Analysis of a tunable CMOS-compatible multilayer waveguide structure for dual polarizer-modulator operation

A multilayer structure using graphene on a silicon waveguide is introduced and optimized to operate as a tunable TE-pass polarizer at 1310 nm or 1550 nm, a tunable TE/TM modulator at 1310 nm or 1550 nm, and a dual operation as a modulator at 1310 nm and a polarizer at 1550 nm. Analysis and optimization are based on the waveguide structure modal loss, geometry, and the 2D graphene layer optical properties dependency on the applied chemical potential. The polarizer tunability at 1310 nm or 1550 nm is attainable setting the applied chemical potential range from 0.55–0.65 eV or 0.45–0.55 eV, respectively. For the modulator tunability at 1310 nm or 1550 nm, the applied chemical potential ranges from 0.45–0.55 eV or 0.35–0.45 eV, respectively. The optimized waveguide silicon layer around 210 nm guarantees an extinction ratio better than 0.056 dB/µm for the polarizer and better than 0.045/0.133 dB/µm for the TE/TM modulator at 1310 nm, and better than 0.034 dB/µm for polarizer and better than 0.053/0.137 dB/µm for TE/TM modulator at 1550 nm. The dual polarizer-modulator operation, e.g., a modulator operating at 1310 nm and a polarizer operating at 1550 nm, is attained at the 0.45–0.55 chemical potential range with an extinction ratio better than 0.045 dB/µm and 0.034 dB/µm, respectively. Compared with other similar devices, the advantage of the structure relies on its versatility to operate as both modulator and polarizer, at different wavelengths, via a proper choice of applied chemical potential, with an insertion loss lower than 0.007 dB/µm.