Width-modulation of Si photonic wires for quasi-phase-matching of four-wave-mixing: experimental and theoretical demonstration

Abstract

We experimentally demonstrate quasi-phase-matched (QPM) four-wave-mixing (FWM) in silicon (Si) nanowire waveguides with sinusoidally modulated width. We perform discrete wavelength conversion over 250 nm, and observe 12 dB conversion efficiency (CE) enhancement for targeted wavelengths more than 100 nm away from the edge of the 3-dB conversion bandwidth. The QPM process in Si nanowires is rigorously modeled, with results explaining experimental observations. The model is further used to investigate the dependence of the CE on key device parameters, and to introduce devices that facilitate wavelength conversion between the C-band and mid-IR. Devices based on a superposition of sinusoidal gratings are investigated theoretically, and are shown to provide CE enhancement over the entire C-band. Width-modulation is further shown to be compatible with zero-dispersion-wavelength pumping for broadband wavelength conversion. The results indicate that QPM via width-modulation is an effective technique for extending the spectral domain of efficient FWM in Si waveguides.

Coupling-length phase matching for nonlinear optical frequency conversion in parallel waveguides

“…The most common implementation of such a "quasi-phase-matching" scheme involves spatial changes of the nonlinear optical response [1,2], as can be obtained, for instance, by periodically poling ferroelectric nonlinear crystals. Alternative approaches involve the modulation of the geometry of a nonlinear waveguide in order to spatially modulate the effective refractive index or the propagation constant of the interacting waves [3][4][5][6].…”

Broadband and efficient wavelength conversion in a slot-width switching silicon–organic hybrid waveguide

“…In addition, the SWS waveguide length is much shorter than that of width-modulated SOI waveguide that reported in [11] and [12], which is 15 mm. This is especially beneficial for the photonic integration.…”

“…For this reason, the idler and signal power will periodically convert back to the pump along the waveguide. Therefore, in recent years, people vary the dimensions of the waveguide periodically along the propagation path to achieve quasi-phase-matching (QPM) [11][12][13]. A recent breakthrough paper in Science shows that by modulating the width of an optical fibre can also keep the phase-matching [14].…”

Quasi-phase-matched χ(3) -parametric interactions in sinusoidally tapered waveguides

“…Alternatively, these estimated tapering periods could be realised sooner using other waveguide platforms such as laser-written and planar waveguides [33,34], which are more promising techniques and will be considered in future investigations as potential candidates for experimental demonstration. In fact, width-modulated sinusoidal tapering with 1 mm tapering period has been demonstrated in high-nonlinear rectangular silicon nanowires over 5-mm long using e-beam lithography [25]. Also in these platforms, temperature-tuning effect [35,36] can be utilised to correct any phase-mismatching introduced by fabrication tolerance via integrating thermo-optic switches.…”

“…This technique is currently hurdled by fabrication methods that limits the tapering period to the millimetre and sub-millimetre range in silicon nanowires [25]. Also, a careful analysis is essential to understand how simultaneous longitudinal variations of both linear and nonlinear properties of the waveguide modifies the well-known QPM condition in periodically-poled structures.…”