Abstract

Recently, as a result of rapid development of the semiconductor epitaxial growth technology, GaAs/AlGaAs multilayers¹ and asymmetric coupled quantum-well domain structures² were used to achieve second-harmonic generation (SHG). To achieve quasi-phase matching (QPM) the thickness of each of the multilayers or the domains is half of the SH wavelength in the material. On the other hand, for a conventional second-order nonlinear material such as KTP or LiNbO₃, it can be periodically poled to achieve SHG.³ In this type of the medium, QPM has been achieved by spatial modulation of the second-order susceptibility such that the fundamental and second-harmonic waves can be in phase when they propagate in the same direction. The thickness of each domain is usually much larger than the wavelength of the fundamental or SH wave. Here, we present our results of investigating possibility of generating a backward SH based on a novel scheme. In this novel configuration the period of the domain structure is equal to the SH wavelength in the material. Therefore the second-order susceptibility has to be modulated spatially with the period much shorter than that achieved before.³ Fundamentally, our configuration is based on the interaction of two counterpropagating waves while the previous ones³ are based on a single fundamental wave. In addition, both the fundamental and SH waves propagate parallel to the same axis while the propagation directions of the fundamental and SH waves in Refs. 1, 2 and 4 are normal to each other. First, we consider a configuration shown in Fig. 1: there is a mirror for the fundamental and SH waves next to the right-side facet Figure 2 shows the conversion efficiency for the backward SH wave as a function of the pump intensity normalized by the saturation intensity:

© 1996 Optical Society of America