Ming Jie Zheng

Tunable hybridization at midzone and anomalous Bloch-Zener oscillations in optical waveguide ladders.

We have studied the optical oscillation and tunneling of light waves in optical waveguide ladders (OWLs) formed by two coupled planar optical waveguide arrays. For the band structure, a midzone gap is formed owing to band hybridization, and its wavenumber position can be tuned throughout the whole Brillouin zone, which is different from the Bragg gap. By imposing a gradient in the propagation constant in each array, Bloch-Zener oscillation (BZO) is realized with Zener tunneling between the bands occurring at the midzone, which is contrary to the common BZO with tunneling at the center or edge of the Brillouin zone. The occurrence of BZO is demonstrated by using the field-evolution analysis. The tunable hybridization at the midzone enhances the tunability of BZO in the OWLs. This Letter may offer new insights into the coherent phenomena in optical lattices.

Steering between Bloch oscillation and dipole oscillation in parabolic optical waveguide arrays

We study the optical oscillations of supermodes in planar optical waveguide arrays with a parabolically graded propagation constant in individual waveguide interacting through nearest neighbor couplings. In these arrays, we have identified a transition between a symmetric dipole oscillation (DO) and a symmetry-breaking Bloch oscillation (BO) under appropriate conditions. There exist obvious correspondences between gradon localization and various optical oscillations. By virtue of an analog between the oscillations of optical system and that of a plane pendulum, we propose a shift of the graded profile to cause a transition from BO to DO. We confirm the optical transition by means of Hamiltonian optics, as well as by the field evolution of the supermodes. The results offer great potential applications in optical switching, which can be applied to design suitable optical devices.

Photonic Bloch–dipole–Zener oscillations in binary parabolic optical waveguide arrays

We have studied the propagation and Zener tunneling of light in a binary parabolic optical waveguide array (BPOWA), which consists of two evanescently coupled dissimilar optical waveguides. Because of Bragg reflections, the BPOWA attains two minibands separated by a minigap at the zone boundary. Various coherent superpositions of optical oscillations and Zener tunneling occur for different parameters on the phase diagram. In particular, Bloch–Zener oscillation and a different type of Bloch–dipole–Zener oscillation are obtained by field-evolution analysis. The results may have potential applications in optical splitting and waveguiding devices and may shed light on the coherent phenomena in optical lattices.

Harmonic oscillations and their switching in elliptical optical waveguide arrays

We have studied harmonic oscillations in an elliptical optical waveguide array in which the coupling between neighboring waveguides is varied in accord with a Kac matrix so that the propagation constant eigenvalues can take equally spaced values. As a result, long-living Bloch oscillations (BO) and dipole oscillations (DO) are obtained when a linear gradient in the propagation constant is applied. Moreover, we achieve a switching from DO to BO or vice versa by ramping up the gradient profile. The various optical oscillations as well as their switching are investigated by field-evolution analysis and confirmed by Hamiltonian optics. The equally spaced eigenvalues in the propagation constant allow viable applications in transmitting images, switching and routing of optical signals.