Yong-Kang Zhang

Microstructured-core photonic-crystal fiber for ultra-sensitive refractive index sensing

We propose a novel photonic crystal fiber refractive index sensor which is based on the selectively resonant coupling between a conventional solid core and a microstructured core. The introduced microstructured core is realized by filling the air-holes in the core with low index analyte. We show that a detection limit (DL) of 2.02×10⁻⁶ refractive index unit (RIU) and a sensitivity of 8500 nm/RIU can be achieved for analyte with refractive index of 1.33.

Design of broadband polarization splitter based on partial coupling in square-lattice photonic-crystal fiber

We propose a design for a novel broadband polarization splitter based on an asymmetric dual-core square-lattice photonic-crystal fiber. The fiber is designed such that index-matched coupling between the two cores can be achieved for one polarization state, while only a part of the energy could be coupled for the other polarization state. Numerical results demonstrate that a device length of 5.9 mm shows extinction ratios as low as -20 dB with bandwidths as great as 101 nm.

Improved design of polarization-maintaining photonic crystal fibers

We propose the realization of single-polarization operation in highly birefringent photonic crystal fibers. The suppression of one of the polarization states is realized by introducing index-matched cladding defect waveguides. The leakage loss of the index-matched polarization state can be enhanced by nearly 4 orders of magnitude. In particular, polarization-dependent loss larger than 2.97 dB/m with transmission loss lower than 0.03 dB/m in a wavelength region ranging from 1.54 to 1.566 μm can be realized in one such fiber.

Bend Insensitive Design of Large-Mode-Area Microstructured Optical Fibers

Numerical investigation on the design of a novel kind of large-mode-area optical fiber is presented. Low bending loss propagation in the fiber is achieved by the introduction of low-index rods with small period and large normalized diameter in one segment of the cladding. Single-mode operation is realized by the introduction of low-index rods with large period and small normalized diameter in another segment of the cladding. When a conventional large-mode-area optical fiber is bent, it will generally experience large bend distortion and the mode area will reduce accordingly. To avoid that, a bend-resistant design by introducing a microstructure into the solid core of the proposed fiber is proposed. In particular, the mode area of one such fiber is always larger than 2000 μ m2 when the bending radius is larger than 30 cm at the wavelength of 1.064 μm.

Design of Asymmetric Large-mode Area Optical Fiber With Low-bending Loss

We propose the design of a simple large-mode area microstructured optical fiber with low bending loss and large loss difference between the fundamental mode and the high-order modes. Single-mode operation in the fiber is realized by the introduction of small diameter holes, whereas the bending loss of the fiber is realized by the introduction of three large holes in the two-ring hole microstructured optical fiber. We also introduce low-index rods into the core of the fiber, which can effectively compensate the reduction of mode area induced by bending the fiber.

Design and Analysis of a Low-Loss Suspended Core Terahertz Fiber and Its Application to Polarization Splitter

We propose the design of a low-loss suspended core terahertz fiber with rectangular-shaped dielectric strips in the fiber cross section. The finite element method is used to analyze the characteristics of the suspended core terahertz fiber. Terahertz wave in a frequency range from 0.74 ~ 0.95 THz is efficiently confined in the suspended core region with a total loss lower than 0.086 dB/cm ( ~ 0.02 cm-1). Meanwhile, any contact on the surface of this fiber will not disturb the field and induce additional losses. A 3.36-cm-long terahertz polarization splitter derived from this fiber with a transmission loss less than 0.89 dB, is also numerically demonstrated. A bandwidth of 0.032 THz at the center frequency of 1 THz with an extinction ratio better than -20 dB is obtained.

Broadband Single-Polarization Operation in Square-Lattice Photonic Crystal Fibers

A broadband single-polarization single-mode optical fiber is proposed. One of the polarized states of the highly birefringent square-lattice photonic crystal fiber is eliminated by index-matched coupling with the modes of two cladding defects. Numerical results show that single-polarization operation with the transmission losses of one polarized state larger than 2 dB/m and the losses of another state lower than 2 dB/km can be realized in a spectral region ranged from 1477 to 1776 nm. In addition, by modifying the air holes surrounding the cladding defects, the losses of the unwanted polarized state can be enhanced to be larger than 10 dB/m, with the losses of the transmission state lower than 0.1 dB/m in a 560-nm-broad spectral region.

Coupling characteristics of three-core photonic crystal fiber couplers

The coupling characteristics of a three-core photonic crystal fiber (PCF) and its application as a broadband directional coupler are investigated. Numerical investigations demonstrated that broadband directional coupling with spectral width as large as 425 nm and polarization-dependent loss lower than 0.06 dB could be achieved in the proposed fiber coupler. In addition, the proposed fiber shows large tolerance to the variation of the fiber parameters. In particular, the fiber allows at least 4% deviation of the air-hole diameters and 10% deviation from the proposed length of 27 mm.The author proposes the methodology of transformation optics in orthogonal coordinates to obtain the material parameters of the transformation media from the mapping in orthogonal coordinates. Several examples are given to show the applications of such a methodology by using the full-wave simulations.

Design of dual-mode optical fibres for the FTTH applications

We present in this article a proposal and design for dual-mode optical fibres for fibre-to-the-home applications. High-order modes in the fibre can be effectively suppressed by the connection of the fibre with standard single-mode optical fibres at the two ends of the fibre. The alignment tolerance at the splicing process is presented. In particular, a low bending loss operation with low splice loss is demonstrated using the proposed technique.

Design and analysis of a low-loss terahertz directional coupler based on three-core photonic crystal fibre configuration

A novel kind of terahertz directional optical fibre coupler is proposed. The coupling characteristics and operation bandwidth of the three-core photonic crystal fibre coupler are investigated. Numerical results show that it is possible to achieve a broadband terahertz fibre coupler with a small fibre length of a few centimetres. In addition, a modified configuration, which can achieve a wider bandwidth and lower absorption loss, is proposed.