Highly Efficient Second-Harmonic Generation in Monolithic Matching Layer Enhanced Al $_x$ Ga $_{1-x}$

In this letter, we demonstrate significant improvement in second-harmonic (SH) generation using matching layer enhanced Al_xGa_1-xAs Bragg reflection waveguide in type-I and type-II phase-matching schemes. For a 1.8-ps pulsed pump around 1550 nm with an average power of 3.3 mW, peak SH powers of 28 and 60 muW were measured in type-I and type-II interactions, respectively. The associated normalized conversion efficiencies were estimated to be 5.30 times 10³% and 1.14 times 10⁴% W^-1 middot cm^-2 with SH process bandwidths of 1.7- and 1.8-nm full-width at half-maximum. Waveguides with various ridge widths ranging between 2.8 and 4.8 mum with 2.17-mm length were characterized.