I. Introduction
IN FUTURE optical networks, it is expected that picosecond return-to-zero pulse sources (RZ-PS) tunable in wave-length, with a single or multiwavelength output, are needed in order to increase the capacity. Some schemes that fulfill these requirements are, e.g., mode locking [1] or ring structures [2]. For upgrading an existing RZ-PS with a fixed wavelength to a wavelength-tunable pulse source (WTPS), one suggested method is using the RZ-PS as the pump in super-continuum spectral slicing [3]. In this letter, a novel approach for upgrading to a WTPS is proposed. It is based on the parametric process in a newly developed highly nonlinear fiber (HNLF) between a RZ-PS signal at a fixed wavelength and a continuous wave (CW) probe tunable in wavelength. The FWM product at the output of the HNLF is a replica of the RZ-PS signal, and can be tuned in wavelength by tuning the wavelength of the CW probe. When the RZ-PS signal acts as the pump in a four-wave mixing (FWM) process, the WTPS can be expanded to a multiwavelength WTPS by launching several CW probes at different wavelengths into the HNLF.
(a) experimental setup of wavelength-tunable pulse source (wtps). gs-dfb: gain-switched distributed feedback laser. cw: continuous wave. edfa: erbium-doped fiber amplifier. obf: optical bandpass filter. pc: polarization controller. (b) spectrum of input signals to highly nonlinear fiber (hnlf). (c) output spectrum from hnlf.