JP3766844B2

JP3766844B2 - Lattice modulation photonic crystal

Info

Publication number: JP3766844B2
Application number: JP30980499A
Authority: JP
Inventors: 彰二郎川上; 康夫大寺; 義剛酒井
Original assignee: AUTOCLONING TECHNOLOGY CO., LTD.
Current assignee: AUTOCLONING TECHNOLOGY CO., LTD.
Priority date: 1999-09-25
Filing date: 1999-09-25
Publication date: 2006-04-19
Anticipated expiration: 2019-09-25
Also published as: JP2001091701A

Description

【０００１】
【発明の属する技術分野】
本発明は、２次元的または３次元的にほぼ周期的な構造をもつ光波帯回路素子およびその作製方法に関する。
【０００２】
【従来技術】
本発明は、光波帯回路素子に関する応用の極めて広い技術に関するものであるため、本発明全体に対応する従来技術を見つけることは難しい。それゆえ、本発明の干渉型フィルタへの応用、プリズムへの応用、導波路への応用、曲がり導波路への応用のそれぞれに関する従来技術を説明する。
【０００３】
誘電体多層膜に垂直または斜めに入射する光の干渉作用を利用する波長フィルタは重要な光学部品である。波長分割多重通信には波長幅１ｎｍ程度の狭帯域性が要求される。複数の波長を利用するので、別々に作製したフィルタをそれぞれの波長で用いる必要があり、システム価格の上昇を招く。また狭帯域のフィルタには高度な膜厚の制御が必要とされるので、製品の良品率は低いという問題もある。
【０００４】
２次元または３次元的に周期的な構造をもつ光波帯回路素子はフォトニック結晶と呼ばれ、後述するように極めて広い応用を持っている。
【０００５】
フォトニック結晶における分散性、異方性を利用して、屈折角が光の波長に対して極めて敏感に変化する「スーパープリズム効果」が近年報告されている（Ｈ．Ｋｏｓａｋａｅｔａｌ．，“Ｓｕｐｅｒｐｒｉｓｍｐｈｅｎｏｍｅｎａｉｎｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｓ”，ＰｈｙｓｉｃａｌＲｅｖｉｅｗＢ，ｖｏｌ．５８，ｎｏ．１６，ｐ．Ｒ１００９６，１９９８）。これは波長分割多重光通信システムにおいて利用価値が高い。フォトニック結晶の内部から外部へ、あるいは逆方向へ光のビームあるいは波束が境界と交叉する時の折れ曲がり角が著しい波長依存性を持つ効果をスーパープリズム効果と呼ぶ。
【０００６】
スーパープリズムにおいては、材料の誘電率、周期構造の単位セルの寸法ないし形状が設計と一致しないとき、ずれが小さくても波長特性の急峻さのために、プリズムの示す屈折特性は設計された所望の特性から大きくずれてしまう。これは製造時の良品率が低いことを意味する。
【０００７】
フォトニック結晶中に設けた導波路として公知のものの代表例は以下の通りである。（１）半導体の柱の列からなる２次元フォトニック結晶から、柱を一列分抜き去って導波路のコアとしたもの（Ａ．Ｍｅｋｉｓｅｔａｌ．，“Ｈｉｇｈｔｒａｎｓｍｉｓｓｉｏｎｔｈｒｏｕｇｈｓｈａｒｐｂｅｎｄｓｉｎｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｗａｖｅｇｕｉｄｅｓ”，ＰｈｙｓｉｃａｌＲｅｖｉｅｗＬｅｔｔｅｒｓ，ｖｏｌ．７７，ｎｏ．１８，ｐ．３７８７，１９９６）、（２）自己クローニング型３次元フォトニック結晶中に成長させた垂直欠陥列をコアとしたもの（Ｏ．Ｈａｎａｉｚｕｍｉｅｔａｌ．，“Ｐｒｏｐａｇａｔｉｏｎｏｆｌｉｇｈｔｂｅａｍｓａｌｏｎｇｌｉｎｅｄｅｆｅｃｔｓｆｏｒｍｅｄｉｎａ−Ｓｉ／ＳｉＯ_２ｔｈｒｅｅ−ｄｉｍｅｎｓｉｏｎａｌｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｓ：Ｆａｂｒｉｃａｔｉｏｎａｎｄｏｂｓｅｒｖａｔｉｏｎ”，ＡｐｐｌｉｅｄＰｈｙｓｉｃｓＬｅｔｔｅｒｓ，ｖｏｌ．７４，ｎｏ．６，ｐ．７７７，１９９９）、（３）同じく自己クローニング型３次元フォトニック結晶中にリソグラフィとドライエッチプロセスにて形成した基板面平行型導波路（川上ほか、特開平１０−３３５７５８，図２８）。（１）の技術では導波路の幅がフォトニック結晶の１周期分であるため、伝搬するモードの界の広がりが１波長程度と極めて小さく、外部の光源や光ファイバと接続した際に大きな損失が生じる。また（２）の技術では、コアの面積を任意に広く作製できるという利点がある一方で、導波路の長さを結晶の厚さ程度、すなわち数μｍ程度までしか長くできないという問題点がある。また（３）の技術には、導波路を形成するために、フォトニック結晶の成長を一時中断し、別のプロセスを施さなければならないという問題点がある。
【０００８】
またフォトニック結晶中の曲がり導波路については、Ｍｅｋｉｓらの前述の構造、馬場らの擬２次元導波構造（Ｔ．Ｂａｂａｅｔａｌ．，“Ｏｂｓｅｒｖａｔｉｏｎｏｆｌｉｇｈｔｐｒｏｐａｇａｔｉｏｎｉｎｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｏｐｔｉｃａｌｗａｖｅｇｕｉｄｅｓｗｉｔｈｂｅｎｄｓ”，ＥｌｅｃｔｒｏｎｉｃｓＬｅｔｔｅｒｓ，ｖｏｌ．３５，ｎｏ．８，ｐ．６５４，１９９９）が知られている。それぞれ９０°の無損失折れ曲がり、６０°の有限損失折れ曲がりが実現できることを示しているが、それらはいずれも折れ曲がり角における大きい反射戻り光の発生を避けられない。折れ曲がり角を小さくして反射を低減することも周期構造の制約上不可能である。
【０００９】
【発明が解決しようとする課題】
基板上に作製され、フォトニック結晶で構成される光素子において、基板面内に直交座標軸ｘｙを、それと直交する厚さ方向にｚ軸をとる。なおこの座標系は以下一貫して用いる。フォトニック結晶の各部各部が示す局所的な平均的光学特性をｘ，ｙ，ｚの関数として任意に制御することができれば、一つの基本技術によって急峻曲がりが可能、ないし高い分散性／プリズム機能を持つ導波路や位置同調型の干渉型フィルタなど多種多様な光機能を実現することができる。本発明はこれらの課題に答えるものである。
【００１０】
【課題を解決するための手段】
フォトニック結晶を形成するもっとも標準的な方法は次の通りである。基板の上に２次元的に周期的に凹凸をリソグラフィおよびエッチングで作製する。その凹凸パターンは基本的には完全に周期的であり、導波路形成のためその中の数個の凹凸を除いたり、直線（線分、半直線を含む）の形やその組み合わせの形状の凹凸を除いたりすることがなされることがある（Ｏ．Ｈａｎａｉｚｕｍｉｅｔａｌ．，ＡｐｐｌｉｅｄＰｈｙｓｉｃｓＬｅｔｔｅｒｓ，前述、Ｔ．Ｂａｂａｅｔａｌ．，ＥｌｅｃｔｒｏｎｉｃｓＬｅｔｔｅｒｓ，前述）。いずれにおいても、周期構造における基本周期長や周期性の方向は基板面上で一様である。その基板の上に、２種類以上の誘電体を順次かつ周期的に積層し、各層に所望の凹凸パターンを持たせる。ｚ方向の周期性を確保するためには一層ごとにリソグラフィやエッチングを用いる方法（Ｊ．Ｇ．Ｆｌｅｍｉｎｇｅｔａｌ．，“Ｔｈｒｅｅ−ｄｉｍｅｎｓｉｏｎａｌｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｗｉｔｈａｓｔｏｐｂａｎｄｆｒｏｍ１．３５ｔｏ１．９５μｍ”，ＯｐｔｉｃｓＬｅｔｔｅｒｓ，ｖｏｌ．２４，ｎｏ．１，ｐ．４９，１９９９）、ボンディングを用いる方法（Ｓ．Ｎｏｄａｅｔａｌ．，“Ｎｅｗｒｅａｌｉｚａｔｉｏｎｍｅｔｈｏｄｆｏｒｔｈｒｅｅ−ｄｉｍｅｎｓｉｏｎａｌｐｈｏｔｏｎｉｃｃｒｙｓｔａｌｉｎｏｐｔｉｃａｌｗａｖｅｌｅｎｇｔｈｒｅｇｉｏｎ”，ＪａｐａｎｅｓｅＪｏｕｒｎａｌｏｆＡｐｐｌｉｅｄＰｈｙｓｉｃｓ，ｖｏｌ．３５，ｎｏ．７Ｂ，ｐ．Ｌ９０９，１９９６）、薄膜形成を繰り返すだけで済む自己クローニング法（Ｓ．Ｋａｗａｋａｍｉｅｔａｌ，“Ｍｅｃｈａｎｉｓｍｏｆｓｈａｐｅｆｏｒｍａｔｉｏｎｏｆ３Ｄｐｅｒｉｏｄｉｃｎａｎｏｓｔｒｕｃｔｕｒｅｓｂｙｂｉａｓｓｐｕｔｔｅｒｉｎｇ”，ＡｐｐｌｉｅｄＰｈｙｓｉｃｓＬｅｔｔｅｒｓ，ｖｏｌ．７４，Ｎｏ．３，ｐ．４６３，１９９９，および川上ほか、前記特開）が知られている。
【００１１】
本発明の基本的考えは、基板の上の周期構造における基本周期長や周期性の方向をｘ，ｙに関し一様としないで、ｘ，ｙに関して徐々にまたは緩やかな階段状に変化させ、ｚ方向にも基本周期長をｚに関して必要により変化させることにより、広範な加工自由度・機能自由度を獲得することにある（格子変調）。即ち従来のフォトニック結晶やフォトニック結晶光回路部品の発想は、２次元であるか３次元であるかを問わず、半導体で代表される天然物質の結晶とのアナロジーから脱却できていないために、天然結晶同様に基本周期長、基本周期の方向は２次元フォトニック結晶（部品）では面内で、３次元フォトニック結晶ではその体積内で、（導波路あるいは共振器に利用される“ｄｅｆｅｃｔ”（欠陥）は周期構造の乱れであるが格子の変調ではなく、かつ構造が狭い範囲で急激に変化する）基本的に一定である。
【００１２】
図１は２次元周期構造や板状３次元周期構造の面内の格子変調の一例を示す。基本的に正方形の格子を持つ周期構造において、ＢＣ間またはｂｃ間は、他の部分に比べて円の径方向の基本周期が１．５倍になっている。即ち周期長が不連続に変化し、その周期長さは複数周期（この場合は２周期）にわたって一定である。これを緩やかな階段状の変化という。また円周上で、周方向の周期長はＡａ間のものが小さく、Ｄｄ間のものが大きく、径方向に徐々に変化している。このような構造は天然物質の結晶には存在しないが、フォトニック結晶では基板を電子ビームリソグラフィーなどで自由に加工でき、自己クローニング法で３次元化できる。なお自己クローニング法では積層の厚さ方向の基本周期を徐々にも不連続にも変化させることが容易にできる。
【００１３】
図２において、周期構造の基本的な周期として、この部分ではＡＢ，ＢＣ，ＣＡの三つのうち任意の二つを取るのが適当である。構造全体にわたる格子変調を表現するためには、ＢＣを除外しないのが適当である。即ちＢＣを含む二つを取るか、あるいはＢＣ，ＡＤの二つを基本的な周期に選んでもよい。要するに、空間全体で周期が一定であるか変化しているかに着目しているので、基本的な周期の方向、長さの定義にはある程度の幅がある。また、３次元フォトニック結晶を作製する自己クローニング法、野田ら、Ｆｌｅｍｉｎｇらの前掲の方法に共通に、センチメートル級の基板上にマイクロメートル級の厚さの周期構造を形成するので、これらを板状フォトニック結晶と総称することにする。板の面の中の方向を面内または面平行な方向、それに垂直な方向を面垂直方向とよぶこととする。
【００１４】
本発明の方法により獲得される光回路素子機能の自由度の広さを以下の実施例によって順次説明する。
【００１５】
【実施例】
［実施例１］
図３は本発明による、通過波長がｘ方向に連続的に変化する干渉フィルタの構成図である。このフィルタは、Ｓｉ（屈折率ｎ＝３．５）１とＳｉＯ_２（ｎ＝１．５）２からなるフォトニック結晶部分がＳｉＯ_２基板３とＳｉＯ_２板４とに挟まれた構造を持ち、自己クローニング法により形成され、ｙ方向には一様な構造を持つ。交互多層膜部分はｚ方向にｘによらず共通な周斯Ｌｚを持つ。また一部のＳｉ層の厚さを他のＳｉ層に比べ厚く、具体的には０．９Ｌｚとし、キャビティ５を形成している。ｘ方向の周期Ｌｘは局所的には一定と見なされるが、ｘの広い範囲にわたっては徐々にまたは階段状に変化しており、ｘ＝Ｘ_１ではＬ_Ｘ＝０．９Ｌ_Ｚ，ｘ＝Ｘ_２，Ｘ_３，Ｘ_４ではそれぞれＬｘ＝Ｌｚ，１．１Ｌｚ，１．２Ｌｚである。ｘｚ断面におけるフォトニック結晶の一周期内の形状を図４に示す。この例ではＳｉ層１とＳｉＯ_２層２の厚さはそれぞれ０．３Ｌｚ，０．７Ｌｚである。電界がｙ軸に平行な光がｚ方向に入射したときのこの構造全体の光透過率を波長の関数として図５に示す。このように干渉フィルタの通過波長を空間的に変化させることは次のような利点を生む。
（１）光通信用の複数の帯域フィルタにおいて、通過帯域が所望の間隔で配置される組み合わせを要する場合がある。本技術によれば、基板上に適切な間隔で複数の利用領域を選べば、１枚の基板上に一回の工程で所望のフィルタ群を形成することが容易にできる。
（２）光通信において極めて狭い通過帯域を持つフィルタ（例えば比帯域幅＝１／２０００）が近年要求されている。このようなフィルタの作製においては不良品の割合が極めて高い。本技術を適用することによって、所定の波長に通過域を持つような基板上の適切な位置を選び出し確実に良品を得ることができる。
（３）広帯域の光ビームを本技術による干渉フィルタ上でｘ方向に掃引することにより、通過波長が連続的に変化するので、それを分光計測用の光源として利用することができる。
【００１６】
また、図３は説明の便のためのものであって、例えば上面図を図６に示すように扇形パターンとし、基本周期長，基本周期を空間的に連続に変化させることにより、個々の単位周期を正方形に極めて近くして入射光の電界の向きによらぬ動作をさせることができる。このとき、利用される領域を図６中の長方形領域６のように限定してもよい。また図７のようにｘ方向の周期をｙ方向の周期とほぼ一致する範囲で変化させ、特性の偏光方向依存性を十分小さくすることもできる。
【００１７】
［実施例２］
３次元フォトニック結晶においてはいわゆるスーパープリズム効果が実験的に見出されており、この効果は理論的には２次元フォトニック結晶でも３次元フォトニック結晶でも生ずることが知られている。即ち、基板上に作製された３次元フォトニック結晶に、外部から光を基板に平行に入射させて、フォトニック結晶内にある屈折角を持って伝わる光としたとき、例えば光波長が１％だけ連続的に変わるとき屈折角を６０°も連続的に変化させることができる。これは通常のプリズムよりも２〜３桁高い波長分散効果である。ゆえに光波長に敏感な合波分波素子を得ることができる。
【００１８】
図８は本発明を上面が三角格子を持つスーパープリズムに適用したものである。基板上に六角形または円形の孔を三角格子状に作製し、その上に屈折率の異なる２種類の誘電体を自己クローニング法により交互に積層して３次元フォトニック結晶を作製する。三角格子のｘ方向周期長はあるｙの値の付近でほとんど一定で有限幅の光ビームに対しては局所的に一定周期構造として働くが、ｙの値と共にｘ方向周期長が徐々に変化する。格子変調のない従来のスーパープリズム構造においては、プリズム効果のもっとも顕著に現れるのは比較的狭い波長範囲に限られる。図８の構造においては、光ビームの入射位置を選択することにより、プリズム効果の顕著に現れる波長範囲の中心を連続的に選択することができ、一個の素子でシステムの中心波長の設計に柔軟性を与えることができると共に、作製技術の側からみると作製誤差を光ビームの入射位置の選択により補償できる長所をも持っている。即ちＡ付近に入射した光はλ_０−Δλからλ_０の範囲で波長変化に敏感であり、Ｂ付近に入射した光はλ_０からλ_０＋Δλの範囲で同じく敏感である。図８中の符号７、８、９はそれぞれ波長λ_０−Δλ，λ_０，λ_０＋Δλの光線を示している。またｚのある範囲に光を閉じ込める平板状の導波構造（後述）を併せ用いることにより、中心波長がｙ方向に連続的に変化している導波型スーパープリズムを得ることができ、入出力側で他の光導波路と結合して用いるとき高い結合効率を得る。
【００１９】
［実施例３］
図９には、本発明を３次元フォトニック結晶型導波路に適用した例を示す。同図において、１０，１１はそれぞれ高屈折率材料（例えばＳｉ）、低屈折率材料（例えばＳｉＯ_２）を示している。３次元フォトニック結晶の内部にチャネル形導波路を形成することの重要性はよく知られているが（例えばＭｅｋｉｓ他、前述２次元導波路、およびＢａｂａ他、前述擬２次元導波路）、本例は
（２）導波路のコア部分がフォトニック結晶の基本周期の数倍以上であること
（３）プロセスの中断を要しない一貫作製プロセスにより形成可能であるとの特徴を持っている点でも上に引用した２例とは全く異なる。図９の構造の導波作用の原理を、簡略化した図１０の構造を用いて説明する。同図はＳｉＯ_２（屈折率ｎ_１＝１．５）１２，ＴｉＯ_２（ｎ_２＝２．５）１３の２種類の誘電体の平坦膜をｚ方向に積層したもので、波長１．５５μｍにおいて用いられる平板形導波路を表わす。周期Λ_ｃｏｒｅ＝０．４２７μｍの３周期からなる中心部が周期Λ_ｃｌａｄ＝０．３２０μｍのクラッド部に包まれたものである。仮想的にｚ方向に−∞から＋∞まで周期Λ_ｃｏｒｅまたはΛ_ｃｌａｄを持つ完全に周期的な構造を考えると、ｙ方向に伝わる波の速度は、Λ_ｃｌａｄを周期として持つ構造の方がもう一方より速く、電磁界はコア内に閉じ込められると予期される。
【００２０】
このような導波効果は、コアの厚さが周期長の数倍以上ある構造に適用されるものである。電磁界方程式を厳密に解いた結果は上の物理的イメージと一致し、図１１の電界分布が得られる。界はコア内でもクラッド内でも局所的な基本周期に同期した細かいリップルを持ち、包絡線がコア内で振動的、クラッド内で減衰的である電界分布が得られる。コアの厚さが基本周期Λｃｏｒｅの３倍である１．２８μｍのとき、その約３倍（約３μｍ）の１／ｅ全幅を持つ基本モードがあることがわかる。このモードは大きいリップルをもちガウス形から遠いように一見されるが、それは正しくなく、ガウス型ビームとの整合性がよいことが検討すれば分かる。この結果と良く一致する実験結果が得られている。なおモードの実効屈折率は１．９３である。図１０、図９の中間として図１２に示すように断面が２次元周期的でｚ方向には一様なチャネル導波路を得る。図９の導波路、図１２の導波路は、（特開平１０−３３５７５８，図２８）の構造とは異なり、凹凸を持つ基板の上に、自己クローニング法によって一貫プロセスにより中断や異種プロセスを挟むことなく作製することができる。例えば図９の構造は図１３に示すような、凹み１４を持つ基板１５の上にＳｉとＳｉＯ_２をそれぞれ拡散入射スパッタリングないしスパッタエッチングを組み合わせて積層することにより作製された。
【００２１】
［実施例４］
フォトニック結晶導波路において、急峻な曲りを低い放射損失と低い反射（光源への戻り光）を持って実現するのに、面内周期の方向を空間的に変調して、周期構造のもつ特性と滑らかな曲がりとを両立させる。即ち概略を図１４に示す構造を自己クローニング法により作製し用いた。
【００２２】
また図１５に示すように３次元フォトニック結晶の中の曲りチャネル導波路を形成することもできる。このような曲り導波路において、フォトニック結晶の基本周期長さは１μｍの数分の１以下であり、光回路の小型化のために必要とされる曲り半径は１０μｍから１００μｍ程度であるから、曲りの内側部と外側部の曲りに沿う方向の周期長さの差はさほど大きくない。また、図１４、図１５において曲りを急峻にしたとき外側へ放射が生ずる。放射に伴う損失を防ぐため、曲りの外側の部分において、半径方向の周期長さを他のクラッド部分の半径方向周期長より小さくした領域を付加して、その部分の実効屈折率を低下させることにより放射を抑圧することができる。
【００２３】
曲り導波路を平面内で一巡させてループを作りリング共振器を形成することができることは言うまでもない。本例では３次元フォトニック結晶について説明したが、２次元導波路で同じ考え方が適用できるのは勿論である。
【００２４】
【発明の効果】
請求項１，２，３，４により、フォトニック結晶の空間的に緩やかな格子変調を利用して巨視的・平均的な媒質定数に傾斜をもたせることができ光回路の設計自由度が大幅に増す。
請求項５，６により透過波長に傾斜のあるフィルタが得られる。
請求項７，８により位置により同調できるスーパープリズムが得られる。
請求項９，１０，１１，１２により、作製が容易・光ファイバとの結合が容易・曲がりによる放射・反射がないフォトニック結晶形導波路が得られる。
【図面の簡単な説明】
【図１】格子変調型周期構造の一例を示す説明図。
【図２】格子変調型周期構造において、基本周期の取り方の例を示す説明図。
【図３】第１の実施例である干渉フィルタの構造を示す説明図。
【図４】第１の実施例である干渉フィルタを構成する周期構造の単位構造（ユニットセル）を示す説明図。
【図５】第１の実施例である干渉フィルタの透過スペクトルを示す説明図。
【図６】第１の実施例である干渉フィルタの動作から、偏波依存性を除去する方法の一例を示す説明図。
【図７】第１の実施例である干渉フィルタの動作から、偏波依存性を除去する方法の一例を示す説明図。
【図８】第２の実施例であり、本発明をスーパープリズムに適用した構造を示す説明図。
【図９】第３の実施例であり、本発明を３次元フォトニック結晶型導波路に適用した構造を示す説明図。
【図１０】図９の構造を簡略化した導波路構造を示す説明図。
【図１１】図１０の導波路構造における、導波モードの電界分布の数値計算例を示す説明図。
【図１２】図９の構造を簡略化したチャネル型導波構造を示す説明図。
【図１３】図９の導波路構造の作製に用いられる基板の形状の一例を示す説明図。
【図１４】第４の実施例である格子変調型曲がり導波路の構造を示す説明図。
【図１５】第４の実施例である３次元フォトニック結晶中の格子変調型曲がり導波路の構造を示す説明図。
【符号の説明】
１Ｓｉ
２ＳｉＯ_２
３ＳｉＯ_２基板
４ＳｉＯ_２板
５キャビティ
６限定された利用領域
７波長λ_０−Δλの光線の軌跡
８波長λ_０の光線の軌跡
９波長λ_０＋Δλの光線の軌跡
１０高屈折率材料（例えばＳｉ）
１１低屈折率材料（例えばＳｉＯ_２）
１２ＳｉＯ_２
１３ＴｉＯ_２
１４基板上の孔
１５基板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveband circuit element having a two-dimensional or three-dimensional substantially periodic structure and a manufacturing method thereof.
[0002]
[Prior art]
Since the present invention relates to a technology having a very wide range of applications related to optical waveband circuit elements, it is difficult to find a prior art corresponding to the entire present invention. Therefore, the prior art relating to the application of the present invention to the interference filter, the application to the prism, the application to the waveguide, and the application to the bent waveguide will be described.
[0003]
A wavelength filter that utilizes the interference action of light that enters the dielectric multilayer film perpendicularly or obliquely is an important optical component. Wavelength division multiplex communication is required to have a narrow bandwidth with a wavelength width of about 1 nm. Since a plurality of wavelengths are used, it is necessary to use filters prepared separately for each wavelength, resulting in an increase in system price. In addition, since a narrow band filter requires a high degree of film thickness control, there is a problem that the yield rate of products is low.
[0004]
An optical waveband circuit element having a two-dimensional or three-dimensional periodic structure is called a photonic crystal and has a very wide application as will be described later.
[0005]
Recently, the “super prism effect” in which the refraction angle changes extremely sensitively to the wavelength of light by utilizing the dispersibility and anisotropy in the photonic crystal has been reported (H. Kosaka et al., “Superprism”). phenomenain photonic crystals ", Physical Review B, vol. 58, no. 16, p. R10096, 1998). This has a high utility value in a wavelength division multiplexing optical communication system. The effect of the wavelength dependence of the bending angle when the light beam or wave packet crosses the boundary from the inside to the outside of the photonic crystal or in the opposite direction is called the super prism effect.
[0006]
In the super prism, when the dielectric constant of the material and the size or shape of the unit cell of the periodic structure do not match the design, the refractive characteristics shown by the prism are designed as desired because of the steepness of the wavelength characteristics even if the deviation is small. It will deviate greatly from the characteristics. This means that the yield rate during production is low.
[0007]
Typical examples of known waveguides provided in the photonic crystal are as follows. (1) A two-dimensional photonic crystal composed of a column of semiconductors, in which one column is extracted as a core of a waveguide (A. Mekis et al., “High transmission through sharp beads inflective crystalline waves,” Review Letters, vol. 77, no. 18, p. 3787, 1996), (2) Cores of vertical defect arrays grown in self-cloning three-dimensional photonic crystals (O. Hanaizumi et al., “Propagation of light beams along line defects formed in a-Si / SiO ₂ three-dimensional photonic crystals : Fabrication and observation ", Applied Physics Letters, vol. 74, no. 6, p. 777, 1999), (3) A substrate surface parallel type formed in a self-cloning type three-dimensional photonic crystal by lithography and dry etching processes. Waveguide (Kawakami et al., JP-A-10-335758, FIG. 28). In the technique (1), since the width of the waveguide is one period of the photonic crystal, the spread of the propagation mode field is as small as about one wavelength, and a large loss occurs when connected to an external light source or optical fiber. Occurs. In addition, the technique (2) has an advantage that the core area can be made arbitrarily wide, but there is a problem that the length of the waveguide can only be increased to the thickness of the crystal, that is, about several μm. Further, the technique (3) has a problem that, in order to form a waveguide, the growth of the photonic crystal must be temporarily stopped and another process must be performed.
[0008]
For bent waveguides in photonic crystals, the aforementioned structure of Mekis et al., The quasi-two-dimensional waveguide structure of Baba et al. (T. Letters, vol.35, no.8, p.654, 1999). Although it has been shown that each of the 90 ° lossless bending and the 60 ° finite loss bending can be realized, it is inevitable that a large reflected return light is generated at the bending angle. It is also impossible to reduce reflection by reducing the bend angle due to restrictions on the periodic structure.
[0009]
[Problems to be solved by the invention]
In an optical element fabricated on a substrate and composed of a photonic crystal, an orthogonal coordinate axis xy is taken in the substrate plane, and a z-axis is taken in a thickness direction perpendicular thereto. This coordinate system is used consistently below. If the local average optical characteristics of each part of the photonic crystal can be arbitrarily controlled as a function of x, y, z, it can be sharply bent by one basic technique, or it has a high dispersibility / prism function. A wide variety of optical functions can be realized, such as a waveguide or a position-tuning interference filter. The present invention answers these problems.
[0010]
[Means for Solving the Problems]
The most standard method for forming a photonic crystal is as follows. Concavities and convexities are formed two-dimensionally and periodically on the substrate by lithography and etching. The concavo-convex pattern is basically completely periodic, and some of the concavo-convex patterns are removed to form a waveguide, and the concavo-convex shape of a straight line (including line segments and half straight lines) or a combination thereof is used. (O. Hanaizumi et al., Applied Physics Letters, supra, T. Baba et al., Electronics Letters, supra). In any case, the basic period length and the direction of periodicity in the periodic structure are uniform on the substrate surface. Two or more kinds of dielectrics are sequentially and periodically stacked on the substrate, and each layer has a desired uneven pattern. In order to ensure the periodicity in the z-direction, a method using lithography or etching for each layer (JG Fleming et al., “Three-dimensional photonic with a stop band from 1.35 to 1.95 μm”, Optics Letters, vol. 24, no. 1, p. 49, 1999), a method using bonding (S. Noda et al., “Newrealization method for three-dimensional phenotypically pure algebraic hydrogen,” .35, no. 7B, p.L909, 1996), thin Self-cloning method that requires only repeated membrane formation (S. Kawakami et al., “Mechanism of shape formation of 3D periodic nanostructures by 3, Bioslic., P. 99, Applied Physics. , The above-mentioned Japanese Laid-Open Patent Publication (Kokai) is known.
[0011]
The basic idea of the present invention is that the basic periodic length and periodicity of the periodic structure on the substrate are not made uniform with respect to x and y, but are gradually or gradually changed with respect to x and y, and z By changing the basic period length in the direction as necessary with respect to z, a wide range of processing freedom and functional freedom is obtained (lattice modulation). In other words, the idea of conventional photonic crystals and photonic crystal optical circuit components has not been able to break away from analogy with natural substance crystals represented by semiconductors, whether they are two-dimensional or three-dimensional. As with natural crystals, the fundamental period length and direction of the fundamental period are in-plane for a two-dimensional photonic crystal (component) and within its volume for a three-dimensional photonic crystal (defect used in a waveguide or resonator). “(Defect) is a periodic structure disturbance but not a lattice modulation, and the structure changes abruptly within a narrow range).
[0012]
FIG. 1 shows an example of in-plane lattice modulation of a two-dimensional periodic structure or a plate-like three-dimensional periodic structure. In a periodic structure having a basically square lattice, the basic period in the radial direction of the circle is 1.5 times between BC or bc compared to other parts. That is, the cycle length changes discontinuously, and the cycle length is constant over a plurality of cycles (in this case, two cycles). This is called a gradual step change. On the circumference, the period length in the circumferential direction is small between Aa and large between Dd, and gradually changes in the radial direction. Such a structure does not exist in a natural substance crystal, but in a photonic crystal, a substrate can be freely processed by electron beam lithography or the like, and can be three-dimensionalized by a self-cloning method. In the self-cloning method, the basic period in the thickness direction of the stack can be easily changed gradually or discontinuously.
[0013]
In FIG. 2, it is appropriate to take any two of AB, BC, and CA as the basic period of the periodic structure in this part. In order to represent lattice modulation throughout the structure, it is appropriate not to exclude BC. In other words, two including BC may be taken, or two of BC and AD may be selected as the basic period. In short, since the focus is on whether the period is constant or changing throughout the space, there is a certain range in the definition of the basic period direction and length. In addition, since a self-cloning method for producing a three-dimensional photonic crystal, Noda et al., Fleming et al. And the above-described method, a periodic structure having a thickness of micrometer class is formed on a centimeter class substrate. It is generically called a plate-like photonic crystal. The direction in the plane of the plate is called in-plane or plane-parallel direction, and the direction perpendicular to it is called the plane perpendicular direction.
[0014]
The degree of freedom of the optical circuit element function obtained by the method of the present invention will be sequentially described by the following examples.
[0015]
【Example】
[Example 1]
FIG. 3 is a configuration diagram of an interference filter according to the present invention in which the passing wavelength continuously changes in the x direction. This filter has a structure in which a photonic crystal portion composed of Si (refractive index n = 3.5) 1 and SiO ₂ (n = 1.5) 2 is sandwiched between an SiO ₂ substrate 3 and an SiO ₂ plate 4. It is formed by the self-cloning method and has a uniform structure in the y direction. The alternating multilayer film portions have a common circumference Lz regardless of x in the z direction. Also, the cavity 5 is formed by making the thickness of a part of the Si layer thicker than other Si layers, specifically 0.9 Lz. Although the period Lx in the x direction is considered to be locally constant, it changes gradually or stepwise over a wide range of x, and when x = X ₁ , L _X = 0.9L _Z , x = X ₂ , X ₃ , and X ₄ are Lx = Lz, 1.1Lz, and 1.2Lz, respectively. The shape within one period of the photonic crystal in the xz section is shown in FIG. In this example, the thicknesses of the Si layer 1 and the SiO ₂ layer 2 are 0.3 Lz and 0.7 Lz, respectively. FIG. 5 shows the light transmittance of the entire structure as a function of wavelength when light whose electric field is parallel to the y-axis is incident in the z direction. Thus, spatially changing the pass wavelength of the interference filter has the following advantages.
(1) In some band filters for optical communication, a combination in which passbands are arranged at desired intervals may be required. According to the present technology, a desired filter group can be easily formed in one step on a single substrate by selecting a plurality of use regions at appropriate intervals on the substrate.
(2) In recent years, a filter having a very narrow pass band (for example, specific bandwidth = 1/2000) has been required in optical communication. In producing such a filter, the proportion of defective products is extremely high. By applying the present technology, it is possible to select a suitable position on the substrate having a pass band at a predetermined wavelength and reliably obtain a non-defective product.
(3) By sweeping a broadband light beam in the x direction on an interference filter according to the present technology, the passing wavelength continuously changes, and therefore, it can be used as a light source for spectroscopic measurement.
[0016]
Also, FIG. 3 is for convenience of explanation. For example, the top view is a fan-shaped pattern as shown in FIG. The operation can be performed regardless of the direction of the electric field of incident light by making the period very close to a square. At this time, the area to be used may be limited to a rectangular area 6 in FIG. Further, as shown in FIG. 7, the period in the x direction can be changed within a range that substantially coincides with the period in the y direction, so that the polarization direction dependency of characteristics can be made sufficiently small.
[0017]
[Example 2]
A so-called super prism effect has been experimentally found in a three-dimensional photonic crystal, and this effect is theoretically known to occur in both a two-dimensional photonic crystal and a three-dimensional photonic crystal. That is, when light is incident on the three-dimensional photonic crystal manufactured on the substrate in parallel to the substrate to be transmitted with a refraction angle in the photonic crystal, for example, the light wavelength is 1%. Only when it changes continuously, the refraction angle can be changed continuously by 60 °. This is a wavelength dispersion effect that is two to three orders of magnitude higher than that of a normal prism. Therefore, a multiplexing / demultiplexing element sensitive to the light wavelength can be obtained.
[0018]
FIG. 8 shows the case where the present invention is applied to a super prism whose upper surface has a triangular lattice. Hexagonal or circular holes are formed on a substrate in a triangular lattice shape, and two types of dielectrics having different refractive indexes are alternately stacked on the substrate by a self-cloning method to manufacture a three-dimensional photonic crystal. Although the periodic length in the x direction of the triangular lattice is almost constant near a certain y value and works locally as a constant periodic structure for a light beam having a finite width, the periodic length in the x direction gradually changes with the y value. . In the conventional super prism structure having no grating modulation, the prism effect is most noticeable only in a relatively narrow wavelength range. In the structure of FIG. 8, by selecting the incident position of the light beam, it is possible to continuously select the center of the wavelength range in which the prism effect is prominent, and to flexibly design the central wavelength of the system with a single element. In addition, the manufacturing technique has an advantage that a manufacturing error can be compensated by selecting an incident position of the light beam. That light incident on the vicinity of A is sensitive to wavelength change in the range of lambda ₀ from lambda ₀ -.DELTA..lambda, light incident on the vicinity of B is also sensitive in the range of lambda _{0 +} [Delta] [lambda] from the lambda _0. Reference numerals 7, 8, and 9 in FIG. 8 indicate rays of wavelengths λ ₀ −Δλ, λ ₀ , λ ₀ + Δλ, respectively. In addition, by using a flat waveguide structure (described later) that confines light within a certain range of z, a waveguide super prism whose center wavelength continuously changes in the y direction can be obtained. When coupled with other optical waveguides on the side, high coupling efficiency is obtained.
[0019]
[Example 3]
FIG. 9 shows an example in which the present invention is applied to a three-dimensional photonic crystal type waveguide. In the figure, reference numerals 10 and 11 denote a high refractive index material (for example, Si) and a low refractive index material (for example, SiO ₂ ), respectively. The importance of forming a channel-type waveguide inside a three-dimensional photonic crystal is well known (eg, Mekis et al., The aforementioned two-dimensional waveguide, and Baba et al., The aforementioned quasi-two-dimensional waveguide). Examples are (2) The core part of the waveguide is more than several times the basic period of the photonic crystal. (3) It can also be formed by an integrated fabrication process that does not require process interruption. It is completely different from the two examples cited above. The principle of the waveguide action of the structure of FIG. 9 will be described using the simplified structure of FIG. In the figure, two types of dielectric flat films of SiO ₂ (refractive index n ₁ = 1.5) 12 and TiO ₂ (n ₂ = 2.5) 13 are laminated in the z direction, and the wavelength is 1.55 μm. Represents a planar waveguide used in FIG. A central part composed of three periods with a period Λ _core = 0.427 μm is surrounded by a _clad part with a period Λ _clad = 0.320 μm. Considering a completely periodic structure with a period Λ _core or Λ _clad from −∞ to + ∞ virtually in the z direction, the velocity of the wave traveling in the y direction is _already greater for structures with Λ _clad as the period On the other hand, the electromagnetic field is expected to be confined within the core.
[0020]
Such a waveguiding effect is applied to a structure having a core thickness several times the periodic length or more. The result of exactly solving the electromagnetic field equation agrees with the above physical image, and the electric field distribution of FIG. 11 is obtained. The field has fine ripples synchronized with the local fundamental period both in the core and in the cladding, and an electric field distribution is obtained in which the envelope is oscillating in the core and attenuating in the cladding. When the core thickness is 1.28 μm, which is three times the basic period Λcore, it can be seen that there is a fundamental mode having a 1 / e full width of about 3 times (about 3 μm). This mode appears to have a large ripple and distant from the Gaussian shape, but it is not correct and can be seen by examining the good matching with the Gaussian beam. Experimental results that are in good agreement with this result have been obtained. The effective refractive index of the mode is 1.93. As shown in FIG. 12 as an intermediate between FIG. 10 and FIG. 9, a channel waveguide having a two-dimensional cross section and uniform in the z direction is obtained. The waveguide of FIG. 9 and the waveguide of FIG. 12 are different from the structure of (Japanese Patent Laid-Open No. 10-335758, FIG. 28). It can produce without. For example, the structure of FIG. 9 was produced by laminating Si and SiO ₂ on a substrate 15 having a recess 14 as shown in FIG. 13 by combining diffusion incident sputtering or sputter etching.
[0021]
[Example 4]
In photonic crystal waveguides, in order to achieve sharp bends with low radiation loss and low reflection (return light to the light source), the characteristics of the periodic structure are spatially modulated by in-plane periodic direction. And smooth bends. That is, the structure schematically shown in FIG. 14 was prepared and used by the self-cloning method.
[0022]
Further, as shown in FIG. 15, a bent channel waveguide in a three-dimensional photonic crystal can be formed. In such a bent waveguide, the basic period length of the photonic crystal is less than a fraction of 1 μm, and the bend radius required for miniaturization of the optical circuit is about 10 μm to 100 μm. The difference in the period length in the direction along the bend of the inner side and the outer side of the bend is not so large. 14 and 15, radiation is generated outward when the curve is sharpened. In order to prevent loss due to radiation, a region where the period length in the radial direction is made smaller than the period length in the radial direction of the other cladding part is added to the outside part of the bend to lower the effective refractive index of that part. Can suppress radiation.
[0023]
It goes without saying that a ring resonator can be formed by making a loop by bending a curved waveguide in a plane. Although the three-dimensional photonic crystal has been described in this example, it is needless to say that the same idea can be applied to the two-dimensional waveguide.
[0024]
【The invention's effect】
According to the first, second, third, and fourth aspects, the macroscopic / average medium constant can be inclined by utilizing spatially gentle lattice modulation of the photonic crystal, and the degree of freedom in designing the optical circuit is greatly increased. Increase.
According to the fifth and sixth aspects, a filter having an inclined transmission wavelength is obtained.
According to claims 7 and 8, a super prism which can be tuned according to the position is obtained.
According to the ninth, tenth, eleventh and twelfth aspects, it is possible to obtain a photonic crystal waveguide that is easy to fabricate, easily coupled to an optical fiber, and free from radiation and reflection due to bending.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a lattice modulation type periodic structure.
FIG. 2 is an explanatory diagram showing an example of how to take a fundamental period in a lattice modulation type periodic structure.
FIG. 3 is an explanatory diagram showing the structure of an interference filter according to the first embodiment.
FIG. 4 is an explanatory diagram showing a unit structure (unit cell) of a periodic structure constituting the interference filter according to the first embodiment.
FIG. 5 is an explanatory diagram showing a transmission spectrum of the interference filter according to the first embodiment.
FIG. 6 is an explanatory diagram showing an example of a method for removing polarization dependence from the operation of the interference filter according to the first embodiment.
FIG. 7 is an explanatory diagram showing an example of a method for removing polarization dependence from the operation of the interference filter according to the first embodiment.
FIG. 8 is an explanatory diagram showing a structure in which the present invention is applied to a super prism according to a second embodiment.
FIG. 9 is an explanatory diagram showing a structure of a third embodiment in which the present invention is applied to a three-dimensional photonic crystal type waveguide.
10 is an explanatory diagram showing a waveguide structure in which the structure of FIG. 9 is simplified.
11 is an explanatory view showing a numerical calculation example of the electric field distribution of the waveguide mode in the waveguide structure of FIG.
12 is an explanatory diagram showing a channel-type waveguide structure in which the structure of FIG. 9 is simplified.
13 is an explanatory diagram showing an example of the shape of a substrate used for manufacturing the waveguide structure of FIG. 9. FIG.
FIG. 14 is an explanatory view showing the structure of a grating modulation type bent waveguide according to the fourth embodiment.
FIG. 15 is an explanatory diagram showing the structure of a lattice modulation type bent waveguide in a three-dimensional photonic crystal according to a fourth embodiment.
[Explanation of symbols]
1 Si
2 SiO ₂
3 SiO ₂ substrate 4 SiO ₂ plate 5 cavity 6 limited available area 7 wavelength lambda ₀ -.DELTA..lambda the ray trajectory 8 wavelength lambda ₀ of the light beam path 9 wavelength lambda ₀ + [Delta] [lambda] of the beam trajectory 10 the high refractive index material (e.g. Si)
11 Low refractive index material (eg, SiO ₂ )
12 SiO ₂
13 TiO ₂
14 hole on substrate 15 substrate

Claims

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, at least a portion where the period of the unevenness of the dielectric constituting the layer changes in a spatially gradually or gently stepped manner in at least one of the in-plane directions An optical functional structure characterized by being included in a part.

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, at least a portion where the period of the unevenness of the dielectric constituting the layer changes in a spatially gradually or gently stepped manner in at least one of the in-plane directions An optical functional structure characterized in that it is included in a part and the used wavelength range belongs to the propagation range of the structure.

Based on a multilayer periodic structure composed of two or more kinds of dielectrics, a three-dimensional period in which each layer includes at least a portion of irregularities due to a dielectric constituting a two-dimensional periodic layer in a plane perpendicular to the stacking direction. In the structure, at least a part of which the period of the unevenness of the dielectric that constitutes the layer in at least one of the in-plane directions changes in a spatially gradually or gently stepped manner is included. A method for producing an optical functional structure, characterized in that it is prepared using at least a part of the self-cloning method.

Based on a multilayer periodic structure composed of two or more kinds of dielectrics, a three-dimensional period in which each layer includes at least a portion of irregularities due to a dielectric constituting a two-dimensional periodic layer in a plane perpendicular to the stacking direction. The structure includes at least a portion in which the period of the unevenness of the dielectric material constituting the layer changes in a spatially gradually or gradually stepped manner in at least one of the in-plane directions, and the wavelength used A method for producing an optical functional structure, wherein a structure characterized in that a region belongs to a propagation region of the structure is created using at least a part of the self-cloning method.

Based on a multilayer periodic structure composed of two or more kinds of dielectrics, a three-dimensional period in which each layer includes at least a portion of irregularities due to a dielectric constituting a two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a structure, the transmittance of light in the direction intersecting the surface is changed by gradually changing the period of the unevenness of the dielectric constituting the layer in a spatially gradually or gradually stepped manner in at least one of the in-plane directions. A wavelength selective filter characterized in that the wavelength dependence of reflectance varies in the plane.

A multilayer periodic structure consisting of two or more dielectric as the base, three-dimensional periodic containing irregularities of a dielectric that each layer constituting the periodic layer of a two-dimensional in a plane perpendicular to the stacking direction at least a portion thereof In a structure, the transmittance of light in the direction intersecting the surface is changed by gradually changing the period of the unevenness of the dielectric constituting the layer in a spatially gradually or gradually stepped manner in at least one of the in-plane directions. A method for producing a wavelength selective filter, characterized in that an optical element characterized in that the wavelength dependence of reflectance is changed in the plane is produced using at least a part of the self-cloning method.

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, the period of the unevenness of the dielectric that constitutes the layer in at least one of the in-plane directions is spatially gradually or gradually changed in a stepped manner. A two-dimensional optical waveguide or a plate-like three-dimensional periodic structure having a plurality of regions having different super-prism effects in the structure, or a plate-like three-dimensional periodic structure having a plane-parallel waveguide structure inside .

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, the period of the unevenness of the dielectric that constitutes the layer in at least one of the in-plane directions is spatially gradually or gradually changed in a stepped manner. A two-dimensional optical waveguide or a plate-like three-dimensional periodic structure having a plurality of regions having different super-prism effects in the structure, or a plate-like three-dimensional periodic structure having a plane-parallel waveguide structure inside Is produced using at least a part of the self-cloning method.

A basic multilayer periodic structure consisting of two or more dielectric, including the irregularities of a dielectric that each layer constitutes a one-dimensional or two-dimensional periodic layers in a plane perpendicular to the stacking direction at least a portion thereof In a two-dimensional or three-dimensional periodic structure, the length of the period of unevenness of the dielectric that forms a layer in a direction parallel to the laminated surface intersecting with the light traveling direction is changed in a spatially gradually or gradually stepped manner. An optical waveguide characterized by having a function of making the region to be guided different from the surrounding periodic structure.

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, the length of the period of unevenness of the dielectric that forms a layer in a direction parallel to the laminated surface intersecting with the light traveling direction is changed in a spatially gradually or gradually stepped manner. An optical waveguide characterized in that an optical waveguide characterized in that the region to be guided has an action different from the surrounding periodic structure is produced using at least a part of the self-cloning method. How to create

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, a dielectric that constitutes one or more layers out of two basic periodic directions in a plane perpendicular to the stacking direction that are perpendicular or form an angle to the light traveling direction An in-plane optical waveguide or a ring-shaped optical resonator is characterized in that the light curvature is realized by the period of irregularities of the light being changed in a spatially gradual or gentle step shape.

Based on a multilayer periodic structure composed of two or more types of dielectrics, each layer includes at least part of the irregularities due to the dielectrics constituting a one-dimensional or two-dimensional periodic layer in a plane perpendicular to the stacking direction. In a two-dimensional or three-dimensional periodic structure, a dielectric that constitutes one or more layers out of two basic periodic directions in a plane perpendicular to the stacking direction that are perpendicular or form an angle to the light traveling direction Self-cloning of in-plane optical waveguides or ring-shaped optical resonators in the thickness direction, which realizes light bending by the period of irregularities in the space changing gradually or gradually in a stepwise manner A method for producing an optical functional element, wherein the effect is produced using at least a part of the effect.