Lou Shu-Qin

Mode classification and degeneracy in photonic crystal fibers.

Based on supercell lattice method, a novel full vector model is presented to analyze the photonic crystal fibers (PCF). From symmetry analysis of modes of a waveguide, we classify the modes of PCF into nondegenerate or degenerate pairs according to the minimum waveguide sectors and its appropriate boundary conditions. We present the modes of PCF can be labeled by its step index fiber analogs, except the modes with the same symmetry as PCF. The doublet of the degenerate pairs in which both have the same symmetry as PCF will be split into two nondegenerate modes.

Supercell lattice method for photonic crystal fibers

A supercell lattice method, believed to be novel, deduced from the plane-wave expansion method and the localized basis function method, is presented for analyzing photonic crystal fibers (PCFs). The electric field is decomposed by use of Hermite-Gaussian functions, and the dielectric constant of PCFs missing a central air hole is considered as the sum of two virtual different periodic dielectric structures of perfect photonic crystals (PCs). The structures of both virtual PCs are expanded in cosine functions. From the wave equation and the orthonormality of the Hermite-Gaussian functions, the propagation characteristics of the PCFs, such as the mode field distribution, the effective area, and the dispersion property, are obtained. The accuracy of the novel method is demonstrated as we obtain the same results when the dielectric constant is split into two virtual ideal PCs in different ways.

Compact supercell method based on opposite parity for Bragg fibers

The supercell- based orthonormal basis method is proposed to investigate the modal properties of the Bragg fibers. A square lattice is constructed by the whole Bragg fiber which is considered as a supercell, and the periodical dielectric structure of the square lattice is decomposed using periodic functions (cosine). The modal electric field is expanded as the sum of the orthonormal set of Hermite-Gaussian basis functions based on the opposite parity of the transverse electric field. The propagation characteristics of Bragg fibers can be obtained after recasting the wave equation into an eigenvalue system. This method is implemented with very high efficiency and accuracy.

Loss properties due to Rayleigh scattering in different types of fiber

The effects of fiber structure on Rayleigh scattering were investigated in detail. Some step-index fibers such as GeO2- and F-doped silica-based fibers and total-internal-reflection photonic crystal fiber are examined. The Rayleigh scattering loss (RSL) depends on the fiber materials and index profiles, and different types of fiber have different dependencies on those parameters because of the different optical power confinement factors in every layer. On the basis of these results, the RSL can be optimized by adjusting the fiber structure or by selecting different materials.

Dependence of mode characteristics on the central defect in elliptical hole photonic crystal fibers

Some mode characteristics are obtained by the full vector supercell overlap method that has been developed to model triangular lattice elliptical hole photonic crystal fibers regardless of whether the light is guided by total internal reflection or a photonic bandgap mechanism. When the central defect hole is large enough, the modes are disordered. Birefringence (Deltan) dependence on the central defect is discussed in detail by numerical analysis.

Full-vectorial analysis of complex refractive-index photonic crystal fibers

We investigated the modal properties of complex refractive-index core photonic crystal fibers (PCFs) with the supercell model. The validity of the approach is shown when we compare our results with those reported earlier on a step complex refractive-index profile. The imaginary part of the electric field results in wave-front distortion in the complex refractive-index profile PCFs, which means that the power flows out or into the doped region according to the sign of the imaginary part of the refractive index. A simple formula is proposed for calculating the gain or loss coefficients of these fibers. The numerical results obtained by the approximation formula agree well with the full-vectorial results.

A New Type of Terahertz Waveguides

A new type of THz waveguides, which employs a solid polyethylene rod as the core and polyethylene tubes in a periodic array of square lattice as the cladding, is proposed. Optical properties of this new THz waveguide, especially in dispersion, confinement loss and single mode property, are investigated in detail with the plane wave expansion method and the beam propagation method. Numerical results demonstrate that the new THz waveguide can reach not only low dispersion but also low confinement loss at single mode propagation. Therefore, the square lattice structure is a better candidate as THz waveguides than the triangular ones.

Investigation on the Fabrication of Photonic Crystal Fibre

Effects of draw parameters, such as drawing temperature and feed speed, on the capillaries and the geometry of the final photonic crystal fibre (PCF) are investigated. Inert gas pressurization is introduced in the preform during the fibre drawing process to finely control the geometry of the PCF so that good uniform in transversal and longitudinal of the final PCF can be realized. Due to the introduction of a special method, the drawing temperature is increased over 1900°C and the strength of the PCF is enhanced.

A novel supercell overlapping method for different photonic crystal fibers

A novel supercell overlapping method is developed to analyze the photonic crystal fibers (PCFs). The electric field is decomposed using the localized Hermite-Gaussian functions, and the dielectric constant of the PCF missing the central air hole is considered as the sum of two different periodic dielectric structures of virtual perfect photonic crystals (PCs). The structures of both virtual PCs are expanded in cosine functions. From the wave equations and the orthonormality of Hermite-Gaussian functions, the propagation characteristics of the PCF, such as the mode field distribution, the effective area, the birefringence, and the dispersion properties, are obtained. There are fewer computations, and all the elements of the eigenvalue equation are analytical. We are convinced that this novel method is accurate and efficient due to the numerical calculation processes and its results.

Propagation properties of an index guiding high birefringence fibre

Based on a full-vector model, a theoretical study on a kind of high birefringence photonic crystal fibre is presented. Due to introducing air holes of two different sizes into the cladding, twofold rotational symmetry was obtained. We demonstrate the possibility of achieving high birefringence that is at least one order of magnitude higher than that of conventional polarization-maintaining fibres. The dependences of modal birefringence, modal field and differential group delay on the structure parameter of the fibres are discussed in detail. The numerical results are in very good agreement with the experimental results in the literature.