Fig. 1. The working principle and schematic of the mapping setup.

a After passing through the single-mode fiber and grating coupler, the probe light is coupled into the silicon microdisk via evanescent coupling from the Si waveguide. b When a 420 nm nanosecond laser is focused onto the top surface of the microdisk, local refractive index changes (∆n₁ and ∆n₂ resulted from FCA and thermal effect, respectively) induce the shifting of the resonance frequencies. For a fixed probe wavelength, the shifts of resonances lead to two opposite changes of transmittance ∆T₁(x, y) and ∆T₂(x, y) that can be measured at the output port