ｂの相対位置をずらして、光入力導波路２のＸ方向の位置をずらすことにより、設定温度において、前記光透過中心波長をグリッド波長等の設定波長とすることができる。
【００９７】
なお、本発明は上記実施形態例に限定されることはなく、様々な実施の態様を採り得る。例えば、上記実施形態例では、長手方向の長さが９０００μｍの第１のスラブ導波路３を、図１に示したように、Ｌ_ｆ１＝８０００μｍ、Ｌ_ｆ２＝１０００μｍとなるように切断面８を切断したが、Ｌ_ｆ１やＬ_ｆ２の長さは特に限定されるものではなく、適宜設定されるものであり、Ｌ_ｆ１>Ｌ_ｆ２となるように切断面８を形成することにより、上記実施形態例と同様の効果を奏することができる。
【００９８】
また、上記実施形態例では、高熱膨張係数部材７としてＡｌの板を用いたが、高熱膨張係数部材７は必ずしもＡｌとするとは限らず、Ａｌ以外の材料により形成してもよい。
【０１０１】
さらに、第１のスラブ導波路３や第２のスラブ導波路５の切断面８は上記実施形態例のようにＸ軸とほぼ平行な面とするとは限らず、Ｘ軸に対して斜めの面としてもよく、切断するスラブ導波路を通る光の経路と交わる切断面で切断分離すればよい。
【０１０２】
さらに、上記実施形態例では、分離スラブ導波路３ａ側を切断面８に沿ってスライド移動させるスライド移動機構を、高熱膨張係数部材７を設けて形成したが、スライド移動機構の構成は特に限定されるものではなく、適宜設定されるものである。すなわち、上記スライド移動機構は、第１のスラブ導波路３を切断面で切断分離して形成した分離スラブ導波路の少なくとも一方側を、前記切断面８に沿ってスライド移動させることにより、アレイ導波路型回折格子の光透過中心波長をシフトできる機能を有していればよい。
【０１０３】
特に、上記スライド移動機構は、上記実施形態例のように、アレイ導波路型回折格子の各光透過中心波長の温度依存変動を低減する方向にスライド移動させる機能を有していれば望ましく、スライド移動機構をこのように構成することにより、上記実施形態例のように、従来のアレイ導波路型回折格子において問題であった光透過中心波長の温度依存性を解消することができ、光波長多重通信用などの実用に適した優れたアレイ導波路型回折格子とすることができる。
【０１０４】
さらに、本発明のアレイ導波路型回折格子を構成する各導波路２，３，４，５，６の等価屈折率や本数、大きさなどの詳細な値は特に限定されるものではなく、適宜設定されるものである。
【０１０５】
【発明の効果】
第１の発明によれば、第１のスラブ導波路を該スラブ導波路を通る光の経路と交わる切断面で切断分離し、この分離したスラブ導波路の少なくとも一方を、前記切断面に沿ってスライド移動させることにより、アレイ導波路型回折格子の各光透過中心波長をシフトさせることができ、しかも、前記切断面を前記光の経路の長手方向中心位置よりもアレイ導波路側に形成したので、前記分離スラブ導波路同士の角度に依存する光透過中心波長シフト変位量を小さくすることができるため、ほぼ設計通り光透過中心波長シフトを行なうことができる。
【０１０６】
また、第２の発明によれば、第１の発明に加えて、前記スライド移動機構による切断面に沿っての移動により、前記各光透過中心波長の温度依存変動を低減する方向にスライド移動させるものであるから、アレイ導波路型回折格子の各光透過中心波長を非常に適切な量だけシフトさせることができ、前記各光透過中心波長の温度依存変動（波長ずれ）を解消することができる。
【０１０７】
また、第２の発明によれば、ペルチェ素子やヒータを用いなくてもアレイ導波路型回折格子の使用環境温度による光透過中心波長ずれを抑制し、光透過中心波長の温度無依存化を行うことができるために、ペルチェ素子やヒータを含む温度調節手段を設ける場合のように、常時通電を必要とすることもないし、部品の組立誤差による温度補正誤差が生じることもなく、さらに、室温以上の温度でアレイ導波路型回折格子を保つことによるアレイ導波路型回折格子と光ファイバとの接続損失増加の虞もない。
【０１０８】
したがって、第２の発明のアレイ導波路型回折格子は、接続相手側の光ファイバとの接続信頼性が高く、確実に光透過中心波長の温度依存性を解消でき、コストが安い優れたアレイ導波路型回折格子とすることができる。
【図面の簡単な説明】
【図１】本発明に係るアレイ導波路型回折格子の一実施形態例を平面図により示す要部構成図である。
【図２】アレイ導波路型回折格子の第１のスラブ導波路を切断したときの導波路形成領域端面角度θに対応する光透過中心波長シフトを説明する説明図である。
【図３】第１のスラブ導波路を光入力導波路に近い側で切断したときの、図２に示した角度θとアレイ導波路型回折格子における光透過中心波長シフト量との関係の算出結果を示すグラフである。
【図４】第１のスラブ導波路をアレイ導波路に近い側で切断したときの、図２に示した角度θとアレイ導波路型回折格子における光透過中心波長シフト量との関係の算出結果を示すグラフである。
【図５】第１のスラブ導波路をアレイ導波路に近い側で切断したときの、図２に示した角度θとアレイ導波路型回折格子における光透過中心波長シフト量との関係の算出結果と実測値とを比較して示すグラフである。
【図６】上記実施形態例のアレイ導波路型回折格子における光透過中心波長の温度依存性を示すグラフである。
【図７】従来提案されている第１のスラブ導波路を切断して形成したアレイ導波路型回折格子の構成を示す説明図である。
【図８】アレイ導波路型回折格子における光透過中心波長シフトと光入力導波路および光出力導波路の位置との関係を示す説明図である。
【図９】ペルチェ素子を設けて構成した従来のアレイ導波路型回折格子を示す説明図である。
【符号の説明】
１ 基板
２ 光入力導波路
３ 第１のスラブ導波路
３ａ，３ｂ 分離スラブ導波路
４ アレイ導波路
５ 第２のスラブ導波路
６ 光出力導波路
７ 高熱膨張係数部材
８，８ａ，８ｂ 切断面
９ ベース
１０，１０ａ，１０ｂ 導波路形成領域
１４ 係止部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an arrayed waveguide grating used as, for example, an optical multiplexer / demultiplexer in wavelength multiplexing optical communication.
[0002]
[Prior art]
In recent years, in optical communication, research and development of optical wavelength division multiplexing communication has been actively conducted as a method for dramatically increasing the transmission capacity, and practical application is being advanced. In optical wavelength division multiplexing, for example, a plurality of lights having different wavelengths are multiplexed and transmitted. In such an optical wavelength division multiplexing system, from the multiplexed light to be transmitted, on the optical receiving side, for each wavelength. In order to extract the light, it is indispensable to provide in the system a light transmission device that transmits only light of a predetermined wavelength.
[0003]
As an example of the light transmissive device, there is an arrayed waveguide grating (AWG) of a flat optical waveguide circuit (PLC) as shown in FIG. The arrayed waveguide type diffraction grating has a waveguide configuration as shown in the figure formed on a substrate 1 made of silicon or the like with a core made of quartz glass or the like.
[0004]
The waveguide configuration of the arrayed waveguide grating is such that the first slab waveguide 3 is connected to the output side of one or more optical input waveguides 2 arranged in parallel, and the first slab waveguide 3 is output. A plurality of arrayed waveguides 4 arranged in parallel are connected to the side, a second slab waveguide 5 is connected to the output side of the arrayed waveguide 4, and a plurality of arrayed waveguides 4 are connected to the output side of the second slab waveguide 5. The optical output waveguides 6 arranged side by side are connected to each other.
[0005]
The arrayed waveguide 4 propagates light derived from the first slab waveguide 3, and is formed to have different lengths. The lengths of the adjacent arrayed waveguides 4 are different from each other by ΔL. The optical input waveguide 2 and the optical output waveguide 6 are provided corresponding to the number of signal lights having different wavelengths that are demultiplexed or combined by, for example, an arrayed waveguide type diffraction grating. The waveguide 4 is usually provided in a large number such as 100, for example, but in the figure, for the sake of simplification of the drawing, each of the optical input waveguide 2, the arrayed waveguide 4, and the optical output waveguide 6 is provided. Is simply shown.
[0006]
For example, a transmission side optical fiber (not shown) is connected to the optical input waveguide 2 so that wavelength division multiplexed light is introduced, and the first slab guide is passed through the optical input waveguide 2. The light introduced into the waveguide 3 spreads by the diffraction effect and enters each arrayed waveguide 4 and propagates through the arrayed waveguide 4.
[0007]
The light propagating through the arrayed waveguide 4 reaches the second slab waveguide 5 and is further collected and output to the optical output waveguide 6, but all the arrayed waveguides 4 have different lengths. Therefore, after propagating through the arrayed waveguide 4, the phase of each light is shifted, and the wavefront of the focused light is tilted according to the shift amount, and the focusing position is determined by the tilt angle.
[0008]
For this reason, the light condensing positions of the light having different wavelengths are different from each other. By forming the light output waveguide 6 at the position, the light having different wavelengths (demultiplexed light) is guided to different light outputs for each wavelength. It can be output from the waveguide 6.
[0009]
In other words, the arrayed waveguide type diffraction grating demultiplexes light of one or more wavelengths from the multiplexed light having a plurality of different wavelengths inputted from the optical input waveguide 2 and outputs them from each optical output waveguide 6. The center wavelength of the light to be demultiplexed is the difference in length (ΔL) of the arrayed waveguide 4 and the effective refractive index n of the arrayed waveguide 4._cIs proportional to
[0010]
  Since the arrayed waveguide type diffraction grating has the characteristics as described above, the arrayed waveguide type diffraction grating can be used as a wavelength multiplexing demultiplexer for wavelength multiplexing transmission.9As shown in FIG. 4, when wavelength multiplexed light of wavelengths λ1, λ2, λ3,..., Λn (n is an integer of 2 or more) is input from one optical input waveguide 2, the light of each wavelength is It is spread by the first slab waveguide 3, reaches the arrayed waveguide 4, passes through the second slab waveguide 5, is condensed at different positions depending on the wavelength as described above, and is different from each other in the light output waveguide 6. Is output from the output end of the light output waveguide 6 through each light output waveguide 6.
[0011]
Then, by connecting an optical fiber for light output (not shown) to the output end of each light output waveguide 6, light of each wavelength is extracted through this optical fiber. When connecting an optical fiber to each optical output waveguide 6 or the above-described optical input waveguide 2, for example, an optical fiber array in which optical fibers are arranged and fixed in a one-dimensional array is prepared, and this optical fiber array is optically output. The optical fiber is connected to the optical output waveguide 6 and the optical input waveguide 2 by being fixed to the connection end face side of the waveguide 6 and the optical input waveguide 2.
[0012]
In the arrayed waveguide type diffraction grating, the light transmission characteristics of light output from each light output waveguide 6 (wavelength characteristics of the transmitted light intensity of the arrayed waveguide type diffraction grating) are the light transmission center wavelengths (for example, λ1, The light transmission characteristic is such that the light transmittance is reduced as the wavelength shifts from the corresponding light transmission center wavelength with λ2, λ3,.
[0013]
Further, since the arrayed waveguide type diffraction grating uses the principle of reciprocity (reversibility) of light, it has a function as an optical demultiplexer as well as a function as an optical multiplexer. That is, conversely to FIG. 9, when light of a plurality of different wavelengths is incident from the respective light output waveguides 6 for each wavelength, these lights pass through the propagation path opposite to that described above, and are array guided. The signals are multiplexed by the waveguide 4 and emitted from one optical input waveguide 2.
[0014]
In such an arrayed waveguide type diffraction grating, ΔL is designed to be large because the wavelength resolution of the diffraction grating is proportional to the difference in length (ΔL) of the arrayed waveguide 4 constituting the diffraction grating, as described above. As a result, optical multiplexing / demultiplexing of wavelength-division multiplexed light with a narrow wavelength interval that could not be realized with conventional diffraction gratings becomes possible, and optical multiplexing / demultiplexing of a plurality of signal lights required for realizing high-density optical wavelength division multiplexing communication is possible. A wave function, that is, a function of demultiplexing or multiplexing a plurality of optical signals having a wavelength interval of 1 nm or less can be achieved.
[0015]
When producing an arrayed waveguide grating as described above, for example, first, an underclad film and a core film are sequentially formed on a silicon substrate using a flame hydrolysis deposition method, and then an arrayed waveguide grating is formed. An arrayed waveguide diffraction grating pattern is transferred to the core film using photolithography and reactive ion etching through a photomask on which the waveguide structure is drawn. Thereafter, an over-cladding film is formed again using the flame hydrolysis deposition method, whereby an arrayed waveguide diffraction grating is manufactured.
[0016]
[Problems to be solved by the invention]
By the way, since the above-mentioned arrayed waveguide type diffraction grating is mainly made of a silica-based glass material, the light transmission center of the arrayed waveguide type diffraction grating is caused by the temperature dependence of the silica-based glass material. The wavelength shifts depending on the temperature. This temperature dependency is such that the transmission center wavelength of light output from one optical output waveguide 6 is λ, and the equivalent refractive index of the core forming the arrayed waveguide 4 is n._cThe coefficient of thermal expansion of the substrate (for example, silicon substrate) 1 is α_sWhen the temperature change amount of the arrayed waveguide type diffraction grating is T, it is represented by (Equation 1).
[0017]
[Expression 1]

[0018]
Here, in the conventional general arrayed waveguide grating, the temperature dependence of the light transmission center wavelength is obtained from (Equation 1). In a conventional general arrayed waveguide grating, dn_c/ DT = 1 × 10^-5(℃^-1), Α_s= 3.0 × 10^-6(℃^-1), N_cSince 1.451 (value at a wavelength of 1.55 μm), these values are substituted into (Equation 1).
[0019]
Further, the wavelength λ is different for each optical output waveguide 6, but the temperature dependence of each wavelength λ is equal. The arrayed waveguide grating currently used is often used for demultiplexing or multiplexing wavelength-multiplexed light in a wavelength band centered on a wavelength of 1550 nm. = 1550 nm is substituted into (Equation 1). Then, the temperature dependence of the light transmission center wavelength of the conventional general arrayed waveguide grating is a value shown in (Expression 2).
[0020]
[Expression 2]

[0021]
The unit of dλ / dT is nm / ° C. For example, if the use environment temperature of the arrayed waveguide grating changes by 20 ° C., the light transmission center wavelength output from each light output waveguide 6 shifts by 0.30 nm, and the use environment temperature changes by 70. When the temperature is higher than or equal to ° C., the shift amount of the light transmission center wavelength becomes 1 nm or more.
[0022]
The arrayed waveguide type diffraction grating is characterized in that the wavelength can be demultiplexed or multiplexed at a very narrow interval of 1 nm or less, and is used for wavelength multiplexing optical communication by taking advantage of this feature. In addition, it is fatal that the light transmission center wavelength is changed by the shift amount due to a change in the use environment temperature.
[0023]
Therefore, the temperature of the Peltier element 30 or the like that keeps the temperature of the arrayed waveguide grating constant based on the detection temperature of the thermistor 31, as shown in FIG. 9, so that the light transmission center wavelength does not change with temperature. An arrayed waveguide type diffraction grating provided with adjusting means has been proposed. In order to keep the temperature of the arrayed waveguide type diffraction grating constant by using the temperature adjusting means, a current of 1 W, for example, is applied to the Peltier element or the like. It has to be performed all the time, which is costly, and the light transmission center wavelength shift may not be able to be accurately suppressed due to misalignment of components forming the Peltier element and its control mechanism.
[0024]
In order to solve the above problems, the present inventor has proposed an arrayed waveguide type diffraction grating having a structure as shown in FIG. 7 (as proposed in Japanese Patent Application Nos. 11-270201 and 2000-021533). And has not yet been released).
[0025]
The arrayed waveguide diffraction grating shown in FIG. 1 has a waveguide forming region 10 formed of quartz glass on a substrate 1. As in the conventional example, the waveguide forming region 10 includes one optical input waveguide 2, a first slab waveguide 3, a plurality of arrayed waveguides 4, a second slab waveguide 5, and a plurality of optical output guides. A waveguide 6 is provided, and the arrayed waveguide 4 and the optical output waveguide 6 are arranged in parallel with each other with a predetermined waveguide interval. In the arrayed waveguide diffraction grating shown in FIG. The first slab waveguide 3 is cut and separated by a cut surface 8 that intersects the light path passing through the first slab waveguide 3.
[0026]
In the figure, the cut surface 8 is in the X direction in the figure, and the waveguide forming region 10 is cut and separated into the waveguide forming region 10a and the waveguide forming region 10b by the cut surface 8. ing.
[0027]
The characteristic feature of the arrayed waveguide grating shown in FIG. 7 is that, as described above, the first slab waveguide 3 is separated slab waveguide at the cut surface 8 where the light path passing through the first slab waveguide 3 intersects. 7a and 3b, and the light transmission center wavelength is shifted by sliding the separated separation slab waveguide 3a side along the cut surface 8 as shown in FIG. The arrayed waveguide type diffraction grating is provided with a slide moving mechanism for performing the slide movement.
[0028]
This slide moving mechanism is a mechanism that slides the separation slab waveguide 3a side along the cut surface 8 in a direction that reduces the temperature-dependent fluctuation of each light transmission center wavelength of the arrayed waveguide diffraction grating. In the configuration shown, a high thermal expansion coefficient member 7, a base 9, and a locking member 14 are provided to constitute the slide moving mechanism.
[0029]
The waveguide forming region 10b on the side where the separation slab waveguide 3b, the arrayed waveguide 4, the second slab waveguide 5, and the light output waveguide 6 are formed, and the substrate 1 thereunder are quartz glass, Invar lot, etc. The base 9 is made of a material having a low coefficient of thermal expansion.
[0030]
The waveguide forming region 10a on the side where the separation slab waveguide 3a and the optical input waveguide 2 are formed and the substrate 1 therebelow are provided slidably with respect to the base 9. One end side of the waveguide forming region 10 a is fixed to the high thermal expansion coefficient member 7 via the adhesive 13, and the other end side is locked to the locking member 14.
[0031]
The high thermal expansion coefficient member 7 has an upper plate portion 7a provided along the upper surface of the waveguide forming region 10a and a side plate portion (not shown) provided along the side surface of the waveguide forming region 10a. A side plate portion is fixed to the base 9 by a fixing portion 11. The high thermal expansion coefficient member 7 has, for example, a thermal expansion coefficient of 2.31 × 10^-5It is made of (1 / K) Al (aluminum).
[0032]
The locking member 14 has an upper plate portion 14a provided along the upper surface of the waveguide forming region 10a and a side plate portion (not shown) provided along the side surface of the waveguide forming region 10a. A side plate portion is fixed to the base 9 by a fixing portion 12. The inner wall of the upper plate portion of the locking member 14 is in contact with the upper surface of the waveguide forming region 10a. When the waveguide forming region 10a slides, the waveguide forming region 10a moves upward (XY). It is designed not to be displaced in the Z-axis direction (perpendicular to the plane). Further, the inner wall of the side plate portion and the side surface of the waveguide forming region 10a are spaced from each other so that the sliding movement of the waveguide forming region 10a can be performed without any trouble.
[0033]
In the arrayed waveguide diffraction grating shown in the figure, when the use environment temperature of the arrayed waveguide diffraction grating changes, the high thermal expansion member 7 expands or contracts more than the waveguide forming region 10, so that the side not fixed to the base The waveguide forming region 10a and its substrate 1 slide along the cut surface 8 in the direction of arrow A or arrow B in the figure, whereby the separation slab waveguide 3a and the optical input waveguide 2 slide. Moving.
[0034]
Since the movement along the cut surface 8 is performed in a direction that reduces the temperature-dependent fluctuation of each light transmission center wavelength of the arrayed waveguide grating, in the proposed arrayed waveguide grating, the array waveguide is arranged. The temperature dependency of each light transmission center wavelength accompanying the change in the use environment temperature of the waveguide diffraction grating is compensated.
[0035]
The above proposal was made by paying attention to the linear dispersion characteristics of the arrayed waveguide type diffraction grating, and the temperature dependence compensation principle of the light transmission center wavelength in the above proposal will be described with reference to FIG. .
[0036]
The light incident from the optical input waveguide 2 in the arrayed waveguide grating is diffracted by the first slab waveguide (input slab waveguide) 3 to excite the arrayed waveguide 4. As described above, the lengths of the adjacent arrayed waveguides 4 are different from each other by ΔL. Therefore, the light propagated through the arrayed waveguide 4 satisfies (Equation 3) and is condensed at the output end of the second slab waveguide (output-side slab waveguide) 5.
[0037]
[Equation 3]

[0038]
In (Equation 3), n_sIs the equivalent refractive index of the first slab waveguide 3 and the second slab waveguide 5, n_cIs the equivalent refractive index of the arrayed waveguide 4, φ is the diffraction angle, m is the diffraction order, d is the spacing between the adjacent arrayed waveguides 4, and λ is output from each optical output waveguide 6 as described above. This is the transmission center wavelength of light.
[0039]
Here, the light transmission center wavelength where the diffraction angle φ = 0 is λ.₀Then λ₀Is represented by (Equation 4). The wavelength λ₀Is generally called the center wavelength of an arrayed waveguide grating.
[0040]
[Expression 4]

[0041]
By the way, in FIG. 8, when the condensing position of the arrayed waveguide type diffraction grating where the diffraction angle φ = 0 is a point O, the diffraction angle φ = φ._pThe light condensing position of light (position at the output end of the second slab waveguide 5) is, for example, the position of the point P (position shifted from the point O in the X direction). Here, if the distance in the X direction between O and P is x, (Equation 5) holds between the wavelength λ.
[0042]
[Equation 5]

[0043]
In (Equation 5), L_fIs the focal length of the second slab waveguide 5 and n_gIs the group index of the arrayed waveguide 4. The group refractive index n of the arrayed waveguide 4_gIs the equivalent refractive index n of the arrayed waveguide 4_cIs given by (Equation 6).
[0044]
[Formula 6]

[0045]
In the above (Equation 5), the input end of the light output waveguide 6 is arranged and formed at a distance dx in the X direction from the focal point O of the second slab waveguide 5 so that light having a wavelength different by dλ can be obtained. It means that it can be taken out.
[0046]
Further, the relationship of (Equation 5) is similarly established for the first slab waveguide 3. That is, for example, when the focal point center of the first slab waveguide 3 is a point O ′ and a point at a position shifted by a distance dx ′ in the X direction from the point O ′ is a point P ′, light is transmitted to the point P ′. When incident, the output wavelength is shifted by dλ ′. This relationship can be expressed by an equation (7).
[0047]
[Expression 7]

[0048]
In (Expression 7), L_f'Is the focal length of the first slab waveguide 3. This (Formula 7) is formed at the focal point O by disposing the output end of the optical input waveguide 2 at a position dx ′ away from the focal point O ′ of the first slab waveguide 3 in the X direction. This means that it is possible to extract light having different wavelengths by dλ ′ in the optical output waveguide 6.
[0049]
Therefore, when the light transmission center wavelength output from the optical output waveguide of the arrayed waveguide type diffraction grating is shifted by Δλ due to a change in the ambient temperature of the arrayed waveguide type diffraction grating, the optical wavelength is set so that dλ ′ = Δλ. If the output end position of the input waveguide 6 is shifted by the distance dx ′ in the X direction, for example, light having no wavelength shift can be extracted in the optical output waveguide 6 formed at the focal point O, and other optical output waveguides can be extracted. 6 also has the same effect, the light transmission center wavelength shift Δλ can be corrected (cancelled).
[0050]
In the proposed example, at least one of the first slab waveguide 3 and the second slab waveguide 5 is cut and separated at the cut surface 8 that intersects the path of light passing through the slab waveguide 5, as shown in FIG. As described above, when it is assumed that the first slab waveguide 3 is cut and separated, the separated slab connected to the optical input waveguide 2 among the separated first slab waveguides, for example. If the waveguide 3a side (including the optical input waveguide 2) is slid along the cut surface by a slide movement mechanism, the light transmission center wavelengths can be shifted.
[0051]
In addition, the slide movement mechanism causes the temperature-dependent fluctuation (wavelength shift) Δλ of each light transmission center wavelength to be equal to dλ, so as to reduce the temperature-dependent fluctuation of each light transmission center wavelength. If the waveguide 3a and the light input waveguide 2 are moved along the cut surface 8, the light transmission center wavelength shift can be eliminated.
[0052]
Further, the relationship between the temperature change amount and the position correction amount of the optical input waveguide 2 is derived as follows. Since the temperature dependence of the light transmission center wavelength (the amount of shift of the light transmission center wavelength depending on the temperature) is expressed by the above (Equation 2), the light transmission center wavelength shift amount Δλ is expressed as 8).
[0053]
[Equation 8]

[0054]
When the temperature change amount T and the optical input waveguide position correction amount dx ′ are obtained from (Equation 7) and (Equation 8), (Equation 9) is derived.
[0055]
[Equation 9]

[0056]
Therefore, in the configuration shown in FIG. 7, the separation slab waveguide 3a and the light of the first slab waveguide 3 are cut along the cut surface 8 by the slide movement mechanism by the position correction amount dx ′ represented by (Equation 9). By sliding the input waveguide 2, it is possible to eliminate the light transmission center wavelength shift.
[0057]
For example, based on each parameter of the waveguide configuration of a conventional general arrayed waveguide grating and (Equation 9), the change amount T of the ambient temperature of the arrayed waveguide grating and the position of the optical input waveguide 2 When the relationship of the correction amount dx ′ is obtained, the relationship shown in (Expression 10) is obtained. In this case, when the operating environment temperature of the arrayed waveguide grating changes by 10 ° C., if the position of the output end of the optical input waveguide 2 is corrected (moved) by about 3.83 μm in the X direction, the center wavelength is shifted by the temperature. Is a calculation that can be corrected.
[0058]
[Expression 10]

[0059]
As described above, the arrayed waveguide grating is formed by utilizing the reciprocity of light, and the separated slab waveguide is separated by cutting the second slab waveguide 5 side. If at least one side is slid in the direction of reducing the temperature-dependent variation of each light transmission center wavelength along the cut surface by a slide movement mechanism, the same effect can be obtained, and each light transmission center wavelength can be obtained. It becomes possible to eliminate the temperature-dependent fluctuation of the.
[0060]
However, a large number of arrayed waveguide diffraction gratings having the configuration as shown in FIG. 7 are manufactured, and in each arrayed waveguide type diffraction grating, the separation waveguide 3a side is moved in the directions of arrows A and B in FIG. When the effect of reducing the temperature dependence of the light transmission center wavelength of the arrayed waveguide type diffraction grating was examined by sliding it to the point, it was found that there were some that could not exhibit sufficient effects.
[0061]
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inexpensive arrayed waveguide grating capable of accurately suppressing the temperature dependence of the light transmission center wavelength. is there.
[0062]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention has the following configuration as means for solving the problems. That is, in the first invention, the first slab waveguide is connected to the output side of one or more optical input waveguides arranged in parallel, and the first slab waveguide is connected to the output side of the first slab waveguide. A plurality of arrayed waveguides having different lengths that propagate light derived from the slab waveguide are connected, and a second slab waveguide is connected to the emission side of the plurality of arrayed waveguides, The output side of the second slab waveguide has a waveguide configuration in which a plurality of light output waveguides arranged in parallel are connected, and have a plurality of different wavelengths inputted from the light input waveguide. A light demultiplexing function of demultiplexing light of one or more wavelengths from the light output and outputting the light from each light output waveguide, and the light transmittance of each light output from each light output waveguide is at least in advance In the specified wavelength range, it is centered on different light transmission center wavelengths of demultiplexed light. In the arrayed waveguide diffraction grating, which becomes smaller as the wavelength shifts from the corresponding light transmission center wavelength, the first slab waveguide is cut and separated at a cut surface that intersects the light path passing through the slab waveguide, Slide at least one side of the separated separated slab waveguide along the cut surface.A slide moving mechanism is provided, and at least one side of the separation slab waveguide is slid along the cut surface by the slide moving mechanism.Thus, the light transmission center wavelength is shifted, and the cut surface is a surface that intersects the light path at a position closer to the array waveguide than the center position in the longitudinal direction of the light path passing through the slab waveguide.The waveguide of the arrayed waveguide diffraction grating is formed on a substrate, and the first slab waveguide is cut and separated integrally with the substrate by a cut surface, and the separated slab guide on one side is separated. The waveguide is configured to slide along the cut surface integrally with the separated substrate, and the slide moving mechanism includes a high thermal expansion coefficient member that expands and contracts according to a temperature change, One end side of the high thermal expansion coefficient member is fixed to the separated substrate on the separated slab waveguide side on the sliding side, and the other end side of the high thermal expansion coefficient member is heated more than the high thermal expansion coefficient member. One of the separated slab waveguides is fixed by being fixed to a base on the fixed side formed of a low thermal expansion coefficient material having a low expansion coefficient, and the high thermal expansion coefficient member expands and contracts according to a temperature change in a use environment. There along said cutting plane, and configured to move the slide in a direction to reduce the temperature-dependent variation of the light transmission central wavelength of the light output from the optical output waveguides of the arrayed waveguide gratingIt is a means to solve the problem with the configuration.
[0065]
Elucidation of the reason why the present inventor has a configuration of the above-described proposed arrayed waveguide diffraction grating as shown in FIG. 7 but cannot sufficiently exhibit the effect of reducing the temperature dependence of the light transmission center wavelength. Therefore, when the arrayed waveguide type diffraction grating is disassembled, the one that cannot sufficiently exhibit the temperature dependency reducing effect is shown in FIG. An angle θ is formed between the end face (cut face 8a) and the end face (cut face 8b) of the waveguide forming region 10b (the slide movement is performed in a state where the cut face 8a and the cut face 8b completely coincide with each other). I understand). In FIG. 2, only the optical input waveguide 2 and the first slab waveguide 3 are shown in the waveguide configuration of the arrayed waveguide type diffraction grating for simplification of the drawing.
[0066]
  Therefore, it is important to make this angle θ close to zero, but the angle θ is not actually as large as shown in FIG. 2 and is at most about 0.5 degrees (in FIG. 2). For ease of explanation, θ is shown as large), and an angle θ of this magnitude is caused by an error in manufacturing an arrayed waveguide grating.AvoidI can't.
[0067]
Therefore, the inventor paid attention to the formation position of the cut surface 8. As a result, the first slab waveguide 3 at the cut surface 8 intersecting the light path at a position closer to the light input waveguide 2 than the center position in the longitudinal direction of the light path passing through the first slab waveguide 3. It was found that the effect of reducing the temperature-dependent fluctuation of each light transmission center wavelength in the arrayed waveguide type diffraction grating could not be sufficiently exhibited due to the balance with the angle θ.
[0068]
Therefore, the inventor considered the relationship between the angle θ and the light transmission center wavelength shift amount in the arrayed waveguide type diffraction grating as follows.
[0069]
That is, as shown in FIG. 2, the output end 20 of the optical input waveguide 2 in the arrayed waveguide grating is formed at the center in the width direction of the first slab waveguide 3 (W1 = W2). ). Light input from the output end 20 of the optical input waveguide 2 to the first slab waveguide 3 propagates through the first slab waveguide 3 while spreading toward the array waveguide 4 side. The intensity of light traveling straight from the output end 20 (C in the figure) toward the center position (position where W1 = W2) B in the width direction at the output end of the first slab waveguide 3 is highest.
[0070]
Therefore, when the angle θ between the end face (cut face 8a) of the waveguide forming area 10a cut by the cut face 8 and the end face (cut face 8b) of the waveguide forming area 10b is 0, that is, the cut face 8a and the cut face. In an ideal case where the angle deviation of the surface 8b does not occur, the intensity center of light propagating through the first slab waveguide 3 is directed to the position B.
[0071]
Here, the angle between the end surface (cut surface 8a) of the waveguide forming region 10a and the end surface (cut surface 8b) of the waveguide forming region 10b is an angle θ with the end A of the cut surface 8 (8a, 8b) as a fulcrum. Consider the case of deviation.
[0072]
Note that the length of the separation slab waveguide 3a (length in the light path direction) is L_f1And the length of the separation slab waveguide 3b (length in the light path direction) is L_f2And the length from the end face E of the arrayed waveguide grating to the output end 20 of the optical input waveguide 2 (C in the figure) is L₀And In addition, since a refractive index matching agent is applied between the cut surface 8a and the cut surface 8b, light is not reflected by the gap between the cut surfaces 8a and 8b.
[0073]
When the angle between the cut surface 8a and the cut surface 8b is θ, the center of the light intensity input from the position C in the figure is dxg upward from the position B in the first slab waveguide 3 in the figure. Since the light travels straight toward the deviated point, the focal length L of this light_fg′ Can be approximated by the distance between CBs. In the figure, point A and point C, point A and point B are connected, and γ₁= Tan^-1(L_f1/ L₀), Γ₂= Tan^-1(L_f2/ L₀), L_AB= (L₀ ²+ L_f2 ²)^1/2, L_AD= (L₀ ²+ L_f2 ²)^1/2・ Cos (θ + γ₂Dxg is expressed by (Equation 11). L_BD= (L₀ ²+ L_f2 ²)^1/2・ Sin (θ + γ₂) And the focal length L_fg'Can be approximated by (Equation 12).
[0074]
## EQU11 ##

[0075]
[Expression 12]

[0076]
Further, in FIG. 2, the angle θ is shown large, but as described above, since θ is actually a very small value, there is no problem even assuming that the linear dispersion characteristic of the arrayed waveguide grating is satisfied. Therefore, the following equation (Equation 13) holds.
[0077]
[Formula 13]

[0078]
Here, ΔL is the optical path length difference of the arrayed waveguide, n_sIs the equivalent refractive index of the first slab waveguide 3, d is the spacing between adjacent arrayed waveguides 4, λ₀Is the light transmission center wavelength where the diffraction angle φ = 0 of the arrayed waveguide grating (generally called the center wavelength of the arrayed waveguide grating), n_gIs the group index of the arrayed waveguide 4. Wavelength λ₀Is represented by the above (Equation 4), and the group refractive index n of the arrayed waveguide 4 is_gIs represented by the above (Equation 6).
[0079]
Therefore, when the cut surface 8 formed so as to intersect the light path passing through the first slab waveguide 3 is formed on the side close to the optical input waveguide 2 and the case where it is formed on the side close to the array waveguide 4. In both cases, using the above (Equation 4), (Equation 6), (Equation 11), (Equation 12), and (Equation 13), the angle θ in the arrayed waveguide grating and the light transmission center wavelength shift amount The relationship was calculated respectively. The calculation results are shown in FIGS.
[0080]
The calculation result was calculated based on the following parameters similar to those in the first embodiment. That is, the diffraction order m is 61, the length difference ΔL between adjacent arrayed waveguides 4 is 65.2 μm, the pitch d of the arrayed waveguides 4 is 15 μm, and the equivalent refractive index n of the arrayed waveguides 4_c1.451, arrayed waveguide group refractive index n_gIs 1.475 and the equivalent refractive index n of the first and second slab waveguides 3 and 5_sWas 1.453 respectively. These equivalent refractive index values are values for light having a wavelength of 1.55 μm, and are values at 25 ° C.
[0081]
When the cut surface 8 is formed on the side close to the optical input waveguide 2 (calculation result shown in FIG. 3), L_f1= 1000 μm, L_f2= 8000 μm, and when the cut surface 8 is formed on the side close to the arrayed waveguide 4 (calculation result shown in FIG. 4), L_f1= 8000μm, L_f2= 1000 μm.
[0082]
As apparent from FIGS. 3 and 4, the light transmission center wavelength shift amount increases as the angle θ increases, and the light transmission center wavelength shift amount is substantially proportional to the angle θ. This means that when the separation slab waveguide 3a side is slid along the cut surface 8 by the slide movement mechanism, an appropriate light transmission center wavelength shift amount (light transmission center wavelength shift amount) to be shifted by this slide movement. This means that the center wavelength of the light transmission center of the arrayed waveguide grating is shifted by an amount corresponding to the angle θ.
[0083]
Therefore, when the angle θ is increased, the light transmission center wavelength cannot be shifted as designed. For example, as shown in FIG. 3, when the cut surface 8 is formed on the side close to the optical input waveguide 2, the light transmission center wavelength shift amount becomes 0.5 nm when the angle θ is 0.1 degree. Therefore, the light transmission center wavelength is shifted by an extra 0.5 nm, which is a problem when wavelength-multiplexed light is separated at an interval of 0.8 nm wavelength by the arrayed waveguide type diffraction grating.
[0084]
On the other hand, when the cut surface 8 is formed on the side close to the arrayed waveguide 4, the light transmission center wavelength shift amount is 0.1 nm when the angle θ is 0.1 degree as shown in FIG. It has been found that by forming the cut surface 8 on the side close to the arrayed waveguide 4, the light transmission center wavelength shift amount depending on the angle θ can be reduced to about one fifth. It should be noted that the light transmission center wavelength shift amount (deviation amount from the design value) is 0.1 nm.
[0086]
  The present invention provides a first slab waveguide based on the above-mentioned consideration results.The roadThe cut surface to be cut is a cut surface that is cut on the side close to the array waveguide side, and an array waveguide type diffraction grating is configured by providing a slide mechanism similar to the configuration of the proposed example as shown in FIG. In addition, an inexpensive arrayed waveguide grating capable of accurately suppressing the temperature dependence of the light transmission center wavelength can be obtained.
[0087]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the present embodiment, the same reference numerals are assigned to the same name portions as in the conventional example, and the duplicate description thereof is omitted. FIG. 1 is a plan view schematically showing an embodiment of an arrayed waveguide grating according to the present invention. The present embodiment example is configured in substantially the same manner as the above-described proposed example shown in FIG. 7, and the present embodiment example is different from the above-described proposed example in that the cut surface 8 is formed on the first slab waveguide 3. That is, the surface intersects with the light path at a position closer to the arrayed waveguide 4 than the center position in the longitudinal direction of the path of the light passing therethrough (position closer to the arrayed waveguide).
[0088]
That is, in the present embodiment, the cut surface 8 is a surface that cuts the first slab waveguide 3 closer to the array waveguide 4 side than the optical input waveguide 2 side. Is the length L in the figure._f1= 8000μm, L_f2= 1000 μm.
[0089]
As described above, in the arrayed waveguide type diffraction grating of the proposed example shown in FIG. 7, the light that passes through the first slab waveguide 3 cannot sufficiently exhibit the effect of reducing the temperature-dependent variation of each light transmission center wavelength. The first slab waveguide 3 is cut at the cut surface 8 that intersects the light path at a position closer to the optical input waveguide 2 than the center position in the longitudinal direction of the path of the path, and the cut surface shown in FIG. It was found that the angle θ between the end surface of the waveguide forming region 10a (cut surface 8a) and the end surface of the waveguide forming region 10b (cut surface 8b) at the cut portion in FIG.
[0090]
Then, the present inventor considers the relationship between the angle θ and the light transmission center wavelength shift amount in the arrayed waveguide grating as described above, and based on the result of the consideration, as described above, the first slab A cut surface 8 is formed on the waveguide 3 on the side closer to the array waveguide 4 side than to the optical input waveguide 2 side, thereby forming the arrayed waveguide type diffraction grating of this embodiment.
[0091]
The present embodiment is configured as described above, and in the arrayed waveguide type diffraction grating of the present embodiment, when the angle θ is actually measured, θ = about 0.05 degrees, and FIG. As shown in the figure, it was found that the arrayed waveguide type diffraction grating in which the light transmission center wavelength hardly fluctuates at the use environment temperature of 0 ° C. to 80 ° C. of the arrayed waveguide type diffraction grating.
[0092]
In FIG. 5, in the arrayed waveguide type diffraction grating of this embodiment, the angle θ is intentionally increased, and the light transmission center wavelength shift amount of the arrayed waveguide type diffraction grating with respect to the angle θ is measured. The result is shown together with the calculated value of the light transmission center wavelength shift amount shown in FIG. 4, and as is clear from FIG. 5, it is formed in the first slab waveguide 3 as in this embodiment. By forming the cut surface 8 on the side close to the arrayed waveguide 4, even if the angle θ in the cut surface 8 is somewhat large, the light transmission center wavelength can be shifted as designed. It was found that the temperature dependence of the light transmission center wavelength in can be efficiently reduced.
[0093]
In FIG. 5, ◯ is the actually measured value, and the characteristic line is the calculated value, and the calculated value and the actually measured value almost coincide.
[0094]
According to the present embodiment, the configuration is almost the same as the proposed example shown in FIG. 7 so that the temperature dependence of the light transmission center wavelength of the arrayed waveguide grating can be reduced. As shown in FIG. 1, the first slab waveguide 3 is formed with a cut surface 8 on the side closer to the array waveguide 4 side than the optical input waveguide 2 side, and the arrayed waveguide type diffraction grating of this embodiment example Thus, an arrayed waveguide type diffraction grating capable of accurately suppressing the temperature dependence of the light transmission center wavelength almost exactly as designed can be obtained.
[0095]
Further, according to the present embodiment example, a slide moving mechanism having a simple configuration is provided which is configured to include the high thermal expansion coefficient member 7, the base 9, and the locking member 14 as in the proposed example shown in FIG. 7. As a result, the temperature dependence of each light transmission center wavelength of the arrayed waveguide type diffraction grating can be efficiently reduced, and the configuration of the arrayed waveguide type diffraction grating can be avoided from being complicated and easy to manufacture. .
[0096]
Furthermore, according to the present embodiment example, the first slab waveguide 3 is cut by the cut surface 8, and therefore, for example, due to a manufacturing error of the arrayed waveguide portion constituting the arrayed waveguide grating. When the light transmission center wavelength is deviated from a set wavelength such as the ITU grid wavelength, the relative positions of the separation slab waveguide 3a and the separation slab waveguide 3b are shifted by that amount, and the X of the light input waveguide 2 is shifted. By shifting the position in the direction, the light transmission center wavelength can be set to a set wavelength such as a grid wavelength at a set temperature.
[0097]
In addition, this invention is not limited to the said embodiment example, Various aspects can be taken. For example, in the above-described embodiment, the first slab waveguide 3 having a length in the longitudinal direction of 9000 μm is changed to L as shown in FIG._f1= 8000μm, L_f2The cut surface 8 was cut so as to be equal to 1000 μm._f1Or L_f2The length of is not particularly limited and is set as appropriate._f1> L_f2By forming the cut surface 8 so as to be, the same effects as in the above embodiment can be obtained.
[0098]
In the above embodiment, an Al plate is used as the high thermal expansion coefficient member 7. However, the high thermal expansion coefficient member 7 is not necessarily made of Al, and may be formed of a material other than Al.
[0101]
Further, the cut surface 8 of the first slab waveguide 3 or the second slab waveguide 5 is not necessarily a plane substantially parallel to the X axis as in the above embodiment, and is a plane oblique to the X axis. Alternatively, it may be cut and separated at a cut surface that intersects the light path passing through the slab waveguide to be cut.
[0102]
  Further, in the above-described embodiment, the slide moving mechanism that slides the separation slab waveguide 3a side along the cut surface 8 is formed by providing the high thermal expansion coefficient member 7, but the configuration of the slide moving mechanism is particularly limited. It is not a thing and is set suitably. In other words, the slide moving mechanism includes the first slab waveguide.3It has the function of shifting the light transmission center wavelength of the arrayed waveguide grating by sliding at least one side of the separation slab waveguide formed by cutting and separating at the cut surface along the cut surface 8. It only has to be.
[0103]
In particular, it is desirable that the slide moving mechanism has a function of sliding in the direction of reducing the temperature-dependent fluctuation of each light transmission center wavelength of the arrayed waveguide type diffraction grating as in the above-described embodiment. By configuring the moving mechanism in this way, the temperature dependence of the light transmission center wavelength, which has been a problem in the conventional arrayed waveguide type diffraction grating, can be eliminated as in the above embodiment, and the optical wavelength multiplexing is performed. An excellent arrayed waveguide type diffraction grating suitable for practical use such as communication can be obtained.
[0104]
Furthermore, the detailed values such as the equivalent refractive index, the number, and the size of each of the waveguides 2, 3, 4, 5, and 6 constituting the arrayed waveguide type diffraction grating of the present invention are not particularly limited, and are appropriately determined. Is set.
[0105]
【The invention's effect】
  According to the first invention, the first slab waveguideTheEach light transmission of the arrayed waveguide grating is performed by cutting and separating at a cutting plane that intersects the path of light passing through the slab waveguide, and sliding at least one of the separated slab waveguides along the cutting plane. Since the center wavelength can be shifted and the cut surface is formed on the arrayed waveguide side with respect to the longitudinal center position of the light path, the light transmission center wavelength depends on the angle between the separated slab waveguides. Since the shift displacement amount can be reduced, the light transmission center wavelength shift can be performed almost as designed.
[0106]
According to the second invention, in addition to the first invention, the slide movement mechanism moves along the cut surface to slide the light transmission center wavelength in a direction to reduce the temperature-dependent fluctuation. Therefore, each light transmission center wavelength of the arrayed waveguide grating can be shifted by a very appropriate amount, and temperature-dependent variation (wavelength shift) of each light transmission center wavelength can be eliminated. .
[0107]
According to the second aspect of the present invention, the shift of the light transmission center wavelength due to the use environment temperature of the arrayed waveguide grating is suppressed without using a Peltier element or a heater, and the temperature of the light transmission center wavelength is made temperature independent. Therefore, as in the case of providing a temperature adjusting means including a Peltier element and a heater, there is no need for constant energization, no temperature correction error due to parts assembly error, and more than room temperature. There is no risk of increasing the connection loss between the arrayed waveguide grating and the optical fiber due to maintaining the arrayed waveguide grating at the temperature of.
[0108]
Therefore, the arrayed waveguide type diffraction grating according to the second aspect of the present invention has high connection reliability with the optical fiber on the other end of the connection, can reliably eliminate the temperature dependence of the light transmission center wavelength, and is an excellent array conductor with low cost. It can be a waveguide type diffraction grating.
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram showing an embodiment of an arrayed waveguide grating according to the present invention in a plan view.
FIG. 2 is an explanatory diagram for explaining a light transmission center wavelength shift corresponding to a waveguide forming region end face angle θ when the first slab waveguide of the arrayed waveguide grating is cut.
FIG. 3 is a calculation of the relationship between the angle θ shown in FIG. 2 and the light transmission center wavelength shift amount in the arrayed waveguide type diffraction grating when the first slab waveguide is cut on the side close to the optical input waveguide. It is a graph which shows a result.
4 is a calculation result of the relationship between the angle θ shown in FIG. 2 and the light transmission center wavelength shift amount in the arrayed waveguide grating when the first slab waveguide is cut on the side close to the arrayed waveguide. It is a graph which shows.
5 is a calculation result of the relationship between the angle θ shown in FIG. 2 and the light transmission center wavelength shift amount in the arrayed waveguide grating when the first slab waveguide is cut on the side close to the arrayed waveguide. It is a graph which compares and shows a measured value.
FIG. 6 is a graph showing temperature dependence of a light transmission center wavelength in the arrayed waveguide grating of the embodiment.
FIG. 7 is an explanatory view showing a configuration of an arrayed waveguide type diffraction grating formed by cutting a conventionally proposed first slab waveguide.
FIG. 8 is an explanatory diagram showing a relationship between a light transmission center wavelength shift and positions of an optical input waveguide and an optical output waveguide in an arrayed waveguide type diffraction grating.
FIG. 9 is an explanatory view showing a conventional arrayed waveguide type diffraction grating configured by providing a Peltier element.
[Explanation of symbols]
1 Substrate
2 Optical input waveguide
3 First slab waveguide
3a, 3b Separated slab waveguide
4 Arrayed waveguide
5 Second slab waveguide
6 Optical output waveguide
7 High thermal expansion coefficient members
8,8a, 8b Cut surface
9 base
10, 10a, 10b Waveguide formation region
14 Locking member

Claims (1)

A first slab waveguide is connected to the output side of one or more optical input waveguides arranged side by side, and the light derived from the first slab waveguide is output to the output side of the first slab waveguide. A plurality of arrayed waveguides having different lengths propagating through the plurality of arrayed waveguides are connected, and a second slab waveguide is connected to the output side of the plurality of arrayed waveguides. The output side has a waveguide configuration in which a plurality of light output waveguides arranged in parallel are connected, and one or more wavelengths from light having a plurality of different wavelengths input from the light input waveguide A light demultiplexing function for demultiplexing the light of each light and outputting the light from each light output waveguide, and the light transmittance of each light output from each of the light output waveguides is separated at least in a predetermined wavelength region Centered light transmission center waves centered on different light transmission center wavelengths of wave light In the arrayed waveguide grating, which becomes smaller as the wavelength shifts from the first slab waveguide, the first slab waveguide is cut and separated at a cut surface that intersects the light path passing through the slab waveguide. There is provided a slide movement mechanism that slides at least one side of the waveguide along the cut surface, and the light is obtained by sliding at least one side of the separation slab waveguide along the cut surface by the slide movement mechanism. form the structure for shifting the transmission center wavelength, the cutting surface is a surface intersecting the optical path of the position of the arrayed waveguide side from the longitudinal center position of the light path through the slab waveguide, said arrayed waveguide The waveguide of the waveguide diffraction grating is formed on a substrate, and the first slab waveguide is cut and separated by a cut surface integrally with the substrate. The separated one-side separated slab waveguide is configured to slide along the cut surface integrally with the separated one-side substrate, and the slide moving mechanism is adapted to change in temperature. A high thermal expansion coefficient member that expands and contracts; one end side of the high thermal expansion coefficient member is fixed to the separated substrate on the separation slab waveguide side on the sliding side; An end side is fixed to a base which is a fixed side formed of a material having a low thermal expansion coefficient lower than that of the high thermal expansion coefficient member, and the high thermal expansion coefficient member expands and contracts according to a temperature change in a use environment. As a result, one side of the separation slab waveguide is slid along the cut surface in a direction to reduce temperature-dependent fluctuation of the light transmission center wavelength of the light output from each light output waveguide of the arrayed waveguide grating. An arrayed waveguide type diffraction grating characterized in that it is configured to move in a ride .

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