Monolithic Photonics Using Second-Order Optical Nonlinearities in Multilayer-Core Bragg Reflection Waveguides

Recent advancements in phase-matching second-order nonlinear processes by using matching-layer-enhanced Bragg reflection waveguides (ML-BRWs) in Al_xGa_1-xAs material system are discussed. The limitations on the choice of the Al_xGa_1-xAs layers for applications that require high pump power operation are highlighted. Multilayer-core ML-BRWs are proposed as a new waveguide design with relaxed constraints over the choice of the Al_xGa_1-xAs layers composition. The tradeoffs associated with material bandgap on the efficiency of second-order nonlinear processes are examined by using this novel structure. The interplay among the various factors, including the nonlinear overlap factor, the effective second-order nonlinearity, and the third-order nonlinear effects result in the presence of an optimum detuning of the core bandgap from the operating wavelength for maximum conversion efficiency. Two different wafer structures are examined by using second-harmonic generation to elucidate these tradeoffs. The conversion efficiency is examined by using 30-ps, 2-ps, and 250-fs pulses at various pump average power levels.