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Acoustically tunable photonic band gap structures

We discuss the formation of a tunable one-dimensional photonic band gap structure through the modulation of the resonance frequency of an optical microcavity by a surface acoustic wave (SAW). The microcavity consists of a λ/2 GaAs layer bounded by AlAs/GaAs Bragg mirrors. The SAW periodically modulates the optical thickness of the cavity layer, leading to a light dispersion relation folded within a mini-Brillouin zone (MBZ) defined by |kx|≤ π/λSAW (kx denotes the photon wave vector component along the SAW propagation direction x-with-caret). In reflection and diffraction experiments, we observe photon modes bounding the gaps in the center and at the boundary of the MBZ as well as a renormalization of the optical energies. Furthermore, the width of the energy gaps can be tuned by changing the acoustic power densities. The experimental results are in good agreement with a simple model for the dispersion in the presence of SAWs. We show the application of acoustically tunable microcavities in efficient optical on/off switches and modulators as well as a tunable cavity operating at 1.3μm.