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It is more than important to sensitively take the temperature in industrial production and experimental study. In this paper, the high-sensitivity temperature sensor based on high birefringent photonic crystal fiber is proposed. To increase the sensitivity, polydimethylsiloxane (PDMS) was filled into the internal elliptical air hole of the photonic crystal fiber (PCF) to propose the PDMS/silica hybrid PCF structures. Temperature is measured by the quantitative change in birefringence of the refractive index of the PDMS material with temperature. We designed it as a detection loop and obtain the temperature detection sensitivity of up to 8.01 nm/°C in the range of −20 °C–20 °C, which was 6.5 times higher compared to the sensitivity obtained by filling with ethanol. This enables the designed PCF temperature sensor to be used for real-time and accurate temperature monitoring in the fields of bio-detection, chemistry, pharmaceuticals, etc. • A birefringent photonic crystal fiber structure is proposed, which has great application potential in temperature detection. • The temperature detection sensitivity was improved 6.5 times than that of filling ethanol. • In the designed optical fiber loop, the temperature range can be adjusted by adjusting the length of the optical fiber. [ABSTRACT FROM AUTHOR]

Abstract In this study, a low-loss hollow-core photonic bandgap fiber (HC-PBF) with an isolated anti-resonance layer is proposed. The fiber cladding structure is the same as that of conventional HC-PBF, while the fiber core is surrounded and formed by an isolated anti-resonance layer which separates the core from the cladding. Simulation results show that the overlap between the fundamental mode and silica-air interfaces is dramatically reduced owing to introduction of the isolated anti-resonance layer, and the fiber loss lower than 3.5 dB/km can be achieved with only ∼ 13- μ m core diameter and ∼ 8- μ m mode field diameter at 1550 nm [ABSTRACT FROM AUTHOR]

Optical thermometry based on Y 3 Al 5 O 12 (YAG) single crystal optical fiber with end Tm 3+ /Yb 3+ co-doped is presented. The YAG crystal fiber with end Tm 3+ /Yb 3+ co-doped was grown by laser heated pedestal growth (LHPG) method. Under a 976 nm laser diode excitation, the upconversion (UC) emissions, originating from 3 F 2,3 → 3 H 6 and 3 H 4 → 3 H 6 transitions of Tm 3 + ions, were investigated in the temperature range from 333 K to 733 K. Interestingly, the UC emission intensity of 3 F 2,3 → 3 H 6 transition was significantly enhanced with increase of temperature, as compared with the other Tm 3+ /Yb 3+ co-doped materials. The temperature dependence of fluorescence intensity ratio (FIR) of these two emission bands ( 3 F 2,3 / 3 H 4 → 3 H 6 ) suggests that this doped YAG crystal fiber can be used as a highly sensitive optical thermal probe, which demonstrates a high absolute sensitivity with the maximum value of 0.021 K − 1 at 733 K. In addition, due to the compact structure, strong mechanical strength and high thermal stability, such thermal probe may be a more promising candidate for temperature sensor with a high spatial resolution. [ABSTRACT FROM AUTHOR]

In this work, the graphene oxide (GO) samples of different oxidation degree prepared by modified Hummers method were drop-coated on sapphire substrates as saturable absorber (SA). On this basis, this work innovatively combines GO, the excellent SA, with single crystal fiber (SCF), the outstanding laser gain medium, for the first time to achieve 1. 03 μ m passively Q-switched pulsed laser output with the maximum average power of 2.183 W and the repetition frequency of 317.42 kHz, which is, to our knowledge, the largest average power of passively Q-switched SCF pulsed laser output reported so far. • The phase, morphology, linear and nonlinear optical properties of graphene oxide (GO) have been studied. • The different degree of oxidation of GO is considered. • The GO saturable absorber is combined with Yb: LuAG single crystal fiber for the first time. • The highest average power of ever reported passively Q-switched single crystal fiber pulsed lasers is achieved. [ABSTRACT FROM AUTHOR]

Digital holographic microtomography is improved and applied to the measurements of three-dimensional refractive index distributions of fusion spliced optical fibers. Tomographic images are reconstructed from full-angle phase projection images obtained with a setup-rotation approach, in which the laser source, the optical system and the image sensor are arranged on an optical breadboard and synchronously rotated around the fixed object. For retrieving high-quality tomographic images, a numerical method is proposed to compensate the unwanted movements of the object in the lateral, axial and vertical directions during rotation. The compensation is implemented on the two-dimensional phase images instead of the sinogram. The experimental results exhibit distinctly the internal structures of fusion splices between a single-mode fiber and other fibers, including a multi-mode fiber, a panda polarization maintaining fiber, a bow-tie polarization maintaining fiber and a photonic crystal fiber. In particular, the internal structure distortion in the fusion areas can be intuitively observed, such as the expansion of the stress zones of polarization maintaining fibers, the collapse of the air holes of photonic crystal fibers, etc. [ABSTRACT FROM AUTHOR]

A kind of multi channel dual-core photonic crystal fiber polarization beam splitter is designed. We analyze the effects of the lattice parameters and the thickness of gold layer on the beam splitting by the finite element method. Numerical results show that the thickness of metal layer and the size of the air holes near the fiber cores are closely linked with the nature of the polarization beam splitter. We also obtain that extinction ratio can reach −73.87 dB at 1 . 55 μ m wavelength and at 1 . 41 μ m, 1 . 65 μ m extinction ratio can reach 30.8978 dB and 31.1741 dB, respectively. The comparison of the effect on the characteristic of the photonic crystal fiber with coating no gold is also taken into account. [ABSTRACT FROM AUTHOR]

In this paper, an optical fiber sensing system based on low coherence interferometry (LCI) is proposed and demonstrated to interrogate sensors comprised of selectively filled double-core photonic crystal fiber (SFDC-PCF). The sensor used here is made by selectively filling about 1/3 area of air holes in the cladding of photonic crystal fiber with distilled water. So the dual-core in the sensor has different effective refractive indices, resulting in a phase delay between two lights transmitting in the fiber. The phase delay of the sensor can be compensated by a Mach-Zehnder interferometer with a scanning optical tunable delay line in one arm of the interferometer, namely temporal interrogation. By tracking the value of phase delay, the change of the measurand can be detected. Temperature measurement is carried out to testify the system performance. An average sensitivity of 0.9 µm/°C is achieved within the temperature range of 29–92 °C. This work provides a new thinking for fiber sensing technology based on LCI. The proposed all-fiber sensing system, with the merits of cost-effective, stability, and flexibility, can demodulate the SFDC-PCF sensor signals well. Further improvements such as better sensitivity, larger measurement range and multiplexing efficiency can be realized by tailoring the PCF sensor's structure. [ABSTRACT FROM AUTHOR]

A dual-wavelength thulium-doped fiber laser with a wide switchable single-wavelength range is demonstrated by employing a polarization-maintaining photonic crystal fiber. A new type of comb filter is designed and its spectrum is simulated. A nonlinear polarization rotation module is inserted into the laser cavity to suppress intense gain competition. An output power instability as low as 0.84 dB has been attained. The switchable range of single-wavelength operation is 43.64 nm, and the slope efficiency is 1.79%, attained by optimizing the splicer parameter between the polarization-maintaining photonic crystal fiber and the single-mode fiber. There are five regions of dual-wavelength output from 1978.04 to 1986.51 nm, and the maximum and minimum wavelength intervals are 6.11 nm and 1.9 nm. • A novel structure and tunable filter using photonic crystal fiber can be utilized in Thulium-doped fiber laser. • The method of reducing welding loss between photonic crystal fiber and single mode fiber is presented. • Switchable single-wavelength emission can be achieved and the selection range is 43.64 nm. • There are five regions of dual-wavelength output from 1978.04 to 1986.51 nm. [ABSTRACT FROM AUTHOR]

The present paper is concerned with the analytical and numerical investigation of the transverse spatio-temporal instabilities in two-level broad-area lasers for the specific class-B case. We show that the two-level class-B broad-area laser tends to naturally operate in the filamentary state. This is revealed to be provided with two causes. First of them is related with the homogeneous output profile being intrinsically unstable due to the traveling-wave instability, independently from the boundary conditions. Secondly, high sensitivity to the boundaries of the pumping region was found for the commonly used top-hat-like profile leading to boundaries-induced filamentary dynamics. Spatio-temporal properties of both instability mechanisms are studied and their effects on the resulting laser dynamical behavior are analyzed. [ABSTRACT FROM AUTHOR]

A design for single-polarization single-mode photonic crystal fiber with rectangular lattice is proposed in this paper. The proposed fiber is studied by the full vector finite element method with perfectly matched layers. The single-polarization single-mode operation region of the fiber is achieved in a certain wavelength range with low confinement loss include the wavelength of 1.55 μm. The loss of one polarization is 0.124 dB/km at the wavelength of 1.55 μm and the confinement loss of the other one polarization is very high which can not ensure the transmission in the fiber. The single-polarization single-mode photonic crystal fiber is desirable for some polarization-sensitive applications such as high-power fiber lasers, fiber optic gyroscopes, current sensors and optical coherent communication systems. [ABSTRACT FROM AUTHOR]

We report a photonic crystal fiber glucose sensor filled with silver nanowires in this paper. The proposed sensor is both analyzed by COMSOL multiphysics software and demonstrated by experiments. The extremely high average spectral sensitivity 19009.17 nm/RIU for experimental measurement is obtained, equivalent to 44.25 mg/dL of glucose in water, which is lower than 70 mg/dL for efficient detection of hypoglycemia episodes. The silver nanowires diameter which may affect the sensor's spectral sensitivity is also discussed and an optimal range of silver nanowires diameter 90–120 nm is obtained. We expect that the sensor can provide an effective platform for glucose sensing and potentially leading to a further development towards minimal-invasive glucose measurement. [ABSTRACT FROM AUTHOR]

An ultra-broad band single-polarization single-mode photonic crystal fiber (SPSM-PCF) is investigated based on zero order surface plasmon polariton mode by using the full vector finite element method (FEM). Highly wavelength-dependent transmission is obtained because of the band gap-liked effect of the bonding zero-order surface plasmon polariton mode stimulated over the interface of gold/liquid. With a filled RI of 1.52, the polarization extinction is higher than 30 dB/cm among a large bandwidth of 360 nm in the second communication window. The proposed SPSM-PCF also presents a large tolerance of the size deviation of gold-coated layer. [ABSTRACT FROM AUTHOR]

We report the construction of a cascaded fiber amplifier where a 40-μm-core-diameter photonic crystal fiber is utilized in the main amplifier stage. Single-transverse-mode, linearly-polarized, 7.5 ns pulses with 1.5 mJ energy, 123 kW peak power and 10 nm spectral bandwidth centered at 1062 nm are generated. To our knowledge, the pulse energy we obtain is the highest from 40-μm-core-diameter photonic crystal fibers, and also the highest for long pulses (>1 ns) with linear polarization and single transverse mode. [ABSTRACT FROM AUTHOR]

In order to enhance the OAM mode purity and quality, we propose a graded-index ring-core photonic crystal fiber (GRC-PCF) and its general design strategy by the finite element method (FEM). In addition, the numerical results turn out that the GRC-PCF is better than conventional step-index ring-core-photonic crystal fiber (SRC-PCF) in terms of mode purity and mode quality, when the two fibers support the same numbers of OAM modes at 1.55 μ m , respectively. After optimizing structural parameters, a GRC-PCF that can support 14 OAM modes without phase distortion and high-radial modes in C+L bands is designed. Particularly, the mode purity and mode quality of all the OAM modes are higher than 97.05% and 98.42%, respectively. The confinement losses are maintained at the order of 1 0 − 11 and flat dispersion. The proposed fiber can be used in the MDM system and realize the stable transmission of the OAM modes. • We propose a GRC-PCF to improve the OAM mode purity and quality. • The proposed GRC-PCF is better than SRC-PCF in terms of mode purity and quality. • The OAM mode purity and quality are higher than 97.05% and 98.42% in C+L bands, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a segmented photonic crystal fiber with segments of varying effective refractive index in the cladding has been proposed. The designs have been analyzed in view of the effect of change in their cladding parameters, such as refractive index contrast, air filling fraction (denoted by normalized air hole diameter), duty cycle of the segments, and core–cladding interface. The periodically varying high and low index regions have been created by considering variations in the air hole size. High index core region has been created by omitting a single air hole from the centre of the lattice. Phosphate glass (n=1.56) has been used as base material. The various designs obtained by varying the controlling parameters, have been investigated for properties such as the effective core and cladding indices, confinement of fundamental mode and higher order mode, and the V parameter values. These parameters have been investigated over near infrared (0.75 –1.4μm) to short wavelength infrared (1.4–2.3μm) spectral range using finite difference time domain method. The expression for V parameter for conventional photonic crystal fiber has been extended to the proposed design and single mode cutoff value for the design has been calculated. The proposed design offers robust single mode confinement over specified infrared (0.75–2.3μm) wavelength range and a broad confinement peak has been observed containing the third optical communication window at 1.55μm. [Copyright &y& Elsevier]

Abstract: Mach–Zehnder interferometer strain sensors made from pieces of photonic crystal fiber spliced to standard single mode fibers are fabricated with different lengths. High strain sensitivity of 2.1pm/με at 1550nm is achieved with the length of 45mm. The interference is induced by the core mode and the high order core mode due to the special air hole structure of PCF, which is independent of the surrounding refractive index. The temperature sensitivity (∼13.24pm/°C) is relatively low. This structure is good in avoiding cross sensitivity in strain measurement and is fabricated with a simple process and low cost. [Copyright &y& Elsevier]

Abstract: We present the practical design of novel three core photonic crystal fiber (TPCF) for optical switching and logic operations by employing all optical control. To accomplish the proposed aim, we put forth two types of symmetrical TPCF designs, one with cores of planar geometry and the other with equilateral triangular geometry. The dynamics of the individual pulse parameters through the proposed geometries are analyzed numerically using split step Fourier method (SSFM). The steering characteristics of the coupler are demonstrated by the transmission curve. The truth tables expressing Boolean algebra for different logic operations are constructed from the transmission curves of the individual coupler configurations. Out of all configurations, we observe that the chloroform filled triangular core demonstrates all the logic operations namely OR, NOR, AND, NAND, X-OR, X-NOR and NOT with low input power. A figure of merit of logic gates (FOMEL) is also made to compare the performance of all the logic gates. [Copyright &y& Elsevier]

Abstract: High energy density per pulse (−15dBmnm−1) supercontinuum (SC) source has been developed as a probe for transient absorption (TrA) spectroscopy of systems with lifetimes from nanoseconds to a few milliseconds. We have generated a 600–1600nm, broadband SC by pumping a 15m photonic crystal fiber (PCF) with relatively high power, 7ns, 1064nm pulses. The SC generated at peak pump power of 7.1kW was randomly polarized and maintained a stable output (6.5% rms average power; 9.1% rms shot-to-shot power). Co-pumping with both 1064 and 532nm light extended the wavelength range of the SC by about 20%, to 500–1700nm. Power conversion efficiency and spectral flatness were improved as well. In the visible range, the single-pump SC shows a flatness of 5dB while the dual-pump SC exhibits 3dB. In the NIR (1100–1600nm), the flatness in single- and dual-pump configurations were 3 and 2dB, respectively. Optically induced fiber breakdown was characterized. [Copyright &y& Elsevier]

Abstract: We report fabrication and performance of the 2×2 photonic crystal fiber (PCF) splitter that enables multi-spectral bands operation of an optical coherence tomography (OCT) system. The PCF splitter was made by coupling PCFs to a planar lightwave circuit (PLC) splitter chip, which worked as a single mode splitter from visible to near infrared wavelengths. The core size of the PLC splitter chip was about 3μm×3μm and the core-cladding index difference was about 0.25%, which gave the cutoff wavelength at 630nm. The implemented PCF-PLC splitter showed a small excess loss of 1.2∼3.3dB and a low polarization-dependent loss of 0.15∼0.19dB over a wide wavelength range from 640nm to 1000nm. With the splitter, OCT images of a human finger and a nail have been successfully obtained at several spectral bands; 680nm, 840nm, and 930nm center wavelengths. [Copyright &y& Elsevier]

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]

Abstract: The Cherenkov radiations (CRs) at visible wavelengths are efficiently generated based on the soliton self-frequency shift (SSFS) by coupling the 120fs pulses into the fundamental mode propagated in the multi-knots of a hollow-core photonic crystal fiber cladding (HC-PCFC). When the pump operates at 830nm with the average power of 300mW at the knots 1–4 , the central wavelengths of generated CRs λ CR are 476nm, 454nm, 554nm, and 580nm, the conversion efficiencies η CR are 33%, 35%, 30%, and 29%, and the corresponding bandwidths B CR are 57nm, 74nm, 25nm, and 50nm, respectively. To the best of our knowledge, η CR of 35% and B CR of 74nm are the best experimental results reported with >100fs pump pulse. The efficient and broadband CRs can be wavelength-tunable over the whole visible wavelength by adjusting the wavelengths of pump pulses coupled into different knots. The result can be used as the multi-channel ultrashort pulse source for many important applications in the multiphoton microscope and ultrafast photonics. [Copyright &y& Elsevier]

Abstract: A temperature-independent refractometer by using a tapered photonic crystal fiber (PCF) based Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated. It is fabricated by sandwiching a tapered PCF of 29mm long between two standard single mode fibers (SMFs) with the fully collapsed air holes of the PCF in the fusion splicing region. It has been found that tapering the PCF greatly enhances the sensitivity of the refractometer. A maximum sensitivity of 1529nm/RIU (refractive index unit) is achieved within the range from 1.3355 to 1.413. The refractometer is nearly temperature-insensitive due to the ultra low temperature dependence of the used. [Copyright &y& Elsevier]

Abstract: We demonstrate a wavelength-tunable source of high-energy sub-100fs light pulses where all the key components, including a master oscillator, an amplifier, and a tunable frequency shifter, are based on photonic-crystal fibers (PCFs). Soliton self-frequency shift in a specifically designed all-solid photonic band-gap fiber with an effective mode area of 110μm2 is used in this system to transform a 1040nm, 50MHz, 100fs amplified output of a large-mode-area ytterbium-doped PCF oscillator–amplifier system into sub-100fs, 6.4nJ light pulses smoothly tunable within the range of wavelengths from 1160 to 1260nm. [Copyright &y& Elsevier]

Abstract: Double-large-microfluidic-channels photonic crystal fiber (PCF) sensors filled with silver nanowires are presented to achieve localized surface plasmon resonance sensors and to overcome the manipulating difficulty in implementing the experimentation. Optical field distribution of the fiber at a certain wavelength is calculated and simulated using the finite element method (FEM), and the sensing properties are discussed in both areas of resonant wavelength and intensity detection. Numerical results show excellent sensing characteristics when diameter and amount of silver nanowires are selected at d=300nm and m=5, respectively. Besides, spectral and amplitude sensitivities are 4400nm/RIU and 1407dB/RIU, respectively. Furthermore, the sensor resolutions are 2.3×10−6 RIU and 3.1×10−5 RIU, respectively. [Copyright &y& Elsevier]

Abstract: A method based on controlled air hole collapse for low-loss fusion splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) was demonstrated. A taper rig was used to control air hole collapse accurately to enlarge the MFDs of PCFs which was then spliced with SMFs using a fusion splicer. An optimum mode field match at the interface of PCF-SMF was achieved and a low-loss with 0.64dB was obtained from 3.57dB for a PCF with 4μm MFD and a SMF with 10.4μm MFD experimentally. [Copyright &y& Elsevier]

Abstract: An intensity curvature sensor using a Photonic Crystal Fiber (PCF) with three coupled cores is proposed. The three cores were aligned and there was an air hole between each two consecutive cores. The fiber had a low air filling fraction, which means that the cores remain coupled in the wavelength region studied. Due to this coupling, interference is obtained in the fiber output even if just a single core is illuminated. A configuration using reflection interrogation, which used a section fiber with 0.13m as the sensing head, was characterized for curvature sensing. When the fiber is bended along the plane of the cores, one of the lateral cores will be stretched and the other compressed. This changes the coupling coefficient between the three cores, changing the output optical power intensity. The sensitivity of the sensing head was strongly dependent on the direction of bending, having its maximum when the bending direction was along the plane of the cores. A maximum curvature sensitivity of 2.0dB/m−1 was demonstrated between 0m and 2.8m. [Copyright &y& Elsevier]

Abstract: We investigate polarization dependent differential group modal index sensitivity to temperature in twin-core photonic crystal fiber. Characteristics of guided modes and the group modal index difference in twin-core photonic crystal fiber (TC-PCF) are numerically analyzed. The geometrical asymmetry between the two cores induces significantly reduced power coupling between two core modes and difference in their effective indices. Two cores form two effective optical paths. We also experimentally demonstrate polarization dependent differential group modal index sensitivity to the temperature. Since the TC-PCF has polarization dependent group modal index difference, TC-PCF based interferometer shows input polarization dependent free spectral range and temperature sensitivities. The effective index difference between the two core modes tends to increase when the temperature increases. [Copyright &y& Elsevier]

Abstract: A single-polarization single-mode (SPSM) photonic crystal fiber with a rectangular array of micro-holes in the core region was designed in the terahertz frequency range near 1THz. Based on the asymmetric arrangement of the micro-holes, birefringence between the fundamental x-polarized and y-polarized modes is introduced. A SPSM operation of the terahertz fiber can be supported due to the different mode indices of the x-polarized and y-polarized modes. The SPSM operation band is about 320GHz with a central frequency of 1THz. In addition, the proposed terahertz fiber also shows a good property of reduced propagation loss comparing with the dielectric absorption. [Copyright &y& Elsevier]

Abstract: Using standard single-mode fiber as high-order soliton compressor for broadening supercontinuum in an 80m long all-normal dispersion photonic crystal fiber is investigated experimentally and numerically. An analytical formula for calculating proper fiber input power to generate the broadest supercontinuum is derived. The numerical results show that the formula is more accurate in high power level corresponding to the soliton order which is larger than two. The measured supercontinuum −20dB bandwidth is broadened from 84.2nm to 277.1nm by using a 20m long standard single-mode fiber without enhancing fiber input power. Numerical calculations of the amplitude noise in the output spectra show that using soliton compression effect can efficiently broaden the spectral bandwidth and not generate obvious noises. [Copyright &y& Elsevier]

Abstract: A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20GHz and 40GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~1.5ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~610fs for 20GHz pulse train and ~570fs for 40GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission. [Copyright &y& Elsevier]

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: We propose a special refractive index sensor design based on a photonic crystal fiber. Two analyte channels are introduced, with one analyte channel coated with gold layer and the other one without gold layer. A hybrid resonance method is used in the sensor to achieve a large dynamic index range, where surface plasmon resonance occurs when the analyte index is lower than that of the fiber material, while the core mode couples with the resonant mode of the adjacent analyte-filled cylinder when the analyte index is larger than the fiber material. When considering fluorinated polymer fibers, a broad index range of analyte refractive index from 1.25 to 1.45 with high sensitivity can be achieved. The maximal sensitivities reach 1.4×104 nm/RIU and 2.7×104 nm/RIU respectively when refractive index is in the range of 1.25 to 1.383 and 1.383 to 1.45. The sensor characteristics, make this simple sensor very interesting for detecting a wide range of fluid''s refractive index or chemical agent concentration. [Copyright &y& Elsevier]

Abstract: Novel evolution dynamics of optical vortices propagating in a dual-core photonic crystal fiber (PCF) is investigated, which can be explained well by using the equivalent dipole mode superposition principle. Thanks to the coupling between the two cores of PCF, exciting vorticity splitting and topological charge-flipping are achieved by inducing a vortex beam into one of the two cores of the PCF. What is more, the evolutions of two vortices located in each core separately can be controlled by means of modulating the initial phase difference of them. Our results may offer possibilities for applications of optical vortices, orbital angular momentum modulations, as well as optical communications. [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]

Abstract: A novel large mode area photonic crystal fiber (PCF) is proposed in this paper. Numerical investigations demonstrate that an endlessly single-mode PCF with improved large mode area can be realised by introducing higher index material in the cladding region. Here we discuss how the V-parameter and effective mode area of the PCF can be improved by manipulating the cladding region rather than the core region itself. Moreover, the influence of doping levels with respect to confinement loss, chromatic dispersion and bending loss of the proposed PCF is also investigated by employing the full-vectorial finite element method (FEM). [Copyright &y& Elsevier]

Abstract: The general principles for designing mode converters based on air-hole collapse in photonic crystal fibers (PCFs) are theoretically investigated in this paper. The splice-like point in mode converters is found unnecessary for mode conversion; however, two different and separated cores, the adiabatic transitional part and the final merged core, are essential. Three structures are investigated using logical deduction, and the numerical results agree well with the logical conclusions. [Copyright &y& Elsevier]

Abstract: A kind of polarization splitter in ZnTe tellurite glass three-core photonic crystal fiber has been proposed. The polarization splitter is based on the phenomenon of resonant tunneling. We use the finite element method and the full-vector beam propagating method to analyze the characteristics of three-core photonic crystal fiber. Compare with the silica glass three-core PCF, the ZnTe tellurite glass three-core PCF have higher extinction ratios and lower coupling loss, the extinction ratios ERA =−164.2681dB and ERC =−37.1742dB at the wavelength λ =1.55 μm, and the coupling loss is lower than 0.02dB. The 8.7983-mm-long splitter is proposed to achieve extinction ratio better than −20dB and a bandwidthof 20nm. [Copyright &y& Elsevier]

Abstract: We report a full modal characterization of the stimulated Brillouin scattering (SBS) properties in small core As2Se3-based chalcogenide photonic crystal fibers (PCFs). Our results include the calculation of Brillouin gain spectrum (BGS), Brillouin gain coefficient (g B ), Brillouin frequency shift (BFS) by taking into account the contribution of the higher-order acoustic modes. We show that for a highly nonlinear PCF having a 2-μm hole-to-hole pitch and a 0.5-μm hole diameter, a Brillouin gain coefficient g B =5.91 10−9 m.W−1 is obtained around the acoustic frequency of 8.19GHz, which is more than 340 times larger than that of the same PCF made with silica glass. We demonstrate that the BGS of small core PCF structures show strong SBS and multipeaked behavior, with a presence of a second peak, when decreasing the core diameter which is to be attributed to the higher-order acoustic modes. We designed small core PCFs with tailored Brillouin response for a wide range of applications. [Copyright &y& Elsevier]

Abstract: In this work, we demonstrate the possibility of fabricating short-length long-period gratings and rocking filters in highly birefringent Photonic Crystal Fiber using a CO2 laser. In our experiments both kinds of gratings were made in the same Boron doped highly birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at different resonances. [Copyright &y& Elsevier]

Abstract: We demonstrate 35W high power all fiber supercontinuum generation by pumping photonic crystal fiber (PCF) with a 57.7W picosecond fiber MOPA. The picosecond fiber MOPA pumped supercontinuum source exhibits an optical-to-optical conversion efficiency of up to 61.7%, covering a spectral range from 600nm to beyond 1700nm. The compact and practical configuration of this supercontinuum source has potential to achieve higher power scale together with perfect continuum spectrum. [Copyright &y& Elsevier]

Abstract: A tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of single-mode highly nonlinear photonic crystal fiber is proposed and demonstrated experimentally. Stable dual-wavelength and triple-wavelength operations at room temperature are achieved by employing the highly nonlinear photonic crystal fiber to induce four-wave mixing effect and a polarization controller to vary the polarization states of propagation lights in the laser cavity. The laser cavity is free from any wavelength selection components. The laser obtains maximal 30dB signal-to-noise ratio and the peak power fluctuations of lasing lines are less than 1.39dB. [Copyright &y& Elsevier]

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]

Abstract: We present an analytical concept for generating shaped femtosecond laser pulses at the distal end of a microstructured hollow core photonic crystal fiber. The properties of the fiber are analyzed and included in the shaping procedure. A parametric pulse shaping method allows for tailoring a sequence of sub-pulses. In this method, each sub-pulse can be individually controlled by its physically intuitive parameters distance in time, energy, phase and chirps as well as the state of polarization including ellipticity, orientation, and helicity. This is demonstrated with a series of double pulses, in which a single parameter is systematically varied, and additionally with more complex example pulses. Further, we investigate the impact of mechanical distortions of the fiber on the pulse shape. The presented method could be beneficially used in endoscopic applications in life sciences. [Copyright &y& Elsevier]

Abstract: A silicon nanowaveguide ring resonator is combined with a photonic-crystal fiber (PCF) frequency shifter to demonstrate an all-optically tunable synthesis of ultrashort pulse trains, modulated by ultrafast photoinduced free-carrier generation in the silicon resonator. Pump–probe measurements performed with a 50-fs, 625-nm second-harmonic output of a Cr:forsterite laser, used as a carrier-injecting pump, and a 1.50–1.56-μm frequency-tunable 100-fs soliton output of a photonic-crystal fiber, serving as a probe, resolve tunable ultrafast oscillatory features in the silicon nanowaveguide resonator response. [Copyright &y& Elsevier]

Abstract: In this article, a new simplified structure of a highly birefringent chalcogenide As2Se3 glass photonic crystal fiber (PCF) is designed and analyzed by using fully vectorial finite element method. The effective indices, confinement loss, birefringence, and chromatic dispersion of fundamental polarized mode are calculated in the proposed PCF for a wide wavelength range. To maintain the polarization in chalcogenide As2Se3 glass PCF, we enlarged two of the central air holes and reduced two transverse air holes for achieving high birefringence. This helps in creating an effective index difference between the two orthogonal polarization modes. It is also shown that As2Se3 glass PCF provides lower chromatic dispersion and less confinement loss compared to silica PCF of the same structure in wavelength range 1.3 to 1.8μm and hence such chalcogenide As2Se3 glass PCF have high potential to be used in dispersion compensating and birefringence application in optical communication systems. In addition to this, the polarization mode dispersion (PMD) result of the proposed PCF is also reported. [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 fiber-optic strain sensor is demonstrated by using a short length of highly birefringent photonic crystal fiber (HiBi-PCF) as the sensing element inserted in a fiber loop mirror (FLM). Due to the ultralow thermal sensitivity of the HiBi-PCF, the proposed strain sensor is inherently insensitive to temperature. When a distributed-feedback (DFB) laser passes through the FLM, the output power is only affected by the transmission spectral change of the FLM caused by the strain applied on the HiBi-PCF. Based on intensity measurement, an optical power meter is adequate to deduce the strain information and an expensive optical spectrum analyzer (OSA) would not be needed. [Copyright &y& Elsevier]

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]

Abstract: We numerically investigate the dynamics of soliton propagation at 850nm in chloroform filled liquid core photonic crystal fiber (LCPCF) by using both finite element method (FEM) and split step Fourier method (SSFM). We propose a novel chloroform filled PCF structure that operates as a single mode at 850nm featuring an enhanced dispersion and nonlinearity for efficient soliton propagation with low input pulse energy and low loss over small distances. We adopt the projection operator method (POM) to derive the pulse parameter equations which clearly describes the impact of fourth order dispersion on the pulse propagation in the proposed PCF. To analyse the quality of the pulse, we perform the stability analysis of pulse propagation numerically and compare our results of the newly designed chloroform filled PCF with that of standard silica PCF. From the stability analysis, we infer that the soliton pulse propagation in modified chloroform filled PCF is highly stable against the perturbation. [Copyright &y& Elsevier]

Abstract: We report the development of theory and experiment for the characterization of polarization maintaining photonic crystal fiber (PM PCF) from far field intensity measurements. In this specially designed photonic crystal fiber, the air hole diameters along orthogonal axes adjacent to the core region are different, and hence create an effective index difference between the two orthogonal polarization modes. From the experimental measurements of the far field radiation pattern, we obtain transmission characteristics of PM PCF in terms of mode field diameters (MFD), V-values along major and minor axes, mode field area, birefringence, core radius, effective refractive index of cladding and numerical apertures along major and minor axes of PM PCFs. It is shown that the experimentally obtained geometrical and wave guiding parameters of the PM PCF match with the manufacturer/simulation/scanning electron microscope (SEM) data within the experimental limits. [Copyright &y& Elsevier]