Silicon-Based 2-D Slab Photonic Crystal TM Polarizer at Telecommunication Wavelength

We report an extremely compact (15.4 $\mu$ m $\times$ 8 $\mu$m) silicon-based 2-D slab nano photonic crystal (PC) transverse-magnetic (TM) polarizer which blocks propagation of the transverse-electric (TE) polarized light but passes TM polarized light around telecommunication wavelength (1550 nm). The TE polarized light totally vanishes but the TM polarized light propagates with some attenuation in a length of mere 4.9 $\mu$m and it has a great potential to be integrated in a complex photonic integrated circuits. To our knowledge, this is the first experimental demonstration of a silicon-based PC TM polarizer at 1.55-$\mu$m wavelength. The plane wave expansion method (PWEM) and 2-D and 3-D finite-difference time-domain (FDTD) simulation were utilized to design a periodic triangular array of air holes in 340-nm-thick silicon with a diameter of 170 nm and pitch distance of 347 nm for the TM polarizer and 371 nm for the input and output waveguide. Such a PC TM polarizer was fabricated in silicon-on-insulator wafer using focused ion beam and reactive ion etching. The device was characterized using tunable lasers in the wavelength range of 1528 nm $\sim$ 1604 nm. Transmitted light intensities of the TE and TM polarized lights were measured which clearly showed the TE polarized light is filtered out around 1.55-$\mu$m wavelength.