PULSED 2ND-HARMONIC GENERATION IN NONLINEAR, ONE-DIMENSIONAL, PERIODIC STRUCTURES

We present a numerical study of second-harmonic (SR) generation in a o ne-dimensional, generic, photonic band-gap material that is doped with a nonlinear chi((2)) medium. We show that a 20-period, 12-mu m struct ure can generate short SH pulses (similar in duration to pump pulses) whose energy and power levels may be 2-3 orders of magnitude larger th an the energy and power levels produced by an equivalent length of a p hase-matched, bulk medium. This phenomenon comes about as a result of the combination of high electromagnetic mode density of states, low gr oup velocity. and spatial phase locking of the fields near the photoni c band edge. The structure is designed so that the pump pulse is tuned near the first-order photonic band edge, and the SH signal is generat ed near the band edge of the second-order gap. This maximizes the dens ity of available field modes for both the pump and SR field. Our resul ts show that the chi(2) response is effectively enhanced by several or ders of magnitude. Therefore, mm- or cm-long, quasi-phase-matched devi ces could be replaced by these simple layered structures of only a few micrometers in length. This has important applications to high-energy lasers, Raman-type sources, and frequency up-and down-conversion sche mes.