Haibin Zhu

Nonreciprocal extraordinary optical transmission through subwavelength slits in metallic film

We demonstrate the phenomenon of nonreciprocal extraordinary optical transmission (NEOT) through metallic film with slits on the substrate of magneto-optical materials. Under uniformly magnetization, the system can show nonreciprocal transmission at near-IR frequency range. With a properly designed structure, the nonreciprocity can be as high as 57.6%. Numerical evidence shows that the nonreciprocal performance is sensitive to the incidence angle, as well as to the thickness of the substrate.

Broadband unidirectional electromagnetic mode at interface of anti-parallel magnetized media

We report a kind of broadband electromagnetic boundary mode at an interface of anti-parallel magnetized media, which can only propagate in one direction perpendicular to the magnetization and parallel to the interface. The unidirectionality of this mode originates from the permeability or permittivity tensor introduced by magnetization. We theoretically and numerically analyze the existence of the unidirectional mode, and point out that this mode can exist in both gyromagnetic and gyroelectric medium. We also propose a one-way waveguide based on this unidirectional mode, which may realize a new kind of electromagnetic isolation differing from those existing ones.

Surface ablation of congruent and Mg-doped lithium niobate by femtosecond laser

Lithium niobate is praised as silicon in nonlinear optics for its wide usage both in fundamental science and applications in optics. But its photorefractive effect hinders it from more extensive application in optics. The deadlock has been broken by doping some metallic elements such as magnesium into the congruent lithium niobate crystal for its high damage resistance. The single-shot and multi-shot surface ablation experiments by femotosecond laser with the wavelength of 800 nm and the duration of 80 fs were conducted in the same condition and the ablation threshold fluence was gained for congruent lithium niobate crystal and 6 mol % Mg-doped lithium niobate crystal. The band gap widening after doping is responsible for the discrepancy of the ablation thresholds between the two samples. The laser threshold fluence dependence of lasershot number demonstrates the difference of the accumulation effect. The large reduction of trapping cross section for electrons after heavy doping of magnesium is focused more to interpret this distinction.

Optical Isolation Based on Nonreciprocal Micro-Ring Resonator

We propose a nonreciprocal waveguide with different wavevectors for forward and backward propagations. Utilizing this nonreciprocal waveguide, we further compose a nonreciprocal micro-ring resonator, which possesses different phase shifts for clockwise and anticlockwise circulatings. Using this nonreciprocal resonator, more than 20 dB optical isolation can be achieved. This work demonstrates that on-chip optical isolations can be accomplished with simple nonreciprocal resonator components, which can show promising applications for integrated optoelectronic systems.

Extraordinary Coupling Into One-Way Magneto-Optical Photonic Crystal Waveguide

We present a two-dimensional magneto-optical photonic crystal waveguide, in which TM mode with proper frequency can propagate only in one direction. The photonic crystal is composed of square-lattice yttrium-iron-garnet (YIG) rods, with static magnetic field applied on it. In a special frequency range, this waveguide possesses only forward mode, while in another special frequency range, only backward mode. We also study the coupling of electromagnetic wave into it from air as well as from conductor waveguides. Numerical results show that the magneto-optical PhCs (MPC) waveguides have special transmitting performance, and can show high efficiency when electromagnetic wave is coupled into this waveguide.

The propagation of hypergeometric beams through an annular apertured paraxial ABCD optical system

By means of expanding the hard aperture function into a finite sum of complex Gaussian functions and based on the generalized Huygens–Fresnel diffraction integral, a novel approximate analytical expression of hypergeometric (HyG) beams passing through a paraxial ABCD optical system with an annular aperture is derived. The results could be reduced to the case of a circular aperture or a circular black screen. Some numerical simulations are also performed and illustrated for the propagation characteristics and focusing properties of a HyG beam through a paraxial ABCD optical system with an annular aperture. The results obtained from the approximate analytical formula provide more efficiency than the usual way of using diffraction integral formula directly.

Jumping phase control in interband photonic transition

Indirect interband photonic transition provides a nonmagnetic and linear scheme to achieve optical isolation in integrated photonics. In this paper, we demonstrate that the nonreciprocal transition can be induced through two pathways respectively by different modulation designs. At the end of those pathways, the two final modes have π phaseshift. We call this phenomenon jumping phase control since this approach provides a method to control the mode phase after the conversion. This approach also yields a novel way to generate nonreciprocal phaseshift and may contribute to chip-scale optoelectronic applications.

GEOMETRY DEPENDENT ONE-WAY PROPAGATION OF LIGHT IN INTEGRATED SILICON PHOTONIC WAVEGUIDE

We report a new one-way propagation effect of light which only occurs in multi-mode waveguide and can be controlled by adjusting the geometry of light source. Based on such effect, an integrated silicon waveguide composed of two planar waveguides with different thickness is proposed. The two-dimensional finite difference time domain (FDTD) simulation results show that complete signal isolation is achieved. Our results suggest that this integrated silicon waveguide may play an important role in future optical devices as long as the ideal source can be generated by the transformation optics method.