Ultracompact Superlattices for Multi-frequency Optical Bloch Oscillations Simultaneously

Abstract

In this paper, we investigate the photonic transmission properties of a kind of one-dimensional optical superlattices composed of alternately stacked metal and dielectric films. A geometric thickness gradient of the dielectric layers, which is analog to an external electric field applied to the electronic crystals for observing electron Bloch oscillations, is introduced in the superlattices along the photonic propagation direction. Analytical results from the transfer matrix method reveal that three sets of photonic Wannier-Stark ladder with different frequency-space in terahertz level exist simultaneously from visible to near infrared frequency domain as the gradient is varied from 0.5 to 0.8, which indicates that the optical superlattices can support three different terahertz Bloch oscillations simultaneously. In particular, at a certain gradient, the Zener tunneling effect between two adjacent Wannier-Stark ladders is achieved. Finite-difference time-domain simulations on the dynamic evolution of photons propagation in the superlattices confirm the analytical predictions. The largest total thickness of the superlattices is around 8 μm, which is a quarter of that of superlattices composed of alternately stacked Bragg reflectors and dielectric microcavities.