We have designed a one-dimensional photonic bandgap crystal to obtain perfect phase-matching conditions for noncollinear type II quadratic processes. The realized sample was 15 periods of Al(0.3)Ga(0.7)As/Al2O3, for a total length of 3.5um. Noncollinear type II phase-matching was obtained at 1510nm. We have experimentally verified the band structure characteristic as well as its perfect phase-matching for the noncollinear type II parametric process. Indeed, noncollinear type II second harmonic generation was obtained for the first time in a PBG crystal1. The experiment demonstrated that the breaking of symmetry, which is artificially induced in such a structure, and the field resonance effect give rise to a relatively efficient second harmonic generation even using a naturally isotropic material (AlGaAs). In fact, we report a nonlinear effective coefficient of the sample equal to (52±12) pm/V.
We present a new concept for efficient second harmonic generation that is based upon the interference of counter-propagating waves in multilayer structures. We show that phase matching and quasi phase matching are not always necessary conditions to provide optimized nonlinear frequency conversion efficiency.
We show that inside a multi-layer dielectric stack, consideration of higher-order, fast-oscillating interference terms between counter-propagating waves can dramatically change the dynamics of second harmonic generation, and thus lead to an unusual result: field confinement and overlap can be far better optimized, and conversion efficiencies further enhanced, in the presence of a phase mismatch. One may therefore conclude that phase matching is not always a necessary condition to provide optimized nonlinear frequency conversion efficiency.