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This paper introduces a new design based on As2Se3 photonic crystal fibers, with the first layer of air holes near the core being removed. Dispersion properties were investigated for fibers with various types of lattice, including circular, square, and hexagonal lattice. Three fibers with a flat, all-normal dispersion, and a low dispersion value are proposed for supercontinuum generation at the same pump wavelength of 5.5 µm. The input pulse has a duration of 180 fs and a low peak power of 2.778 kW propagating in 10 cm fibers length, generating supercontinuum spectrums at 30 dB levels of 5.725 µm, 5.348 µm, and 5.936 µm, respectively, for circular, square, and hexagonal lattices. In addition, the fiber with the hexagonal lattice has the highest nonlinear coefficient of 862.654 W−1.km−1 and the lowest confinement loss of 0.137 dB/m, causing the largest bandwidth. The supercontinuum generation with low peak power using optimized PCFs with high nonlinearity and low confinement loss, makes them suitable for many application areas, e.g., the polarization-maintaining, coherent optical communications, nonlinear optics, etc. [ABSTRACT FROM AUTHOR]

In this paper, a new photonic crystal fiber with hollow core filled by styrene (PCFS) has been designed for coherent supercontinuum generation. Its main optical characterisitcs are simulated for different lattice microstructure. The PCFS2,0.3 with lattice pitch Λ=2 μm, filling factor d/Λ=0.3 and styrene core of diameter of 3.34 μm, owning the flat and anomalous dispersion in the near infrared range from 1.33 μm, lower confinement loss, higher effective refractive index at pump wavelength, and smaller effective mode area is chosen to invetigate the supercontinuum spectrum (SC). The spectrum broadening of SC depending on the fiber's length, pump duration and pump energy is simulated and discussed in comperison to that obtained in the photonic crystal fibers with hollow core filled with toluene (PCFT2,0.3). [ABSTRACT FROM AUTHOR]

Ultrastructural, hydrodynamic, rheological, and emulsifying properties of chitin nanowhisker dispersions from commercial (C) and laboratory (L) origin were analyzed at pHs 2–3.5. Nanowhiskers were rod-like shaped and their hydrodynamic properties changed in range: particle size: 90–560 nm; ζ potential: 26–42 mV; polydispersity 0.175–0.850. Flow curves indicated a shear-thinning behavior for both samples. At pH 2 dispersions were more consistent than at pH 3.5, but in both cases L showed higher consistency than C. Both C and L exhibited a non-stationary (thixotropic) flow at pH ≥ 2.5. The coexistence of two shear-induced domains was found in the oscillatory tests. The emulsifying ability of both C and L samples at a low (0.5%) concentration was dependent on pH. So, at pH 2, the L sample showed a greater emulsifying ability (98%) and emulsion stability (92-90%) than the C sample (emulsion stability ≈74%). • Shrimp chitin was hydrolyzed to form rod-like structures that aggregate al low pH. • Rheological properties of chitin whiskers are dependent on pH in the range studied. • A shear thinning effect was observed; samples at pH 2 were more consistent. • At pH 3, chitin whiskers exhibited the highest thixotropy. • Whiskers dispersed at pH 2 showed higher emulsion ability/stability than at pH 3.5 [ABSTRACT FROM AUTHOR]

The absence of Raman and unique pressure-tunable dispersion is the characteristic feature of gas-filled photonic crystal fiber (PCF), and its zero dispersion points can be extended to the near-infrared by increasing gas pressure. The generation of dispersive wave (DW) in the normal group velocity dispersion (GVD) region of PCF is investigated. It is demonstrated that considering the self-steepening (SS) and introducing the chirp of the initial input pulse are two suitable means to control the DW generation. The SS enhances the relative average intensity of blue-shift DW while weakening that of red-shift DW. The required propagation distance of DW emission is markedly varied by introducing the frequency chirp. Manipulating DW generation in gas-filled PCF by the combined effects of either SS or chirp and three-order dispersion (TOD) provides a method for a concentrated transfer of energy into the targeted wavelengths. [ABSTRACT FROM AUTHOR]

Dielectric properties of single-crystalline BaTiO3in the direction to <001> were investigated by impedance spectroscopy. The complex plane plots showed high- and low-frequency semicircles and an inclined spike at 548–648 K. The spectroscopic plots ofM″ comprised a single relaxation peak at 102–104Hz, whereas those ofZ″ exhibited a peak at high frequencies (102–104Hz), a low-frequency peak, and dispersion. The high-frequency relaxation was attributed to the ferroelectric bulk. The low-frequency peak and dispersion were associated with the charge transfer and the Warburg impedance, respectively. The low-frequency impedance response implied the ionic conduction of BaTiO3. [ABSTRACT FROM PUBLISHER]

We propose an As2Se3-based highly nonlinear photonic quasi-crystal fiber with dual zero-dispersion wavelengths (ZDWs). Using a full-vector finite element method, the proposed fiber is optimized to obtain high nonlinear coefficient, low confinement loss and two zero-dispersion points by optimizing the structure parameters. Numerical results demonstrate that the proposed photonic quasi-crystal fiber (PQF) has dual ZDWs and the nonlinear coefficient up to 2600 W−1 km−1within the wavelength range from 2 to 5.5 μm. Due to the introduction of the large air holes in the third ring of the proposed fiber, the ability of confining the fundamental mode field can be improved effectively and thus the low confinement loss can be obtained. The proposed PQF with high nonlinearity and dual ZDWs will have a number of potential applications in four-wave mixing, super-continuum generation, and higher-order dispersion effects. [ABSTRACT FROM AUTHOR]

This study presents a novel techniquefor the controllable preparationof aragonite CaCO3whiskers using a microdispersion process.Calcium dodecyl benzenesulfonate [Ca(Ar–SO3)2] was first used as an additive for controlling the crystallineform. A homogeneous concentration distribution in the system was achieveddue to the efficient micromixing. The effects of various operationparameters on the whiskers were determined, and the reaction conditionswere optimized. The mechanism of the additive was discussed. The dynamicadsorption of Ca(Ar–SO3)2on the surfaceof whiskers was experimentally demonstrated to be in charge of maintainingthe one-dimensional growth and the high purity of the crystals. AragoniteCaCO3with a crystalline purity of 98–99.5% wascontrollably synthesized at room temperature. The whiskers were approximately27 μm in length and had an aspect ratio of about 58. [ABSTRACT FROM AUTHOR]

In this paper, we numerically investigate the dynamics of soliton-effect compression of femtosecond optical pulses in silica-core photonic crystal fiber (PCF) at 850 nm using both empirical relations method and symmetrized split-step Fourier method. We propose a novel nano-size silica PCF structure featuring a minimum anomalous group velocity dispersion, small higher-order dispersions and enhanced nonlinearity for efficient soliton-effect compression of femtosecond optical pulses with subnanojoule input pulse energies over small distances. [ABSTRACT FROM AUTHOR]

In the work, we have presented the technique based on the graphics processing unit accelerated finite-difference time-domain (FDTD) method for characterization of a single-mode photonic crystal fiber (PCF) with an arbitrary refractive index profile. In contrast to other numerical methods, the FDTD allows studying the mode propagation along the fiber. Particularly, we have focused attention on the method details that allowed us to reduce dramatically the computation time. It has been demonstrated that the accuracy of dispersion obtained by the FDTD method is comparable to the one provided by the finite elements method while possessing lower computation time. The method has been used to determine the fundamental mode cut-off of all-normal dispersion PCF and to find fiber losses beyond this wavelength. [ABSTRACT FROM AUTHOR]

Abstract: Intermodal dispersion (IMD) in a two-core fiber can distort or even breakup pulses propagating in the fiber, and thus limit the usefulness of the fiber for applications that involve the transmission of ultrashort pulses. In this paper, we analyze a two-core photonic crystal fiber (PCF) for the elimination of IMD. The refractive index of the two cores required is slightly lower than the surrounding index and can serve as an effective parameter for the control of the wavelength at which the IMD disappears. The fiber has a conventional PCF structure and is compatible with the existing PCF fabrication technology. [Copyright &y& Elsevier]

To our knowledge, efficient generation of broadband four-wave mixing cascades centered at 1 μm and spanning 600 nm is experimentally demonstrated for the first time. This frequency comb is generated from a two-tone seed with a maximum peak power of 25 W in a low-dispersion photonic crystal fiber. It consists of up to 44 new idler waves generated symmetrically around the seed. [ABSTRACT FROM AUTHOR]

Abstract: We proposed a new structure of highly nonlinear low-dispersion photonic crystal fiber with high birefringence for four-wave mixing. Its dispersion and nonlinear coefficient are investigated simultaneously by using the full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that the dispersion variation is within ±0.7pskm−1 nm−1 in the C band, and the corresponding nonlinear coefficient and birefringence are about 60.5W−1 km−1 and 4.92×10−3 at 1.55μm, respectively. The proposed PCF with low dispersion, high nonlinearity, and high birefringence can have important application in four-wave mixing. [Copyright &y& Elsevier]

Abstract: Large solid-core fiber designs constructed by omitting nine air-holes at the center of square-lattice silica photonic crystals with square shaped air-holes have been investigated theoretically and their characteristics have been compared with those of circular ones. The V-parameter was estimated by using the step-index fiber approximation and the effective mode area calculated for the structures considered. To estimate the effective core radius of the structure with square shaped air-holes an approximation based on the air-filling fraction was used. The dispersion and confinement losses were also obtained and compared for both of the structures. [Copyright &y& Elsevier]

The methods using femtosecond lasers are very popular in the world recently. They are used for different research methods. We begin to use a multi-photon autofluorescence method for cancer tissue detection. We plan to use this method with special photonic crystal fiber optic sensors. We would like to use to this detection femtosecond oscillator for 800 nm region. However, according to our information there is no fiber which can provide these femtosecond signals at 800 nm region without dispersion and nonlinear effect. Applying typical fiber causes dispersion of guided signals. Therefore we are preparing suitably designed fibers. Double-clad photonic fibers can play a dual role of ultrashort pulse delivery and efficient collection of nonlinear optical signals. In the paper a new design of double cladding small dispersion photonic crystal fiber is proposed. Simulations of both structure and dispersion in proposed fibers are presented. [ABSTRACT FROM AUTHOR]

Abstract: A novel dispersion compensating fiber (DCF) with multiple windows is proposed, which is based on hybrid photonic crystal fibers. This type of DCF has a characteristic of multiple negative dispersion windows by the coupling between the hybrid guiding mode in the boundary of each band-gap of the core region and the index guiding mode in the cladding defect area. This is entirely different from the ordinary dual-core mechanism. The proposed DCF can compensate multiple dispersion wavelengths at the same time. [Copyright &y& Elsevier]

We present a technique based on the optofluidic method to design a photonic crystal fiber (PCF) experiencing small dispersion over a broad range of wavelengths. Without nano-scale variation in the air-hole diameter or the lattice constant of Λ, or even changing the shape of the air holes, this approach allows us to control the dispersion of the fundamental mode in a PCF simply by choosing a suitable refractive index of the liquid to infiltrate into the air holes of the PCF. Moreover, one can design a different PCF such as a dispersion flattened fiber (DFF), dispersion shifted fiber (DSF), by utilizing fluids of various refractive indices. [ABSTRACT FROM AUTHOR]

Abstract: We have proved that in an all-normal dispersion-flattened photonic crystal fiber (PCF), the four-wave mixing (FWM) process dominantly affects the flatness of the generated supercontinuum (SC). The numerical results show that pulses with steepened edges can enhance the FWM conversion efficiency during the SC’s generation and the minima of the spectral oscillatory structure will be smoothed. A double-pass Littman–Metcalf optical bandpass filter is used to make the 1.60ps hyperbolic-Secant shaped pulses obtain steepened edges. The experimental results show that the flatness of the SC generated from the 4nm filtered pulses is improved by 0.21dB. The SC with 10–65nm tunable bandwidths is obtained by adjusting the filter bandwidth from 1nm to 7nm. Further numerical results show that the filter induced SC’s flatness improvement is more effective for pulses with 2.0–4.0ps FWHM. The improved SC can be used for applications which require stable modulation carriers and flexible bandwidth. [Copyright &y& Elsevier]

A theoretical investigation on the parabolic pulse nonlinear propagation and spectral compression in all-normal dispersion photonic crystal fibers (PCFs) is presented. It is found that use of larger chirp can obtain higher quality transform-limited spectrally compressed parabolic pulses due to almost purely the effects of self-phase modulation (SPM) - because of its all-normal dispersion with smaller group velocity dispersion (GVD). Also, use of long initial negatively chirped parabolic pulses can lead to the most efficient transform-limited spectral compression under the optimal compression condition. [ABSTRACT FROM AUTHOR]

Using a photonic crystal fiber with a zero dispersion wavelength of the fundamental mode at 780 nm designed and fabricated in our lab, the ultraviolet and mid-infrared continua are generated by cross-phase modulation between red-shift solitons and blue-shift dispersive waves. The dependences of continuum on the pump power and wavelength are investigated. With the pump working at 820 nm, when the pump power increases from 300 to 500 mW, the bandwidths of ultraviolet and mid-infrared continua change from 80 to 140 nm and 100 to 200 nm, respectively. The wavelength of ultraviolet continuum is below 246 nm, and the wavelength of mid-infrared continuum exceeds 2500 nm. Moreover, the influences of pump power on wavelength and conversion efficiency of different parts of continua are also demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we investigate the generation of supercontinuum (SC) light source based on a highly nonlinear Germanium (Ge) doped photonic crystal fiber (HNL-GePCF) with all normal group velocity dispersion (GVD). By doping 3% higher refractive index Ge inside silica, nonlinear coefficient is increased as large as 110.6W−1 km−1 at . Using finite element method (FEM) with a circular perfectly matched boundary layer (PML), it is shown through simulations that the proposed HNL-GePCF offers an efficient SC generation for dental optical coherence tomography (OCT) applications at . By propagating sech2 picosecond optical pulses having 2.5ps and 1.0ps pulsewidth at a full width at half maximum (FWHM) through the proposed HNL-GePCF, output optical pulses are analyzed by the split-step Fourier method to obtain the spectral contents. Simulation results show that 105m of the proposed HNL-GePCF can produce 100nm spectrum (10dB bandwidth) at for 2.5ps input optical pulse and 110m of such HNL-GePCF can produce 140nm spectrum (10dB bandwidth) for 1.0ps input optical pulse. Therefore, the highest longitudinal resolutions in the depth direction for dental OCT are found about for enamel and for dentin. [Copyright &y& Elsevier]

Abstract: A theoretical investigation on the two pulses copropagation and the red-shifted radiation generation in a photonic crystal fiber with two zero-dispersion wavelengths are presented. It is found the intensity of the red-shifted radiation components can be enhanced when the fiber is pumped with two pulses and the pulse trapping occurs. As the input peak power of the pump pulse is increased under the phenomenon of pulse trapping, the intensity of the red-shift radiation can be further enhanced. The above effects can be explained by the energy transfer from the Raman soliton to the red-shifted radiation components due to the effect of pulse trapping and the effect of higher-order dispersion. [Copyright &y& Elsevier]

In this paper, we propose the design of tunable and robust wavelength converters which can perform the polarity-preserved or polarity-inverted wavelength conversion by using the cross-phase modulation (XPM) in a dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF). The newly designed wavelength converter consists of a DF-HNL-PCF and an optical band-pass filter in the simple straight-line configuration, where XPM leads to broadening the spectrum of a continuous-wave probe light and the polarity-preserved, tunable wavelength conversion is then implemented by filtering out the blue-chirped or red-chirped spectral component of a probe light. The experimental results show that the polarity-preserved wavelength converter using a DF-HNL-PCF can achieve the error-free conversion of 10 Gbit s-1 optical data signals with the maximum power penalty of less than 2.1 dB over a wavelength range of nearly 34 nm. This wavelength tunability is actually limited by an operational wavelength range of the tunable optical band-pass filter that is used to extract the wavelength-converted signal in our experiment. Moreover, the polarity-inverted wavelength conversion is observed at the XPM-based wavelength converter using a DF-HNL-PCF, for the first time. This is achieved by tuning the central wavelength of an optical band-pass filter to coincide with that of a chirped probe light. [ABSTRACT FROM AUTHOR]

Abstract: Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494fs (with 56nJ pulse energy) to 1.24ps (with 49nJ pulse energy) at 55MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation. [Copyright &y& Elsevier]

Abstract: Cladding-ring-equivalent effective index method (CREEIM) is proposed to analyze the propagation characteristics in the multi-cladding photonic crystal fibers (MCPCFs). The effective indices and dispersions of the step index two and three-cladding structures are calculated with the Sellmeier formula. The accuracy of CREEIM is competitive to the results calculated by the multipole method (MPM). With different structure parameters, the differences between two methods are evaluated with the relative error R E of effective index and relative difference R D of dispersion. This method is also used to analyze the mode cut-off and nonlinear characteristics in the three-cladding structure PCFs by calculating the mode effective index n eff instead of complex mode field distribution. [Copyright &y& Elsevier]

In this study, a new photonic crystal fibre (PCF) structure is proposed which is suitable for optical telecommunications. This PCF has some features including low- and ultra-flattened dispersion and low confinement loss as well as a large effective area in a wide range of wavelengths. To analyse this PCF, finite-difference time-domain (FDTD) method with the perfectly matched layers boundary conditions has been used. For the proposed PCF, dispersion has small variations about 0.8 ps/(nm km) in the wavelength range from 1.1 to 1.7 µm and dispersion value is less than 2.5 ps/(nm km) in applicable wavelengths. The confinement loss is obtained less than 10-6 dB/km in this range, whereas the effective area is around 61.2 µm2 at 1.55 µm wavelength. The results show that the confinement loss of the designed hexagonal PCF is small, although the effective area is large. The optimal structural parameters are designed to achieve minimum confinement loss, dispersion and dispersion variation which can be properly utilised in broadband optical transmission applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a highly nonlinear dispersion flattened hexagonal photonic crystal fiber (HNDF-HPCF) with nonlinear coefficients as large as 57.5W km at 1.31 μm wavelength for dental optical coherence tomography (OCT) applications. This HNDF-HPCF offers not only large nonlinear coefficient but also very flat dispersion slope and very low confinement losses. Using these characteristics of our proposed PCF, it is shown through simulations by using finite difference method with an anisotropic perfectly matched boundary layer that this PCF offers the efficient supercontinuum (SC) generation for dental OCT applications at 1.31 μm wavelength using a picosecond pulse easily produced by commercially available less expensive laser sources. Coherent length of light source using SC is found 10 μm and the spatial resolutions in the depth direction for dental applications of OCT are found about 6.1 μm for enamel and 6.5 μm for dentin. [ABSTRACT FROM AUTHOR]

An index-guided, two-dimensional photonic crystal fiber (PCF) with triangular lattice and solid air core was designed and investigated using the effective index method. A modal analysis of three-ring elliptical air hole photonic crystal fiber is presented: first the innermost ring was made elliptical and then the cells of the inner two rings were made elliptical and finally all three rings contained elliptical cells. The above configuration was then compared with three-ring circular air hole photonic crystal fiber keeping the area of air holes and simulation parameters of the wafer the same to obtain the fundamental space-filling mode (FSM). The analysis was performed using full vector FDTD for TE and TM polarizations. The complex effective refractive index generated was then used to calculate the chromatic dispersion and birefringence properties of the PCF. [ABSTRACT FROM PUBLISHER]

Abstract: We report results of experimental studies of the ac susceptibility of a Nb single crystal at low frequencies in swept magnetic fields applied parallel to the surface. Analysis of the experimental data shows that the swept magnetic field significantly changes the bulk conductivity for . It becomes dissipative with substantial frequency dispersion. At the surface, a layer with enhanced conductivity in comparison to the bulk was detected for . This layer provides a considerable contribution to the shielding and absorption of the ac field even in the mixed state. There is anomaly of an ac susceptibility in the field near the transition between Abrikosov’s phase and surface superconducting states. Conductivity of the surface layer in large dc fields , measured in point-by-point mode, and in a swept field is unexpectedly small in spite of the large value of the order parameter near the surface. We demonstrate that the swept magnetic field affects the ac response of the surface superconducting states. [Copyright &y& Elsevier]

Abstract: A highly birefringent index-guiding photonic crystal fibers with flattened dispersion and low effective area is proposed by introducing elliptical air holes in the cladding and small holes both in the core area and in the cladding. With the plane wave expansion (PWE) method, the birefringent, dispersion and effective area of the fundamental modes in such photonic crystal fibers are analyzed in detail. The simulation result shows that high birefringence with a magnitude of the order of 10−3, flattened chromatic dispersion from 1100nm to 1800nm and low effective area (which mean high nonlinearity) are obtained. Furthermore, the influences on the birefringence and dispersion by geometrical parameters have also been discussed and a modest number of design parameters are given. [Copyright &y& Elsevier]

Abstract: Biobased nanocomposites based on cellulose nanowhiskers (CNWs) and cellulose acetate butyrate (CAB) were prepared using solvent exchange of CNWs to ethanol by sol–gel method followed by casting. The strong flow birefringence of the solutions indicated evenly dispersed cellulose nanowhiskers in the dissolved polymer CAB. Scanning electron microscopy of the nanocomposites confirmed well dispersed CNWs in the CAB matrix, which was further supported by the high transparency exhibited by the nanocomposites. The results of tensile tests indicated significant improvements in the mechanical properties of nanocomposites by increasing the CNWs contents. The Young’s modulus and strength increased 83% and 70%, respectively, for nanocomposites with 12wt% of CNW, and the strain was not suppressed compared to the neat CAB. The dynamic mechanical thermal analysis demonstrated significant improvement in storage modulus with increasing CNW contents, and the tan δ peak position was moved towards higher temperature when CNW was added. It is expected that solvent exchange by the sol–gel route followed by casting of nanocomposites from the same solvent will provide a promising route for obtaining cellulose nanocomposites with well dispersed CNW, leading to improved mechanical properties, even with low nanowhisker contents. [Copyright &y& Elsevier]

Abstract: A novel kind of large mode area photonic crystal fibers (PCFs) are proposed in this paper. In order to achieve large effective mode area, a novel technique is applied to seven missing air hole PCF structures. The modal characteristics of PCF structures such as effective mode area, confinement loss, chromatic dispersion properties with doped cores, are investigated by employing the full vectorial finite element method (FEM). Simulation results demonstrate that effective mode area and confinement losses of fundamental mode simultaneously improved by applying our novel technique to proposed structures. The effects of bending on confinement losses of the proposed PCFs have been thoroughly investigated. Additionally, confinement losses of first higher order modes are presented and the possibility of stripping them in a simple way is discussed. [Copyright &y& Elsevier]

The article presents a study which examines the efficiency of a highly nonlinear octagonal photonic crystal fiber (HN-OPCF) with Germanium (Ge)-doped core for use in optical coherence tomography (OCT). The study performs simulations for two HN-OPCF with high nonlinear coefficient and flattened dispersion at 1.31µm wavelength bands. Result shows high nonlinear coefficient and flattened dispersion of HN-OPCF, which can enable supercontinuum generation, which is critical in OCT.

Abstract: We propose a new type of birefringent index guiding photonic crystal fiber (PCF) with two hollow GeO2-doped silica ring defects imbedded in a hexagonal hole arrays. Rigorous finite element method (FEM) using the perfectly matched layer (PML) was applied to calculate complex propagation constant and analyze optical transmission characteristics. Birefringence was flexibly controlled independent of chromatic dispersion, and improvement in confinement loss was achieved by optimizing hollow ring defect parameters. [Copyright &y& Elsevier]

Dispersion properties, birefringence and confinement loss between the circular air-hole photonic crystal fiber (CAHPCF) and rotational elliptical air-hole photonic crystal fiber (REAHPCF) are investigated numerically by means of a plane-wave expansion method and a finite element method. Results show that the performances of REAHPCF on flatter dispersion curve, single mode, high birefringence and low confinement loss is better than that of CAHPCF. [ABSTRACT FROM AUTHOR]

Using the photonic crystal fiber (PCF) with zero dispersion wavelengths of the fundamental mode and the second-order mode at 985 nm and 885 nm designed and fabricated in our lab, the anti-Stokes signals from 586.5 to 558 nm are efficiently generated in the second-order mode. When the pump working wavelength λ increases from 830 to 880 nm and the input average power P reduces from 43 to 25 mW, the output power of anti-Stokes signal increases 1.76 times, the power ratio of anti-Stokes signal at 558 nm to the residual pump component at 880 nm is estimated as 5:1, and the maximal conversion efficiency P/ P can be up to 36%. The possible reasons for the difference from theoretical results are discussed. The combined effects of the interval between the pump working wavelength and zero dispersion wavelength and the input power on the signal conversion process are analyzed. [ABSTRACT FROM AUTHOR]

In the present work, a multiwavelength Raman fiber laser based in a Sagnac configuration is presented. The Sagnac configuration is composed of a Hi-Bi photonic crystal fiber in the middle of two dispersion compensation fibers. The pump power induces two random mirrors to work in opposite directions in the Sagnac, leading to the amplified signal and the multiple scattering signals from the random mirror traveling through the Hi-Bi photonic crystal fiber in a counter-propagating way interfering in the output port. [ABSTRACT FROM AUTHOR]

Depending on the properties of photonic band gap materials, a novel photonic crystal fiber (PCF), formed by lithium niobate and liquid crystal, has been studied numerically. Dispersion relationships and transmission spectra of the PCF are calculated by methods of the full-vector modal and the finite difference time domain, respectively. The parameter-dependent dispersion and transmission of the PCF have been found. It is shown that the design of the novel photonic crystal fiber could be supported by the theoretical analysis in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Supercontinuum generation by dual-wavelength nanosecond pumping in the vicinity of both zero-dispersion wavelengths of a photonic crystal fiber (PCF) is experimentally demonstrated. It is shown in particular that two pumps at 1535nm and 767nm simultaneously pumping near the two zero-dispersion wavelengths of a specially designed PCF yields a combined visible and infrared supercontinuum spectrum spanning from 0.55μm to 1.9μm. We discuss the generation mechanisms underlying the continuum formation in terms of modulation instability and cascaded Raman generation. [ABSTRACT FROM AUTHOR]

Abstract: A photonic crystal fiber (PCF) is proposed that, through novel design, achieves an enhanced effective mode area. The PCF is composed of two concentric elliptical cores. The central core is un-doped silicon whilst the second, outer core region, is doped. The outer doped region is also bordered by lightly doped half ellipse segments. The effective mode area of the structure was calculated and compared with the mode area of conventional PCF''s. Our results show that the mode area and chromatic dispersion are very sensitive to the geometry, dimensions and placement of the lightly doped segments. The chromatic dispersion, bend losses and the nonlinear coefficient are also numerically simulated and presented in this paper. [Copyright &y& Elsevier]

By using appropriate self-similar scaling analysis, we delineate the generation of linearly chirped solitary pulses in photonic crystal fiber (PCF) at 850 nm to obtain the short pulses with large compression factor and minimal pedestal energy when compared to adiabatic compression scheme. The dispersion and nonlinearity varying nonlinear Schrödinger equation aptly models the pulse propagation in such a PCF. The analytical results demand that the effective dispersion must decrease exponentially while the nonlinearity must increase exponentially in the PCF. Thus, based on the analytical results, we propose the new design of tapered PCF by varying the pitch and diameter of the air hole. We adopt the projection operator method to derive the pulse parameter equations which indeed very clearly describe the self-similar pulse compression process at different parts of the PCF structures. As we are interested in constructing compact compressor, we also introduce another designing of PCF by filling chloroform in the core region. The chloroform filled tapered PCF exhibits low dispersion length for efficient pulse compression with low input pulse energy over small propagation distances. [ABSTRACT FROM PUBLISHER]

Abstract: Glass fiber polymer composites embedded with tetra-needle-like zinc oxide (ZnO) nanowhiskers were prepared. The prepared composites exhibited excellent mechanical properties after the effective dispersion of ZnO nanowhiskers in the resin. The static and dynamic compressive properties of the composites were tested in the thickness and in-plane directions. The macro- and microfracture morphologies of the damaged specimens were obtained by using a scanning electron microscope. The results show that the compressive properties of the composites could be significantly affected by strain rates. As the strain rate increases, the composites have a higher strength. The compressive properties of the composites are affected by the content of ZnO nanowhiskers in the resin. The high strength of the composites can be attributed to the three-dimensional structures of ZnO nanowhiskers and the corresponding stress transfer. [Copyright &y& Elsevier]

rigorous method of integral equations has been used to calculate the dispersion characteristics, fields, and radiation patterns of the leaky modes of photonic-crystal fibers with a shell in the form of a bounded 2D photonic crystal composed of parallel quartz capillaries contacting each other and a core in the form of a defect of a photonic crystal with one capillary removed. It is shown that, when thick-walled capillaries (with an air content in the shell of about 28%) are used, these fibers can be single mode and have an overlap integral of the fundamental-mode field with the dielectric medium that is smaller by a factor of more than two (in comparison with similar fibers formed by air channels of circular cross section). The significant dispersion of the group velocity of the fundamental modes of fibers near the edge of the photonic crystal band gap has been found. [ABSTRACT FROM AUTHOR]

Abstract: A large mode area photonic crystal fiber (LMA PCF) with an effective area of 180μm2 is used to generate a high energy, micro-joule range, flat, octave spanning supercontinuum (SC) extending from ~600nm to ~1720nm. A train of femtosecond pulses from a widely-tunable parametric amplifier pumped by a Ti:Sapphire regenerative amplifier system are coupled into a 20cm length of LMA PCF generating a SC of 1.4μJ energy. We present an experimental study of the high energy SC as a function of the input power and the pumping wavelength. The spectrum obtained at a pump wavelength of 1260nm presents spectral flatness variation less than 12dB over more than 1.1 octave bandwidth. The physical processes behind the SC formation are described in the normal and the anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation. [ABSTRACT FROM AUTHOR]

Abstract: We study the supercontinuum process in optical fibers numerically for a variety of dispersion profiles to investigate how a specific dispersion profile controls the emission of dispersive waves. We conclude that the number of zero-dispersion points in the dispersion profile of a fiber is an excellent predictor of the dispersive-wave peaks when it is pumped with femtosecond pulses in the anomalous dispersion regime. Our study reveals that two or more such peaks can form on the same side of the input wavelength in specially designed and practically achievable dispersion profiles. We show that dispersive waves are emitted even in the case of normal dispersion where soliton fission does not occur. We suggest that a phenomenon related to soliton spectral tunneling is responsible for this radiation. Distinct dispersive peaks may also appear when an optical pulse, launched in the normal dispersion region, later begins to propagate in the anomalous dispersion regime because of its spectral broadening. Several dispersion profiles are numerically employed to show how the soliton fission process creates non-solitonic radiation even under normal dispersion pumping. A time-domain picture clearly shows this radiation when the conventional phase matching condition is satisfied. We also propose a realistic photonic crystal fiber with a dispersion profile that supports dispersive-wave generation in the normal-dispersion region. Our study should prove useful for experiments designed to control the generation of blue light by launching femtosecond pulses into optical fibers. [Copyright &y& Elsevier]

Existence of solitons in nonlinear optical fibres was first predicted by Hasegawa and Tappert in 1973 and its experimental verification came in 1980. Ever since, both experimental and theoretical physicists have shown keen interest in this topic due to its versatile applications. Optical solitons are formed due to the balance between the group velocity dispersion and the self phase modulation in the anomalous dispersion regime, and the governing wave equation is the Nonlinear Schröddinger (NLS) equation. Optical solitons can exist in various systems like photonic crystal fibres, bulk materials like photorefractive materials, photopolymers, etc. What follows is an introduction to optical soiltons and their applications [ABSTRACT FROM AUTHOR]

Abstract: A new high negative dispersion photonic crystal fiber is proposed. It has double-core structure. The inner core has a circle germanium-doped region. The outer core is formed by removing the 3rd ring air-holes around the core. There are two ring air-holes between the two cores, Diameter of the 1st ring air holes is bigger than that of the 2nd ring air-holes, this can make mode coupling between inner mode and outer mode and showed that the high negative PCF is the result of this structure characteristics. There are honeycomb photonic lattice in the PCF''s cladding. The influence of the structure parameters deviated from the design those on the chromatic dispersion are evaluated. When the structure parameters Λ=1.50μm, d core=2.10μm, d 1=0.90μm, d 2=0.44μm and d 3=1.04μm, the dispersion coefficient D is −1320ps/(nm·km) at 1550nm. This is a new kind of chromatic dispersion compensation PCF. [Copyright &y& Elsevier]

An elliptical air-hole golden spiral photonic crystal fiber (EGS-PCF) is analyzed with the full-vectorial finite element method. The air-holes in the EGS-PCF are arranged in a spiral pattern governed by the Golden Ratio, where the design has been inspired by the optimal arrangement of seeds found in nature. The EGS-PCF exhibits extremely high birefringence (∼0.022 at operating wavelength 1550 nm) which is particularly useful for generating a polarization stable supercontinuum (SC). The fiber can also be designed to have a Zero Dispersion Wavelength (ZDW) at a suitable wavelength for only one polarization and large negative dispersion for the other, leading to a single-polarization SC. In addition, the fiber dispersion can be designed to obtain ZDWs at 800 nm and 1064 nm simultaneously, which can facilitate broadband supercontinuum generation (SCG) through multi-wavelength pumping. [ABSTRACT FROM AUTHOR]

Abstract: We propose a novel method to achieve highly nonlinear photonic crystal fiber (PCF) by filling highly nonlinear liquid chloroform in the core of hollow-core PCF (HCPCF). The dispersion properties and electric field distribution of the fundamental mode are calculated by using the full-vector finite element method (FVFEM). Simulation results indicate that the zero-dispersion wavelength (ZDWL) of the chloroform-filled PCF is adjustable around 800nm. Hence the femtosecond laser pulses with central wavelength at 800nm can propagate in anomalous dispersion regime of the PCF, inducing the spectra broadening. [Copyright &y& Elsevier]

Abstract: In this paper, we report a chalcogenide As2Se3 glass photonic crystal fiber (PCF) for dispersion compensating application. We have used the improved fully vectorial effective index method (IFVEIM) for comparing the dispersion properties (negative and zero dispersion) and effective area in hexagonal and square lattice of As2Se3 glass PCF using different wavelength windows. It has been demonstrated that due to their negative dispersion parameter and negative dispersion slope in wavelength range 1.2–2.5μm, both lattice structures of As2Se3 glass PCFs, with pitch (Λ =2μm), can be used as dispersion compensating fibers. Further, design parameters have been obtained to achieve zero dispersion in these fibers. It is also shown that As2Se3 glass PCF provides much higher negative dispersion compared to silica PCF of the same structure, in wavelength range 1.25–1.6μm and hence such PCF have high potential to be used as a dispersion compensating fiber in optical communication systems. [Copyright &y& Elsevier]