Xia Yu

Low-loss all-solid photonic bandgap fiber

We report the fabrication and characterization of a new type all-solid photonic bandgap fiber. By introducing an index depressed layer around the high-index rod in the unit cell of photonic crystal cladding, transmission loss as low as 2 dB/km within the first bandgap is realized for the all-solid photonic bandgap fiber with a bandwidth of over 700 nm. The bend loss experiment shows that the photonic bandgap fiber is much less bend sensitive than single-mode fiber.

Theoretical Study of Dual-Core Photonic Crystal Fibers With Metal Wire

In this paper, we, for the first time, systematically study a new structure of a dual-core photonic crystal fiber filled with a metal wire in the center air hole. Theoretical analysis based on the supermode theory and the coupled-mode theory shows that the directional power transfer between the two fiber cores is enhanced by the resonant coupling between the surface plasmon modes and the fiber core-guided modes. A coupling length reduction of more than one order of magnitude is demonstrated for the new structure in the near-infrared regime. As a new fiber coupler device, the highest coupling efficiency is 81.82%, the insertion loss is as low as 0.87 dB, and the extinction ratio is 30.54 dB at 1550 nm for the optimized design configuration. The new structure is compact in size and easy to fabricate, making it promising for miniaturized complex communication devices.

Seed-mediated Plasmon-driven Regrowth of Silver Nanodecahedrons (NDs)

We report the synthesis of silver nanodecahedrons (NDs) for extending the localized surface plasmon resonance (LSPR) of silver nanostructures from blue to green-orange (~590xa0nm), which will enable much wider application opportunities using common laser light sources. In our photo-assisted method, we use a light-emitting-diode (LED) to control regrowth of silver ND from precursor seeds. Highly uniform silver NDs are synthesized when the LED emission peak coincides with the LSPR peak of the seeds. A two-step process involving precursor self-transformation into silver nanoprisms and nanoplates, and subsequent photo-activated regrowth of silver NDs has been proposed. Surface-enhanced Raman scattering of silver NDs in different sizes has been studied, and the average enhancement factor for each size is estimated to be in the order of ~106.

Low-loss air-core polarization maintaining terahertz fiber

We propose a low-loss air-core polarization maintaining polymer fiber for terahertz (THz) wave guiding. The periodic arrangement of square holes with round corners in the cladding offers a bandgap effect for mode guiding. Numerical simulations show that the bandgap effect repels the modal power from the absorbent background polymers, resulting in a significant suppression of absorption loss of the polymers by a factor of more than 25. The phase-index birefringence of the proposed THz fiber is in the order of 10(-3).

Theoretical investigation of highly birefringent all-solid photonic bandgap fiber with elliptical cladding rods

We theoretically study for the first time the waveguiding properties of an all-solid photonic bandgap fiber with elliptical cladding rods. High birefringence in the order of 10-3 is easily achievable in such fibers. The contributions of the cladding rods ellipticity, the lattice ratio of the cladding microstructure as well as the index contrast of two soft glasses to the birefringence are systematically evaluated. The evolutions of birefringence with the structure and material variations show that our highly birefringent fiber design can be tailored

Design of All-Solid Bandgap Fiber With Improved Confinement and Bend Losses

We propose a new design of low-contrast all-solid bandgap fiber with low confinement and bend losses within low-order bandgaps. By introducing an index depressed layer around the high index rod in fiber cladding, we theoretically predict that the confinement loss of the proposed all-solid bandgap fiber would be significantly improved. Due to the enlarged index mismatch of the guided core mode and the edge of the bandgaps, the critical bend radius of the proposed fiber is remarkably reduced

Analytical method for band structure calculation of photonic crystal fibers filled with liquid crystal

An analytical method for band structure calculations of photonic crystal fibers with liquid crystal infiltrations is presented. The scalar eigenvalue equation is extended to treat both isotropic and anisotropic materials by introducing a coefficient to describe the index contrast between the extraordinary and ordinary refractive index of the liquid crystal. The simple model provides a fast insight into bandgap formation in photonic crystal fibers filled with anisotropic material such as liquid crystal, which would be useful to aid the design based on such fibers.

Radially graded index whispering gallery mode resonator for penetration enhancement

This paper theoretically analyzes a hollow cylindrical whispering gallery mode resonator with radially inhomogeneous cladding. We propose an index profile of n(r) = b/r to enhance field penetration towards the resonator core. With such index profile, externally coupled evanescent wave can easily penetrate the resonator cladding without any potential barrier.

Polarization-Dependent Bandgap Splitting and Mode Guiding in Liquid Crystal Photonic Bandgap Fibers

A theoretical investigation is presented for nematic liquid crystal photonic bandgap fibers (LCPBGFs), in which the rotation angle of liquid crystals director n could be arbitrarily controlled by external electric field. Based on the investigation on the polarization effect of photonic bands, we propose two orthogonal polarization-dependent bandgap maps to describe the mode guiding behavior. The symmetry properties analysis of photonic band structure reveals that the bandgap map of LCPBGFs is approximately independent of the rotation angle of director. The guiding properties of LCPBGFs including the position and width of high transmission windows, single-mode single-polarization or ultrahigh birefringence guiding, confinement loss, and coupling loss are investigated. Specifically, the high loss peaks due to the coupling between guided mode and polarization-dependent photonic bands will greatly narrow the transmission windows of the LCPBGFs. The polarization axis of the guided mode is determined by the rotation angle of the director, which could be controlled by external electric field.

Study of Polarization-Dependent Bandgap Formation in Liquid Crystal Filled Photonic Crystal Fibers

The mechanism of polarization-dependent bandgap formation for nematic liquid crystal filled photonic crystal fibers (LCPCFs) is presented. The total polarization-independent bandgap map is not applicable for describing the mode guiding in LCPCF. We propose the formation of two orthogonal polarization-dependent bandgap maps to describe the mode guiding behavior. The formation of polarization-dependent bandgap caused by the high index difference between the ordinary and the extraordinary dielectric indexes of liquid crystal offers single-mode single-polarization or ultrahigh birefringence guiding for LCPCFs.