Thermo-optically tunable spectral broadening in a nonlinear ultra-silicon-rich nitride Bragg grating

Spectral tunability methods used in optical communications and signal processing leveraging optical,electrical,and acousto-optic effects typically involve spectral truncation that results in energy loss.Here we demonstrate temperature tunable spectral broadening using a nonlinear ultra-silicon-rich nitride device consisting of a 3-mm-long cladding-modulated Bragg grating and a 7-mm-long nonlinear channel waveguide.By operating at frequencies close to the grating band edge,in an apodized Bragg grating,we access strong grating-induced dispersion while maintaining low losses and high transmissivity.We further exploit the redshift in the Bragg grating stopband due to the thermo-optic effect to achieve tunable dispersion,leading to varying degrees of soliton-effect compression and self-phase-modulation-induced spectral broadening.We observe an increase in the bandwidth of the output pulse spectrum from 69 to 106 nm as temperature decreases from 70℃ to 25℃,in good agreement with simulated results using the generalized nonlinear Schrödinger equation.The demonstrated approach provides a new avenue to achieve on-chip laser spectral tuning without loss in pulse energy.