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A novel circular shaped metamaterial optical fiber with semiconductor core, metal/dielectric clad is numerically investigated. To surpass higher absorption loss and instability of noble metal, the core guiding medium of the fiber is comprised by crystalline germanium (Ge). The fiber is interrogated in terms of uniaxial permittivity, mode index, dispersion profile, effective area, nonlinearity, power fraction for different thickness (Cm = Cd, Cm > Cd, Cm < Cd) of Ag/Al2O3 using finite element method. In addition, it is shown how increased Ag/Al2O3 pair enhances optical properties especially for low loss which is reported as 0.025 dB/m with AMM cladding and 0.007 dB/m for layered cladding region. Hence, the proposed structure with comprising material is a promising candidate for mid-infrared applications. [ABSTRACT FROM AUTHOR]

A further output power scaling of Yb-doped double-cladding photonic crystal fiber lasers, required for practical applications in many industrial fields, is currently prevented by thermal effects, which significantly worsen the beam quality. In this work the mode interaction and, consequently, the single-mode regime of Yb-doped air-silica symmetry-free photonic crystal fibers have been numerically investigated in different heat load conditions using simulation tools based on the finite element method. The effect of the main inner cladding geometric parameters, in particular of the inner cladding dimension, on the guided-mode delocalization has been analyzed, with the aim to identify a design of the large mode area active fiber providing single-mode operation despite the presence of thermal effects. Simulation results have demonstrated that the inner cladding enlargement causes a stronger coupling between core-guided and cladding modes, as well as an increase of the differential overlap between fundamental and first higher-order mode for moderate heat load values. However, the inner cladding influence becomes less important under severe heat load, being the fiber behaviour mainly affected by the thermally-induced refractive index change in the doped core. [ABSTRACT FROM AUTHOR]

A general method for analyzing the multilayer metamaterial optical waveguides with the Kerr-type nonlinear cladding was proposed. To prove the accuracy of the proposed general method, a degenerated example was introduced. The analytical and numerical results show excellent agreement. The similar process can also be used to analyze TM waves propagating in the multilayer metamaterial waveguide structure with the Kerr-type nonlinear cladding. [ABSTRACT FROM AUTHOR]

A different silicon photonic wire waveguide is proposed, which uses multiple thin cladding layers in order to reduce the index contrast between core and cladding interface. The reduced index contrast in the proposed waveguide has led to reduction in the scattering losses by 37% as compared to silicon wire waveguide for 400 nm × 220 nm waveguide dimension. The proposed waveguide has shown significant reduction in bending losses. It offers the bending loss of 0.0118 dB at the radius of 1 μm and 0.0063 dB for a radius of 2 μm at 1.55 μm wavelength as compared to 0.086 and 0.013 dB at the radius of 1 and 2 μm, respectively, offered by silicon photonic wire waveguide at 1.5 μm wavelength. The use of polymer material as top cladding layer resulted in decreasing the sensitivity of effective index against temperature for the designed waveguide by a factor of 2 as compared to silicon wire waveguide. [ABSTRACT FROM AUTHOR]

A novel microstructure fiber based on side-polished fiber (SPF) was demonstrated. Polystyrene microspheres were self-assembled onto the side-polished surface of SPF to form the colloidal crystal cladding of the microstructure fiber. Because of the Bragg reflection of the colloidal crystals cladding and the strong interaction between evanescent field and colloidal crystal, three main valleys were observed in the transmission spectrum. The modulation amplitude of the valley was up to 12 dB. Furthermore, the transmission valley showed a high sensitivity of temperature. At the wavelength of 1524.25 nm-the position of valley, transmission optical power showed a maximum optical power variation of 14.7 dB in the range of 20-50 °C, the sensitivity of temperature was up to 0.487 dB/°C. The linear correlation coefficient was 99.84%. This SPF with colloidal crystals cladding shows a good potential in fiber sensing and other photonic applications. [ABSTRACT FROM AUTHOR]

Double-air-cladding Tm-doped silica fiber with a large core is fabricated by stacking capillaries method. By the excitation at 1064 nm, the optical properties of this fiber doped with 0.1 mol% Tm are studied. The blue and near-infrared emissions around 473 and 793 nm are experimentally observed. In addition, the up-conversion mechanism of Tm in glass is investigated. The results show that the Tm-doped fiber with a large core can be used as the potential optical material for the high power fiber laser which operates at the blue and near-infrared wavelengths. [ABSTRACT FROM AUTHOR]

We present a numerical analysis of multi-mode pump absorption in recently proposed double-clad fiber with stadium-like cross section of the inner cladding and asymmetrically placed rare-earth doped core. Such a cross section allows easy splicing of the multi-mode pump fiber and single-mode signal fiber to the double-clad fiber. The full-vector finite element beam propagation method was used as a numerical tool. In order to allow excitation of the structure by arbitrary field profile, definite set of functionals satisfying unisolvence condition together with hybrid edge-nodal finite element basis was derived. The flat-top field profile and more realistic speckle pattern were considered in the analysis. The effect of coiling and simultaneous twisting of the fiber was taken into account. It was found that the twisting of the DC fiber significantly improves the pump absorption. [ABSTRACT FROM AUTHOR]

We proposed a novel design of photonic crystal fiber with the characteristics of high birefringence and zero dispersion. The structure of the photonic crystal fiber is composed of the rectangular lattice with double-cladding and there is an elliptical air hole in the core of the photonic crystal fiber which has the same size with the holes of inner ring. Simulation results show that the elliptical air hole in the core can enhance the performance of mode birefringence and control the properties of chromatic dispersion at the same time. We obtain the high birefringence B = 2.1 × 10 and B = 2.9 × 10 at the wavelength of 1.31 and 1.55 μm respectively and the zero dispersion point at the wavelength of 1.31 μm. The proposed photonic crystal fiber with high birefringence and zero dispersion will be important in the applications of polarization maintaining transmission systems. [ABSTRACT FROM AUTHOR]

To elastically design a dual-concentric-core photonic crystal fiber (DCC-PCF) for dispersion compensation, we use double layers of cladding holes as an outer ring core (ORC), instead of single layer ORC, of the DCC-PCF. For a DCC-PCF with single ORC structure, the design process of maximum dispersion coefficient becomes entangled with that of the compensated wavelength. By using double ORC, the optimum value of chromatic dispersion can be kept when the compensated wavelength is adjusted. The numeric results indicate that the negative chromatic dispersion coefficient for the proposed DCC-PCF is approximately 15 % larger than that of the previous DCC-PCF at around the wavelength of $$1.55\,\upmu \hbox {m}$$ . [ABSTRACT FROM AUTHOR]

A ridge-type semiconductor laser with partially formed anti-guiding cladding layers is proposed, and lasing characteristics are simulated. With increases in the height and the width of the partially formed anti-guiding cladding layers, both kink-level and threshold current increase. When the height is 100 nm and the width is greater than or equal to 15 $$\upmu \hbox {m}$$ for the partially formed anti-guiding cladding layers, kink-free operation is obtained up to the injected current of 2 A. The lowest threshold current for the kink-free operation is 57.0 mA when the height is 100 nm and the width is 15 $$\upmu \hbox {m}$$ for the partially formed anti-guiding cladding layers. [ABSTRACT FROM AUTHOR]

A ridge-type semiconductor laser with selective double-sided anti-guiding and partially undoped cladding layers is proposed, and lasing characteristics are simulated. With increases in the height and width of the selective double-sided anti-guiding layers, both kink-level and threshold current increase. With an increase in the thickness of the partially undoped cladding layers, the kink-level increases. There is an optimum value for the thickness of the partially undoped cladding layers to minimize the threshold current with maintaining kink-free operation. The lowest threshold current for kink-free operation is 46.1 mA, which is much lower than the previous lowest value of 57.0 mA. [ABSTRACT FROM AUTHOR]

To stop the light group velocity by metamaterial waveguides, for applying in several usages is the matter of attention in recent years. The new researches work on compensating losses in metamaterial waveguides with non-zero loss on metamaterial articles. In the present study, a structure of five layers is suggested, in which the side thickness of metamaterial core is variable but the central thickness is constant. In a part of center there located an active ZnO/Au in cladding layer; By pumping a proper magnitude of external optical field with specific wavelength, different from internal optic wavelength to it, there appears a non-linear optical effect. Theoretical and numerical analysis results show that in the mentioned part losses of the waveguide are compensated and exactly equal to the time of the pump pulse, light group velocity will be zero. [ABSTRACT FROM AUTHOR]

Segmented cladding fiber (SCF) is capable of single mode operation over an extended range of wavelengths while maintaining large mode area. In this paper we report the design of an SCF with mode area as large as 1,825 $$\upmu \hbox {m}^{2}$$ , suitable for delivery of high peak power femtosecond laser pulses at 1550 and 1064 nm wavelengths. An SCF with such a large-mode area is a few-moded fiber and its design requires careful choice of design parameters to have robustness against mode-coupling effects and bend loss. In this paper we address these issues and report a design of an SCF showing near distortion-free propagation of 100-fs, 53-kW peak power pulses at 1550-nm wavelength with 1,825- $$\upmu \hbox {m}^{2}$$ mode area through fundamental mode. The same fiber can also deliver 250-fs, 15-kW peak power pulses at 1064-nm wavelength with 1,793- $$\upmu \hbox {m}^{2}$$ mode area. The fiber has been analyzed by using the radial effective-index method in conjunction with transfer matrix method and the pulse propagation has been studied by solving the nonlinear Schroedinger equation by split-step Fourier method. Such a fiber would find applications in multiphoton microscopy and in biomedical engineering. [ABSTRACT FROM AUTHOR]

A ridge-type semiconductor laser with selectively proton-implanted cladding layers for separate confinement of horizontal transverse modes and carriers is proposed, and lasing characteristics are simulated. Light is confined by the proton-implanted n-cladding layer; carriers are confined by the proton-implanted p-cladding layer. It is found that light output operating in the fundamental transverse mode is enhanced and threshold current is decreased. [ABSTRACT FROM AUTHOR]

A highly birefringent elliptic porous-core photonic crystal fiber with kagome lattice cladding has been presented for terahertz (THz) wave transmission. The slotted airholes inside the elliptic core effectively disrupt the symmetry of the porous-core which offers extremely high modal birefringence whereas the kagome cladding structure results in significantly low effective material loss (EML). The birefringence of the proposed structure is 9.73×10-2 and the EML is 0.056cm-1 for y-polarized mode at an operating frequency of 1 THz. The suggested structure also provides very flat dispersion over a bandwidth of 300 GHz. It is highly expected that this elliptic core waveguide would be remarkably useful in numerous polarization maintaining THz applications. [ABSTRACT FROM AUTHOR]

An ultrabroadband mid-infrared (MIR) region supercontinuum (SC) is demonstrated numerically through dispersion-engineered traditional chalcogenide (ChG) photonic crystal fiber (PCF). By varying structural parameters pitch (hole to hole spacing) and air-hole diameter to pitch ratio, a number of 10-mm-long hexagonal PCFs made employing GeAsSe ChG glass as a core and air-holes of hexagonal lattice running through their lengths as a cladding are optimized to predict an efficient mid-infrared region SC spectral emission by pumping them using a tunable pump source between 2.9 and 3.3 µm. Simulations are carried out using an ultrashort pump pulse of 100-fs duration with a low pulse peak powers of between 3 and 4 kW into the optimized designs. It is found through numerical analysis that efficient SC spectral broadening with flattened output can be obtained by increasing the PCF pitch rather than increasing the PCF cladding containing air-hole diameter although a larger nonlinear coefficient could be obtained through increasing air-hole diameter of an optimized design. Simulation results show that the SC spectra can be broadened up to 12.2 µm for a certain design with a peak power of 3 kW. Using a peak power of 4 kW, it is possible to obtain SC spectral broadening beyond 14 µm with an optimized design spanning the wavelength range from 1.8 to 14 µm which covers the electromagnetic spectrum required for MIR molecular fingerprint region applications such as sensing and biological imaging. [ABSTRACT FROM AUTHOR]