Fig. 2. A Mach-Zehnder interferometer with both arms covered with 20-nm-thick Sb₂S₃.

a Sb₂S₃ phase shifter schematic (the encapsulation ALD Al₂O₃ layer is not shown). b Optical and (c) SEM images of the Sb₂S₃ phase shifter. d Optical micrograph of the 50:50 splitting ratio multi-mode interferometer. e, f Transmission spectra at both bar and cross ports for (e) a-Sb₂S₃ (RESET: an 8.1 V, 150 ns, 197 nJ pulse) and (f) c-Sb₂S₃ (SET: two 1.7 V, 200 ms, 12 mJ pulses). The green and red lines represent the measured transmission at cross and bar ports. The shaded region indicates the standard deviation of transmission for 5 cycles of measurements.