Runwu Peng

Absolute left-handed behaviors in a triangular elliptical-rod photonic crystal.

In this paper we theoretically study the left-handed behaviors in a two-dimensional triangular photonic crystal made of elliptical rods in air. An absolute left-handed region is found in the second photonic band by using the plane wave expansion method to analyze the photonic band structure and equifrequency contours. Typical left-handed behaviors such as negative refraction, flat superlensing and plano-concave lensing are demonstrated by the finite-difference time-domain simulations. These behaviors are also compared with the quasi-negative refraction and the resulted focusing effects in a square-lattice two-dimensional photonic crystal.

Transverse intensity distributions of a broadband laser modulated by a hard-edged aperture

By means of the Huygens-Fresnel diffraction integral, the field representation of a laser beam modulated by a hard-edged aperture is derived. The near-field and far-field transverse intensity distributions of the beams with different bandwidths are analyzed by using the representation. The numerical calculation results indicate that the amplitudes and numbers of the intensity spikes decrease with increasing bandwidth, and beam smoothing is achieved when the bandwidth takes a certain value in the near field. In the far field, the radius of the transverse intensity distribution decreases as the bandwidth increases, and the physical explanation of this fact is also given.

Optical properties of a square-lattice photonic crystal within the partial bandgap

Optical properties of a two-dimensional square-lattice photonic crystal are systematically investigated within the partial bandgap through anisotropic characteristics analysis and numerical simulation of field pattern. Using the plane-wave expansion method and Hellmann-Feynman theorem, the relationships between the incident and refracted angles for both phase and group velocities are calculated to analyze light propagation from air to photonic crystals. Three kinds of flat slab focusing are summarized and demonstrated by numerical simulations using the multiple scattering method.

Subwavelength imaging by a dielectric-tube photonic crystal

In contrast to previous two-dimensional coated photonic crystals, in this paper we propose a left-handed one that is made of dielectric tubes arranged in a close-packed hexagonal lattice. Without metallic cores, this structure is low-loss and convenient to fabricate. Negative refraction and its resulting focusing are investigated by dispersion characteristic analysis and numerical simulation of the field pattern. With proper modification at the interface, the image is improved. With better isotropy than that with noncircular rods, planoconcave lenses made by dielectric tubes focus a Gaussian beam exactly at R/|n−1|.

Effect of bandwidth on the intensities of an apertured laser in the near and far fields

By means of the Huygens-Fresnel diffraction integral, the propagation expression of a laser beam passing through a hard-edged aperture is derived. The effects of the bandwidth on the transverse intensity distributions of the beam in the near and far fields are analyzed. It is found that, in the near field, the beam uniformity is improved with increasing the bandwidth and the broader the spectrum, the smoother the transverse intensity distribution is. Intensity spikes produced by low-frequency diffraction are eliminated in the diffraction patterns and the transverse intensity distribution near axis tends to smooth when the bandwidth increases. The intensity spikes produced by high-frequency diffraction still exist with increasing the bandwidth, but the amplitudes and numbers of them decrease. In the far field, there are only a few differences among the transverse intensity distributions of the beams with different bandwidthes. However, The secondary maximum intensity still presents for the beam with small bandwidth, and it decreases with increasing the bandwidth and is eliminated with large bandwidth.