Nonlinear optics on silicon-rich nitride--a high nonlinear figure of merit CMOS platform[Invited]

CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition,silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters(5 x–500 x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.

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.