Kim Sangsik, Qi Minghao
School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907 USA.
Sci Rep. 2015 Dec 18;5:18378. doi: 10.1038/srep18378.
Hybrid plasmonic (HP) modes allow strong optical field confinement and simultaneously low propagation loss, offering a potentially compact and efficient platform for on-chip photonic applications. However, their implementation is hampered by the low coupling efficiency between dielectric guided modes and HP modes, caused by mode mismatch and polarization difference. In this work, we present a mode-evolution-based polarization rotation and coupling structure that adiabatically rotates the TE mode in a silicon waveguide and couples it to the HP mode in a strip silicon-dielectric-metal waveguide. Simulation shows that high coupling factors of 92%, 78%, 75%, and 73% are achievable using Ag, Au, Al, and Cu as the metal cap, respectively, at a conversion length of about 5 μm. For an extremely broad wavelength range of 1300-1800 nm, the coupling factor is >64% with a Ag metal cap, and the total back-reflection power, including all the mode reflections and backscattering, is below -40 dB, due to the adiabatic mode transition. Our device does not require high-resolution lithography and is tolerant to fabrication variations and imperfections. These attributes together make our device suitable for optical transport systems spanning all telecommunication bands.
混合等离子体（HP）模式能够实现强光学场限制，同时具有低传播损耗，为片上光子应用提供了一个潜在的紧凑且高效的平台。然而，由于模式失配和偏振差异，介电导模与HP模式之间的低耦合效率阻碍了它们的应用。在这项工作中，我们提出了一种基于模式演化的偏振旋转和耦合结构，该结构能使硅波导中的TE模式绝热旋转，并将其耦合到条形硅 - 介质 - 金属波导中的HP模式。仿真表明，使用Ag、Au、Al和Cu作为金属帽时，在约5μm的转换长度下，耦合系数分别可达到92%、78%、75%和73%。对于1300 - 1800nm的极宽波长范围，使用Ag金属帽时耦合系数>64%，并且由于绝热模式转换，包括所有模式反射和反向散射在内的总背向反射功率低于 - 40dB。我们的器件不需要高分辨率光刻，并且能够容忍制造变化和缺陷。这些特性共同使得我们的器件适用于跨越所有电信频段的光传输系统。
