Second harmonic generation in GaN transverse quasi-phase-matched waveguide pumped with femtosecond laser

A wavelength conversion device with an input grating coupler that enables easy alignment was fabricated using a vertically polarity inverted GaN layer. The device was excited with a femtosecond laser, and a second harmonic wave with a peak wavelength of 438.4 nm was obtained. A normalized wavelength conversion efficiency of 4.7 × 10−4% W−1and a spectral bandwidth of the second harmonic wave of 2.9 nm were comparable to the theoretical estimations taking into account serious walk-off and waveguide losses. High efficiency of 33%–34% W−1can be expected under continuous-wave excitation.