Studies on Wavelength Selective Filter and Light Source for Wavelength Division Multiplexing Utilizing the Third-Order Nonlinear Effect in Optical Fibers

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1. When a fiber directional coupler that is fabricated by fusing and elongating two single-mode fibers is excited with an intense laser light, an intensity dependent index of refraction is induced due to an optical Kerr effect and it modifies the linear coupling characteristics of the coupler. An abrupt change of power transmission at coupled and through ports in the coupler can be observed at a certain wavelength of incident light and it was found that the critical wavelength is shifted to a longer wavelength as the incident power increases. The experimental verification using a mode-locked Ti : sapphire laser that produces approximately 50 femtosecond pulses at wavelengths of 800-850nm with a repetition rate of 80MHz is followed by the theory. Although some discrepancies exist between theoretical calculations and experimental results, all-optical switching of the femtosecond pulses was confirmed in a nonlinear directional fiber coupler.2. The supercontinuum (SC) generation in optical … More fibers is attractive for high-condensed wavelength-division (or frequency-division) multiplexing system since it provides short optical pulses over a broad spectrum range. In this study, some computer simulations are carried out for the SC spectrum from adispersion-flattened fiber with group velocity dispersion varied along the axis. Taking into account of higher-order dispersion effects (the third, fourth, and fifth-order ones), higher-order nonlinear effects (self-steepening and stimulated Raman scattering (SRS) effects), and wavelength dependent losses, we concluded that ( i )a dispersion-decreasing fiber with group velocity dispersion being convex of the wavelength at two zero-dispersion wavelengths as well as ( ii )a fiber having an increasing nonlinear effect (or equivalently, decreasing effective core area) along the axis, and for an incident pulse (iii)the excitation of higher-order soliton that accompanies a higher peak power of optical pulses are desirable for efficient SC generation. Less