JP2005055774A

JP2005055774A - Optical intensity modulator

Info

Publication number: JP2005055774A
Application number: JP2003288170A
Authority: JP
Inventors: Hidetaka Kosho; 英高古庄
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 2003-08-06
Filing date: 2003-08-06
Publication date: 2005-03-03

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical intensity modulator capable of effectively modulating optical intensity at low voltage. <P>SOLUTION: Upper part electrodes 15 are formed at upper parts of light guides 12 via buffer layers 13 at a part where the two light guides 12 are formed to be parallel to each other at the center of a substrate 11. The upper part electrodes 15 are formed with widths L wider than the average widths M of the light guides 12 at width wider parts 15b far from the lower ends 15a coming in contact with the buffer layers 13 and narrowed acutely toward the lower ends 15a from the width wider parts 15b. The upper electrodes 15 are formed with widths W narrower than the average widths M of the light guides 12 at the lower ends 15a. The upper electrodes 15 is formed so as to be narrowed at an obtuse angle toward further upper parts from the width wider parts 15b, that is, toward the direction far from the light guides 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、光導波路とこの光導波路を挟んで上下方向に電極を有する光強度変調器に関するものである。 The present invention relates to an optical waveguide and an optical intensity modulator having electrodes in the vertical direction across the optical waveguide.

ＬｉＮｂＯ_３などの電気光学効果を有する材料に導波路および電極を形成した光デバイスは、光通信などの分野で広く用いられている。こうした光デバイスのうち、光強度変調器は電極にパルス信号を入力すると高速で光をオン・オフして光信号を発生する素子であり、光通信システムの中心的な構成部品として用いられている。 An optical device in which a waveguide and an electrode are formed on a material having an electro-optic effect such as LiNbO ₃ is widely used in fields such as optical communication. Among these optical devices, a light intensity modulator is an element that generates an optical signal by turning on and off light at high speed when a pulse signal is input to an electrode, and is used as a central component of an optical communication system. .

こうした光強度変調器は、電気光学効果を有する基板に光導波路を形成し、この基板上面に沿って並列するように電極を配置した、いわゆるコプレナー（ＣＰＬ）タイプが従来より知られている。こうしたＣＰＬタイプの光強度変調器の改良型として、基板の厚み方向に沿って光導波路の上下に電極を形成した光強度変調器が知られている。（例えば、特許文献１参照）。
特許第２８０５０２７号公報 As such a light intensity modulator, a so-called coplanar (CPL) type in which an optical waveguide is formed on a substrate having an electro-optic effect and electrodes are arranged in parallel along the upper surface of the substrate is conventionally known. As an improved version of such a CPL type light intensity modulator, a light intensity modulator is known in which electrodes are formed above and below an optical waveguide along the thickness direction of a substrate. (For example, refer to Patent Document 1).
Japanese Patent No. 2805027

しかしながら、特許文献１に記載されたような構成の光強度変調器の場合、光導波路の下側に形成された下部電極が、光導波路の上部の上部電極よりも幅が広く形成されているために電界が拡散し易く、効率的に光強度を変調するのに難があった。 However, in the case of the light intensity modulator configured as described in Patent Document 1, the lower electrode formed on the lower side of the optical waveguide is formed wider than the upper electrode on the upper side of the optical waveguide. However, the electric field easily diffuses, and it is difficult to efficiently modulate the light intensity.

本発明は、上記事情に鑑みてなされたものであって、低電圧で効率的に光強度の変調が可能な光強度変調器を提供することを目的とする。 The present invention has been made in view of the above circumstances, and an object thereof is to provide a light intensity modulator capable of efficiently modulating light intensity at a low voltage.

上記の目的を達成するために、本発明によれば、屈折率を上昇させる拡散物質を基板の上面の一部に拡散形成された導波路と、前記導波路の両側で該導波路に沿って前記基板に掘り込まれた溝と、該基板の下面に形成された下部電極と、下端が前記導波路に接続されるとともに前記導波路の幅よりも狭く形成され、上端に向かって前記導波路の幅よりも広く広げられた上部電極とを備えたことを特徴とする光強度変調器が提供される。 In order to achieve the above object, according to the present invention, a waveguide is formed by diffusing a diffusion material for increasing the refractive index in a part of the upper surface of a substrate, and along the waveguide on both sides of the waveguide. A groove dug in the substrate, a lower electrode formed on the lower surface of the substrate, a lower end connected to the waveguide and formed narrower than a width of the waveguide, and the waveguide toward the upper end The light intensity modulator is provided with an upper electrode that is wider than the width of the upper electrode.

このような光強度変調器によれば、上部電極の電界を光導波路に向けて集中させることが可能になる。さらに光導波路の両側に溝を形成して、光導波路を基板の上面から突出させることで上部電極の電界の拡散が更に抑制され、光導波路に効率よく電界を集中できる。こうして光導波路に向けて電界を効率よく集中させることができれば、低電圧で光導波路を流れる光の強度を変調することができる。よって、低電圧動作の光強度変調器を実現できる。 According to such a light intensity modulator, the electric field of the upper electrode can be concentrated toward the optical waveguide. Further, by forming grooves on both sides of the optical waveguide and projecting the optical waveguide from the upper surface of the substrate, diffusion of the electric field of the upper electrode is further suppressed, and the electric field can be efficiently concentrated on the optical waveguide. If the electric field can be efficiently concentrated toward the optical waveguide in this way, the intensity of light flowing through the optical waveguide can be modulated with a low voltage. Therefore, a light intensity modulator operating at a low voltage can be realized.

前記上部電極は、前記導波路に向けて鋭角に窄まり、前記導波路から遠ざかる方向に向けて鈍角、または円弧状に窄まる形状に形成されていれば好ましい。 It is preferable that the upper electrode is formed in a shape that narrows at an acute angle toward the waveguide and is obtuse or arcuate in a direction away from the waveguide.

以上、詳細に説明したように、本発明によれば、上部電極の電界を光導波路に向けて集中させることが可能になる。さらに光導波路の両側に溝を形成して、光導波路を基板の上面から突出させることで上部電極の電界の拡散が更に抑制され、光導波路に効率よく電界を集中できる。こうして光導波路に向けて電界を効率よく集中させることができれば、低電圧で光導波路を流れる光の強度を変調することができる。よって、低電圧動作の光強度変調器を実現できる。 As described above in detail, according to the present invention, the electric field of the upper electrode can be concentrated toward the optical waveguide. Further, by forming grooves on both sides of the optical waveguide and projecting the optical waveguide from the upper surface of the substrate, diffusion of the electric field of the upper electrode is further suppressed, and the electric field can be efficiently concentrated on the optical waveguide. If the electric field can be efficiently concentrated toward the optical waveguide in this way, the intensity of light flowing through the optical waveguide can be modulated with a low voltage. Therefore, a light intensity modulator operating at a low voltage can be realized.

以下、本発明の実施の形態を図面を参照して説明する。図１は、本発明の光強度変調器の概略を示す外観斜視図である。光強度変調器１０は、例えばＬｉＮｂＯ_３などの電気光学効果を有する材料から形成されてなる基板１１を備えている。この基板１１には、屈折率を上昇させるＴｉなどの拡散物質を表面に堆積し、基板１１の厚み方向に拡散させて形成された、３次元の光導波路１２が形成されている。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view showing an outline of a light intensity modulator of the present invention. The light intensity modulator 10 includes a substrate 11 made of a material having an electro-optic effect such as LiNbO ₃ . The substrate 11 is formed with a three-dimensional optical waveguide 12 formed by depositing a diffusion material such as Ti for increasing the refractive index on the surface and diffusing it in the thickness direction of the substrate 11.

光導波路１２は、両端で１本の光導波路が途中で２つに分岐され、中央部分では２本の光導波路１２が平行して形成された構造を成している。こうした光導波路１２の上面には、光導波路１２に沿って誘電体薄膜からなるバッファ層１３が形成されている。こうしたバッファ層１３は、例えばＳｉＯ_２やＡｌ_２Ｏ_３などで形成されていれば良い。 The optical waveguide 12 has a structure in which one optical waveguide is branched into two in the middle at both ends, and two optical waveguides 12 are formed in parallel at the central portion. A buffer layer 13 made of a dielectric thin film is formed along the optical waveguide 12 on the upper surface of the optical waveguide 12. Such buffer layer 13, for example, may be formed by such as SiO ₂ or _Al 2 _{O 3.}

図２は、図１に示す光強度変調器の断面Ｓでの形状を示した断面図である。基板１１の中央で光導波路１２が２本に平行して形成された部分には、光導波路１２の上部にバッファ層１３を介して上部電極１５が形成されている。 FIG. 2 is a cross-sectional view showing the shape of the light intensity modulator shown in FIG. An upper electrode 15 is formed on the upper portion of the optical waveguide 12 with a buffer layer 13 in a portion where the optical waveguide 12 is formed in parallel at the center of the substrate 11.

上部電極１５は、バッファ層１３と接する下端１５ａから遠ざかった幅広部１５ｂで光導波路１２の平均幅Ｍよりも広い幅Ｌで形成され、幅広部１５ｂから下端１５ａに向けて鋭角に窄まる。そして、下端１５ａでは光導波路１２の平均幅Ｍよりも狭い幅Ｗに形成されている。また、幅広部１５ｂから更に上方、すなわち光導波路１２から遠ざかる方向に向けて、上部電極１５は鈍角に窄まるように形成されている。なお、上部電極１５の周囲は絶縁材等で覆われているのが好ましい。 The upper electrode 15 is formed with a wide width 15b that is farther from the lower end 15a in contact with the buffer layer 13 and with a width L wider than the average width M of the optical waveguide 12, and constricts at an acute angle from the wide portion 15b toward the lower end 15a. The lower end 15 a is formed with a width W narrower than the average width M of the optical waveguide 12. Further, the upper electrode 15 is formed to be constricted at an obtuse angle further upward from the wide portion 15b, that is, in a direction away from the optical waveguide 12. The periphery of the upper electrode 15 is preferably covered with an insulating material or the like.

基板１１には、光導波路１２の両側に沿って溝１６が形成されている。こうした溝１６によって、光導波路１２の上部は基板１１の上面で突条を成して延びる形状を成す。なお溝１６は、基板１１上にバッファ層１３を形成した後、光導波路１２に相当する部分をレジストで覆ってからエッチングを行なって基板１１を掘り下げることで形成すれば良い。 Grooves 16 are formed in the substrate 11 along both sides of the optical waveguide 12. Due to the grooves 16, the upper portion of the optical waveguide 12 has a shape extending in a protruding manner on the upper surface of the substrate 11. The groove 16 may be formed by forming the buffer layer 13 on the substrate 11, covering the portion corresponding to the optical waveguide 12 with a resist, and performing etching to dig up the substrate 11.

光導波路１２の下側には、基板１１を介して下部電極１８が形成されている。こうした下部電極１８は、例えば光導波路１２の平均幅Ｍとほぼ同じ幅ｍで形成されれば好ましい。 A lower electrode 18 is formed below the optical waveguide 12 through the substrate 11. Such a lower electrode 18 is preferably formed, for example, with a width m substantially the same as the average width M of the optical waveguide 12.

このように、上部電極１５を略水滴状の多角形に形成し、かつ、下部電極１８を光導波路１２の平均幅とほぼ同じ幅に形成することによって、上部電極１５の電界を光導波路１２に向けて集中させることが可能になる。さらに光導波路１２の両側に溝１６を形成して、光導波路１２を基板１１の上面から突出させることで上部電極１５の電界の拡散が更に抑制され、光導波路１２に効率よく電界を集中できる。こうして光導波路１２に向けて電界を効率よく集中させることができれば、低電圧で光導波路１２を流れる光の強度を変調することができる。よって、低電圧動作の光強度変調器を実現できる。 In this manner, the upper electrode 15 is formed in a substantially waterdrop-shaped polygon, and the lower electrode 18 is formed to have a width substantially the same as the average width of the optical waveguide 12, whereby the electric field of the upper electrode 15 is applied to the optical waveguide 12. It becomes possible to concentrate towards. Further, by forming grooves 16 on both sides of the optical waveguide 12 and projecting the optical waveguide 12 from the upper surface of the substrate 11, diffusion of the electric field of the upper electrode 15 is further suppressed, and the electric field can be efficiently concentrated on the optical waveguide 12. If the electric field can be efficiently concentrated toward the optical waveguide 12 in this way, the intensity of light flowing through the optical waveguide 12 can be modulated with a low voltage. Therefore, a light intensity modulator operating at a low voltage can be realized.

なお、こうした上部電極１５の形状は、図２に示したもの以外にも、例えば、図３に示すように、断面が略逆三角形の上部電極２１であっても良い。こうした上部電極２１においても、バッファ層１３と接する下端１５ａから遠ざかった幅広部２１ｂで光導波路１２の平均幅Ｍよりも広い幅Ｌで形成され、幅広部２１ｂから下端２１ａに向けて鋭角に窄まる。そして、下端２１ａで光導波路１２の平均幅Ｍよりも狭い幅Ｗに形成されている。また、幅広部２１ｂから更に上方に向けて、上部電極２１は円弧状に窄まるように形成されている。これにより、上部電極２１の電界を光導波路１２に向けて集中させ、低電圧で光導波路１２を流れる光の強度を変調することができる。 The shape of the upper electrode 15 other than that shown in FIG. 2 may be, for example, an upper electrode 21 having a substantially inverted triangular cross section as shown in FIG. Also in such an upper electrode 21, the wide portion 21 b far from the lower end 15 a in contact with the buffer layer 13 is formed with a width L wider than the average width M of the optical waveguide 12, and narrows at an acute angle from the wide portion 21 b toward the lower end 21 a. . The lower end 21 a is formed to have a width W narrower than the average width M of the optical waveguide 12. Further, the upper electrode 21 is formed so as to be constricted in an arc shape upward from the wide portion 21b. Thereby, the electric field of the upper electrode 21 can be concentrated toward the optical waveguide 12, and the intensity of light flowing through the optical waveguide 12 can be modulated with a low voltage.

本出願人は、本発明の光強度変調器の効果を検証した。まず、上部電極１５がバッファ層１３を介して光導波路１２に対面する先端形状を段階的に変化させた複数の光強度変調器を作成して、電界強度を測定した。検証にあたって、図４に示す各形状のサンプルを準備した。各サンプルは上部電極１５の下端１５ａを全て７μｍとして、この下端１５ａから遠ざかる方向の上部電極１５の角度を０°（傾斜なし），１１°，２０°，２９°，４０°にそれぞれ形成したサンプルＮｏ．１〜５を準備した。なお、図中の寸法表示の単位はμｍとした。 The applicant has verified the effect of the light intensity modulator of the present invention. First, a plurality of light intensity modulators were formed in which the tip shape of the upper electrode 15 facing the optical waveguide 12 via the buffer layer 13 was changed stepwise, and the electric field strength was measured. In the verification, samples of each shape shown in FIG. 4 were prepared. In each sample, the lower end 15a of the upper electrode 15 is all 7 μm, and the angle of the upper electrode 15 in the direction away from the lower end 15a is 0 ° (no inclination), 11 °, 20 °, 29 °, and 40 °, respectively. No. 1-5 were prepared. The unit of dimension display in the figure was μm.

そして、上述した各サンプル１〜５の上部電極１５の下端１５ａにおける電界強度をそれぞれ測定した。これら上部電極１５の角度を変えた電界強度の測定結果を図５に示す。図５に示す結果によれば、上部電極１５が下端１５ａから遠ざかる方向の角度を１０°〜３０°に設定すれば、上部電極１５の下端１５ａでの電界強度を３５００００（Ｖ／ｍ）以上の高いレベルに保てることが判明した。また、上部電極１５が下端１５ａから遠ざかる方向の角度を１０°〜４０°に設定すれば、上部電極１５の下端１５ａでの電界強度を３４００００（Ｖ／ｍ）以上のレベルに保てることが判明した。 And the electric field strength in the lower end 15a of the upper electrode 15 of each sample 1-5 mentioned above was measured, respectively. FIG. 5 shows the measurement results of the electric field strength obtained by changing the angle of the upper electrode 15. According to the result shown in FIG. 5, if the angle in the direction in which the upper electrode 15 moves away from the lower end 15 a is set to 10 ° to 30 °, the electric field strength at the lower end 15 a of the upper electrode 15 is 350,000 (V / m) or more. It turns out that it can be kept at a high level. It was also found that the electric field strength at the lower end 15a of the upper electrode 15 can be maintained at a level of 340000 (V / m) or more by setting the angle in the direction in which the upper electrode 15 moves away from the lower end 15a to 10 ° to 40 °. .

次に、図６に示す各形状のサンプル、すなわち上部電極１５の幅広部１５ｂでの幅を２７μｍに揃えてた上で、下端１５ａから幅広部１５ｂに向かう角度を０°（傾斜なし），１１°，２２°，３１°，３９°，４５°にそれぞれ形成したサンプルＮｏ．６〜１１を準備した。なお、図中の寸法表示の単位はμｍとした。 Next, after the samples of each shape shown in FIG. 6, that is, the width of the wide portion 15b of the upper electrode 15 is set to 27 μm, the angle from the lower end 15a toward the wide portion 15b is 0 ° (no inclination), 11 Sample Nos. Formed at °, 22 °, 31 °, 39 °, and 45 °, respectively. 6-11 were prepared. The unit of dimension display in the figure was μm.

そして、上述した各サンプル６〜１１の上部電極１５の下端１５ａにおける電界強度をそれぞれ測定した。これら上部電極１５の角度を変えた電界強度の測定結果を図７に示す。図７に示す結果によれば、幅広部１５ｂの幅が一定であれば、上部電極１５が下端１５ａから遠ざかる方向の角度を４０°近傍に設定すれば、上部電極１５の下端１５ａでの電界強度を最も強い３７００００（Ｖ／ｍ）以上の高いレベルに保てることが判明した。また、例えば２５°〜４５°の範囲にすれば、上部電極１５の下端１５ａでの電界強度を３４００００（Ｖ／ｍ）以上に保てることが判明した。 And the electric field strength in the lower end 15a of the upper electrode 15 of each sample 6-11 mentioned above was measured, respectively. FIG. 7 shows the measurement results of the electric field strength obtained by changing the angle of the upper electrode 15. According to the results shown in FIG. 7, if the width of the wide portion 15b is constant, the electric field strength at the lower end 15a of the upper electrode 15 can be obtained by setting the angle in the direction in which the upper electrode 15 moves away from the lower end 15a to about 40 °. It has been found that can be maintained at a high level of 370000 (V / m) or more, the strongest. Further, for example, it was found that the electric field strength at the lower end 15a of the upper electrode 15 can be maintained at 340000 (V / m) or more if the range is 25 ° to 45 °.

更に、図２に示す光導波路１２の両側に沿って基板１１に形成された溝１６の深さＤを０〜７μｍに１μｍ毎に設定して、上部電極１５の下端１５ａにおけるそれぞれの電界強度を測定した（深さＤ＝０μｍは溝を形成しない場合）。これら溝１６の効果を検証した測定結果を図８に示す。図８によれば、溝を３μｍ以上深く、例えば３〜７μｍの範囲に形成することによって、上部電極１５の下端１５ａにおける電界強度を５００００００（Ｖ／ｍ）以上の高いレベルに保てることが判明した。 Further, the depth D of the groove 16 formed in the substrate 11 along both sides of the optical waveguide 12 shown in FIG. 2 is set to 0 to 7 μm every 1 μm, and each electric field strength at the lower end 15a of the upper electrode 15 is set. Measured (depth D = 0 μm when no groove is formed). The measurement results verifying the effects of these grooves 16 are shown in FIG. According to FIG. 8, it was found that the electric field strength at the lower end 15a of the upper electrode 15 can be kept at a high level of 5000000 (V / m) or more by forming the groove 3 μm or more deep, for example, in the range of 3 to 7 μm. .

図１は、本発明の光強度変調器を示す外観斜視図である。FIG. 1 is an external perspective view showing a light intensity modulator of the present invention. 図２は、図１に示す光強度変調器の断面図である。FIG. 2 is a cross-sectional view of the light intensity modulator shown in FIG. 図３は、本発明の光強度変調器の他の実施形態を示す断面図である。FIG. 3 is a cross-sectional view showing another embodiment of the light intensity modulator of the present invention. 図４は、実施例として検証に用いた光強度変調器のサンプルを示す説明図である。FIG. 4 is an explanatory diagram illustrating a sample of a light intensity modulator used for verification as an example. 図５は、光強度変調器の第１の検証結果を示すグラフである。FIG. 5 is a graph showing a first verification result of the light intensity modulator. 図６は、実施例として検証に用いた光強度変調器のサンプルを示す説明図である。FIG. 6 is an explanatory diagram illustrating a sample of a light intensity modulator used for verification as an example. 図７は、光強度変調器の第２の検証結果を示すグラフである。FIG. 7 is a graph showing a second verification result of the light intensity modulator. 図８は、光強度変調器の第３の検証結果を示すグラフである。FIG. 8 is a graph showing a third verification result of the light intensity modulator.

Explanation of symbols

１０光強度変調器
１１基板
１２光導波路（導波路）
１３バッファ層
１５上部電極
１５ａ下端
１６溝
１８下部電極 10 Optical intensity modulator 11 Substrate 12 Optical waveguide (waveguide)
13 Buffer layer 15 Upper electrode 15a Lower end 16 Groove 18 Lower electrode

Claims

A waveguide formed by diffusing a diffusing material for increasing the refractive index on a part of the upper surface of the substrate, grooves digged into the substrate along the waveguide on both sides of the waveguide, and a lower surface of the substrate A lower electrode formed, and an upper electrode having a lower end connected to the waveguide and formed narrower than the width of the waveguide, and wider than the width of the waveguide toward the upper end. A light intensity modulator characterized by.

The light intensity modulator according to claim 1, wherein the upper electrode is formed in a shape constricted at an acute angle toward the waveguide, and obtuse or arcuate in a direction away from the waveguide.