JPH08211349A - Wavelength variable optical filter - Google Patents
Wavelength variable optical filterInfo
- Publication number
- JPH08211349A JPH08211349A JP3896895A JP3896895A JPH08211349A JP H08211349 A JPH08211349 A JP H08211349A JP 3896895 A JP3896895 A JP 3896895A JP 3896895 A JP3896895 A JP 3896895A JP H08211349 A JPH08211349 A JP H08211349A
- Authority
- JP
- Japan
- Prior art keywords
- surface acoustic
- acoustic wave
- optical waveguide
- waveguide
- optical filter
- 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.)
- Pending
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
- G02F1/125—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves in an optical waveguide structure
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、光波長多重伝送システ
ムや光周波数多重伝送システムにおいて、任意の波長
（周波数）の光信号に対して合波および分波を行なう波
長可変光合分波器などに利用される波長可変光フィルタ
に関し、特に、音響光学効果を利用したＴＥモード−Ｔ
Ｍモード変換型の光フィルタであって、サイドローブを
十分に抑圧することができる波長可変光フィルタに関す
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable optical multiplexer / demultiplexer for multiplexing and demultiplexing an optical signal of an arbitrary wavelength (frequency) in an optical wavelength multiplex transmission system or an optical frequency multiplex transmission system. Tunable optical filter used in a T-mode-T using an acousto-optic effect
The present invention relates to a tunable optical filter that is an M-mode conversion type optical filter and that can sufficiently suppress side lobes.
【０００２】[0002]
【従来の技術】表面弾性波と光波との間において作用す
る音響光学効果を用いたＴＥモード−ＴＭモード変換型
の光フィルタは、例えばJ.Opt.Soc.Amer.,Vol.59,744(1
969)（文献１）、IEEE J.Quantum Electronics,Vol.QE-
13,43(1977) （文献２）、Electronics Letters,Vol.2
5,158(1989)（文献３）などに記載されている。ＴＥモ
ード−ＴＭモード変換型の光フィルタの基本的な構造を
図４に示す。同図に示される光フィルタは、誘電体基板
（結晶方位ＸカットのＬｉＮｂＯ3 結晶）１に、一組の
電極からなる交差指状電極６と、一組の表面弾性波障壁
２、３に挟まれた直線状の表面弾性波導波路４と、この
表面弾性波導波路４内に形成された直線状の光導波路１
５とが設けられており、さらに、特定方向の偏波だけを
結合させる入射光用偏光子９と、前記光導波路１５の出
射光を偏光成分に応じて分離する出射光用偏光子１０と
を有する。表面弾性波障壁２、３は、Ｔｉ蒸着膜の熱拡
散により形成され、この熱拡散領域では表面弾性波の速
度が約１％高くなって表面弾性波の障壁となる。このた
め、両障壁に挟まれた領域が表面弾性波導波路４とな
る。光導波路１５は、屈折率が表面弾性波導波路４より
も高い領域であり、Ｔｉ蒸着膜の熱拡散により形成され
る。なお、図中の７、８は、吸音材である。2. Description of the Related Art A TE mode-TM mode conversion type optical filter using an acousto-optic effect acting between a surface acoustic wave and a light wave is disclosed in J. Opt. Soc. Amer., Vol. 59, 744 (1).
969) (reference 1), IEEE J. Quantum Electronics, Vol.QE-
13,43 (1977) (Reference 2), Electronics Letters, Vol.2
5,158 (1989) (Reference 3) and the like. FIG. 4 shows the basic structure of a TE mode-TM mode conversion type optical filter. The optical filter shown in the figure is sandwiched between a dielectric substrate (LiNbO 3 crystal with crystal orientation X-cut) 1 and a pair of interdigital electrodes 6 and a pair of surface acoustic wave barriers 2 and 3. Linear surface acoustic wave waveguide 4 and linear optical waveguide 1 formed in the surface acoustic wave waveguide 4
5 is provided, and further includes an incident light polarizer 9 for coupling only polarized light in a specific direction, and an outgoing light polarizer 10 for separating outgoing light of the optical waveguide 15 according to a polarization component. Have. The surface acoustic wave barriers 2 and 3 are formed by thermal diffusion of the Ti vapor deposition film, and the velocity of the surface acoustic wave is increased by about 1% in this thermal diffusion region to serve as a surface acoustic wave barrier. Therefore, the region sandwiched by both barriers becomes the surface acoustic wave waveguide 4. The optical waveguide 15 is a region whose refractive index is higher than that of the surface acoustic wave waveguide 4, and is formed by thermal diffusion of a Ti vapor deposition film. In addition, 7 and 8 in the figure are sound absorbing materials.
【０００３】交差指状電極６によって励起される表面弾
性波は、入射光波に対して周期性の屈折率グレーティン
グとしてはたらく。光導波路１５では、偏波方向が結晶
方位Ｚと平行なＴＥモード波と、偏波方向が結晶方位Ｘ
と平行なＴＭモード波とで、屈折率、波数が異なる。あ
る波長の光のＴＥモードの波数とＴＭモードの波数との
差が表面弾性波の波数とほぼ同じであるとき、位相整合
ができ、表面弾性波との相互作用で光のモードが変換さ
れる。具体的には、入射光側偏光子９を透過したＴＥモ
ード波が、表面弾性波との相互作用でＴＭモード波に変
換され、これが出射光用偏光子１０により分離される。
したがって、表面弾性波の波長を適宜選択することによ
り、入射された波長多重光から特定波長の光だけを分離
することが可能になる。The surface acoustic wave excited by the interdigital electrode 6 acts as a periodic refractive index grating for the incident light wave. In the optical waveguide 15, the TE mode wave whose polarization direction is parallel to the crystal orientation Z and the polarization direction is the crystal orientation X
And the TM mode wave in parallel with each other have different refractive indices and wave numbers. When the difference between the TE mode wave number and the TM mode wave number of light of a certain wavelength is almost the same as the surface acoustic wave wave number, phase matching is possible, and the mode of light is converted by the interaction with the surface acoustic wave. . Specifically, the TE mode wave transmitted through the incident light side polarizer 9 is converted into a TM mode wave by the interaction with the surface acoustic wave, and the TM mode wave is separated by the outgoing light polarizer 10.
Therefore, by appropriately selecting the wavelength of the surface acoustic wave, it becomes possible to separate only the light of the specific wavelength from the incident wavelength multiplexed light.
【０００４】図４に示す構造の光フィルタにおいて、光
波と表面弾性波との相互作用の強度は、吸音材によって
決定される作用範囲の外ではゼロである。したがって結
合係数は、作用範囲の中では一定不変で、作用範囲の外
ではゼロになる。その結果、フィルタ透過特性は図７に
示すようになる。図７において、第１サイドローブは、
中心透過波長強度に対し９．５ dB しか減衰していな
い。したがって、光波長多重伝送または周波数多重伝送
の場合、チャンネル間のクロストークが大きくなってし
まう。そのため、チャンネル設置の最適化をはかるか、
チャンネル間の間隔を大きくしなければならない。In the optical filter having the structure shown in FIG. 4, the intensity of the interaction between the light wave and the surface acoustic wave is zero outside the working range determined by the sound absorbing material. Therefore, the coupling coefficient is constant within the working range and becomes zero outside the working range. As a result, the filter transmission characteristic becomes as shown in FIG. In FIG. 7, the first side lobe is
Only 9.5 dB is attenuated with respect to the central transmission wavelength intensity. Therefore, in the case of optical wavelength multiplex transmission or frequency multiplex transmission, crosstalk between channels becomes large. Therefore, do you want to optimize the channel installation?
The spacing between channels must be large.
【０００５】図５に、IEEE Trans.Ultrason.Ferroelec
t.Freq.Cont.,Vol.40,814(1993)（文献４）に記載され
ている構成の光フィルタを示す。この光フィルタは、表
面弾性波障壁２２、２３に挟まれる表面弾性波導波路２
４の形状が直線状ではなく、所定の関数にしたがって変
化する構成を有する。この構成以外は、図４に示す光フ
ィルタと同様である。この光フィルタでは、光伝播方向
において表面弾性波強度および結合係数が光導波路中で
漸増し、最大値に達した後、漸減する。このため、サイ
ドローブの抑圧が可能である。文献４には、第１サイド
ローブの中心透過波長強度に対する減衰率を１５ dB に
できると記載されている。FIG. 5 shows the IEEE Trans.Ultrason.Ferroelec.
An optical filter having a configuration described in t.Freq.Cont., Vol.40, 814 (1993) (reference 4) is shown. This optical filter includes a surface acoustic wave waveguide 2 sandwiched between surface acoustic wave barriers 22 and 23.
The shape of No. 4 is not linear but changes according to a predetermined function. Except for this configuration, the optical filter is similar to that shown in FIG. In this optical filter, the surface acoustic wave intensity and the coupling coefficient gradually increase in the light propagation direction in the optical waveguide, reach a maximum value, and then gradually decrease. Therefore, side lobes can be suppressed. Document 4 describes that the attenuation factor for the central transmission wavelength intensity of the first side lobe can be set to 15 dB.
【０００６】また、特開平５−３２３２４８号公報に
は、可同調光フィルタにおいて、光導波路を伝播する光
信号と表面弾性波との相互作用領域における伝播方向の
結合係数を、所定の関数で分布させる曲率半径を有する
湾曲形状の電極を設ける発明が記載されている。この光
フィルタでは、図５の光フィルタと同様に、光導波路内
の表面弾性波強度が変化するので、サイドローブの抑圧
が可能である。Further, in Japanese Patent Laid-Open No. 5-323248, in a tunable optical filter, a coupling coefficient in a propagation direction in an interaction region between an optical signal propagating in an optical waveguide and a surface acoustic wave is distributed by a predetermined function. The invention has been described in which a curved electrode having a radius of curvature that causes it is provided. Similar to the optical filter of FIG. 5, this optical filter can suppress the side lobes because the surface acoustic wave intensity in the optical waveguide changes.
【０００７】しかし、文献４および特開平５−３２３２
４８号公報にそれぞれ記載されている構成では、入力パ
ワーの閉じ込めが難しく、損失が大きくなる。例えば、
文献４には、高周波駆動パワーが１．０W であった旨の
記載がある。損失が大きくなる理由としては、高次モー
ドとなることが挙げられる。また、表面弾性波障壁が湾
曲している文献４の構成では、表面弾性波の導波路に沿
った閉じ込めが十分でなく、誘電体基板へのリークが生
じることが挙げられる。このように損失が多いと高い駆
動電圧が必要とされ、また、素子の発熱も多くなるので
好ましくない。However, Document 4 and Japanese Patent Laid-Open No. 5-3232
In the configurations described in Japanese Patent Laid-Open No. 48, it is difficult to confine the input power and the loss becomes large. For example,
Document 4 describes that the high frequency drive power was 1.0 W. The reason why the loss becomes large is that it becomes a higher-order mode. Further, in the configuration of Document 4 in which the surface acoustic wave barrier is curved, it is possible that the surface acoustic waves are not sufficiently confined along the waveguide, and leakage to the dielectric substrate occurs. If the loss is large as described above, a high driving voltage is required, and more heat is generated in the element, which is not preferable.
【０００８】米国特許第５，００２，３４９号明細書に
は、ＴＭモード透過偏光子を介して、図４に示す構成の
光フィルタを光伝播方向に直列に２段接続した構成の光
フィルタが記載されている。この光フィルタでは、第１
段からの出力光が第２段に入射するため、全体の結合係
数は各段における結合係数の積となってサイドローブが
抑制される。US Pat. No. 5,002,349 discloses an optical filter having a structure in which two optical filters having the structure shown in FIG. 4 are connected in series in the light propagation direction via a TM mode transmitting polarizer. Has been described. In this optical filter,
Since the output light from each stage is incident on the second stage, the overall coupling coefficient is the product of the coupling coefficients in each stage, and side lobes are suppressed.
【０００９】しかし、上記明細書記載の２段構成の光フ
ィルタは、各段が音響的に孤立しているため、各段に表
面弾性波励起用の電極が必要である。その結果、素子の
寸法が大きくなり、また、製造工程が複雑になる。ま
た、両段の特性を厳密に一致させることが難しいため、
第１段で共鳴しなかった光が第２段で共鳴してフィルタ
がかかってしまうことがあり、ノイズが大きくなること
も考えられる。However, in the two-stage optical filter described in the above specification, since each stage is acoustically isolated, each stage requires an electrode for exciting a surface acoustic wave. As a result, the size of the device becomes large, and the manufacturing process becomes complicated. Also, because it is difficult to exactly match the characteristics of both stages,
Light that did not resonate in the first stage may resonate in the second stage and be filtered, which may increase noise.
【００１０】[0010]
【発明が解決しようとする課題】本発明の目的は、ＴＥ
モード−ＴＭモード変換型の光フィルタであって、小さ
い駆動電力で透過特性のサイドローブの抑圧が可能であ
り、しかも小型で構造の簡単な波長可変光フィルタを提
供することである。The object of the present invention is to provide a TE
It is an object of the present invention to provide a wavelength-tunable optical filter which is a mode-TM mode conversion type optical filter, which can suppress side lobes having a transmission characteristic with a small driving power, and which is small and has a simple structure.
【００１１】[0011]
【課題を解決するための手段】このような目的は、下記
（１）〜（２）のいずれかの構成により達成される。 （１）誘電体基板上に、対向する一組の表面弾性波障壁
により挟まれた直線状の表面弾性波導波路と、この表面
弾性波導波路内に設けられた光導波路と、表面弾性波を
励起するために表面弾性波導波路の少なくとも一端部に
設けられた交差指状電極と、この交差指状電極を挟み、
表面弾性波導波路の入射光側端部および出射光側端部に
それぞれ設けられた入射光側吸音材および出射光側吸音
材とを有し、さらに、光導波路からの出射光を偏光成分
に応じて分離する出射光用偏光子を有し、誘電体基板表
面において光導波路と表面弾性波障壁との距離を測定し
たとき、光導波路の入射光側端部付近および／または出
射光側端部付近に、前記距離が光導波路中央付近よりも
小さくなる領域が存在する波長可変光フィルタ。 （２）光導波路端部付近における光導波路と表面弾性波
障壁との距離が、光導波路中央付近における前記距離の
１０〜２０％である上記（１）の波長可変光フィルタ。Such an object is achieved by any one of the following constitutions (1) and (2). (1) A linear surface acoustic wave waveguide sandwiched by a pair of opposing surface acoustic wave barriers on a dielectric substrate, an optical waveguide provided in this surface acoustic wave waveguide, and surface acoustic wave excitation In order to do so, sandwich the interdigital electrode and the interdigital electrode provided on at least one end of the surface acoustic wave waveguide,
The surface acoustic wave waveguide has an incident light side sound absorbing material and an outgoing light side sound absorbing material provided at the incident light side end portion and the output light side end portion, respectively. When the distance between the optical waveguide and the surface acoustic wave barrier on the surface of the dielectric substrate is measured, the optical waveguide has a polarizer for outgoing light that is separated by In the tunable optical filter, there is a region where the distance is smaller than near the center of the optical waveguide. (2) The tunable optical filter according to (1), wherein the distance between the optical waveguide and the surface acoustic wave barrier near the end of the optical waveguide is 10 to 20% of the distance near the center of the optical waveguide.
【００１２】[0012]
【作用および効果】本発明の波長可変光フィルタは、図
１および図２に示すように、光導波路５が直線状ではな
く、その少なくとも一方の端部付近が、その中央付近よ
りも表面弾性波障壁２、３のいずれかに近くなってい
る。表面弾性波は、表面弾性波障壁２、３間において強
度分布をもつため、光波と表面弾性波との相互作用の強
度、すなわち結合係数は、光導波路の光伝播方向に沿っ
て変化する。この結果、作用領域の始端付近および／ま
たは終端付近において結合係数のゆるやかな変化が実現
でき、フィルタの透過特性におけるサイドローブの抑圧
ができる。In the tunable optical filter of the present invention, as shown in FIGS. 1 and 2, the optical waveguide 5 is not linear, and at least one end portion thereof is closer to the surface acoustic wave than the central portion thereof. It is close to either of barriers 2 and 3. Since the surface acoustic wave has an intensity distribution between the surface acoustic wave barriers 2 and 3, the intensity of the interaction between the light wave and the surface acoustic wave, that is, the coupling coefficient, changes along the light propagation direction of the optical waveguide. As a result, a gradual change in the coupling coefficient can be realized near the start end and / or the end end of the action area, and the side lobe in the transmission characteristic of the filter can be suppressed.
【００１３】上記した従来の光フィルタの一部では、表
面弾性波導波路の形状を表面弾性波伝播方向に沿って変
化させることでサイドローブの抑圧を行なっているた
め、損失が大きくなるが、本発明では表面弾性波導波路
を直線状とするので上述した損失は生じず、低パワーで
の駆動が可能である。また、本発明の波長可変光フィル
タは、図４に示す従来の基本的な構成において光導波路
の形状を変更するだけで済むので、素子の大型化や製造
工程の複雑化が避けられる。In some of the conventional optical filters described above, the side lobe is suppressed by changing the shape of the surface acoustic wave waveguide along the surface acoustic wave propagation direction, so that the loss becomes large. In the invention, since the surface acoustic wave waveguide has a linear shape, the above-mentioned loss does not occur and driving with low power is possible. Further, in the wavelength tunable optical filter of the present invention, it is only necessary to change the shape of the optical waveguide in the conventional basic configuration shown in FIG. 4, so it is possible to avoid an increase in the size of the device and a complicated manufacturing process.
【００１４】[0014]
【実施例】以下、本発明を実施例に基づいて詳細に説明
する。DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.
【００１５】図１および図２に、本発明の波長可変光フ
ィルタの構成例を示す。図１および図２に示される波長
可変光フィルタは、対向する一組の表面弾性波障壁２、
３により形成された平行直線状の表面弾性波導波路４
と、この表面弾性波導波路４内に設けられた光導波路５
と、表面弾性波導波路４の入射光側に設けられ、表面弾
性波を励起する一組の電極からなる交差指状電極６と、
この交差指状電極６を挟むように設けられた入射光側吸
音材７と出射光側吸音材８とを有する誘電体基板１を有
し、さらに、特定方向の偏波だけを光導波路に入射させ
る入射光用偏光子９と、前記光導波路からの出射光を偏
光成分に応じて分離する出射光用偏光子１０とを有す
る。FIG. 1 and FIG. 2 show examples of the structure of the wavelength tunable optical filter of the present invention. The tunable optical filter shown in FIGS. 1 and 2 has a pair of opposed surface acoustic wave barriers 2,
Parallel linear surface acoustic wave waveguide 4 formed by 3
And an optical waveguide 5 provided in the surface acoustic wave waveguide 4.
And an interdigitated electrode 6 which is provided on the incident light side of the surface acoustic wave waveguide 4 and includes a pair of electrodes for exciting the surface acoustic wave.
The dielectric substrate 1 having the incident light side sound absorbing material 7 and the outgoing light side sound absorbing material 8 provided so as to sandwich the interdigital electrode 6 is further provided, and only polarized light in a specific direction is incident on the optical waveguide. The incident light polarizer 9 and the outgoing light polarizer 10 for separating the outgoing light from the optical waveguide according to the polarization component.
【００１６】なお、交差指状電極６は、表面弾性波導波
路４の出射光側に設けられてもよい。また、入射光用偏
光子９は、設けなくてもよい。The interdigital electrodes 6 may be provided on the outgoing light side of the surface acoustic wave waveguide 4. Further, the incident light polarizer 9 may not be provided.
【００１７】これらの波長可変光フィルタでは、誘電体
基板１表面において光導波路５と表面弾性波障壁２、３
との距離を測定したとき、光導波路の入射光側端部付近
および／または出射光側端部付近に、前記距離が光導波
路の中央付近よりも小さくなる領域が存在する。すなわ
ち、光導波路５の少なくとも一方の端部付近、好ましく
は両端部付近を、表面弾性波障壁２、３のいずれかに接
近した構成とする。通常は、光導波路の中央付近から少
なくとも一方の端部付近にかけて、光導波路が次第に表
面弾性波障壁に接近する構成とする。In these wavelength tunable optical filters, the optical waveguide 5 and the surface acoustic wave barriers 2, 3 are provided on the surface of the dielectric substrate 1.
When the distance between and is measured, there is a region near the end of the optical waveguide on the incident light side and / or near the end of the outgoing light on the side where the distance is smaller than near the center of the optical waveguide. That is, at least one end portion, preferably both end portions, of the optical waveguide 5 is configured to be close to one of the surface acoustic wave barriers 2 and 3. Normally, the optical waveguide is configured to gradually approach the surface acoustic wave barrier from the vicinity of the center to the vicinity of at least one end of the optical waveguide.
【００１８】図１に示すように、表面弾性波伝播方向を
ｘ軸とし、誘電体基板面内においてｘ軸と直交する方向
をｙ軸としたとき、ｙ軸方向における表面弾性波の強度
分布は、下記数１の式IIのＰ（ｘ，ｙ）にほぼしたが
う。As shown in FIG. 1, when the surface acoustic wave propagation direction is the x-axis and the direction orthogonal to the x-axis in the plane of the dielectric substrate is the y-axis, the intensity distribution of the surface acoustic wave in the y-axis direction is , P (x, y) of the formula II of the following formula 1 is substantially obeyed.
【００１９】[0019]
【数１】 [Equation 1]
【００２０】式IIにおいて、Ａは定数であり、ｙ軸の原
点は２つの表面弾性波障壁２、３間の中央にある。In equation II, A is a constant and the origin of the y-axis is in the center between the two surface acoustic wave barriers 2, 3.
【００２１】本発明では、このような表面弾性波強度分
布をもつ表面弾性波導波路内に、直線状ではない光導波
路を設けることにより、光導波路内の光伝播方向におい
て表面弾性波の強度分布を設けることができる。本発明
では、表面弾性波の強度が低い領域に光導波路の端部付
近が存在するように構成するので、透過特性グラフにお
いて中心透過波長強度に対する第１サイドローブの減衰
量を大きくすることができる。光導波路の具体的形状
は、この減衰量が大きくなるように決定すればよいが、
具体的には、光導波路端部付近における光導波路と表面
弾性波障壁との距離が、光導波路中央付近における前記
距離の１０〜２０％程度となるようにすることが好まし
い。In the present invention, by providing a non-linear optical waveguide in the surface acoustic wave waveguide having such a surface acoustic wave intensity distribution, the intensity distribution of the surface acoustic wave in the light propagation direction in the optical waveguide can be obtained. Can be provided. In the present invention, since the vicinity of the end of the optical waveguide exists in the region where the surface acoustic wave intensity is low, the attenuation amount of the first side lobe with respect to the central transmission wavelength intensity can be increased in the transmission characteristic graph. . The specific shape of the optical waveguide may be determined so that this attenuation amount increases,
Specifically, it is preferable that the distance between the optical waveguide and the surface acoustic wave barrier near the end of the optical waveguide is about 10 to 20% of the distance near the center of the optical waveguide.
【００２２】そして、より具体的には、光導波路内にお
ける表面弾性波の強度が、下記式Ｉで表わされるＷ
（ｘ，ｙ）にしたがって分布していることが好ましい。More specifically, the intensity of the surface acoustic wave in the optical waveguide is represented by the following formula I: W
It is preferably distributed according to (x, y).
【００２３】式Ｉ Ｗ（ｘ，ｙ）＝（１−ａ）＋ａｃｏ
ｓ2 （πｘ／Ｌ）Formula I W (x, y) = (1-a) + aco
s 2 (πx / L)
【００２４】式Ｉにおいて−Ｌ／２≦ｘ≦Ｌ／２であ
り、Ｌは作用領域の長さ、すなわち、図１では交差指状
電極６と出射光側吸音材８との間の距離であり、ｘ軸の
原点は作用領域の中央である。また、式Ｉにおいて、 ０＜ａ＜１ であり、好ましくは ０．６０≦ａ≦０．８０ である。In the formula I, -L / 2≤x≤L / 2, where L is the length of the working region, that is, the distance between the interdigital finger 6 and the sound absorbing member 8 on the outgoing light side in FIG. Yes, the origin of the x-axis is the center of the working area. In the formula I, 0 <a <1 and preferably 0.60 ≦ a ≦ 0.80.
【００２５】なお、交差指状電極６が出射光側吸音材８
側にあるとき、Ｌは交差指状電極６と入射光側吸音材７
との間の距離である。It should be noted that the interdigital finger-shaped electrode 6 is the sound absorbing material 8 on the outgoing light side.
When it is on the side, L is the interdigital electrode 6 and the incident light side sound absorbing material 7.
Is the distance between.
【００２６】光導波路においてこのような表面弾性波強
度分布をもたせるためには、Ｗ（ｘ，ｙ）の最大値とＰ
（ｘ，ｙ）の最大値とが等しくなるとして式IIの定数Ａ
を決定し、次いで、Ｗ（ｘ，ｙ）＝Ｐ（ｘ，ｙ）とおい
てｘに対するｙの値を求めることにより、光導波路の形
状を決定すればよい。なお、以上では式Ｉに基づいて説
明したが、これに限らず、上記の方法により、光導波路
内における表面弾性波の強度分布が所望のものとなるよ
うに光導波路の形状を設計することができる。In order to have such a surface acoustic wave intensity distribution in the optical waveguide, the maximum value of W (x, y) and P
Assuming that the maximum values of (x, y) are equal, the constant A of formula II
Then, the shape of the optical waveguide may be determined by setting W (x, y) = P (x, y) and determining the value of y with respect to x. Although the above description is based on Formula I, the present invention is not limited to this, and the shape of the optical waveguide may be designed by the above method so that the intensity distribution of the surface acoustic wave in the optical waveguide becomes a desired one. it can.
【００２７】上記式Ｉにおいて、例えばａ＝０．７５の
とき、 Ｗ（ｘ，ｙ）＝０．２５＋０．７５ｃｏｓ2 （πｘ／
Ｌ） となり、このときフィルタの透過特性は図６のグラフで
表わされ、中心透過波長強度に対する第１サイドローブ
の減衰量は１５ dB となる。この減衰量は前記した文献
４記載の光フィルタと同等であるが、本発明の波長可変
光フィルタでは表面弾性波導波路が直線状であるため、
文献４の光フィルタに比べ損失が著しく少なくなる。す
なわち、文献４では１．０W の電力が必要であったが、
図１および図２の構成の光フィルタでは、同じ減衰量の
ときの消費電力の実測値は０．１mW以下であった。In the above formula I, for example, when a = 0.75, W (x, y) = 0.25 + 0.75cos 2 (πx /
L), and the transmission characteristic of the filter is represented by the graph of FIG. 6, and the attenuation amount of the first side lobe with respect to the central transmission wavelength intensity is 15 dB. This attenuation amount is equivalent to that of the optical filter described in the above-mentioned reference 4, but in the wavelength tunable optical filter of the present invention, since the surface acoustic wave waveguide is linear,
The loss is significantly smaller than that of the optical filter of Document 4. That is, although the power of 1.0 W was required in Document 4,
In the optical filters having the configurations of FIG. 1 and FIG. 2, the measured value of the power consumption at the same attenuation amount was 0.1 mW or less.
【００２８】なお、図２の光導波路５は、中央から入射
光用偏光子９側端部までの領域は図１の光導波路と同一
の形状であり、かつ前記中央に対して点対称である。こ
のため、光導波路５における表面弾性波の強度分布は図
１の構成と図２の構成とで同一となるので、サイドロー
ブの減衰も両構成で同一となる。したがって、どちらの
構成を選択してもよいが、一般に、図２のように光導波
路の形状が点対称であるほうが光導波路の屈曲点や変曲
点を少なくし得るので好ましい。光導波路は、屈曲点を
もたない曲線状とすることが好ましいが、屈曲点をもつ
形状であっても本発明の効果は実現する。The optical waveguide 5 of FIG. 2 has the same shape as that of the optical waveguide of FIG. 1 in the region from the center to the end of the incident light polarizer 9, and is symmetrical with respect to the center. . Therefore, since the intensity distribution of the surface acoustic wave in the optical waveguide 5 is the same in the configuration of FIG. 1 and the configuration of FIG. 2, the side lobe attenuation is also the same in both configurations. Therefore, either configuration may be selected, but in general, it is preferable that the shape of the optical waveguide is point-symmetrical as shown in FIG. 2 because bending points and inflection points of the optical waveguide can be reduced. It is preferable that the optical waveguide has a curved shape without a bending point, but the effect of the present invention can be realized even if the optical waveguide has a shape having a bending point.
【００２９】本発明の波長可変光フィルタに用いる表面
弾性波の周波数は、通常、１７０〜２１０MHz 程度であ
り、光波長は、通常、１．３〜１．５５μm 程度であ
る。表面弾性波導波路の幅は、表面弾性波の波長等に応
じて適宜決定すればよいが、通常、８０〜１５０μm 程
度であり、表面弾性波障壁の最大深さは、通常、１５〜
３０μm 程度である。光導波路の幅は、光波長等に応じ
て適宜決定すればよいが、通常、６〜９μm 程度であ
り、光導波路の最大深さは、通常、３〜５μm 程度であ
る。作用領域の長さＬは、駆動電力、透過半値幅等に応
じて適宜決定すればよいが、通常、１０〜３０mm程度で
ある。The frequency of the surface acoustic wave used in the tunable optical filter of the present invention is usually about 170 to 210 MHz, and the light wavelength is usually about 1.3 to 1.55 μm. The width of the surface acoustic wave waveguide may be appropriately determined according to the wavelength of the surface acoustic wave and the like, but is usually about 80 to 150 μm, and the maximum depth of the surface acoustic wave barrier is usually 15 to 15 μm.
It is about 30 μm. The width of the optical waveguide may be appropriately determined according to the wavelength of light and the like, but is usually about 6 to 9 μm, and the maximum depth of the optical waveguide is usually about 3 to 5 μm. The length L of the action region may be appropriately determined according to the driving power, the transmission half width, etc., but is usually about 10 to 30 mm.
【００３０】本発明は、前述した米国特許第５，００
２，３４９号明細書に記載されているような多段構成の
光フィルタも含む。本発明における多段構成の光フィル
タの構成例を、図３に示す。本発明における多段構成の
光フィルタでは、入射光側吸音材７から出射光側吸音材
８までを１単位としたとき、少なくとも２単位以上が直
列に設けられ、各単位の光導波路は相互に接続される。
図３において、各単位の構成は、図１の光フィルタと同
じである。各単位間には、図示するように偏光子２５
（図示例の構成ではＴＭモード透過型を用いる）が設け
られる。このような多段構成では、全体の結合係数は各
単位における結合係数の積となるため、サイドローブは
強力に抑制される。なお、多段構成の光フィルタでは、
前述したように製造工程の複雑化やノイズの増大などの
問題が生じやすいが、本発明の光フィルタでは、米国特
許第５，００２，３４９号明細書記載の多段フィルタに
比べ、サイドローブの抑制がより強力となるため、多段
構成とするメリットは大きい。The present invention is based on the aforementioned US Pat.
It also includes a multi-stage optical filter as described in the specification of US Pat. No. 2,349. FIG. 3 shows a configuration example of an optical filter having a multi-stage configuration according to the present invention. In the multi-stage optical filter of the present invention, when the unit from the incident light side sound absorbing material 7 to the outgoing light side sound absorbing material 8 is one unit, at least two units are provided in series, and the optical waveguides of each unit are connected to each other. To be done.
3, the configuration of each unit is the same as that of the optical filter of FIG. Between each unit, a polarizer 25
(TM mode transmission type is used in the configuration of the illustrated example). In such a multi-stage configuration, the overall coupling coefficient is the product of the coupling coefficients in each unit, so the side lobes are strongly suppressed. In addition, in the multistage optical filter,
As described above, problems such as complication of the manufacturing process and increase of noise are likely to occur, but the optical filter of the present invention suppresses side lobes as compared with the multistage filter described in US Pat. No. 5,002,349. Is more powerful, and the advantage of using a multi-stage configuration is great.
【００３１】本発明の波長可変光フィルタは、表面弾性
波導波路および光導波路を有する従来の光フィルタと同
様な方法で製造すればよい。誘電体基板１には、例えば
ＬｉＮｂＯ3 結晶をＸカットまたはＹカットして用いれ
ばよいが、この他、ＬｉＴａＯ3 などを用いてもよい。The tunable optical filter of the present invention may be manufactured by a method similar to that of a conventional optical filter having a surface acoustic wave waveguide and an optical waveguide. For the dielectric substrate 1, for example, LiNbO 3 crystal may be X-cut or Y-cut and used, but LiTaO 3 or the like may be used.
【００３２】表面弾性波障壁は、ＴｉやＭｇ、Ｎｉ、Ｃ
ｕ、Ｚｎ、Ｔａ等の薄膜を結晶方位Ｚ軸と直交する方向
に存在するように蒸着等により形成した後、誘電体基板
中に熱拡散させて形成する。この熱拡散は、通常、９０
０〜１１００℃程度で１５〜３５時間程度の熱処理によ
って行なえばよい。The surface acoustic wave barrier is made of Ti, Mg, Ni or C.
A thin film of u, Zn, Ta or the like is formed by vapor deposition or the like so as to exist in a direction orthogonal to the crystal orientation Z axis, and then thermally diffused in the dielectric substrate. This thermal diffusion is usually 90
The heat treatment may be performed at 0 to 1100 ° C. for about 15 to 35 hours.
【００３３】光導波路は、ＴｉやＭｇ、Ｎｉ、Ｃｕ、Ｚ
ｎ、Ｔａ等の薄膜を所定の形状となるように蒸着等によ
り形成した後、誘電体基板中に熱拡散させて形成する。
この熱拡散は、通常、９００〜１１００℃程度で５〜１
０時間程度の熱処理によって行なえばよい。交差指状電
極６は、ＡｕやＡｌなどを用いて蒸着やめっきなどによ
り形成すればよい。吸音材には、通常、ゴムやテープな
どが用いられる。The optical waveguide is made of Ti, Mg, Ni, Cu, Z.
A thin film of n, Ta or the like is formed by vapor deposition or the like so as to have a predetermined shape, and is then thermally diffused in the dielectric substrate.
This thermal diffusion is usually 5 to 1 at about 900 to 1100 ° C.
The heat treatment may be performed for about 0 hours. The interdigital electrodes 6 may be formed by vapor deposition or plating using Au, Al, or the like. Rubber or tape is usually used for the sound absorbing material.
【図１】本発明の波長可変光フィルタの構成例を示す平
面図である。FIG. 1 is a plan view showing a configuration example of a tunable optical filter of the present invention.
【図２】本発明の波長可変光フィルタの構成例を示す平
面図である。FIG. 2 is a plan view showing a configuration example of a tunable optical filter of the present invention.
【図３】本発明の波長可変光フィルタの構成例を示す平
面図である。FIG. 3 is a plan view showing a configuration example of a tunable optical filter of the present invention.
【図４】従来の光フィルタの構成例を示す平面図であ
る。FIG. 4 is a plan view showing a configuration example of a conventional optical filter.
【図５】従来の光フィルタの構成例を示す平面図であ
る。FIG. 5 is a plan view showing a configuration example of a conventional optical filter.
【図６】本発明の波長可変光フィルタの透過特性を示す
グラフである。FIG. 6 is a graph showing transmission characteristics of the wavelength tunable optical filter of the present invention.
【図７】従来の光フィルタの透過特性を示すグラフであ
る。FIG. 7 is a graph showing the transmission characteristics of a conventional optical filter.
１ 誘電体基板 ２、３、２２、２３ 表面弾性波障壁 ４、２４ 表面弾性波導波路 ５、１５ 光導波路 ６ 交差指状電極 ７ 入射光側吸音材 ８ 出射光側吸音材 ９ 入射光用偏光子 １０ 出射光用偏光子 ２５ 偏光子 1 Dielectric Substrate 2, 3, 22, 23 Surface Acoustic Wave Barrier 4, 24 Surface Acoustic Wave Waveguide 5, 15 Optical Waveguide 6 Interdigital Finger 7 Incident Light Side Sound Absorbing Material 8 Emitting Light Side Sound Absorbing Material 9 Polarizer for Incident Light 10 Polarizer for outgoing light 25 Polarizer
Claims (2)
性波障壁により挟まれた直線状の表面弾性波導波路と、
この表面弾性波導波路内に設けられた光導波路と、表面
弾性波を励起するために表面弾性波導波路の少なくとも
一端部に設けられた交差指状電極と、この交差指状電極
を挟み、表面弾性波導波路の入射光側端部および出射光
側端部にそれぞれ設けられた入射光側吸音材および出射
光側吸音材とを有し、 さらに、光導波路からの出射光を偏光成分に応じて分離
する出射光用偏光子を有し、 誘電体基板表面において光導波路と表面弾性波障壁との
距離を測定したとき、光導波路の入射光側端部付近およ
び／または出射光側端部付近に、前記距離が光導波路中
央付近よりも小さくなる領域が存在する波長可変光フィ
ルタ。1. A linear surface acoustic wave waveguide sandwiched by a pair of opposed surface acoustic wave barriers on a dielectric substrate,
The optical waveguide provided in the surface acoustic wave waveguide, the interdigital electrode provided at least at one end of the surface acoustic wave waveguide for exciting the surface acoustic wave, and the interdigital electrode sandwiching the interdigital electrode It has an incident light side sound absorbing material and an outgoing light side sound absorbing material provided at the incident light side end portion and the outgoing light side end portion of the wave waveguide, respectively. Furthermore, the output light from the optical waveguide is separated according to the polarization component. When the distance between the optical waveguide and the surface acoustic wave barrier on the surface of the dielectric substrate is measured, the polarizer for outgoing light is provided, and the light near the end on the incident light side and / or near the end on the outgoing light side of the optical waveguide. A tunable optical filter having a region where the distance is smaller than near the center of the optical waveguide.
面弾性波障壁との距離が、光導波路中央付近における前
記距離の１０〜２０％である請求項１の波長可変光フィ
ルタ。2. The wavelength tunable optical filter according to claim 1, wherein the distance between the optical waveguide and the surface acoustic wave barrier near the end of the optical waveguide is 10 to 20% of the distance near the center of the optical waveguide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3896895A JPH08211349A (en) | 1995-02-03 | 1995-02-03 | Wavelength variable optical filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3896895A JPH08211349A (en) | 1995-02-03 | 1995-02-03 | Wavelength variable optical filter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH08211349A true JPH08211349A (en) | 1996-08-20 |
Family
ID=12539969
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3896895A Pending JPH08211349A (en) | 1995-02-03 | 1995-02-03 | Wavelength variable optical filter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH08211349A (en) |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0887688A2 (en) * | 1997-06-25 | 1998-12-30 | Nec Corporation | Wavelength tunable optical filters |
| US6400881B1 (en) | 1997-08-11 | 2002-06-04 | Fujitsu Limited | Optical device having thin film formed over optical waveguide |
| US6466705B2 (en) | 2000-01-25 | 2002-10-15 | Fujitsu Limited | Acousto-optic variable-wavelength TE/TM mode converter, and a variable-wavelength optical filter using this converter |
| US6594069B1 (en) | 2001-12-28 | 2003-07-15 | Fujitsu Limited | Control method and control apparatus of optical wavelength variable filter |
| US6783282B2 (en) | 2001-12-28 | 2004-08-31 | Fujitsu Limited | Optical wavelength filter |
| US6870972B2 (en) | 2001-12-28 | 2005-03-22 | Fujitsu Limited | Connecting method of optical devices, and optical apparatus |
| US6895141B2 (en) | 2001-12-28 | 2005-05-17 | Fujitsu Limited | Control method and device for optical filter, and optical node device |
| US6917732B2 (en) | 2001-12-28 | 2005-07-12 | Fujitsu Limited | Connecting method of optical function devices, and optical apparatus |
| US6934433B2 (en) | 2001-12-28 | 2005-08-23 | Fujitsu Limited | Control method and control apparatus of optical device |
| US7120321B2 (en) | 2001-12-28 | 2006-10-10 | Fujitsu Limited | Control method and device for optical filter |
| US7340115B2 (en) | 2005-08-08 | 2008-03-04 | Fujitsu Limited | Optical wavelength tunable filter |
-
1995
- 1995-02-03 JP JP3896895A patent/JPH08211349A/en active Pending
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0887688A2 (en) * | 1997-06-25 | 1998-12-30 | Nec Corporation | Wavelength tunable optical filters |
| EP0887688A3 (en) * | 1997-06-25 | 1999-04-21 | Nec Corporation | Wavelength tunable optical filters |
| US6400881B1 (en) | 1997-08-11 | 2002-06-04 | Fujitsu Limited | Optical device having thin film formed over optical waveguide |
| US6466705B2 (en) | 2000-01-25 | 2002-10-15 | Fujitsu Limited | Acousto-optic variable-wavelength TE/TM mode converter, and a variable-wavelength optical filter using this converter |
| US6870972B2 (en) | 2001-12-28 | 2005-03-22 | Fujitsu Limited | Connecting method of optical devices, and optical apparatus |
| US6783282B2 (en) | 2001-12-28 | 2004-08-31 | Fujitsu Limited | Optical wavelength filter |
| US6594069B1 (en) | 2001-12-28 | 2003-07-15 | Fujitsu Limited | Control method and control apparatus of optical wavelength variable filter |
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| US6925214B2 (en) | 2001-12-28 | 2005-08-02 | Fujitsu Limited | Connecting method of optical function devices, and optical apparatus |
| US6934433B2 (en) | 2001-12-28 | 2005-08-23 | Fujitsu Limited | Control method and control apparatus of optical device |
| US7120321B2 (en) | 2001-12-28 | 2006-10-10 | Fujitsu Limited | Control method and device for optical filter |
| US7362925B2 (en) | 2001-12-28 | 2008-04-22 | Fujitsu Limited | Control method and control apparatus of optical device |
| US7340115B2 (en) | 2005-08-08 | 2008-03-04 | Fujitsu Limited | Optical wavelength tunable filter |
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