JP6226427B2 - Polarization rotation element - Google Patents
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- JP6226427B2 JP6226427B2 JP2014101099A JP2014101099A JP6226427B2 JP 6226427 B2 JP6226427 B2 JP 6226427B2 JP 2014101099 A JP2014101099 A JP 2014101099A JP 2014101099 A JP2014101099 A JP 2014101099A JP 6226427 B2 JP6226427 B2 JP 6226427B2
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- 238000005253 cladding Methods 0.000 claims description 20
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 16
- 229910052710 silicon Inorganic materials 0.000 description 16
- 239000010703 silicon Substances 0.000 description 16
- 238000004891 communication Methods 0.000 description 12
- 239000000463 material Substances 0.000 description 12
- 238000000034 method Methods 0.000 description 12
- 125000006850 spacer group Chemical group 0.000 description 7
- 239000000758 substrate Substances 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 229910052814 silicon oxide Inorganic materials 0.000 description 6
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- 229910052581 Si3N4 Inorganic materials 0.000 description 3
- 238000001312 dry etching Methods 0.000 description 3
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 3
- 238000009826 distribution Methods 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
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- 230000005540 biological transmission Effects 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
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Description
本発明は、光通信における偏波制御技術に関し、特に偏波回転技術に関するものである。 The present invention relates to a polarization control technique in optical communication, and more particularly to a polarization rotation technique.
光通信の大容量化に伴い、基幹網に加え加入者網でも光通信装置の小型高密度集積化が求められている。光通信装置を小型高密度集積化するためには、光集積回路を小型化する必要があり、強い光閉じ込めが可能なシリコン系材料を用いた光集積回路の開発が進んでいる。 Along with the increase in capacity of optical communication, there is a demand for small-scale and high-density integration of optical communication apparatuses in subscriber networks as well as backbone networks. In order to miniaturize and integrate an optical communication device, it is necessary to downsize the optical integrated circuit, and development of an optical integrated circuit using a silicon-based material capable of strong light confinement is progressing.
シリコン系材料を用いた光集積回路は、シリコンをコアとし、シリコン酸化物等をクラッドとすることで強い光閉じ込めにより、数マイクロメートルと言った急峻な曲げ導波路を実現することで形成される。このようなシリコン細線型光導波路の光学特性は、コアサイズやクラッド材料の屈折率に敏感であり、大きな構造複屈折を生む。結果として偏波依存性が大きくなる。 An optical integrated circuit using a silicon-based material is formed by realizing a steep bent waveguide of several micrometers by strong optical confinement using silicon as a core and silicon oxide as a cladding. . The optical characteristics of such a silicon fine wire type optical waveguide are sensitive to the core size and the refractive index of the cladding material, and produce a large structural birefringence. As a result, the polarization dependency is increased.
一般に長距離通信向け光通信装置は、環境温度等が比較的安定な局舎内だけでなく、海底、地中、屋外などにも設置されるため、環境変動を受けやすい。安定な光通信を実現するためには、光通信装置は、環境変動に対し頑強な構成をしていることが求められる。振動や温度変化は光の偏波状態を変動させるため、光通信装置の偏波依存性を低減することが必要である。更に、近年は偏波多重による大容量化が進んでおり、光通信装置の偏波依存性を低減することが急務となっている。 In general, an optical communication device for long-distance communication is not only installed in a station building where the environmental temperature and the like are relatively stable, but also installed on the sea floor, underground, outdoors, and the like, and thus is susceptible to environmental fluctuations. In order to realize stable optical communication, the optical communication device is required to have a configuration that is robust against environmental fluctuations. Since vibration and temperature change fluctuate the polarization state of light, it is necessary to reduce the polarization dependence of the optical communication device. Furthermore, in recent years, the capacity has been increased by polarization multiplexing, and there is an urgent need to reduce the polarization dependence of optical communication devices.
シリコン細線型光導波路の偏波依存性の低減に向け、偏波制御に関する基盤技術の研究開発が進んでいる。特許文献１はシリコン細線型光導波路の偏波回転を実現するものである。当該手法では第一コアの中心軸と第二コアの中心軸が一致しない偏芯二重コア構造を用いている。偏芯二重コア構造では、光学的な固有軸が基板に対し斜め４５度傾いた状態になるため、基板に対し水平あるいは垂直に傾いた偏波が入射され、所定の距離伝搬することで偏波面が９０度回転するものである。 Research and development of basic technology related to polarization control is advancing to reduce the polarization dependence of silicon wire optical waveguides. Patent Document 1 realizes polarization rotation of a silicon fine wire type optical waveguide. In this method, an eccentric double core structure in which the central axis of the first core and the central axis of the second core do not coincide is used. In the eccentric double core structure, since the optical natural axis is inclined 45 degrees with respect to the substrate, polarized light that is horizontally or vertically inclined with respect to the substrate is incident and propagated for a predetermined distance. The wavefront rotates 90 degrees.
偏芯二重コア構造による偏波回転素子は、偏波回転の機能は満たすものの、別の新たな課題を生ずる。図９（Ａ）〜図９（Ｉ）は特許文献１に開示された従来の偏芯二重コア構造による偏波回転素子の製造工程の例を示す工程断面図である。偏芯二重コアは、基板１１上に形成された下部クラッド１２の上部に形成される。シリコンからなる第一コア１３は、屈折率がシリコンより小さい材料からなる第二コア１６により包含される形で形成される。第二コア１６は、シリコン窒化物あるいはシリコン酸窒化物から構成されることが多いが、これらの材料に含まれるＮＨ基は、光通信で用いる光波長帯域１．５マイクロメートル付近の波長の光に対し吸収性を有する。一方で、これらの第二コア材料は、微細加工で用いられるドライエッチングプロセスにおいて、第一コア材料であるシリコンに近い選択比を持つ。 Although the polarization rotation element having the eccentric double core structure satisfies the function of polarization rotation, it causes another new problem. 9A to 9I are process cross-sectional views illustrating an example of a manufacturing process of a polarization rotation element having a conventional eccentric double core structure disclosed in Patent Document 1. FIG. The eccentric double core is formed on the lower clad 12 formed on the substrate 11. The first core 13 made of silicon is formed in a form encompassed by the second core 16 made of a material having a refractive index smaller than that of silicon. The second core 16 is often composed of silicon nitride or silicon oxynitride, but the NH group contained in these materials is light having a wavelength in the vicinity of an optical wavelength band of 1.5 micrometers used for optical communication. Absorptive. On the other hand, these second core materials have a selectivity close to that of silicon, which is the first core material, in a dry etching process used in microfabrication.
図９（Ａ）、図９（Ｄ）、図９（Ｇ）に示すように、光集積回路の下部クラッド１２の上には、偏波回転素子の第一コア１３と同じシリコンからなる光導波路１４が形成される。上記のとおり第二コア材料はドライエッチングプロセスにおいてシリコンに近い選択比を持つため、図９（Ａ）に示す光集積回路の上に第二コア材料１５を成膜した後に（図９（Ｂ））、光導波路１４の周辺から第二コア材料１５を選択的に除去して（図９（Ｃ））、偏波回転素子の第一コア１３の近傍部分のみに第二コア１６を形成することは困難である。 As shown in FIGS. 9A, 9D, and 9G, an optical waveguide made of the same silicon as the first core 13 of the polarization rotation element is formed on the lower cladding 12 of the optical integrated circuit. 14 is formed. As described above, since the second core material has a selectivity close to that of silicon in the dry etching process, the second core material 15 is formed on the optical integrated circuit shown in FIG. 9A (FIG. 9B). The second core material 15 is selectively removed from the periphery of the optical waveguide 14 (FIG. 9C), and the second core 16 is formed only in the vicinity of the first core 13 of the polarization rotation element. It is difficult.
また、第二コア材料は、化学気相堆積法により成膜されることが多い。このため、図９（Ｄ）に示す第一コア１３のみを覆うように第二コア材料１５を成膜し（図９（Ｅ））、この第二コア材料１５を加工して（図９（Ｆ））、第一コア１３の近傍部分のみに第二コア１６を形成することも困難である。 The second core material is often formed by chemical vapor deposition. For this reason, the second core material 15 is formed so as to cover only the first core 13 shown in FIG. 9D (FIG. 9E), and the second core material 15 is processed (FIG. 9D F)), it is also difficult to form the second core 16 only in the vicinity of the first core 13.
結果として、図９（Ｇ）に示す光集積回路の全域にわたり第二コア材料１５を成膜した後に（図９（Ｈ））、偏波回転素子の近傍の一部の第二コア材料１５のみを選択的に除去することになる（図９（Ｉ））。偏波回転素子の第一コア１３とは異なる光導波路１４の周辺は、第二コア材料１５で埋め尽くされる。これは、光導波路１４のクラッド材料が、偏波回転素子の第二コア１６と同じ組成になることを意味する。エバネッセント成分としてクラッド材料に浸み出す光の割合は、コア材料に閉じ込められる光の割合に比べて十分に少ないが、その影響が光集積回路全体にわたるため、従来の偏波回転素子を用いると、光集積回路における光吸収が大きくなり、光伝搬損失が大きくなるという問題点があった。 As a result, after forming the second core material 15 over the entire area of the optical integrated circuit shown in FIG. 9G (FIG. 9H), only a portion of the second core material 15 in the vicinity of the polarization rotation element is obtained. Are selectively removed (FIG. 9I). The periphery of the optical waveguide 14 different from the first core 13 of the polarization rotation element is filled with the second core material 15. This means that the clad material of the optical waveguide 14 has the same composition as the second core 16 of the polarization rotation element. The proportion of light that penetrates into the cladding material as an evanescent component is sufficiently small compared to the proportion of light that is confined in the core material, but because the effect extends to the entire optical integrated circuit, using a conventional polarization rotation element, There is a problem in that light absorption in the optical integrated circuit is increased and light propagation loss is increased.
本発明はこのような課題を解決するものであり、第二コア材料による光吸収を最小限に抑えながら、偏波回転を実現する偏波回転素子を提供することを目的としている。 The present invention solves such problems, and an object of the present invention is to provide a polarization rotation element that realizes polarization rotation while minimizing light absorption by the second core material.
本発明の偏波回転素子は、光伝搬方向と垂直な断面が矩形の第一コアと、光伝搬方向と垂直な断面が矩形の第二コアと、前記第一、第二コアを覆うように配置されたクラッドとから構成され、前記第一コアの屈折率が前記第二コアおよび前記クラッドの屈折率よりも大きく、前記第二コアの屈折率が前記クラッドの屈折率よりも大きく、前記第二コアは、前記第一コアから水平方向および垂直方向に離間して配置され、光の伝搬方向に沿って複数の前記第二コアを前記第一コアの両脇に交互に配置したことを特徴とするものである。
また、本発明の偏波回転素子の１構成例において、前記第二コアは、厚さ一定のまま光の伝搬方向に沿って漸次断面積が大きくなるテーパ状の入力端部と、厚さ一定のまま光の伝搬方向に沿って漸次断面積が小さくなるテーパ状の出力端部とを備えることを特徴とするものである。
The polarization rotation element of the present invention covers the first core having a rectangular cross section perpendicular to the light propagation direction, the second core having a rectangular cross section perpendicular to the light propagation direction, and the first and second cores. A refractive index of the first core is larger than that of the second core and the cladding, a refractive index of the second core is larger than a refractive index of the cladding, and The two cores are arranged separately from the first core in the horizontal direction and the vertical direction, and a plurality of the second cores are alternately arranged on both sides of the first core along the light propagation direction. It is what.
Further, in one configuration example of the polarization rotation element of the present invention, the second core has a tapered input end portion in which a cross-sectional area gradually increases along the light propagation direction with a constant thickness, and a constant thickness. And a tapered output end portion that gradually decreases in cross-sectional area along the light propagation direction .
本発明によれば、第一コアの光伝搬方向の中心軸と第二コアの光伝搬方向の中心軸が一致しない偏芯二重コア構造において、第二コアを第一コアから水平方向および垂直方向に離間して配置することにより、第二コアによる光吸収を最小限に抑えながら、偏波回転を実現することができ、従来の偏波回転素子と比較して光伝搬損失を小さくすることができる。 According to the present invention, in the eccentric double core structure in which the center axis of the light propagation direction of the first core and the center axis of the light propagation direction of the second core do not coincide with each other, the second core is moved horizontally and vertically from the first core. By arranging them apart in the direction, polarization rotation can be realized while minimizing light absorption by the second core, and light propagation loss can be reduced compared to conventional polarization rotation elements. Can do.
［第１の参考例］
以下、本発明の参考例について図面を参照して説明する。本参考例は、高屈折率材料からなる第一コアと、中程度の屈折率材料からなる第二コアと、低屈折率材料からなるクラッドとから構成され、第一コアと第二コアの光伝搬方向の中心軸が異なる偏芯二重コア光導波路を用いて、偏波回転を実現する。さらに、本参考例では、第二コアを、第一コアから水平方向および垂直方向に離間して配置する。
[ First Reference Example ]
Hereinafter, reference examples of the present invention will be described with reference to the drawings. This reference example is composed of a first core made of a high refractive index material, a second core made of a medium refractive index material, and a clad made of a low refractive index material. Polarization rotation is realized by using an eccentric double-core optical waveguide with a different central axis in the propagation direction. Furthermore, in the present reference example , the second core is disposed away from the first core in the horizontal direction and the vertical direction.
図１は本発明の第１の参考例に係る偏波回転素子の構造を示す断面図である。ここでは、偏波回転素子の光の導波軸に対する断面構造を示している。すなわち、図１の紙面に対して垂直な方向が光伝搬方向である。
シリコン基板１の上にはシリコン酸化膜からなる下部クラッド２が形成され、下部クラッド２の上には正方形断面を有する第一コア３が形成されている。この第一コア３を覆うように上部クラッド６が形成され、この上部クラッド６中に正方形断面を有する第二コア５が形成されている。第一コア３と第二コア５との間にある正方形断面の上部クラッド６は、上部クラッド６と同一の材料からなるスペーサ４としての役割を果たす。
FIG. 1 is a cross-sectional view showing the structure of a polarization rotation element according to a first reference example of the present invention. Here, a cross-sectional structure with respect to the light guide axis of the polarization rotation element is shown. That is, the direction perpendicular to the paper surface of FIG. 1 is the light propagation direction.
A lower clad 2 made of a silicon oxide film is formed on the silicon substrate 1, and a first core 3 having a square cross section is formed on the lower clad 2. An upper clad 6 is formed so as to cover the first core 3, and a second core 5 having a square cross section is formed in the upper clad 6. The upper clad 6 having a square cross section between the first core 3 and the second core 5 serves as a spacer 4 made of the same material as the upper clad 6.
例えば、第一コア３は２２０ナノメートル四方のシリコンからなり、第二コア５は６００ナノメートル四方のシリコン窒化膜からなり、スペーサ４は１００ナノメートル四方のシリコン酸化膜からなる。下部クラッド２と上部クラッド６もシリコン酸化膜からなる。すなわち、本参考例では、第一コアの屈折率＞第二コアの屈折率＞クラッドの屈折率という関係が成立する。上記のとおり、下部クラッド２と上部クラッド６は共にシリコン酸化膜であるので、下部クラッド２の厚さが３マイクロメートル程度と十分厚ければ上下方向に対称であるとみなせる。結果として、第一コア３と第二コア５とから形成される光導波路の固有軸（伝搬固有モードの軸）Ａ，Ｂは図１に示すようにシリコン基板１に対して４５°の傾きを持つ。 For example, the first core 3 is made of 220 nm square silicon, the second core 5 is made of a 600 nm square silicon nitride film, and the spacer 4 is made of a 100 nm square silicon oxide film. The lower clad 2 and the upper clad 6 are also made of a silicon oxide film. That is, in this reference example , the relationship of the refractive index of the first core> the refractive index of the second core> the refractive index of the cladding is established. As described above, since the lower clad 2 and the upper clad 6 are both silicon oxide films, if the thickness of the lower clad 2 is sufficiently thick, such as about 3 micrometers, it can be regarded as being symmetrical in the vertical direction. As a result, the eigen axes (propagation eigenmode axes) A and B of the optical waveguide formed by the first core 3 and the second core 5 are inclined at 45 ° with respect to the silicon substrate 1 as shown in FIG. Have.
図２（Ａ）〜図２（Ｅ）は本参考例の偏波回転素子の製造工程の例を示す工程断面図である。まず、偏波回転素子の第一コア３および偏波回転素子の第一コア３とは異なる光導波路７を、下部クラッド２上に形成する（図２（Ａ））。続いて、第一コア３および光導波路７を覆うように上部クラッド６の第一層６ａを成膜する（図２（Ｂ））。上部クラッド６の第一層６ａ層上面の平坦性を保つために、化学機械研磨を施しても良い。この上部クラッド６の第一層６ａの上に第二コア材料５ａを成膜し（図２（Ｃ））、この第二コア材料５ａを加工して第二コア５を形成する（図２（Ｄ））。最後に、第二コア５を覆うように上部クラッド６の第二層６ｂを成膜する（図２（Ｅ））。 2A to 2E are process cross-sectional views illustrating an example of a manufacturing process of the polarization rotation element of this reference example . First, an optical waveguide 7 different from the first core 3 of the polarization rotation element and the first core 3 of the polarization rotation element is formed on the lower cladding 2 (FIG. 2A). Subsequently, a first layer 6a of the upper cladding 6 is formed so as to cover the first core 3 and the optical waveguide 7 (FIG. 2B). In order to maintain the flatness of the upper surface of the first layer 6a of the upper cladding 6, chemical mechanical polishing may be performed. A second core material 5a is formed on the first layer 6a of the upper clad 6 (FIG. 2C), and the second core material 5a is processed to form the second core 5 (FIG. 2 ( D)). Finally, a second layer 6b of the upper clad 6 is formed so as to cover the second core 5 (FIG. 2E).
第一層６ａおよび第二層６ｂからなる上部クラッド６はＮＨ基を含まず、第二コア５は光導波路７とは直接接していないため、第二コア５の材料による光吸収の影響はない。第二コア５の形成は、微細加工で用いられるドライエッチングプロセスで可能であり、最後に上部クラッド６の第二層６ｂを堆積することにより所望のデバイス構造を得ることができる。 Since the upper clad 6 composed of the first layer 6a and the second layer 6b does not contain an NH group and the second core 5 is not in direct contact with the optical waveguide 7, there is no influence of light absorption by the material of the second core 5. . The second core 5 can be formed by a dry etching process used in microfabrication. Finally, a desired device structure can be obtained by depositing the second layer 6b of the upper cladding 6.
図３は本参考例の偏波回転素子における固有モードの電場強度分布と実効屈折率とをモードソルバによって計算した例を示す図である。ここでは、第一コア３は屈折率３．４７８で２２０ナノメートル四方の断面形状を有し、第二コア５は屈折率２．０００で６００ナノメートル四方の断面形状を有し、スペーサ４は屈折率１．４６５で１００ナノメートル四方の断面形状を有するものとし、下部クラッド２の屈折率を１．４４４、上部クラッド６の屈折率を１．４６５とした。また、第一コア３および第二コア５に入射する光の波長を１．５５マイクロメートルとした。２つの直交する固有モードのうちモード１の実効屈折率は１．６４０４であり、モード２の実効屈折率は１．６３０５であった。この２つの固有モードの実効屈折率の差から、概ねの長さが７８マイクロメートルの偏波回転素子中を光が伝搬すれば、偏波は９０度回転することが分かる。 FIG. 3 is a diagram showing an example in which the electric field intensity distribution and effective refractive index of the natural mode in the polarization rotation element of this reference example are calculated by a mode solver. Here, the first core 3 has a refractive index of 3.478 and a cross section of 220 nm square, the second core 5 has a refractive index of 2.000 and a cross section of 600 nm square, and the spacer 4 has The refractive index is 1.465 and the cross section is 100 nm square, the lower cladding 2 has a refractive index of 1.444, and the upper cladding 6 has a refractive index of 1.465. The wavelength of light incident on the first core 3 and the second core 5 was 1.55 micrometers. Of the two orthogonal eigenmodes, the effective refractive index of mode 1 was 1.6404, and the effective refractive index of mode 2 was 1.6305. From the difference in effective refractive index between the two eigenmodes, it can be seen that if light propagates through a polarization rotation element having a length of approximately 78 micrometers, the polarization rotates by 90 degrees.
図４は本参考例の偏波回転素子を上方から見た平面図である。ここでは、上部クラッド６の下にある第一コア３、第二コア５および下部クラッド２を透視しているものとする。図４に示すように、第二コア５の光伝搬方向の長さは、第一コア３の光伝搬方向の長さよりも短い。このような偏波回転素子に光を入射させる場合には、第一コア３の入力端（図４の例では左端）に光を入射させればよい。入射光は、第一コア３、第二コア５を伝搬する際に偏波が回転し、所望の回転角だけ回転した後に第一コア３の出力端（図４の例では右端）から出射する。 FIG. 4 is a plan view of the polarization rotation element of this reference example as viewed from above. Here, it is assumed that the first core 3, the second core 5, and the lower clad 2 under the upper clad 6 are seen through. As shown in FIG. 4, the length of the second core 5 in the light propagation direction is shorter than the length of the first core 3 in the light propagation direction. When light is incident on such a polarization rotation element, the light may be incident on the input end of the first core 3 (the left end in the example of FIG. 4). Incident light is rotated in polarization when propagating through the first core 3 and the second core 5, and after being rotated by a desired rotation angle, is emitted from the output end (right end in the example of FIG. 4). .
以上のように、本参考例では、第一コア３の光伝搬方向の中心軸と第二コア５の光伝搬方向の中心軸が一致しない偏芯二重コア構造を採用し、この偏芯二重コア構造の光導波路中を光を一定距離伝搬させることで、偏波状態を変化させることができる。そして、本参考例では、このような偏芯二重コア構造において第二コア５を第一コア３から水平方向（図１左右方向）および垂直方向（積層方向、図１上下方向）に離間して配置することにより、第二コア５による光吸収を最小限に抑えながら、偏波回転を実現することができる。 As described above, this reference example employs an eccentric double core structure in which the central axis in the light propagation direction of the first core 3 and the central axis in the light propagation direction of the second core 5 do not coincide with each other. The polarization state can be changed by propagating light through the optical waveguide having the heavy core structure for a certain distance. In this reference example , in such an eccentric double core structure, the second core 5 is separated from the first core 3 in the horizontal direction (left-right direction in FIG. 1) and in the vertical direction (stacking direction, up-down direction in FIG. 1). Accordingly, polarization rotation can be realized while minimizing light absorption by the second core 5.
なお、第二コア５の材料としては、第一コア３とクラッドの中間の屈折率を持つシリコン窒化膜やシリコン酸窒化膜、１．５以上の屈折率を持つポリマ材料などを使用すればよい。クラッドの材料としては、シリコン酸化膜、ポリイミド樹脂、エポキシ樹脂、その他の各種ポリマなどを使用すればよい。 As the material of the second core 5, a silicon nitride film or silicon oxynitride film having an intermediate refractive index between the first core 3 and the clad, or a polymer material having a refractive index of 1.5 or more may be used. . As a clad material, a silicon oxide film, a polyimide resin, an epoxy resin, or other various polymers may be used.
［第２の参考例］
次に、本発明の第２の参考例について説明する。図５は本発明の第２の参考例に係る偏波回転素子を上方から見た平面図であり、図１、図４と同様の構成には同一の符号を付してある。図４と同様に、ここでは上部クラッド６の下にある第一コア３、第二コア５および下部クラッド２を透視しているものとする。本参考例は、第二コア５の入力端部８を、厚さ一定のまま光の伝搬方向に沿って漸次断面積が大きくなるテーパ状とし、第二コア５の出力端部９を、厚さ一定のまま光の伝搬方向に沿って漸次断面積が小さくなるテーパ状としたことを特徴とする。この図５では第二コア５の平面図が台形となっているが，第二コア５の入力端部８および出力端部９は有限の先端幅を持つ形状でも良い。言い換えると、第二コア５の平面形状は六角形でも良い。
[ Second Reference Example ]
Next, a second reference example of the present invention will be described. FIG. 5 is a plan view of the polarization rotator according to the second reference example of the present invention as viewed from above, and the same components as those in FIGS. 1 and 4 are denoted by the same reference numerals. As in FIG. 4, it is assumed here that the first core 3, the second core 5, and the lower cladding 2 under the upper cladding 6 are seen through. In this reference example , the input end 8 of the second core 5 is tapered so that the cross-sectional area gradually increases along the light propagation direction while the thickness is constant, and the output end 9 of the second core 5 is thick. It is characterized by a taper shape in which the cross-sectional area gradually decreases along the light propagation direction while maintaining a constant value. In FIG. 5, the plan view of the second core 5 is trapezoidal, but the input end 8 and the output end 9 of the second core 5 may have a shape having a finite tip width. In other words, the planar shape of the second core 5 may be a hexagon.
本参考例では、第二コア５にテーパ構造を導入したことにより、入力端部８および出力端部９での光の反射を抑制することができ、偏波回転素子の透過特性、波長特性などを改善することができる。 In this reference example , by introducing a taper structure to the second core 5, reflection of light at the input end 8 and the output end 9 can be suppressed, and the transmission characteristics, wavelength characteristics, etc. of the polarization rotation element, etc. Can be improved.
［第１の実施の形態］
次に、本発明の第１の実施の形態について説明する。図６は本発明の第１の実施の形態に係る偏波回転素子を上方から見た平面図であり、図１、図４、図５と同様の構成には同一の符号を付してある。図４と同様に、ここでは上部クラッド６の下にある第一コア３、第二コア５および下部クラッド２を透視しているものとする。本実施の形態は、光の伝搬方向に沿って複数の第二コア５−１，５−２，５−３，５−４，・・・・を第一コア３の両脇に交互に配置したことを特徴とする。
[ First Embodiment ]
Next, a first embodiment of the present invention will be described. FIG. 6 is a plan view of the polarization rotator according to the first embodiment of the present invention as viewed from above, and the same reference numerals are given to the same components as those in FIGS. . As in FIG. 4, it is assumed here that the first core 3, the second core 5, and the lower cladding 2 under the upper cladding 6 are seen through. In this embodiment, a plurality of second cores 5-1, 5-2, 5-3, 5-4,... Are alternately arranged on both sides of the first core 3 along the light propagation direction. It is characterized by that.
本実施の形態では、第一コア３、第二コア５（５−１〜５−４）、スペーサ４の断面形状は、いずれも正方形である必要は無い。これらの断面形状が正方形でない場合、第二コア５の固有軸はシリコン基板に対し、４５度未満の傾きになるが、光導波路の固有軸がＸ度だけ傾いている第二コア５−１，５−２，５−３，５−４，・・・・をＮ回通過すると、偏波は２ＸＮ度だけ回転する。例えば固有軸が１５度だけ傾いている第二コア５を３回通過すると、９０度の偏波回転が得られる。よって、コア断面形状やスペーサ断面形状に制限があって、コアやスペーサの正方形断面を実現できない場合であっても、９０度の偏波回転を実現できるという効果がある。 In the present embodiment, the first core 3, the second core 5 (5-1 to 5-4), and the spacer 4 do not have to be square in cross section. When these cross-sectional shapes are not square, the natural axis of the second core 5 has an inclination of less than 45 degrees with respect to the silicon substrate, but the intrinsic axis of the optical waveguide is inclined by X degrees. When passing through 5-2, 5-3, 5-4,... N times, the polarization rotates by 2 × N degrees. For example, when passing through the second core 5 whose natural axis is inclined by 15 degrees three times, a polarization rotation of 90 degrees is obtained. Therefore, even if there is a limitation in the core cross-sectional shape and the spacer cross-sectional shape, and a square cross-section of the core or spacer cannot be realized, there is an effect that 90 degree polarization rotation can be realized.
なお、図６では各々の第二コア５−１，５−２，５−３，５−４，・・・・は入力端部と出力端部にテーパ構造を備えているが、テーパ構造を備えていない図４に示したような第二コアを、光の伝搬方向に沿って第一コア３の両脇に交互に配置してもよい。 In FIG. 6, each of the second cores 5-1, 5-2, 5-3, 5-4,... Has a taper structure at the input end and the output end. The second cores as shown in FIG. 4 that are not provided may be alternately arranged on both sides of the first core 3 along the light propagation direction.
［第２の実施の形態］
第１、第２の参考例および第１の実施の形態では、第二コア５を第一コア３の上方に配置しているが、図７に示すように第二コア５を第一コア３の下方に配置してもよい。
図８（Ａ）〜図８（Ｅ）は本実施の形態の偏波回転素子の製造工程の例を示す工程断面図である。まず、第二コア材料５ａを下部クラッド２上に成膜し（図８（Ａ））、この第二コア材料５ａを加工して第二コア５を形成する（図８（Ｂ））。続いて、第二コア５を覆うように上部クラッド６の第一層６ａを成膜する（図８（Ｃ））。上部クラッド６の第一層６ａ層上面の平坦性を保つために、化学機械研磨を施しても良い。この上部クラッド６の第一層６ａの上に偏波回転素子の第一コア３および偏波回転素子の第一コア３とは異なる光導波路７を形成する（図８（Ｄ））。最後に、第一コア３および光導波路７を覆うように上部クラッド６の第二層６ｂを成膜する（図８（Ｅ））。
[ Second Embodiment ]
In the first and second reference examples and the first embodiment , the second core 5 is disposed above the first core 3, but the second core 5 is replaced with the first core 3 as shown in FIG. You may arrange | position below.
8A to 8E are process cross-sectional views illustrating an example of a manufacturing process of the polarization rotation element of the present embodiment. First, the second core material 5a is formed on the lower clad 2 (FIG. 8A), and the second core material 5a is processed to form the second core 5 (FIG. 8B). Subsequently, the first layer 6a of the upper clad 6 is formed so as to cover the second core 5 (FIG. 8C). In order to maintain the flatness of the upper surface of the first layer 6a of the upper cladding 6, chemical mechanical polishing may be performed. On the first layer 6a of the upper clad 6, a first core 3 of the polarization rotator and an optical waveguide 7 different from the first core 3 of the polarization rotator are formed (FIG. 8D). Finally, a second layer 6b of the upper clad 6 is formed so as to cover the first core 3 and the optical waveguide 7 (FIG. 8E).
本実施の形態では、第１、第２の参考例および第１の実施の形態で説明した効果に加えて、さらに第二コア５を第一コア３よりも先に形成することで、第二コア５のエッチングによる第一コア３のダメージを低減できるという効果がある。 In the present embodiment, in addition to the effects described in the first and second reference examples and the first embodiment , the second core 5 is further formed before the first core 3, so that the second There is an effect that damage to the first core 3 due to etching of the core 5 can be reduced.
本発明は、光通信装置に適用することができる。 The present invention can be applied to an optical communication device.
１…シリコン基板、２…下部クラッド、３…第一コア、４…スペーサ、５…第二コア、６…上部クラッド、７…光導波路、８…入力端部、９…出力端部。 DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Lower clad, 3 ... 1st core, 4 ... Spacer, 5 ... 2nd core, 6 ... Upper clad, 7 ... Optical waveguide, 8 ... Input end part, 9 ... Output end part.
Claims (2)
光伝搬方向と垂直な断面が矩形の第二コアと、
前記第一、第二コアを覆うように配置されたクラッドとから構成され、
前記第一コアの屈折率が前記第二コアおよび前記クラッドの屈折率よりも大きく、
前記第二コアの屈折率が前記クラッドの屈折率よりも大きく、
前記第二コアは、前記第一コアから水平方向および垂直方向に離間して配置され、
光の伝搬方向に沿って複数の前記第二コアを前記第一コアの両脇に交互に配置したことを特徴とする偏波回転素子。 A first core having a rectangular cross section perpendicular to the light propagation direction;
A second core having a rectangular cross section perpendicular to the light propagation direction;
The first and second clads are arranged to cover the second core,
The refractive index of the first core is greater than the refractive index of the second core and the cladding;
The refractive index of the second core is greater than the refractive index of the cladding;
The second core is spaced apart from the first core in the horizontal direction and the vertical direction ,
A polarization rotation element , wherein a plurality of the second cores are alternately arranged on both sides of the first core along a light propagation direction .
前記第二コアは、
厚さ一定のまま光の伝搬方向に沿って漸次断面積が大きくなるテーパ状の入力端部と、
厚さ一定のまま光の伝搬方向に沿って漸次断面積が小さくなるテーパ状の出力端部とを備えることを特徴とする偏波回転素子。 The polarization rotation element according to claim 1,
The second core is
A tapered input end with a gradually increasing cross-sectional area along the light propagation direction with a constant thickness;
A polarization rotation element comprising: a tapered output end portion that gradually decreases in cross-sectional area along the light propagation direction with a constant thickness .
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