Engineering wavelength conversion span in cascaded broadband Cherenkov radiation

Abstract

Summary form only given. Optical Cherenkov radiation (OCR) is referred to as dispersive wave (DW) generation or non-solitonic radiation originating from soliton propagation perturbed by high order dispersion (HOD). The OCR becomes of particular importance for octave-spanning spectral broadening and blue-shifted supercontinuum generation (SCG) [1]. When the OCR generation lies in the anomalous GVD region and tends to be a soliton state, the phase-matching (PM) condition between linear DWs and the soliton could become a soliton PM condition: β<;sub>s<;/sub>(ω<;sub>s<;/sub>) = β<;sub>s<;/sub>(ω<;sub>r<;/sub>), provided that v<;sub>g<;/sub>(ω<;sub>s<;/sub>) = v<;sub>g<;/sub>(ω<;sub>r<;/sub>). β<;sub>s<;/sub>(ω<;sub>k<;/sub>) ≡ β(ω<;sub>k<;/sub>) + (ω-ω<;sub>k<;/sub>)/v<;sub>g<;/sub>(ω<;sub>k<;/sub>) + q<;sub>k<;/sub> reflects the nondispersive nature of the soliton at the center frequency ω<;sub>k<;/sub> and v<;sub>g<;/sub>(ω<;sub>k<;/sub>) is the group velocity. k = r, s represents the radiation or soliton wave. A sharp spectral switching of the soliton due to the soliton spectral tunneling (SST) effect in the photonic crystal fibers (PCFs) can occur across a normal group velocity dispersion (GVD) region, which is sandwiched in the anomalous GVD regions [2]. This approach shows a new efficient wavelength conversion scheme, and we explore the cascaded OCR to enlarge the span of the wavelength conversion.We show the flexible dispersion profiles with three controlled ZDWs, λ1 <; λ2 <; λ3, as shown in Fig. 1(a), by tuning the pitch Δ and the relative hole size D = d/Δ in PCFs. λ2 and λ3 shift to longer wavelengths as the increase of D. Three anomalous GVD regions separated normal GVD are formed. Fig. 1(b) shows the predicted PM wavelength versus soliton wavelength when the input pulse has a full width at half-maximum (FWHM) of 50 fs and the soliton number N = 1. The soliton PM condition is satisfied at a so-called critical point (CP), where two radiation bands are degenerate. Two different CPs are chosen to make soliton spectral tunneling in two-segment PCFs.