A liquid-crystal-filled polymer photonic crystal fiber is designed and numerically analysised for terahertz wave guiding. Bandgap-guiding terahertz fiber is obtained by infiltrating the cladding air holes of index guiding Topas photonic crystal fiber with liquid crystal 5CB. Structural parameter dependence and thermal tunability of the photonic bandgaps, mode properties and confinement losses of the designed fiber are investigated by using the finite element method. The bandgaps are formed based on antiresonances of the individual liquid crystal inclusions, so the positions of bandgaps depend strongly on the cladding hole diameter and weakly on the lattice constant. Bandgaps and the positions of the confinement loss minimum or peaks of the transmission spectra shift toward lower frequency as temperature increased from 25 °C to 34 °C due to the positive dno/dT of 5CB. Average thermal tuning sensitivity of -30 GHz/°C is achieved for the designed fiber. At the central frequency of the transmission band, high power transmission coefficient and thus low splicing loss between the aligned liquid-crystal-filled polymer photonic crystal fiber and the unfilled section is obtained. Our results provide theoretical references for applications of liquid-crystal photonic crystal fiber in sensing and tunable fiber-optic devices in terahertz frequencies.
The fabrication technology of refractive microlens array (MLA) with self-assembly of drops of various thermoplastic optical polymer solutions is reported. In order to develop a conventional drop-on-demand type ink-jet printing method for fabricating high quality microlens array, Firstly, we tried to prepare a series of optical polymer inks. These inks compose of high quality optical polymers, polymethylmethacrylate (PMMA), dopant, and functional organic molecules such as laser dye, nonlinear organic dye, and rare earth ion chelates with a suitable organic solvent. Effects of surface tension on the polymer solution drops induced the self-formation of microlenses. This process exhibited a completely self-assembly characteristic without any chemical and photochemical post-treatment. The resulting microlens array displayed diameters varying from 1mm to 5mm and focal lengths from less than one millimeter to a few millimeters. Observation with an atomic force microscope reveals that the surface roughness of the lens is 0.9 nm. The transmittance spectrum of the lens is also measured.
We report a new technology to fabricate microstructured polymer optical fiber (MPOF, also named polymer photonic crystal fiber, pPCF) preform rods by in-situ polymerization of monomer in a mould. Series of pPCF preform rods including elliptic core fiber preform rod, single-mode fiber preform rod and ring-type holes structured preform rods have been fabricated. The optimum conditions for monomer-based fabrication of pPCF preform rods were investigated. Then, drawing from primary preform rods to secondary preform rods was carried out in a home-made furnace. Finally, optical and thermal properties of these pPCF preform rods, such as transmittance, a glass transition temperature, and the distribution of molecular weight were investigated. Optically functional dye-doped pPCF preform rods, rhodamines-doped PMMA preform rods were successfully fabricated.
Since the gradient index material has important applications at photoelectric system, imaging system, and integrated-optical system. Now, researches on gradient index material containing silver ions are more popular, it is difficult to get glass with high silver content as silver ion is extruded from molten glass at the molten temperature. Two-step ion-exchange process including Ag +- Na+ and Na+ - Ag + ion-exchange is used to get gradient index. This paper is based on the research in our lab, by adjusting the glass composition to get a series of sodium-rich glass then drawing the fusioned glass into fiber with diameter of 1mm used for ion-exchange. We used mixed molten salt for ion- exchange, then we researched on the choice of silver salt, the advantage and disadvantage of mixed molten salt and single molten salt, and the coloring up problem after ion-exchange.
To test the dynamic photorefractive grating during holographic recording, as usual, the signal wave is blocked from time to time and simultaneously the diffracted beam of the reference wave is tested. This kind of measurement destroys the continuity of the holographic recording and increases the random noise and results in bad repeatability and reliability. In this paper, the phase-conjugate technique is used to overcome the above drawbacks. The reference wave and the object wave are much stronger than the probe beam propagating along the counter-direction of the reference wave. Thus the real-time and non-destructive testing of the dynamic holograms can be obtained by measuring the phase-conjugate wave of the object wave.