Towards efficient broadband parametric conversion in ultra-long Si3N4 waveguides.

Broadband continuous-wave parametric gain and efficient wavelength conversion is an important functionality to bring on-chip. Recently, meter-long silicon nitride waveguides have been utilized to obtain continuous-traveling-wave parametric gain, establishing the great potential of photonic-integrated-circuit-based parametric amplifiers. However, the effect of spiral structure on the performance and achievable bandwidth of such devices have not yet been studied. In this work, we investigate the efficiency-bandwidth performance in up to 2 meter-long waveguides engineered for broadband operation. Moreover, we analyze the conversion efficiency fluctuations that have been observed in meter-long Si3N4 waveguides and study the use of temperature control to limit the fluctuations.

Polarization selective ultra-broadband wavelength conversion in silicon nitride waveguides.

We experimentally demonstrate broadband degenerate continuous-wave four-wave mixing in long silicon nitride (Si3N4) waveguides for operation both in the telecommunication L-band and the thulium band near 2 µm by leveraging polarization dependence of the waveguide dispersion. Broadband conversion is typically demonstrated in short milimeter long waveguides as the bandwidth is linked to the interaction length. This makes it challenging to simultaneously push bandwidth and efficiency, imposing stringent constraints on dispersion engineering. In this work, we show conversion bandwidths larger than 150 nm in the L-band when pumping in the transverse magnetic (TM) mode and larger than 120 nm at 2 µm when using transverse electric excitation, despite the use of 0.5 m long waveguides. In addition, we also show how extreme polarization selectivity can be leveraged in a single waveguide to enable switchable distant phase-matching based on higher-order dispersion. Relying on this approach, we demonstrate the selective conversion of light from the telecom band to the O-band for TM polarization or to the mid-infrared light up to 2.5 µm in TE. Our experiments are in excellent agreement with simulations, showing the high potential of the platform for broadband and distant conversion beyond the telecom band.

Strain Engineering of Germanium Nanobeams by Electrostatic Actuation.

Germanium (Ge) is a promising material for the development of a light source compatible with the silicon microfabrication technology, even though it is an indirect-bandgap material in its bulk form. Among various techniques suggested to boost the light emission efficiency of Ge, the strain induction is capable of providing the wavelength tunability if the strain is applied via an external force. Here, we introduce a method to control the amount of the axial strain, and therefore the emission wavelength, on a suspended Ge nanobeam by an applied voltage. We demonstrate, based on mechanical and electrical simulations, that axial strains over 4% can be achieved without experiencing any mechanical and/or electrical failure. We also show that the non-uniform strain distribution on the Ge nanobeam as a result of the applied voltage enhances light emission over 6 folds as compared to a Ge nanobeam with a uniform strain distribution. We anticipate that electrostatic actuation of Ge nanobeams provides a suitable platform for the realization of the on-chip tunable-wavelength infrared light sources that can be monolithically integrated on Si chips.