Characterization of Integrated Planar Photonic Crystal Circuits Fabricated by a CMOS Foundry

Integrated planar photonic crystal circuits in silicon on insulator were fabricated with a single-etch-step process by a foundry using complementary metal-oxide-semiconductor processing techniques. The devices studied integrate three key elements: i) input/output grating couplers consisting of 2D uniform arrays of holes, ii) single transverse electric (TE)/single transverse magnetic (TM) mode channel waveguides, and iii) a photonic crystal linear three hole defect (L3) microcavity. Experimentally measured s- and p-polarized transmission, both from grating-to-grating through a uniform silicon slab region, and through the channel waveguide/L3 cavity circuit, were quantitatively compared with finite-difference time-domain simulations. Excellent agreement is achieved assuming circular, vertical side-wall holes, but this requires accurate post-fabrication characterization of actual versus nominal device parameters, including especially the silicon device layer thickness. While s-polarized incident radiation excites TE modes that exhibit typical resonant cavity (filter-like) transmission, p-polarized incident radiation excites TM modes that non-resonantly propagate through the circuit with comparable transmission efficiency. The dependence of the grating coupler tuning range on hole diameter, and the addition of a photoresist covering is determined.