Mid-IR non-volatile silicon photonic switches using nanoscale Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} embedded in SOI waveguide

Abstract: We propose and numerically analyze the hybrid Si-Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} strip waveguide switches for Mid-IR wavelength of 2.1 $\mu$m. The switches investigated are one input-one output (on-off) type and one input-two outputs (directional coupler) type. The reversible transition between the switch states is achieved by inducing the phase transition from crystalline to amorphous and vice-versa by application of voltage pulses. The approach of embedding the nanoscale active material Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} 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 case of one input-one output switch, an extinction ratio of 33.79 dB along with an extremely low insertion loss of 0.52 dB is achieved using optimum Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} length of only 0.92 $\mu$m. For one input-two outputs switch, an extinction ratio of 10.33 dB and 5.23 dB is obtained in cross and bar state respectively using an active length of 52 $\mu$m. 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 Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} to facilitate the electrical conduction needed for Joule heating. A suitable gap of 100 nm is kept between the active and passive arm of the directional coupler switch. The electro-thermal co-simulations confirm that phase change occurs in whole of the Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} region in both types of switches.