Abstract
The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of ∼14.8 μm length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by ∼48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m–1 W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such as frequency combs and quantum light sources.
Highlights
The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest
F ollowing recent innovations in integrated optical frequency comb sources and their spectroscopy techniques, breakthroughs have been demonstrated in many fields of study, including precision spectroscopy,[1,2] low-noise frequency synthesis,[3] distance ranging,[4] and quantum light sources.[5]
Two techniques are among the most frequently used for comb generation: the supercontinuum generation (SCG) process in nonlinear fibers or waveguides pumped with femtosecond mode-locked lasers and the four-wave mixing (FWM) process in microresonators pumped with continuouswave lasers
Summary
With the addition of the few-layer WS2 flake, the fwhm of output pulses increased by ∼48.8% at ∼1.35 kW pump power and ∼36.4% at ∼2.7 kW pump power These results translate into a maximum pulse broadening factor of ∼17.5 (WS2 covered waveguide pumped at ∼2.7 kW pulse peak power), the 13 nm wide input pulses broadens to ∼228 nm in the heterogeneous WS2−SiN waveguide of 4 mm total length. The lower effective nonlinear coefficient retrieved at higher pump power is most likely due to the limitation of the broadening effect arising from the stronger linear absorption in WS2 at wavelengths close to 600 nm For both power levels, the TPA coefficient of WS2 that provides the best fitting is ∼158 cm/GW, which agrees with the experimentally measured values of ∼525 ± 205 cm/GW reported in ref 33. GaS-SiN aλ, center wavelength of optical characterizations; Pp, pump peak power; γeff, effective nonlinear coefficient; k, enhancement factor of the effective nonlinear coefficient; α2, retrieved TPA coefficient; Si, silicon
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