Compact and ultra-broadband all-silicon TM-pass and TE-reflected polarizer using grating based weakly coupled nanowires.

On-chip silicon polarizers with broad operating bandwidth and compact footprint have recently attracted increasing attention for their applications in large capacity and high density integrated optical systems. However, strong waveguide dispersion usually limits the bandwidth of the silicon polarizers, especially for the TM-pass polarizers. In this paper, we overcome the bandwidth limit of the TM polarizer by utilizing a novel waveguide structure composed of two weakly coupled nanowires with gratings sandwiched in between. Such a structure can effectively enlarge the bandgap for the undesired TE polarized light, while act as a low loss subwavelength metamaterial for TM polarized light over an extremely large wavelength range. In simulation, we obtain a compact polarizer of 13.6 µm × 1.3 µm in size with an ultra-broad operating bandwidth of ∼362 nm for extinction ratios (ERs) >21 dB and insertion losses (ILs) <1 dB, which covers E-, S-, C-, L-, and U-bands and part of O-band. The measurements of fabricated devices show that the device performed well in the test wavelength range from 1300 to 1600 nm with an ER >15 dB and an average IL ∼1 dB, consistent with the simulation results. This work paves a new way for designing compact and ultra-broadband on-chip polarizers.