UV-Induced Absorption in All-Fiber Frequency Doublers: Characterization and Photobleaching

Periodic UV exposure of thermally poled optical fibers is usually used to produce efficient all-fiber frequency doublers based on second-order nonlinearity. To date, no data regarding UV-induced absorption in poled fibers have been reported. In this study, we measured this absorption and showed how it affects the conversion efficiency of second harmonic generation at wavelengths below similar to 800 nm. Color centers responsible for induced absorption in poled GeO2-doped fibers were identified and photobleached by continuous-wave radiation at 532 nm. We demonstrated that photobleaching does not affect the value of nonlinearity but improves the conversion efficiency of all-fiber frequency doublers. The results obtained can be used to improve the efficiency of all-fiber second harmonic generation in the blue-green part of the spectrum.