Physics

Pulse compression

Cladding (metalworking)

Laser

Doppler broadening

Resonator

Optics

Astronomy

Spectral width

Metallurgy

Materials science

Grating

Computer science

Fiber Bragg grating

Spectral line

Apodization

Stopband

Optoelectronics

Radar

Telecommunications

Photonics Research

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°C to 25°C, 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.

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