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

•Second-harmonic generation (SHG) in thermally-poled silica fiber was studied.•Quasi-phase-matching (QPM) was performed by periodic depoling with UV exposure.•Exposures with an excimer laser and a mercury lamp were compared.•Optimization of the QPM was performed by stretch of the fiber.•Increase in the SH power by a factor of up to 4 was obtained by fiber stretch.

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.