Photonic crystals: putting a new twist on light. Optical Waves in Layered Media (Wiley, New York, 1988). Principles of Optics (Pergamon, Oxford, 1980). Quantum engineering of optical non linearities. Phase-matched harmonic generation in a laminar structure with wave propagation in the plane of the layers. Wavelength conversion by difference frequency generation in AlGaAs waveguides with periodic domain inversion achieved by wafer bonding. Second-harmonic generation in GaAs stack of plates using high power CO2laser radiation. Quasi-phase-matched 1.064-µm-pumped optical parametric oscillator in bulk periodically poled LiNbO3. Quasi-phase-matched second harmonic generation: Tuning and tolerances. Interactions between light waves in a non linear dielectric. As GaAs is the material of choice for semiconductor lasers, such optical sources could be integrated in the core of frequency converters based on these composite structures.Īrmstrong, J. Here we demonstrate a different route to phase matching - based on a concept proposed by Van der Ziel 22 years ago 7 - which exploits the artificial birefringence of multilayer composites of GaAs and oxidised AlAs. 4), provide a route to circumventing this problem 5, 6, but the difficulty of producing the required pattern of nonlinear properties in isotropic materials, particularly semiconductors, has limited the practical utility of such approaches. Quasi-phase-matching schemes 1, 3, which have achieved considerable success in LiNbO 3 ( ref. But this is not possible for optically isotropic materials, and as a result, cubic materials such as GaAs (which otherwise have attractive nonlinear optical properties) have been little exploited for frequency conversion applications. In anisotropic birefringent crystals such as LiNbO 3 or KH 2PO 4 (‘KDP’), phase matching can be achieved between electromagnetic waves having different polarizations. For efficient conversion, it is necessary to compensate for optical dispersion, which results in different phase velocities for light of different frequencies. Frequency conversion in nonlinear optical crystals 1, 2 is an effective means of generating coherent light at frequencies where lasers perform poorly or are unavailable.
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