Phase-matched second-harmonic generation of infrared wavelengths in optical fibers

Abstract

Second harmonic generation in optical fibers through the self written grating or external seeding process has been so far limited to fundamental wavelengths not much longer than 1 micron. However, it is shown in this paper that fibers prepared at the sensitive wavelengths are also phase matched at longer wavelengths but for different mode combinations. By judicious choice of the fiber parameters, phase matching at any wavelength is possible. It is also shown that a set of fundamental and second harmonic modes which are phase matched through mode dispersion at some arbitrary wavelength, (lambda) , are also phase-matched at wavelengths on either side of (lambda) . Internally written grating-phase-matching is thus possible in these fibers for the same set of modes at longer wavelengths. It is also possible to design a fiber so that the frequency doubling bandwidth characteristics at the long wavelength is the same or better than the preparation wavelength; in particular broadband frequency doubling is possible under certain conditions.