WO2009084545A1 - 光変調器 - Google Patents
光変調器 Download PDFInfo
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- WO2009084545A1 WO2009084545A1 PCT/JP2008/073467 JP2008073467W WO2009084545A1 WO 2009084545 A1 WO2009084545 A1 WO 2009084545A1 JP 2008073467 W JP2008073467 W JP 2008073467W WO 2009084545 A1 WO2009084545 A1 WO 2009084545A1
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- waveguide
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- polarization plane
- optical modulator
- polarization
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- 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
- G02F1/21—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 by interference
- G02F1/225—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 by interference in an optical waveguide structure
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- the present invention relates to an optical modulator, and more particularly to an optical modulator using orthogonal polarization combining.
- wavelength multiplexing transmission in which a plurality of signal lights having different wavelengths are multiplexed and transmitted on one optical fiber has been the mainstream in order to realize long-distance and large-capacity transmission.
- the transmission capacity can be easily expanded with respect to the existing transmission line.
- the wavelength intervals of the signal lights must be made dense.
- interference called coherent crosstalk occurs between the leaked light from the adjacent wavelength signal and the signal light itself, thereby causing signal degradation.
- Patent Document 1 proposes a so-called orthogonal polarization multiplexing method in which the polarization states of adjacent signal lights are orthogonal to each other during wavelength multiplexing.
- an odd-numbered channel multiplexer that synthesizes odd-numbered signal lights of a plurality of signal lights having different wavelengths to generate multiplexed light A that is randomly polarized light, and a multiplexed light B that is random-polarized light by combining even-numbered signal lights.
- a polarization beam combiner combines vertical polarization multiplexed light and horizontal polarization multiplexed light to generate orthogonal polarization multiplexed light.
- the components used are polarization beam splitters (PBS), interleavers, arrayed waveguide diffraction gratings (AWG), variable voltage attenuators (VOA), and variable optical attenuators (VOAs). Expensive parts are required, and the manufacturing cost of the apparatus is extremely high.
- PBS polarization beam splitters
- AVG arrayed waveguide diffraction gratings
- VOA variable voltage attenuators
- VOAs variable optical attenuators
- the problem to be solved by the present invention is to solve the above-mentioned problems, and can be configured as a single optical element, has a small number of parts, is highly reliable, and has a relatively low manufacturing cost. It is to provide an optical modulator utilizing the above.
- the invention according to claim 1 is directed to a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and an optical waveguide formed on the substrate and propagating through the optical waveguide.
- the optical waveguide includes an input waveguide that guides the optical wave input to the optical modulator, a branching waveguide that branches from the input waveguide, and the optical waveguide An output waveguide for coupling a branching waveguide and guiding a light wave to the outside of the optical modulator, provided at a part of the branching waveguide, at least a part of the modulation electrode being disposed, A modulation means for modulating the light wave propagating through the branching waveguide and a polarization unit for controlling the polarization plane of the light wave that is arranged in a part of the optical waveguide until the branching waveguide is coupled.
- a wavefront selecting means and the polarization plane selecting means And a polarization plane adjusting means for adjusting the polarization plane so that the polarization planes of the light waves propagating through the branching waveguides are orthogonal to each other before being coupled to the branching waveguide. It is characterized by that.
- the arrangement location of the polarization plane selection means may be either before or after the modulation means.
- the optical modulator according to the first aspect, wherein the polarization plane selecting means is an optical waveguide between the input end face of the optical waveguide or the branch waveguide coupled from the input end face. It is arrange
- the polarization plane selection unit and the polarization plane adjustment unit are disposed close to the traveling direction of the light wave.
- the polarization plane selection unit and the polarization plane adjustment unit are continuously arranged.
- the polarization plane adjusting means is located at a position close to a portion where the branching waveguide is coupled to the traveling direction of the light wave. It is characterized by being arranged. More preferably, the polarization plane selection unit and the polarization plane adjustment unit are arranged between the modulation unit and the part where the branch waveguide is coupled, and the polarization plane adjustment unit is coupled to the branch waveguide as described above. Place it near the position.
- the invention according to claim 5 is the optical modulator according to any one of claims 1 to 4, wherein the optical waveguide has a polarization maintaining function.
- the invention according to claim 6 is the optical modulator according to any one of claims 1 to 5, wherein the polarization plane selecting means is a metal loaded polarizer formed on the optical waveguide, or of the optical waveguide. It is a thin plate polarizer disposed in the input end face or in the optical waveguide.
- the invention according to claim 7 is the optical modulator according to any one of claims 1 to 6, wherein the polarization plane adjusting means is a wave plate arranged in at least one branching waveguide. To do.
- the wave plate is a wave plate set so as to be approximately ⁇ / 2 with respect to the wavelength ⁇ of the light wave propagating through the optical waveguide. It is characterized by being.
- the invention according to claim 9 is the optical modulator according to any one of claims 1 to 7, wherein the polarization plane adjusting means rotates the polarization plane of the light wave propagating through the optical waveguide by 45 °.
- the polarization plane adjusting means is arranged in each branch waveguide so that the polarization plane rotates in different directions.
- a loss imparting unit having a loss substantially equal to the wave plate is installed in the branch waveguide where the wave plate is not disposed. It is characterized by that.
- the loss imparting means includes quartz, glass, an adhesive, a polymer, a metal thin film, or a composite thereof arranged across the optical waveguide. It is a material.
- the thin plate polarizer, the wave plate, or the loss providing means is disposed in the optical waveguide.
- the surfaces of these various members that cross the optical waveguide are arranged so as to be inclined with respect to the plane perpendicular to the traveling direction of the light wave in the optical waveguide.
- a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation for modulating a light wave formed on the substrate and propagating through the optical waveguide
- the optical waveguide is coupled to the input waveguide for guiding the light wave input to the optical modulator, the branch waveguide branched from the input waveguide, and the branch waveguide.
- the branch waveguide is coupled from the wavefront selection means.
- a polarization plane adjustment means for adjusting the polarization plane so that the polarization planes of the light waves propagating through the branched waveguides are orthogonal to each other.
- the polarization plane selecting means is disposed on the input end face of the optical waveguide or a part of the optical waveguide from the input end face to the time when the branching waveguide is coupled. It becomes possible to easily incorporate the polarization plane selection means for controlling the polarization plane of the light wave modulated in step 1 into a single optical element.
- the polarization plane controlled by the polarization plane selection means is the polarization plane adjustment. It is possible to suppress the polarization state from changing before reaching the means, and to control and adjust the polarization plane more appropriately.
- the polarization plane selection means and the polarization plane adjustment means in succession, it becomes possible to eliminate changes in the polarization state between the two.
- the polarization plane adjusting means is disposed at a position close to the portion where the branching waveguide is coupled to the traveling direction of the light wave, the polarization plane adjusted by the polarization plane adjusting means is branched. It is possible to suppress the polarization state from changing before reaching the coupling portion of the waveguide, and it is possible to perform orthogonal polarization synthesis in an appropriate state.
- the polarization plane selection means and the polarization plane adjustment means are arranged between the modulation means and the portion where the branch waveguide is coupled, and the polarization plane adjustment means is close to the portion where the branch waveguide is coupled as described above.
- the optical waveguide since the optical waveguide has a polarization maintaining function, control or adjustment was performed when the light wave propagated through the optical waveguide after controlling or adjusting the polarization plane of the light wave. It becomes possible to maintain the state of the polarization plane. Accordingly, it is possible to reliably perform orthogonal polarization combining, and furthermore, it is possible to output a light wave that maintains the state of orthogonal polarization combining from the optical modulator.
- the polarization plane selecting means is a metal loaded polarizer formed on the optical waveguide, or a thin plate polarizer disposed in the input end surface of the optical waveguide or in the optical waveguide, Polarization plane selection means for controlling the polarization plane of the light wave can be easily incorporated into a single optical element.
- a cutting process such as forming a groove in the substrate and an etching process are not required, and the manufacturing process is not complicated and is produced. It is possible to suppress a decrease in property and an increase in cost.
- the polarization plane adjusting means is a wave plate disposed in at least one branching waveguide, the polarization planes of the light waves propagating through the branching waveguides are orthogonal to each other. It becomes possible to easily incorporate a polarization plane adjusting means for adjusting the polarization plane into a single optical element.
- the wave plate is a wave plate set so as to be approximately ⁇ / 2 with respect to the wavelength ⁇ of the light wave propagating through the optical waveguide, so that the polarization plane of the light wave is rotated by 90 °.
- the polarization plane adjusting means rotates the polarization plane of the light wave propagating through the optical waveguide by 45 °, and the polarization plane adjusting means rotates the polarization plane in different directions. Since each branch waveguide is arranged, not only the state of the light wave propagating through each branch waveguide is adjusted to an orthogonal state, but also the light wave loss (deterioration of light intensity) due to the wave plate in each branch waveguide is aligned. be able to. In addition, since the rotation angle is small compared to the case of 90 ° rotation, the thickness of the polarization plane adjusting means in the optical axis direction (light wave propagation direction) can be reduced.
- the width of the groove formed in the substrate when installing the polarization plane adjusting means can be narrowed, and the mechanical force applied to the substrate is reduced.
- the load can be reduced.
- the loss imparting means is quartz, glass, an adhesive, a polymer, a metal thin film, or a composite material thereof disposed across the optical waveguide, the loss imparting means is a single optical. It can be easily incorporated into the element.
- the surfaces of these various members that cross the optical waveguide are in the optical waveguide. Since the light wave is disposed in a state tilted from a surface perpendicular to the traveling direction of the light wave, even when the light wave is reflected by the surface, the return light propagating in the reverse direction is suppressed. This prevents inter-signal interference and signal level degradation due to return light, stabilizes the operation of the optical modulator, and makes the return light incident on a light source such as a semiconductor laser, thereby destabilizing the operation of the light source. Can also be suppressed.
- FIG. 6 is a schematic diagram showing a fifth embodiment of the optical modulator of the present invention. It is the schematic which shows the 6th Example of the optical modulator of this invention. It is a figure which shows the example of a loss provision means (plate-shaped member). It is a figure which shows the example of a loss provision means (filler). It is a figure which shows the example of a loss provision means (film body).
- FIG. 1 is a diagram showing a first embodiment of an optical modulator according to the present invention.
- the optical modulator of the present invention modulates a light wave that is formed on a substrate 1 made of a material having an electrooptic effect, an optical waveguide 2 formed on the substrate, and propagates through the optical waveguide.
- the optical waveguide 2 includes an input waveguide 21 for guiding a light wave input to the optical modulator, and branch waveguides 23 and 24 branched from the input waveguide.
- an output waveguide 30 that couples the branch waveguide and guides a light wave to the outside of the optical modulator, provided at a part of the branch waveguide, A part of the optical waveguide is disposed at a part of the optical waveguide until the branching waveguide is coupled to the modulation means 25 and 26 for modulating the light wave propagating through the branching waveguide.
- Polarization plane selection to control the polarization plane of the modulated light wave It is arranged in a part of the optical waveguide between stage 4 and the polarization plane selecting means until the branch waveguide is coupled, and the polarization planes of the light waves propagating through the branch waveguides are polarized so that they are orthogonal to each other. It has polarization plane adjusting means 5 for adjusting the wavefront.
- An input optical fiber 7 is connected to the input side of the optical modulator, and an output optical fiber 8 is connected to the output side. Arrows A and B indicate the propagation direction of the light wave.
- lithium niobate lithium tantalate
- PLZT lead lanthanum zirconate titanate
- quartz-based materials quartz-based materials, and combinations thereof
- lithium niobate (LN) or lithium tantalate (LT) crystals having a high electro-optic effect are preferably used.
- the optical waveguide As a method for forming the optical waveguide, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. Further, as in Patent Document 2, it is also possible to form an optical waveguide by forming a ridge on the surface of the substrate 1 in accordance with the shape of the optical waveguide.
- the optical waveguide preferably has a polarization maintaining function. As described later, after controlling or adjusting the polarization plane of the light wave, it becomes possible to maintain the state of the polarization plane that has been controlled or adjusted when the light wave propagates through the optical waveguide. This is because orthogonal polarization combining can be performed, and furthermore, an optical wave maintaining the state of orthogonal polarization combining can be output from the optical modulator. JP-A-6-289341
- the modulation electrode constituting the modulation means can be formed on the front surface or the back surface of the substrate by forming a Ti / Au electrode pattern, a gold plating method, or the like.
- the modulation electrode includes a signal electrode that propagates a modulation signal and a ground electrode that is disposed around the signal electrode.
- FIG. 1 only the signal electrodes 61 and 62 are shown as an example.
- the shape and arrangement of the signal electrode and the ground electrode can be appropriately set according to what kind of modulation is performed by the modulation means 25 and 26 and the type of substrate to be used (X-cut plate or Z-cut plate).
- a buffer layer can be formed between the substrate 1 and the modulation electrode formed on the substrate. Accordingly, it is possible to effectively prevent the light wave propagating through the optical waveguide from being absorbed or scattered by the modulation electrode. In addition, it is possible to improve velocity matching between the modulation signal applied from the modulation electrode and the light wave guided in the optical waveguide.
- an important structure as the optical modulator of the present invention is an input waveguide 21 that guides the light wave input to the optical modulator, and branches from the input waveguide.
- Modulation means 25 and 26 for modulating the light wave propagating through the waveguide are formed.
- a modulation means a method using Mach-Zehnder type optical waveguides 25 and 26 as shown in FIG. 1, or a nested type optical waveguide 31 used in an SSB modulator or the like as shown in the second embodiment of FIG. , 32 can be used.
- the optical modulator of the present invention controls the polarization plane of each modulated light wave and synthesizes each light wave with orthogonal polarization
- the polarization plane selection means 4 for controlling the polarization plane of the light wave and the polarization plane of each light wave are
- a metal loaded polarizer formed on the optical waveguide, or an input end face of the optical waveguide or a thin plate polarizer disposed in the optical waveguide can be used.
- a metal-loaded polarizer is a metal film such as aluminum disposed on an optical waveguide, absorbs a polarization plane perpendicular to the metal film (TE mode light), and a polarization plane parallel to the metal film (TM mode). Light). It is also possible to form a ridge along the optical waveguide and load a metal film on the side surface of the ridge. In this case, the TM mode light is absorbed and the plane of polarization is controlled by the TE mode light.
- any one of the polarization plane selection means 41, 42, 43 may be provided at any position on the light wave input side of the modulation means 25, 26 as shown in the third embodiment of FIG. good.
- the transverse plane is from a plane perpendicular to the propagation direction of the light wave. Place it in a tilted state. This is to avoid the generation of so-called return light in which light waves are reflected by the polarization plane selection means and light propagates in the opposite direction.
- the return light causes interference between signals and a decrease in signal level, and is incident on a light source such as a semiconductor laser to cause various problems such as destabilizing the operation of the light source. It is desirable to take similar measures for the polarization plane adjusting means and the loss providing means described later.
- FIG. 4 is a diagram showing a fourth embodiment of the optical modulator of the present invention.
- the polarization plane selection means is not specified, but the polarization plane selection means can be appropriately arranged in the substrate 1 as shown in FIGS. 1 to 3.
- a polarization plane selection means is separately arranged inside the element of the optical modulator. do not have to.
- the present invention includes such a device in which the polarization plane selecting means is arranged outside the element.
- the polarization plane adjusting means 5 and 52 rotates the polarization plane of at least one light wave propagating through each branch waveguide so that the polarization planes of the light waves propagating through the respective branch waveguides are orthogonal to each other. The angle is adjusted.
- a wave plate can be used.
- a wave plate that is approximately ⁇ / 2 with respect to the wavelength ⁇ of the light wave propagating through the optical waveguide can be suitably used. It is.
- the wave plate a material having birefringence such as quartz, butyl, garnet and the like can be used.
- the polarization plane of the light wave propagating through the optical waveguide may be rotated by 45 °.
- two polarization plane adjusting means are prepared and arranged in each branch waveguide so that the polarization plane of the light wave propagating through each branch waveguide rotates 45 degrees in different directions.
- the thickness of the polarization plane adjusting means in the optical axis direction can be reduced. For this reason, it is possible to reduce the loss of light waves and the variation in polarization rotation caused by the polarization plane adjusting means, and furthermore, the width of the groove formed in the substrate when the polarization plane adjusting means is installed can be narrowed, and the mechanical applied to the substrate The load can be reduced.
- a polarization plane adjusting means a material having birefringence such as quartz, butyl, garnet, and the like, in which the thickness in the traveling direction of the light wave is appropriately adjusted, can be used.
- the polarization plane adjusting means includes a method of forming a groove across the optical waveguide in one of the branched waveguides, and inserting and arranging a wave plate therein, and the distance between the branched waveguides is several hundred ⁇ m. Since they are very close to each other, it is possible to form a groove 51 extending over a plurality of branching waveguides as shown in FIG. 4 and arrange a wave plate 52 in the groove.
- the polarization plane adjusting means may be arranged in at least one branching waveguide.
- the polarization plane selection means is arranged in the branching waveguide, it is preferable to arrange the polarization plane selection means after the polarization plane selection means and before the multiplexing unit 29.
- the polarization plane selection means and the polarization plane adjustment means are preferably arranged as close as possible to the traveling direction of the light wave. This is to prevent the polarization state controlled by the polarization plane selection unit from changing before the polarization plane adjustment unit reaches the polarization plane adjustment unit.
- the polarization plane selection unit and the polarization plane adjustment unit are continuously arranged.
- the polarization plane adjusting means is disposed at a position close to a portion where the branching waveguide is coupled to the traveling direction of the light wave. This is to prevent the polarization state from being changed before the polarization plane adjusted by the polarization plane adjusting means reaches the coupling portion of the branching waveguide.
- a polarization plane selection unit and a polarization plane adjustment unit are arranged between the modulation unit and the part where the branching waveguide is coupled, and the polarization plane adjustment unit is close to the part where the branching waveguide is coupled as described above.
- the branched waveguide in which the polarization plane adjusting means is not disposed is substantially equal to the polarization plane adjusting means (wave plate).
- Loss imparting means 53 and 54 for generating loss and / or substantially equal phase differences are provided.
- a polarization plane adjusting unit that rotates 45 ° in the other direction may be arranged.
- 6 may be a polarization plane adjusting unit that rotates 45 ° in one direction, and a polarization plane adjusting unit that rotates 45 ° in the other direction may be disposed instead of the loss applying unit 54.
- quartz, glass, an adhesive, a polymer, a metal thin film, or a composite material thereof arranged across the optical waveguide can be used.
- 7 to 9 show examples of the arrangement state of the loss imparting means.
- a groove 90 is formed in the substrate 1 so as to cross the optical waveguide 2, and a plate shape such as quartz or glass is formed in the groove.
- the member 91 is arranged.
- the groove 90 is filled with a filler 92 such as an adhesive or a polymer.
- FIG. 9 shows a case where a film body 93 such as a polymer or a metal thin film is formed on one side surface of the groove 90.
- the groove formed in the substrate for disposing the loss imparting means is not limited to the method of forming only in the branched waveguide to be formed as shown in FIG. 5, but as shown in FIG. It is also possible to share the groove 51 for the purpose.
- the optical modulator of the present invention is not limited to the above-described one.
- the polarization plane selection unit and the polarization plane adjustment unit are used together, for example, a thin plate polarizer and a wave plate are overlapped in a groove crossing the optical waveguide. It is also possible to arrange them. It is also possible to arrange a polarizer for selecting TM mode light in one of the branch waveguides and a polarizer for selecting TE mode light in the other branch waveguide.
- a plurality of metal-loaded polarizers, thin plate polarizers, etc. are arranged in the branching waveguide as necessary to maintain the polarization plane properly. It is also possible.
- the light wave incident from the input optical fiber 7 propagates through the input waveguide 21, is divided into two by the branching portion 22, and propagates through the branching waveguides 23 and 24.
- the number of branches is not limited to two and can be changed according to the number of necessary modulation channels.
- the branched light waves are modulated by the modulation means 25 and 26, and propagated through the branched waveguides 27 and 28 in the subsequent stages as modulated light.
- the plane of polarization is made uniform by the polarization plane selection means 4, and then the polarization plane of one modulated light is rotated by 90 ° by the polarization plane adjustment means 5.
- the modulated lights having the polarization planes orthogonal to each other in this way are combined by the multiplexing unit 29 and propagated through the output waveguide 30 to the output optical fiber 8 connected to the optical modulator. In this way, it is possible to easily achieve orthogonal polarization combining with a single optical modulator.
- an optical modulator using orthogonal polarization combining that can be configured as a single optical element, has a small number of components, is highly reliable, and is relatively inexpensive to manufacture. Become.
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Abstract
Description
一例として、波長が異なる複数の信号光の奇数信号光を合成してランダム偏光である多重光Aを生成する奇数チャンネル合波器と、偶数信号光を合成してランダム偏光である多重光Bを生成する偶数チャンネル合波器とを設け、各チャンネル合波器から出力される多重光A及びBを、多チャンネル偏波制御器により垂直方向及び水平方向の直線偏光多重光に変換し、さらに、偏波合成器で垂直偏波多重光と水平偏波多重光とを合成し、直交偏波多重光を生成している。
偏波面選択手段の配置場所は、本発明からも明らかなように、変調手段の前の段階でも後の段階でも、いずれであっても良い。
2 光導波路
4,41,42,43 偏波面選択手段
5,52 偏波面調整手段
7 入力用光ファイバー
8 出力用光ファイバー
21 入力導波路
22 分岐部
23,24,27,28 分岐導波路
25,26,31,32 変調手段
29 合波部
30 出力導波路
51,90 溝
53,91,92,93 損失付与手段
図1は、本発明の光変調器の第1の実施例を示す図である。
本発明の光変調器は、電気光学効果を有する材料で構成された基板1と、該基板に形成された光導波路2と、該基板に形成され、該光導波路を伝搬する光波を変調するための変調電極61,62とを有する光変調器において、該光導波路2は、該光変調器に入力された光波を導く入力導波路21と、該入力導波路から分岐する分岐導波路23,24,27,28と、該分岐導波路を結合すると共に該光変調器の外部に光波を導く出力導波路30とを少なくとも有し、該分岐導波路の一部に設けられ、該変調電極の少なくとも一部が配置されると共に、該分岐導波路を伝搬する光波を変調するための変調手段25,26と、該分岐導波路を結合するまでの光導波路の一部に配置され、該変調手段で変調される光波の偏波面を制御する偏波面選択手段4と、該偏波面選択手段から該分岐導波路を結合するまでの間の光導波路の一部に配置され、各分岐導波路を伝搬する光波の偏波面が直交する関係となるように偏波面を調整する偏波面調整手段5とを有することを特徴とする。光変調器の入力側には入力用光ファイバー7が、出力側には出力用光ファイバー8が、各々接続されている。なお、矢印A,Bは光波の伝搬方向を示す。
本発明の光変調器においては、光導波路は偏光保持機能を有しているのが好ましい。これは、後述するように光波の偏波面を制御あるいは調整した後で、光波が光導波路を伝搬する際に、制御や調整が行われた偏波面の状態を維持することが可能となり、確実に直交偏波合成を行うことができ、さらには、直交偏波合成した状態を維持した光波を光変調器から出力することができるためである。
変調手段としては、図1に示すようにマッハツェンダー型光導波路25,26を用いる方法や、図2の第2の実施例に示すように、SSB変調器などで利用されるネスト型光導波路31,32を用いる方法など、種々の変調方式が採用可能である。当然、分岐導波路毎に異なる変調方式を採用することも可能である。
金属装荷型偏光子とは、光導波路の上にアルミニウムなどの金属膜を配置し、該金属膜に垂直な偏波面(TEモード光)を吸収し、該金属膜に平行な偏波面(TMモード光)に制御するものである。また、光導波路に沿ってリッジを形成し、該リッジの側面に金属膜を装荷させることも可能である。この場合は、TMモード光が吸収されTEモード光に偏波面が制御されることとなる。
図4では、偏波面選択手段が明記されていないが、図1乃至3のように偏波面選択手段を基板1内に適宜配置することが可能である。また、光変調器に入力される光波Aを、予め偏波面をTEモード光又はTMモード光のいずれかに制御している場合には、光変調器の素子内部に偏波面選択手段を別途配置する必要はない。本発明は、このように偏波面選択手段を素子外に配置するものも含むものである。
偏波面調整手段は、各分岐導波路を伝搬する光波の偏波面が直交する関係となるように、各分岐導波路を伝搬する少なくとも一つの光波の偏波面を回転させ、各光波の偏波面の角度を調整するものである。
具体的には、波長板が利用可能であり、特に、光波の偏波面を90°回転させるため、光導波路を伝搬する光波の波長λに対し略λ/2となる波長板が好適に利用可能である。
波長板としては、水晶、ブチル、ガーネットなどの複屈折を有する材料が利用可能である。
このような偏波面調整手段としては、水晶、ブチル、ガーネットなどの複屈折を有する材料を利用し、光波の進行方向の厚みを適宜調整したものが利用可能である。
図7乃至9は、損失付与手段の配置状態の例を示すものであり、図7では、基板1に光導波路2を横切るように溝90を形成し、該溝内に石英やガラスなど板状部材91を配置するものである。図8は、該溝90に接着剤やポリマーなどの充填材92に充填するものである。また、図9は、溝90の一側面にポリマー又は金属薄膜などの膜体93を形成するものである。
入力用光ファイバー7から入射した光波は、入力導波路21を伝搬し、分岐部22で2つに分けられ、分岐導波路23,24を伝搬する。分岐する数は2つに限らず、必要な変調チャンネル数に応じて変更可能である。
Claims (12)
- 電気光学効果を有する材料で構成された基板と、
該基板に形成された光導波路と、
該基板に形成され、該光導波路を伝搬する光波を変調するための変調電極とを有する光変調器において、
該光導波路は、該光変調器に入力された光波を導く入力導波路と、該入力導波路から分岐する分岐導波路と、該分岐導波路を結合すると共に該光変調器の外部に光波を導く出力導波路とを少なくとも有し、
該分岐導波路の一部に設けられ、該変調電極の少なくとも一部が配置されると共に、該分岐導波路を伝搬する光波を変調するための変調手段と、
該分岐導波路を結合するまでの光導波路の一部に配置され、該変調手段で変調される光波の偏波面を制御する偏波面選択手段と、
該偏波面選択手段から該分岐導波路を結合するまでの間の光導波路の一部に配置され、各分岐導波路を伝搬する光波の偏波面が直交する関係となるように偏波面を調整する偏波面調整手段とを有することを特徴とする光変調器。 - 請求項1に記載の光変調器において、該偏波面選択手段が、該光導波路の入力端面、または該入力端面から該分岐導波路を結合するまで間の光導波路の一部に配置されていることを特徴とする光変調器。
- 請求項1又は2に記載の光変調器において、該偏波面選択手段と該偏波面調整手段とは光波の進行方向に対して近接して配置されていることを特徴とする光変調器。
- 請求項1乃至3のいずれかに記載の光変調器において、該偏波面調整手段は、光波の進行方向に対して該分岐導波路を結合する部分に近い位置に配置されることを特徴とする光変調器。
- 請求項1乃至4のいずれかに記載の光変調器において、該光導波路は偏光保持機能を有していることを特徴とする光変調器。
- 請求項1乃至5のいずれかに記載の光変調器において、該偏波面選択手段は、該光導波路上に形成された金属装荷型偏光子、あるいは該光導波路の入力端面または該光導波路中に配置された薄板偏光子であることを特徴とする光変調器。
- 請求項1乃至6のいずれかに記載の光変調器において、該偏波面調整手段は、少なくとも一つの分岐導波路中に配置された波長板であることを特徴とする光変調器。
- 請求項7に記載の光変調器において、該波長板は、該光導波路を伝搬する光波の波長λに対し略λ/2となるように設定された波長板であることを特徴とする光変調器。
- 請求項1乃至7のいずれかに記載の光変調器において、該偏波面調整手段は、該光導波路を伝搬する光波の偏波面を45°回転させるものであり、該偏波面調整手段を異なる方向に偏波面が回転するように各分岐導波路に配置したことを特徴とする光変調器。
- 請求項7又は8に記載の光変調器において、該波長板が配置されていない分岐導波路には、該波長板と略等しい損失を有する損失付与手段を設置することを特徴とする光変調器。
- 請求項10に記載の光変調器において、該損失付与手段は、該光導波路を横切って配置される石英、ガラス、接着剤、ポリマー、金属薄膜、若しくはこれらの複合材であることを特徴とする光変調器。
- 請求項6乃至11のいずれかに記載の光変調器において、該光導波路中に該薄板偏光子、該波長板、又は該損失付与手段のいずれかを配置する際には、これらの各種部材の光導波路を横切る面は、該光導波路中の光波の進行方向に対し垂直となる面から傾けた状態で配置されること特徴とする光変調器。
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JP5673283B2 (ja) * | 2011-03-28 | 2015-02-18 | 住友大阪セメント株式会社 | 偏波合成装置 |
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JP5660095B2 (ja) * | 2012-08-31 | 2015-01-28 | 住友大阪セメント株式会社 | 光変調器 |
CN104142585A (zh) * | 2013-05-09 | 2014-11-12 | 鸿富锦精密工业(深圳)有限公司 | 电光调制器 |
FR3023627B1 (fr) * | 2014-07-08 | 2016-07-29 | Ixblue | Dispositif optique polarisant a guide d'onde |
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