Second-harmonic generation in single-mode and multimode fibers

Abstract
We report efficient second-harmonic generation in several commercially available telecommunication-grade single-mode and multimode optical fibers. We have investigated the effect of standard dopants such as germanium, phosphorous, and fluorine, and find that the efficient second-harmonic generation is associated with germania-related photosensitive color centers. We observed a 1.5% conversion efficiency in single-mode fibers with germanium-, phosphorous-, and fluorine-doped cores and high hydroxyl levels.