Highly Nonlinear Fibers in All-Optical Modulators

We demonstrate the advantages of using a Highly Nonlinear Fiber (HNLF) in an all-optical modulator based on a nonlinear optical loop minor (NOLM). The use of a HNLF allows for a compact design, since a low pump power and a relatively short length of fiber are required in order to obtain optimal switching conditions for the NOLM. Furthermore, the low dispersion and dispersion-flattened features of the HNLF offer increased flexibility for operating the modulator since walk-off effects between the pump and the signal are significantly reduced. The modulator was incorporated in a tunable mode-locked semiconductor fiber laser (SFL) and its performance was evaluated under different operating conditions. The output characteristics of the SFL are sustained regardless of the wavelength and duty cycle of the pump signal. The same laser configuration also allows for clock recovery of input signals, independently of the signal wavelength.