Ultrasmall Si-nanowire-based polarization rotator

A polarization rotator based on asymmetrical Si nanowires is presented and optimized for high polarization rotation efficiency (almost 100%). The present polarization rotator has a very small conversion length $(\sim 10\mathrm{\mu }\mathrm{m})$ and consequently becomes very compact. The analysis of the wavelength dependence shows the present polarization rotator has a broad bandwidth $(\sim 120\mathrm{nm})$ for high conversion efficiency $(>97\%)$. The tolerance to various fabrication errors is also numerically studied. To compensate the fabrication error, a postcompensation method is introduced by modifying the refractive index of the up-cladding.