技术领域technical field
本发明涉及一种具有高耦合效率的光子晶体槽波导结构，属于微型光电子器件技术领域。The invention relates to a photonic crystal groove waveguide structure with high coupling efficiency, which belongs to the technical field of micro-optoelectronic devices.
背景技术Background technique
光子晶体槽波导是2008年提出的一种新型结构(文献1.A.Di Falco，L. O’Faolain，T.F.Krauss.“Photonic crystal slotted slab waveguides.”Photonics and Nnostructures-Fundamentalsand Applications，2008，6：38-41.)，它结合了光子晶体波导与普通槽波导的优点，空气槽内可以填充电光或低折射率待测材料，慢光被束缚在很窄的低折射率介质槽内，空间上增加了信号的强度，进一步加强慢光与槽内低折射率物质的相互作用，可以用来实现小体积、高灵敏度的各种全光器件(文献2.J.D.Ryckman，S.M.Weiss.“Localized field enhancementsin guided and defect modes of a periodic slot waveguide.”IEEE Photonics Journal，2011，3(6)：986-995.)。Photonic crystal slotted slab waveguides are a new type of structure proposed in 2008 (document 1.A.Di Falco, L. O'Faolain, T.F.Krauss. "Photonic crystal slotted slab waveguides." Photonics and Nnostructures-Fundamentals and Applications, 2008, 6: 38-41.), it combines the advantages of photonic crystal waveguide and ordinary slot waveguide, the air slot can be filled with electro-optic or low refractive index materials to be tested, and the slow light is bound in a very narrow low refractive index dielectric slot, spatially The strength of the signal is increased, and the interaction between the slow light and the low refractive index material in the groove is further strengthened, which can be used to realize various all-optical devices with small volume and high sensitivity (document 2.J.D.Ryckman, S.M.Weiss. "Localized field enhancements in guided and defect modes of a periodic slot waveguide.” IEEE Photonics Journal, 2011, 3(6): 986-995.).
在实际应用中，光子晶体槽波导与普通光纤间的耦合是必不可少的。普通光纤发出的发散光首先经光纤透镜准直聚焦后进入脊波导，然后再由脊波导出来进入光子晶体槽波导。当光从脊波导入射到光子晶体槽波导时，由于两者之间光传播模式以及折射率的不同而导致严重的阻抗失配，光会被剧烈的反射回来，由此带来的损耗被称为耦合损耗。2012年，美国学者将脊波导末端切割成一个非常尖的锥形结构，再在光子晶体槽波导的端口引出两个凹形的槽波导，将两者很好的吻合在一起。这样在脊波导中的光传播模式就会转变为槽波导模式并耦合进光子晶体槽波导中。同时，逐渐改变输入和输出端的波导宽度形成渐变结构，这样光在光子晶体中的折射率就会逐渐升高，最终将脊波导与光子晶体槽波导之间的透射率提高到60％左右(文献3.C.Y. Lin，A.X.Wang，W.C.Lai，et al.Coupling lossminimization of slow light slotted photonic crystal waveguides using mode matching withcontinuous group index perturbation.Optics Letters，2012，37(2)：232-234.)。但是该耦合结构需要在光子晶体槽波导的端口引出一段非常窄的凹形槽波导，不仅增加了制备的复杂性而且会影响器件的机械稳定性。In practical applications, the coupling between photonic crystal slot waveguides and common optical fibers is essential. The divergent light emitted by the ordinary optical fiber first enters the ridge waveguide after being collimated and focused by the fiber lens, and then is guided by the ridge wave to enter the photonic crystal groove waveguide. When light is incident from the ridge waveguide to the photonic crystal groove waveguide, due to the serious impedance mismatch caused by the difference in light propagation mode and refractive index between the two, the light will be strongly reflected back, and the resulting loss is called is the coupling loss. In 2012, American scholars cut the end of the ridge waveguide into a very sharp tapered structure, and then led out two concave groove waveguides at the port of the photonic crystal groove waveguide, so that the two are well matched together. In this way, the light propagating mode in the ridge waveguide will be transformed into a groove waveguide mode and coupled into the photonic crystal groove waveguide. At the same time, the width of the waveguide at the input and output ends is gradually changed to form a graded structure, so that the refractive index of light in the photonic crystal will gradually increase, and finally the transmittance between the ridge waveguide and the photonic crystal groove waveguide will be increased to about 60% (ref. 3. C.Y. Lin, A.X.Wang, W.C.Lai, et al. Coupling loss minimization of slow light slotted photonic crystal waveguides using mode matching with continuous group index perturbation. Optics Letters, 2012, 37(2): 232-234.). However, this coupling structure needs to lead out a very narrow concave groove waveguide at the port of the photonic crystal groove waveguide, which not only increases the complexity of preparation but also affects the mechanical stability of the device.
发明内容Contents of the invention
(一)要解决的技术问题(1) Technical problems to be solved
本发明的主要目的在于解决脊波导与光子晶体槽波导之间的耦合损耗问题，提供一种具有高耦合效率的光子晶体槽波导结构。The main purpose of the present invention is to solve the coupling loss problem between the ridge waveguide and the photonic crystal groove waveguide, and provide a photonic crystal groove waveguide structure with high coupling efficiency.
(二)技术方案(2) Technical solutions
为达到上述目的，本发明提供了一种具有高耦合效率的光子晶体槽波导结构。该结构是在光子晶体槽波导的两端，同时引入锥形渐变结构和谐振结构，使从脊波导出来的光束在光子晶体槽波导的入口和出口处发生干涉，因而产生自准直效应，实现脊波导与光子晶体槽波导之间的高效率耦合。To achieve the above purpose, the present invention provides a photonic crystal slot waveguide structure with high coupling efficiency. The structure is at both ends of the photonic crystal slot waveguide, and at the same time introduces a tapered gradient structure and a resonant structure, so that the light beam derived from the ridge wave interferes at the entrance and exit of the photonic crystal slot waveguide, thus generating a self-collimation effect and realizing High-efficiency coupling between ridge waveguides and photonic crystal groove waveguides.
上述方案中，所述的光子晶体槽波导结构可以在半导体材料基板绝缘体上硅(Silicon OnInsulator，SOI)上利用掩膜、电子束曝光、离子刻蚀、干法刻蚀、湿法腐蚀等技术形成空气桥结构的光子晶体槽波导。In the above scheme, the photonic crystal groove waveguide structure can be formed on the semiconductor material substrate Silicon On Insulator (Silicon On Insulator, SOI) using a mask, electron beam exposure, ion etching, dry etching, wet etching, etc. Photonic crystal slot waveguide with air bridge structure.
上述方案中，所述的光子晶体结构采用的是三角晶格结构，空气孔的半径r＝0.32a(其中a为光子晶体的晶格常数，即相邻空气孔之间的间距)，为保证光子晶体器件工作在传输损耗比较小的1550nm波段，一般晶格常数a取400nm左右。In the above-mentioned scheme, what described photonic crystal structure adopted is triangular lattice structure, and the radius r=0.32a of air hole (wherein a is the lattice constant of photonic crystal, i.e. the spacing between adjacent air holes), in order to ensure Photonic crystal devices work in the 1550nm band with relatively small transmission loss, and the general lattice constant a is about 400nm.
上述方案中，所述的光子晶体槽波导结构中，背景介质采用纯硅，折射率n＝3.48，硅厚度h＝400nm；所有空气孔中均是空气，折射率均为n0＝1。In the above scheme, in the photonic crystal groove waveguide structure, the background medium is pure silicon, the refractive index n=3.48, and the silicon thickness h=400nm; all the air holes are air, and the refractive index is n0 =1.
上述方案中，所述的光子晶体槽波导，是指在普通的硅介质背景空气孔结构光子晶体的基础上，去掉中间的一排空气孔形成W1结构的光子晶体波导，再在缺陷中心处放置一个宽度为ω＝0.3a的空气槽。In the above scheme, the photonic crystal slot waveguide refers to a photonic crystal waveguide with a W1 structure formed by removing a row of air holes in the middle on the basis of an ordinary silicon medium background air hole structure photonic crystal waveguide, and then placing it at the center of the defect An air slot of width ω=0.3a.
上述方案中，所述的锥形渐变结构，是指在光子晶体槽波导的入口和出口处，去掉靠近空气槽的第一排空气孔中的两个空气孔，同时去掉靠近空气槽的第二排空气孔中的一个空气孔，最后将空气槽的长度缩短，使其两端距光子晶体槽波导的边界均为s＝2.9a，形成出口和入口完全对称的光子晶体槽波导锥形渐变结构。In the above scheme, the tapered gradient structure refers to removing two air holes in the first row of air holes near the air groove at the entrance and exit of the photonic crystal groove waveguide, and removing the second row of air holes near the air groove at the same time. Exhaust one of the air holes in the air hole, and finally shorten the length of the air slot so that both ends are s=2.9a from the boundary of the photonic crystal slot waveguide, forming a tapered tapered structure of the photonic crystal slot waveguide with completely symmetrical exit and entrance .
上述方案中，所述的谐振结构，是指在锥形渐变结构的基础上，在靠近空气槽的第二排空气孔两端各引入一个半径为r1＝0.45a的空气孔，使其与相邻的空气孔间距为一个晶格常数a；在靠近空气槽的第一排空气孔两端各引入一个半径为r2＝0.38a的空气孔，使其与相邻的空气孔间距为一个晶格常数a；同时，在空气槽的两端各引入一个半径为r3＝0.18a的空气孔，使其与空气槽末端的距离为1.9a；最后，将脊波导的宽度增加至ω0＝4.3a，在光子晶体槽波导的入口和出口处形成完全一致的谐振结构。In the above scheme, the resonant structure refers to the introduction of an air hole with a radius of r1 =0.45a at both ends of the second row of air holes close to the air groove on the basis of the tapered gradual change structure, so that it is compatible with the The distance between adjacent air holes is a lattice constant a; an air hole with a radius of r2 =0.38a is introduced at both ends of the first row of air holes close to the air groove, so that the distance between the adjacent air holes is a lattice constant a; at the same time, introduce an air hole with a radius of r3 =0.18a at both ends of the air groove, so that the distance from the end of the air groove is 1.9a; finally, increase the width of the ridge waveguide to ω0 =4.3a, a completely consistent resonant structure is formed at the entrance and exit of the photonic crystal slot waveguide.
(三)有益效果(3) Beneficial effects
从上述技术方案可以看出，本发明具有以下有益效果：As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:
1)本发明提供的一种具有高耦合效率的光子晶体槽波导结构，采用渐变结构和谐振结构相结合的方法，只需要引入三种孔径的空气孔就可以实现高效率的耦合，这样可降低制备工艺的复杂性。1) A photonic crystal slot waveguide structure with high coupling efficiency provided by the present invention adopts the method of combining a graded structure and a resonant structure, and only needs to introduce air holes with three apertures to achieve high-efficiency coupling, which can reduce The complexity of the preparation process.
2)本发明提供的一种具有高耦合效率的光子晶体槽波导结构，可以将脊波导与光子晶体槽波导间的透射率提高到90％，且其透射率具有很好的一致性，为光子晶体槽波导在光电子器件中的实际应用提供了基础。2) A photonic crystal groove waveguide structure with high coupling efficiency provided by the present invention can increase the transmittance between the ridge waveguide and the photonic crystal groove waveguide to 90%, and its transmittance has a good consistency, which is the photonic crystal groove waveguide. Crystal slot waveguides provide the basis for practical applications in optoelectronic devices.
附图说明Description of drawings
以下各图所取的光子晶体槽波导的结构参数均与具体实施方式中相同。The structural parameters of the photonic crystal slot waveguide shown in the following figures are the same as those in the specific embodiment.
图1为脊波导与光子晶体槽波导的耦合结构示意图；Fig. 1 is a schematic diagram of the coupling structure of a ridge waveguide and a photonic crystal groove waveguide;
图2为引入光子晶体槽波导耦合结构前后的光透射谱对比图。Fig. 2 is a comparison diagram of the light transmission spectrum before and after introducing the photonic crystal slot waveguide coupling structure.
具体实施方式Detailed ways
为使本发明的目的、技术方案和优点更加清楚明白，以下结合具体实施例，并参照附图，对本发明的具体结构作进一步的详细说明。In order to make the object, technical solution and advantages of the present invention clearer, the specific structure of the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.
本发明提出了一种具有高耦合效率的光子晶体槽波导结构，如图1所示为脊波导与光子晶体槽波导的耦合结构示意图，它是通过在脊波导与光子晶体槽波导的入口和出口处，同时引入锥形渐变结构和谐振结构而形成的。The present invention proposes a photonic crystal groove waveguide structure with high coupling efficiency, as shown in Figure 1 is a schematic diagram of the coupling structure of the ridge waveguide and the photonic crystal groove waveguide, it is through the entrance and exit of the ridge waveguide and the photonic crystal groove waveguide At the same time, it is formed by introducing a tapered gradient structure and a resonant structure.
脊波导和光子晶体槽波导采用相同的制备工艺在一块绝缘体上硅材料上加工，其中脊波导为纯硅材料，光子晶体槽波导是在普通的三角晶格光子晶体中，将中间一排空气孔换成宽度为ω＝0.3a的空气槽形成的。在光子晶体槽波导的结构中，a为晶格常数，即相邻空气孔之间的间距，空气孔的半径为r＝0.32a。所有空气孔的折射率均为1，介质背景采用纯硅，折射率为n＝3.48，硅厚度为h＝400nm。如图1所示，在脊波导和光子晶体槽波导的入口和出口处，引入相同的锥形渐变结构和谐振结构。其中锥形渐变结构是通过去掉靠近空气槽的第一排空气孔中的两个空气孔，同时去掉靠近空气槽的第二排空气孔中的一个空气孔，最后将空气槽的长度缩短，使其两端距光子晶体槽波导的边界均相距s＝2.9a，这样便在光子晶体槽波导的入口和出口处引入了完全对称的锥形渐变结构。而谐振结构是在锥形渐变结构的基础上，在靠近空气槽的第二排空气孔两端各引入一个半径为r1＝0.45a的空气孔，使其与相邻的空气孔间距为一个晶格常数a；在靠近空气槽的第一排空气孔两端各引入一个半径为r2＝0.38a的空气孔，使其与相邻的空气孔间距为一个晶格常数a；同时，在空气槽的两端各引入一个半径为r3＝0.18a的空气孔，使其与空气槽末端的距离为1.9a；最后，将脊波导的宽度增加至ω0＝4.3a，在光子晶体槽波导的入口和出口处形成完全一致的谐振结构。通过引入锥形渐变和谐振结构，从脊波导出来的光束将会在接口处发生干涉，因而产生自准直效应，减少由于阻抗失配引起的反射损耗，实现脊波导与光子晶体波导之间的高效率耦合。The ridge waveguide and the photonic crystal groove waveguide are processed on a piece of silicon-on-insulator material by the same preparation process, in which the ridge waveguide is pure silicon material, and the photonic crystal groove waveguide is in the ordinary triangular lattice photonic crystal, with a row of air holes in the middle Replaced by an air groove with a width of ω=0.3a. In the structure of the photonic crystal slot waveguide, a is the lattice constant, that is, the distance between adjacent air holes, and the radius of the air holes is r=0.32a. The refractive index of all air holes is 1, the dielectric background is made of pure silicon, the refractive index is n=3.48, and the silicon thickness is h=400nm. As shown in Fig. 1, at the entrance and exit of the ridge waveguide and the photonic crystal groove waveguide, the same tapered tapered structure and resonant structure are introduced. Among them, the tapered gradual change structure is by removing two air holes in the first row of air holes near the air groove, and simultaneously removing one air hole in the second row of air holes near the air groove, and finally shortening the length of the air groove, so that Both ends of the photonic crystal slot waveguide are s=2.9a away from the boundary of the photonic crystal slot waveguide, so that a fully symmetrical tapered tapered structure is introduced at the entrance and exit of the photonic crystal slot waveguide. The resonant structure is based on the tapered gradual change structure, and an air hole with a radius of r1 =0.45a is introduced at both ends of the second row of air holes close to the air groove, so that the distance between it and the adjacent air holes is one Lattice constant a; an air hole with a radius of r2 =0.38a is introduced at both ends of the first row of air holes close to the air groove, so that the distance between it and the adjacent air hole is a lattice constant a; at the same time, An air hole with a radius of r3 =0.18a is introduced at both ends of the air groove, so that the distance from the end of the air groove is 1.9a; finally, the width of the ridge waveguide is increased to ω0 =4.3a, in the photonic crystal groove A perfectly consistent resonant structure is formed at the entrance and exit of the waveguide. By introducing a tapered gradient and a resonant structure, the light beam derived from the ridge wave will interfere at the interface, thus producing a self-collimation effect, reducing the reflection loss caused by impedance mismatch, and realizing the coupling between the ridge waveguide and the photonic crystal waveguide. Efficient coupling.
图2所示为利用麻省理工学院的MEEP软件仿真得到的引入光子晶体槽波导耦合结构前后光透射谱对比图，Curve1为引入光子晶体槽波导耦合结构前的光透射谱，Curve2为引入光子晶体槽波导耦合结构后的光透射谱。从图中可以看出，引入光子晶体槽波导耦合结构后，可以将脊波导与光子晶体槽波导间的透射率提高到90％。在引入光子晶体槽波导耦合结构前，由于脊波导与光子晶体槽波导之间存在严重的阻抗失配，光束在两者的接口处会产生Fabry-Perot反射，光透射谱中会由于干涉条纹的存在而有严重的抖动。引入光子晶体槽波导耦合结构可以减小阻抗失配，Fabry-Perot反射产生的干涉条纹幅度会大大降低，得到一致性比较好的透射谱，透射率整体提高了50％，在靠近带边的高群折射率区域透射率提高了60％。Figure 2 shows the comparison of the light transmission spectrum before and after the introduction of the photonic crystal slot waveguide coupling structure obtained by the MEEP software simulation of the Massachusetts Institute of Technology. Curve1 is the light transmission spectrum before the introduction of the photonic crystal slot waveguide coupling structure, and Curve2 is the introduction of the photonic crystal slot waveguide coupling structure. Optical transmission spectrum after the slot waveguide coupling structure. It can be seen from the figure that after introducing the photonic crystal groove waveguide coupling structure, the transmittance between the ridge waveguide and the photonic crystal groove waveguide can be increased to 90%. Before introducing the photonic crystal groove waveguide coupling structure, due to the serious impedance mismatch between the ridge waveguide and the photonic crystal groove waveguide, the light beam will produce Fabry-Perot reflection at the interface between the two, and the light transmission spectrum will be due to interference fringes. Severe jitter exists. The introduction of photonic crystal slot waveguide coupling structure can reduce the impedance mismatch, the interference fringe amplitude generated by Fabry-Perot reflection will be greatly reduced, and the transmission spectrum with better consistency can be obtained. The group index region transmittance has been increased by 60%.
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