Second harmonic generation in thin optical fibers via cladding modes

Abstract

Since silica goes under the category of amorphous materials, it is difficult to investigate important processes such as second harmonic generation (SHG) in silica-based fibers. In this paper, we proposed a method for SHG relaying on cladding modes as pump modes. Cladding modes are introduced in optical fibers through tilted long period grating (T-LPG), where power of core mode is transferred into cladding modes. By functionalizing T-LPG with nonlinear coating, the interaction occurs between cladding modes and the coating material, consequently second harmonic signal (SHS) is generated with efficiency up to 0.14%.

Deep-ultraviolet second-harmonic generation by combined degenerate four-wave mixing and surface nonlinearity polarization in photonic crystal fiber

“…Compared with silicon-based waveguides, the SHG in optical fibers is limited in principle because silica glass as an amorphous material with inversion symmetry does not have second-order nonlinearity. Up to now, several methods, which include poling the optical fibers using the external light or electric fields 17 – 20 and functionalizing the surface of the optical fiber tapers with different nonlinear materials 21 – 24 , were developed to induce second-order nonlinearity in the optical fibers. However, these methods suffer from thermo-instability and long-term instability of the induced second-order nonlinearity susceptibility, the difficulty in fabricating the ideal optical fiber tapers, and the necessity to consider the complex optical properties of the nonlinear materials.…”