Photonic band gap of 2D complex lattice photonic crystal

It is of great significance to present a photonic crystal lattice structure with a wide photonic bandgap. A two-dimension complex lattice photonic crystal is proposed. The photonic crystal is composed of complex lattices with triangular structure, and each single cell is surrounded by six scatterers in an hexagon. The photonic band gaps are calculated based on the plane wave expansion (PWE) method. The results indicate that the photonic crystal has tunable large TM polarization band gap, and a gap-midgap ra...

Design and analysis of superlens based on complex two-dimensional square lattice photonic crystal

We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(FDTD) method is employed to calculate the band structure and simulate image construction. The band diagram of the complex structure is significantly compressed. Negative refraction occurs in the second energy band with negative phase velocity at a frequency of 0.228(2πc/a), which is lower than results from previous studies. Lower negative refraction frequency leads to higher image resolution. Numerical results show that the spatial resolution of the system reaches 0.7296λ, which is lower than the incident wavelength.

Ultrasonic generation via direct interaction between photons and phonons in anharmonic lattice of ionic crystals

A theory of ultrasonic generation via direct interaction of transverse optic (TO) phonons with photons in anharmonic lattice of ionic crystals is presented. There are two methods of supplying light energy for the excitation of TO lattice wave as a high frequency ultrasound: (A) incident light comes from the source outside the cavity? fulfilled with ionic crystal medium, (B) photon mode of the cavity possesses the gain of amplification by stimulated radiation of active atoms doping in the medium. More attention is drawn to the case (B). The working system of case (B), as a mixture of lasing action and ultrasonic generation, has the threshold phenomena like usual laser. And the linear stability analysis shows that the nonlineax phonon-photon coupling and the interaction among phonons themselves, both of which reflect the anharmonicity of lattice vibration, are necessary to the stable ultrasonic output. So this laser-ultrasonic generation mixture would be also a measure to investigate the lattice-dynamic nonlinearity and correlated electromagnetic properties of ionic crystals.

Gap-type dark localized modes in a Bose-Einstein condensate with optical lattices

Bose-Einstein condensate(BEC)exhibits a variety of fascinating and unexpected macroscopic phenomena,and has attracted sustained attention in recent years-particularly in the field of solitons and associated nonlinear phenomena.Meanwhile,optical lattices have emerged as a versatile toolbox for understanding the properties and controlling the dynamics of BEC,among which the realization of bright gap solitons is an iconic result.However,the dark gap solitons are still experimentally unproven,and their properties in more than one dimension remain unknown.In light of this,we describe,numerically and theoretically,the formation and stability properties of gap-type dark localized modes in the context of ultracold atoms trapped in optical lattices.Two kinds of stable dark localized modes-gap solitons and soliton clusters-are predicted in both the one-and two-dimensional geometries.The vortical counterparts of both modes are also constructed in two dimensions.A unique feature is the existence of a nonlinear Bloch-wave background on which all above gap modes are situated.By employing linear-stability analysis and direct simulations,stability regions of the predicted modes are obtained.Our results offer the possibility of observing dark gap localized structures with cutting-edge techniques in ultracold atoms experiments and beyond,including in optics with photonic crystals and lattices.