Multichannel mode selective silicon photonic add/drop multiplexer with phase change material
A multichannel mode selective silicon photonic add/drop multiplexer is proposed by introducing asymmetric directional couplers (ADCs) assisted with phase change material (PCM) strips. Each ADC consists of a multimode bus waveguide and a single mode access waveguide with a thin PCM strip on the top. For the present mode selective add/drop multiplexer, the PCM of Ge2Sb2Se4Te1 (GSST) is used, and the PCM loaded access waveguide is designed optimally by engineering the effective index and the modal field profile. When the switching state of the add/drop multiplexer is OFF with crystal GSST, all the mode channels go through with very low excess losses. Otherwise, when it is ON, by switching the GSST PCM strip to be amorphous, the desired TE mode channel can be selectively added to or dropped from the multimode bus waveguide, while the other mode channels still stay and propagate in the multimode bus waveguide. The simulated results show that the designed mode selective silicon photonic add/drop multiplexer utilizing a single ADC has low excess losses of <0.5dB and low intermodal crosstalk of 15dB over the C band for all the mode channels. Furthermore, using the design with cascaded ADCs for each mode selective add/drop switch, the crosstalk can be suppressed to 20dB, and the excess losses are less than 1 dB over an 80 nm broad wavelength band from 1505 to 1585 nm.