JP3755961B2 - Optical wavelength router and waveguide array - Google Patents

Description

また、弱導波路部分２６では、コア層３０の両側にもＳｉＯ₂ 層３４（屈折率ｎ＝１．４５）を設けて、横方向（ＳｉＯ₂ 基板１０の主表面に沿った方向）の光の閉じ込めを弱くしてある。すなわち、屈折率比Δ₂ は、下記の式（６）で与えられる。
【００５３】

また、この実施の形態においては、図２の（Ａ）に示すように、導波路を伝搬する光の単一モードを維持するために、非弱導波路部分２８の幅（２μｍ）を、弱導波路部分２６の幅（６μｍ）よりも狭くしてある。また、入力側スターカプラ１２と弱導波路部分２６との接続部分には、この接続部分における光の損失の発生を抑制するために、テーパ部３６を設けてある。このテーパ部３６の入力側スターカプラ１２との接続点での幅は１２μｍであり、５００μｍの長さをかけて、弱導波路部分２６の幅である６μｍに収束している。また、弱導波路部分２６と非弱導波路部分２８との接続部分（終点２６ｅ）にも、この接続部分における光の発生を抑制するために、テーパ部３８を設けてある。
【００５４】
（弱導波路部分の寸法精度について）
次に、弱導波路部分２６の寸法精度について検討する。一般に、導波路の幅ＷがΔＷだけ変化したときの当該導波路の透過屈折率の変化δｎ_e は、下記の（７）式で与えられる。
【００５５】
δｎ_e ＝∂ｎ_e ／∂Ｗ・ΔＷ ・・・（７）
透過屈折率の変化に対して、導波路を伝搬する光の選択波長特性は、下記の（８）式で示すΔλだけずれる。
【００５６】
Δλ＝λ₀ ・δｎ_e ／ｎ_e ・・・（８）
ここで、λ₀ は、波長多重された光の中心波長を表す。
【００５７】
また、上記の（７）式について下記の（９）式の近似が成り立つ場合には、上記の（８）式は、下記の（１０）式で表すことができる。
【００５８】
∂ｎ_e ／∂Ｗ・ΔＷ≒Δｎ・ΔＷ／Ｗ ・・・（９）
Δλ＝Δｎ／ｎ_e ・ΔＷ／Ｗ＝λ₀ Δ・ΔＷ／Ｗ ・・・（１０）
ところで、従来は、光の閉じ込めが強くなるように、屈折率比Δ＝１％程度としていた。その場合、Δλ≒２×１０^-4程度の精度を得るためには、上述した（１０）式から、ΔＷ／Ｗ≒２％の精度が必要であることが分かる。この場合、例えば、弱導波路部分２６の幅がＷ＝６μｍの場合は、０．１μｍ程度の幅の寸法精度が必要となる。
【００５９】
これに対して、弱導波路部分２６においては、光の閉じ込めが弱くても良いので、屈折率比を例えばΔ＝０．１％程度まで小さくすることができる。その場合、Δλ≒２×１０^-4程度の精度を得るためには、上述した（１０）式から、ΔＷ／Ｗ≒２０％の精度が必要であることが分かる。この場合、例えば、導波路の幅Ｗ＝６μｍの場合は、弱導波路部分２６の幅の寸法に要求される精度を、従来の１０倍の１μｍ程度まで緩和することができる。
【００６０】
（第２の実施の形態）
次に、図３を参照して、第２の実施の形態の光波長ルータについて説明する。図３は、第２の実施の形態の光波長ルータの説明に供する構成図である。
【００６１】
先ず、図３を参照して、第２の実施の形態の光波長ルータについて説明する。図３の（Ａ）は、第２の実施の形態の光波長ルータの説明に供する構成図である。また、図３の（Ｂ）は、光波長ルータの入力側スターカプラ付近の拡大図である。
【００６２】
第２の実施の形態の光波長ルータ２００は、ＳｉＯ₂ 基板４０上に、通常は一定の肉厚の板状体の平面導波路を以ってそれぞれ構成され、互いに対向した入力面および出力面をそれぞれ有する入力側スターカプラ４２および出力側スターカプラ４４を具えている。これら入力面および出力面は外向に凸状の面であって、図の紙面内ではそれぞれ一定の曲率半径を持った円弧状をしているが、肉厚方向では面は直線的となっている。
【００６３】
この光波長ルータ２００は、ＳｉＯ₂ 基板４０上に、この入力側スターカプラ４２の入力面４２ａと複数の入力ポート４６とを接続する入力導波路アレイ４８を具えている。また、この光波長ルータ２００は、ＳｉＯ₂ 基板４０上に、入力側スターカプラ４２の出力面４２ｂと出力側スターカプラ４４の入力面４４ａとを接続する接続導波路アレイ５０を具えている。また、この光波長ルータ２００は、ＳｉＯ₂ 基板４０上に、出力側スターカプラ４４の出力面４４ｂと複数の出力ポート５２とを接続する出力導波路アレイ５４とを具えている。
【００６４】
そして、接続導波路アレイ５０を構成する各接続導波路は、それぞれ弱導波型導波路部分（弱導波路部分）５６と非弱導波型導波路部分（非弱導波路部分）５８とを以って構成してある。後述するように、弱導波路部分５６では、非弱導波路部分５８よりも幅広に形成してあるので、図３中、弱導波路部分５６を太い線で示し、非弱導波路部分５８を細い線で示してある。
【００６５】
ここでは、接続導波路の各々において、非弱導波型導波路部分５８は、入力側スターカプラ４２の出力面４２ｂに接続した部分と、出力側スターカプラ４４の入力面４４ａに接続した部分との２箇所に分けて設けてある。そして、各接続導波路において、２箇所の非弱導波路部分５８を弱導波路部分５６で接続してある。
【００６６】
また、各接続導波路の弱導波型導波路部分５６は、それぞれ直線状に設けてあり、かつ、隣り合った弱導波型導波路部分５６どうし間の長さの差を等しくするように、それぞれ弱導波路部分５６の長さを定めてある。そして、これら弱導波路部分５６をその長さの順に並べてある。また、接続導波路の各々の非弱導波型導波路部分５８の長さを等しくしてある。従って、各接続導波路をそれぞれ伝搬する光に与えられる位相差は、直線状の弱導波路部分４６で生じる。
【００６７】
また、この実施の形態の光波長ルータ２００は、多入力×多出力型としても用いることができる。
【００６８】
また、この実施の形態においては、光波長ルータ２００の構成は、図の紙面内でみると、接続導波路アレイ５０の中央部分を縦断する対称軸の線に対して対称となっている。この対称軸の線を図３の（Ａ）に一点鎖線Ｚ−Ｚで示す。対称軸の右側の出力側の部分の構成も、対称軸の左側の入力側の部分の構成と同じであるので、図３の（Ｂ）には、入力側スターカプラ４２の周辺部の拡大図を示して、対称軸の線よりも左側の入力側の部分の構成について代表して説明する。また、図３の（Ｂ）には、図３の（Ａ）で例示した６本の接続導波路のうち、図の上側の３本の接続導波路を図示して、他の接続導波路の図示を省略してある。
【００６９】
入力側スターカプラ４２は、図の紙面内では、対称軸Ｘ−Ｘに関して左右対称の構造となっている。そして、この対称軸Ｘ−Ｘは、入力側スターカプラ４２の入力面４２ａおよび出力面４２ｂとそれぞれ点Ｏ₂ および点Ｏ₁ で交わる。また、入力面４２ａは、点Ｏ₁ を中心とした半径ｒの円弧をなしており、また、出力面４２ｂは、点Ｏ₂ を中心とした半径ｒの円弧を成している。
【００７０】
そして、入力側スターカプラ４２の入力面４２ａには、入力導波路アレイ４８を構成する例えば３本の入力導波路がそれぞれ接続してある。３本のうちの中央の入力導波路は、入力面４２ａ上の点Ｏ₂ に対応する位置に接続してあり、両側の入力導波路は、入力面４２ａ上の、対称軸Ｘ−Ｘを挟んで対称となる位置（点Ｏ₂ から等距離にある。）に、それぞれ接続してある。
【００７１】
また、接続導波路アレイ５０の各接続導波路の非弱導波路部分５８は、それぞれ直線部分５８ａおよび曲線部分（湾曲部分）５８ｂより構成してある。そして、各直線部分５８ａは、当該直線部分５８ａの延長線が入力側スターカプラ４２の入力面上の点Ｏ₂ に集中する配置で設けてある。すなわち、各非弱導波路部分５８の直線部分５８ａは、点Ｏ₂ を中心として放射状に延在するように設けてある。
【００７２】
また、入力側スターカプラ４２の入力面４２ａ上の点Ｏ₂ と出力側スターカプラ４４の出力面４４ｂ上の点Ｏ₃ とを結ぶ直線を直線Ｈ−Ｈとする。そして、各直線部分５８ａと直線Ｈ−Ｈとの成す角度をθ_i とする。また、隣り合った直線部分５８ａの延長線の交差する角度をΔθ_i （＝θ_i+1 −θ_i ）とする。
【００７３】
また、ここでは、各非弱導波路部分５８の直線部分５８ａの長さを、便宜的に点Ｏ₁ から直線部分５８ａの終点５８ａｅまでの長さＬｒ_i で表す。実際の直線部分５８ａの長さは、このＬｒ_i から入力側スターカプラ４２の点Ｏ₂ から出力面４２ｂまでの半径ｒを引いた長さである。また、隣り合った直線部分５８ａどうし間の長さの差をΔＬｒ_i （＝Ｌｒ_i+1 −Ｌｒ_i ）とする。
【００７４】
そして、この直線部分５８ａの終点５８ａｅには、非弱導波路部分５８の曲線部分５８ｂが接続してある。この実施の形態においては、各接続導波路の非弱導波路部分５８の曲線部分５８ｂをいずれも長さが等しい円弧形状として設けてある。そして、各接続導波路毎に、非弱導波路部分５８の円弧の曲率半径Ｒ_i を異なる値に設定してある。ここで、ｉを接続導波路アレイ５０を構成する接続導波路の図面の下側からの順番を表す番号とする（図３の（Ａ）では接続導波路アレイを６本の接続導波路で構成してあるので、ｉ＝１、２、３、４、５、６となる。）。
【００７５】
ここでは、各接続導波路の非弱導波路部分５８の長さＬ_i （図３ではＬ_i を図示せず）を、直線部分５８ａの長さＬｒ_i と曲線部分５８ｂとの和で表す。そして、この非弱導波路部分５８の長さＬ_i は、上述したように一定である。従って、各接続導波路どうし間の長さの差は、直線状の弱導波路部分５６の長さの差ΔＬｅのみによって生じる。
【００７６】
ここで、接続導波路アレイ５０を構成する各接続導波路の弱導波路部分５６および非弱導波路部分５８についての上述の種々の条件をそれぞれ満足した光波長ルータを設計する一例について説明する。
【００７７】
先ず、各接続導波路の非弱導波路部分５８を、前述の直線Ｈ−Ｈに投影した投影長をＬｐ_i とすると、点Ｏ₂ からこの直線Ｈ−Ｈと対称軸の線Ｚ−Ｚとの交点Ｍまでの直線Ｈ−Ｈに沿った距離は、Ｌｐ_i ＋Ｌｓ_i で与えられる。
【００７８】
そこで、導波路の長さＬ_i を、このＬｐ_i ＋Ｌｓ_i を基準として表した長さをＬｅ_i とすると、Ｌｅ_i は、下記の（１１）式で表される。
【００７９】

ところで、非弱導波路部分５８の長さＬ_i が一定であるので、各接続導波路どうし間の長さの差ΔＬｅは、下記の（１２）式で与えられる。
【００８０】
ΔＬｅ＝−ΔＬｐ_i ・・・（１２）
したがって、上記の（１２）式と、Ｌ_i ＝一定に基づいて、これらを偏分した後、隣り合った直線部分５８ａどうし間の長さの差ΔＬｒ_i を、隣り合った直線部分５８ａの延長部分が交差する角度Δθ_i の関数として表すと、下記の（１３）式の逐次計算式が得られる。
【００８１】
ΔＬｒ_i ＝［ -ΔLe+ {Lr_i sinθ_i- R_i( cosθ~_i- sin θ~_i/ θ~_i)}］／［cos θ~_i+ sin θ~_i/ θ~_i］ ・・・（１３）
また、上記の（１３）式と同様にして、上記の（１２）式と、Ｌ_i ＝一定に基づいて、これらを偏分した後、各接続導波路の非弱導波路部分５８の隣り合った曲線部分５８ｂどうし間の曲率半径の差ΔＲ_i をΔθ_i の関数として表すと、下記の（１４）式が得られる。
【００８２】
ΔＲ_i ＝［ΔＬｒ_i −Ｒ_i Δθ_i ］／［θ~_i］ ・・・（１４）
但し、θ~_iは、θ_i+1 とθ_i との平均である。
【００８３】
そして、１番目の導波路の非弱導波路部分５８の曲線部分５８ｂの曲率半径Ｒ₁ 、非弱導波路部分５８の直線部分５８ａの便宜的な長さＬｒ₁ および直線部分５８ａが直線Ｈ−Ｈと成す角度θ₁ を決めれば、ｉ＋１番目の導波路の非弱導波路部分５８の曲率半径Ｒ_i+1 は、上記の（１３）式および（１４）式を用いて、下記の（１５）式で順次に与えられる。
【００８４】
Ｒ_i+1 ＝Ｒ_i ＋ΔＲ_i ・・・（１５）
また、ｉ＋１番目の導波路の非弱導波路部分５８の直線部分５８ａの便宜的な長さＬｒ_i+1 は、上記の（１３）式を用いて、下記の（１６）式で順次に与えられる。
【００８５】
Ｌｒ_i+1 ＝Ｌｒ_i ＋ΔＬｅ・・・（１６）
また、ｉ＋１番目の導波路の非弱導波路部分５８の直線部分５８ａが直線Ｈ−Ｈと成す角度θ_i+1 は、上記の（１３）式を用いて、下記の（１７）式で順次に与えられる。
【００８６】
θ_i+1 ＝θ_i ＋Δθ_i ・・・（１７）
このようにして、各非弱導波路部分５８の直線部分５８ａの長さおよび延在方向、および、各非弱導波路部分５８の曲線部分５８ｂの曲率半径および円弧の角度を順次に決定することにより、接続導波路アレイ５０を設計することができる。
【００８７】
（導波路の構造について）
次に、図４を参照して、弱導波路部分５６および非弱導波路部分５８の構造の一例について説明する。図４は、非弱導波路部分５８の終点５８ｂｅ付近の要部切欠斜視図である。
【００８８】
この実施の形態においては、弱導波路部分５６および非弱導波路部分５８のコア層６０をＧｅ（ゲルマニウム）を添加したＳｉＯ₂ で以って構成してある。このコア層６０の屈折率はｎ₁ ＝１．４６である。また、コア層６０の厚さは、６μｍである。
【００８９】
また、このコア層６０は、屈折率ｎ₀ ＝１．４５のＳｉＯ₂ 基板４０上に設けてある。このＳｉＯ₂ 基板４０は、下側クラッド層として働く。また、コア層６０の上側には、屈折率ｎ₀ ＝１．４５のＳｉＯ₂ 層６２を設けてある。このＳｉＯ₂ 層６２は、上側クラッド層として働く。
【００９０】
そして、非弱導波路部分５８では、コア層６０の、光の伝搬方向に垂直な断面形状を、上下２段のリッジ形状としてある。そして、非弱導波路部分５８のコア層６０の下段部分６０ａの断面形状は幅広の長方形であり、上段部分６０ｂの断面形状は幅狭の長方形であって、下段部分６０ａのほぼ中央に上段部分６０ｂが乗った、上下に段差のある構造としてある。そして、この上段部分の両側を空気（屈折率ｎ≒１）として、横方向（ＳｉＯ₂ 基板４０の主表面に沿った、上段部分６０ｂの側壁に直交する方向）の光の閉じ込めを強くしてある。すなわち、屈折率比Δ₁ は、下記の式（１８）で与えられる。
【００９１】

また、非弱導波路部分コア層６０の下段部分の両側には、ＳｉＯ₂ 層６４（屈折率ｎ＝１．４５）を設けてある。
【００９２】
また、弱導波路部分５６では、コア層６０の光の伝搬方向に垂直な断面形状を、横長の長方形としてある。そして、非弱導波路部分のコア層６０の両側にもＳｉＯ₂ 層６４（屈折率ｎ＝１．４５）を設けて、横方向（ＳｉＯ₂ 基板４０の主表面に沿った、コア層６０の側壁に直交する方向）の光の閉じ込めを弱くしてある。すなわち、屈折率比Δ₂ は、下記の式（１９）で与えられる。
【００９３】

また、この実施の形態においては、図４に示すように、導波路を伝搬する光の単一モードを維持するために、非弱導波路部分５８の幅（２μｍ）を弱導波路部分５６の幅（６μｍ）よりも狭くしてある。また、入力側スターカプラ４２と弱導波路部分５６との接続部分には、非弱導波路部分５８の小さなビームスポットサイズを弱導波路部分５６の大きなビームポットサイズに滑らかに変換してこの部分における光の損失の発生を抑制するために、テーパ部６６を設けてある。
【００９４】
また、第２の実施の形態においても、第１の実施の形態と同様に、弱導波路部分５６の幅の寸法の精度を緩和することができる。
【００９５】
上述した各実施の形態では、これらの発明を特定の材料を用い、特定の条件で構成した例についてのみ説明したが、これらの発明は多くの変更および変形を行うことができる。例えば、上述した実施の形態では、非弱導波路部分の湾曲部分を円弧形状としたが、この発明の光波長ルータにおいては、湾曲部分は必ずしも円弧形状でなくとも良い。
【００９６】
また、上述した実施の形態では、一つの接続導波路に弱導波路を１箇所または２箇所に分けて設けた例について説明したが、この発明では、接続導波路を３つ以上に分けて設けても良い。
【００９７】
【発明の効果】
このように、この発明の光波長ルータによれば、接続導波路アレイを構成する各接続導波路をそれぞれ、互いに等しい長さずつ長さの異なる直線状の弱導波型導波路部分（弱導波路部分）と、長さが互いに等しい非弱導波型導波路部分（非弱導波路部分）とを以って構成する。
【００９８】
そして、この発明の光波長ルータによれば、弱導波路部分では、屈折率比が小さいため、屈折率比のゆらぎが小さい。その上、弱導波路部分を直線状としてあるので、互いに異なる接続導波路の弱導波路部分どうし間では、伝搬定数差がない。このため、弱導波路部分に起因する位相誤差の発生を抑制することができる。
【００９９】
また、この発明の光波長ルータによれば、各接続導波路の一部分を弱導波路部分を以って構成してあるので、各接続導波路を非弱導波型導波路部分のみで構成した場合に比べて、非弱導波路部分の長さが短い。このため、屈折率のゆらぎが大きい部分の長さが短い。従って、接続導波路を非弱導波型導波路部分のみで構成した場合に比べて、各接続導波路における位相誤差の抑制を図ることができる。
【０１００】
また、この発明の光波長ルータによれば、非弱導波路部分の長さを互いに等しくすることにより、非弱導波路部分どうし間の長さのばらつきを抑制する。その結果、その非弱導波路部分どうしに起因する位相誤差を抑制することができる。
【０１０１】
したがって、この発明の光波長ルータによれば、弱導波路部分および非弱導波路部分それぞれにおいて位相誤差を抑制するので、位相誤差に起因するクロストーク特性の劣化の抑制を図ることができる。
【０１０２】
また、この発明の光波長ルータにおいて、非弱導波路部分を円弧状とすれば、非弱導波路部分を容易に設計することができる。
【０１０３】
また、この発明の導波路は、その一部分を弱導波型導波路部分を以って構成してある。弱導波型導波路部分においては、非弱導波型導波路部分に比べて屈折率比のゆらぎが小さい。また、弱導波型導波路部分においては、導波路の寸法の精度を緩和することができる。また、この発明の導波路は、この発明の光波長ルータの導波路アレイを構成する接続導波路に用いて好適である。
【図面の簡単な説明】
【図１】（Ａ）は、第１の実施の形態の光波長ルータの説明に供する構成図であり、（Ｂ）は、光波長ルータの入力側スターカプラ付近の拡大図である。
【図２】（Ａ）は、導波路アレイを構成する導波路の導波層（コア）の平面パターンであり、（Ｂ）は、弱導波路部分の終点付近の要部切欠斜視図である。
【図３】（Ａ）は、第２の実施の形態の光波長ルータの説明に供する構成図であり、（Ｂ）は、光波長ルータの入力側スターカプラ付近の拡大図である。
【図４】弱導波路部分の終点付近の要部切欠斜視図である。
【符号の説明】
１００、２００：光波長ルータ
１０、４０：ＳｉＯ₂ 基板
１２、４２：入力側スターカプラ
１２ａ、１４ａ、４２ａ、４４ａ：入力面
１２ｂ、１４ｂ、４２ｂ、４４ｂ：出力面
１４、４４：出力側スターカプラ
１６、４６：入力ポート
１８、４８：入力導波路アレイ
２０、５０：接続導波路アレイ
２２、５２：出力ポート
２４、５４：出力導波路アレイ
２６、５６：弱導波型導波路部分（弱導波路部分）
２６ｅ：終点
２８、５８：非弱導波型導波路部分（非弱導波路部分）
５８ａ：直線部分
５８ｂ：曲線部分
５８ａｅ、５８ｂｅ：終点
３０、６０：コア層
６０ａ：下段部分
６０ｂ：上段部分
３２、６２：ＳｉＯ₂ 層（上側クラッド層）
３４、６４：ＳｉＯ₂ 層
３６、６６：テーパ部
３８：テーパ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wavelength router suitable for use in setting an optical wavelength multiplexed signal path for each wavelength.
[0002]
[Prior art]
An example of a conventional optical wavelength router is disclosed in the document: “Micro Optics Conference (MOC) '95, Proceedings, pp. 140-143, October 1995”. According to the optical wavelength router disclosed in this document, two star couplers are connected by a waveguide array in which a plurality of waveguides having curved portions with different curvatures are arranged side by side. The lengths of these waveguides are set so that the difference in length between adjacent waveguides is equal, and the waveguides are arranged in the order of their lengths. is there. As a result, the light propagating through these adjacent waveguides is given an equal phase difference between the light beams due to the difference in length between the waveguides, and enters the output star coupler. The lights incident on the output side star coupler interfere with each other. These lights concentrate on the output surface of the output side star coupler and interfere with each other on this output surface. The position where the light is strengthened by the interference on the output surface of the output side star coupler differs depending on the wavelength. Therefore, this optical wavelength router takes out light of different wavelengths for each output waveguide from a plurality of output waveguides connected to different positions on this output surface, and sets the light path for each wavelength. can do.
[0003]
[Problems to be solved by the invention]
By the way, in order to reduce the size of the optical wavelength router disclosed in the above document, it is desirable to further reduce the area occupied by the waveguide array. As one method for that purpose, it is conceivable to reduce the area occupied by the waveguide array by bending each waveguide constituting the waveguide array with a large curvature.
[0004]
However, the propagation constant of the waveguide varies depending on the curvature of the waveguide. As the curvature of the waveguide increases, the propagation constant of the waveguide also increases. For this reason, when the curvature of each waveguide of the waveguide array is increased, the difference in propagation constant (propagation constant difference) between the curved portions of each waveguide increases. When the difference in propagation constant between the curved portions of each waveguide increases, the phase difference between the lights propagating through different waveguides deviates from the design value, resulting in a phase error. The reason is that, in general, the phase error is the product of the propagation constant difference and the deviation (length variation) from the design value of the length difference between the waveguide portions where the propagation constant difference occurs. This is because it is proportional to
[0005]
In addition, in order to form a waveguide as a curved waveguide having a large curvature, it is necessary to strengthen light confinement in the waveguide and minimize light leakage. In order to strengthen the light confinement in the waveguide, it is necessary to increase the refractive index ratio (also referred to as “relative refractive index difference”) Δ between the waveguide layer and the cladding layer constituting the waveguide.
[0006]
However, when the refractive index ratio Δ is increased, the fluctuation of the refractive index ratio Δ also increases. When the fluctuation of the refractive index ratio Δ increases, the phase error between the lights propagating through different waveguides increases. The reason is that the phase error is generally proportional to the product of the magnitude of the fluctuation of the refractive index ratio Δ and the length of the waveguide portion in which the fluctuation of the refractive index ratio Δ occurs.
[0007]
When the phase error between the light beams propagating through the waveguides constituting the waveguide array increases, the peak of the light intensity distribution for each wavelength on the output surface of the star coupler on the output side decreases, and on the output surface. The light intensity distribution becomes gentle as a whole.
[0008]
Originally, there is a one-to-one relationship between the wavelength and the peak position of the light intensity at which the light of that wavelength should be concentrated, but it is actually concentrated at the position where light of a specific wavelength should be concentrated by design. The wavelength of the light to be shifted may deviate from the selected wavelength at the time of design due to the phase error described above. That is, a shift of the selection wavelength occurs. As a result, the crosstalk of the selected wavelength output from the optical wavelength router increases. That is, the crosstalk characteristic (wavelength characteristic) of the optical wavelength router deteriorates.
[0009]
For this reason, it has been desired to realize an optical wavelength router capable of suppressing the deterioration of the crosstalk characteristic due to the phase error.
[0010]
[Means for Solving the Problems]
As a result of various examinations and experiments, the inventor according to the present invention suppresses the occurrence of phase error if a part of each waveguide constituting the waveguide array is formed into a linear weak waveguide type waveguide. It was discovered that it was possible to arrive at this invention.
[0011]
Here, the weak waveguide type waveguide means a waveguide with weak optical confinement. Specifically, it means a waveguide in which the power of light propagating through the waveguide is 50% or less in the waveguide layer (core layer) surrounded by the cladding layer. In addition, the weak waveguide type waveguide corresponds to an optical fiber having a weak waveguide structure in terms of light confinement strength.
[0012]
Therefore, according to the optical wavelength router of the present invention, each is configured with a planar waveguide (also referred to as “slab optical waveguide” or “planar optical waveguide”) having input and output surfaces facing each other. Input side star coupler and output side star coupler,
An input waveguide array connecting the input surface of the input side star coupler and a plurality of input ports;
A connection waveguide array for connecting the output surface of the input side star coupler and the input surface of the output side star coupler;
In an optical wavelength router comprising an output waveguide array connecting an output surface of an output side star coupler and a plurality of output ports,
Connections that make up the connection waveguide array Connection Each of the waveguides is composed of a weak waveguide type waveguide portion and a non-weak waveguide type waveguide portion,
Each of the weak waveguide type waveguide portions of the connecting waveguide is provided in a straight line, and the difference in length between adjacent weak waveguide type waveguide portions is made equal to each other. In order of length, and
The lengths of the non-weakly guided waveguide portions of the connecting waveguide are equal to each other
It is characterized by that.
[0013]
As described above, according to the optical wavelength router of the present invention, each of the connection waveguides constituting the connection waveguide array is made of a linear weak waveguide type waveguide portion (hereinafter, referred to as “longitudinal”) having a length equal to each other. And a non-weak waveguide type waveguide portion (hereinafter also referred to as “non-weak waveguide portion”) having the same length.
[0014]
According to the optical wavelength router of the present invention, since the refractive index ratio is small in this weak waveguide portion, the fluctuation of the refractive index ratio is small. Moreover, there is no difference in propagation constant between the weak waveguide portions of the connection waveguides that are different from each other because the weak waveguide portions are respectively linear. For this reason, generation | occurrence | production of the phase error resulting from a weak waveguide part can be suppressed.
[0015]
In addition, according to the optical wavelength router of the present invention, since a part of each connection waveguide is configured with a weak waveguide part, each connection waveguide is configured only with a non-weak waveguide type waveguide. The length of the non-weak waveguide portion is shorter than that of. Therefore, the refractive index fluctuation is big The length of the important part is short. Therefore, compared to the case where the connection waveguide is composed only of non-weak waveguides, the fluctuation of the refractive index ratio in each connection waveguide and the fluctuation thereof. But The phase error given by the product of the length of the generated portion can be suppressed.
[0016]
Further, according to the optical wavelength router of the present invention, the lengths of the non-weak waveguide portions are made equal to each other, so Road Suppresses the variation in length between parts. As a result, non-weak waveguide Road Difference of propagation constant between parts and its non-weak wave guide Road Variation in length between parts of Phase error proportional to the product, ie its non-weak waveguide Road A phase error caused by the portions can be suppressed.
[0017]
Therefore, according to the optical wavelength router of the present invention, the phase error is suppressed in each of the weak waveguide portion and the non-weak waveguide portion. Concerning It is possible to suppress the deterioration of the crosstalk characteristics.
[0018]
In addition, when each connection waveguide is divided into two or more locations and the non-weak waveguide portion is provided, the total length of the non-weak waveguide portions may be equal between the connection waveguides.
[0019]
In the optical wavelength router of the present invention, it is preferable that the weak waveguide type waveguide portion has two portions, a portion connected to the output surface of the input side star coupler and a portion connected to the input surface of the output side star coupler. It is good to have it divided into.
[0020]
In the optical wavelength router according to the present invention, preferably, the non-weak waveguide type waveguide portion includes two portions, ie, a portion connected to the output surface of the input side star coupler and a portion connected to the input surface of the output side star coupler. It is good to have it divided into places.
[0021]
In the optical wavelength router of the present invention, preferably, the non-weak waveguide type waveguide portion is provided in an arc shape. If the non-weak waveguide portion is arcuate, non-weak waveguide portions that include curves and are equal in length can be easily designed as will be described in the following embodiments.
[0022]
Moreover, according to the waveguide of the present invention,
It is composed of a weak waveguide type waveguide part and a non-weak waveguide part,
One end of the weak waveguide type waveguide portion is connected to one end of the non-weak waveguide type waveguide portion
It is characterized by that.
[0023]
A part of the waveguide of the present invention is constituted by a weak waveguide type waveguide. In the weak waveguide type waveguide portion, the fluctuation of the refractive index ratio is smaller than that in the non-weak waveguide type waveguide portion. Further, in the weak waveguide type waveguide portion, the accuracy of the waveguide dimension can be relaxed, as will be described in the embodiments described later. The waveguide of the present invention is suitable for use as a connection waveguide constituting the waveguide array of the optical wavelength router of the present invention.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the optical wavelength router according to the present invention will be described with reference to the drawings. It should be noted that the drawings to be referred to merely schematically show the sizes, shapes, and arrangement relationships of the constituent components to the extent that the present invention can be understood. Therefore, the present invention is not limited to the illustrated example.
[0025]
(First embodiment)
First, a configuration example of the optical wavelength router according to the first embodiment will be described with reference to FIG. FIG. 1A is a configuration diagram for explaining the optical wavelength router according to the first embodiment. FIG. 1B is an enlarged view of the vicinity of the input side star coupler of the optical wavelength router.
[0026]
The optical wavelength router 100 of the first embodiment is made of SiO. ₂ On the substrate 10, an input side star coupler 12 and an output side star coupler 14 each having a planar waveguide which is usually a plate having a constant thickness are provided. These input-side star coupler 12 and output-side star coupler 14 have an input surface and an output surface that face each other. These input surface and output surface are outwardly convex surfaces, and each has an arc shape with a constant radius of curvature in the drawing, but the surfaces are straight in the thickness direction.
[0027]
This optical wavelength router 100 is made of SiO. ₂ An input waveguide array 18 for connecting the input surface 12 a of the input side star coupler 12 and a plurality of input ports 16 is provided on the substrate 10. Further, this optical wavelength router 100 is made of SiO. ₂ On the substrate 10, a connection waveguide array 20 is provided for connecting the output surface 12 b of the input side star coupler 12 and the input surface 14 a of the output side star coupler 14. Further, this optical wavelength router 100 is made of SiO. ₂ An output waveguide array 24 that connects the output surface 14 b of the output-side star coupler 14 and the plurality of output ports 22 is provided on the substrate 10.
[0028]
Each of the connection waveguides constituting the connection waveguide array 20 includes a weak waveguide type waveguide portion (weak waveguide portion) 26 and a non-weak waveguide type waveguide portion (non-weak waveguide portion) 28. Thus, it is configured. As will be described later, since the weak waveguide portion 26 is formed wider than the non-weak waveguide portion 28, the weak waveguide portion 26 is indicated by a thick line in FIG. It is shown with a thin line.
[0029]
Here, in each of the connection waveguides, the weak waveguide type waveguide portion 26 includes a portion connected to the output surface 12 b of the input side star coupler 12 and a portion connected to the input surface 14 a of the output side star coupler 14. It is divided into two places.
[0030]
Each weak waveguide type waveguide portion 26 of the connection waveguide is linearly provided, and the difference in length between the adjacent weak waveguide type waveguide portions 26 is equal to each other. Thus, the length of each weak waveguide portion 26 is determined. These weak waveguide portions 26 are arranged in the order of their lengths. Further, the lengths of the non-weak waveguide type waveguide portions 28 of the connection waveguides are made equal to each other. Therefore, the phase difference given to the light propagating through each connection waveguide is generated in the linear weak waveguide portion 26.
[0031]
The optical wavelength router 100 of this embodiment can also be used as a multi-input × multi-output type.
[0032]
Further, in this embodiment, the configuration of the optical wavelength router 100 is symmetric with respect to the line of the symmetry axis that cuts the central portion of the connection waveguide array 20 when viewed in the drawing. The line of the symmetry axis is shown by a one-dot chain line YY in FIG. Since the configuration of the output side portion on the right side of the symmetry axis is the same as that of the input side portion on the left side of the symmetry axis, FIG. 1B is an enlarged view of the peripheral portion of the input side star coupler 12. The configuration of the portion on the input side on the left side of the line of the symmetry axis will be representatively described. FIG. 1B shows only the upper three connection waveguides of the six connection waveguides exemplified in FIG. 1A, and shows other connection waveguides. The illustration is omitted.
[0033]
Further, the input side star coupler 12 has a left-right symmetrical structure with respect to the symmetry axis XX in the drawing sheet. The axis of symmetry XX is respectively connected to the input surface 12a and the output surface 12b of the input side star coupler 12 with a point O. ₂ And point O ₁ Intersect. Further, the input surface 12a has a point O ₁ And the output surface 12b is a point O. ₂ Is a circular arc with a radius r centered at.
[0034]
For example, three input waveguides constituting the input waveguide array 18 are connected to the input surface 12 a of the input side star coupler 12. The central input waveguide of the three is a point O on the input surface 12a. ₂ The input waveguides on both sides are symmetrical with respect to the symmetry axis XX (point O) on the input surface 12a. ₂ Is equidistant from. ).
[0035]
Further, the linear weak waveguide portion 26 of each connection waveguide of the connection waveguide array 20 has an extension line of the point O on the input surface of the input side star coupler 12. ₂ It is provided in an arrangement that concentrates on. That is, each linear weak waveguide portion 26 has a point O. ₂ Is provided so as to extend radially from the center.
[0036]
In addition, here, the length of each weak waveguide portion 26 is set to a point O for convenience. ₂ To the end point 26e of the weak waveguide portion 26 _i Represented by The actual length of the weak waveguide portion 26 is the Lr _i To point O of the input side star coupler 12 ₂ Is a length obtained by subtracting the radius r from the output surface 12b. Each weak waveguide portion 26 has a length Lr by ΔLe from each other. _i Has been changed. This ΔLe is made constant.
[0037]
Further, the weak waveguide portion 26 is connected to the non-weak waveguide portion 28 at the end point 26e. In this embodiment, each of the non-weak waveguide portions 28 of each connection waveguide is provided in an arc shape having the same length. For each connecting waveguide, the radius of curvature R of the arc of the non-weak waveguide portion 28 _i Is set to a different value. Here, i is a number indicating the order of the connection waveguides constituting the connection waveguide array 20 from the lower side of the drawing (in FIG. 1A, the connection waveguide array 20 is defined as six connection waveguides). I = 1, 2, 3, 4, 5, 6).
[0038]
Here, an example of a specific design method of the arrangement of the connection waveguide array 20 will be described.
[0039]
In designing an optical wavelength router that satisfies the above-described various conditions for the weak waveguide portion 26 and the non-weak waveguide portion 28 of each connection waveguide constituting the connection waveguide array 20, as an example, the following ( 1) There is a method for satisfying the equation. ΔR _i Represents the difference in the radius of curvature between the non-weak waveguide portions 28 of adjacent connecting waveguides.
[0040]
ΔR _i = [-L _e + {(L _ri + ΔL _e / 2) sin (θ _i + Δθ _i / 2) + R _i (1-cos (sinθ _i + Δθ _i / 2))} Δθ _i ] / [-(Θ _i + Δθ _i / 2)] sin (θ _i + Δθ _i / 2) + (cos (sinθ _i + Δθ _i / 2) -1) Δθ _i / 2] (1)
However, in the above equation (1), θ _i Is a point O on the input surface 12 a of the input side star coupler 12. ₂ And a point O on the output surface 14b of the output side star coupler 14 _Three Is an angle at which the straight line H-H intersects the extended portion of the weak waveguide 26. Point O _Three Is the point O ₂ And the line Y-Y of the above-described symmetry axis are in a line-symmetric position. Δθ _i Is the angle between adjacent weak waveguide portions 26.
[0041]
In the above equation (1), the length L of each connection waveguide _i (= Lr _i + Lc _i ) Is a point of intersection M and a point O between the line YY of the axis of symmetry and the line HH for convenience. ₂ And the length of the distance Lp and the point O ₂ And the length along the waveguide between the line of symmetry YY, ie L _i -Lp is given.
[0042]
In the above equation (1), in order to facilitate the design, the radius of curvature R of each non-weak waveguide portion 28 is set. _i The angle θ at which both ends of the non-weak waveguide portion 28 are looked up from the position corresponding to the center point _i And an angle θ formed between each weak waveguide portion 26 and the straight line HH described above. _i Are equal to each other. Therefore, the length Lc of each non-weak waveguide portion 28 in the input half is Lc regardless of i. _i = R _i θ _i = Constant.
[0043]
And the radius of curvature of the non-weak waveguide portion 28 of the first waveguide, the convenient length R of the weak waveguide portion. ₁ And the angle θ formed by the waveguide ₁ Is determined, the radius of curvature R of the non-weak waveguide portion 28 of the (i + 1) th waveguide is determined. _{i + 1} Are sequentially given by the following equation (2) using the above equation (1).
[0044]
R _{i + 1} = R _i + ΔR _i ... (2)
Further, a convenient length Lr of the weak waveguide portion 26 of the i + 1-th waveguide. _{i + 1} Are sequentially given by the following equation (3) using the above equation (1).
[0045]
Lr _{i + 1} = Lr _i + ΔLe (3)
In addition, the angle θ of the i + 1-th waveguide _{i + 1} Are sequentially given by the following equation (4) using the above equation (1).
[0046]
θ _{i + 1} = Θ _i + Δθ _i ... (4)
In this way, the connection waveguide array 20 is designed by sequentially determining the length and extending direction of each weak waveguide portion 26 and the curvature radius and arc angle of each non-weak waveguide portion 28. can do.
[0047]
In this embodiment, the non-weak waveguide portion 28 is only a curved portion (curved portion). However, in the present invention, the non-weak waveguide portion 28 may be provided with a straight portion. Even when the non-weak waveguide portion 28 is provided with a straight line portion, the total lengths of the non-weak waveguide portions 28 of the connection waveguides are made equal to each other.
[0048]
(About waveguide structure)
Next, an example of the structure of the weak waveguide portion 26 and the non-weak waveguide portion 28 will be described with reference to FIG. FIG. 2A shows a planar pattern of the waveguide layer (core layer) of the connection waveguide constituting the connection waveguide array 20. 2B is a perspective cutaway view of the main part near the end point 26e of the weak waveguide portion 26. FIG.
[0049]
In this embodiment, the core layer 30 of the weak waveguide portion 26 and the non-weak waveguide portion 28 is made of SiO added with Ge (germanium). ₂ It is configured by. The refractive index of the core layer 30 is n ₁ = 1.46. The core layer 30 has a uniform thickness of 6 μm.
[0050]
The core layer 30 has a refractive index n ₀ = 1.45 SiO ₂ It is provided on the substrate 10. This SiO ₂ The substrate 10 serves as a lower cladding. Further, on the upper side of the core layer 30, a refractive index n ₀ = 1.45 SiO ₂ Layer 32 is provided. This SiO ₂ Layer 32 serves as the upper cladding.
[0051]
Further, in the non-weak waveguide portion 28, both sides of the core layer 30 are air layers (refractive index n≈1), and the lateral direction (SiO 2 ₂ Light confinement in the direction along the main surface of the substrate 10 is strengthened. That is, the refractive index ratio Δ ₁ Is given by the following equation (5).
[0052]

In the weak waveguide portion 26, SiO 2 is also formed on both sides of the core layer 30. ₂ Layer 34 (refractive index n = 1.45) is provided and the lateral direction (SiO ₂ Light confinement in the direction along the main surface of the substrate 10 is weakened. That is, the refractive index ratio Δ ₂ Is given by the following equation (6).
[0053]

Further, in this embodiment, as shown in FIG. 2A, in order to maintain a single mode of light propagating through the waveguide, the width (2 μm) of the non-weak waveguide portion 28 is reduced. It is narrower than the width (6 μm) of the waveguide portion 26. In addition, a tapered portion 36 is provided at a connection portion between the input side star coupler 12 and the weak waveguide portion 26 in order to suppress generation of light loss at the connection portion. The width of the tapered portion 36 at the connection point with the input side star coupler 12 is 12 μm, and converges to 6 μm, which is the width of the weak waveguide portion 26, over a length of 500 μm. In addition, a tapered portion 38 is also provided at a connection portion (end point 26e) between the weak waveguide portion 26 and the non-weak waveguide portion 28 in order to suppress generation of light at the connection portion.
[0054]
(About dimensional accuracy of weak waveguide part)
Next, the dimensional accuracy of the weak waveguide portion 26 will be examined. In general, a change in transmission refractive index δn of a waveguide when the width W of the waveguide changes by ΔW _e Is given by the following equation (7).
[0055]
δn _e = ∂n _e / ∂W · ΔW (7)
With respect to the change in the transmission refractive index, the selective wavelength characteristic of the light propagating through the waveguide is shifted by Δλ shown in the following equation (8).
[0056]
Δλ = λ ₀ ・ Δn _e / N _e ... (8)
Where λ ₀ Represents the center wavelength of wavelength-multiplexed light.
[0057]
In addition, when approximation of the following equation (9) is established for the above equation (7), the above equation (8) can be expressed by the following equation (10).
[0058]
N _e / ∂W · ΔW ≒ Δn · ΔW / W (9)
Δλ = Δn / n _e ・ ΔW / W = λ ₀ Δ ・ ΔW / W (10)
Conventionally, the refractive index ratio Δ is about 1% so that light confinement becomes strong. In that case, Δλ≈2 × 10 ^-Four In order to obtain a certain degree of accuracy, it can be seen from the above-described equation (10) that an accuracy of ΔW / W≈2% is necessary. In this case, for example, when the width of the weak waveguide portion 26 is W = 6 μm, a dimensional accuracy of a width of about 0.1 μm is required.
[0059]
On the other hand, in the weak waveguide portion 26, since the light confinement may be weak, the refractive index ratio can be reduced to, for example, about Δ = 0.1%. In that case, Δλ≈2 × 10 ^-Four In order to obtain a certain degree of accuracy, it can be seen from the above-described equation (10) that an accuracy of ΔW / W≈20% is necessary. In this case, for example, when the width W of the waveguide is 6 μm, the accuracy required for the width dimension of the weak waveguide portion 26 can be relaxed to about 1 μm, which is ten times the conventional size.
[0060]
(Second Embodiment)
Next, an optical wavelength router according to the second embodiment will be described with reference to FIG. FIG. 3 is a configuration diagram for explaining the optical wavelength router according to the second embodiment.
[0061]
First, an optical wavelength router according to the second embodiment will be described with reference to FIG. FIG. 3A is a configuration diagram for explaining an optical wavelength router according to the second embodiment. FIG. 3B is an enlarged view of the vicinity of the input side star coupler of the optical wavelength router.
[0062]
The optical wavelength router 200 of the second embodiment is made of SiO. ₂ An input-side star coupler 42 and an output-side star coupler 44 each having an input surface and an output surface that are opposed to each other are formed on a substrate 40, each of which is configured by a planar waveguide of a plate-like body having a constant thickness. It has. These input surface and output surface are outwardly convex surfaces, and each has an arc shape with a certain radius of curvature in the drawing, but the surface is linear in the thickness direction. .
[0063]
This optical wavelength router 200 is composed of SiO ₂ An input waveguide array 48 for connecting the input surface 42 a of the input side star coupler 42 and a plurality of input ports 46 is provided on the substrate 40. Further, the optical wavelength router 200 is made of SiO. ₂ On the substrate 40, there is provided a connection waveguide array 50 for connecting the output surface 42b of the input side star coupler 42 and the input surface 44a of the output side star coupler 44. Further, the optical wavelength router 200 is made of SiO. ₂ An output waveguide array 54 that connects the output surface 44 b of the output side star coupler 44 and a plurality of output ports 52 is provided on the substrate 40.
[0064]
Each of the connection waveguides constituting the connection waveguide array 50 includes a weak waveguide type waveguide portion (weak waveguide portion) 56 and a non-weak waveguide type waveguide portion (non-weak waveguide portion) 58. Thus, it is configured. As will be described later, since the weak waveguide portion 56 is formed wider than the non-weak waveguide portion 58, the weak waveguide portion 56 is indicated by a thick line in FIG. It is shown with a thin line.
[0065]
Here, in each of the connection waveguides, the non-weak waveguide type waveguide portion 58 includes a portion connected to the output surface 42b of the input side star coupler 42 and a portion connected to the input surface 44a of the output side star coupler 44. It is divided into two places. In each connection waveguide, two non-weak waveguide portions 58 are connected by a weak waveguide portion 56.
[0066]
Further, the weak waveguide type waveguide portions 56 of the connection waveguides are respectively provided in a straight line, and the length difference between adjacent weak waveguide type waveguide portions 56 is made equal. , The length of the weak waveguide portion 56 is determined. These weak waveguide portions 56 are arranged in the order of their lengths. Further, the lengths of the non-weak waveguide type waveguide portions 58 of the connection waveguides are made equal. Therefore, the phase difference given to the light propagating through each connection waveguide is generated in the linear weak waveguide portion 46.
[0067]
The optical wavelength router 200 of this embodiment can also be used as a multi-input × multi-output type.
[0068]
In this embodiment, the configuration of the optical wavelength router 200 is symmetric with respect to the line of the symmetry axis that cuts the central portion of the connection waveguide array 50 when viewed in the drawing. The line of this symmetry axis is shown by a one-dot chain line ZZ in FIG. Since the configuration of the output side portion on the right side of the symmetry axis is the same as that of the input side portion on the left side of the symmetry axis, FIG. 3B is an enlarged view of the peripheral portion of the input side star coupler 42. The configuration of the part on the input side on the left side of the line of the symmetry axis will be described as a representative. FIG. 3B shows the three connection waveguides on the upper side of the six connection waveguides exemplified in FIG. 3A, and shows other connection waveguides. The illustration is omitted.
[0069]
The input side star coupler 42 has a symmetrical structure with respect to the symmetry axis XX in the drawing sheet. The axis of symmetry X-X is respectively connected to the input surface 42a and the output surface 42b of the input side star coupler 42 with point O ₂ And point O ₁ Intersect. Further, the input surface 42a has a point O. ₁ And an output surface 42b is formed with a point O. ₂ Is a circular arc with a radius r centered at.
[0070]
For example, three input waveguides constituting the input waveguide array 48 are connected to the input surface 42 a of the input side star coupler 42. Of the three, the central input waveguide is a point O on the input surface 42a. ₂ The input waveguides on both sides are symmetric with respect to the axis of symmetry XX (point O) on the input surface 42a. ₂ Is equidistant from. ) Are connected to each other.
[0071]
The non-weak waveguide portion 58 of each connection waveguide of the connection waveguide array 50 is composed of a straight portion 58a and a curved portion (curved portion) 58b, respectively. Each straight line portion 58a has an extension line of the straight line portion 58a at a point O on the input surface of the input side star coupler 42. ₂ It is provided in an arrangement that concentrates on. That is, the straight line portion 58a of each non-weak waveguide portion 58 has a point O. ₂ Is provided so as to extend radially from the center.
[0072]
The point O on the input surface 42a of the input side star coupler 42 is also shown. ₂ And a point O on the output surface 44b of the output side star coupler 44. _Three A straight line connecting the two lines is defined as a straight line HH. The angle formed between each straight line portion 58a and the straight line HH is θ _i And Further, the angle at which the extension lines of adjacent straight portions 58a intersect is expressed as Δθ _i (= Θ _{i + 1} −θ _i ).
[0073]
In addition, here, the length of the straight portion 58a of each non-weak waveguide portion 58 is represented by a point O for convenience. ₁ Lr from the end point 58ae of the straight line portion 58a to the end point 58ae _i Represented by The actual length of the straight portion 58a is the Lr _i To point O of the input side star coupler 42 ₂ Is a length obtained by subtracting the radius r from the output surface 42b. Further, the difference in length between the adjacent straight portions 58a is expressed as ΔLr. _i (= Lr _{i + 1} -Lr _i ).
[0074]
The curved portion 58b of the non-weak waveguide portion 58 is connected to the end point 58ae of the straight portion 58a. In this embodiment, the curved portions 58b of the non-weak waveguide portions 58 of the connection waveguides are all provided in an arc shape having the same length. For each connecting waveguide, the radius of curvature R of the arc of the non-weak waveguide portion 58 _i Is set to a different value. Here, i is a number indicating the order of the connection waveguides constituting the connection waveguide array 50 from the lower side of the drawing (in FIG. 3A, the connection waveguide array is composed of six connection waveguides). Therefore, i = 1, 2, 3, 4, 5, 6.)
[0075]
Here, the length L of the non-weak waveguide portion 58 of each connection waveguide _i (L in FIG. 3 _i (Not shown), the length Lr of the straight portion 58a _i And the curve portion 58b. The length L of the non-weak waveguide portion 58 is _i Is constant as described above. Accordingly, the difference in length between the connection waveguides is caused only by the difference ΔLe in the length of the linear weak waveguide portion 56.
[0076]
Here, an example of designing an optical wavelength router that satisfies the above-described various conditions for the weak waveguide portion 56 and the non-weak waveguide portion 58 of each connection waveguide constituting the connection waveguide array 50 will be described.
[0077]
First, the projection length obtained by projecting the non-weak waveguide portion 58 of each connection waveguide onto the straight line HH is expressed as Lp. _i Then point O ₂ The distance along the line HH from the line HH to the intersection M of the line ZZ of the axis of symmetry is Lp _i + Ls _i Given in.
[0078]
Therefore, the length L of the waveguide _i , This Lp _i + Ls _i The length expressed with reference to Le _i Then Le _i Is represented by the following equation (11).
[0079]

By the way, the length L of the non-weak waveguide portion 58 _i Is constant, the length difference ΔLe between the connecting waveguides is given by the following equation (12).
[0080]
ΔLe = −ΔLp _i (12)
Therefore, the above equation (12) and L _i = Based on a constant value, after dividing these, the difference in length ΔLr between the adjacent straight line portions 58a _i At an angle Δθ at which the extended portions of adjacent straight portions 58a intersect. _i When expressed as a function of the following, a sequential calculation formula of the following formula (13) is obtained.
[0081]
ΔLr _i = [-ΔLe + {Lr _i sinθ _i -R _i (cosθ ~ _i -sin θ ~ _i / θ ~ _i )}] / [Cos θ ~ _i + sin θ ~ _i / θ ~ _i ] (13)
Further, in the same manner as the above expression (13), the above expression (12) and L _i = Based on the constant, after these are divided, the difference ΔR in the radius of curvature between the adjacent curved portions 58b of the non-weak waveguide portion 58 of each connecting waveguide _i Δθ _i The following expression (14) is obtained.
[0082]
ΔR _i = [ΔLr _i -R _i Δθ _i ] / [Θ ~ _i ] (14)
However, θ ~ _i Is θ _{i + 1} And θ _i And the average.
[0083]
And the radius of curvature R of the curved portion 58b of the non-weak waveguide portion 58 of the first waveguide ₁ The convenient length Lr of the straight portion 58a of the non-weak waveguide portion 58 ₁ And the angle θ between the straight line portion 58a and the straight line HH. ₁ Is determined, the radius of curvature R of the non-weak waveguide portion 58 of the (i + 1) th waveguide is determined. _{i + 1} Are sequentially given by the following equation (15) using the above equations (13) and (14).
[0084]
R _{i + 1} = R _i + ΔR _i (15)
Further, the convenient length Lr of the straight portion 58a of the non-weak waveguide portion 58 of the i + 1-th waveguide. _{i + 1} Are sequentially given by the following equation (16) using the above equation (13).
[0085]
Lr _{i + 1} = Lr _i + ΔLe (16)
The angle θ formed by the straight line portion 58a of the non-weak waveguide portion 58 of the i + 1th waveguide and the straight line HH. _{i + 1} Are sequentially given by the following equation (17) using the above equation (13).
[0086]
θ _{i + 1} = Θ _i + Δθ _i ... (17)
In this way, the length and extending direction of the straight portion 58a of each non-weak waveguide portion 58 and the radius of curvature and the arc angle of the curved portion 58b of each non-weak waveguide portion 58 are sequentially determined. Thus, the connection waveguide array 50 can be designed.
[0087]
(About waveguide structure)
Next, an example of the structure of the weak waveguide portion 56 and the non-weak waveguide portion 58 will be described with reference to FIG. FIG. 4 is a cutaway perspective view of a main part near the end point 58be of the non-weak waveguide portion 58. FIG.
[0088]
In this embodiment, the core layer 60 of the weak waveguide portion 56 and the non-weak waveguide portion 58 is made of SiO added with Ge (germanium). ₂ It is configured by. The refractive index of the core layer 60 is n ₁ = 1.46. The core layer 60 has a thickness of 6 μm.
[0089]
The core layer 60 has a refractive index n. ₀ = 1.45 SiO ₂ It is provided on the substrate 40. This SiO ₂ The substrate 40 serves as a lower cladding layer. Further, on the upper side of the core layer 60, the refractive index n ₀ = 1.45 SiO ₂ Layer 62 is provided. This SiO ₂ Layer 62 serves as the upper cladding layer.
[0090]
In the non-weak waveguide portion 58, the cross-sectional shape of the core layer 60 perpendicular to the light propagation direction is a two-step ridge shape. The cross-sectional shape of the lower step portion 60a of the core layer 60 of the non-weak waveguide portion 58 is a wide rectangle, the cross-sectional shape of the upper step portion 60b is a narrow rectangle, and the upper step portion is substantially at the center of the lower step portion 60a. It is a structure with a step difference on the top and bottom on which 60b rides. Then, both sides of this upper stage portion are set to air (refractive index n≈1), and the lateral direction (SiO 2 ₂ Light confinement in the direction perpendicular to the side wall of the upper portion 60b along the main surface of the substrate 40 is strengthened. That is, the refractive index ratio Δ ₁ Is given by the following equation (18).
[0091]

In addition, on both sides of the lower portion of the non-weak waveguide partial core layer 60, SiO ₂ Layer 64 (refractive index n = 1.45) is provided.
[0092]
In the weak waveguide portion 56, the cross-sectional shape perpendicular to the light propagation direction of the core layer 60 is a horizontally long rectangle. And it is SiO on both sides of the core layer 60 in the non-weak waveguide portion. ₂ Layer 64 (refractive index n = 1.45) is provided and the lateral direction (SiO ₂ The light confinement in the direction perpendicular to the side wall of the core layer 60 along the main surface of the substrate 40 is weakened. That is, the refractive index ratio Δ ₂ Is given by the following equation (19).
[0093]

Further, in this embodiment, as shown in FIG. 4, in order to maintain a single mode of light propagating through the waveguide, the width (2 μm) of the non-weak waveguide portion 58 is set to that of the weak waveguide portion 56. It is narrower than the width (6 μm). Further, at the connection portion between the input side star coupler 42 and the weak waveguide portion 56, the small beam spot size of the non-weak waveguide portion 58 is smoothly converted into the large beam pot size of the weak waveguide portion 56, and this portion is obtained. In order to suppress the occurrence of light loss, a tapered portion 66 is provided.
[0094]
Also in the second embodiment, the accuracy of the width dimension of the weak waveguide portion 56 can be relaxed as in the first embodiment.
[0095]
In each of the above-described embodiments, only examples in which these inventions are configured using specific materials and under specific conditions have been described. However, these inventions can be modified and modified in many ways. For example, in the above-described embodiment, the curved portion of the non-weak waveguide portion has an arc shape. However, in the optical wavelength router of the present invention, the curved portion does not necessarily have an arc shape.
[0096]
In the above-described embodiment, the example in which the weak waveguide is provided in one or two locations in one connection waveguide has been described. However, in the present invention, the connection waveguide is provided in three or more locations. May be.
[0097]
【The invention's effect】
As described above, according to the optical wavelength router of the present invention, each of the connection waveguides constituting the connection waveguide array is formed of a linear weak waveguide type waveguide portion (weakly conductive) having different lengths by the same length. (Waveguide portion) and a non-weak waveguide type waveguide portion (non-weak waveguide portion) having the same length.
[0098]
According to the optical wavelength router of the present invention, since the refractive index ratio is small in the weak waveguide portion, the fluctuation of the refractive index ratio is small. In addition, since the weak waveguide portion is linear, there is no difference in propagation constant between the weak waveguide portions of different connection waveguides. For this reason, generation | occurrence | production of the phase error resulting from a weak waveguide part can be suppressed.
[0099]
In addition, according to the optical wavelength router of the present invention, a part of each connection waveguide is configured with a weak waveguide part, so each connection waveguide is configured only with a non-weak waveguide type waveguide part. Compared to the case, the length of the non-weak waveguide portion is short. For this reason, the length of the portion where the refractive index fluctuation is large is short. Therefore, it is possible to suppress the phase error in each connection waveguide as compared with the case where the connection waveguide is configured by only the non-weak waveguide type waveguide portion.
[0100]
Further, according to the optical wavelength router of the present invention, the length of the non-weak waveguide portions is made equal to each other, thereby suppressing variations in length between the non-weak waveguide portions. As a result, the phase error caused by the non-weak waveguide portions can be suppressed.
[0101]
Therefore, according to the optical wavelength router of the present invention, since the phase error is suppressed in each of the weak waveguide portion and the non-weak waveguide portion, it is possible to suppress the deterioration of the crosstalk characteristics due to the phase error.
[0102]
In the optical wavelength router of the present invention, if the non-weak waveguide portion is formed in an arc shape, the non-weak waveguide portion can be easily designed.
[0103]
In addition, the waveguide of the present invention is partially configured with a weak waveguide type waveguide portion. In the weak waveguide type waveguide portion, the fluctuation of the refractive index ratio is smaller than that in the non-weak waveguide type waveguide portion. Further, in the weak waveguide type waveguide portion, the accuracy of the dimensions of the waveguide can be relaxed. The waveguide of the present invention is suitable for use as a connection waveguide constituting the waveguide array of the optical wavelength router of the present invention.
[Brief description of the drawings]
FIG. 1A is a configuration diagram for explaining an optical wavelength router according to a first embodiment, and FIG. 1B is an enlarged view of the vicinity of an input side star coupler of an optical wavelength router.
FIG. 2A is a plan pattern of a waveguide layer (core) of a waveguide constituting a waveguide array, and FIG. 2B is a cutaway perspective view of a main part near an end point of a weak waveguide portion. .
FIG. 3A is a configuration diagram for explaining an optical wavelength router according to a second embodiment, and FIG. 3B is an enlarged view of the vicinity of an input side star coupler of the optical wavelength router;
FIG. 4 is a cutaway perspective view of a main part near an end point of a weak waveguide portion.
[Explanation of symbols]
100, 200: Optical wavelength router
10, 40: SiO ₂ substrate
12, 42: Input side star coupler
12a, 14a, 42a, 44a: input surface
12b, 14b, 42b, 44b: output surface
14, 44: Output side star coupler
16, 46: Input port
18, 48: Input waveguide array
20, 50: Connection waveguide array
22, 52: Output port
24, 54: Output waveguide array
26, 56: Weak waveguide type waveguide portion (weak waveguide portion)
26e: end point
28, 58: Non-weak waveguide type waveguide part (non-weak waveguide part)
58a: Straight line portion
58b: Curve portion
58ae, 58be: end point
30, 60: Core layer
60a: Lower part
60b: Upper part
32, 62: SiO ₂ Layer (upper cladding layer)
34, 64: SiO ₂ layer
36, 66: Tapered portion
38: Tapered portion

Claims (5)

An input-side star coupler and an output-side star coupler each configured with a planar waveguide, each having an input surface and an output surface facing each other;
An input waveguide array connecting the input surface of the input side star coupler and a plurality of input ports;
A connection waveguide array connecting the output surface of the input-side star coupler and the input surface of the output-side star coupler;
In an optical wavelength router comprising an output waveguide array that connects the output surface of the output side star coupler and a plurality of output ports,
Each connection waveguide constituting the connection waveguide array is constituted by a weak waveguide type waveguide portion and a non-weak waveguide type waveguide portion, respectively.
The weak waveguide type waveguide portions of each of the connection waveguides are linearly provided, and the difference in length between adjacent weak waveguide type waveguide portions is made equal. , Ordered by length, and
An optical wavelength router characterized in that the lengths of the non-weakly waveguide-type waveguide portions of the connection waveguides are equal to each other. The optical wavelength router according to claim 1,
The weak waveguide type waveguide portion is provided in two parts, a portion connected to the output surface of the input side star coupler and a portion connected to the input surface of the output side star coupler. Optical wavelength router. The optical wavelength router according to claim 1,
The non-weak waveguide type waveguide portion is provided in two parts, a portion connected to the output surface of the input side star coupler and a portion connected to the input surface of the output side star coupler. An optical wavelength router. In the optical wavelength router in any one of Claims 1-3,
An optical wavelength router, wherein the non-weak waveguide type waveguide portion is provided in an arc shape. The Jakushirubeha waveguide portion and the non-weak waveguide type waveguide section and a waveguide is constructed I hereinafter, is constituted by a plurality lined,
Each of the weak waveguide type waveguide portions of the waveguide is provided in a straight line,
The difference in length between the weak waveguide-type waveguide portions constituting the adjacent waveguides is all set equally between any adjacent waveguides,
The lengths of the respective non-weak waveguide type waveguide portions of the waveguide are set to be equal to each other,
The waveguide array, wherein the waveguides are arranged in the order of the lengths of the respective weak waveguide type waveguide portions .

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