Up-conversion of optical signals with multi-longitudinal-mode pump lasers

Multi-longitudinal-mode lasers have been believed to be good candidates as pump sources for optical frequency conversion. However, we present a semiclassical model for the frequency conversion of optical signals with a multimode pump laser, which shows that fluctuations of the instantaneous pump power limit the conversion efficiency. In an experiment, we up-converted a 1.55-μm optical signal in a periodically poled lithium niobate waveguide using a multi-longitudinal-mode laser and observed a maximum conversion efficiency of 68%, in good agreement with our theoretical model. Compared to single-mode pumping, multimode pumping is not a suitable technique for attaining stable near-unity-efficiency frequency conversion. However, our results could find application in the characterization of the spectral or temporal structure of multi-longitudinal-mode lasers.