Zhaolun Liu

Photonic crystal fiber for dispersion compensation

The dispersion and mode characteristics in a dual-concentric-core photonic crystal fiber, based on pure silica, are simulated by the multipole method. The fiber exhibits very large negative dispersion due to anticrossing of two individual inner core and outer core modes. Near the wavelength of 1.55 microm, we could obtain narrowband dispersion-compensating fiber with dispersion values of -23,000 ps/km/nm, broadband dispersion-compensating fiber with dispersion values from -1000 ps/km/nm to -2500 ps/km/nm over a 200 nm range, and kappa values near 300 nm, which matched well with standard single mode fiber. It shows that even if there are some changes in the structure parameters during fabrication, these fibers can still maintain a fine dispersion-compensating property.

Improved fully vectorial effective index method in photonic crystal fiber

In the simulation of photonic crystal fibers, the fixed value of the normalized equivalent core radius (p/Lambda) in the fully vectorial effective index method is inaccurate. For what is believed to be the first time, the relation of p/Lambda with normalized frequency (Lambda/lambda) and hole-to-pitch ratio (d/Lambda) is obtained. The improved fully vectorial effective index method (IFVEIM) is proposed. The modal properties computed with the IFVEIM, such as the effective index and the total dispersion, are closely matched to those of the multipole method as well as to experimental values, and the errors of the effective index have been reduced by 2 to 3 orders of magnitude.

Numerical calculation of phase-matching properties in photonic crystal fibers with three and four zero-dispersion wavelengths

Photonic crystal fibers with three and four zero-dispersion wavelengths are presented through special design of the structural parameters, in which the closing to zero and ultra-flattened dispersion can be obtained. The unique phase-matching properties of the fibers with three and four zero-dispersion wavelengths are analyzed. Variation of the phase-matching wavelengths with the pump wavelengths, pump powers, dispersion properties, and fiber structural parameters is analyzed. The presence of three and four zero-dispersion wavelengths can realize wavelength conversion of optical soliton between two anomalous dispersion regions, generate six phase-matching sidebands through four-wave mixing and create more new photon pairs, which can be used for the study of supercontinuum generation, optical switches and quantum optics.

Study on dual-concentric-core dispersion compensation photonic crystal fiber

The dual-concentric-core photonic crystal fiber composed of pure silica and air is proposed in this paper. Around 1.55 ¼m, it exhibits a negative chromatic dispersion as high as -5850 ps/km/nm. Based on multipole method, a systemic and in-depth simulation is realized to investigate the mode characteristics. The explanations to propagation states of the fundamental mode and the second mode are given elaborately. Finally, the variation of structural parameters is investigated to evaluate the tolerance of the fabrication. As a result, the designed fiber can be fabricated easily.

Multi-Hole Core Photonic Crystal Fiber Guiding Light in Subwavelength Air Holes

We present a novel multi-hole core photonic crystal fiber for guiding and confining light in subwavelength-diameter low-refractive-index air holes of core, even when light is guided based on total internal reflection. The low-loss, broadband and single-mode guiding properties of the fiber are studied. The propagation mechanism in subwavelength and low-refractive-index holes is analyzed by evanescent wave coupling. Light confinement and enhancement are caused by large discontinuity of the electric field at dielectric interfaces. Multiple subwavelength air holes in the core can guide light together, coupling and coherent with each other. Arrays of air holes in the core can be used as a means of patterning light on a submicrometer regime. The high light intensity in multiple long holes enables a variety of applications in nonlinear light management, optical modulation, and gas sensing.

Validity condition of separating dispersion of PCFs into material dispersion and geometrical dispersion

When using normalized dispersion method for the dispersion design of photonic crystal fibers (PCFs), it is vital that the group velocity dispersion of PCF can be seen as the sum of geometrical dispersion and material dispersion. However, the error induced by this way of calculation will deteriorate the final results. Taking 5 ps/(km·nm) and 5% as absolute error and relative error limits, respectively, the structure parameter boundaries of PCFs about when separating total dispersion into geometrical and material components is valid are provided for wavelength shorter than 1700 nm. By using these two criteria together, it is adequate to evaluate the simulated dispersion of PCFs when normalized dispersion method is employed.

Study on highly nonlinear microstructured fibers

A highly nonlinear dispersion flattened microstructured fiber is proposed. The new structure adopts two claddings with different pitches, air-holes diameters and air-holes arrayed fashions. The characteristics of such microstructured fiber such as nonlinearity and dispersion properties are investigated. The influence of the cladding structure parameters on the nonlinear coefficient and geometric dispersion is analyzed by full-vector finite element method with perfectly matched layer. Highly nonlinear coefficient and the dispersion properties of fibers are tailored by adjusting the cladding structure parameters. A novel microstructured fiber with highly nonlinear coefficient and dispersion flattened which is suited for supercontinuum generation is designed.

Measurement of the bandgap in hollow-core microstructure fibers

Using an efficient, full-vectorial numerical simulation method, we analyze the existent conditions of the photonic bandgap (PBG), which is further demonstrated through experimental research. We utilize the method of transmission spectrum to measure the hollow-core microstructure fibers (HC-MSFs) in the visible and near infrared regions. The signal is obtained by detecting light from the end of the fiber. The experimental results indicate that there are several strong transmission bands in the near infrared region, but hardly any bandgaps in the visible region. Furthermore the attenuation in the visible wavelength is very considerable. The parameters of the HC-MSFs structure used in the measurement are the distance of nearest air holes pitch Λ (2.65μm), the diameter of air holes in the cladding d (2.10μm), and the central air core diameter (8.37μm). The spectrum positions of the bandgap in the spectrogram are 2297nm, 2406nm, and 2525nm, respectively. The repetition of the experimental results is fine.