Maximizing the FWM conversion efficiency in a PCF with a randomly varying pitch

We theoretically investigate the generation of visible light using four-wave mixing (FWM) in photonic crystal fibers (PCFs), whose input is produced by a high-power continuous wave (CW) or quasi-CW fiber laser. We analyze the impact on the conversion efficiency of the randomly varying pitch along the fiber, which in turn leads to variations of the FWM wavelength. We show that the conversion efficiency is maximized when the mean pitch and hole diameters are chosen so that the derivative of the FWM wavelength with respect to the pitch is zero. We then use this criterion to determine the maximum conversion efficiency over a wavelength range of 650–850 nm with a pump at 1064 nm.