JP3374990B2 - Optical circuit characteristic adjustment method - Google Patents
Optical circuit characteristic adjustment methodInfo
- Publication number
- JP3374990B2 JP3374990B2 JP9312593A JP9312593A JP3374990B2 JP 3374990 B2 JP3374990 B2 JP 3374990B2 JP 9312593 A JP9312593 A JP 9312593A JP 9312593 A JP9312593 A JP 9312593A JP 3374990 B2 JP3374990 B2 JP 3374990B2
- Authority
- JP
- Japan
- Prior art keywords
- optical
- refractive index
- optical waveguide
- waveguide
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12166—Manufacturing methods
- G02B2006/12169—Annealing
- G02B2006/12171—Annealing using a laser beam
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Integrated Circuits (AREA)
Description
【発明の詳細な説明】
【０００１】
【産業上の利用分野】本発明は、基板上に形成された光
導波路で構成される光回路の特性を調整する方法に関す
るものである。
【０００２】
【従来の技術】石英ガラス基板やシリコン基板上に形成
可能な石英系光導波路は、損失が低い、安定性が高い、
加工性が良い、石英系光ファイバとの整合性が良い等の
特徴があるため、光合分波回路等の実用的な光回路を構
成する上で非常に有用であることが知られている。最
近、前述した特徴を活かして、より高機能化高集積化し
た平面型光回路の作製が進められているが、その中で、
光の位相を利用した光回路は電子回路では実現しにくい
回路を可能にするため、重要性が高い。
【０００３】石英系光導波路では、シリコン基板上にア
ンダークラッド層堆積→コア層堆積→コアエッチング→
オーバークラッド層堆積という作製プロセスを施すこと
によりコア・クラッド構造が形成されるが、光の位相を
利用した高機能化高集積化光回路において、光の位相は
導波路の屈折率と伝搬長（光路長）に依存するので、作
製上の微小な屈折率や導波路形状の変動及び導波路にか
かる応力が素子特性に大きく影響する。従って、高機能
化高集積化光回路において生産性を向上させるために
は、作製上の微小な変動等を修正する必要があり、局部
的な屈折率の制御を可能とする光回路の特性調整方法の
実現が望まれていた。
【０００４】前述した平面型光回路を構成する重要な要
素である、マッハ・ツェンダ（Mach-Zehnder：ＭＺ）干
渉計を一例として挙げ、以下に局部的な屈折率制御の重
要性について述べる。ＭＺ干渉計は光スイッチや光分波
器を構成する上で欠かすことのできない部品であり、図
２にその一例を示す。
【０００５】図２において、１ａ，１ｂは２つの方向性
結合器、２ａ，２ｂは該方向性結合器１ａ，１ｂを結ぶ
２本の光導波路であり、これらはシリコン基板３上に形
成されている。また、４ａ，４ｂ，４ｃ，４ｄは２本の
光導波路２ａ，２ｂの両端に接続された光ファイバであ
る。
【０００６】ＭＺ干渉計では、石英系光導波路に限ら
ず、微小な屈折率や導波路形状の変動及び導波路にかか
る応力が素子特性に大きく影響する。前述した２本の光
導波路２ａ，２ｂの光路長差がｎf ・Ｌ1 であるとする
と、出力光強度は、入射光の周波数ｆ（又は波長λ）に
関して、
ｆsr＝ｃ／ｎf ・Ｌ1 （但し、ｃは光の速度）
を周期とする特性を有することが知られており、この出
力光強度の周期特性を利用して、光スイッチ、光周波数
合分波器等として動作する光デバイスが実現されてい
る。
【０００７】しかしながら、導波路の屈折率、幅等の作
製誤差は、光干渉計の周期特性の位相によるずれをもた
らし、光スイッチ、光周波数合分波器としての動作特性
に著しい劣化を生じさせることになる。従って、ＭＺ干
渉計を用いた光回路において生産性を向上させるために
は、作製上の微小な変動を補償する必要性があり、効果
的な調節法が望まれていた。
【０００８】光干渉計において位相誤差を補償する方法
の一つとして、可視光もしくは紫外レーザ光を照射する
ことによって生じる屈折率変化（光誘起屈折率変化）を
利用する方法が報告されている（例えば、PTL, (3), 19
91, Hibino, et al., pp640-642 参照）。
【０００９】また、光導波路の屈折率制御に関する類似
の報告として、光ファイバの屈折率の変化に関するもの
がある（例えば、Opt.Lett., vol.15, 1990, B.Molo, e
t al., pp953-955参照）。これによれば、ＧｅＯ2 添加
石英系光ファイバにおいて紫外線照射によりコアの屈折
率が３×１０-5だけ変化することが観測されている。ま
た、シリコン基板上に形成された石英系光導波路におい
ても同様な光誘起屈折率変化Δｎが観測されている。
【００１０】しかしながら、シリコン基板上に作製され
た石英系光導波路における光誘起屈折率変化の敏感性
は、光ファイバに比べて弱いものであった。このことは
応用例の一つである光誘起屈折率分布型グレーティング
の作製時に長い光照射時間を必要とし、より安定な光照
射の光学系が必要とされる等の困難を生じさせた。その
ため、屈折率変化の効率を高めるための処理方法が提案
された。
【００１１】一つは、水素雰囲気下で高温（500 ℃程
度）熱処理を行うことにより、光誘起屈折率変化の敏感
性（効率）を高めることを可能としたものである（例え
ば、Opt.Lett., vol.18, 1993, K.D.Simmons, et al.,
pp25-27 参照）（以下、高温水素化処理法と称す）。し
かしながら、水素雰囲気で高温熱処理を行うことは安全
性に欠け、また、高温熱処理を行うための特殊な電気炉
等を必要とし、さらにまた、近赤外領域における損失も
数ｄＢ以上増加する等の問題があった（例えば、Electr
on Lett., (28), 1992, G.D.Maxwell, et al., pp2106-
2107参照）。
【００１２】また、もう一つは、水素バーナー、ＬＰＧ
バーナー等の火炎で光導波路を炙ることにより、光誘起
屈折率変化の敏感性（効率）を高めることを可能とした
ものである（例えば、OFC '93, K.O.Hill, et al. 参
照）（以下、火炎掃引法（flame brushing）と称す）。
この方法は、簡便に屈折率変化の効率を高めることがで
きる点で優れているが、その制御性及び再現性に問題が
あった。
【００１３】
【発明が解決しようとする課題】本発明は前記従来の問
題点に鑑み、光誘起屈折率変化の敏感性を簡便且つ安全
にしかも制御性良く高めることができ、光回路を構成す
る光導波路の局部的な屈折率もしくは光路長の制御を効
率良く行うことを可能とする光回路の特性調整方法を提
供することを目的とする。
【００１４】
【課題を解決するための手段】本発明では前記目的を達
成するため、基板上に形成されたコア及びクラッドから
なり、紫外領域に吸収を有し、紫外線に敏感なドーパン
トとしてＧｅＯ 2 ，ＴｉＯ 2 ，Ｃｅ 2 Ｏ 3 のいずれかを添加
した石英系光導波路で構成される光回路の特性調整方法
であって、前記光導波路に室温で水素を含浸させる第１
の工程と、前記第１の工程に続いて、前記光導波路に熱
処理を行う第２の工程と、前記第２の工程の後に、前記
光導波路に局部的に可視光又は紫外光を照射する第３の
工程とを備えた光回路の特性調整方法を提案する。
【００１５】
【作用】本発明によれば、水素を含浸させる工程と熱処
理を行う工程とを分離しているため、水素を含浸させる
工程は室温で行うことができ、高温水素化処理法に比べ
て、より安全性が高く、また、大気中或いはＨｅ雰囲気
下で熱処理を行うため、通常の電気炉等を用いることが
でき、簡単に熱処理を行うことができる。また、水素を
含浸させる工程における水素圧力と水素雰囲気下に導波
路を置く時間、並びに熱処理工程における熱処理温度と
熱処理時間により、屈折率変化の敏感性（効率）の制御
性及び再現性を持たせることができる。
【００１６】
【実施例】以下、図面を用いて本発明の実施例を説明す
る。
【００１７】図１は本発明の第１の実施例を示すもの
で、ここでは光誘起屈折率変化の敏感性向上処理を行っ
た後、石英系光導波路においてエキシマレーザによりＭ
Ｚ干渉計の特性を調節した例を示す。
【００１８】図２において、１０はＭＺ干渉計であり、
シリコン基板１１上に形成された２つの方向性結合器１
２ａ，１２ｂ及びこれらを結ぶ２本の光導波路１３ａ，
１３ｂからなっている。また、２１ａ，２１ｂ，２１
ｃ，２１ｄは２本の光導波路１３ａ，１３ｂの両端に接
続された光ファイバ、２２は遮蔽用の金属膜、２３はＫ
ｒＦエキシマレーザ、２４はミラー、２５はレンズ、２
６はシリンドリカルレンズである。
【００１９】前記ＭＺ干渉計１０は非対称型であり、光
導波路１３ａが１３ｂより長くなっている。このタイプ
のＭＺ干渉計は周波数又は波長分波器として動作する。
ここでは、２つの光導波路１３ａ，１３ｂの光路長差Δ
Ｌ2 を約１ｃｍとし、周波数１０ＧＨｚ間隔で入射光を
分波できるように設計した。
【００２０】以下、本発明方法を説明する。
【００２１】まず、通常の方法でシリコン基板１１上に
ＧｅＯ2 添加石英系ガラス導波路型のＭＺ干渉計１０を
作製した。ここで、導波路のコアは矩形とし、サイズは
７×７μｍとした。また、コアとクラッドとの屈折率差
は0.75％とした。方向性結合器１２ａ，１２ｂでは結合
率が波長1.3 μｍでほぼ５０％になるようにした。
【００２２】前記作製したＭＺ干渉計１０を、図３に示
すようなＨ2 ガス高圧封入容器に入れ、水素ガス圧力を
５気圧に設定し、水素の含浸を約２４時間行った。な
お、図３において、２７は容器、２８は水素ガス供給
系、２９は圧力ゲージ、３０はリーク用バルブである。
続いて、水素を含浸させたＭＺ干渉計１０を、電気炉に
よって200 ℃で約２４時間アニーリングを行い、光誘起
屈折率変化の敏感性向上処理を行った。
【００２３】前述した処理を行った導波路型ＭＺ干渉計
１０にＫｒＦエキシマレーザ２３より、ミラー２４、レ
ンズ２５及びシリンドリカルレンズ２６を介して、波長
248ｎｍの紫外レーザ光を照射し、照射前後の特性変化
を調べた。レーザ光はＭＺ干渉計１０の上部より、金属
膜２２で覆われていない部分を照射した。従って、該レ
ーザ光は光導波路１３ａの一部分だけに屈折率変化を誘
起することになる。この際、ＫｒＦエキシマレーザ２３
の照射パワーは100 ｍＪ／ｃｍ2 ・pulse 、パルス繰り
返し周波数は５Ｈｚ、照射時間は２分間とした。
【００２４】前述したＭＺ干渉計１０の特性を調べるた
め、中心波長1.3 μｍの電流掃引型半導体レーザを光フ
ァイバ２１ａから導入した。本実施例では、レーザ光の
照射中にＭＺ干渉計１０の特性変化をモニターすること
ができた。
【００２５】図４は２分間照射後における光ファイバ２
１ｃからの出力の波長依存性を、照射前と比較して示す
ものである。図４に示すように、照射前は光周波数ｆi
で消光していたＭＺ干渉計１０の特性を、照射後、所望
の光周波数ｆ0 で消光するように調整することができ
た。この光周波数ｆi からｆ0 への調整はＫｒＦエキシ
マレーザ光照射による光誘起屈折率変化Δｎによるもの
である。
【００２６】従来の光導波路では、光周波数ｆi からｆ
0 への変化に相当する屈折率変化Δｎを得るためには、
ＫｒＦエキシマレーザの照射パワー100 ｍＪ／ｃｍ2 ・
pulse 、パルス繰り返し周波数５０Ｈｚ、照射時間約２
０分間を要していた。従って、本発明により、光誘起屈
折率変化の敏感性（効率）は、約100 倍向上したことが
確認された。
【００２７】なお、前記光誘起屈折率変化の敏感性向上
処理に用いた水素ガスは、石英ガラスに含浸し還元反応
する気体のものであれば代用することができる。また、
本発明はアモルファスシリコン或いはステンレス等の金
属を光導波路に部分的に密着させ、光回路の一部分にの
み水素の含浸を行い、選択的に光誘起屈折率変化の敏感
性を向上させることも可能である。また、シリコン系樹
脂等を光導波路に密着させ、加熱処理を行うことによ
り、同様に光誘起屈折率変化の敏感性を向上させること
もできる。
【００２８】また、コアの屈折率変化は波長240 ｎｍの
ＧｅＯ2 に関連した吸収に起因するため、屈折率変化に
用いるレーザは240 ｎｍ付近に発振波長を有するもので
あれば良い。また、可視域に発振波長を有するレーザも
使用可能である。なぜなら、可視域のレーザでも２光子
吸収により同様の変化を誘起するからである。まとめる
と、本発明で使用するレーザは、Ｈｅ−Ｃｄレーザ、Ｎ
2 レーザ、各種エキシマレーザ、Ａｒイオンレーザ、Ｎ
ｄ3+：ＹＡＧレーザ、アレキサンドライト（Ｃｒ3+：Ｂ
ｅＡｌ2 Ｏ4 ）レーザの第２次，３次，４次高調波等、
紫外・可視領域の波長を有するものであれば良い。
【００２９】なお、ＧｅＯ2 濃度に関しては、ＭＺ干渉
計の長さにより調節が可能であるから、特に制限するも
のではない。また、前記実施例ではドーパントとしてＧ
ｅＯ2 を用いたが、その外にＴｉＯ2 ，Ｃｅ2 Ｏ3 等、
紫外領域に吸収を有し、紫外線に敏感なドーパントを用
いても良い。また、本発明は、光ファイバ２１ａ〜２１
ｄに偏波保持性を有する光ファイバを用いることを妨げ
るものではない。
【００３０】図５は本発明の第２の実施例を示すもの
で、ここでは光誘起屈折率変化の敏感性向上処理を行っ
た後、石英系光導波路において光誘起グレーティングの
作製を行った例を示す。
【００３１】図５において、４０は石英系光導波路、４
１はアレキサンドライト（Ｃｒ3+：ＢｅＡｌ2 Ｏ4 ）レ
ーザ、４２ａ，４２ｂは波長変換素子（ＢＢＯ）、４３
は波長選択ミラー、４４ａ，４４ｂ，４４ｃ，４４ｄは
ミラー、４５はレンズ、４６はシリンドリカルレンズ、
４７はハーフミラーである。
【００３２】以下、本発明方法を説明する。
【００３３】まず、通常の方法でシリコン基板上にＧｅ
Ｏ2 添加石英系ガラス導波路４０を作製した。ここで、
導波路のコアは矩形とし、サイズは７×７μｍとした。
また、コアとクラッドとの屈折率差は0.75％とした。
【００３４】前記作製した石英系光導波路４０を、図３
に示したＨ2 ガス高圧封入容器に入れ、水素ガス圧力を
５気圧に設定し、水素の含浸を約７２時間行った。続い
て、水素を含浸させた光導波路４０を、電気炉によって
200 ℃で約７２時間アニーリングを行い、光誘起屈折率
変化の敏感性向上処理を行った。
【００３５】前述した処理を行った光導波路４０にアレ
キサンドライトレーザ４１より、波長変換素子４２ａ，
４２ｂ、波長選択ミラー４３、ミラー４４ａ〜４４ｄ、
レンズ４５、シリンドリカルレンズ４６及びハーフミラ
ー４７を介して、第３高調波（３ω）を上部から約８分
間照射し、光誘起グレーティングを作製した。この際、
レーザ光強度は約400 ｍＪ／ｃｍ2 ・pulse 、パルス繰
り返し周波数は２０Ｈｚ、照射した光導波路の長さは１
０ｍｍとした。
【００３６】グレーティングの特性を調べるため、中心
波長1.55μｍのＬＥＤからの光をファイバで光導波路へ
導入し、スペクトラムアナライザを用いて測定した。
【００３７】図６は本発明により作製した光導波路の反
射スペクトル特性を、通常の光導波路と比較して示すも
のである。
【００３８】通常の石英系光導波路に、同様の光照射条
件で光誘起グレーティングを作製するためには、数１０
分間以上に及ぶ光照射時間を要するが、その間、図５に
示したような光照射の光学系を安定に保つことは困難で
あったため、十分な特性が得られなかったが、本発明の
光誘起屈折率変化の敏感性向上処理を行うことにより、
十分な反射率、ここでは約８５％を示す光誘起グレーテ
ィングを作製することができた。
【００３９】
【発明の効果】以上説明したように本発明によれば、水
素を含浸させる工程と熱処理を行う工程とを分離してい
るため、水素を含浸させる工程は室温で行うことがで
き、高温水素化処理法に比べて、より安全性が高く、ま
た、大気中或いはＨｅ雰囲気下で熱処理を行うため、通
常の電気炉等を用いることができ、簡単に熱処理を行う
ことができる。また、水素を含浸させる工程における水
素圧力と水素雰囲気下に導波路を置く時間、並びに熱処
理工程における熱処理温度と熱処理時間により、屈折率
変化の敏感性（効率）の制御性及び再現性を持たせるこ
とができ、従来の光回路の作製法の変更を必要とせず、
効果的にしかも簡便に特性を調節した光回路を提供する
ことができる。また、本発明によれば、既に作製された
光回路を対象として実施できるため、規格外の出力特性
の回路を所望の特性にすることができ、光回路の生産性
が向上する。また、本発明によれば、短時間の光照射に
より大きな屈折率変化Δｎが得られるため、光誘起グレ
ーティングの特性を向上させることができる。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting characteristics of an optical circuit composed of an optical waveguide formed on a substrate. A quartz optical waveguide which can be formed on a quartz glass substrate or a silicon substrate has low loss, high stability,
It is known that it is very useful in constructing a practical optical circuit such as an optical multiplexing / demultiplexing circuit because it has features such as good workability and good matching with a silica-based optical fiber. Recently, the production of highly functional and highly integrated planar optical circuits utilizing the above-mentioned features has been promoted.
Optical circuits that use the phase of light are of great importance because they enable circuits that are difficult to implement with electronic circuits. In a quartz optical waveguide, an under cladding layer is deposited on a silicon substrate → a core layer is deposited → a core etching →
A core-cladding structure is formed by performing a manufacturing process called over-cladding layer deposition. In a highly functional and highly integrated optical circuit using optical phase, the optical phase is determined by the refractive index of the waveguide and the propagation length ( (Optical path length), a small change in the refractive index and waveguide shape in fabrication and stress applied to the waveguide greatly affect device characteristics. Therefore, in order to improve the productivity of a highly functional and highly integrated optical circuit, it is necessary to correct minute fluctuations in the fabrication and the like, and to adjust the characteristics of the optical circuit to enable local control of the refractive index. The realization of the method was desired. An example of a Mach-Zehnder (MZ) interferometer, which is an important element constituting the above-mentioned planar optical circuit, will be described below, and the importance of local refractive index control will be described below. The MZ interferometer is a component that is indispensable in configuring an optical switch and an optical demultiplexer, and an example is shown in FIG. In FIG. 2, reference numerals 1a and 1b denote two directional couplers, and 2a and 2b denote two optical waveguides connecting the directional couplers 1a and 1b. I have. 4a, 4b, 4c and 4d are optical fibers connected to both ends of two optical waveguides 2a and 2b. In the MZ interferometer, not only the silica-based optical waveguide but also a minute refractive index, a change in the waveguide shape, and a stress applied to the waveguide greatly affect the element characteristics. Two optical waveguides 2a described above, the optical path length difference between 2b is assumed to be n f · L1, the output light intensity, in frequency f of the incident light (or wavelength λ), f sr = c / n f · L1 (Where c is the speed of light). It is known that the optical device operates as an optical switch, an optical frequency multiplexer / demultiplexer, or the like using the periodic characteristic of the output light intensity. Has been realized. However, manufacturing errors such as the refractive index and width of the waveguide cause a shift in the phase of the periodic characteristics of the optical interferometer, and significantly degrade the operating characteristics of the optical switch and the optical frequency multiplexer / demultiplexer. Will be. Therefore, in order to improve the productivity of the optical circuit using the MZ interferometer, it is necessary to compensate for a small variation in the fabrication, and an effective adjustment method has been desired. As a method of compensating for a phase error in an optical interferometer, a method utilizing a refractive index change (light-induced refractive index change) caused by irradiation with visible light or ultraviolet laser light has been reported ( For example, PTL, (3), 19
91, Hibino, et al., Pp640-642). A similar report on the control of the refractive index of an optical waveguide includes a change in the refractive index of an optical fiber (for example, Opt. Lett., Vol. 15, 1990, B. Molo, e.
t al., pp953-955). According to this, it has been observed that the refractive index of the core changes by 3 × 10 −5 by irradiation of ultraviolet rays in the GeO 2 -doped quartz optical fiber. Further, a similar photoinduced refractive index change Δn has been observed in a quartz optical waveguide formed on a silicon substrate. [0010] However, the sensitivity of the optically induced refractive index change in the silica-based optical waveguide fabricated on the silicon substrate is weaker than that of the optical fiber. This requires a long light irradiation time when producing a photo-induced refractive index distribution type grating, which is one of the applied examples, and causes difficulties such as a need for a more stable light irradiation optical system. Therefore, a processing method for increasing the efficiency of the refractive index change has been proposed. One is that the sensitivity (efficiency) of the photoinduced refractive index change can be increased by performing a high-temperature (about 500 ° C.) heat treatment in a hydrogen atmosphere (for example, Opt. Lett.). ., vol. 18, 1993, KDSimmons, et al.,
pp25-27) (hereinafter referred to as high temperature hydrotreating method). However, performing high-temperature heat treatment in a hydrogen atmosphere lacks safety, requires a special electric furnace for performing high-temperature heat treatment, and further increases the loss in the near infrared region by several dB or more. There was a problem (for example, Electr
on Lett., (28), 1992, GDMaxwell, et al., pp2106-
2107). Another is a hydrogen burner, LPG
By burning the optical waveguide with a flame such as a burner, the sensitivity (efficiency) of the light-induced refractive index change can be increased (for example, see OFC '93, KOHill, et al.) Flame brushing).
This method is excellent in that the efficiency of change in refractive index can be easily increased, but has a problem in its controllability and reproducibility. SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention makes it possible to easily and safely enhance the sensitivity of a photoinduced refractive index change, and to form an optical circuit. It is an object of the present invention to provide a method for adjusting the characteristics of an optical circuit that enables efficient control of a local refractive index or an optical path length of an optical waveguide. [0014] Since the present invention SUMMARY OF THE INVENTION To achieve the above object, Ri Na <br/> a core and a clad formed on a substrate, has an absorption in the ultraviolet region, sensitive to ultraviolet Dopan
Addition of either GeO 2, TiO 2, Ce 2 O 3 as a preparative
A method for adjusting characteristics of an optical circuit comprising a quartz optical waveguide, wherein the optical waveguide is impregnated with hydrogen at room temperature .
And a second step of performing a heat treatment on the optical waveguide following the first step, and a second step of locally irradiating the optical waveguide with visible light or ultraviolet light after the second step . A method for adjusting the characteristics of an optical circuit, comprising the steps of According to the present invention, the step of impregnating hydrogen and the step of heat treatment are separated from each other, so that the step of impregnating hydrogen can be performed at room temperature. Therefore, since the heat treatment is performed with higher safety and in the atmosphere or in the He atmosphere, a normal electric furnace or the like can be used, and the heat treatment can be easily performed. In addition, the sensitivity (efficiency) of refractive index change controllability and reproducibility are provided by the hydrogen pressure in the step of impregnating hydrogen and the time for placing the waveguide under a hydrogen atmosphere, and the heat treatment temperature and heat treatment time in the heat treatment step. be able to. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. In this embodiment, after a process for improving the sensitivity of a photo-induced refractive index change is performed, an M excimer laser is used in a quartz optical waveguide.
An example in which the characteristics of the Z interferometer are adjusted is shown. In FIG. 2, reference numeral 10 denotes an MZ interferometer,
Two directional couplers 1 formed on a silicon substrate 11
2a, 12b and two optical waveguides 13a,
13b. Also, 21a, 21b, 21
c and 21d are optical fibers connected to both ends of the two optical waveguides 13a and 13b, 22 is a metal film for shielding, and 23 is K
rF excimer laser, 24 is a mirror, 25 is a lens, 2
Reference numeral 6 denotes a cylindrical lens. The MZ interferometer 10 is an asymmetric type, and the optical waveguide 13a is longer than 13b. This type of MZ interferometer operates as a frequency or wavelength splitter.
Here, the optical path length difference Δ between the two optical waveguides 13a and 13b
The L 2 of about 1 cm, was designed to demultiplex incoming light at a frequency 10GHz intervals. Hereinafter, the method of the present invention will be described. First, a GeO 2 -doped silica glass waveguide type MZ interferometer 10 was formed on a silicon substrate 11 by a usual method. Here, the core of the waveguide was rectangular and the size was 7 × 7 μm. The refractive index difference between the core and the clad was set to 0.75%. In the directional couplers 12a and 12b, the coupling ratio was set to be approximately 50% at a wavelength of 1.3 μm. The manufactured MZ interferometer 10 was placed in an H 2 gas high-pressure sealed container as shown in FIG. 3, the hydrogen gas pressure was set to 5 atm, and hydrogen impregnation was performed for about 24 hours. In FIG. 3, 27 is a container, 28 is a hydrogen gas supply system, 29 is a pressure gauge, and 30 is a leak valve.
Subsequently, the MZ interferometer 10 impregnated with hydrogen was annealed in an electric furnace at 200 ° C. for about 24 hours to perform a process for improving the sensitivity of the photoinduced refractive index change. The waveguide MZ interferometer 10 having undergone the above-described processing is subjected to wavelength conversion by a KrF excimer laser 23 via a mirror 24, a lens 25 and a cylindrical lens 26.
Irradiation with ultraviolet laser light of 248 nm was performed, and changes in characteristics before and after the irradiation were examined. The laser beam was irradiated from above the MZ interferometer 10 to a portion not covered by the metal film 22. Therefore, the laser light induces a change in the refractive index only in a part of the optical waveguide 13a. At this time, the KrF excimer laser 23 is used.
The irradiation power was 100 mJ / cm 2 · pulse, the pulse repetition frequency was 5 Hz, and the irradiation time was 2 minutes. In order to examine the characteristics of the MZ interferometer 10, a current sweep type semiconductor laser having a center wavelength of 1.3 μm was introduced from the optical fiber 21a. In this embodiment, a change in the characteristics of the MZ interferometer 10 could be monitored during the irradiation of the laser beam. FIG. 4 shows the optical fiber 2 after irradiation for 2 minutes.
7 shows the wavelength dependence of the output from 1c in comparison with that before irradiation. As shown in FIG. 4, before irradiation, the optical frequency f i
The characteristics of the MZ interferometer 10, which had been quenched by the above, could be adjusted to be quenched at a desired optical frequency f 0 after irradiation. The adjustment from the optical frequency f i to f 0 is based on the photo-induced refractive index change Δn due to KrF excimer laser light irradiation. In the conventional optical waveguide, the optical frequencies f i to f
To obtain a refractive index change Δn corresponding to a change to 0 ,
Irradiation power of KrF excimer laser 100 mJ / cm 2 ·
pulse, pulse repetition frequency 50Hz, irradiation time about 2
It took 0 minutes. Therefore, according to the present invention, it was confirmed that the sensitivity (efficiency) of the photoinduced refractive index change was improved about 100 times. The hydrogen gas used in the process for improving the sensitivity of the photo-induced refractive index change can be used as long as it is a gas that impregnates quartz glass and undergoes a reduction reaction. Also,
According to the present invention, a metal such as amorphous silicon or stainless steel can be partially adhered to the optical waveguide, and only a part of the optical circuit can be impregnated with hydrogen, thereby selectively improving the sensitivity of the photoinduced refractive index change. is there. Further, by bringing a silicon resin or the like into close contact with the optical waveguide and performing a heat treatment, the sensitivity of the photoinduced refractive index change can be similarly improved. Since the change in the refractive index of the core is caused by absorption related to GeO 2 having a wavelength of 240 nm, the laser used for the change in the refractive index may be any laser having an oscillation wavelength near 240 nm. Further, a laser having an oscillation wavelength in the visible region can also be used. This is because even a laser in the visible range induces a similar change by two-photon absorption. In summary, the laser used in the present invention is He-Cd laser, N
2 lasers, various excimer lasers, Ar ion lasers, N
d 3+ : YAG laser, alexandrite (Cr 3+ : B
eAl 2 O 4 ) 2nd, 3rd, 4th harmonic of laser, etc.
Any material having a wavelength in the ultraviolet / visible region may be used. The GeO 2 concentration is not particularly limited because it can be adjusted by the length of the MZ interferometer. In the above embodiment, G was used as the dopant.
eO 2 was used, but TiO 2 , Ce 2 O 3, etc.
A dopant having absorption in the ultraviolet region and sensitive to ultraviolet light may be used. In addition, the present invention relates to optical fibers 21a to 21a.
This does not prevent the use of an optical fiber having a polarization maintaining property for d. FIG. 5 shows a second embodiment of the present invention. In this embodiment, after performing a process for improving the sensitivity of a photoinduced refractive index change, a photoinduced grating is produced in a quartz optical waveguide. Is shown. In FIG. 5, reference numeral 40 denotes a quartz optical waveguide,
1 is an alexandrite (Cr 3+ : BeAl 2 O 4 ) laser, 42a and 42b are wavelength conversion elements (BBO), 43
Is a wavelength selection mirror, 44a, 44b, 44c and 44d are mirrors, 45 is a lens, 46 is a cylindrical lens,
47 is a half mirror. Hereinafter, the method of the present invention will be described. First, Ge is formed on a silicon substrate by an ordinary method.
An O 2 -doped quartz glass waveguide 40 was produced. here,
The core of the waveguide was rectangular and the size was 7 × 7 μm.
The refractive index difference between the core and the clad was set to 0.75%. The quartz optical waveguide 40 manufactured as described above is
Placed in the H 2 gas pressure sealed container shown in, the hydrogen gas pressure is set to 5 atm, it was impregnated hydrogen about 72 hours. Subsequently, the optical waveguide 40 impregnated with hydrogen is placed in an electric furnace.
Annealing was performed at 200 ° C. for about 72 hours to perform a process for improving the sensitivity of the photoinduced refractive index change. An Alexandrite laser 41 feeds the wavelength conversion element 42a,
42b, a wavelength selection mirror 43, mirrors 44a to 44d,
The third harmonic (3ω) was irradiated from above through the lens 45, the cylindrical lens 46, and the half mirror 47 for about 8 minutes to produce a light-induced grating. On this occasion,
The laser light intensity is about 400 mJ / cm 2 · pulse, the pulse repetition frequency is 20 Hz, and the length of the irradiated optical waveguide is 1
0 mm. In order to examine the characteristics of the grating, light from an LED having a center wavelength of 1.55 μm was introduced into the optical waveguide through a fiber, and measured using a spectrum analyzer. FIG. 6 shows the reflection spectrum characteristics of an optical waveguide manufactured according to the present invention in comparison with a normal optical waveguide. In order to fabricate a light-induced grating in a normal quartz optical waveguide under the same light irradiation conditions, several tens of
Although a light irradiation time of more than one minute is required, it was difficult to keep the optical system for light irradiation as shown in FIG. 5 stable during that time, so that sufficient characteristics could not be obtained. By performing the process of improving the sensitivity of the induced refractive index change,
A light-induced grating exhibiting sufficient reflectivity, here about 85%, could be produced. As described above, according to the present invention, since the step of impregnating hydrogen and the step of performing heat treatment are separated, the step of impregnating hydrogen can be performed at room temperature. Compared to the high-temperature hydrogenation method, the safety is higher, and the heat treatment is performed in the air or in the He atmosphere. Therefore, a normal electric furnace or the like can be used, and the heat treatment can be easily performed. In addition, the sensitivity (efficiency) of refractive index change controllability and reproducibility are provided by the hydrogen pressure in the step of impregnating hydrogen and the time for placing the waveguide under a hydrogen atmosphere, and the heat treatment temperature and heat treatment time in the heat treatment step. Without the need to change the method of fabricating conventional optical circuits,
An optical circuit whose characteristics are adjusted effectively and easily can be provided. Further, according to the present invention, since the present invention can be implemented for an optical circuit that has already been manufactured, a circuit having an output characteristic that is out of the standard can be made a desired characteristic, and the productivity of the optical circuit is improved. Further, according to the present invention, a large change in refractive index Δn can be obtained by short-time light irradiation, so that the characteristics of the light-induced grating can be improved.
【図面の簡単な説明】
【図１】本発明の第１の実施例を示す光学系の配置図
【図２】ＭＺ干渉計の一例を示す構成図
【図３】水素ガス高圧封入容器の一例を示す図
【図４】第１の実施例における出力光波長スペクトル特
性を示す図
【図５】本発明の第２の実施例を示す光学系の配置図
【図６】第２の実施例における反射スペクトル特性を示
す図
【符号の説明】
１０…ＭＺ干渉計、１１…シリコン基板、１２ａ，１２
ｂ…方向性結合器、１３ａ，１３ｂ…光導波路、２１ａ
〜２１ｄ…光ファイバ、２２…金属膜、２３…ＫｒＦエ
キシマレーザ、２４，４４ａ〜４４ｄ…ミラー、２５，
４５…レンズ、２６，４６…シリンドリカルレンズ、４
０…石英系光導波路、４１…アレキサンドライトレー
ザ、４２ａ，４２ｂ…波長変換素子、４３…波長選択ミ
ラー、４７…ハーフミラー。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an arrangement diagram of an optical system showing a first embodiment of the present invention. FIG. 2 is a configuration diagram showing an example of an MZ interferometer. FIG. FIG. 4 is a diagram showing an output light wavelength spectrum characteristic in the first embodiment. FIG. 5 is an arrangement diagram of an optical system showing a second embodiment of the present invention. FIG. 6 is a diagram in the second embodiment. Diagram showing reflection spectrum characteristics [Description of symbols] 10 ... MZ interferometer, 11 ... Silicon substrate, 12a, 12
b: directional coupler, 13a, 13b: optical waveguide, 21a
-21d: optical fiber, 22: metal film, 23: KrF excimer laser, 24, 44a-44d: mirror, 25,
45: lens, 26, 46: cylindrical lens, 4
0: quartz optical waveguide, 41: alexandrite laser, 42a, 42b: wavelength conversion element, 43: wavelength selection mirror, 47: half mirror.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 河内 正夫 東京都千代田区内幸町１丁目１番６号 日本電信電話株式会社内 (72)発明者 山田 裕朗 東京都千代田区内幸町１丁目１番６号 日本電信電話株式会社内 (56)参考文献 特開 平６−118257（ＪＰ，Ａ) 山田裕明 他，石英系光導波路におけ る光誘起屈折率変化，1992年電子情報通 信学会秋季大会講演論文集，1992年９月 15日，分冊４，ｐｐ．４−205 Ｒ．Ｍ．ＡＴＫＩＮＳ，ｅｔ．ａ ｌ．，Ｊｏｕｒｎａｌ ｏｆ Ａｐｐｌ ｉｅｄ Ｐｈｙｓｉｃｓ，1992年７月15 日，Ｖｏｌ．72，Ｎｏ．２，ｐｐ．344 −348 (58)調査した分野(Int.Cl.7，ＤＢ名) G02F 1/35 G02B 6/122 G02F 1/035 ＪＩＣＳＴファイル（ＪＯＩＳ)──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Kawachi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Hiroo Yamada 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan (56) References JP-A-6-118257 (JP, A) Hiroaki Yamada et al., Photoinduced refractive index change in silica-based optical waveguides, Proceedings of the 1992 IEICE Autumn Conference. , September 15, 1992, Volume 4, pp. 4-205 R.C. M. ATKINS, et. a l. , Journal of Applied Physics, July 15, 1992, Vol. 72, No. 2, pp. 344 −348 (58) Fields surveyed (Int.Cl. 7 , DB name) G02F 1/35 G02B 6/122 G02F 1/035 JICST file (JOIS)
Claims (1)
らなり、紫外領域に吸収を有し、紫外線に敏感なドーパ
ントとしてＧｅＯ 2 ，ＴｉＯ 2 ，Ｃｅ 2 Ｏ 3 のいずれかを添
加した石英系光導波路で構成される光回路の特性調整方
法であって、 前記光導波路に室温で水素を含浸させる第１の工程と、 前記第１の工程に続いて、前記光導波路に熱処理を行う
第２の工程と、 前記第２の工程の後に、前記光導波路に局部的に可視光
又は紫外光を照射する第３の工程とを備えたことを特徴
とする光回路の特性調整方法。(57) [Claim 1] GeO 2 , TiO 2 , Ce 2 O 3 , comprising a core and a clad formed on a substrate, having absorption in an ultraviolet region and being sensitive to ultraviolet rays. A method for adjusting the characteristics of an optical circuit composed of a silica-based optical waveguide to which any of the above is added, wherein a first step of impregnating the optical waveguide with hydrogen at room temperature, and An optical circuit, comprising: a second step of performing a heat treatment on the optical waveguide; and a third step of locally irradiating the optical waveguide with visible light or ultraviolet light after the second step. Characteristics adjustment method.
Priority Applications (1)
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|---|---|---|---|
| JP9312593A JP3374990B2 (en) | 1993-04-20 | 1993-04-20 | Optical circuit characteristic adjustment method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9312593A JP3374990B2 (en) | 1993-04-20 | 1993-04-20 | Optical circuit characteristic adjustment method |
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| Publication Number | Publication Date |
|---|---|
| JPH06308546A JPH06308546A (en) | 1994-11-04 |
| JP3374990B2 true JP3374990B2 (en) | 2003-02-10 |
Family
ID=14073807
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| JP9312593A Expired - Lifetime JP3374990B2 (en) | 1993-04-20 | 1993-04-20 | Optical circuit characteristic adjustment method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3996971B2 (en) * | 1997-05-06 | 2007-10-24 | 日本電信電話株式会社 | Manufacturing method of optical waveguide filter |
| JP3183223B2 (en) | 1997-07-30 | 2001-07-09 | 日本電気株式会社 | Optical circuit |
| JP2000047046A (en) * | 1998-07-31 | 2000-02-18 | Toshiyuki Watanabe | Manufacture of refractive index distribution type optical formed body |
| JP2002530689A (en) * | 1998-11-12 | 2002-09-17 | ザ・ユニバーシティ・オブ・シドニー | Adjustment of optical devices |
| US6442311B1 (en) * | 1999-07-09 | 2002-08-27 | Agere Systems Guardian Corp. | Optical device having modified transmission characteristics by localized thermal treatment |
| WO2001038909A1 (en) * | 1999-11-24 | 2001-05-31 | Mitsubishi Cable Industries, Ltd. | Coated optical fiber, optical fiber assembly, methods for the same, and optical fiber substrate |
| AUPR230200A0 (en) * | 2000-12-22 | 2001-01-25 | Redfern Optical Components Pty Ltd | Tuning of optical devices |
-
1993
- 1993-04-20 JP JP9312593A patent/JP3374990B2/en not_active Expired - Lifetime
Non-Patent Citations (2)
| Title |
|---|
| Ｒ．Ｍ．ＡＴＫＩＮＳ，ｅｔ．ａｌ．，Ｊｏｕｒｎａｌ ｏｆ Ａｐｐｌｉｅｄ Ｐｈｙｓｉｃｓ，１９９２年７月１５日，Ｖｏｌ．７２，Ｎｏ．２，ｐｐ．３４４−３４８ |
| 山田裕明 他，石英系光導波路における光誘起屈折率変化，１９９２年電子情報通信学会秋季大会講演論文集，１９９２年９月１５日，分冊４，ｐｐ．４−２０５ |
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