Selective engineering of cavity resonance for frequency matching in optical parametric processes

Abstract

We propose to selectively engineer a single cavity resonance to achieve frequency matching for optical parametric processes in high-Q microresonators. For this purpose, we demonstrate an approach, selective mode splitting (SMS), to precisely shift a targeted cavity resonance, while leaving other cavity modes intact. We apply SMS to achieve efficient parametric generation via four-wave mixing in high-Q silicon microresonators. The proposed approach is of great potential for broad applications in integrated nonlinear photonics.Optical parametric processes, including four-wave mixing (FWM), second-/third-harmonic generation (SHG/THG), parametric down-conversion (PDC), etc., have broad applications ranging from photonic signal processing 1,2 , tunable coherent radiation 3 , frequency metrology 4 , to quantum information processing 5 . In recent years, there has been increasing interest in optical parametric processes in high-Q micro-/nano-cavities, which exhibit great potential for dramatically enhancing parametric generation [6][7][8][9][10][11][12][13][14][15][16][17][18][19] . However, their efficiencies rely crucially on frequency matching among the interacting cavity modes, which is generally deteriorated by device dispersion. Frequency matching is particularly challenging in high-Q cavities, due to the narrow linewidths of cavity resonances.To date, a variety of methods have been proposed for frequency matching. For FWM, a χ (3) nonlinear process, current methods primarily focus on engineering groupvelocity dispersion of the devices 7,8,10,13,14,20 . For SHG, a χ (2) nonlinear process, intermodal dispersion or birefringence is generally employed to mitigate the frequency mismatch 11,12,[15][16][17][18][19] . These methods rely on manipulating material/waveguide dispersion of devices, which collectively shifts the resonance frequencies of all cavity modes by different extents.In this paper, we propose and demonstrate an effective approach for frequency matching that can be applied universally to optical parametric processes. Instead of modifying all cavity resonances via dispersion engineering, we directly shift a single cavity resonance to a desired frequency, while leaving other cavity modes intact. This is realized by splitting the targeted cavity mode at ω m into two modes at new frequencies ω m ± β m . By controlling the magnitude of splitting, one resonance can be shifted to coincide with the desired frequency ( Fig. 1(a)). We term this approach selective mode splitting (SMS).SMS can be applied to various χ (2) /χ (3) processes ( Fig. 1(b-d)). For example, degenerate FWM requires three interacting cavity modes to be equally spaced in a) Electronic mail: qiang.lin@rochester.edu. frequency, ω signal −ω pump = ω pump −ω idler , which is often not satisfied due to device dispersion. The problem can be solved by shifting one cavity mode to the desired frequency, thus enabling parametric generation ( Fig. 1(b)). SMS is particularly useful for nonlinear processes including SHG/THG and PDC ( Fig. 1(c)(d)), where ...

Normal‐dispersion microcombs enabled by controllable mode interactions

“…The use of coupled microresonators for improving the phase matching conditions for efficient four‐wave mixing and parametric oscillation has been analyzed and demonstrated . The introduction of periodic perturbations to a waveguide, thus creating coupling between contra‐directional modes, has also been demonstrated for this purpose . With respect to microcomb generation, the possibility of reducing the pump threshold with the aid of coupled microresonators has been studied via simulation .…”

Critical couplings in topological-insulator waveguide-resonator systems observed in elastic waves

“…Obviously, they can no longer be regarded as a superposition of two independent circulating modes with spin +½ and spin −½ around the cavity boundary. Their appearance is essentially due to the inevitable reduced geometric symmetry of the closed TI cavity boundary loop (see the theoretical deduction in Supplementary Note I), also observed in non-TI systems [ 52 , 53 ], and the final form of their presentation is indeed spilt SWMs [ 45–48 ], which have been systematically studied in optical microcavities, especially for sensing. When the TI cavity operates at these nondegenerate frequencies, the cavity should be treated as a whole instead of a closed loop, supporting only the collective resonance of the standing wave throughout its region.…”

Stretching the spectra of Kerr frequency combs with self-adaptive boundary silicon waveguides

“…This enables the periodic structure to operate as a homogeneous material [58][59][60] in which the frequency-wavevector curve is much less dispersive than those near the band edge. Despite the fact that photonic bandgap effects from this periodic structure do not spoil the predicted dispersion and the overall validity of the proposed design, previous studies 61,62 have indicated that splitting of some resonant peaks can be observed under a certain grating phase condition. However, this high-order grating effect is much slighter than the first one and is not included in our discussion.…”