Fig. 1. Layout design and thermal distribution simulation results. (a)(d) I-shaped structure; (b)(e) butterfly-shaped structure and (c)(f) U-shaped structure

Fig. 2. Potential distribution of the U-shaped heating region (the solid line box representing the metal electrode, the ITO heater in the dashed line box and the arrow representing the direction of current I)

Fig. 3. Device fabrication process and characterization. (a) Device fabrication process; (b) microscope characterization; (c) scanning electron microscopy characterization

Fig. 4. In-situ modulation testing system and test results. (a) Schematic diagram of the device testing system, with insets illustrating the fiber array alignment and probe operation details; (b) device test results, normalized transmittance across different operational states (bar chart) and fitted transmittance curve (curve segment)