A single-mode highly birefringent dispersion-compensating photonic crystal fiber using hybrid cladding

Based on the hybrid cladding design, a single-mode photonic crystal fibre (PCF) is proposed to achieve an ultra-high birefringence and large negative dispersion coefficient using finite-element method. Simulation results reveal that with optimal design parameters, it is possible to achieve an ultra-high birefringence of 2.64 × 10^?2 at the excitation wavelength of 1.55 μm. The designed structure also shows large dispersion coefficient about ?242.22 to ?762.6 ps/nm/km over the wavelength ranging from 1.30 to 1.65 μm. Moreover, residual dispersion, effective dispersion, effective area, confinement loss and nonlinear coefficient of the proposed PCF are discussed thoroughly.     

Design of ultra-flattened nearly zero dispersion and ultrahigh non-linear slot microfibres with ultrahigh birefringence

We proposed a new simple design of microfibre employing an elliptical silica rod in the centre of fibre core region as a slot core for the purpose of controlling the chromatic dispersion properties of the microfibre and enhancing the performance of non-linearity and birefringence. The simulation results show that the proposed slot microfibre has ultra-flattened near-zero dispersion of 0.94 ps/(nm km) for quasi-TE mode over a 50-nm wavelength range, ultrahigh birefringence up to the order of 10^?1, and ultrahigh non-linear coefficients of 38.35 and 37.92 W^?1 m^?1 for the fundamental quasi-TE mode and quasi-TM mode at the wavelength of 1.55 μm. The outstanding advantage of this new design is that nearly zero ultraflattened dispersion, ultrahigh modal birefringence and ultrahigh non-linearity can be realized simultaneously simply using a slot fibre core. Benefiting from its excellent performance, the proposed slot microfibre will have great potential for all-optical signal processing applications.     

Ultra-flattened negative dispersion for residual dispersion compensation using soft glass equiangular spiral photonic crystal fiber

Abstract

We present a numerical investigation of an equiangular spiral photonic crystal fibre (ES-PCF) in soft glass for negative flattened dispersion and ultra-high birefringence. An accurate numerical approach based on finite element method is used for the simulation of the proposed structure. It is demonstrated that it is possible to obtain average negative dispersion of –526.99 ps/nm/km over 1.05–1.70 μm wavelength range with dispersion variation of 3.7 ps/nm/km. The proposed ES-PCF also offers high birefringence of 0.0226 at the excitation wavelength of 1.55 μm. The results here show that the idea of using the proposed fibre can be potential means of effectively directing for residual dispersion compensation, fibre sensor design, long distance data transmission system and so forth.     

Tailoring of broadband dispersion-compensating photonic crystal fibre

This paper presents a broadband dispersion-compensating photonic crystal fibre (B-DCPCF) with a high compensation ratio of 30:1. We theoretically tailored the negative dispersion in a photonic crystal fibre (PCF) to nullify the positive dispersion in the transmission fibre over a bandwidth range of as wide as possible. The numeric results indicate that the effective dispersion within ±0.64 ps/nm/km over a bandwidth range of 226 nm (from 1338 to 1564 nm), cover the E + S + C wavelength bands. Finally, the confinement loss and the modal properties were examined to verify that the proposed B-DCPCF with extremely low confinement loss and should be operated in single mode throughout the operating band.     

Design of ultra-low and ultra-flattened dispersion single mode photonic crystal fiber by DE/EDA algorithm

This paper proposes a combination of differential evolution (DE) and estimation of distribution algorithm (EDA) to design photonic crystal fiber structures with desired properties over the C communication band. In order to determine the effective index of propagation of the mode and then, the other properties of structure, a finite difference frequency domain (FDFD) solver is applied. The results revealed that the proposed method is a powerful tool for solving this optimization problem. The optimized PCF exhibits a dispersion of 0.22 ps nm^?1 km^?1 at 1.55 µm wavelength with a variance of ±0.4 ps nm^?1 km^?1 over the C communication band and a nearly zero dispersion slope.     

Behaviour of multiphase PVDF in (1−x)PVDF/(x)BaTiO<Subscript>3</Subscript> nanocomposite films: structural,optical, dielectric and ferroelectric properties

The present paper deals with the synthesis and characterization of (1?x)PVDF/(x)BaTiO₃ nanocomposite films with x?=?0.1, 0.2, 0.3, 0.4 and 0.5. The samples were synthesized by simple solution mixing method followed by tape casting process. FESEM images show the homogeneous dispersion of BaTiO₃ nanoparticles within the matrix of poly(vinylidene fluoride) (PVDF) with slight agglomeration. An improvement in the thermal stability of nanocomposite film is observed by TGA results. XRD as well as FTIR analysis indicate the α–β phase transition of PVDF in the nanocomposite films. The embedded BaTiO₃ forms an intermediate band among the PVDF structures and thus decreases the band gap of nanocomposite films by absorbing the wavelength of lower energies. The band gap of nanocomposite films for x?=?0.4 decreases to 2.4 eV as compared to 5.0 eV for pristine PVDF. The dielectric constant (?′) of pristine PVDF at 50 Hz is 8.9, which increases to 26.7 for (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film. An increase in the charge storage ability is observed from PE loops, as (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film has highest value of polarization (0.093 µC cm^?2) as compared to pristine PVDF (0.020 µC cm^?2). This shows an increase in the charge storage ability of (1?x)PVDF/(x)BaTiO₃ nanocomposite films as compared to pristine PVDF.     

High-birefringence dual-wavelength single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance

A dual communication band single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance is presented in this paper. Numerical simulation results demonstrate that the resonance strength of x- and y-polarized direction can reach 569.83 and 719.25?dB.cm^?1 simultaneously at the communication wavelength of 1.31 and 1.55?µm. By filling liquid analyte, the confinement loss of x- and y-polarized direction can simultaneously reach 831.7 and 580.53?dB.cm^?1 at the wavelength of 1.31 and 1.55?µm. Furthermore, when the fibre length L is equal to 700?µm, the peak value of the crosstalk can reach 493.86 and ?323.67?dB at the same time at the wavelength of 1.31 and 1.55?µm, and when the length of the fibre L is 400?µm, the bandwidths of the crosstalk better than 20?dB and less than ?20?dB are about 160 and 210?nm, respectively. These performances make it an ideal candidate for designing dual-band polarization filter equipment.     

Characterisation of CorGlaes<Superscript>®</Superscript> Pure 107 fibres for biomedical applications

A degradable ultraphosphate (55?mol?% P₂O₅) quinternary phosphate glass composition has been characterised in terms of its chemical, mechanical and degradation properties both as a bulk material and after drawing into fibres. This glass formulation displayed a large processing window simplifying fibre drawing. The fibres displayed stiffness and strength of 65.5?±?20.8?GPa and 426±143 MPa. While amorphous discs of the glass displayed a linear dissolution rate of 0.004?mg cm^?2?h^?1 at 37?°C, in a static solution with a reduction in media pH. Once drawn into fibres, the dissolution process dropped the pH to <2 in distilled water, phosphate buffer saline and corrected-simulated body fluid, displaying an autocatalytic effect with >90?% mass loss in 4 days, about seven times faster than anticipated for this solution rate. Only cell culture media was able to buffer the pH taking over a week for full fibre dissolution, however, still four times faster dissolution rate than as a bulk material. However, at early times the development of a HCA layer was seen indicating potential bioactivity. Thus, although initial analysis indicated potential orthopaedic implant applications, autocatalysis leads to accelerating degradation in vitro.     

Superradiance and lasing properties of new two-photon absorption dye DEASPS

Pumped by picosecond pulses from a Nd:YAG laser, a new lasing dye, trans-4-[4′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated to DEASPS), shows both intense superradiance and strong lasing properties in benzyl alcohol solution. By using streak camera systems, the superradiance and lasing can be distinguished both spectrally and temporally. It has been found that the peak wavelength of lasing is at 620 nm with a red-shift of about 12 nm to the superradiance wavelength. The lasing pulse shows an oscillatory effect that it is not found in the superradiance pulse. The fluorescence lifetime is 529 ± 40 ps and the effective molecular two-photon absorption is (1.25 ± 0.1) × 10^?48 cm⁴ ·s·photon ^?1, measured using a nonlinear transmittance method. This dye shows effective optical limiting of the pumping wavelength.     

Thermal stability and fire behavior of aluminum diethylphosphinate-epoxy resin nanocomposites

The flame retardancy of 2, 2-bis(4-glycidyloxyphenyl)propane (DGEBA)-aluminum diethylphosphinate (AlPi) nanocomposites (EP-AlPi/(P ? x), x = 1, 2, 3 %) was greatly enhanced by ultrasonic dispersion of nano-sized AlPi into epoxy resin. The UL 94 V-0 rating can be reached for EP-AlPi nanocomposites with a relatively low addition amount of AlPi (on the account of 8.4 wt% or phosphorus content of 2 wt%) as well as the LOI value over 37.2. The glass transition temperature (T _g) enhanced properties were investigated by DTA, which showed that: T _gs were about 5 °C higher than that of neat epoxy resin; T _g increased along with content increasing of AlPi. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of EP-AlPi/(P ? x) composites were studied by Kissinger’s, Ozawa’s, Flynn–Wall–Ozawa’s and Coast-Redfern’s methods, which suggested the conversion function f (α) = 1/2α ^?1 or f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 1 %); f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 2 %) and EP-AlPi/(P ? 3 %) during the investigated process. The epoxy resin nanocomposites obtained in this study are green functional polymers and will become flame retardant potential candidates in electronic fields such as printed wiring boards with high performance.     

High-power,high-repetition-rate picosecond optical parametric oscillators for the near-to mid-infrared

Abstract

We report high-repetition-rate, singly-resonant, picosecond optical parametric oscillators based on the nonlinear crystals LiB₃O₅ and KTiOAsO₄ which are synchronously pumped by a self-mode-locked Ti:sapphire laser operating at 81 MHz. These devices allow tunable pulse generation from 1·116-3·160 μm to be achieved. The LiB₃O₅ system produces average nearinfrared output powers of 325 mW and is continuous tuning over the wavelength range 1·16-2·26 μm. For 1·8 ps input pump pulses, transform-limited signal pulses with durations of 1-1·2 ps and idler pulses with durations of 2-2·2 ps have been generated over 1·2-2·2 μm, without requirement for dispersion compensation. The KTiOAsO₄ system produces average near-infrared output powers of 403 mW, with the signal tuning over 1·116-1·281 μm and idler tuning over 2·260-3·160 μm. Without dispersion compensation, signal (idler) pulses with durations between 1·01-1·03 (1·61-2·91) ps have been obtained for 1·2 ps input pump pulses.     

Tailoring the time delay of optical pulse/sequence employing cascaded SOA and band-pass filter

Abstract

A tunable time delay for a 100-ps pulse is achieved via a SOA cascaded band-pass filter, which can be tailored by tuning the filter or changing the SOA injection current. For a single pulse, when the pulse propagates through the cascaded system, a delay of 99.6 ps and an advance of 42.6 ps can be achieved by altering the SOA injection current at two different wavelengths located in the red band and blue band of the filter, respectively. The corresponding tunable delay range is 165 ps, and the maximum delay-bandwidth product (DBP) is 1.65. For an optical sequence, to our knowledge, it is the first time that the time delay is tailored over 145.6 ps corresponding to a DBP of 1.46 by tuning the wavelength from 1556.075 to 1556.955 nm, and 45.2 ps (95.6 ps) advance (delay) by tuning the injection current from 100 to 500 mA at 1556.155 nm (1556.955 nm). The dependence of the time delay on the injection current and filtering configuration has been discussed based on plenty of experiments data. Based on SOA’s fast switching, this device can be used for signal synchronization and bit-by-bit signal processing in a communication system.     

Characterization of birefringence dispersion in polarization-maintaining fibers by use of white-light interferometry

A new method for measuring the birefringence dispersion in polarization-maintaining fibers (PMFs) with high sensitivity and accuracy is presented. The method employs white-light interferences between two orthogonally polarized modes of PMFs. The group birefringence of the fiber is calibrated first. Then the birefringence dispersion and its variation along different fiber sections are acquired by analyzing the broadening of interferograms at different fiber lengths. The main sources of error are investigated. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm). A measurement repeatability of 0.001 ps/(km nm) is achieved.     

Three octave spanning supercontinuum by red-shifted dispersive wave in photonic crystal fibers

This article presents a three-layer index guided lead silicate (SF57) photonic crystal fiber which simultaneously promises to yield large effective optical nonlinear coefficient and low anomalous dispersion that makes it suitable for supercontinuum (SC) generation. At an operating wavelength 1550 nm, the typical optimized value of anomalous dispersion and effective nonlinear coefficient turns out to be ~4 ps/km/nm and ~1078 W^?1km^?1, respectively. Through numerical simulation, it is realized that the designed fiber promises to exhibit three octave spanning SC from 900 to 7200 nm using 50 fs ‘sech’ optical pulses of 5 kW peak power. Due to the cross-phase modulation and four-wave mixing processes, a long range of red-shifted dispersive wave generated, which assists to achieve such large broadening. In addition, we have investigated the compatibility of SC generation with input pulse peak power increment and briefly discussed the impact of nonlinear processes on SC generation.     

Generation of soliton and bound soliton pulses in mode-locked erbium-doped fiber laser using graphene film as saturable absorber

We report an observation of soliton and bound-state soliton in passive mode-locked fibre laser employing graphene film as a passive saturable absorber (SA). The SA was fabricated from the graphene flakes, which were obtained from electrochemical exfoliation process. The graphene flakes was mixed with polyethylene oxide solution to form a polymer composite, which was then dried at room temperature to produce a film. The film was then integrated in a laser cavity by attaching it to the end of a fibre ferrule with the aid of index matching gel. The fibre laser generated soliton pulses with a 20.7 MHz repetition rate, 0.88 ps pulse width, 0.0158 mW average output power, 0.175 pJ pulse energy and 18.72 W peak power at the wavelength of 1564 nm. A bound soliton with pulse duration of ~1.04 ps was also obtained at the pump power of 110.85 mW by carefully adjusting the polarization of the oscillating laser. The formation of bound soliton is due to the direct pulse to pulse interaction. The results show that the proposed graphene-based SA offers a simple and cost efficient approach of generating soliton and bound soliton in mode-locked EDFL set-up.     

Comparison of compressive and splitting tensile strength of autoclaved aerated concrete (AAC) containing water hyacinth and polypropylene fibre subjected to elevated temperatures

This paper described the results of an extensive experimental study on the comparative between compressive and splitting tensile behavior of autoclaved aerated concrete (AAC) containing water hyacinth fibre (WHF) with AAC mixed with polypropylene (PP) fibre. The specimens of AAC-WHF and the AAC-PP were subjected to elevated temperatures (100, 200, 400, 800 and 1000 °C). Test results indicated that an optimum water hyacinth and PP fibre dosage was at 0.5 and 0.75 % by volume respectively. The maximum residual in compressive strength and the splitting tensile strength of AAC-WHF and AAC-PP were 0.43 and 0.16 N/mm² and 0.51 and 0.18 N/mm² respectively. In addition, the loss in residual strength of AAC mixed PP fibre was slower than AAC mixed WHF. The splitting tensile strength of AACs was more sensitive to high temperatures than the compressive strength. A severe strength loss was observed for all of the AAC after exposure to 800 °C. Based on the test results, it can be concluded that the addition of PP fibers can significantly promote the residue mechanical properties of AAC during heating.     

Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

Photothermal beam deflection spectroscopy (BDS) with a red He–Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He–Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2?×?2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29?±?3; Chernozem typical [Voronic Chernozems, Pachic], 9.9?±?0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7?±?0.9 cm²·h^?1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53?±?4 cm²·h^?1 and 45?±?4 cm²·h^?1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10–14 cm, and a parent rock with Fe illuviation, depth 180–185 cm) also show a significant difference, thermal diffusivities are 9.5?±?0.8 cm²·h^?1 and 27?±?2 cm²·h^?1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.     

Effects of High Pressure on the Physical Properties of MgB2

The synthesis of MgB₂-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8?C1.0×10⁶ A/cm² in the self-field and 10³ A/cm² in a magnetic field of 8 T at 20 K, 5?C3×10⁵ A/cm² in self-field at 30 K, the corresponding critical fields being H _c2=15 T at 22 K and irreversible fields H _irr=13 T at 20 K, and H _irr=3.5 T at 30 K, thermal conduction of 53±2 W/(m?K), the Vickers hardness H _V =10.12±0.2 GPa under a load of 148.8 N and the fracture toughness K _1C =7.6±2.0 MPa?m^0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that high-pressure-prepared materials are promising for application in transformer-type fault current limiters working at 20?C30 K.     

Visible quantum cutting in Tb<Superscript>3+</Superscript> doped BaGdF<Subscript>5</Subscript> phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb³⁺) doped BaGdF₅ phosphor. This phosphor was synthesized by varying molar concentration of Tb³⁺ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF₅:Tb³⁺ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb³⁺ and Tb³⁺ or Tb³⁺ and Gd³⁺ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.     

Self-mode-locking effects in heavily doped single-clad Tm3+-doped silica fibre lasers

Self-mode-locking in single-clad Tm-doped silica fibre lasers operating at 1.92?µm is reported with 100% modulated mode-locked pulses observed for longer fibre lengths up to 6?m. The self-mode-locking was accompanied by self Q-switching. A mode-locked pulse duration of 191?ps has been measured using an autocorrelator based on a two-photon absorption detector for operation at 2?µm assembled for the purpose of this experiment. The experimental pulse train characteristics are found to be consistent with mode-locking theoretical analysis. The origin and properties of self-mode-locking in heavily Tm-doped fibre lasers are discussed.