Highly efficient broadband second harmonic generation mediated by mode hybridization and nonlinearity patterning in compact fiber-integrated lithium niobate nano-waveguides

Abstract

The inherent trade-off between efficiency and bandwidth of three-wave mixing processes in χ2 nonlinear waveguides is the major impediment for scaling down many well-established frequency conversion schemes onto the level of integrated photonic circuit. Here, we show that hybridization between modes of a silica microfiber and a LiNbO3 nanowaveguide, amalgamated with laminar χ2 patterning, offers an elegant approach for engineering broadband phase matching and high efficiency of three-wave mixing processes in an ultra-compact and natively fiber-integrated setup. We demonstrate exceptionally high normalized second harmonic generation (SHG) efficiency of up to ηnor ≈ 460% W−1 cm−2, combined with a large phase matching bandwidth of Δλ ≈ 100 nm (bandwidth-length product of Δλ · L ≈ 5 μm2) near the telecom bands, and extraordinary adjustment flexibility.

Temporal quadratic solitons and their interaction with dispersive waves in lithium niobate nanowaveguides

“…2(e). More details about this structure can be found in previous work [14,15,22]. Figure 2(d) shows simulated n eff data for FF and SH modes in this waveguide.…”

“…The small mode size in these nanowaveguides enhances nonlinearity [11], therefore reducing required peak powers to achieve efficient nonlinear interactions. Their strong guidance also provides geometrically tuneable dispersion allowing direct phase matching between modes [13,14], as well as considerable reduction of group velocity mismatch between FF and SH modes within wide frequency ranges [15]. Continued research has seen the loss in these structures fall as low as 0.027 dB/cm [16], further improving the prospects of these structures for practical application.…”

Fano Resonance on Nanostructured Lithium Niobate for Highly Efficient and Tunable Second Harmonic Generation

“…As for the choice of material, lithium niobate (LN) is a biocompatible material which has a large second-order nonlinearity (the largest one is d 33 = 27 pm/V at 1550 nm) [16,17,18]. Even though it shows slightly weaker nonlinear properties than some semiconductor materials, it has a wide transparency spectral range spanning visible to infrared light (0.42–5 μm).…”

Fabrication and Characteristics of Heavily Fe-Doped LiNbO3/Si Heterojunction

“…As a strong contender for "optical silicon", LN is applied for optical waveguides, electro-optical modulation, holographic storage, optical parametric oscillators, etc. [3,4,5,6,7,8]. However, LN is generally considered to be an insulator, and acts as a passive component in the above applications [9].…”