Tingting Sun

Highly birefringent elliptical-hole photonic crystal fiber with squeezed hexagonal lattice

We propose a novel polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core and a cladding with squeezed-hexagonal-lattice elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental modes in such PCFs. Numerical result shows that very high modal birefringence with a magnitude of the order of 10(-2) around 1550 nm has been obtained. Furthermore, large normal dispersion appears over a wide range of wavelengths in both orthogonal polarizations.

Transformation of a transmission mechanism by filling the holes of normal silica-guiding microstructure fibers with nematic liquid crystal

Transformation of an optical transmission mechanism was achieved when the holes of normal silica-guiding microstructure fiber (MF) were filled with nematic liquid crystal (NLC). Moreover, two photonic bandgaps (PBGs) were obtained by using a plane-wave method to create the pattern. The wavelength dependence of the effective mode area, leakage loss, and group velocity dispersion (GVD) has been theoretically investigated by using a full-vector finite-element method with anisotropic perfectly matched layers. The results reveal that the characteristics of the NLC-filled PBG-MFs are particularly wavelength dependent. This research gives a physical insight into the propagation mechanism in MFs and is crucial for future transmission applications.

Highly Birefringent Elliptical-Hole Photonic Crystal Fiber With Two Big Circular Air Holes Adjacent to the Core

In this letter, we propose a novel design for a polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core, two big circular air holes near the core, and a cladding with elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental mode in such a PCF. The numerical result shows that very high modal birefringence with magnitude of order of 10-3 has been obtained, which are higher than the birefringence induced by adding two big air holes near the core or using elliptical air holes in cladding separately

Coupling and decoupling of dual-core photonic bandgap fibers.

Coupling characteristics of dual-core photonic bandgap fibers with triangular photonic crystal cladding are investigated by use of a vector plane-wave expansion method and a vector finite-element method. We demonstrate the eigenmodes and the coupling length for two orthogonal polarizations. A decoupling phenomenon is found at a certain wavelength in this fiber configuration. The decoupling effect is attributed to the effect of surface modes on the eigenmodes. The decoupling wavelength decreases as the ratio of core radius to cladding air-hole pitch increases from 1.05 to 1.15.

Tunable highly birefringent photonic bandgap fibers

A novel tunable highly birefringent photonic bandgap fiber (PBGF) is designed theoretically by filling its air holes with high-index material. The transmission band can be continuously tuned by changing the refractive index of the filling material. Accordingly, the tunable modal birefringence and polarization mode dispersion of the PBGFs are investigated by adjusting the refractive index of the filling material. Furthermore, we have also analyzed the effect of surface modes in the photonic bandgap on the characteristics of the tunable PBGFs. The simulation results show the feasibility of constructing birefringence-tunable photonic crystal fibers and related fiber devices in practical applications.

Broadband Single-Polarization Single-Mode Photonic Crystal Fiber Coupler

In this letter, a novel design for a photonic crystal fiber coupler with single-polarization single-mode (SPSM) functionality is proposed and investigated using a vector plane-wave expansion method and a vector finite-element method. We study the changes in the coupling lengths between the two orthogonal polarizations and the width of the SPSM coupling region with respect to the air-hole parameters. We demonstrate that the SPSM coupling range can be more than 200 nm wide for a variety of air-hole parameters and show that the position and width of the SPSM coupling region can be tailored via the diameters of the large inner air holes and the small cladding air holes

Modal cutoff properties in germanium-doped photonic crystal fiber

The germanium-doped photonic crystal fiber (PCF) has some characteristics that differentiate it from pure-silica PCF for a germanium element being doped in the core, such as the intensified nonlinearity, the enhanced photosensitivity, and so on. To pave the way for the application of the Ge-doped PCF successfully, it is necessary to study its properties. We investigated the modal cutoff properties of Ge-doped PCF quantitatively by using the beam propagation method. The numerical results show that the effective refractive indices and the normalized frequency V of Ge-doped PCF not only depend on the normalized pitch delta/lambda but also depend on the normalized hole size d/delta, the modal cutoff boundary for the single mode-multimode of the Ge-doped PCF shift to the low d/delta side in contrast to the pure-silica PCF.

Enhanced nonlinearity in photonic crystal fiber by germanium doping in the core region

Germanium doping in silica can be used as a method for nonlinearity enhancement. Properties of the enhanced nonlinearity in photonic crystal fiber (PCF) with a GeO2-doped core are investigated theoretically by using all-vector finite element method. Numerical result shows that the nonlinear coefficient of PCF is greatly enhanced with increasing doping concentration, furthermore, optimal radius of the doped region should be considered for the desired operating wavelength.

Directional couplers operated by resonant coupling in all-solid photonic bandgap fibers

We have proposed directional couplers operated by resonant coupling in all-solid photonic bandgap fibers structure which consist of a cladding with an array of high-index rods in silica background, two cores formed by omitting two rods, and some defect rods introduced by reducing the diameter of the high-index rods between the cores. The resonant effect induced by the avoided crossing between core-guided supermodes and defect-guided modes significant decreases the coupling length. The directional couplers proposed in this paper are almost polarization independent and have potential application in realizing integrating all-fiber communication devices.

Design of tunable bandgap guidance in high-index filled microstructure fibers

Tunable photonic bandgap (PBG) microstructure fibers, which were filled nematic liquid crystals (NLC), were theoretically investigated based on bandgap theory. By means of the modified plane-wave method, it is found that PBGs shift to the longer wavelength with increasing refractive index of NLC [ny(θ)] for y-polarized light. Fundamental modes are found in these PBG reigns, whose effective mode area, leakage loss and group velocity dispersion (GVD) have been calculated by using the full-vector finite-element method with anisotropic perfectly matched layers. The mode fields become larger with the increase of ny(θ), whereas the leakage loss varies slightly. Moreover, GVD is strongly dependent on ny(θ) and wavelength, which is much larger than the material dispersion of silica.