Overview of photonic devices based on functional materials-integrated photonic crystal fibers

Photonic crystal fibers (PCFs) have brought tremendous advancements due to their predominant features of peculiar air-holes arrangement in two-dimentional direction. Functional materials like metals, magnetic fluids, nematic liquid crystals, graphene and so on, are extensively adopted to integrate with PCFs to get extraordinary transmission properties. This review takes the development stages of photonic devices based on functional materials-infiltrated PCFs into consideration, covering the overview of common materials and their photoelectric characteristics, the state-of-art infiltrating/coating techniques, as well as the corresponding applications involving polarization filtering and splittering devices in optical communication and sensing elements related to multiple parameters measurement. The cladding air hole of PCFs provides a natural optofluidic channel for materials being introduced, light-matter interaction being enhanced, and transmission properties being extended, where a lab on a fiber are able to be proceeded. It paves a space for the development of photonic devices in the aspects of compact, multi-functional integration, and electromagnetic resistance as well. According to surface plasmon resonance, the property of tunable refractive indices, and the flexible geometry structures, it comes up to some representative researches on polarization filters, multiplexer-demultiplexers, splitters, couplers and sensors, making a candidate for widespread fields of telecommunication, signal-capacity, and high-performance sensing.

NONLINEAR PROPERTIES OF STRUCTURAL HETEROGENEOUS PHOTONIC CRYSTAL FIBERS WITH As2Se3 SUBSTRATE

We examine the possibility of improving the nonlinear properties of photonic crystal fibers (PCFs) with As2Se3 substrates by creating a difference in the diameters of the air holes of the rings around the core. With the new design, all-normal dispersion properties, small effective mode area, high nonlinear coefficient, and low confinement loss were achieved in the long-wavelength range of 2.0–7.0 µm. The highest nonlinear coefficient is 4414.918 W-1.km-1 at 4.5 µm for the lattice constant (Ʌ) of 3.0 µm and the filling factor (d/Ʌ) of 0.85, while the lowest loss is 1.823´10-21 dB/cm with Ʌ = 3.5 µm and d/Ʌ = 0.8. Based on the numerical simulation results, the characteristics of two optimal structures have been analyzed in detail to guide the application in supercontinuum generation.

Effects of Air Holes in the Cladding of Photonic Crystal Fibers on Dispersion and Confinement Loss of Orbital Angular Momentum Modes

In the development of orbital angular momentum (OAM) mode division multiplexing (MDM), the capacity of optical fiber communication must be improved. However, owing to dispersion and confinement loss, many OAM modes do not propagate stably over a long distance in optical fibers. In this work, the effects of the size, number, shape, number of layers, and layer spacing of air holes in the cladding of the fiber on the dispersion and confinement loss are analyzed based on a simple structure. The trends are studied and summarized to facilitate the design of optical fibers to achieve stable transmission of OAM modes over a long distance.

Calculation of Bandwidth of Multimode Step-Index Polymer Photonic Crystal Fibers

By solving the time-dependent power flow equation, we present a novel approach for evaluating the bandwidth in a multimode step-index polymer photonic crystal fiber (SI PPCF) with a solid core. The bandwidth of such fiber is determined for various layouts of air holes and widths of Gaussian launch beam distribution. We found that the lower the NA of SI PPCF, the larger the bandwidth. The smaller launch beam leads to a higher bandwidth for short fibers. The influence of the width of the launch beam distribution on bandwidth lessens as the fiber length increases. The bandwidth tends to its launch independent value at a particular fiber length. This length denotes the onset of the steady state distribution (SSD). This information is useful for multimode SI PPCF applications in telecommunications and optical fiber sensing applications.

Lossy mode resonances in photonic crystal fibers

The interaction effect of the fundamental mode in a special photonic crystal fiber (PCF) with a thin-film absorbing coating deposited on a surface of a fiber cladding on the optical transmission of the PCF is theoretically studied. It is shown that the transmission has a multi-peak spectrum that is determined by the resonance capture of the fundamental PCF mode energy by the coating. In some cases, this capture is explained by a resonance coupling between the fundamental core mode and leaky modes of the coating, or between the fundamental PCF mode and cladding modes located between PCF air channels and the coating. Examples are presented of using this effect to develop fiber-optic sensors of refractive index or pressure, and to sense a nanoscale adsorption layer of ammonia molecules deposited on a coating surface contacting air.

COMPARISON OF DISPERSION CHARACTERISTICS OF SOLID-CORE PCFs INFILTRATED WITH PROPANOL AND ETHANOL

In this paper, we propose the solid-core photonic crystal fibers (PCFs) with hexagonal cladding infiltrated with propanol in the air-holes. The dispersion characteristics and zero- dispersion wavelengths of these PCFs have been compared with previous publications and analyzed in detail. By investigating the dependence of the dispersion characteristics on the air-hole diameters, we determine the optimal structures with 1 µm of that. The PCF infiltrated with propanol exhibits flatter and smaller dispersion characteristic and the zero-dispersion wavelength shifted towards a longer wavelength, 24 nm compared with ethanol permeable PCFs [17]. This result shows that structure with a diameter of air-holes by 1µm is suitable for supercontinuum (SC) generation in the near- infrared wavelength range.