Periodically erasing the second-order optical nonlinearity in thermally poled optical fibers with UV light

Abstract

In the paper, we report experimental results of the effect of UV-light exposure on the profile of thermal poling induced second-order optical nonlinearity (SON) in twin-hole optical fibers. Before UV-exposure, uniform thermal poling at 320°C and 3.5 kV along a 5-7 cm long section of twin-hole fiber produced a uniform SON of 0.263 pm/V in the fiber core. A focused light beam from a frequency-doubled Ar+ laser operating at 244 nm was used to locally erase the induced nonlinearity in the fibers to create a periodic structure for quasi-phase matching applications. The UV-exposed fibers were then observed under a second-harmonic microscope to characterize the distribution profile of any residual nonlinearity after exposure. Effects of scanning speeds of the laser beam on the length of nonlinearity-erased section and amplitude of the residual nonlinearity were investigated. It was found that the required UV-light fluence to fully erase the induced nonlinearity is only ~0.5% of that typically required for fabricating fiber Bragg gratings.