Dai Daoxin, Bowers John E
Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA.
Opt Express. 2011 May 23;19(11):10940-9. doi: 10.1364/OE.19.010940.
A novel concept for an ultracompact polarization splitter-rotator is proposed by utilizing a structure combining an adiabatic taper and an asymmetrical directional coupler. The adiabatic taper structure is singlemode at the input end while it becomes multimode at the other end. When light propagates along the adiabatic taper structure, the TM fundamental mode launched at the narrow end is efficiently (close to 100%) converted to the first higher-order TE mode at the wide end because of the mode coupling between them. By using an asymmetrical directional coupler that has two adjacent waveguides with different core widths, the first higher-order TE mode is then coupled to the TE fundamental mode of the adjacent narrow waveguide. On the other hand, the input TE polarization does not change when it goes through the adiabatic taper structure. In the region of the asymmetrical directional coupler, the TE fundamental mode in the wide waveguide is not coupled to the adjacent narrow waveguide because of phase mismatch. In this way, TE- and TM- polarized light are separated while the TM fundamental mode is also converted into the TE fundamental mode. A design example of the proposed polarization splitter-rotator is given by using silicon-on-insulator nanowires and the total length of the device is less than 100μm. Furthermore, only a one-mask process is needed for the fabrication process, which is compatible with the standard fabrication for the regular photonic integrated circuits based on SOI nanowires.
提出了一种超紧凑型偏振分束-旋转器的新颖概念，该概念利用了绝热锥度和非对称定向耦合器相结合的结构。绝热锥度结构在输入端是单模的，而在另一端变为多模。当光沿绝热锥度结构传播时，由于窄端发射的TM基模与宽端的第一高阶TE模之间的模式耦合，窄端发射的TM基模在宽端被高效地（接近100%）转换为第一高阶TE模。通过使用具有两个相邻芯宽不同的波导的非对称定向耦合器，第一高阶TE模随后被耦合到相邻窄波导的TE基模。另一方面，输入的TE偏振光通过绝热锥度结构时不会改变。在非对称定向耦合器区域，由于相位失配，宽波导中的TE基模不会耦合到相邻的窄波导。通过这种方式，TE偏振光和TM偏振光被分离，同时TM基模也被转换为TE基模。给出了一个使用绝缘体上硅纳米线的所提出的偏振分束-旋转器的设计示例，该器件的总长度小于100μm。此外，制造过程仅需要一个掩膜工艺，这与基于SOI纳米线的常规光子集成电路的标准制造工艺兼容。
