JPH05127033A - Optical waveguide and its production - Google Patents
Optical waveguide and its productionInfo
- Publication number
- JPH05127033A JPH05127033A JP28687091A JP28687091A JPH05127033A JP H05127033 A JPH05127033 A JP H05127033A JP 28687091 A JP28687091 A JP 28687091A JP 28687091 A JP28687091 A JP 28687091A JP H05127033 A JPH05127033 A JP H05127033A
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- single crystal
- optical waveguide
- optical
- substrate
- waveguide
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、基板にニオブ酸リチウ
ム単結晶を用いた光導波路及びその製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide using a lithium niobate single crystal as a substrate and a method for manufacturing the same.
【０００２】[0002]
【従来の技術】ニオブ酸リチウム（LiNbO 3 ；以下ＬＮ
と略記する）単結晶は、電気光学定数等の光学的特性に
優れており、光を薄膜のような狭い領域内に閉じ込めて
伝送する、いわゆる光導波路の基板材料として注目され
ている。2. Description of the Related Art Lithium niobate (LiNbO 3 ; hereinafter referred to as LN)
The single crystal is excellent in optical characteristics such as electro-optical constants, and is attracting attention as a substrate material for a so-called optical waveguide that confine and transmit light in a narrow region such as a thin film.
【０００３】上記光導波路の代表的なものとして、ＬＮ
単結晶の基板に帯状に金属を拡散させて屈折率を周囲よ
り高め、光をできるだけ逃がさないようにした光導波路
があり、金属を拡散したチャネルの両側に電極を設け
て、これに電圧を印加することによって光のスイッチン
グを行うことができる。A typical example of the above-mentioned optical waveguide is LN.
There is an optical waveguide in which the metal is diffused in a band shape on the single crystal substrate to raise the refractive index higher than the surroundings to prevent light from escaping as much as possible, and electrodes are provided on both sides of the metal diffused channel, and voltage is applied to this. By doing so, light switching can be performed.
【０００４】従来、上記光導波路の製法に関して種々の
方法が提案されてきた。例えば、光伝搬損失の低減、よ
り大きな屈折率変化、より薄い高屈折率層の形成（光導
波路の２次元化）および製造の容易さという観点から、
金属の熱拡散法が一般に行われてきた。これは、図３
（ａ）に示すようにＬＮ単結晶の基板Ｓ上にパターニン
グしたレジストを被着形成し、このレジスト上及び基板
Ｓ上に金属膜を被着形成し、その後レジストを消失させ
て所望の形状の金属層Ｍを形成し、さらに、図３（ｂ）
に示すように、金属層Ｍのイオンを基板Ｓに熱拡散する
ことによって、基板Ｓの表層に組成変化を生ぜしめ、基
板Ｓ上に高屈折率層Ｈを形成して光導波路化するもので
ある。これまでの研究報告から、上記金属としてTiを用
いた場合が最も良好な光伝搬特性を有するとされてい
る。Conventionally, various methods have been proposed for manufacturing the above optical waveguide. For example, from the viewpoints of reduction of light propagation loss, larger change in refractive index, formation of thinner high refractive index layer (two-dimensionalization of optical waveguide) and ease of manufacturing,
Metal thermal diffusion methods have been commonly practiced. This is shown in Figure 3.
As shown in (a), a patterned resist is deposited on the LN single crystal substrate S, a metal film is deposited on the resist and the substrate S, and then the resist is removed to obtain a desired shape. A metal layer M is formed, and further, FIG.
As shown in FIG. 2, the ions of the metal layer M are thermally diffused into the substrate S to cause a composition change in the surface layer of the substrate S, and a high refractive index layer H is formed on the substrate S to form an optical waveguide. is there. From the research reports so far, it is considered that the case where Ti is used as the metal has the best light propagation characteristics.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、上記の
ように作製された光導波路は、Ｘ線トポグラフによりミ
クロ観察を行うと、高屈折率層Ｔには数多くの微小欠陥
が存在し、ミスフィット転位の他に数多くの微小クラッ
クが生じていることが明らかにされている。殊に、基板
Ｓのａ軸方向には、Δａ／ａがほぼ103 程度の格子変化
が生じており、これが光散乱損失の要因となっているこ
とが報告されている（K.Sugii et al.;J.Mater.Sci. 13
(1978)523 ）。However, when the optical waveguide manufactured as described above is microscopically observed by an X-ray topography, a large number of minute defects are present in the high refractive index layer T, and misfit dislocations are present. In addition to the above, it has been clarified that many microcracks are generated. In particular, it has been reported that a lattice change with Δa / a of about 10 3 occurs in the a-axis direction of the substrate S, which causes the light scattering loss (K. Sugii et al. .; J.Mater.Sci. 13
(1978) 523).
【０００６】また、金属の拡散条件等により、ＬＮ基板
自体や金属拡散層の変質が起きること（M. N. Armenise
et al.;J. Appl. Phys. 55(1984)3531 ）、Ti拡散時に
基板表面に凹凸が発生すること（R. J. Holmes and D.
M. Smyth;J. Appl. Phys. 55(1984)3531）などが報告さ
れており、金属拡散層の変質や基板表面の凹凸の発生に
より屈折率が局所的に変動し、その結果、光導波路とし
ての光伝搬性能の劣化を招来することになり問題であっ
た。また、時間の経過とともに金属の拡散が進行し、経
時変化による光伝搬特性などの光学的特性が変動するな
どして問題であるうえ、金属の拡散の状態も個々の光導
波路について均一の揃えることが困難となり、個々の光
導波路間での光学的特性のバラツキが大きく問題であっ
た。[0006] Further, alteration of the LN substrate itself or the metal diffusion layer may occur due to metal diffusion conditions and the like (MN Armenise
et al.; J. Appl. Phys. 55 (1984) 3531), and irregularities occur on the substrate surface during Ti diffusion (RJ Holmes and D.
M. Smyth; J. Appl. Phys. 55 (1984) 3531) have been reported, and the refractive index locally changes due to the alteration of the metal diffusion layer and the generation of irregularities on the substrate surface, which results in the optical waveguide. As a result, the light propagation performance is deteriorated, which is a problem. In addition, metal diffusion progresses with the passage of time, and optical characteristics such as light propagation characteristics change due to changes over time, which is a problem, and the metal diffusion state should be uniform for each optical waveguide. However, the dispersion of the optical characteristics among the individual optical waveguides is a serious problem.
【０００７】[0007]
【目的】そこで、本発明は、光散乱損失の要因となる格
子欠陥が少なく、光学的特性のバラツキや性能劣化を極
力防止し、良好な光導波路特性を再現性よく得ることが
できる光導波路及びその製造方法を提供することを目的
とする。[Object] Therefore, the present invention provides an optical waveguide in which there are few lattice defects that cause a light scattering loss, variation in optical characteristics and performance deterioration are prevented as much as possible, and good optical waveguide characteristics can be obtained with good reproducibility. It is intended to provide a manufacturing method thereof.
【０００８】[0008]
【課題を解決するための手段】上記目的を達成するため
に、本発明の光導波路は、ニオブ酸リチウム単結晶の基
板上に、ニオブ酸リチウム単結晶よりも高い屈折率を有
し、かつ透明な単結晶薄膜を形成して成ることを特徴と
する。In order to achieve the above object, the optical waveguide of the present invention has a higher refractive index than a lithium niobate single crystal on a substrate of a lithium niobate single crystal and is transparent. It is characterized in that it is formed by forming a simple single crystal thin film.
【０００９】また、その製造方法は、ニオブ酸リチウム
単結晶の基板の一主面に溝を形成し、該溝にニオブ酸リ
チウム単結晶よりも高い屈折率を有し、かつ透明な単結
晶薄膜をエピタキシャル成長させて導波路層を形成した
ことを特徴とする。Further, the manufacturing method is such that a groove is formed on one main surface of a substrate of a lithium niobate single crystal, and the groove has a higher refractive index than the lithium niobate single crystal and is a transparent single crystal thin film. Is epitaxially grown to form a waveguide layer.
【００１０】[0010]
【実施例】本発明に係る一実施例を詳細に説明する。ま
ず、本発明と比較するための試料を以下のように作製し
た。光学研磨されたオプティカルグレイドのＬＮ単結晶
の基板表面上に、リフトオフ法によりTiの導波路パター
ンを形成し、これを1040℃，7 時間熱拡散を行うことに
より、図２に示すような深さ約 4μm , 幅約 8μm のＹ
分岐形状の導波路層Ｔを有する分岐干渉型光スイッチ素
子(30 mm× 8mm×1mm) Ｙを 6個試作した。EXAMPLE An example according to the present invention will be described in detail. First, a sample for comparison with the present invention was prepared as follows. A Ti waveguide pattern is formed on the optically polished LN single crystal substrate surface by the lift-off method, and thermal diffusion is performed at 1040 ° C for 7 hours to obtain the depth shown in Fig. 2. Y of about 4 μm and width of about 8 μm
Six branch interference type optical switch elements (30 mm × 8 mm × 1 mm) Y each having a branched waveguide layer T were prototyped.
【００１１】上記各試料をＸ線トポグラフによるミクロ
観察を行ったところ、導波路層Ｔに多数の微小クラック
が存在していた。また、この試料の光導波路としての光
伝搬特性を確認するため、約1.3 μm の半導体レーザ光
を導波路層Ｔに導入し、入力光と出力光との差を計測し
て挿入損失を測定した結果、試料間で約 5〜10dBの大き
なバラツキが生じていた。Microscopic observation of each of the above samples by X-ray topography revealed that a large number of minute cracks were present in the waveguide layer T. In order to confirm the light propagation characteristics of this sample as an optical waveguide, a semiconductor laser beam of about 1.3 μm was introduced into the waveguide layer T, and the insertion loss was measured by measuring the difference between the input light and the output light. As a result, there was a large variation of about 5 to 10 dB among the samples.
【００１２】次に、本発明に係る試料の作製を以下のよ
うにして行った。図１（ａ）に示すように、光学研磨さ
れたオプティカルグレイドのＬＮ単結晶の基板Ｓ表面
に、反応性イオンエッチング法により深さ約 4μm , 幅
約 8μm , 長さ約30mmの溝Ｄを形成した。すなわち、ア
ルゴンガス雰囲気中に四塩化炭素（CCl 4 ) やフッ化炭
素(CF 4 ) などのエチングガスを導入して、レーザ光に
よるサブミクロン加工を行って溝Ｄを形成した。なお、
このエッチングは上記方法の他に、イオンビームエッチ
ング法、プラズマエッチング法、レーザアシスト法など
既に確立された種々のエッチング法を用いて行うことが
できる。Next, the sample according to the present invention was manufactured as follows. As shown in FIG. 1A, a groove D having a depth of about 4 μm, a width of about 8 μm, and a length of about 30 mm is formed on the surface S of an optically polished LN single crystal substrate S by a reactive ion etching method. did. That is, an etching gas such as carbon tetrachloride (CCl 4 ) or fluorocarbon (CF 4 ) was introduced into an argon gas atmosphere and submicron processing was performed by laser light to form the groove D. In addition,
In addition to the above method, this etching can be performed using various established etching methods such as an ion beam etching method, a plasma etching method, and a laser assist method.
【００１３】上記エッチングの後に、レーザ光を用いた
光ＣＶＤ法により、図１（ｂ）に示すような溝Ｄ中にTi
Ｏ2 単結晶の薄膜Ｆを膜厚約4μm に形成した。ここ
で、薄膜Ｆの形成は四塩化チタン（TiCl4 ）と酸素ガス
を導入してクロム等の板材でマスキングを行いながら気
相エピタキシャル成長させて形成した。なお、この形成
は上記光ＣＶＤ法の他に、ＭＯＣＶＤ法などの各種のＣ
ＶＤ法やＭＢＥ（分子線エピタクシー）法など既に確立
された種々の薄膜形成法を用いることができる。また、
このエピタキシャル成長は気相エピタキシャル成長に限
定されるものではなく、例えば上記溝にTiＯ2 の粉末を
ＨＩＰなどにより圧粉成形した後に加熱して固相エピタ
キシャル成長を行わせてもよい。After the above etching, a Ti film is formed in the groove D as shown in FIG. 1B by a photo-CVD method using a laser beam.
A thin film F of O 2 single crystal was formed to a film thickness of about 4 μm. Here, the thin film F was formed by vapor phase epitaxial growth while introducing titanium tetrachloride (TiCl 4 ) and oxygen gas and masking with a plate material such as chromium. In addition to the above photo CVD method, this formation is performed by various C such as MOCVD method.
Various established thin film forming methods such as the VD method and the MBE (Molecular Beam Epitaxy) method can be used. Also,
This epitaxial growth is not limited to vapor phase epitaxial growth. For example, solid phase epitaxial growth may be performed by pressing the TiO 2 powder in the groove by HIP or the like and then heating.
【００１４】このようにして、薄膜Ｓを導波路層とする
上記比較例と同様な形態の分岐干渉型スイッチ素子を 6
個試作し、これら試料のそれぞれについてＸトポグラフ
によるミクロ観察を行ったところ、導波路層にはほとん
どクラックは発生していなかった。また、挿入損失も全
ての試料で約 1dB程度であり、バラツキもほとんどなか
った。このように単結晶薄膜としたので従来の金属拡散
層の諸問題を解消することができた。In this way, a branching interference type switching device having the same configuration as that of the above-mentioned comparative example using the thin film S as a waveguide layer is provided.
As a result of making trial productions and micro-observing each of these samples by X topography, almost no cracks were generated in the waveguide layer. Moreover, the insertion loss was about 1 dB in all samples, and there was almost no variation. Since the single crystal thin film is used as described above, various problems of the conventional metal diffusion layer can be solved.
【００１５】なお、本実施例は導波路層にTiＯ2 単結晶
を用いた例を示したが、これに限定されるものではな
く、ＬＮ（屈折率ｎ≒2.2)よりも高屈折率なSrTiＯ3 (
ｎ≒2.41) ，Bi12SiＯ20( ｎ≒2.54) ，ダイヤモンド
（ｎ≒2.42))など無色透明な単結晶であればよい。なお
また、これら単結晶の固溶体も屈折率がＬＮより下回ら
ない組成範囲内で適宜変更し実施しうる。Although this embodiment shows an example in which a TiO 2 single crystal is used for the waveguide layer, the present invention is not limited to this, and SrTiO having a refractive index higher than LN (refractive index n≈2.2) is used. 3 (
Any colorless and transparent single crystal such as n≈2.41), Bi 12 SiO 20 (n≈2.54), diamond (n≈2.42)) may be used. Further, these single crystal solid solutions may be appropriately modified and implemented within a composition range in which the refractive index is not lower than LN.
【００１６】[0016]
【発明の効果】以上詳述したように、ニオブ酸リチウム
単結晶の基板上に、ニオブ酸リチウム単結晶よりも高い
屈折率を有し、かつ透明な単結晶薄膜から成る導波路層
を形成した本発明の光導波路及びその製造方法によれ
ば、従来の光導波路に比して導波路層内の欠陥密度を著
しく低下させ、光散乱を極力防止した光導波路を提供す
ることができる。As described above in detail, a waveguide layer formed of a transparent single crystal thin film having a higher refractive index than the lithium niobate single crystal is formed on the substrate of the lithium niobate single crystal. According to the optical waveguide and the method of manufacturing the same of the present invention, it is possible to provide an optical waveguide in which the defect density in the waveguide layer is remarkably reduced as compared with the conventional optical waveguide, and light scattering is prevented as much as possible.
【００１７】また、導波路層が完全な単結晶であるの
で、従来の金属拡散層の諸問題を全て解消することがで
き、光伝搬特性の経時変化がなく、しかも個々の光導波
路間の光学的特性のバラツキもほとんどない。また単結
晶による光学的異方性を利用することにより、基板との
導波路層との屈折率差を効果的に制御でき、これにより
光伝搬損失が最小で、かつバラツキの極めて少ない光導
波路を再現性良く提供することができる。Further, since the waveguide layer is a perfect single crystal, it is possible to solve all the problems of the conventional metal diffusion layer, there is no change in the light propagation characteristics with time, and moreover, the optics between the individual optical waveguides. There is almost no variation in characteristics. In addition, by utilizing the optical anisotropy of the single crystal, it is possible to effectively control the difference in the refractive index between the substrate and the waveguide layer, which results in an optical waveguide with minimal optical propagation loss and very little variation. It can be provided with good reproducibility.
【００１８】さらに、本発明の光導波路の製造方法は、
従来の金属の熱拡散による導波路層の形成方法は拡散の
分布の調整が困難であったのに対し、より容易にかつ精
度良く導波路層を形成することができる。Further, the method of manufacturing the optical waveguide of the present invention is
In the conventional method of forming a waveguide layer by thermal diffusion of metal, it is difficult to adjust the distribution of diffusion, but the waveguide layer can be formed more easily and accurately.
【図１】（ａ）は基板を所定溝形状にエッチングした様
子を示す図であり、（ｂ）は基板の溝部に高屈折率単結
晶薄膜層を形成した様子を示す図である。FIG. 1A is a diagram showing a state where a substrate is etched into a predetermined groove shape, and FIG. 1B is a diagram showing a state where a high refractive index single crystal thin film layer is formed in a groove portion of the substrate.
【図２】熱拡散法により作製した分岐干渉型光スイッチ
素子の平面図である。FIG. 2 is a plan view of a branch interference type optical switch element manufactured by a thermal diffusion method.
【図３】（ａ）はリフトオフによる金属パターンを形成
した様子を示す図であり、（ｂ）は基板に金属の熱拡散
を行った様子を示す図である。FIG. 3A is a diagram showing a state in which a metal pattern is formed by lift-off, and FIG. 3B is a diagram showing a state in which metal is thermally diffused on a substrate.
Ｍ ・・・ 金属層 Ｓ ・・・ 基板 Ｔ ・・・ 高屈折率層 Ｄ ・・・ 溝 Ｆ ・・・ 薄膜 Ｙ ・・・ 分岐干
渉型光スイッチ素子M ... Metal layer S ... Substrate T ... High refractive index layer D ... Groove F ... Thin film Y ... Branch interference type optical switch element
Claims (2)
オブ酸リチウム単結晶よりも高い屈折率を有し、かつ透
明な単結晶薄膜から成る導波路層を形成したことを特徴
とする光導波路。1. An optical waveguide comprising a lithium niobate single crystal substrate and a waveguide layer formed of a transparent single crystal thin film having a refractive index higher than that of the lithium niobate single crystal. ..
に溝を形成し、該溝にニオブ酸リチウム単結晶よりも高
い屈折率を有し、かつ透明な単結晶薄膜をエピタキシャ
ル成長させて導波路層を形成したことを特徴とする光導
波路の製造方法。2. A groove is formed on one main surface of a substrate of a lithium niobate single crystal, and a transparent single crystal thin film having a higher refractive index than that of the lithium niobate single crystal and epitaxially grown is formed. A method of manufacturing an optical waveguide, characterized in that a waveguide layer is formed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28687091A JPH05127033A (en) | 1991-10-31 | 1991-10-31 | Optical waveguide and its production |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28687091A JPH05127033A (en) | 1991-10-31 | 1991-10-31 | Optical waveguide and its production |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH05127033A true JPH05127033A (en) | 1993-05-25 |
Family
ID=17710072
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP28687091A Pending JPH05127033A (en) | 1991-10-31 | 1991-10-31 | Optical waveguide and its production |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH05127033A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021031416A1 (en) * | 2019-08-22 | 2021-02-25 | 苏州易锐光电科技有限公司 | Lithium niobate optical waveguide chip |
-
1991
- 1991-10-31 JP JP28687091A patent/JPH05127033A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021031416A1 (en) * | 2019-08-22 | 2021-02-25 | 苏州易锐光电科技有限公司 | Lithium niobate optical waveguide chip |
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