Design and analysis of nonvolatile GSST-based modulator utilizing engineered Mach-Zehnder structure with graphene heaters

Photonic integrated circuits (PICs) are the foundation of on-chip optical technologies. In these circuits, MachZehnder modulators (MZMs) are versatile building blocks which mostly rely on weak and volatile optical effects in materials. In contrast, phase change materials (PCMs) such as Ge2Sb2Se4Te1 (GSST) are promising candidates to realize efficient and nonvolatile reconfigurable photonic devices. However, the phase transitions of PCMs are also accompanied by large changes in the imaginary parts of their refractive indices which make the design of MZMs challenging. In this paper, two interesting design methods named as "loss-balancing" and "preequalization" are introduced to propose high-performance GSST-based MZMs. In this regard, a GSST-based waveguide with graphene as a microheater is proposed which plays the role of configurable active switch in both the introduced methods. In order to improve the speed and efficiency of the device, a suspended graphene sheet is applied as the heater to excite GSST. According to the presented analysis, a nonvolatile MZM with active length of 4.725 mu m and insertion loss of less than 2 dB at the wavelength of 1550 nm is realizable. Finally, thermal simulation of the proposed GSST-based waveguide is performed to show that the required voltages for amorphization (erasing) and crystallization (writing) processes are 12 V and 4.3 V, respectively.