JP3702445B2 - Optical element and apparatus using the optical element - Google Patents

Description

の関係が満たされるように構成されている。
【００３３】
この条件（１）の下では、微細柱１０２を含む構造が波長に比較して十分に微細であり、透過光に対して１次以上の回折光が生じない。すなわち、鋭角曲げ構造やスーパープリズム等に利用される周期的微細構造、所謂フォトニック結晶に比較して、一層微細な構造である。しかしながら、電子ビーム描画装置の一般的な性能として、５０ｎｍ程度のレジストパターンが形成可能であるため、可視光から赤外光に至る領域の光に対して上記の条件（１）を満たす構造を作製することは可能である。例えば、電子ビーム描画装置によって形成された微細パターンマスクを利用して、反応性イオンエッチング等で所要パターンに即した微細柱１０２を作製できる。
【００３４】
本発明では、微細柱１０２の断面積を制御して、材料の局所的実効屈折率を制御する。図２の領域Ａでは、微細柱１０２の断面積が大きく、実効屈折率が高くなり、領域Ｂでは、実効屈折率が小さくなる。透過型で利用する場合、０次近似では、実効比誘電率は、微細柱のない部分（通常は、空気乃至真空で、比誘電率約１）と微細柱１０２部分の比誘電率の体積加重平均となる。例えば、円形の微細柱１０２に対して、Ｌm を１．５５μｍ、ｎp （微細柱１０２部分の屈折率）を１．５、Ｌdx及びＬdyを０．２５μｍ、Ｄhx及びＤhyを０．１〜０．２５μｍ、微細柱１０２の高さを５μｍとする。このとき、実効屈折率は１．０７６〜１．４０８まで変化させることが可能であり、最大位相差として２．１４πが得られる。
【００３５】
このようにして、局所的な実効屈折率を制御することにより、各種の回折光学素子を実現することが可能になる。図３に、具体的な回折光学素子の一例であるフレネルレンズ１０３を示す。図３（ａ）はそのフレネルレンズ１０３の平面図、（ｂ）はその光軸から片側の実効屈折率分布を示す図、（ｃ）、（ｄ）はその異なる２つの部分における微細柱１０２の形状を示す図である。この例は、本発明による屈折率制御によってフレネルレンズ１０３を実現したものである。実効屈折率の小さい部分には断面積の小さい微細柱１０２を（図３（ｄ））、大きい部分には断面積の大きい微細柱１０２を（図３（ｃ））並べて実現される。従来のレリーフ型ホログラムのように高さ方向の制御は行わないので、１回の描画・エッチングプロセスでフレネルレンズ等の回折光学素子を容易に作製することが可能である。また、格子間隔Ｌdx、Ｌdyが狭いため、本質的にゴースト像が発生しない利点がある。
【００３６】
以上の実施形態の説明では、断面が円の微細柱１０２を前提にして説明したが、他の形状でもよい。図４に示す光学素子では、微細柱ではなく微細穴１０４を形成する場合である。この場合は、基板側からの入射角をｑとして前記の式（１）を満たされなくてはならない。ただし、この場合は、Ｌdxはｘ方向の微細穴１０４の繰り返し周期、Ｌdyはｙ方向の微細穴１０４の繰り返し周期である。図４中の領域Ｃは、微細穴１０４の断面積が大きく実効屈折率が小さい。領域Ｄでは、逆に実効屈折率が大きい。
【００３７】
図５（ａ）に示すのは、微細柱１０２（微細穴１０４）の断面形状を円形ではなく矩形としたものである。矩形の方が占有率（格子内の微細柱（微細穴）の占める割合）を増やすことができるので、回折光学素子を構成する場合に、高さを低くすることができる。図５（ｂ）に示すのは、断面形状を円形ではなく楕円としたものである。このように異方性を持たせると、実効屈折率にも異方性を持たせることが可能であり、偏光素子への適用が可能になる。図５（ｃ）に示すのは、正方格子でなく六方格子を利用するものである。また、図５（ｄ）に示すのは、正方格子でなく、一般の矩形格子を利用するものである。また、図６に示すのは、左回りに徐々に小さい断面積の微細柱１０２とする構成である。その他、上記の組み合わせが考えられるが、微細構造の断面形状と配置を制御することによって、実効屈折率を制御する点では同一であり、本発明に含まれるものである。また、各格子に配置される微細柱１０２（微細穴１０４）の断面形状は、互いに相似形でなくともよいのは言うまでもない。
【００３８】
（第２の実施形態）
図７に、本発明による光学素子の第２の実施形態を示す。図７（ａ）はこの光学素子である導波路の平面図、（ｂ）はその側面図、（ｃ）は（ｂ）の上部クラッド層部の拡大図である。ここで、４０１は基板、４０２は下部クラッド層、４０３はコア層、４０４は上部クラッド層である。導波路は、ガラス、半導体、誘電体等で構成されている。本実施形態では、上部クラッド層４０４に周期的構造４０５が形成されている。周期的構造４０５中のクラッド材質の占める部分が多い領域は、実効屈折率が高くなり（図の“Ｈ”）、クラッド材質の占める部分が少ない領域は実効屈折率が低く（図の“Ｌ”）なる。このような構造４０５を導波光の電界が存在する部分に配置すると、通常の回折格子と同様に特定の波長近傍の波長に対して高い反射率を持たせることができる。このときの中心波長をＬm 、高屈折領域の屈折率と伝搬方向の長さをｎ_H 、Ｌ_H 、低屈折率領域の屈折率と伝搬方向の長さをｎ_L 、Ｌ_L とすれば、次式が満たされる。
【００３９】
４ｎ_L Ｌ_L ＝４ｎ_H Ｌ_H ＝Ｌm ・・・（２）
図８（ａ）に示すように、同様の周期的構造４０５の法線方向を光の伝搬方向に対して傾けると、この図に示すように、ＴＥモードとＴＭモードを分離するモード分離回路を構成することができる。なお、図８（ｂ）は（ａ）の周期的構造４０５の拡大図である。
【００４０】
（第３の実施形態）
図９に、本発明による光学素子の第３の実施形態を示す。図９（ａ）にこの光学素子である導波路の平面図、（ｂ）に側面図、（ｃ）に右端面図である。ここで、５０１は下部基板、５０２は誘電体多層膜ミラー、５０３はコア層、５０４は誘電体多層膜ミラー、５０５は上部基板である。また、コア層５０３は、高屈折率微細領域５０６、低屈折率微細領域５０７、微細構造のない部分５０８に分けられる。この構成において、下部基板５０１上に、誘電体多層膜ミラー５０２、高屈折率微細領域５０６、低屈折率微細領域５０７、微細構造のない部分５０８を作製し、別途上部基板５０５上に誘電体多層膜ミラー５０４を作製して、両者を貼り合わせて作製される。また、高屈折率微細領域５０６の実効屈折率をｎ_H 、低屈折率微細領域５０７の実効屈折率をｎ_L とすると、次式が成立する。
【００４１】
ｎ_H ＞ｎ_L ・・・（３）
このとき、基板５０１、５０５に垂直な方向に対しては、非導波構造であるが、上下誘電体多層膜ミラー５０２、５０４との界面で光は全反射して閉じ込められる。また、基板５０１、５０５の面内方向に対しては、高屈折率微細領域５０６が低屈折率微細領域５０７に対して高い屈折率を持つため、光が閉じ込められる。
【００４２】
従来のコア空洞型導波路では、コア層側面のエッチングの際に平滑なエッチングが難しく、低損失な導波路を作製することができなかったが、上記の方法によって低損失な導波路を構成することができる。
【００４３】
また、図９に示す本実施形態においても、高屈折率微細領域５０６を空洞としたコア空洞型導波路にすることも可能である。この場合、低屈折率微細領域５０７は波長程度の大きい周期を持たせ、高い反射率を持つようにする。この導波路では、光伝搬領域における物質密度が低いため、温度依存性の小さい導波回路を構成することが可能となる。
【００４４】
また、図１０に図９と同様の図を示すように、誘電体多層膜ミラー５０２及び５０４の代わりに、クラッド層５０９及び５１０を利用することができる。この場合は、上下方向にも通常の導波構造となり、クラッド層５０９及び５１０の屈折率をｎ_cl1 及びｎ_cl2 とすると、次式が満たされる。
【００４５】
ｎ_H ＞ｎ_cl1 ，ｎ_cl2 ・・・（４）
（第４の実施形態）
図１１に、本発明による光学素子の第４の実施形態の図２と同様の図を示す。
本実施形態では、微細柱１０２や微細穴１０４の重心位置を格子点から意図的に変位させる。本実施形態では、第１の実施形態と異なり、（平均）格子間隔がＬm ／｛２（１＋ｓｉｎｑ）｝よりも大きい場合もある。微細柱１０２や微細穴１０４の重心位置を変位させないで格子点上に配置した場合は、コヒーレントな垂直入射光は図１２（ａ）に散乱角を示すような角度に回折される。重心位置を図１１に示すように格子点からランダムに変位させると、図１２（ｂ）に示すように回折角度が分布する。すなわち、入射光を効果的に散乱させることが可能になり、物体の照明に有効な光学素子となる。また、同様の効果は、微細柱あるいは微細穴の断面積をランダムに変化させることによっても実現可能である。これらのランダムな変位は、計算機の疑似雑音発生関数等を利用して容易に設定することが可能である。その変位の平均値、分布関数を選択することによって、散乱角度分布を制御することも可能である。例えば正規分布に従う雑音を利用すれば、正規分布型の散乱角度分布を実現することが可能である。また、変位の平均値に比例して角度分布が広がることになる。
【００４６】
（第５の実施形態）
図１３に、本発明による光学素子の第５の実施形態を示す。図１３（ａ）は図２と同様の図であり、（ｂ）はその微細柱１０２又は微細穴１０４の存在を数列で表現した図である。本実施形態では、微細柱１０２又は微細穴１０４が格子上に存在するか、あるいは、存在しないかをＭ系列等の２値の疑似雑音系列によって決定する。例えば、図１３では、第１行はＭ系列に属する１５ビットの系列（１，１，０，０，０，１，０，０，１，１，０，１，０，１，１）に従って微細柱１０２（微細穴１０４）の有無を決定している。第２行以下は、同じ系列を１ビット分サイクリックにシフトして微細柱１０２（微細穴１０４）の有無を決定している。Ｍ系列では、サイクリックにシフトした系列も同じＭ系列に属する。
また、このようにすれば、列方向にも同じ１５ビットのＭ系列になっていることは言うまでもない。本実施形態では、説明の都合で短い１５ビット×１５ビットのセルを構成しているが、長いＭ系列を利用すれば、大きいセルが構成できることは言うまでもない。このような疑似雑音系列を利用すると、図１４（ａ）に示すように、多数の（図では全部示していない）回折ピークが生じる。これに、第４の実施形態に示したような変位を加えると、図１４（ｂ）に示すように、各回折ピークが広がり、広い角度範囲にわたって均一に光を散乱する光学素子を実現することが可能になる。また、図１５（ａ）及び（ｂ）の矢印に示すように、疑似雑音系列の微細柱１０２又は微細穴１０４の有無のマッピングの順序は、各種の方法を利用することができるのは言うまでもない。図１５（ａ）の場合は、中心から外周へ螺旋状に疑似雑音系列を適用する。疑似雑音系列が途中で切れた場合は、その次から同じ疑似雑音系列を繰り返す。図１５（ｂ）の場合は、疑似雑音系列の適用を行が替わる毎に反転させている。
【００４７】
（第６の実施形態）
図１６（ａ）に、本発明による光学素子を用いた装置の第６の実施形態を示す。ここで、８０１及び８０２は位置合わせを行う物体、８０３ａ及び８０３ｂは正レンズ、８０４ａ及び８０４ｂは第５の実施形態の２値の疑似雑音系列に従って作製された微細柱（穴）アレイの同一のものであって、それぞれ位置合わせを行う物体８０１、８０２に取り付けられている。８０５は受光素子である。この系では４ｆ光学系を構成しており、２つの微細柱（穴）アレイ８０４ａと８０４ｂが互いに等倍結像の関係になるように、すなわち、正レンズ８０３ａの焦点距離の２倍の距離の物体面に微細柱（穴）アレイ８０４ａが配置され、正レンズ８０３ａの焦点距離の２倍の距離の像面に微細柱（穴）アレイ８０４ｂが配置されている。
【００４８】
本実施形態に利用する微細柱（穴）アレイ８０４ａ及び８０４ｂでは、微細柱（穴）の高さ（深さ）を微細柱（穴）のない部分に比較して位相差がπになるように設定されている。このため、微細柱（穴）アレイ８０４ａと８０４ｂが完全に互いに１：１で結像する位置にあるとき、平面波を入射して微細柱（穴）アレイ８０４ａ及び８０４ｂの両者を透過させると、微細柱（穴）による位相変化がキャンセルされて（２πになって）再び平面波になり、正レンズ８０３ｂで点状に集光され、受光素子８０５に入射する。ところが、微細柱（穴）アレイ８０４ａと８０４ｂの位置が相対的にずれていると、微細柱（穴）アレイ８０４ａと８０４ｂの両者を透過した光は、疑似雑音系列に基づく位相変化をシフトして２回受けている。ここで、Ｍ系列の場合は、これに対応するシフト演算を行うと、再びＭ系列が生じることが数学的に示されている。すなわち、微細柱（穴）アレイ８０４ｂを透過した透過光は、結局疑似雑音系列に従って位相変化を受けていることになるため、正レンズ８０３ｂで集光すると、微細柱（穴）アレイ８０４ｂが正レンズ８０３ｂの前側焦点面に配置され、受光素子８０５が後側焦点面に配置されているので、微細柱（穴）アレイ８０４ｂでの回折角度が集光位置に変換され、多数の点に結像する。受光素子８０５の受光面を十分に小さくしておけば、微細柱（穴）アレイ８０４ａと８０４ｂの位置が一致する場合と不一致な場合での受光光強度が変化するので、この情報を利用して物体８０１及び８０２の位置合わせを高精度で行うことが可能になる。
【００４９】
図１６（ｂ）は、位置合わせを行う物体８０１と８０２が極めて近接している場合であり、図１６（ａ）の正レンズ８０３ａを除いて、入射光が続けて微細柱（穴）アレイ８０４ａと８０４ｂを透過するように配置したものであり、図１６（ａ）の場合と同様に、物体８０１及び８０２の位置合わせを高精度で行うことが可能である。
【００５０】
（第７の実施形態）
図１７に、本発明による光学素子を用いた装置の第７の実施形態を示す。ここで、９０１は光信号を入力する光ファイバ、９０２ａ及び９０２ｂは正レンズ、９０３ａ及び９０３ｂは第５の実施形態の２値の疑似雑音系列に従って作製された微細柱（穴）アレイの同一のもの、９０４は受光素子である。
【００５１】
本実施形態は、空間光通信装置に疑似雑音系列による位相フィルタを適用したものである。空間光通信装置では、望遠レンズを利用して送信器からの光を受光器に結像するが、周囲からの迷光が避けられず、Ｓ／Ｎ比が悪くなりがちである。本実施形態では、第６の実施形態と同様に、送信側で疑似雑音系列による位相フィルタ、すなわち、微細柱（穴）アレイ９０３ａを透過した信号は、受信側の位相フィルタ、すなわち、微細柱（穴）アレイ９０３ｂでキャンセルされるので、受光素子９０４上に結像するが、迷光は受信側でのみ位相フィルタ９０３ｂを透過するので、拡散されて受光素子９０４上にはほとんど結像しない。この効果を利用して、Ｓ／Ｎの高い空間光通信装置を構成できる。また、疑似雑音系列を秘密とすれば、通信の秘匿性も高めることができる。
【００５２】
以上、本発明の光学素子及びその光学素子を用いた装置をいくつかの実施形態に基づいて説明してきたが、本発明はこれらの実施形態に限定されず種々の変形が可能である。
【００５３】
【発明の効果】
以上の説明から明らかなように、本発明によれば、微細柱又は微細穴の断面形状を制御することによって、局所的な屈折率を制御することが可能になり、多彩な光学素子を作製することができる。この場合に、微細柱の高さ、微細穴の深さは一定であるため、１回のエッチングプロセスで作製することができる。また、１次以上の回折光を生じないので、ゴースト像も発生しない。さらに、疑似雑音系列を利用して微細柱又は微細穴の重心位置、断面積、有無をランダムに変化させることによって、等方的にあるいは任意の角度分布で光を散乱させる光散乱素子を作製することが可能になる。さらには、このような光学素子を用いて２つの物体の位置合わせを高精度で行う装置や、Ｓ／Ｎの高い空間光通信装置等を構成することができる。
【図面の簡単な説明】
【図１】本発明による光学素子の第１の実施形態の斜視図である。
【図２】図１の光学素子の微細柱部分の基板に平行な断面図である。
【図３】具体的な回折光学素子の一例であるフレネルレンズを示す図である。
【図４】微細柱の変わりに微細穴を形成する場合の図２と同様の図である。
【図５】微細柱（微細穴）の断面形状の変形例を示す図である。
【図６】微細柱（微細穴）の断面形状の他の変形例を示す図である。
【図７】本発明による光学素子の第２の実施形態を示す図である。
【図８】第２の実施形態の光学素子の変形例を示す図である。
【図９】本発明による光学素子の第３の実施形態を示す図である。
【図１０】第３の実施形態の光学素子の変形例を示す図である。
【図１１】本発明による光学素子の第４の実施形態の図２と同様の図である。
【図１２】図１１の構成で重心位置を変位させない場合と変位させた場合の回折角分布を示す図である。
【図１３】本発明による光学素子の第５の実施形態を示す図である。
【図１４】第５の実施形態の光学素子の回折角分布を示す図である。
【図１５】疑似雑音系列の微細柱又は微細穴の有無のマッピングの順序の例を示す図である。
【図１６】本発明による光学素子を用いた装置の第６の実施形態を示す図である。
【図１７】本発明による光学素子を用いた装置の第７の実施形態を示す図である。
【図１８】従来技術のサブ波長構造を有する回折格子を説明するための図である。
【図１９】従来技術の低反射構造を説明するための図である。
【図２０】従来技術のレリーフ型ホログラムを説明するための図である。
【図２１】従来技術の非導波構造を利用する導波路を説明するための図である。
【符号の説明】
１０１…基板
１０２…微細柱
１０３…フレネルレンズ
１０４…微細穴
２０１…下部基板
２０２…下部クラッド層
２０３…コア部（空洞）
２０４…上部クラッド層
２０５…上部基板
２０６…多層膜ミラー又は金属ミラー
４０１…基板
４０２…下部クラッド層
４０３…コア層
４０４…上部クラッド層
４０５…周期的構造
５０１…下部基板
５０２…誘電体多層膜ミラー
５０３…コア層
５０４…誘電体多層膜ミラー
５０５…上部基板
５０６…高屈折率微細領域
５０７…低屈折率微細領域
５０８…微細構造のない部分
５０９、５１０…クラッド層
８０１、８０２…位置合わせを行う物体
８０３ａ、８０３ｂ…正レンズ
８０４ａ、８０４ｂ…微細柱（穴）アレイ
８０５…受光素子
９０１…光信号を入力する光ファイバ
９０２ａ、９０２ｂ…正レンズ
９０３ａ、９０３ｂ…微細柱（穴）アレイ
９０４…受光素子
ｐ…位相部
ｂ…基板
ｓ…セル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical element and an apparatus using the optical element, and more particularly to an optical element in which a fine column or a fine hole structure is formed on a substrate surface and an apparatus using the optical element.
[0002]
[Prior art]
The optical element according to the present invention to be described later modulates the wavefront of light and has functions such as imaging, collimation, and spectroscopy, and is effective when applied to a wide range of optical systems.
[0003]
Conventionally, a photonic crystal in which a large number of minute holes (columns) are regularly arranged on a substrate is a known technique. In photonic crystals, various devices having a high-resolution spectroscopic function, an acute angle optical path conversion function, and the like can be realized. In this photonic crystal, in order to have a strong interaction with light at the wavelength used, the first-order diffracted light must be reflected multiple times.
[0004]
Incidentally, since the first and second optical elements of the present invention described later function in a region where diffracted light having a diffraction order of the first order or higher does not occur, a photonic crystal using such first-order diffracted light Are different.
[0005]
Furthermore, there has been no technique for controlling the local refractive index by locally modulating the shape of the fine holes (columns) in the photonic crystal.
[0006]
Further, in the fifth and tenth optical elements of the present invention to be described later, since the minute holes or the minute pillars are intentionally displaced randomly from the lattice position or the shape is changed randomly, the conventional photonic crystal is Is different.
[0007]
The eleventh to fifteenth optical elements and devices of the present invention are different from conventional photonic crystals in that a large number of lattice defects are provided according to a pseudo-noise sequence.
[0008]
Specific applications of the optical element according to the present invention will be apparent from the following description, and are (1) a diffractive optical element, (2) an optical waveguide element, and (3) a light scattering element.
[0009]
As a prior art relating to (1), there are a diffraction grating having a sub-wavelength structure shown in FIG. 18, a low reflection structure shown in FIG. 19, and a relief hologram shown in FIG. FIG. 18A is a plan view of the phase portion p, and FIG. 18B is a cross-sectional view thereof. In this diffraction grating, the period of the phase portion p is set so that D1 <Lm <D2 with respect to the operating wavelength Lm. Similar to the blazed diffraction grating, this diffraction grating can increase the diffraction efficiency of + (−) first-order diffracted light. Further, this low reflection structure, which is a plan view of the phase portion p in FIG. 19A and a cross-sectional view thereof in FIG. 19B, reduces the effective refractive index of the surface by the fine structure of the phase portion p and is perpendicular to the surface. By providing a gradient in the phase portion p in the direction (direction toward the substrate b), it is possible to reduce the reflectance. In these prior arts, there is no two-dimensional modulation of the shape of a fine column or fine hole to provide an imaging function, a collimating function, or the like.
[0010]
20A is a plan view, and FIG. 20B is a relief hologram showing a cross-sectional view along the line AB in FIG. 20A, the phase of the hologram surface is modulated by modulating the height of each cell s. A hologram is constructed. FIG. 20 shows that the height varies between cells A and B for each cell s. Such a relief hologram has a high diffraction efficiency, but a hologram having many phase steps requires a number of etching processes and is difficult to manufacture. In addition, there is a problem that high-order diffracted light corresponding to the period (spatial frequency) of the cell s is generated.
[0011]
In addition, the diffraction grating in the conventional waveguide is manufactured by modulating the position of the cladding outside the waveguide layer or the interface between the cladding layer and the core layer, or by utilizing the ultraviolet light induced refractive index change. The refractive index control range is small.
[0012]
Further, there is a waveguide using a non-waveguide structure as shown in a plan view in FIG. 21A, a side view in FIG. 21B, and a right end view in FIG. Here, 201 is a lower substrate, 202 is a lower clad layer, 203 is a core (cavity), 204 is an upper clad layer, 205 is an upper substrate, and 206 is a multilayer mirror or a metal mirror. The locations where the upper and lower substrates are bonded are indicated by dotted lines. In a normal waveguide, the refractive index of the core portion is made higher than that of the surrounding cladding portion to confine light. However, in the non-waveguide structure of FIG. 21, the propagating waveguide is the hollow core 203 and the surrounding cladding portions 202 and 204. , 206 is propagated by total reflection (including multilayer and metal reflection). That is, in the direction perpendicular to the substrate, confinement is performed by a non-waveguide structure due to reflection by the multilayer mirror or metal mirror 206. Further, since the groove widths at the upper and lower portions of the cavity are different from each other in the direction parallel to the substrate, the effective refractive index on both sides of the cavity core 203 is lowered and light is confined. The problem with this configuration is that the loss in the lateral direction (direction parallel to the substrate) is increased due to the disorder of the etching end face (cavity interface).
[0013]
Further, the conventional light scattering element is configured by providing disordered scratches on the surface or dispersing particles like a colloid in order to scatter like frosted glass, for example. In these methods, the scattering angle distribution of the scattered light cannot be freely controlled, and generally, the light having an angle component in the same direction as the incident light increases.
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems of the prior art, and its purpose is to have high diffraction efficiency, various functions such as imaging and collimation, easy production, and hardly generating a ghost image. It is to provide a diffractive optical element. Another object is to provide a diffraction grating structure having a wide refractive index control range that can be used for a waveguide. Still another object is to provide an optical waveguide device having a low-loss non-waveguide structure. Another object of the present invention is to provide a light scattering element capable of controlling the scattering angle distribution of scattered light and capable of scattering light isotropically. Is to provide a device.
[0015]
[Means for Solving the Problems]
The first optical element of the present invention has a plurality of fine pillars on a substrate, a used wavelength is Lm, an incident angle to the substrate is q, and an x-direction lattice spacing on an axis (x, y) orthogonal to the substrate. Is Ldx and the y-direction lattice spacing is Ldy,
Ldx <Lm / {2 (1 + sinq)},
Ldy <Lm / {2 (1 + sinq)}
... (1)
And the fine column cross-sectional area is modulated according to the position on the substrate surface, where the x-direction cross-sectional width of the fine column is Dhx (<Ldx) and the y-direction cross-sectional width of the fine column is Dhy (<Ldy) Further, it is characterized in that first-order or higher-order diffracted light does not occur in a portion where the cross-sectional area of the fine column adjacent to the transmitted light is the same.
[0016]
The second optical element of the present invention has a plurality of fine holes on the substrate, the wavelength used is Lm, the incident angle to the substrate is q, and the x-direction lattice spacing on the axes (x, y) orthogonal to the substrate. Is Ldx and the y-direction lattice spacing is Ldy,
Ldx <Lm / {2 (1 + sinq)},
Ldy <Lm / {2 (1 + sinq)}
... (1)
And the cross-sectional area of the microhole is modulated according to the position on the substrate surface, where Dhx (<Ldx) is the cross-sectional width of the microhole and Dhy (<Ldy) is the cross-sectional width of the microhole. It is characterized in that first-order or higher-order diffracted light does not occur at a location where the cross-sectional area of the fine hole adjacent to the transmitted light is the same.
[0017]
According to a third optical element of the present invention, in an optical waveguide comprising a lower cladding layer, a core layer, and an upper cladding layer formed on a substrate, the fineness of the first or second optical element is formed on the upper cladding layer or the lower cladding layer. Columns or fine holes are formed.
[0018]
According to a fourth optical element of the present invention, in the optical waveguide composed of a lower clad layer, a core layer, and an upper clad layer formed on a substrate, a fine column or fine hole of the first or second optical element is formed in the core layer. It is characterized by being formed.
[0019]
The fifth optical element of the present invention has a plurality of fine pillars on the substrate, and with respect to lattice points of the x-direction lattice spacing Ldx and the y-direction lattice spacing Ldy on the axes (x, y) perpendicular to the substrate. The center of gravity of the cross section of the fine column is randomly displaced.
[0020]
The sixth optical element of the present invention has a plurality of fine holes on the substrate, and the lattice points of the x-direction lattice spacing Ldx and the y-direction lattice spacing Ldy on the axes (x, y) perpendicular to the substrate. The center of gravity of the cross section of the fine hole is randomly displaced.
[0021]
The seventh optical element of the present invention is characterized in that, in the fifth or seventh optical element, the displacement of the center of gravity is determined by a pseudo-noise sequence and is pseudo-disorderly displaced.
[0022]
The eighth optical element of the present invention is characterized in that, in the first or sixth optical element, the area of the fine column cross section changes randomly.
[0023]
The ninth optical element of the present invention is characterized in that, in the second or seventh optical element, the area of the cross section of the fine hole is changed randomly.
[0024]
The tenth optical element of the present invention is characterized in that, in the eighth or ninth optical element, the displacement of the area is determined by a pseudo-noise sequence and changes pseudo-disorderly.
[0025]
The eleventh optical element of the present invention has a plurality of fine columns on the substrate, and the lattice points of the x-direction lattice spacing Ldx and the y-direction lattice spacing Ldy on the axes (x, y) perpendicular to the substrate. Then, the binary value when the fine column is present and when the fine column is not present are modulated in accordance with a pseudo noise sequence.
[0026]
The twelfth optical element of the present invention has a plurality of fine holes on the substrate, and the lattice points of the x-direction lattice spacing Ldx and the y-direction lattice spacing Ldy on the axes (x, y) perpendicular to the substrate. Then, the binary value when the fine hole is present and when the fine hole is not present are modulated in accordance with the pseudo-noise sequence.
[0027]
In a thirteenth object aligning device of the present invention, two of the eleventh or twelfth optical elements that are the same are attached to two objects, and light is transmitted or reflected in tandem with the optical elements. It is characterized by comprising a condensing optical system that collects and collects transmitted or reflected light and a detection element that detects the collected light.
[0028]
The fourteenth optical communication apparatus of the present invention comprises one of two eleventh or twelfth optical elements that are the same on the emission surface of the transmitter for spatial light communication, and the other optical element. It is provided on the incident surface of the receiver for spatial light communication.
[0029]
In the optical element of the present invention and the apparatus using the optical element, it is possible to control the local refractive index by controlling the cross-sectional shape of the fine column or the fine hole. An element can be manufactured. In this case, since the height of the fine column and the depth of the fine hole are constant, the fine column can be manufactured by a single etching process. Further, since no first-order or higher-order diffracted light is generated, no ghost image is generated. Furthermore, a light scattering element that scatters light isotropically or with an arbitrary angular distribution is produced by randomly changing the center of gravity position, cross-sectional area, and presence / absence of a minute column or hole using a pseudo noise sequence. It becomes possible. Furthermore, it is possible to configure a device that highly accurately aligns two objects using such an optical element, a spatial optical communication device with a high S / N, and the like.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an optical element of the present invention and an apparatus using the optical element will be described below in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.
[0031]
(First embodiment)
FIG. 1 shows a perspective view of a first embodiment of an optical element according to the present invention. Here, reference numeral 101 denotes a substrate, and reference numeral 102 denotes a fine column manufactured on the substrate 101. For example, as the substrate 101 and the fine pillars thereon, a glass material such as quartz, a semiconductor material such as silicon, a ceramic material such as alumina, an organic material such as polyimide and PMMA, and a metal material such as nickel can be used. . When this optical element is used as a reflection type, a metal such as gold or chromium may be deposited on the surface. FIG. 2 shows a cross-sectional view parallel to the substrate 101 in the fine pillar 102 portion. Here, Ldx is the lattice spacing in the x direction (repetition period of the fine pillars 102), Ldy is the lattice spacing in the y direction, Dhx is the sectional width of the fine pillars 102 in the x direction, and Dhy is the sectional width of the fine pillars 102 in the y direction. It is.
[0032]
In this embodiment, assuming that the operating wavelength is Lm and the incident angle from the substrate 101 side is q,

It is configured so that the relationship is satisfied.
[0033]
Under this condition (1), the structure including the fine pillars 102 is sufficiently fine compared to the wavelength, and first-order or higher-order diffracted light is not generated with respect to transmitted light. That is, it is a finer structure than a periodic fine structure used for an acute angle bending structure, a super prism, or the like, a so-called photonic crystal. However, as a general performance of an electron beam lithography system, a resist pattern of about 50 nm can be formed, and thus a structure satisfying the above condition (1) is produced for light in a region from visible light to infrared light. It is possible to do. For example, by using a fine pattern mask formed by an electron beam drawing apparatus, the fine pillars 102 conforming to a required pattern can be produced by reactive ion etching or the like.
[0034]
In the present invention, the local effective refractive index of the material is controlled by controlling the cross-sectional area of the fine column 102. In the area A of FIG. 2, the cross-sectional area of the fine column 102 is large and the effective refractive index is high, and in the area B, the effective refractive index is low. When the transmission type is used, in the zero order approximation, the effective relative permittivity is the volume weight of the relative permittivity of the portion without the fine column (usually, air or vacuum, the relative permittivity is about 1) and the portion of the fine column 102. Average. For example, with respect to the circular fine column 102, Lm is 1.55 μm, np (refractive index of the fine column 102 portion) is 1.5, Ldx and Ldy are 0.25 μm, and Dhx and Dhy are 0.1 to 0.3. The height of the fine column 102 is 5 μm. At this time, the effective refractive index can be changed from 1.076 to 1.408, and 2.14π is obtained as the maximum phase difference.
[0035]
In this way, various diffractive optical elements can be realized by controlling the local effective refractive index. FIG. 3 shows a Fresnel lens 103 as an example of a specific diffractive optical element. 3A is a plan view of the Fresnel lens 103, FIG. 3B is a diagram showing the effective refractive index distribution on one side from the optical axis, and FIGS. 3C and 3D are views of the fine column 102 in two different portions. It is a figure which shows a shape. In this example, the Fresnel lens 103 is realized by the refractive index control according to the present invention. The fine column 102 having a small cross-sectional area (FIG. 3D) is arranged in a portion having a small effective refractive index (FIG. 3D), and the fine column 102 having a large cross-sectional area is arranged in a large portion (FIG. 3C). Since the height direction is not controlled unlike a conventional relief hologram, it is possible to easily produce a diffractive optical element such as a Fresnel lens by one drawing / etching process. In addition, since the lattice spacings Ldx and Ldy are narrow, there is an advantage that a ghost image does not occur essentially.
[0036]
In the above description of the embodiment, the description has been made on the premise of the fine column 102 having a circular cross section, but other shapes may be used. In the optical element shown in FIG. 4, the minute hole 104 is formed instead of the minute pillar. In this case, the above formula (1) must be satisfied with the incident angle from the substrate side as q. However, in this case, Ldx is the repetition period of the micro hole 104 in the x direction, and Ldy is the repetition period of the micro hole 104 in the y direction. In the region C in FIG. 4, the cross-sectional area of the microhole 104 is large and the effective refractive index is small. In the region D, the effective refractive index is large.
[0037]
FIG. 5A shows that the cross-sectional shape of the fine column 102 (fine hole 104) is not circular but rectangular. Since the rectangular shape can increase the occupation ratio (ratio occupied by fine columns (fine holes) in the lattice), the height can be lowered when a diffractive optical element is formed. FIG. 5B shows a cross-sectional shape that is not a circle but an ellipse. When anisotropy is provided in this way, the effective refractive index can also be provided with anisotropy and can be applied to a polarizing element. FIG. 5 (c) uses a hexagonal lattice instead of a square lattice. Further, FIG. 5D shows that a general rectangular lattice is used instead of a square lattice. Further, FIG. 6 shows a configuration in which the fine pillars 102 having a gradually small cross-sectional area are formed counterclockwise. In addition, the above combinations are conceivable, but the same is true in that the effective refractive index is controlled by controlling the cross-sectional shape and arrangement of the fine structure, and are included in the present invention. Needless to say, the cross-sectional shapes of the fine pillars 102 (fine holes 104) arranged in each lattice need not be similar to each other.
[0038]
(Second Embodiment)
FIG. 7 shows a second embodiment of the optical element according to the present invention. FIG. 7A is a plan view of a waveguide which is this optical element, FIG. 7B is a side view thereof, and FIG. 7C is an enlarged view of the upper clad layer portion of FIG. Here, 401 is a substrate, 402 is a lower cladding layer, 403 is a core layer, and 404 is an upper cladding layer. The waveguide is made of glass, semiconductor, dielectric, or the like. In the present embodiment, the periodic structure 405 is formed in the upper cladding layer 404. In the periodic structure 405, a region where the cladding material occupies a large portion has a high effective refractive index ("H" in the figure), and a region where the cladding material occupies a small portion has a low effective refractive index ("L" in the drawing). )Become. When such a structure 405 is arranged in a portion where an electric field of guided light exists, a high reflectance can be given to a wavelength near a specific wavelength as in a normal diffraction grating. The central wavelength at this time is Lm, and the refractive index of the high refractive region and the length in the propagation direction are n. _H , L _H , The refractive index of the low refractive index region and the length in the propagation direction are n _L , L _L Then, the following equation is satisfied.
[0039]
4n _L L _L = 4n _H L _H = Lm (2)
As shown in FIG. 8A, when the normal direction of a similar periodic structure 405 is tilted with respect to the light propagation direction, a mode separation circuit for separating the TE mode and the TM mode is provided as shown in FIG. Can be configured. FIG. 8B is an enlarged view of the periodic structure 405 in FIG.
[0040]
(Third embodiment)
FIG. 9 shows a third embodiment of the optical element according to the present invention. FIG. 9A is a plan view of a waveguide as the optical element, FIG. 9B is a side view, and FIG. 9C is a right end view. Here, 501 is a lower substrate, 502 is a dielectric multilayer mirror, 503 is a core layer, 504 is a dielectric multilayer mirror, and 505 is an upper substrate. The core layer 503 is divided into a high refractive index fine region 506, a low refractive index fine region 507, and a portion 508 having no fine structure. In this configuration, a dielectric multilayer film mirror 502, a high refractive index fine region 506, a low refractive index fine region 507, and a portion 508 having no fine structure are formed on a lower substrate 501, and a dielectric multilayer is separately formed on the upper substrate 505. The film mirror 504 is manufactured and bonded together. Further, the effective refractive index of the high refractive index fine region 506 is set to n _H , The effective refractive index of the low refractive index fine region 507 is n _L Then, the following equation is established.
[0041]
n _H > N _L ... (3)
At this time, although it has a non-waveguide structure in the direction perpendicular to the substrates 501 and 505, light is totally reflected and confined at the interface with the upper and lower dielectric multilayer mirrors 502 and 504. In addition, in the in-plane direction of the substrates 501 and 505, the high refractive index fine region 506 has a higher refractive index than the low refractive index fine region 507, so that light is confined.
[0042]
In conventional core-cavity waveguides, smooth etching is difficult when etching the side surface of the core layer, and a low-loss waveguide cannot be produced. However, a low-loss waveguide is formed by the above method. be able to.
[0043]
Also in the present embodiment shown in FIG. 9, it is possible to make a core cavity type waveguide having the high refractive index fine region 506 as a cavity. In this case, the low refractive index fine region 507 has a period as large as the wavelength, and has a high reflectance. In this waveguide, since the material density in the light propagation region is low, it is possible to configure a waveguide circuit with low temperature dependence.
[0044]
Further, as shown in FIG. 10 similar to FIG. 9, cladding layers 509 and 510 can be used instead of the dielectric multilayer mirrors 502 and 504. In this case, a normal waveguide structure is formed also in the vertical direction, and the refractive indexes of the cladding layers 509 and 510 are set to n. _cl1 And n _cl2 Then, the following equation is satisfied.
[0045]
n _H > N _cl1 , N _cl2 ... (4)
(Fourth embodiment)
FIG. 11 is a view similar to FIG. 2 of the fourth embodiment of the optical element according to the present invention.
In this embodiment, the gravity center positions of the fine pillars 102 and the fine holes 104 are intentionally displaced from the lattice points. In the present embodiment, unlike the first embodiment, the (average) lattice spacing may be larger than Lm / {2 (1 + sinq)}. When the centroid positions of the fine pillars 102 and the fine holes 104 are arranged on the lattice points without being displaced, the coherent perpendicular incident light is diffracted to an angle that indicates a scattering angle in FIG. When the position of the center of gravity is randomly displaced from the lattice point as shown in FIG. 11, the diffraction angles are distributed as shown in FIG. That is, incident light can be effectively scattered, and the optical element is effective for illuminating an object. The same effect can also be realized by randomly changing the cross-sectional area of the fine column or fine hole. These random displacements can be easily set using a pseudo-noise generation function of a computer. It is also possible to control the scattering angle distribution by selecting the average value of the displacement and the distribution function. For example, if noise according to a normal distribution is used, a normal distribution type scattering angle distribution can be realized. In addition, the angular distribution spreads in proportion to the average value of displacement.
[0046]
(Fifth embodiment)
FIG. 13 shows a fifth embodiment of the optical element according to the present invention. FIG. 13A is a diagram similar to FIG. 2, and FIG. 13B is a diagram expressing the presence of the minute pillars 102 or the minute holes 104 in several sequences. In the present embodiment, whether or not the fine column 102 or the fine hole 104 exists on the lattice is determined by a binary pseudo noise sequence such as an M sequence. For example, in FIG. 13, the first row is in accordance with a 15-bit sequence (1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1) belonging to the M sequence. The presence / absence of the fine column 102 (fine hole 104) is determined. In the second and subsequent rows, the same series is cyclically shifted by 1 bit to determine the presence / absence of the fine pillars 102 (fine holes 104). In the M series, the cyclically shifted series also belongs to the same M series.
It goes without saying that if this is done, the same 15-bit M-sequence is formed in the column direction. In this embodiment, a short 15-bit × 15-bit cell is configured for convenience of explanation, but it goes without saying that a large cell can be configured by using a long M-sequence. When such a pseudo-noise sequence is used, a large number of diffraction peaks (not shown in the figure) are generated as shown in FIG. When a displacement as shown in the fourth embodiment is added to this, as shown in FIG. 14B, each diffraction peak spreads, and an optical element that uniformly scatters light over a wide angular range is realized. Is possible. Further, as shown by the arrows in FIGS. 15A and 15B, it is needless to say that various methods can be used for the order of mapping of the presence / absence of the fine column 102 or the fine hole 104 of the pseudo noise sequence. . In the case of FIG. 15A, a pseudo noise sequence is applied spirally from the center to the outer periphery. When the pseudo noise sequence is cut off halfway, the same pseudo noise sequence is repeated from the next. In the case of FIG. 15B, the application of the pseudo noise sequence is reversed every time the line is changed.
[0047]
(Sixth embodiment)
FIG. 16A shows a sixth embodiment of an apparatus using an optical element according to the present invention. Here, 801 and 802 are objects to be aligned, 803a and 803b are positive lenses, and 804a and 804b are the same micro-column (hole) arrays produced according to the binary pseudo-noise sequence of the fifth embodiment. In this case, they are attached to the objects 801 and 802 for positioning. Reference numeral 805 denotes a light receiving element. This system constitutes a 4f optical system so that the two fine column (hole) arrays 804a and 804b are in the same magnification imaging relationship with each other, that is, with a distance twice as long as the focal length of the positive lens 803a. A fine column (hole) array 804a is arranged on the object plane, and a fine column (hole) array 804b is arranged on the image plane whose distance is twice the focal length of the positive lens 803a.
[0048]
In the fine column (hole) arrays 804a and 804b used in the present embodiment, the phase difference is π compared to the height (depth) of the fine column (hole) compared to the portion without the fine column (hole). Is set. For this reason, when the fine column (hole) arrays 804a and 804b are completely in a position where they form an image of 1: 1, if a plane wave is incident and transmitted through both of the fine column (hole) arrays 804a and 804b, The phase change due to the pillar (hole) is canceled (2π), and becomes a plane wave again. The light is condensed into a point shape by the positive lens 803b and enters the light receiving element 805. However, if the positions of the fine column (hole) arrays 804a and 804b are relatively shifted, the light transmitted through both the fine column (hole) arrays 804a and 804b shifts the phase change based on the pseudo-noise sequence. I have received it twice. Here, in the case of the M series, it is mathematically shown that when the shift operation corresponding to this is performed, the M series is generated again. That is, the transmitted light that has passed through the fine column (hole) array 804b eventually undergoes a phase change according to the pseudo-noise sequence, and therefore when condensed by the positive lens 803b, the fine column (hole) array 804b becomes the positive lens. Since the light receiving element 805 is disposed on the rear focal plane, the diffraction angle at the fine column (hole) array 804b is converted into a condensing position and images are formed on a large number of points. . If the light receiving surface of the light receiving element 805 is made sufficiently small, the received light intensity varies depending on whether the positions of the fine column (hole) arrays 804a and 804b coincide with each other. It becomes possible to align the objects 801 and 802 with high accuracy.
[0049]
FIG. 16B shows a case where the objects 801 and 802 to be aligned are very close to each other, and except for the positive lens 803a shown in FIG. 16A, incident light continues and a fine column (hole) array 804a. 804b, and the objects 801 and 802 can be aligned with high accuracy as in the case of FIG.
[0050]
(Seventh embodiment)
FIG. 17 shows a seventh embodiment of the apparatus using the optical element according to the present invention. Here, 901 is an optical fiber for inputting an optical signal, 902a and 902b are positive lenses, 903a and 903b are the same micro-column (hole) array produced according to the binary pseudo-noise sequence of the fifth embodiment. , 904 are light receiving elements.
[0051]
In the present embodiment, a phase filter based on a pseudo-noise sequence is applied to a spatial light communication device. In a spatial light communication apparatus, a telephoto lens is used to form an image of light from a transmitter on a light receiver. However, stray light from the surroundings cannot be avoided, and the S / N ratio tends to deteriorate. In the present embodiment, as in the sixth embodiment, the signal transmitted through the phase filter based on the pseudo noise sequence on the transmission side, that is, the fine column (hole) array 903a, is transmitted to the phase filter on the reception side, ie, the fine column ( Hole) Since it is canceled by the array 903b, it forms an image on the light receiving element 904. However, since stray light passes through the phase filter 903b only on the receiving side, it is diffused and hardly forms an image on the light receiving element 904. Utilizing this effect, a spatial optical communication device with a high S / N can be configured. If the pseudo-noise sequence is kept secret, the confidentiality of communication can be improved.
[0052]
As mentioned above, although the optical element of this invention and the apparatus using the optical element have been demonstrated based on some embodiment, this invention is not limited to these embodiment, A various deformation | transformation is possible.
[0053]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to control the local refractive index by controlling the cross-sectional shape of the fine pillars or fine holes, thereby producing various optical elements. be able to. In this case, since the height of the fine column and the depth of the fine hole are constant, the fine column can be manufactured by a single etching process. Further, since no first-order or higher-order diffracted light is generated, no ghost image is generated. Furthermore, a light scattering element that scatters light isotropically or with an arbitrary angular distribution is produced by randomly changing the center of gravity position, cross-sectional area, and presence / absence of a minute column or hole using a pseudo noise sequence. It becomes possible. Furthermore, it is possible to configure a device that highly accurately aligns two objects using such an optical element, a spatial optical communication device with a high S / N, and the like.
[Brief description of the drawings]
FIG. 1 is a perspective view of a first embodiment of an optical element according to the present invention.
2 is a cross-sectional view parallel to the substrate of the fine column portion of the optical element of FIG.
FIG. 3 is a diagram showing a Fresnel lens as an example of a specific diffractive optical element.
FIG. 4 is a view similar to FIG. 2 in the case where a fine hole is formed instead of a fine pillar.
FIG. 5 is a diagram showing a modification of the cross-sectional shape of a fine column (fine hole).
FIG. 6 is a view showing another modification of the cross-sectional shape of the fine pillar (fine hole).
FIG. 7 is a diagram showing a second embodiment of an optical element according to the present invention.
FIG. 8 is a diagram showing a modification of the optical element of the second embodiment.
FIG. 9 is a diagram showing a third embodiment of an optical element according to the present invention.
FIG. 10 is a diagram illustrating a modification of the optical element according to the third embodiment.
FIG. 11 is a view similar to FIG. 2 of the fourth embodiment of the optical element according to the present invention.
12 is a diagram showing a diffraction angle distribution when the center of gravity position is not displaced and when it is displaced in the configuration of FIG.
FIG. 13 is a diagram showing a fifth embodiment of an optical element according to the present invention.
FIG. 14 is a diagram illustrating a diffraction angle distribution of an optical element according to a fifth embodiment.
FIG. 15 is a diagram illustrating an example of an order of mapping of presence / absence of a minute column or a minute hole of a pseudo noise sequence;
FIG. 16 is a diagram showing a sixth embodiment of an apparatus using an optical element according to the present invention.
FIG. 17 is a diagram showing a seventh embodiment of the apparatus using the optical element according to the present invention.
FIG. 18 is a diagram for explaining a diffraction grating having a sub-wavelength structure according to the prior art.
FIG. 19 is a diagram for explaining a conventional low reflection structure.
FIG. 20 is a diagram for explaining a conventional relief hologram.
FIG. 21 is a diagram for explaining a waveguide using a conventional non-waveguide structure;
[Explanation of symbols]
101 ... Board
102 ... Fine pillar
103 ... Fresnel lens
104 ... Fine hole
201 ... lower substrate
202 ... lower clad layer
203 ... Core part (hollow)
204 ... upper clad layer
205 ... Upper substrate
206 ... Multilayer mirror or metal mirror
401 ... Board
402 ... Lower cladding layer
403 ... Core layer
404 ... upper clad layer
405 ... Periodic structure
501 ... Lower substrate
502 ... Dielectric multilayer mirror
503 ... Core layer
504 ... Dielectric multilayer mirror
505 ... Upper substrate
506 ... High refractive index fine region
507 ... Low refractive index fine region
508 ... Part without fine structure
509, 510 ... cladding layer
801, 802 ... Objects to be aligned
803a, 803b ... Positive lens
804a, 804b ... Fine column (hole) array
805 ... Light receiving element
901 ... Optical fiber for inputting optical signal
902a, 902b ... Positive lens
903a, 903b ... Fine column (hole) array
904 ... Light receiving element
p: Phase part
b ... Board
s ... cell

Claims (14)

The substrate has a plurality of fine columns, the used wavelength is Lm, the incident angle to the substrate is q, the x-direction lattice spacing on the axis (x, y) orthogonal to the substrate is Ldx, and the y-direction lattice spacing is Ldy. and when,
Ldx <Lm / {2 (1 + sinq)},
Ldy <Lm / {2 (1 + sinq)}
... (1)
And the fine column cross-sectional area is modulated according to the position on the substrate surface, where the x-direction cross-sectional width of the fine column is Dhx (<Ldx) and the y-direction cross-sectional width of the fine column is Dhy (<Ldy) An optical element characterized in that first-order or higher-order diffracted light does not occur in a portion where the cross-sectional area of the fine column adjacent to transmitted light is the same . The substrate has a plurality of fine holes, the used wavelength is Lm, the incident angle to the substrate is q, the x-direction lattice spacing on the axis (x, y) orthogonal to the substrate is Ldx, and the y-direction lattice spacing is Ldy. and when,
Ldx <Lm / {2 (1 + sinq)},
Ldy <Lm / {2 (1 + sinq)}
... (1)
And the cross-sectional area of the microhole is modulated according to the position on the substrate surface, where Dhx (<Ldx) is the cross-sectional width of the microhole and Dhy (<Ldy) is the cross-sectional width of the microhole. An optical element characterized in that first-order or higher-order diffracted light does not occur at a location where the cross-sectional area of the fine hole adjacent to the transmitted light is the same .   3. An optical waveguide comprising a lower clad layer, a core layer and an upper clad layer formed on a substrate, wherein the fine pillars or fine holes according to claim 1 or 2 are formed in the upper clad layer or the lower clad layer. An optical element.   An optical element comprising an optical waveguide comprising a lower clad layer, a core layer, and an upper clad layer formed on a substrate, wherein the fine pillars or fine holes according to claim 1 or 2 are formed in the core layer.   The position of the center of gravity of the cross section of the fine pillar with respect to the lattice points of the x-direction lattice spacing Ldx and the y-direction lattice spacing Ldy on the axes (x, y) orthogonal to each other on the substrate. An optical element characterized in that is displaced randomly.   The position of the center of gravity of the cross section of the fine hole with respect to the lattice points of the x-direction lattice interval Ldx and the y-direction lattice interval Ldy on the axes (x, y) orthogonal to each other on the substrate. An optical element characterized in that is displaced randomly.   7. The optical element according to claim 5, wherein the displacement of the center of gravity is determined by a pseudo-noise sequence and is displaced in a pseudo-random manner.   7. The optical element according to claim 1, wherein an area of the cross section of the fine column changes randomly.   The optical element according to claim 2 or 7, wherein an area of the cross section of the fine hole is randomly changed.   The optical element according to claim 8 or 9, wherein the displacement of the area is determined by a pseudo-noise sequence and changes pseudo-disorderly.   A plurality of fine pillars on a substrate, and the fine pillars exist at lattice points of x-direction lattice spacing Ldx and y-direction lattice spacing Ldy on axes (x, y) orthogonal to each other on the substrate; An optical element obtained by modulating a binary value when not present according to a pseudo-noise sequence.   A plurality of fine holes on the substrate, and the fine holes exist at lattice points of the x-direction lattice interval Ldx and the y-direction lattice interval Ldy on the axes (x, y) perpendicular to the substrate; An optical element obtained by modulating a binary value when not present according to a pseudo-noise sequence.   13. The optical element according to claim 11 or 12, wherein two identical elements are attached to two objects, the optical elements are arranged in a column so as to transmit or reflect light, and the transmitted or reflected light is collected. An object alignment apparatus comprising: a condensing optical system for detecting the light and a detection element for detecting the condensed light.   13. The optical element according to claim 11 or 12, wherein one of the same two optical elements is provided on the outgoing surface of the transmitter for spatial light communication, and the other optical element is provided on the incident surface of the receiver for spatial light communication. An optical communication device comprising:

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