Second harmonic generation in single-mode and multimode fibers.

Abstract

It is reported that second-harmonic generation in glass fibers is much more prevalent than previously thought and that neither the single-mode operation nor phosphorous doping is essential for the second-harmonic generation. Efficient second-harmonic generation has been observed in several fibers prepared by exposing them to both the fundamental and its second harmonic. In particular, results reported on include: (1) efficient second-harmonic generation in phosphorous-free single-mode fibers with germanium-doped core and pure silica cladding; (2) second-harmonic generation in high-numerical-aperture graded-index multimode fibers; and (3) second-harmonic generation is not observed in pure silica core fibers with fluorine-doped cladding. The physical process involved in the second-harmonic generation remains unexplained.