JP5494400B2 - Optical waveguide device - Google Patents
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- JP5494400B2 JP5494400B2 JP2010222695A JP2010222695A JP5494400B2 JP 5494400 B2 JP5494400 B2 JP 5494400B2 JP 2010222695 A JP2010222695 A JP 2010222695A JP 2010222695 A JP2010222695 A JP 2010222695A JP 5494400 B2 JP5494400 B2 JP 5494400B2
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Description
本発明は、光導波路素子に関し、特に、電気光学効果を有する厚さが３０μｍ以下の基板に光導波路が形成された光導波路基板と、該光導波路基板が補強基板と接着剤層を介して接合されている光導波路素子に関する。 The present invention relates to an optical waveguide device, and in particular, an optical waveguide substrate in which an optical waveguide is formed on a substrate having an electrooptic effect and a thickness of 30 μm or less, and the optical waveguide substrate is bonded to a reinforcing substrate via an adhesive layer. The present invention relates to an optical waveguide device.
光導波路素子の中でも、光変調器は、変調帯域の広帯域化や駆動電圧の低減のため、光導波路が形成された主基板を、１０μｍ程度まで薄板化し、電界効率の向上や速度整合条件を調整し、光変調器の変調性能の向上を図っている。また、このような薄く加工された基板を、安定的に製造プロセスで取り扱うことを可能とし、また製品としての機械的強度を確保するため、特許文献１に示すように、薄板化される主基板に、補強基板を接着させた構造を持つ光導波路素子が提案されている。 Among optical waveguide elements, the optical modulator is designed to reduce the main substrate on which the optical waveguide is formed to about 10 μm to improve the electric field efficiency and adjust the speed matching conditions in order to widen the modulation band and reduce the drive voltage. However, the modulation performance of the optical modulator is improved. In addition, in order to make it possible to stably handle such a thinly processed substrate in a manufacturing process and to ensure mechanical strength as a product, as shown in Patent Document 1, a main substrate to be thinned In addition, an optical waveguide device having a structure in which a reinforcing substrate is bonded has been proposed.
図１は、従来の光導波路素子の断面図であり、光導波路が形成された主基板（光導波路基板）の上面には、信号電極や接地電極などから構成される制御電極が設けられ、主基板の下面には、接着剤層を介して補強基板が接続されている。 FIG. 1 is a cross-sectional view of a conventional optical waveguide device. On the upper surface of a main substrate (optical waveguide substrate) on which an optical waveguide is formed, a control electrode including a signal electrode and a ground electrode is provided. A reinforcing substrate is connected to the lower surface of the substrate via an adhesive layer.
このように光導波路が薄い主基板上に形成されている場合、光導波路の分岐部や結合部などから漏れた光波は、主基板内をスラブ導波路として伝搬し、後方の光導波路と干渉して、信号光の消光比の劣化や、信号光をモニターする受光素子で受光信号の位相差が発生するなどの問題を生じていた。このような問題は、主基板の厚みが１００μｍ以上のものにおいては重大なものではない。これは、基板の厚み方向で、光導波路から離れる方向に漏れ光が進行し、光導波路と再結合する機会が少ないためである。 When the optical waveguide is formed on a thin main substrate in this way, light waves leaking from the branching portion or coupling portion of the optical waveguide propagate as a slab waveguide in the main substrate and interfere with the rear optical waveguide. As a result, problems such as deterioration of the extinction ratio of the signal light and a phase difference of the received light signal occur in the light receiving element that monitors the signal light. Such a problem is not serious when the thickness of the main substrate is 100 μm or more. This is because leakage light advances in the direction away from the optical waveguide in the thickness direction of the substrate, and there are few opportunities to recombine with the optical waveguide.
薄板化された主基板を使用する光導波路素子において、光導波路の外側を伝播している光が後段の光導波路と干渉することの無いようにするため、特許文献２又は３に示すように、光導波路に三分岐光導波路を形成するなど、高次モード光を導出するための分岐導波路を信号光が伝搬する光導波路に接続する方法や、特許文献４又は５に示すように、光導波路の近傍に遮光手段や迷光除去手段を配置する方法などが提示されている。 In the optical waveguide element using the thinned main substrate, in order to prevent light propagating outside the optical waveguide from interfering with the optical waveguide in the subsequent stage, as shown in Patent Document 2 or 3, A method of connecting a branched waveguide for deriving higher-order mode light to an optical waveguide through which signal light propagates, such as forming a three-branched optical waveguide in the optical waveguide, or as disclosed in Patent Document 4 or 5, A method of arranging a light shielding means and a stray light removing means in the vicinity of is proposed.
しかしながら、分岐導波路を別途設ける方法については、設計上のマージンが少なく、製造上の僅かなプロセス誤差により、満足する特性が得られないという問題がある。また、光導波路の近傍に遮光手段等を配置する方法は、遮光手段の設置場所が限られ、局所的な遮光手段では、十分に漏出光などを吸収できないなどの問題を生じていた。 However, the method of separately providing the branching waveguide has a problem that a margin in design is small and satisfactory characteristics cannot be obtained due to a slight process error in manufacturing. Further, the method of arranging the light shielding means in the vicinity of the optical waveguide has a problem that the installation location of the light shielding means is limited, and the local light shielding means cannot sufficiently absorb the leaked light.
本発明が解決しようとする課題は、上述したような問題を解決し、薄板化した主基板を伝播する信号光の光学的な特性劣化を抑制し、製品の光学特性を向上させることが可能な光導波路素子を提供することである。 The problem to be solved by the present invention is to solve the above-described problems, suppress optical characteristic deterioration of signal light propagating through the thinned main substrate, and improve the optical characteristics of the product. An optical waveguide device is provided.
上記課題を解決するため、請求項１に係る発明は、電気光学効果を有する厚さが３０μｍ以下の基板に光導波路が形成された光導波路基板と、該光導波路基板には、該光導波路に電界を印加する制御電極が形成され、さらに、該光導波路基板が補強基板と接着剤層を介して接合されている光導波路素子において、該光導波路基板の該補強基板側の面上であって、該光導波路が形成された部分にバッファ層が形成され、該バッファ層を覆うように該光導波路基板の該補強基板側に、光吸収膜が形成されており、該光吸収膜が半導体膜又は該制御電極と電気的に接続していない金属膜のいずれかであることを特徴とする。 In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an optical waveguide substrate in which an optical waveguide is formed on a substrate having an electrooptic effect and a thickness of 30 μm or less, and the optical waveguide substrate includes an optical waveguide. In an optical waveguide element in which a control electrode for applying an electric field is formed, and the optical waveguide substrate is bonded to the reinforcing substrate via an adhesive layer , the optical waveguide substrate is on the reinforcing substrate side surface. A buffer layer is formed in the portion where the optical waveguide is formed, and a light absorbing film is formed on the reinforcing substrate side of the optical waveguide substrate so as to cover the buffer layer, and the light absorbing film is a semiconductor film Alternatively, it is any metal film that is not electrically connected to the control electrode .
請求項１に係る発明により、電気光学効果を有する厚さが３０μｍ以下の基板に光導波路が形成された光導波路基板と、該光導波路基板が補強基板と接着剤層を介して接合されている光導波路素子において、該光導波路基板の該補強基板側の面上であって、該光導波路が形成された部分にバッファ層が形成され、該バッファ層を覆うように該光導波路基板の該補強基板側に、光吸収膜が形成されているため、光吸収膜の配置場所を広くとることができ、光導波路基板の表面に配置した膜体だけで、効率良く漏出光を吸収することができる。このため、漏出光などの光導波路の外側を伝播する光が後段の光導波路に再結合することが抑制される。 According to the first aspect of the present invention, an optical waveguide substrate in which an optical waveguide is formed on a substrate having an electro-optic effect and a thickness of 30 μm or less, and the optical waveguide substrate are bonded to a reinforcing substrate via an adhesive layer. In the optical waveguide element, a buffer layer is formed on a surface of the optical waveguide substrate on the reinforcing substrate side where the optical waveguide is formed, and the reinforcement of the optical waveguide substrate is covered so as to cover the buffer layer. Since the light absorption film is formed on the substrate side, the arrangement place of the light absorption film can be widened, and the leakage light can be efficiently absorbed only by the film body arranged on the surface of the optical waveguide substrate. . For this reason, it is suppressed that the light propagating outside the optical waveguide, such as leaked light, is recombined with the optical waveguide at the subsequent stage.
また、光導波路と光吸収膜との間に、光の吸収を抑制するバッファ層が形成されているため、光導波路と光吸収膜との距離を適切に保持することができ、例えば信号光が光吸収膜に吸収されるのを抑制することも可能となる。さらに、バッファ層を光導波路とほぼ同じパターンで形成し、それを覆うように光吸収膜を光導波路基板に形成するだけで、光導波路に接触せず、かつ光導波路の近傍に配置された光吸収膜を設けることが可能となる。さらに、光吸収膜はバッファ層を覆うように、光導波路基板の全面に付けると、漏出光の大部分を吸収できる。 In addition, since a buffer layer that suppresses light absorption is formed between the optical waveguide and the light absorption film, the distance between the optical waveguide and the light absorption film can be appropriately maintained. It is also possible to suppress absorption by the light absorption film. Furthermore, the buffer layer is formed in almost the same pattern as the optical waveguide, and the light absorbing film is formed on the optical waveguide substrate so as to cover it, and the light disposed in the vicinity of the optical waveguide without contacting the optical waveguide. An absorption film can be provided. Furthermore, when the light absorption film is attached to the entire surface of the optical waveguide substrate so as to cover the buffer layer, most of the leaked light can be absorbed.
さらに、請求項１に係る発明により、光吸収膜が半導体膜又は浮遊金属膜（制御電極と電気的に接続していない金属膜）のいずれかであるため、簡便に光吸収膜を形成することができる。しかも、半導体膜の場合は、金属膜と比較し、信号電極の損失が少なく、大きなインピーダンス変化も抑制され、光導波路素子の光学特性の劣化を防止することができる。また、浮遊金属膜とすることで、制御電極が形成する電界分布に与える影響を最小限とすることが可能となる。 Furthermore, according to the invention of claim 1 , since the light absorption film is either a semiconductor film or a floating metal film (metal film not electrically connected to the control electrode) , the light absorption film can be easily formed. Can do. In addition, in the case of the semiconductor film, the loss of the signal electrode is less than that of the metal film, a large impedance change is suppressed, and deterioration of the optical characteristics of the optical waveguide element can be prevented. In addition, by using the floating metal film, the influence on the electric field distribution formed by the control electrode can be minimized.
以下、本発明の光導波路素子について、詳細に説明する。
本発明の光導波路素子は、図２又は３に示すように、電気光学効果を有する厚さが３０μｍ以下の基板に光導波路が形成された光導波路基板と、該光導波路基板が補強基板と接着剤層を介して接合されている光導波路素子において、該光導波路基板の該補強基板側の面上であって、該光導波路が形成された部分にバッファ層が形成され、該バッファ層を覆うように該光導波路基板の該補強基板側に、光吸収膜が形成されていることを特徴とする。
Hereinafter, the optical waveguide device of the present invention will be described in detail.
As shown in FIG. 2 or 3, the optical waveguide element of the present invention includes an optical waveguide substrate in which an optical waveguide is formed on a substrate having an electro-optic effect and a thickness of 30 μm or less, and the optical waveguide substrate is bonded to a reinforcing substrate. In the optical waveguide element bonded through the agent layer, a buffer layer is formed on a surface of the optical waveguide substrate on the reinforcing substrate side where the optical waveguide is formed, and covers the buffer layer As described above, a light absorption film is formed on the reinforcing substrate side of the optical waveguide substrate.
電気光学効果を有する材料としては、例えば、ニオブ酸リチウム、タンタル酸リチウム、ＰＬＺＴ（ジルコン酸チタン酸鉛ランタン）、及びこれらの組み合わせが利用可能である。特に、電気光学効果の高いニオブ酸リチウム（ＬＮ）結晶が好適に利用される。 As a material having an electro-optic effect, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), and combinations thereof can be used. In particular, a lithium niobate (LN) crystal having a high electro-optic effect is preferably used.
光導波路の形成方法としては、Ｔｉなどを熱拡散法やプロトン交換法などで基板表面に拡散させることにより形成することができる。また、特許文献６のように、薄板１の表面に光導波路の形状に合わせてリッジを形成し、光導波路を構成することも可能である。さらに、リッジ型導波路と拡散導波路とを併用することも可能である。 As a method for forming the optical waveguide, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. Further, as in Patent Document 6, it is possible to form an optical waveguide by forming a ridge on the surface of the thin plate 1 in accordance with the shape of the optical waveguide. Furthermore, a ridge type waveguide and a diffusion waveguide can be used in combination.
光変調器や光スイッチなどの光導波路素子の場合には、光導波路に電界を印加するため、信号電極や接地電極などからなる制御電極が、光導波路基板の表面などに形成される。制御電極は、Ｔｉ・Ａｕの電極パターンの形成及び金メッキ方法などにより形成することが可能である。電気光学効果を有する材料は全て酸化物であり、その材料の酸素と電極材料が結合し、低誘電率層（酸化物層）が形成される。金（Ａｕ）は基本的に酸化し難い材料であるため、電極材料にはＴｉ等の材料が含まれることが望ましい。 In the case of an optical waveguide device such as an optical modulator or an optical switch, in order to apply an electric field to the optical waveguide, a control electrode including a signal electrode and a ground electrode is formed on the surface of the optical waveguide substrate. The control electrode can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like. All materials having an electro-optic effect are oxides, and oxygen of the material and the electrode material are combined to form a low dielectric constant layer (oxide layer). Since gold (Au) is basically a material that is not easily oxidized, it is desirable that the electrode material includes a material such as Ti.
光導波路素子を構成する主基板（光導波路基板）の薄板化方法は、数百μｍの厚さを有する基板に上述した光導波路を形成し、基板の裏面を研磨して、３０μｍ以下の厚みを有する薄板を作成する。その後薄板の表面に制御電極を作り込む。また、光導波路や制御電極などの作り込みを行った後に、基板の裏面を研磨することも可能である。なお、光導波路形成時の熱的衝撃や各種処理時の薄膜の取り扱いによる機械的衝撃などが加わると、薄板が破損する危険性もあるため、これらの熱的又は機械的衝撃が加わり易い工程は、基板を研磨して薄板化する前に行うことが好ましい。 The method of thinning the main substrate (optical waveguide substrate) constituting the optical waveguide element is to form the above-described optical waveguide on a substrate having a thickness of several hundreds μm, and polish the back surface of the substrate to have a thickness of 30 μm or less. Create a thin plate with. Thereafter, control electrodes are formed on the surface of the thin plate. It is also possible to polish the back surface of the substrate after making the optical waveguide, the control electrode, and the like. In addition, there is a risk that the thin plate may be damaged when a thermal shock during the formation of the optical waveguide or a mechanical shock due to the handling of the thin film during various treatments. It is preferably performed before the substrate is polished and thinned.
図２又は３に示すように、薄板化された光導波路基板を補強するため、補強基板が接着剤層を介して光導波路基板に接合されている。補強基板に使用される材料としては、種々のものが利用可能であり、例えば、薄板化される主基板と同様の材料を使用する他に、石英、ガラス、アルミナなどのように薄板より低誘電率の材料を使用したり、または、特許文献６のように薄板と異なる結晶方位を有する材料を使用することも可能である。ただし、線膨張係数が薄板と同等である材料を選定することが、温度変化に対する光変調素子の変調特性を安定させる上で好ましい。仮に、同等の材料の選定が困難である場合には、薄板と補強板とを接合する接着剤に、薄板と同等な線膨張係数を有する材料を選定する。 As shown in FIG. 2 or 3, in order to reinforce the thinned optical waveguide substrate, the reinforcing substrate is bonded to the optical waveguide substrate via an adhesive layer. Various materials can be used for the reinforcing substrate. For example, in addition to using the same material as the main substrate to be thinned, the dielectric material has a lower dielectric than that of a thin plate such as quartz, glass, and alumina. It is also possible to use a material having a ratio of crystal or a material having a crystal orientation different from that of a thin plate as in Patent Document 6. However, it is preferable to select a material having a linear expansion coefficient equivalent to that of the thin plate in order to stabilize the modulation characteristics of the light modulation element with respect to temperature changes. If it is difficult to select an equivalent material, a material having a linear expansion coefficient equivalent to that of the thin plate is selected as an adhesive for joining the thin plate and the reinforcing plate.
光導波路基板と補強基板との接合には、接着剤層として、エポキシ系接着剤、熱硬化型接着剤、紫外線硬化性接着剤、半田ガラス、熱硬化性、光硬化性あるいは光増粘性の樹脂接着剤シートなど、種々の接着材料を使用することが可能である。 For bonding between the optical waveguide substrate and the reinforcing substrate, as an adhesive layer, an epoxy adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, solder glass, a thermosetting, photocurable or photothickening resin Various adhesive materials such as adhesive sheets can be used.
本発明の光導波路素子の特徴は、光導波路基板の補強基板側の面に光吸収膜を形成することであり、光吸収膜としては、ＳｉやＳｉＮなどの半導体膜や、ＡｌやＡｕなどの浮遊金属膜が使用可能である。特に、光吸収膜を設ける前の従来の光導波路素子と比較して、光学特性の変化を少なくするためには、光吸収膜として半導体膜を使用することが好ましい。また金属膜は浮遊させることで、制御電極が形成する電場に与える影響を最小限とすることが可能となる。 A feature of the optical waveguide device of the present invention is that a light absorption film is formed on the surface of the optical waveguide substrate on the reinforcing substrate side. As the light absorption film, a semiconductor film such as Si or SiN, Al or Au, or the like is used. A floating metal film can be used. In particular, it is preferable to use a semiconductor film as the light absorption film in order to reduce the change in optical characteristics as compared with the conventional optical waveguide element before the light absorption film is provided. Further, by floating the metal film, it is possible to minimize the influence on the electric field formed by the control electrode.
半導体膜は、金属膜より光吸収機能が低いため、光導波路基板の面においては、金属膜より、より広い領域に配置することが必要である。また、特定の箇所に離散的に金属膜を設けるような配置パターンではなく、図１に示すように、光導波路基板の全面に渡って光吸収膜である半導体膜を配置することが好ましい。 Since the semiconductor film has a lower light absorption function than the metal film, it is necessary to dispose the semiconductor film in a wider area than the metal film on the surface of the optical waveguide substrate. Further, it is preferable to arrange a semiconductor film as a light absorption film over the entire surface of the optical waveguide substrate, as shown in FIG. 1, instead of an arrangement pattern in which metal films are discretely provided at specific locations.
本発明では、光導波路近傍の裏面にも、半導体膜や浮遊金属膜などの光吸収膜を形成すると、光導波路を伝播する信号光も吸収し、光導波路の損失が増加することとなる。この問題を防ぐため、光導波路と光吸収膜との間に、光の吸収を抑制するバッファ層が形成することが好ましい。バッファ層には、信号光を吸収しないＳｉＯ２など、屈折率の小さい誘電体を用いることができる。なお、浮遊金属膜が導波光を吸収することを防ぐためには、バッファ層の厚みは０．６μｍ以上必要である。 In the present invention, when a light absorption film such as a semiconductor film or a floating metal film is formed on the back surface in the vicinity of the optical waveguide, the signal light propagating through the optical waveguide is also absorbed, and the loss of the optical waveguide increases. In order to prevent this problem, it is preferable to form a buffer layer for suppressing light absorption between the optical waveguide and the light absorption film. For the buffer layer, a dielectric having a low refractive index, such as SiO 2 that does not absorb signal light, can be used. In order to prevent the floating metal film from absorbing the guided light, the thickness of the buffer layer needs to be 0.6 μm or more.
なお、図３に示すように、バッファ層を用いず、光導波路の下側などを避けるように、光吸収膜をパターニングして形成することも可能である。このような場合には、接着剤層に、屈折率の低い材料を使用することが重要である。 In addition, as shown in FIG. 3, it is also possible to pattern and form the light absorption film so as to avoid the lower side of the optical waveguide without using the buffer layer. In such a case, it is important to use a material having a low refractive index for the adhesive layer.
主基板（光導波路基板）及び補強基板として、ニオブ酸リチウム（ＬＮ）基板を用い、屈折率が１．５程度の接着剤を用いて変調器を作製した場合について、本発明の光導波路素子の効果を検証した。 In the case where a modulator is manufactured using a lithium niobate (LN) substrate as a main substrate (optical waveguide substrate) and a reinforcing substrate, and an adhesive having a refractive index of about 1.5, the optical waveguide element of the present invention is used. The effect was verified.
主基板となるＬＮの裏面の光導波路近傍のみに、ＳｉＯ２の誘電体膜をバッファ層として成膜する。このときのバッファ層の厚さは、０．６μｍとし、この後、主基板の裏面全面に、光吸収膜として、Ｓｉの半導体膜を形成した。この膜の厚さについては、主基板内を伝搬する不要光を充分に吸収できる厚さに設定した。 A dielectric film of SiO 2 is formed as a buffer layer only in the vicinity of the optical waveguide on the back surface of the LN serving as the main substrate. At this time, the thickness of the buffer layer was 0.6 μm, and thereafter, a Si semiconductor film was formed as a light absorption film on the entire back surface of the main substrate. The thickness of this film was set to a thickness that can sufficiently absorb unnecessary light propagating in the main substrate.
本発明の光導波路素子と光吸収膜を形成していない従来品とについて、光変調器の消光比、及びモニタＰＤの位相差特性を測定したところ、いずれも本発明品の方が良好であることを確認した。特に、消光比については、２５ｄＢ以上が得られた。 When the extinction ratio of the optical modulator and the phase difference characteristic of the monitor PD were measured for the optical waveguide element of the present invention and the conventional product in which the light absorption film was not formed, both of the products of the present invention were better. It was confirmed. In particular, an extinction ratio of 25 dB or more was obtained.
以上説明したように、本発明によれば、薄板化した主基板を伝播する信号光の光学的な特性劣化を抑制し、製品の光学特性を向上させることが可能な光導波路素子を提供することが可能となる。 As described above, according to the present invention, it is possible to provide an optical waveguide element capable of suppressing optical characteristic deterioration of signal light propagating through a thinned main substrate and improving product optical characteristics. Is possible.
Claims (1)
該光導波路基板の該補強基板側の面上であって、該光導波路が形成された部分にバッファ層が形成され、
該バッファ層を覆うように該光導波路基板の該補強基板側に、光吸収膜が形成されており、該光吸収膜が半導体膜又は該制御電極と電気的に接続していない金属膜のいずれかであることを特徴とする光導波路素子。 An optical waveguide substrate in which an optical waveguide is formed on a substrate having a thickness of 30 μm or less having an electro-optic effect, a control electrode for applying an electric field to the optical waveguide is formed on the optical waveguide substrate, and the optical waveguide In the optical waveguide device in which the substrate is bonded to the reinforcing substrate via the adhesive layer,
A buffer layer is formed on a portion of the optical waveguide substrate on the reinforcing substrate side where the optical waveguide is formed,
A light absorption film is formed on the reinforcing substrate side of the optical waveguide substrate so as to cover the buffer layer, and the light absorption film is either a semiconductor film or a metal film that is not electrically connected to the control electrode. optical waveguide device which is characterized in that the or.
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