Self-Organization in Optical Fibers for Efficient Phase-Matching of Harmonic Generation.

We propose a mechanism in which a phase-matched second-order nonlinearity can be photo-induced in an optical fiber. The process is self-organizing in the sense that the third-order mixing of pump and sum-frequency waves that makes the second- order nonlinearity dipole-allowed also provides the alternation of sign along the fiber length needed for phase-matching. This mechanism is supported by experiments in which a second- order nonlinearity builds up in a few minutes by seeding a single-mode fiber with the 532 nm second-harmonic along with a 1.06micron pump wave.