Backward frequency doubling of near infrared picosecond pulses

Abstract

We report on backward second-harmonic generation using ps laser pulses in congruent lithium niobate with 3.2 µm periodic poling. Three resonant peaks were measured between 1530 and 1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders in the backward configuration, with a conversion efficiency of 4.75 x 10-5%/W for the 16th order. We could also discriminate the contributions from inverted domains randomized in duty-cycle

Integrated Backward Second-Harmonic Generation Through Optically Induced Quasi-Phase Matching

“…In this work, for the first time, we demonstrate AOP induced first-order QPM gratings with sub-micron periods (Λ BSHG = λ 2|n2ω+nω| see Fig. 1b) enabling BSHG with on-chip conversion efficiency (CE), defined as η 2ω = P 2ω /P 2 ω , of 1.2 × 10 −4 %/W, which in the C-band is comparable with the highest CE value reached in any platform [32]. We achieve this by leveraging the selforganization properties of the optically written gratings, and by seeding the AOP process with counterpropagating coherent pump and SH seed light, bypassing the complex fabrication steps utilized in other platforms.…”

“…As predicted by the theory, we observe that only the nonlinear grating strength changes with changing seeding conditions. The poled waveguides show extremely narrow QPM spectra, highly tunable with temperature, with CE of 1.2 × 10 −4 %/W, comparable to the highest one achieved in C-band so far [32]. We theoretically explain the reduction of efficiencies compared to FSHG due to the screening of electric fields with sub-micron periods.…”

“…As such, while BSHG has been studied theoretically for several configurations [30,31], there have been limited experimental demonstrations. BSHG has been achieved in bulk materials such as periodically poled lithium niobate (PPLN) [32] and potassium titanyl phosphate (KTP) using high-order QPM [33][34][35], or stacked metasurfaces [36] with first-order QPM. There is also a continuous effort to achieve BSHG in integrated photonics.…”

“…There is also a continuous effort to achieve BSHG in integrated photonics. Current demonstrations include using plasmonic structures with negative refractive index materials relying on perfect phase-matching [37,38] as well as PPLN waveguide with higher-order QPM [32].…”

Backward Second-Harmonic Generation in Optically Poled Silicon Nitride Waveguides

“…This opens the possibility to implement novel applications such as mirrorless OPOs [1] or to produce extremely narrow QPM bandwidth, which could be an advantage for the quality of SPDC processes [2]. There have been several candidates for BSHG such as periodically poled lithium niobate (PPLN) [3], stacked metasurfaces [4], and negative index materials [5]. Because of the need for very short QPM periods in order to compensate for large wavevector mismatch (see Fig.…”