摘要:
基于光子晶体的自准直效应和禁带特性,提出了一种具有非正交异质结结构的光子晶体偏振分束器.无需引入缺陷或波导,可使光波在该结构中准直无发散地传输并实现分束功能,对制造工艺的要求大大降低.利用Rsoft软件,结合平面波展开法和二维时域有限差分法,对提出的偏振分束器进行了仿真研究.结果表明,该偏振分束器在一个较大的频率范围f=0.275—0.285(a/λ)内可实现横电(TE)和横磁(TM)模的大角度偏振分离,TE和TM模的透过率均在88%以上,偏振消光比分别大于26.57 dB和17.50 dB.该结构可应用到太赫兹波段的传输系统中,a=26μm,尺寸大小为572μm×546μm,在91—95μm波长范围内可实现TE和TM模的分离.利用该结构可设计用于光通信系统(n=3.48)的偏振分束器,a=426.25 nm,结构仅为9.38μm×8.95μm.本方案结构简单,易于集成,有望在集成光路的发展中发挥重要作用.
Abstract:
Polarization beam splitter (PBS) is an important device in optical system, in which the optical signal can be separated into two mutually orthogonal polarized light and transmit along different paths. It is difficult for the traditional PBS to meet the needs of the modern optical integrated systems because of its low transmission efficiency and high dependence on the incident angle. Therefore, it is necessary to design more efficient and compact PBSs. In recent years, photonic crystals have attracted more attention due to their ability to manipulate photon motion. In this paper, a photonic crystal PBS with a non-orthogonal heterojunction structure is proposed, which is based on the self-collimation effect and bandgap properties of photonic crystal. The proposed PBS structure is composed of two square lattice photonic crystals with the same lattice constant and different air hole radii in silicon (Si), in which the beam can be self-collimated and propagate without diffraction, and the polarization separation of and transverse electric (TE) mode from transverse magnetic (TM) mode is realized at the interface. The self-collimation effect can be used to control the transmission of light in order to realize the general light guiding of the waveguide, and it can greatly reduce the difficulty in manufacturing process because of no additional defects introduced. The splitting properties, transmission properties and polarization extinction ratio of the PBS are numerically simulated and analyzed by using Rsoft software combined with the plane wave expansion method and the two finite-difference time-domain method. It is shown that a high efficiency and a large separating angle for TE and TM modes in a wide frequency range 0.275–0.285 (a/λ) can be achieved. The transmission efficiency is above 88% for both TE and TM modes, and the extinction ratios are more than 26.57 dB for TE mode and 17.50 dB for TM mode, respectively. This structure can be applied to the transmission system of terahertz band: a = 26 μm, the size is 572 μm × 546 μm, and the separation of TE mode from TM mode can be achieved in a wavelength range of 91–95 μm. A PBS for optical communication system can be also designed by using the same structure: n=3.48, a=426.25 nm, and the proposed PBS is only 9.38 μm × 8.95 μm in size, which can separate these two polarization beams in a wavelength range of 1511–1579 nm. What is more, the proposed PBS based on photonic crystal is simple and easy to integrate, which has important application value in optical communication technology.
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