  Bragg gratings offer high-performance filtering and routing of light on-chip
through a periodic modulation of a waveguide's effective refractive index.
Here, we model and experimentally demonstrate the use of Sb2Se3, a nonvolatile
and transparent phase-change material, to tune the resonance conditions in two
devices which leverage periodic Bragg gratings: a stopband filter and
Fabry-Perot cavity. Through simulations, we show that similar refractive
indices between silicon and amorphous Sb2Se3 can be used to induce broadband
transparency, while the crystalline state can enhance the index contrast in
these Bragg devices. Our experimental results show the promise and limitations
of this design approach and highlight specific fabrication challenges which
need to be addressed in future implementations.
