JP3848093B2 - Optical waveguide device, optical wavelength conversion device, and optical waveguide device manufacturing method - Google Patents

Description

【０１１２】
（比較例１）
実施例１と同様に、３度オフカット基板のＸ面（８７°Ｚカット）のＭｇＯを５ｍｏｌ％ドープしたニオブ酸リチウム材料９（厚さ０．５ｍｍ）に、電圧印加法によって、周期３．２μｍ、分極反転深さ２μｍの周期分極反転構造５を形成した。
【０１１３】
次いで、ピロリン酸を用いたプロトン交換法によって、基板の分極反転パターンに対して垂直な方向へと延びる三次元光導波路を形成した。具体的には、タンタルからなるマスクによって、基板の表面をマスクした。この際、マスクには、幅４μｍの細長い直線的な開口を形成しておいた。この基板を、２００℃に加熱されたピロリン酸中に１０分間浸漬した。マスクを基板から除去し、基板を大気中で３５０°で４時間アニール処理し、三次元光導波路を形成した。基板を切断し、長さ１０ｍｍの素子を作成した。光導波路の両端面を化学機械研磨した。
【０１１４】
この素子を使用し、チタン−サファイアレーザーを使用し、第二高調波を発生させた。位相整合波長が８５０ｎｍであり、第二高調波の波長は４２５ｎｍであった。ＳＨＧ変換効率は約５００％／Ｗであった。第二高調波出力が約１５ｍＷに達するまでは、光損傷等の特性劣化を起こすことはなく、安定した第二高調波の発振が可能であった。しかし、第二高調波の出力が約１５ｍＷを超えると、光損傷によって出射ビームの変動が生じた。この出力が２０ｍＷに達すると、第二高調波の安定した発振は不可能であった。
【０１１５】
（実施例２）
図６に示す光導波路素子１Ｄを製造した。具体的には、実施例１と同様にして、３度オフカット基板のＸ面（８７°Ｚカット）のＭｇＯを５ｍｏｌ％ドープしたニオブ酸リチウム材料９（厚さ０．５ｍｍ）に、電圧印加法によって、周期３．２μｍ、分極反転深さ２μｍの周期分極反転構造５を形成した。
【０１１６】
次いで、材料９の接合面上に、分極反転パターンの方向とは垂直な方向に、幅４μｍ、厚さ３００ｎｍの縞状（ストライプ状）のＮｂ₂ Ｏ₅ 膜（誘電体層）を形成した。
【０１１７】
次いで、材料９の接合面９ａと、基板２の表面２ａ（ｘカットのニオブ酸リチウム基板、厚さ１ｍｍ）とを接着した。接着剤としては、エポキシ系の室温硬化型樹脂を使用した。接着層３の厚さは約０．５μｍとした。
【０１１８】
次いで、材料９を機械研削装置によって研削加工し、材料９Ａの厚さを２０μｍとした。次いで、ダイシング加工装置を用いて、図６に示す凹部１１を形成した。この際、延設部１５の厚さが３μｍとなるようにした。ダイシングブレードとしては、レジンボンドのダイヤモンド砥石「ＳＤ５０００」（外径φ約５２ｍｍ、厚さ０．１ｍｍ）を使用した。ブレードの回転数は１０，０００ｒｐｍとし、ブレードの送り速度を０．５ｍｍ／秒とした。基板をその横断面方向に切断し、長さ１０ｍｍの素子を形成した。光導波路の両端面を化学機械研磨した。
【０１１９】
この素子を使用し、チタン−サファイアレーザーを使用し、第二高調波を発生させた。位相整合波長が８５０ｎｍであり、第二高調波の波長は４２５ｎｍであった。ＳＨＧ変換効率は約５００％／Ｗであった。基本波の入射出力が１００ｍＷのときに、５０ｍＷの第二高調波出力が得られ、第二高調波において、光損傷等による特性劣化は観測されなかった。
【０１２０】
（実施例３）
図１５（ａ）−（ｃ）の手順に従い、図１４に示す素子１Ｌを製造した。
【０１２１】
具体的には、実施例１と同様にして、３度オフカット基板のＸ面（８７°Ｚカット）のＭｇＯを５ｍｏｌ％ドープしたニオブ酸リチウム材料９に、電圧印加法によって、周期２．８μｍ、分極反転深さ２. ５μｍの周期分極反転構造５を形成した。
【０１２２】
次いで、材料９の表面に、エキシマレーザーを用いたレーザー加工によって、深さ１．５μｍ、幅５μｍの溝２３を２列形成した。一対の溝２３間の間隔は５μｍにした。
【０１２３】
次いで、材料９の溝加工した表面９ａを、基板２（Ｘカットのニオブ酸リチウム基板、厚さ１ｍｍ）の表面２ａとを接着した。接着剤としては、アクリル系の室温硬化型樹脂を使用した。接合層３の厚さは約０．３μｍとした。溝２３中は接着剤によって充填されている。
【０１２４】
次いで、材料９を機械研削装置によって研削加工し、図１４の構造を得た。肉厚部分８の厚さは３μｍにした。この基板をその横断面方向に切断し、長さ１０ｍｍの素子を形成した。光導波路の両端面を化学機械研磨した。
【０１２５】
この素子を使用し、チタン−サファイヤレーザーを使用し、第二高調波を発生させた。位相整合波長は８２０ｎｍであり、第二高調波の波長は４１０ｎｍであった。基本波の入力が１００ｍＷのときに、６０ｍＷの第二高調波が得られ、光損傷等による特性劣化は観測されなかった。
【０１２６】
（実施例４）
ＭｇＯを５ｍｏｌ％ドープしたＺカットのニオブ酸リチウム材料９（厚さ０．３ｍｍ）にコロナ帯電法によって周期２．８μｍの周期分極反転構造を形成した。具体的には、基板の＋Ｚ面にピッチ２．７μｍの周期分極反転構造を形成し、基板の−Ｚ面にコロナワイヤを走査することによって、分極反転構造を生成させた。分極反転構造は、基板の厚み方向の全体にわたって均一に形成されていた。
【０１２７】
次いで、材料９からＹ方向に幅０．５ｍｍの短冊状のプレートを切り出し、プレートの切断面（Ｘ）を化学機械研磨した。
【０１２８】
次いで、前記短冊状のプレートのＸ面と、基板（単結晶シリコン、厚さ０．３５ｍｍ）を接着した。接着剤としては、アクリル系室温硬化型樹脂を使用した。接着層３の厚さは約０．３μｍとした。次いで、材料９を機械研削装置によって研削し、材料９Ａの厚さを３．５μｍとした。次いで、材料９Ａの表面に、エキシマレーザーを用いたレーザー加工によって、深さ２μｍ、幅５μｍの溝２３を２列形成した。一対の溝２３間の間隔は４μｍにした。
【０１２９】
次いで、基板をその横断面方向に切断し、長さ１０ｍｍの素子を形成した。光導波路の両端面を化学機械研磨した。
【０１３０】
この素子を使用し、チタン−サファイアレーザーを使用し、第二高調波を発生させた。位相整合波長は８２０ｎｍであり、第二高調波の波長は４１０ｎｍであった。基本波の入力が１５０ｍＷのときに１００ｍＷの第二高調波が得られ、光損傷等による特性劣化は観測されなかった。
【０１３１】
【発明の効果】
以上から明らかなように、本発明によれば、光導波路型デバイスにおいて、光導波路からの出射光の出力を増加させたときにも、出力の変動を少なくし、安定した発振を実現できる。
【図面の簡単な説明】
【図１】（ａ）は、本発明の一実施形態に係る光導波路素子１Ａを概略的に示す断面図であり、リッジ型の三次元光導波路４および周期分極反転構造５が形成されている。（ｂ）は、図１（ａ）の素子を概略的に示す斜視図である。
【図２】（ａ）、（ｂ）は、図１の光導波路素子の作成プロセスを概略的に示す断面図である。
【図３】図１の素子のリッジ構造の部分の拡大図である。
【図４】本発明の他の実施形態に係る光導波路素子１Ｂを概略的に示す断面図であり、図１の素子から肉厚部分８が除去されている。
【図５】本発明の他の実施形態に係る光導波路素子１Ｃを概略的に示す断面図であり、基板２に溝２ｃが形成されている。
【図６】本発明の他の実施形態に係る光導波路素子１Ｄを概略的に示す断面図であり、基板２に溝２ｃが形成されており、図５の素子から肉厚部分８が除去されている。
【図７】本発明の他の実施形態に係る光導波路素子１Ｅを概略的に示す断面図であり、誘電体装荷型の光導波路１０が形成されている。
【図８】（ａ）、（ｂ）は、図７の光導波路素子の作成プロセスを概略的に示す断面図である。
【図９】本発明の他の実施形態に係る光導波路素子１Ｆを概略的に示す断面図であり、図７の光導波路素子から肉厚部分が除去されている。
【図１０】本発明の他の実施形態に係る光導波路素子１Ｇを概略的に示す断面図であり、誘電体１２が光導波路１０上に装荷されている。
【図１１】本発明の他の実施形態に係る光導波路素子１Ｈを概略的に示す断面図であり、図１０の素子から肉厚部分８が除去されている。
【図１２】本発明の一実施形態に係る素子１Ｊを概略的に示す断面図であり、溝７が接合層３内にまで形成されており、延設部１５が除去されている。
【図１３】本発明の他の実施形態に係る素子１Ｋを概略的に示す断面図であり、素子の表面全体にオーバーコート層２１が形成されており、光導波路を被覆している。
【図１４】本発明の他の実施形態に係る素子１Ｌを概略的に示す断面図であり、素子１Ｌが、一対の延設部２６と、延設部２６から接合層３側へと向かって突出するリッジ型の光導波路２４とを備えている。
【図１５】（ａ）、（ｂ）、（ｃ）は、図１４の素子の製造工程を示す断面図である。
【図１６】本発明の素子において、一対の延設部をリッジ型の光導波路の両側に形成した場合の、基本波（励起光）および高調波のシングルモード伝搬条件を計算するモデルを示す。
【図１７】リッジ部分４の高さｔ１を１．０μｍとし、リッジ部分４の幅ｗと延設部１５の厚さｔ２とを変化させた場合の導波路のシングルモード条件を示すグラフである。
【図１８】リッジ部分４の高さｔ１を２．０μｍとし、リッジ部分４の幅ｗと延設部１５の厚さｔ２とを変化させた場合の導波路のシングルモード条件を示すグラフである。
【図１９】光導波路と接合層の屈折率差と電界分布の関係を示すグラフである。
【図２０】MgO ドープLiNbO3を光導波路としたときの光導波路と接合層との屈折率差ｄｎと、シングルモード条件を満足する最大の厚みとの関係を示すグラフである。
【図２１】導波路、接合層（接合層の屈折率＜基板の屈折率）、基板の３層構造をとった場合の、各層の屈折率の関係を示す模式図である。
【図２２】接合層を有する場合の導波光強度と深さとの関係を示すグラフである。
【図２３】接合層を有しない場合の導波光強度と深さとの関係を示すグラフである。
【図２４】接合層の厚みと位相整合波長および実効屈折率との関係を示すグラフである。
【図２５】オフカット基板に電圧印加法を適用している状態を示す斜視図である。
【図２６】オフカット基板における分極反転パターンの方向を示す模式図である。
【図２７】本発明の一実施形態に係る素子１Ｍを示す断面図であり、三次元光導波路３４が一対の突出部３４ａおよび３４ｂを備えている。
【図２８】本発明の一実施形態に係る素子１Ｎを示す断面図であり、基板２の表面２ａ側に凹部３１が形成されている。
【図２９】本発明の一実施形態に係る素子１Ｐを示す断面図であり、基板２の表面２ａ側に凹部３１が形成されており、光導波路２４Ａの一部が凹部３１内に挿入されている。
【図３０】本発明の一実施形態に係る素子１Ｑを示す断面図であり、基板２の表面２ａ側に凹部３１が形成されており、三次元光導波路３４が一対の突出部３４ａおよび３４ｂを備えており、突出部３４ｂが凹部３１内に挿入されている。
【図３１】本発明の一実施形態に係る素子１Ｒを示す断面図であり、二種類の接合層３Ｂおよび３Ｃを使用している。
【符号の説明】
１Ａ、１Ｂ、１Ｃ、１Ｄ、１Ｅ、１Ｆ、１Ｇ、１Ｈ、１Ｊ、１Ｋ、１Ｌ、１Ｍ、１Ｎ、１Ｐ、１Ｑ、１Ｒ 光導波路素子 ２ 基板 ２ａ基板の表面 ２ｂ 基板の突起 ２ｃ 基板の溝
３、３Ａ、３Ｂ、３Ｃ 接合層 ４、２４ リッジ型の三次元光導波路
５ 周期分極反転構造 ７ 溝 ８ 肉厚部分 ９光導波路成形用材料 ９ａ 材料９の接合面 １０ 誘電体装荷型の三次元光導波路 １１ 凹部 １２ 誘電体層 １５、２６ 一対の延設部 １７ リッジ構造の両側の溝 １８ リッジ構造
２１ オーバーコート層 ２２ 溝２３に充填された非晶質材料
２３ 光導波路２４と肉厚部分８との間の溝 ３０ 光導波路４の下地層 ３４ 一対の突出部を有する三次元光導波路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide element suitable for, for example, a quasi phase matching type second harmonic generation device and a method of manufacturing the same.
[0002]
[Prior art]
In general optical information processing technology, in order to realize high-density optical recording, there is a demand for a blue light laser that stably oscillates blue light having a wavelength of about 400 to 430 nm with an output of 30 mW or more. Has been done. As a blue light source, an optical waveguide type wavelength conversion element combining a laser that oscillates with infrared light as a fundamental wave and a quasi phase matching second harmonic generation element is expected.
[0003]
In the second harmonic generator using a lithium niobate single crystal, if the output of light propagating in the crystal increases, the refractive index changes in the crystal due to optical damage, so there is a limit to increasing the output. is there. In addition, the shorter the wavelength of light, the more significant the light damage. It is known that when a substrate in which MgO is added to lithium niobate is used, resistance against photodamage increases, and the addition ratio of MgO at this time is usually about 5 mol%.
[0004]
For example, according to the description on pages 806-807 of “Electronics Letters, 24th April, 1997. Vol. 33, No. 9”, a periodically poled structure is formed on a lithium niobate substrate doped with MgO. On the other hand, a proton exchange optical waveguide is formed in a direction perpendicular to the optical waveguide, thereby realizing an optical waveguide type second harmonic generator.
[0005]
[Problems to be solved by the invention]
However, in this type of second harmonic generator, when the blue light oscillation output is increased, a stable output cannot be obtained due to optical damage. For example, when a periodically poled structure is formed in lithium niobate doped with 5 mol% of MgO, a proton exchange optical waveguide is formed in a direction orthogonal to this structure, and blue light having a wavelength of 420 nm is oscillated, When the output was 10 mW or more, particularly about 15 mW or more, the output beam and output fluctuated greatly due to optical damage. The cause of such fluctuations in the output beam and its output has not been clear.
[0006]
An object of the present invention is to reduce fluctuations in output and enable stable oscillation even when the output of light emitted from an optical waveguide is increased in an optical waveguide device.
[0007]
Another object of the present invention is to provide a wavelength conversion element that uses a quasi-phase matching method when the wavelength of the emitted light is shortened, preferably in the blue region, and the output of the emitted light from the optical waveguide is increased. This is to reduce output fluctuations and enable stable oscillation.
[0008]
[Means for Solving the Problems]
The present invention provides a three-dimensional optical waveguide made of a bulk nonlinear optical crystal, a substrate bonded to the optical waveguide, a bonding layer made of an amorphous material bonding the optical waveguide and the substrate, WithAnd the refractive index of the bonding layer is 5% or more lower than the refractive index of the optical waveguide.The present invention relates to an optical waveguide element.
[0010]
In addition, the present invention joins an optical waveguide molding material made of a bulk nonlinear optical crystal to a separate substrate through a joining layer, and at this time, the refractive index of the joining layer is higher than the refractive index of the crystal. The present invention relates to a method for manufacturing an optical waveguide element, wherein the optical waveguide is formed by lowering the rate and then processing the material.
[0011]
Further, the present invention is a method of bonding an optical waveguide molding material comprising a bulk nonlinear optical crystal to a separate substrate, wherein the refractive index of the substrate is lower than the refractive index of the crystal, The present invention relates to a method of manufacturing an optical waveguide element, wherein the optical waveguide is formed by processing the material.
[0013]
The inventor bonded a three-dimensional optical waveguide made of a bulk nonlinear optical crystal directly to a substrate via a bonding layer or without a bonding layer, By using the substrate as an underclad, even if the output of light propagating in the optical waveguide is increased and / or the wavelength is shortened, optical damage is remarkably suppressed and fluctuations in output are prevented. The headline, the present invention has been reached.
[0014]
The present invention will be further described with reference to FIG.
[0015]
In the optical waveguide element 1 </ b> A shown in FIG. 1, the optical waveguide 4 is bonded onto the surface 2 a of the substrate 2 via the bonding layer 3. The optical waveguide 4 is of a ridge type, and a flat plate-like extending portion 15 is extended on each side of the optical waveguide 4 in the cross-sectional direction. In this example, a thick portion 8 is further formed at each end of each extending portion 15 (outside the groove 7). A space or groove 7 for forming a ridge type optical waveguide is formed above each extending portion 15. Reference numeral 5 denotes a periodically poled structure. In this example, the non-polarization inversion portion 6 remains in the upper portion of the optical waveguide, but this may be omitted. As a result, the ridge-type optical waveguide 4 takes a form of floating on the separate support substrate 2 via the bonding layer 3. Such a three-dimensional optical waveguide is unparalleled. The “three-dimensional optical waveguide” refers to an optical waveguide that confines light in the height direction (vertical direction) and the horizontal direction (horizontal direction) of the waveguide.
[0016]
Such a three-dimensional optical waveguide can be obtained by physically processing and molding a nonlinear optical crystal by, for example, machining or laser processing.
[0017]
On the other hand, the conventional three-dimensional optical waveguide is usually formed as follows.
(1) A surface region of a substrate made of a nonlinear optical crystal is altered and its composition is partially changed to provide an altered layer having a high refractive index, such as a titanium diffusion layer or a proton exchange layer, in the surface region of the substrate.
(2) A single crystal film having a refractive index higher than that of the substrate is formed on the surface of the substrate made of the nonlinear optical crystal, and the single crystal film is processed into an elongated planar shape.
[0018]
However, it is difficult to form, for example, a periodically poled structure in the single crystal film after the single crystal film is formed. On the other hand, as described above, it is known that a proton exchange layer having a periodically poled structure is formed on the surface region of a lithium niobate single crystal substrate and used as an optical waveguide. However, such second harmonic generators are severely damaged by light.
[0019]
In such a second harmonic generation device, for example, when light having a short wavelength of 400 to 430 nm is propagated at a high output, the cause of optical damage is that the output density of the light confined in the optical waveguide is It may also be caused by exceeding the light damage threshold.
[0020]
However, when the present inventor prototyped an apparatus as shown in FIG. 1 and propagated short-wavelength light at a high output density, the output fluctuation of the second harmonic emitted from the optical waveguide was suppressed, and the optical waveguide It was found that photodamage was suppressed. That is, for example, even when light having a short wavelength of 400 to 430 nm is propagated at a high output, the output density of the light confined in the optical waveguide does not exceed the threshold of light damage inherent to the crystal. , I found that I can afford. At the same time, it was discovered that the optical damage when the optical waveguide is formed by the proton exchange method is due to the deterioration of the crystallinity of the surface region in the proton exchange process and the accompanying damage resistance.
[0021]
As a result, according to the present invention, it is possible to provide an optical waveguide device that is extremely less damaged by light and that suppresses fluctuations in light output.
[0022]
At the same time, it is important that a bulk three-dimensional optical waveguide formed by machining or the like is bonded to a substrate through a bonding layer made of an amorphous material. For example, when a three-dimensional optical waveguide is bonded to a substrate without a bonding layer, thermal expansion between the substrate and the optical waveguide occurs during a temperature drop process after bonding or due to a temperature change after bonding. Due to the difference, great stress is applied to the optical waveguide. This is because there is always a difference in thermal expansion due to the difference in composition between the substrate and the optical waveguide, the crystal orientation of the substrate is different from the crystal orientation of the optical waveguide, and the substrate is better than the optical waveguide. Since it is much larger and bulky, a large stress is applied from the substrate to the optical waveguide, causing distortion in the optical waveguide. For this reason, the waveguide mode of light propagating in the optical waveguide is likely to change or optical damage is likely to occur.
[0023]
Further, when a single crystal is used as a material for the bonding layer, distortion is likely to occur in the optical waveguide due to the difference between the crystal orientation in the bonding layer and the crystal orientation in the optical waveguide. In addition, when polycrystal is used as the material for the bonding layer, the light oozing out from the optical waveguide to the bonding layer side is scattered at the crystal grain boundary or the like in the bonding layer, and propagation loss increases.
[0024]
On the other hand, in the present invention, by joining a bulky three-dimensional optical waveguide on a substrate, in addition to utilizing the good crystallinity inherent to the bulk, the optical waveguide is in direct contact. Since the bonding layer, which is a layer and not a substrate, is much smaller in volume than the substrate, stress tends to escape to the bonding layer, so that it is difficult to apply large stress from the bonding layer to the optical waveguide. In addition, since the bonding layer is made of an amorphous material, the stress applied to the bonding layer is easily dispersed, and the distortion of the optical waveguide is further reduced.
[0025]
According to the technical report "TECHNICICAL REPORT OF IEICE US95-24: EMD95-20: CPM95-32 (1995-07), pages 31-38, the lithium niobate substrate is directly bonded to the lithium tantalate substrate. However, the lithium niobate substrate is made into a thin piece and an optical waveguide structure is prototyped, which uses the intermolecular force of the hydroxyl groups adsorbed on the substrate surface to directly bond the substrates together. Is different.
[0026]
In addition, according to the description of JP-A-7-225403, an optical waveguide device including a core made of a non-linear optical material and a clad substrate surrounding the core is disclosed. This is different from the structure in which the original optical waveguide is bonded to the substrate via an amorphous material.
[0027]
In the present invention, a periodically poled structure is formed at least in the optical waveguide, and the optical waveguide element can function as a harmonic generation element. In this case, since the light having a shorter wavelength (higher energy) than the fundamental wave propagates in the optical waveguide, the effect of the present invention is particularly great.
[0028]
When the element of the present invention is used as a harmonic generator, particularly as a second harmonic generator, the wavelength of the harmonic is preferably 330 to 550 nm, particularly preferably 400 to 430 nm.
[0029]
In a preferred embodiment, the optical waveguide is a ridge type optical waveguide protruding from the bonding layer or the substrate.
[0030]
In a preferred embodiment, a pair of extending portions extending toward both sides in the cross-sectional direction of the optical waveguide are provided. Such an extended portion stabilizes the bonding state of the optical waveguide on the substrate. Further, by providing extending portions on both sides of the optical waveguide, the light propagation state is also symmetric.
[0031]
The nonlinear optical crystal constituting the optical waveguide is not particularly limited, but a ferroelectric single crystal that easily forms a periodically poled structure is preferable, and lithium niobate (LiNbO) is preferable._Three ), Lithium tantalate (LiTaO)_Three ), Lithium niobate-lithium tantalate solid solution, K_Three Li₂ Nb_Five O₁₅Each single crystal is particularly preferable.
[0032]
In such a crystal, in order to further improve the light damage resistance of the three-dimensional optical waveguide, at least one selected from the group consisting of magnesium (Mg), zinc (Zn), scandium (Sc), and indium (In) is used. Metal elements can be contained, and magnesium is particularly preferred.
[0033]
When a periodically poled structure is formed in an optical waveguide, from the viewpoint that the polarization inversion characteristics (conditions) are clear, a lithium niobate single crystal, a lithium niobate-lithium tantalate solid solution single crystal, or these Those added with magnesium are particularly preferred.
[0034]
When providing the bonding layer, the material of the substrate is not particularly limited as long as it has a predetermined structural strength. However, it is preferable that the optical waveguide and the physical properties such as the thermal expansion coefficient are close to each other, and lithium niobate (LiNbO_Three ), Lithium tantalate (LiTaO)_Three ), Lithium niobate-lithium tantalate solid solution, K_Three Li₂ Nb_Five O₁₅Each single crystal is particularly preferable.
[0035]
Further, another film can be formed on the surface of the substrate. Examples of the film forming method include a liquid phase epitaxial method, a sputtering method, a vapor deposition method, a spin coating method, and a chemical vapor deposition method. The material of the film is not limited, and examples thereof include silicon oxide, niobium pentoxide, tantalum pentoxide, lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate solid solution.
[0036]
When at least the surface region of the substrate functions as an underclad, the refractive index of at least the surface region of the substrate needs to be lower than the refractive index of the optical waveguide material.
[0037]
The refractive index of the material of the bonding layer is higher than the refractive index of the material of the optical waveguide.5% or moreIt needs to be lowered. This difference in refractive index is more preferably 10% or more. The material of the bonding layer is preferably organic resin or glass (particularly preferably low melting point glass). Examples of the organic resin include acrylic resins, epoxy resins, and silicone resins. As the glass, low melting glass mainly composed of silicon oxide is preferable.
[0038]
In addition, in order for the bonding layer to function as an underclad, the thickness of the bonding layer is preferably 0.1 μm or more, and more preferably 0.2 μm or more. In addition, from the viewpoint of positional stability of the three-dimensional optical waveguide, it is preferable that the thickness of the bonding layer is 3 μm or less.
[0039]
The optical waveguide device shown in FIGS. 1A and 1B is manufactured by, for example, the following method. That is, as shown in FIG. 2A, the periodically poled structure 5 is formed on the surface of the optical waveguide molding material 9. A surface (bonding surface) 9 a on the structure 5 side of the optical waveguide molding material 9 is bonded to the surface 2 a of the substrate 2. Next, as shown in FIG. 2B, the back surface (non-joint surface) 9b of the optical waveguide molding material 9 is ground to thin the material 9A. At this stage, it is difficult to make the material 9A thin enough to confine the light in the thickness direction. Next, as shown in FIG. 1, a groove 7 is formed, and an optical waveguide 4 having a ridge structure is formed. At this time, the thickness of the optical waveguide is also adjusted. Such processing can be performed by, for example, a dicing apparatus or a laser processing apparatus, but mechanical processing such as dicing is preferable.
[0040]
The method for forming the periodically poled structure is not limited. As a method for forming a periodically poled structure on an electro-optic crystal substrate, for example, a lithium niobate substrate, a diffusion method in Ti, Li₂ O out-diffusion method, SiO₂ A loading heat treatment method, a Ti thermal oxidation method, a proton exchange heat treatment method, an electron beam scanning irradiation method, a voltage application method, a corona charging method and the like are preferable. Among these methods, the voltage application method is particularly preferable when using an X-cut or Y-cut or its off-cut substrate from the viewpoint of forming a deep periodic domain-inverted structure with high accuracy. Moreover, when using a Z cut board | substrate, it is especially preferable to carry out by the corona charging method or the voltage application method.
[0041]
As a method of grinding the height of the optical waveguide to a predetermined dimension, the distance between the cutting outer peripheral blade that rotates perpendicularly to the bottom surface of the optical waveguide and the bottom surface of the optical waveguide is set to a predetermined height and the cutting is performed. Accordingly, it is preferable to set the thickness of the optical waveguide to a necessary value. The reason is as follows.
[0042]
Conventionally, when the thickness of a substantially flat workpiece is prepared by grinding, it has been common to grind the surface of the workpiece with an outer peripheral blade that rotates parallel to the surface. However, with this method, the thickness tends to become non-uniform due to the slight inclination of the rotating surface of the outer peripheral blade. Therefore, the height of the elongated optical waveguide having a width of several μm and a length of about 1 mm is set to the order of submicron. It was difficult to control with.
[0043]
On the other hand, if the distance between the cutting outer peripheral blade rotating perpendicularly to the bottom surface and the bottom surface of the optical waveguide is set to a predetermined height and cutting is performed, by adjusting the height of the outer peripheral blade, Adjustment can be performed easily, and the accuracy at this time follows the processing accuracy (submicron order) of general processing equipment.
[0044]
As in the optical waveguide element 1B of FIG. 4, the thick portion 8 of the extending portion can be omitted. The thick portion 8 can be removed by the dicing apparatus described above, for example.
[0045]
In forming the ridge structure, a groove can also be formed in the substrate. For example, the optical waveguide element 1C in FIG. 5 is basically the same as the optical waveguide element 1A in FIG. 1, but the substrate 2 is also formed with grooves 2c, and the grooves 17 on both sides of the ridge structure 8 are formed. Even inside the substrate 2. As a result, the ridge structure 18 includes a substrate protrusion 2 b, a bonding layer 3 on the protrusion 2 b, and an optical waveguide 4 on the bonding layer 3.
[0046]
Also in the optical waveguide element 1D of FIG. 6, the groove 2c is formed in the substrate similarly to the optical waveguide element 1C, and thereby the protrusion 1b of the substrate 2 is formed. In addition, although 20 is the same material as the joining layer 3, the thick part 8 is removed.
[0047]
In FIGS. 1, 4, 5, and 6, the lower portion of the optical waveguide is the polarization inversion portion 5, and the upper portion is the non-inversion portion 6. However, the entire optical waveguide may be a polarization inversion portion. In some cases, the upper portion of the optical waveguide becomes the polarization inversion portion 5 and the lower portion becomes the non-inversion portion 6.
[0048]
In one embodiment of the present invention, a so-called dielectric-loaded three-dimensional optical waveguide can be used. For example, in the optical waveguide element 1E of FIG. 7, the three-dimensional optical waveguide 10, the pair of extending portions 15, and the pair of thick portions 8 are bonded to the surface 2a of the substrate 2 via the bonding layer 3. The three-dimensional optical waveguide 10 and the extending portion 15 constitute a thin portion, and the thickness of the thin portion is set to a thickness that enables confinement in the thickness direction of light. The three-dimensional optical waveguide 10 is formed on the dielectric layer 12 by forming a predetermined dielectric layer 12 on the surface of the thin portion. In this example, the dielectric layer 12 protrudes into the bonding layer 3.
[0049]
For example, the following method is used to manufacture the optical waveguide device shown in FIG. That is, as shown in FIG. 8A, the periodically poled structure 5 is formed on the surface of the optical waveguide molding material 9, and the dielectric layer 12 is further formed. The material of the dielectric layer 12 is not particularly limited as long as the refractive index is higher than that of the material 9, but for example, niobium pentoxide is preferable. A joining surface 9 a of the optical waveguide molding material 9 is joined to the surface 2 a of the substrate 2. Next, as shown in FIG. 8B, the back surface (non-joint surface) 9b of the material 9 is ground to thin the material 9A. Subsequently, as shown in FIG. 7, the recessed part 11 is formed, and the thick part 8 and the thin parts 10 and 15 are formed. For such processing, the above-described processing method can be diverted.
[0050]
As in the optical waveguide element 1F in FIG. 9, the thick portion 8 of the extending portion can be omitted.
[0051]
Further, the dielectric can be loaded on the upper side of the optical waveguide (on the opposite side of the substrate). In the optical waveguide device 1G of FIG. 10, a dielectric 12 is loaded on the optical waveguide 10. Further, in the optical waveguide element 1H of FIG. 11, the dielectric 12 is loaded on the optical waveguide 10, and the thick portion 8 of the extending portion is omitted in the element of FIG.
[0052]
In the present invention, in FIG. 1, the extended portion 15 can be removed by further increasing the depth of the groove 7 to form the groove into the bonding layer 3. In this case, for example, as in the element 1J shown in FIG. 12, the groove 7 reaches the bonding layer 3, and the ridge-type optical waveguide 4 projects directly from the bonding layer 3.
[0053]
Moreover, an overcoat layer covering at least the optical waveguide can be provided. FIG. 13 shows an element 1K according to this embodiment. The surface of the element on the optical waveguide 4 side is covered with an overcoat layer 21.
[0054]
Thus, the surface of the optical waveguide comes into contact with the overcoat layer without directly touching the atmosphere. For this reason, for example, when the surface of the optical waveguide is rough or has a fine chip, light scattering is reduced as compared with the case where the optical waveguide is exposed to the atmosphere.
[0055]
The material of the overcoat layer is not limited. For example, silicon oxide (SiO₂ ), Niobium pentoxide, tantalum pentoxide, or various resin materials.
[0056]
In a preferred embodiment, the optical waveguide device of the present invention includes a pair of extending portions and a ridge-shaped optical waveguide protruding from the extending portions toward the bonding layer. FIG. 14 shows an element 1L according to this embodiment.
[0057]
A pair of thick portions 8, a pair of extending portions 26, and an optical waveguide 24 that protrudes from the extending portions toward the bonding layer 3 are provided on the substrate 2. A pair of grooves 23 are formed between the thick portion 8 and the optical waveguide 24, and the grooves 23 are filled with an amorphous material 22. It is preferable that the filling 22 of the amorphous material is continuous with the bonding layer 3.
[0058]
In this example, the optical waveguide 24 includes a periodic polarization inversion portion 5 and a protruding portion 25 that has not undergone polarization inversion, and the polarization inversion portion 5 is provided on the tip side close to the substrate 2.
[0059]
According to such a structure, the surface of the optical waveguide is in contact with the amorphous material. For this reason, for example, when the surface of the optical waveguide is rough or has a fine chip, light scattering is reduced as compared with the case where the optical waveguide is exposed to the atmosphere. Therefore, the variation in optical insertion loss is reduced.
[0060]
Although the manufacturing method of such an element is not specifically limited, It is preferable to divert the above-mentioned manufacturing method. That is, as shown in FIG. 15A, the periodically poled structure 5 is formed on the surface of the optical waveguide molding material 9. Next, as shown in FIG. 15B, the groove 23 having a predetermined shape is formed by the above-described machining and laser processing, and the optical waveguide 24 having a ridge structure is formed between the pair of grooves 23.
[0061]
Next, as shown in FIG. 15 (c), a surface (bonding surface) 9 a on the structure 5 side of the optical waveguide molding material 9 is bonded to the surface 2 a of the substrate 2. At this time, the groove 23 is filled with the amorphous material 22. Next, the back surface (non-joint surface) 9b of the optical waveguide molding material 9 is ground to reduce the thickness of the material 9, thereby forming the thick portion 8 and the extending portion 26 in FIG.
[0062]
In a preferred embodiment, when a pair of extending portions extending toward both sides in the cross-sectional direction of the optical waveguide is provided, both the fundamental wavelength of the harmonic generation element and the wavelength of the wavelength conversion wave are provided. Single mode propagation. Particularly preferably, the width of the optical waveguide is 1-10 μm, the height from the extended portion of the optical waveguide is 0.2-5 μm, and the thickness of the extended portion is 0.5-5 μm.
[0063]
This embodiment will be described.
[0064]
In order to find a waveguide structure in which both pumping light and wavelength-converted light have a single mode condition, detailed examination was performed using an optical waveguide structure analysis method by a finite element method, and the characteristics were confirmed by experiments. As a result, it has been found that, for example, the waveguide of FIG. 1 satisfies this condition and the waveguide dimension tolerance for realizing high performance is extremely large, so that the manufacture is easy.
[0065]
The element shown in FIG. 1 includes a portion of the three-dimensional optical waveguide 4 and a pair of extending portions 15 extending on both sides thereof. Such a structure can also be seen in the elements of FIGS. 3, 4, 13, and 14.
[0066]
A specific study was performed with the wavelength of excitation light λ1 = 810 nm and the wavelength of converted light λ2 = 405 nm. In this examination, examination was based on the model shown in FIG. Here, 2 is a substrate, 3 is a bonding layer, 4 is a ridge portion, and 30 is a lower portion of the conductive path divided for the purpose of calculating the structure of FIG.
[0067]
An example of the calculation result of the coupling loss when direct optical coupling is established between the pumping light laser and the waveguide fundamental mode (wavelength λ1) is shown in FIGS. In the calculation examples in FIGS. 17 and 18, the material of the ridge portion 4 and the extending portion 15 is the same nonlinear optical material, and this nonlinear optical material is refracted with respect to the wavelength λ1 and the refractive index of 2.14 and λ2. The rate was 2.29. Further, the refractive index of the bonding layer 3 was set to a refractive index of 1.51 for both wavelengths λ1 and λ2. Further, a Gaussian beam having an x-direction radius of 1.5 μm and a y-direction radius of 1.0 μm was assumed as a spot of the excitation light laser to be coupled with the present waveguide.
[0068]
The width w of the ridge portion 4 is taken on the horizontal axis. The vertical axis represents the coupling loss η between the waveguide mode field and a Gaussian beam having an x-direction diameter of 3 μm and a y-direction diameter of 2 μm assuming a pumping light laser. In FIG. 17, the height t1 of the ridge portion 4 is fixed to 1.0 μm, and in FIG. 18, t1 is fixed to 2.0 μm. In each graph, the thickness t2 of the extended portion was changed between 1.0 and 4.0 mm. The portion indicated by the solid line in FIGS. 17 and 18 is a single mode propagation region.
[0069]
In each graph, a certain threshold value ws exists in the width W of the ridge portion 4. For example, it can be seen that when t1 = 1.0 μm and t2 is 2.0 μm or more, single mode propagation occurs under w below each threshold value. In FIG. 17, ws varies within a range of 4 to 10 μm. However, when w becomes smaller than necessary, it becomes a state close to the slab mode, and a cut-off state is entered (η increases). When t2 is about 1.0 μm or less, the confinement state becomes extremely strong, and in order to satisfy the single mode condition, it becomes w to 1.0 μm or less, and the coupling loss increases.
[0070]
In the calculation example of FIG. 17, the waveguide is a single mode in the vicinity of the width w of the ridge portion 4 = 2.5 μm, the height t1 of the ridge portion 4 = 1.0 μm, and the thickness t2 of the extended portion = 1.5 μm. In such a range, the optimum structure with the minimum coupling loss is obtained.
[0071]
Similarly, in the calculation example of FIG. 18, a waveguide structure in the vicinity of w = 2.5 μm, t1 = 2.0 μm, and t2 = 1.5 μm is the optimum structure.
[0072]
In this calculation example, only the cases where t1 is 1.0 and 2.0 μm are described, but it is obvious that similar single mode propagation regions can be obtained for other t1. It has been confirmed by calculation / experiment that the threshold value ws decreases by increasing t1 because the confinement of the waveguide becomes stronger.
[0073]
In addition, t2 is described only in the cases of t2 = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 μm, but a similar single mode propagation region exists in other t2. Increasing t2 results in weak waveguide confinement, so the threshold value ws increases. On the other hand, by reducing t2, the confinement of the waveguide becomes stronger and ws tends to decrease.
[0074]
Further, the relative refractive index difference (n1−n2) / n2 between the refractive index (n1) of the ridge portion 4 and the extended portion 15 and the refractive index (n2) of the base layer 30 and the ridge portion 4 and the extended portion 15 One of the refractive index difference (n1) and the relative refractive index difference (n1-n2) / n2 between the refractive index (n1) and the refractive index of air (the refractive index of the overcoat layer instead of air when overcoating the optical waveguide) (n2) Or if both become large, refractive index n1, n2 is large.KisaRegardless, the confinement of the waveguide becomes strong and ws decreases. On the other hand, if one or both of the relative refractive index differences are reduced, the confinement of the waveguide is weakened and ws is increased regardless of the magnitude of n1 and n2.
[0075]
In this calculation example, only the spot radius of the pumping laser is 1.5 μm in the x direction and 1.0 μm in the y direction, but the spot radius of the pumping laser depends on the application, operating wavelength, and the appropriate material, composition, structure, The dimensions are chosen and the size is determined by the combination. Further, in some cases, it is possible to couple with an optical waveguide through a lens. In consideration of these, the effective spot diameter is different from about 0.5 μm to about 5 μm.
[0076]
For example, when a laser with a small effective spot diameter is used, w and t2 at which the coupling loss η between the pumping light laser and this optical waveguide is minimized are decreased, or when the spot diameter of the pumping light laser is increased, w And t2 will increase.
[0077]
Although an example has been shown in this study, the refractive index of a general nonlinear optical crystal or nonlinear polymer material is in the range of 1.3 to 2.5 considering the fact that the refractive index varies greatly depending on the operating environment temperature. The refractive index ranges from 1.3 to 2.0. Therefore, as a structure that satisfies the single mode condition according to the present invention with respect to the effective spot diameter of the laser used and reduces the coupling loss with the laser, the shape of the ridge-type optical waveguide is the width of the ridge portion 4. A single mode is obtained in the range of 1 to 10 μm, the height of the ridge portion 4 is 0.2 to 5 μm, and the thickness of the extended portion 15 and the underlayer 30 is 0.5 to 5 μm.
[0078]
It is also obvious that the results of the study are the same for both models when there is a substrate layer that functions as a cladding and when there is no substrate layer.
[0079]
(Regarding the refractive index of the bonding layer)
  When an optical waveguide type optical wavelength conversion element is formed, the overlapping of fundamental and harmonic modes in the optical waveguide greatly affects the conversion efficiency. The shape of the waveguide mode is affected by the refractive index of the bonding layer. FIG. 19 shows the relationship between the refractive index difference between the waveguide and the bonding layer and the electric field distribution. Wavelength 850nm, waveguide LiNbO _Three (Refractive index 2.166) and the substrate is LiTaO _Three Calculation was performed with a refractive index of 2.158. As the refractive index difference increased, the symmetry of the mode profile increased and the confinement improved. As can be seen from FIG. 19, when the refractive index difference Δn between the waveguide and the bonding layer is 5% or more, the symmetry of the mode is increased, and high efficiency is achieved. Furthermore, when Δn is 10% or more, confinement is strengthened and conversion efficiency can be improved.
[0080]
(Establishment of single mode conditions)
In a waveguide type optical wavelength conversion element, in order to perform highly efficient wavelength conversion, it is indispensable to satisfy the conditions for single mode propagation of the optical waveguide. In particular, it is desirable that the optical waveguide satisfies the single mode condition for the fundamental wave (when the wavelength of the converted light is smaller than the fundamental wave). The reason is that, when a fundamental wave is input to the waveguide, in the multimode waveguide, the propagating fundamental wave may be dispersed into a plurality of waveguide modes. In the optical wavelength conversion element, since the conversion efficiency depends on the power density of the fundamental wave, if the propagation mode of the fundamental wave is dispersed in the multimode waveguide, the conversion efficiency is extremely lowered. Furthermore, there arises a problem that the output becomes unstable due to dispersion of the guided propagation mode.
[0081]
The single mode condition in the optical waveguide will be described. FIG. 20 shows the relationship between the refractive index difference dn from the bonding layer and the maximum thickness satisfying the single mode condition when MgO-doped LiNbO3 is used as the waveguide layer for light with a wavelength of 800 nm. When the refractive index difference Δn = 5%, the single mode depth is about 1 μm. As the refractive index difference increases, the single mode condition becomes more severe. This result shows that the thickness of the waveguide layer must be controlled to 1 μm or less in order to realize the refractive index (5% or more) with the bonding layer for realizing the above-mentioned highly confined optical waveguide. ing. However, reducing the thickness of the waveguide increases the aspect ratio of the waveguide mode, and the aspect ratio of the mode profile of the emitted light is proportional to this, so that when the light is collected by the lens system, the beam shaping of the emitted light is performed. Etc. are required. Further, when light is coupled to the waveguide, it is greatly different from the beam profile of a normal semiconductor laser or solid-state laser, which causes a decrease in coupling efficiency. In addition to the thickness variation of the waveguideEffectiveSince the change in refractive index is large, the non-uniformity of the waveguide increases. To improve this, it is necessary to increase the single mode depth of the waveguide. Considering high-efficiency coupling with a semiconductor laser, the single mode depth is required to be 1 μm or more. Therefore, a material having a refractive index difference of 5% or less from the optical waveguide is required as the refractive index of the bonding layer. Therefore, it becomes difficult to realize an optical waveguide structure having excellent symmetry and strong confinement.
[0082]
Therefore, a new waveguide structure is proposed as a method for increasing the single mode depth. When the refractive index distribution in the depth direction of the waveguide has a three-layer structure of a waveguide, a bonding layer (the refractive index of the bonding layer <the refractive index of the substrate), and the substrate as shown in FIG. In the state where the electric field distribution of the propagating light exists on the substrate side, the single-mode condition of the optical waveguide is found to depend largely on the refractive index difference between the waveguide and the substrate, not the refractive index difference between the waveguide and the junction layer. It was. That is, the single mode condition of the waveguide can be greatly relaxed by using a substrate having a refractive index close to that of the optical waveguide.
[0083]
Specifically, the relationship between the refractive index difference and the single mode depth shown in FIG. 20 is substantially the same by replacing the refractive index difference with the refractive index difference between the waveguide and the substrate. That is, in order to make the depth of a single mode waveguide 1 μm or more, it is possible to set the refractive index difference between the substrate and the waveguide to 5% or less. On the other hand, the electric field distribution of the guided light existing in the optical waveguide can be controlled by the refractive index of the bonding layer. As described above, by improving the refractive index of the bonding layer by 5% or more than the refractive index of the waveguide, it is possible to improve the symmetry of the electric field distribution of the waveguide mode and enhance the confinement. By providing the bonding layer, the single mode condition of the waveguide and the electric field distribution of the waveguide mode can be designed independently. (However, this condition is limited when the electric field distribution of the waveguide mode exists on the substrate side. The reason is that if the junction layer becomes too thick, the waveguide mode does not exist on the substrate side. This is because the single mode condition is satisfied by the difference in refractive index of
[0084]
The following two points are necessary as conditions for the waveguide through the bonding layer.
The refractive index of the bonding layer is lower than the refractive index of the substrate.
The electric field distribution of the waveguide mode propagating through the waveguide exists on the substrate. Specifically, it is necessary that the electric field strength in the substrate is 1/1000 or more of the maximum value of the electric field strength in the waveguide. When the value is smaller than this, the influence of the substrate on the waveguide mode does not appear.
[0085]
22 and 23 show electric field distributions with and without a junction layer, and it can be seen that the inclusion of the junction layer greatly increases the confinement of the waveguide and increases the symmetry. As a result, it was found that the overlap between the fundamental wave and the harmonics in the waveguide can be increased, and that the conversion efficiency is increased more than twice in the waveguide having the junction layer.
[0086]
(Junction layer thickness)
The thickness of the bonding layer will be described. When the thickness of the bonding layer is increased, as described above, the influence of the substrate on the waveguide is eliminated, so that it is difficult to satisfy the single mode condition. On the other hand, when the thickness of the bonding layer decreases, the influence of the thickness of the bonding layer on the effective refractive index of the waveguide increases. This indicates that the uniformity of the optical waveguide device greatly depends on the thickness of the bonding layer. Waveguide-type optical wavelength conversion elements have a very severe phase matching wavelength tolerance of about 0.1 nm. Therefore, if the phase matching is partially different due to the non-uniformity of the waveguide, the conversion efficiency may be extremely lowered. Become.
[0087]
FIG. 24 shows the relationship between the thickness of the bonding layer and the phase matching wavelength. When the thickness of the bonding layer is 0.1 μm or less, the dependency of the phase matching wavelength on the thickness of the bonding layer is large. When the thickness is 0.15 μm or more, the dependency gradually decreases, and when the thickness is 0.2 μm or less, the dependency is further reduced. Therefore, the thickness of the bonding layer is preferably such that the phase matching wavelength is less dependent on the thickness of the bonding layer. At the same time, it is necessary to thin the waveguide mode electric field distribution to the extent that it exists on the substrate side.
[0088]
In the above description, the electric field distribution in the depth direction of the waveguide is described. However, the present invention can be applied to any waveguide such as a loaded waveguide, a ridge waveguide, and a machined waveguide. In order to realize the lateral confinement of the waveguide, it is necessary to adopt these structures.
[0089]
(Formation of periodically poled structure using off-cut substrate)
In order to construct a highly efficient optical wavelength conversion element, it is important to increase the overlap between the periodically poled structure and the light propagating through the optical waveguide. Assuming a case where a second harmonic wave having a wavelength of about 410 nm is generated from a fundamental wave having a wavelength of about 820 nm as the optical waveguide shape, the depth of the periodic polarization inversion is 2 μm or more because the depth of the optical waveguide is about 2 μm. Necessary.
[0090]
As a method of forming a deep domain-inverted structure, there is a method of using an off-cut substrate having a crystal axis inclined with respect to the substrate surface. For example, in an X off-cut substrate, the X axis and the Z axis of an X plate (a substrate in which the X axis of the crystal is perpendicular to the substrate surface) are inclined by θ around the Y axis. In the Y off-cut substrate, the Y axis and the Z axis of the Y plate (the substrate in which the Y axis of the crystal is perpendicular to the substrate surface) are inclined by θ around the X axis. By forming a domain-inverted structure using such an X-off-cut substrate and a Y-off-cut substrate, it is possible to form a deep domain-inverted structure, thereby realizing high efficiency of the optical wavelength conversion element. The polarization inversion depth increases as the offcut angle increases. For example, when the period of the periodically poled structure is 3 μm, when the off-cut angle θ = 1.5 °, the polarization inversion depth is 1 μm, θ = 3 ° is 1.7 μm, and θ = 5 ° is 2.5 μm. A periodic polarization inversion structure can be realized. Therefore, in order to realize sufficient overlap between the optical waveguide and the periodically poled structure, a substrate having an offcut angle θ of 3 ° or more is desirable.
[0091]
However, when forming a domain-inverted structure on an off-cut substrate, there are the following problems.
(1) When the proton exchange optical waveguide is applied to an offcut substrate, the propagation loss increases in proportion to the offcut angle.
(2) When a proton exchange optical waveguide is formed on a Y off-cut substrate, there is a propagation loss twice or more that of an X off-cut substrate.
[0092]
That is, in the case of a proton exchange optical waveguide that has been used in an optical waveguide type wavelength conversion element in the past, attempting to use deep polarization inversion by an offcut substrate results in degradation of the characteristics due to the propagation loss of the optical waveguide, and at most. Only X off-cut substrates with θ less than 3 ° are used. When a Y-off cut substrate is used, the propagation loss of the optical waveguide becomes 4-5 dB / cm or more, which significantly deteriorates the characteristics of the second harmonic generation element.ExchangeThere was a problem that it was difficult to use with an optical waveguide. The cause of propagation loss in these optical waveguides is due to chemical damage that occurs during proton exchange.
[0093]
As a method for solving these problems, the optical wavelength conversion element of the present invention is very effective. Since the optical wavelength conversion element of the present invention can form an optical waveguide without using a proton exchange process, chemical damage does not occur. Therefore, it is possible to use an X off-cut substrate or a Y off-cut substrate having an off-cut angle of 3 ° or more, which has been difficult to use conventionally. When an X and Y off-cut substrate with θ = 5 ° was used, there was a waveguide loss of 2 dB / cm or more in the X-cut substrate and 4-5 dB / cm or more in the Y off-cut substrate. However, with the configuration of the present invention, it is possible to form an optical waveguide having a propagation loss of 1 dB / cm or less and a low propagation loss even when an off-cut substrate with θ = 5 ° is used. As a result, it became possible to increase the conversion efficiency of the second harmonic generation element more than twice by using a deep polarization inversion and a low-loss waveguide structure.
[0094]
Furthermore, it has been clarified that a more efficient structure of the optical wavelength conversion element can be obtained by using a Y-off cut substrate (substrate whose X axis is parallel to the substrate surface). It has been found that a thicker domain-inverted structure is formed in the Y off-cut substrate than in the conventionally used X off-cut substrate. In the case of the Y off-cut substrate, a domain-inverted portion 1.2 times deeper than that of the X off-cut substrate was obtained. As a result, the conversion efficiency of the optical wavelength conversion element can be increased by 1.2 times. Also, with respect to the polarization inversion period, the inversion structure formed on the Y off-cut substrate can be made shorter, and is advantageous for realizing an optical wavelength conversion element with a short wavelength. In a conventional optical wavelength conversion device using a proton exchange optical waveguide, the Y-off cut substrate has not been studied because of its large waveguide loss. However, by using the optical wavelength conversion device of the present invention, a low-loss optical waveguide can be obtained. A waveguide structure can be formed, and a highly efficient optical wavelength conversion element can be realized.
[0095]
(Element modification)
In one embodiment of the present invention, the three-dimensional optical waveguide includes a protruding portion protruding in a direction away from the substrate and a protruding portion protruding in a direction approaching the substrate with respect to the extending portion. An element 1M shown in FIG. 27 relates to this embodiment.
[0096]
In the element 1M, the surface of the substrate 2, the three-dimensional optical waveguide 34, and the pair of extending portions 15 are joined by the joining layer 3A. The three-dimensional optical waveguide includes a protrusion 34b extending in the direction of the substrate 2, a protrusion 34a extending in a direction away from the substrate, and a central portion 34c sandwiched between the protrusions 34a and 34b. . The protrusions 34a and 34b are substantially symmetrical when viewed from the central portion 34c.
[0097]
When such a three-dimensional optical waveguide is employed, the cross-sectional shape of the light beam propagating in the optical waveguide is close to a perfect circle. Therefore, the coupling loss when the element is coupled to an external optical fiber is further reduced. Or the energy loss at the time of condensing and focusing the light which propagates an optical waveguide is reduced.
[0098]
It is also possible to form a recess or protrusion on the surface 2 a of the substrate 2. In a particularly preferred embodiment, the thickness of the bonding layer is increased between the three-dimensional optical waveguide and the surface of the substrate, and the thickness of the bonding layer is decreased between the extended portion and the substrate surface. Alternatively, a three-dimensional optical waveguide is provided on the concave portion of the substrate surface. As a result, the stress applied to the three-dimensional optical waveguide from the bonding layer and the substrate side is further reduced.
[0099]
FIG. 28 shows an element 1N according to this embodiment. A recess 31 is formed in the surface 2 a of the substrate 2. The three-dimensional optical waveguide 4 and the pair of extending portions 15 are bonded to the substrate surface 2a via the bonding layer 3. The three-dimensional optical waveguide 4 is positioned on the recess 31, and the bonding layer material 32 is also filled in the recess 31. As a result, the thickness of the bonding layer is relatively large between the three-dimensional optical waveguide and the substrate, and relatively small between the extending portion and the substrate.
[0100]
In such an embodiment, the ratio between the thickness of the bonding layer between the three-dimensional optical waveguide and the substrate and the thickness of the bonding layer between the extending portion and the substrate is preferably 10-1: 1.
[0101]
In a preferred embodiment, a recess is provided on the substrate surface, and at least a part of the three-dimensional optical waveguide is located in the recess. FIG. 29 shows an element 1P according to this embodiment.
[0102]
In the element 1P, a recess 31 is formed on the surface 2a of the substrate 2. Further, the three-dimensional optical waveguide 24A protrudes toward the substrate 2 and the tip portion of the optical waveguide 24A is located in the recess 31. The concave portion 31 is filled with a bonding layer material 32. Since the surface of this element is substantially flat, the above-described operational effects can be obtained.
[0103]
Furthermore, in the element 1Q shown in FIG. 30, a recess 31 is formed in the surface 2a of the substrate 2. The three-dimensional optical waveguide 34 includes a pair of protrusions 34 a and 34 b, and the tip of the protrusion 34 b is located in the recess 31.
[0104]
Further, it is not necessary that the bonding layer is continuously provided over the entire surface of the substrate between the three-dimensional optical waveguide and the substrate or between the extending portion and the substrate. For example, a part between the three-dimensional optical waveguide and the substrate may be a gap, or a filling material other than the bonding material may be filled in the gap. Moreover, a part between the extended portion and the substrate may be a gap, or a filling material other than the bonding material may be filled in the gap.
[0105]
Further, the bonding layer may be made of a plurality of types of materials. For example, in the element 1R of FIG. 31, the surface 2a of the substrate 2 and the extending portion 15 and the three-dimensional optical waveguide 4 are joined by two kinds of joining layers 3B and 3C.
[0106]
Hereinafter, more specific examples will be described.
(Example 1)
An optical waveguide element 1A shown in FIG. 1 was manufactured. Specifically, the lithium niobate material 9 (thickness 0.5 mm) doped with 5 mol% of MgO on the X-plane (87 ° Z cut) of the 3 ° off-cut substrate has a period of 3.2 μm by a voltage application method, A periodically poled structure 5 having a domain inversion depth of 2 μm was formed. Specifically, as shown in FIG. 25 and FIG. 26, the polarization inversion structure 25 is generated by a voltage application method on the off-cut (3 degrees) X plate 21 (made of MgO-doped lithium niobate) with a pitch of 3.2 μm. It was. Comb electrodes 23 and stripe electrodes 22 were formed on the surface 21a of the substrate 21 so as to extend in the Z direction and to face each other. A uniform planar electrode 24 was formed on the back surface 21 b of the substrate 21. By applying voltages of V1 = 5 kV / mm and V2 = 5 kV / mm between the comb electrode 23 and the planar electrode 24 (V1) and between the comb electrode 23 and the stripe electrode 22 (V2), respectively, A periodic domain-inverted structure 25 was formed.
[0107]
Here, since the substrate 21 is off-cut, the formed inversion pattern extends along the polarization direction (Ps) of the substrate. Therefore, the substrate 21 moves from the substrate surface 21a toward the inside of the substrate to the surface 21a. It extends in a direction inclined by 3 degrees.
[0108]
Next, the bonding surface 9a of the material 9 and the surface 2a of the substrate 2 (x-cut lithium niobate substrate, thickness 1 mm) were bonded. As the adhesive, low melting glass mainly composed of silicon oxide was used. The bonding temperature was about 500 ° C. The thickness of the adhesive layer 3 was about 0.5 μm.
[0109]
Next, the material 9 was ground by a mechanical grinding device, and the thickness of the material 9A was 50 μm. Next, the ridge structure shown in FIGS. 1 and 3 was formed using a dicing apparatus. At this time, in FIG. 3, the thickness A of the extended portion 15 was 1 μm, the height (ridge height) B of the optical waveguide 4 was 1.5 μm, and the width C of the ridge structure was 4 μm. As the dicing blade, a resin bonded diamond grinding stone “SD6000” (outer diameter φ: about 52 mm, thickness: 0.1 mm) was used. The rotation speed of the blade was 30,000 rpm, and the feed rate of the blade was 1.0 mm / second. After the ridge structure was formed, the substrate was cut in the cross-sectional direction to form an element having a length of 10 mm. Both end surfaces of the optical waveguide 4 were subjected to chemical mechanical polishing.
[0110]
Using this element, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength was 850 nm, and the second harmonic wavelength was 425 nm. The SHG conversion efficiency was about 500% / W. When the incident power of the fundamental wave was 100 mW, a second harmonic output of 50 mW was obtained, and no characteristic deterioration due to light damage or the like was observed in the second harmonic. Table 1 shows the relationship between the fundamental wave output and the second harmonic output.
[0111]
[Table 1]

[0112]
(Comparative Example 1)
In the same manner as in Example 1, the lithium niobate material 9 (thickness 0.5 mm) doped with 5 mol% of MgO on the X-plane (87 ° Z cut) of the 3 ° off-cut substrate was subjected to a period of 3. A periodically poled structure 5 having a thickness of 2 μm and a domain inversion depth of 2 μm was formed.
[0113]
Next, a three-dimensional optical waveguide extending in a direction perpendicular to the polarization inversion pattern of the substrate was formed by a proton exchange method using pyrophosphoric acid. Specifically, the surface of the substrate was masked with a mask made of tantalum. At this time, an elongated linear opening having a width of 4 μm was formed in the mask. This substrate was immersed in pyrophosphoric acid heated to 200 ° C. for 10 minutes. The mask was removed from the substrate, and the substrate was annealed in the atmosphere at 350 ° for 4 hours to form a three-dimensional optical waveguide. The board | substrate was cut | disconnected and the element of length 10mm was created. Both ends of the optical waveguide were subjected to chemical mechanical polishing.
[0114]
Using this element, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength was 850 nm, and the second harmonic wavelength was 425 nm. The SHG conversion efficiency was about 500% / W. Until the second harmonic output reached about 15 mW, characteristic deterioration such as optical damage was not caused, and stable second harmonic oscillation was possible. However, when the output of the second harmonic exceeded about 15 mW, the output beam fluctuated due to optical damage. When this output reached 20 mW, stable oscillation of the second harmonic was impossible.
[0115]
(Example 2)
An optical waveguide device 1D shown in FIG. 6 was manufactured. Specifically, in the same manner as in Example 1, voltage was applied to the lithium niobate material 9 (thickness 0.5 mm) doped with 5 mol% of MgO on the X-plane (87 ° Z cut) of the three-off cut substrate. By the method, a periodically poled structure 5 having a period of 3.2 μm and a domain inversion depth of 2 μm was formed.
[0116]
Next, striped Nb having a width of 4 μm and a thickness of 300 nm is formed on the bonding surface of the material 9 in a direction perpendicular to the direction of the domain-inverted pattern.₂ O_Five A film (dielectric layer) was formed.
[0117]
Next, the bonding surface 9a of the material 9 and the surface 2a of the substrate 2 (x-cut lithium niobate substrate, thickness 1 mm) were adhered. As the adhesive, an epoxy-based room temperature curable resin was used. The thickness of the adhesive layer 3 was about 0.5 μm.
[0118]
Next, the material 9 was ground by a mechanical grinding device, and the thickness of the material 9A was 20 μm. Subsequently, the recessed part 11 shown in FIG. 6 was formed using the dicing apparatus. At this time, the thickness of the extended portion 15 was set to 3 μm. As the dicing blade, a resin bonded diamond grindstone “SD5000” (outer diameter: about 52 mm, thickness: 0.1 mm) was used. The rotation speed of the blade was 10,000 rpm, and the blade feed rate was 0.5 mm / second. The board | substrate was cut | disconnected in the cross-sectional direction, and the element of length 10mm was formed. Both ends of the optical waveguide were subjected to chemical mechanical polishing.
[0119]
Using this element, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength was 850 nm, and the second harmonic wavelength was 425 nm. The SHG conversion efficiency was about 500% / W. When the incident power of the fundamental wave was 100 mW, a second harmonic output of 50 mW was obtained, and no characteristic deterioration due to light damage or the like was observed in the second harmonic.
[0120]
(Example 3)
The element 1L shown in FIG. 14 was manufactured according to the procedure of FIGS.
[0121]
Specifically, in the same manner as in Example 1, the lithium niobate material 9 doped with 5 mol% of MgO on the X-plane (87 ° Z cut) of the 3 ° off-cut substrate was cycled by 2.8 μm by a voltage application method. Then, a periodically poled structure 5 having a domain inversion depth of 2.5 μm was formed.
[0122]
Next, two rows of grooves 23 having a depth of 1.5 μm and a width of 5 μm were formed on the surface of the material 9 by laser processing using an excimer laser. The distance between the pair of grooves 23 was 5 μm.
[0123]
Next, the grooved surface 9a of the material 9 was bonded to the surface 2a of the substrate 2 (X-cut lithium niobate substrate, thickness 1 mm). As the adhesive, an acrylic room temperature curable resin was used. The thickness of the bonding layer 3 was about 0.3 μm. The groove 23 is filled with an adhesive.
[0124]
Next, the material 9 was ground by a mechanical grinding device to obtain the structure of FIG. The thickness of the thick portion 8 was 3 μm. This substrate was cut in the cross-sectional direction to form an element having a length of 10 mm. Both ends of the optical waveguide were subjected to chemical mechanical polishing.
[0125]
Using this element, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength was 820 nm, and the second harmonic wavelength was 410 nm. When the input of the fundamental wave was 100 mW, a second harmonic of 60 mW was obtained, and no characteristic deterioration due to optical damage was observed.
[0126]
(Example 4)
A periodically poled structure having a period of 2.8 μm was formed on a Z-cut lithium niobate material 9 (thickness: 0.3 mm) doped with 5 mol% of MgO by a corona charging method. Specifically, a periodically poled structure having a pitch of 2.7 μm was formed on the + Z plane of the substrate, and a corona wire was scanned on the −Z plane of the substrate to generate the domain-inverted structure. The domain-inverted structure was uniformly formed throughout the thickness direction of the substrate.
[0127]
Next, a strip-shaped plate having a width of 0.5 mm was cut out from the material 9 in the Y direction, and the cut surface (X) of the plate was subjected to chemical mechanical polishing.
[0128]
Next, the X surface of the strip-shaped plate and the substrate (single crystal silicon, thickness 0.35 mm) were bonded. As the adhesive, an acrylic room temperature curable resin was used. The thickness of the adhesive layer 3 was about 0.3 μm. Next, the material 9 was ground by a mechanical grinding apparatus, and the thickness of the material 9A was 3.5 μm. Next, two rows of grooves 23 having a depth of 2 μm and a width of 5 μm were formed on the surface of the material 9A by laser processing using an excimer laser. The distance between the pair of grooves 23 was 4 μm.
[0129]
Next, the substrate was cut in the cross-sectional direction to form an element having a length of 10 mm. Both ends of the optical waveguide were subjected to chemical mechanical polishing.
[0130]
Using this element, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength was 820 nm, and the second harmonic wavelength was 410 nm. When the input of the fundamental wave was 150 mW, a second harmonic of 100 mW was obtained, and no characteristic deterioration due to optical damage was observed.
[0131]
【The invention's effect】
As is apparent from the above, according to the present invention, in the optical waveguide device, even when the output of the emitted light from the optical waveguide is increased, fluctuations in output can be reduced and stable oscillation can be realized.
[Brief description of the drawings]
FIG. 1A is a cross-sectional view schematically showing an optical waveguide device 1A according to an embodiment of the present invention, in which a ridge-type three-dimensional optical waveguide 4 and a periodically poled structure 5 are formed. . FIG. 2B is a perspective view schematically showing the element of FIG.
2A and 2B are cross-sectional views schematically showing a process for producing the optical waveguide device of FIG.
3 is an enlarged view of a ridge structure portion of the element of FIG. 1;
4 is a cross-sectional view schematically showing an optical waveguide device 1B according to another embodiment of the present invention, in which a thick portion 8 is removed from the device of FIG.
5 is a cross-sectional view schematically showing an optical waveguide device 1C according to another embodiment of the present invention, in which a groove 2c is formed in a substrate 2. FIG.
6 is a cross-sectional view schematically showing an optical waveguide device 1D according to another embodiment of the present invention, in which a groove 2c is formed in a substrate 2, and a thick portion 8 is removed from the device of FIG. ing.
FIG. 7 is a cross-sectional view schematically showing an optical waveguide device 1E according to another embodiment of the present invention, in which a dielectric-loaded optical waveguide 10 is formed.
8A and 8B are cross-sectional views schematically showing a process for producing the optical waveguide device of FIG.
9 is a cross-sectional view schematically showing an optical waveguide device 1F according to another embodiment of the present invention, in which a thick portion is removed from the optical waveguide device of FIG.
10 is a cross-sectional view schematically showing an optical waveguide device 1G according to another embodiment of the present invention, in which a dielectric 12 is loaded on the optical waveguide 10. FIG.
11 is a cross-sectional view schematically showing an optical waveguide device 1H according to another embodiment of the present invention, in which a thick portion 8 is removed from the device of FIG.
12 is a cross-sectional view schematically showing an element 1J according to an embodiment of the present invention, in which a groove 7 is formed even in the bonding layer 3 and an extending portion 15 is removed. FIG.
FIG. 13 is a cross-sectional view schematically showing an element 1K according to another embodiment of the present invention, in which an overcoat layer 21 is formed on the entire surface of the element and covers an optical waveguide.
FIG. 14 is a cross-sectional view schematically showing an element 1L according to another embodiment of the present invention, in which the element 1L has a pair of extending portions 26 and the extending portions 26 toward the bonding layer 3 side. And a protruding ridge-type optical waveguide 24.
15A, 15B, and 15C are cross-sectional views showing manufacturing steps of the element of FIG.
FIG. 16 shows a model for calculating fundamental mode (excitation light) and harmonic single-mode propagation conditions when a pair of extending portions are formed on both sides of a ridge-type optical waveguide in the element of the present invention.
FIG. 17 is a graph showing a single mode condition of a waveguide when the height t1 of the ridge portion 4 is 1.0 μm and the width w of the ridge portion 4 and the thickness t2 of the extending portion 15 are changed. .
FIG. 18 is a graph showing a single mode condition of a waveguide when the height t1 of the ridge portion 4 is 2.0 μm and the width w of the ridge portion 4 and the thickness t2 of the extending portion 15 are changed. .
FIG. 19 is a graph showing the relationship between the refractive index difference between the optical waveguide and the bonding layer and the electric field distribution.
FIG. 20 is a graph showing the relationship between the refractive index difference dn between the optical waveguide and the bonding layer and the maximum thickness that satisfies the single mode condition when MgO-doped LiNbO 3 is used as the optical waveguide.
FIG. 21 is a schematic diagram showing a relationship among refractive indexes of respective layers when a three-layer structure of a waveguide, a bonding layer (the refractive index of the bonding layer <the refractive index of the substrate), and the substrate is adopted.
FIG. 22 is a graph showing the relationship between guided light intensity and depth when a bonding layer is provided.
FIG. 23 is a graph showing the relationship between guided light intensity and depth when no bonding layer is provided.
FIG. 24 is a graph showing the relationship between the thickness of the bonding layer, the phase matching wavelength, and the effective refractive index.
FIG. 25 is a perspective view showing a state in which a voltage application method is applied to an offcut substrate.
FIG. 26 is a schematic diagram showing the direction of the polarization inversion pattern on the offcut substrate.
FIG. 27 is a cross-sectional view showing an element 1M according to an embodiment of the present invention, in which a three-dimensional optical waveguide 34 includes a pair of protrusions 34a and 34b.
28 is a cross-sectional view showing an element 1N according to an embodiment of the present invention, in which a recess 31 is formed on the surface 2a side of the substrate 2. FIG.
29 is a cross-sectional view showing an element 1P according to an embodiment of the present invention, in which a recess 31 is formed on the surface 2a side of the substrate 2, and a part of the optical waveguide 24A is inserted into the recess 31. FIG. Yes.
30 is a cross-sectional view showing an element 1Q according to an embodiment of the present invention, in which a recess 31 is formed on the surface 2a side of the substrate 2, and the three-dimensional optical waveguide 34 has a pair of protrusions 34a and 34b. The protrusion 34 b is inserted into the recess 31.
FIG. 31 is a cross-sectional view showing an element 1R according to an embodiment of the present invention, in which two types of bonding layers 3B and 3C are used.
[Explanation of symbols]
1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J, 1K, 1L, 1M, 1N, 1P, 1Q, 1R Optical waveguide element 2 Substrate 2a Substrate surface 2b Substrate protrusion 2c Substrate groove
3, 3A, 3B, 3C Junction layer 4, 24 Ridge type three-dimensional optical waveguide
DESCRIPTION OF SYMBOLS 5 Periodic polarization inversion structure 7 Groove 8 Thick part 9 Optical waveguide shaping | molding material 9a Joint surface of material 9 10 Dielectric loading type three-dimensional optical waveguide 11 Recessed part 12 Dielectric layer 15, 26 A pair of extension part 17 Ridge structure Grooves on both sides of the 18 ridge structure
21 Overcoat layer 22 Amorphous material filled in groove 23
23 A groove between the optical waveguide 24 and the thick portion 8 30 A base layer of the optical waveguide 4 34 A three-dimensional optical waveguide having a pair of protrusions

Claims (24)

A three-dimensional optical waveguide made of a bulk nonlinear optical crystal, a substrate bonded to the optical waveguide, and a bonding layer made of an amorphous material bonding the optical waveguide and the substrate. The optical waveguide device is characterized in that the refractive index of the bonding layer is 5% or more lower than the refractive index of the optical waveguide. The optical waveguide device according to claim 1, wherein the bonding layer functions as an underclad of the optical waveguide. The optical waveguide device according to claim 1, wherein the substrate functions as an underclad of the optical waveguide. The periodic polarization inversion structure is formed at least in the optical waveguide, and the optical waveguide element functions as a harmonic generation element. Optical waveguide element. The optical waveguide device according to any one of claims 1 to 4, wherein a cross-sectional shape of the optical waveguide is substantially rectangular. The optical waveguide device according to claim 1, wherein the optical waveguide is formed by machining the nonlinear optical crystal. The optical waveguide element according to any one of claims 1 to 6, wherein the optical waveguide is a ridge-type optical waveguide protruding from the bonding layer. The optical waveguide device according to any one of claims 1 to 7, further comprising a pair of extending portions extending toward both sides of the optical waveguide in a cross-sectional direction. 9. The optical waveguide element according to claim 8, wherein the optical waveguide protrudes from the extending portion toward the bonding layer. A thick portion made of a bulk nonlinear optical crystal is provided on the outside of each extending portion, and a recess is formed between the thick portion and the optical waveguide, and the non-existing portion is formed in the recess. The optical waveguide device according to claim 9, wherein the optical waveguide device is filled with a crystalline material. The optical waveguide according to claim 1, wherein the optical waveguide is a dielectric-loaded optical waveguide, and includes a dielectric layer for forming the optical waveguide. Optical waveguide element. 12. The optical waveguide element according to claim 11, wherein the dielectric layer faces the substrate with the bonding layer interposed therebetween. The optical waveguide device according to any one of claims 8 to 12, wherein single-mode propagation is performed with respect to both a wavelength of a fundamental wave and a wavelength of a wavelength converted wave of the harmonic generation device. . The width of the optical waveguide is 1-10 μm, the height from the extended portion of the optical waveguide is 0.2-5 μm, and the thickness of the extended portion is 0.5-5 μm. The optical waveguide device according to claim 13, wherein the optical waveguide device is characterized. The refractive index of the substrate is slightly lower than the refractive index of the optical waveguide, and an electric field distribution of an optical waveguide mode propagating through the optical waveguide exists in the substrate. An optical waveguide device according to one claim. Wherein the difference between the refractive index and the refractive index of the waveguide of the substrate is 5% or less, according to claim 1 5 optical waveguide device according. The optical waveguide element according to any one of claims 1 to 16 , wherein the bonding layer is made of glass containing silicon oxide as a main component. The optical waveguide, characterized by comprising the non-linear optical material composed mainly of LiNbx Ta (1-x) O3 (0 ≦ x ≦ 1), in any one of claims 1-1 7 The optical waveguide device described. 19. The optical waveguide device according to claim 18 , wherein the bonding layer is made of glass containing silicon oxide as a main component, and the thickness of the bonding layer is 0.1 [mu] m or more. The optical waveguide device according to any one of claims 1 to 19 , further comprising an overcoat layer covering at least the optical waveguide. An optical waveguide molding material made of a bulk nonlinear optical crystal is joined to a separate substrate through a joining layer made of an amorphous material. At this time, the joining is made more than the refractive index of the nonlinear optical crystal. A method of manufacturing an optical waveguide element, wherein the three-dimensional optical waveguide is formed by lowering the refractive index of the layer and then processing the optical waveguide molding material. An optical waveguide molding material made of bulk nonlinear optical crystal is joined to a separate substrate through a joining layer made of an amorphous material, and the substrate has a refractive index higher than that of the nonlinear optical crystal. A method for producing an optical waveguide element, wherein the three-dimensional optical waveguide is formed by lowering the refractive index of the optical waveguide and then processing the optical waveguide molding material. The previously formed periodically poled on the bonding surface side to the substrate of the optical waveguide forming material, characterized by joining the optical waveguide forming material after this to the substrate, according to claim 21 or 22 The manufacturing method of the optical waveguide element of description. The optical waveguide element manufacturing method according to any one of claims 21 to 23 , wherein the optical waveguide molding material is machined after the optical waveguide molding material is bonded to the substrate. Method.

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