Second-harmonic generation with monolithic walk-off-compensating periodic structures I Theory

Abstract

Second-harmonic generation in a periodic structure made from N pairs of optically contacted, birefringence phase-matched, walk-off-compensating bulk plates is theoretically investigated. In the undepleted-pump approximation, analytical (heuristic) expressions for conversion efficiency versus N are derived for both type I and type II phase matching. An explicit split-step beam propagation scheme that solves exactly the coupled paraxial-wave equations is used to check the validity of the heuristic results. For type II, stronger conversion enhancement than for bulk crystal is predicted in the low-depletion regime, whereas for type I such structures avoid harmonic beam ellipticity. The periodic structures are found to behave as nonlinear harmonic birefringent filters because of the presence of periodic wave-vector mismatch grating ±Δk that results from walk-off compensation. The effect of periodicity imperfections, such as residual plate orientation mismatches, was found to be responsible for broadening of the tuning bandwidth in walk-off-compensating devices.