Mid-infrared non-volatile silicon photonic switches using nanoscale GeSbTe embedded in silicon-on-insulator waveguides.

We propose and numerically analyze hybrid Si-GeSbTe strip waveguide switches for the mid-infrared wavelength of 2.1 μm. The switches investigated are of one input-one output (on-off) and one input-two outputs (directional coupler) types. The reversible transition between the switch states is achieved by inducing phase transition from crystalline to amorphous and vice-versa by application of voltage pulses. The approach of embedding the nanoscale active material GeSbTe within the Si waveguide is taken to enhance the interaction of light with the active region of the switches. The dimensions of the active regions of the switches are optimized to achieve low insertion loss, low switching energy and high extinction ratio. In the case of the on-off switch, an extinction ratio of 33.79 dB along with an extremely low insertion loss of 0.52 dB is achieved using an optimum GeSbTe length of only 0.92 μm. For the directional coupler switch, an extinction ratio of 10.33 dB and 5.23 dB is obtained in the cross and bar states respectively using an active length of 52 μm. These values of extinction ratio, which are otherwise 18.59 dB and 8.33 dB respectively, are due to the necessity of doping the Si beneath the GeSbTe to facilitate the electrical conduction needed for Joule heating. A suitable gap of 100 nm is maintained between the active and passive arm of the directional coupler switch. Electro-thermal co-simulations confirm that phase change occurs in the whole of the GeSbTe region in both types of switches.