Six Bit Optical Phase States Realized in Nonvolatile Phase Shifter Based on N-Doped Sb2Se3

Due to the nonvolatile and large optical contrast of phase-change materials (PCMs), PCM-based optical phase shifters have been considered as a powerful technology for a variety of emerging applications, such as optical switching, optical memory, and neuromorphic computing. However, due to the lack of a phase-change material with low-loss and high optical contrast, the phase modulation space of current PCM-based phase shifters still falls short of meeting the requirements for real-world applications. To address these issues, it is necessary to develop a phase-change material with a high optical contrast to enhance the phase modulation capability of optical phase shifters. In this work, we have designed a new optical PCM by doping Sb2Se3 with the nitrogen element (N), which can improve the optical refractive index of Sb2Se3 from 0.67 to 1.10 and keep its optical loss near 0 at communication bands. By integrated N-doped Sb2Se3 with unbalanced Mach-Zehnder interferometer (MZI), an optical phase shifter with a high phase modulation space is successfully developed and achieves 84 distinct optical phase states (>6 bit). Finally, an artificial neural network (ANN) is established using the optical phase shifter as an optical synapse. The multiwavelength and multistate encoding enabled by this optical phase shifter can not only reduce hardware costs by more than 75%, but also maintain a high image recognition rate (96.67%). This work provides an effective approach for designing PCMs with high phase modulation space, which is significant for constructing high-performance programmable optical phase shifts.