Experimental studies of two sets of four-wave mixing processes in a single-zero-dispersion microstructured fiber by the same pump

Abstract

A highly nonlinear microstructured fiber with single-zero-dispersion wavelength is designed and drawn by reducing the core area in order to observe two groups of four-wave mixing processes by a single pump. The foundational material of the fiber is silica and its cladding is comprised of seven-layer air holes. The air holes are arranged in a hexagonal lattice and the lattice pitch is =2.5 m. The radius of each of the air holes is r=1.03 m. There is just one zero-dispersion wavelength in our considerable wavelength range for the microstructured fiber and the corresponding wavelength D is nearly 0.85 m（D=0.85 m). The basic properties of the fiber including effective refractive index, dispersion coefficient, and nonlinear coefficient are calculated by the finite element method. The effective mode area is 4.4 m2 and the nonlinear coefficient is 0.057 m-1W-1 for the foundation mode near the wavelength of 0.8 m, and the nonlinear coefficient reaches 0.053 m-1W-1 near the zero dispersion wavelength of 0.85 m. In short, the optical fiber has a stable and high nonlinear coefficient in the whole experimental band（0.80-0.83 m), which provides an important guarantee for the occurrence of four-wave mixing double parameter gain process. In addition, the phase mismatch curve is simulated by using the four-wave mixing phase mismatch formulation. Numerical simulation shows that two sets of four-wave mixing processes can occur in the designed fiber. At the normal dispersion wavelengths of 0.800, 0.810 and 0.820 m with different powers, the experimental result shows a significant feature of four gain wavebands located at both sides of the pump wavelength. By comparing experimental data with the phase mismatch curve, we find that the band generation meets four-wave mixing phase matching condition, thus, the simultaneous occurrence of two groups of four-wave mixing processes observed in the experiment is explained in theory. The experimental results are consistent well with the theoretical predictions. This also proves the theoretical predictions that two sets of parametric gain processes and two pairs of signal and idle frequency waves can be generated in PCF. The four-wave mixing effect occurring in the normal dispersion region can be attributed to the contribution of negative fourth-order dispersion to the phase matching process. The present work can provide valuable reference to designing the microstructure fibers and developing the multi-wavelength conversion technology based on four-wave mixing effect. At the same time, this work can also supply guidance for developing the uncommon waveband lasers and broadband light sources.