Nonlinear Optics in a Fiber Laser-Enhancement of Nonlinear Effects

Nonlinear optical phenomena have many applications but since they tend to be weak effects they need to be enhanced by, for example, by using a waveguide with a small cross-sectional area. The strength of the nonlinear optical effects experienced by an optical signal can also be enhanced by modulating its intensity. For example, for a given value of the material properties, the effective Kerr nonlinearity of a signal with a sinusoidal intensity profile is 50 % larger than that of a cw signal with the same average intensity. The reason is that the enhanced nonlinear effects at the peaks of the modulated signal more than make up for reduced nonlinear effects in the valleys. By adding additional harmonic frequencies, the effect can be further enhanced. We have experimentally demonstrated this using a fiber laser that includes a programmable phase mask. We used this device to program specific dispersion profiles that maximize the enhancement. By combining five different frequency components we observed an enhancement of approximately 3.5 for a deeply modulated soliton pulse. I will discuss the underlying theory, the experimental setup, as well as our experimental results, as well as the implications of this work.