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We have observed the second harmonic generation from a single crystal LiNbO3 fiber with a diameter of 63 μm. Femtosecond laser pulses form a modelocked oscillator was focused perpendicularly onto the fiber. Scattered second harmonic was analyzed in polarization and the conversion efficiency was estimated. Comparing to a bulk nonlinear crystal, the striking feature of the SHG from the microcylinder is that the nonlinear conversion takes place out off phase-matching condition. For the fundamental at 850 nm the phase-mismatching is negative, even so, a relative important conversion efficiency of 3.7 × 10 -4 was obtained for incident 1.1-nJ and 150-fs pulses (peak intensity of 1.0 x 10 9 W/cm 2 ) This conversion efficiency, independent to the phase matching, should not exhibit the sharp variation as for a bulk crystal when the incident fundamental is tuned across the phase-matched wavelength. The fiber provides then a wide bandwidth doubler. We applied this microdoubler in a second order autocorrelator.

LiNbO(3) single-crystal fibers with diameters of 63 and 230 mum were grown, and the second-harmonic-generation (SHG) process was studied with femtosecond laser pulses perpendicularly focused to the fiber. SHG occurred without collinear phase matching, leading to wavelength-independent overall conversion efficiency, unlike in a bulk crystal. The scattering pattern of the second harmonic exhibited an intense forward peak and an almost-uniform, less-intense distribution around the fiber, owing to trapping in high-Q whispering modes. Implementation of a second-order autocorrelator with the 63-mum fiber demonstrates its application potential.