Supercontinuum generation in bandgap engineered, back‐end CMOS compatible silicon rich nitride waveguides

Abstract

CMOS‐compatible nonlinear optics platforms with negligible nonlinear losses and high nonlinearity are of great merit. Silicon, silicon nitride and Hydex glass have made significant headway in nonlinear optical signal processing, though none of these platforms possesses the highly sought after combination of high nonlinearity and negligible nonlinear losses. In this manuscript, we present a nonlinear optics platform based on silicon‐rich nitride, deposited at a low temperature of 250°C compatible with back‐end CMOS processing. The silicon‐rich nitride is designed and engineered in composition to have a bandgap of 2.05 eV, such that the two‐photon absorption edge is well below 1.55 μm. The designed and developed waveguides have a nonlinear parameter of 550 W−1/m, 500 times larger than that in silicon nitride waveguides, while at the same time not possessing two‐photon and free‐carrier losses. Using 500‐fs pulses, we generate supercontinuum exceeding 0.6 of an octave.

Octave-spanning supercontinuum generation in a silicon-rich nitride waveguide

“…This allows thick crack-free film growth in a single deposition step with minimized process complexity. The resulting so-called silicon-rich nitride [12] shows a higher refractive index and an increased material absorption loss than stoichiometric silicon nitride, but this is compensated for by a higher nonlinear Kerr coefficient [13,14].…”

Wideband nonlinear spectral broadening in ultra-short ultra - silicon rich nitride waveguides

“…Waveguides used in this experiment have a length of ∼1 mm. Using the previously measured n 2 value of the film25, the nonlinear parameter for this waveguide is calculated to be ∼550 W −1 /m. This implies a dispersive length ( L D ) of 32 cm and a nonlinear length ( L NL ) of <0.19 mm for peak powers >10 W. Given that the L D is much longer and the L NL is much shorter than the physical waveguide length, the pulse dynamics will be dominated by the nonlinearity rather than dispersion in the waveguide.…”

“…Especially, self-steepening at the trailing edge of the pulse produces optical shock formation29. When loss is assumed to be zero for simplicity, the shock distance z s defined as ∼0.43 L NL / s for hyperbolic secant pulse typical in a fiber laser (Where parameter s = 1/ ω 0 T 0, ω 0  = angular frequency, T 0  =  T FWHM /1.76 for hyperbolic secant pulse, T FWHM  = 500 fs)25. The shock distance, z s at P peak  = 66W is around 4 mm at 1.55 μm, respectively.…”

“…When we consider the third order dispersion (TOD), TOD length, defined as L D ′ =  T 0 3 / β 3 , is ∼0.3 m ( β 3  = 68 ps 3 /km at 1.555 μm)25. L D and L D ′ are about 0.3 m–4 orders of magnitude larger magnitude than L NL and 300 times larger than the waveguide length in USRN_SWG (∼1 mm).…”

Nonlinear Silicon Photonic Signal Processing Devices for Future Optical Networks

“…Moreover, the silicon nitride Kerr coefficient is substantially lower than that in silicon [64] (two orders of magnitude lower), further reducing the strength of the nonlinear effects. Recently, a number of research groups have proposed the use of silicon-enriched silicon nitride compounds, aiming to increase the device nonlinear response [59,[65][66][67][68]. This direction, however, introduces additional losses in the waveguides [66,68], that may compromise their suitability for practical applications.…”