Phase change material integrated silicon photonics: GST and beyond

The traditional ways of tuning a Silicon photonic network are mainly based on the thermal-optic effect or the free carrier effect of silicon. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Δn<0.01). In order to achieve low energy consumption and smaller footprint for applications such as photonic memories or computing, it is essential that the two optical states of the system exhibit high optical contrast and remain non-volatile. Phase change materials (PCMs) such as GST provide a solution in that it exhibits drastic contrast in refractive index between the two non-volatile crystallographic states which can be switched reversibly. Here, we first show that GST can be integrated with a Si ring resonator to demonstrate a quasi-continuous optical switch with extinction ratio as high as 33dB. Secondly, we demonstrated GST-integrated 1×2 and 2×2 Si photonic switches using a three-waveguide coupler design which exhibits a low insertion loss of ~1dB and a compact coupling length of ~30μm. The crosstalk is as small as -10dB over a bandwidth of 30nm. Lastly, we explore the potential of two emerging PCMs Sb2S3 and GeSe for extreme low loss operation of reconfigurable photonic integrated circuit (PIC).