Phase change reconfigurable grating couplers with ultrahigh modulation contrast

Abstract

Silicon photonics has matured over the last decade as a unique platform for highly miniaturized photonic integrated systems seamlessly integrated with electronics allowing the realization and commercialization of highly compact devices with ultrafast data transfer rates and significantly reduced power consumption. Although such submicron scale photonic and waveguide structures enable dense on-chip device integration, they also result in reduced efficiency in fiber-to-waveguide coupling mainly due to increased mode area mismatch. As a result, one of the key challenges faced in current technology platforms has been to efficiently couple light without additional fabrication, post-processing, and complex optical alignment. In-plane grating couplers (GC) have been a widely preferred coupling platform, mainly because of low fabrication costs, ease of alignment and high-level of flexibility in circuit design. A wide range of coupling platform designs have been investigated in the last decade including both passive and active designs. In passive design the coupling efficiency (CE) is fixed once the device is fabricated, however in active designs various tuning mechanism have been explored to modulate the CE, but at the expense of increased power consumption and reduced CE. Using inverse design techniques, we demonstrate CMOS compatible, reconfigurable phase change chalcogenide-on-insulator based apodised GC having maximized CE of more than 50% at λ=1550nm when the phase of the chalcogenide is in amorphous state. When the phase is switched to crystalline state, a near zero CE is shown allowing the design to be both non-volatile and reversibly reconfigurable with highest transmission modulation contrast of more than 50db.