Effect of fiber stretch on quasi-phase-matching for second-harmonic generation in thermally poled twin-hole silica-glass fiber

Abstract

Optimization of the quasi-phase-matching (QPM) for second-harmonic generation in thermally-poled twin-hole fiber was performed by stretch of the fiber. The periodic structure for QPM was fabricated by erasure of the second-order nonlinearity by exposure with ultraviolet light through a mask. Exposures with a KrF excimer laser and a low-pressure mercury lamp were compared. The fundamental-wave source was a Q-switched Nd:YAG laser. The dependence of the second-harmonic output on the strain induced by the stretch of the fiber was measured. For periodic depoling by excimer-laser exposure, the second-harmonic power increased by a factor of up to 4 by the stretch. For periodic depoling by mercury-lamp exposure, the maximum increase by the stretch was also by a factor of up to 4. The fiber stretch was effective for fine tuning of QPM for poled fibers.