Fig. 3

Fabricated RAFT spectrometer. a False-colored optical micrography of a RAFT spectrometer after Ge epitaxy growth for PD. b SEM image of an MRR without SiO₂ upper cladding. c SEM image of a tunable MRR with isolation trenches and TiN heater. d Optical micrography of a waveguide-coupled Ge-on-SOI photodetector