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We propose a relatively simple technique to infer the birefringence on single mode low-birefringence optical fibers based on the use of the Faraday effect. The theoretical model for Faraday rotation in the presence of nonnegligible fiber birefringence and a suitable measurement technique offer a fast and efficient way to determine low values of linear birefringence employing short fiber lengths. Alternative known techniques are not sensitive enough or they are of more difficult implementation. The method is used in only ∼1 m-long single-mode optical fibers to obtain the upper-limit birefringence that can be tolerated in order to retain good current sensing sensitivity. The temperature dependence of the Faraday rotation and its causes are also investigated.

We demonstrate the fabrication of a novel type of optical fibers with multiple parallel air-suspended cores by the sheet-stacking method. Using this technique we have constructed optical fibers with up to 10 parallel micron-size suspended cores. No extra scattering loss from the fabrication process was observed in a fabricated dual air-suspended core fiber. The sheet-stacking method opens the way towards using a wide range of optical glasses for manufacturing multiple parallel suspended-core specialty optical fibers with novel optical functionalities such as dispersion tunability. Fusion splicing has also been successfully used to connect such a multiple core fiber with a conventional silica fiber.

International audience; We report our recent progress on fabricating dehydrated tellurite glass fibers. Low OH content (1 ppm in wt.) has been achieved in a new halogen-​contg. lead tellurite glass fiber. Low OH-​induced attenuation of 10 dB​/m has been confirmed in the range of 3-​4 μm using three measurement methods. This shows the dehydrated halo-​tellurite glass fiber is a promising candidate for nonlinear applications in a 2-​5 μm region.

In this paper, we discuss nanotube diameter selectivity in DNA wrapping of single-walled carbon nanotubes (SWNTs) under high-shear sonication and present Raman evidence for the selective wrapping. The DNA wrapping induces an upshift (an increase in wavenumber) of the radial breathing mode (RBM) bands in the Raman spectra of SWNTs, which indicates strong interaction between nanotubes and DNA. The extent of the upshift correlates well with the change in the intensity of the RBM bands upon DNA wrapping, and larger upshifts correspond to larger intensity changes. The intensity changes represent wrapping selectivity, and differ from tube to tube due to varying diameters and electronic properties. The shift of the RBM bands thus represents a practical probe for wrapping selectivity and the extent of the shifts indicates different electronic structures of core nanotubes hybridized with DNA. © IOP Publishing Ltd.

The development of super continuum sources is driven by the requirements of a wide range of emerging applications. This paper points out how non-silica fibers are of benefit not only because their broad mid-IR transparency enables continuum generation in the 2–5µm region but also since the high intrinsic nonlinearity of the glasses reduces the power-threshold for devices at wavelengths below 2µm. For these glasses, the material zero-dispersion wavelength is typically shifted to long wavelengths compared to silica so dispersion tailoring is key to creating sources based on practical, near-IR, solid state pump lasers. We show how modeling work has produced fiber designs that provide flattened dispersion profiles with high nonlinearity coefficients and zero-dispersion wavelengths in the near-IR. Building on this flexibility, modeling of the pulse dynamics then demonstrates how coherent mid-IR supercontinuum sources could be developed. We also show the importance of the second zero-dispersion wavelength using bismuth fibers as an example. Nonlinear mode-coupling is shown to be a factor in larger core fibers for high-power applications. Demonstrations of supercontinuum in microstructured tellurite fibers, all-solid lead–silicate (SF57) fibers and in bismuth fibers and tapers are then reported to show what has been achieved experimentally using a range of materials and fiber geometries.

We investigate efficient broadband infrared supercontinuum generation in meter-length single-mode small-core tellurite holey fiber. The fiber is pumped by 1.06µm picosecond pulses in the normal dispersion region. The high Raman gain coefficient and the broad Raman gain bands of the tellurite glass are exploited to generate a cascade of Raman Stokes orders, which initiate in the highly normal dispersion region and quickly extend to longer wavelengths across the zero dispersion wavelength with increasing pump power. A broadband supercontinuum from 1.06µm to beyond 1.70µm is generated. The effects of the pump power and of the fiber length on the spectrum and on the power conversion efficiency from the pump to the supercontinuum are discussed. Power scaling indicates that using this viable normal dispersion pumping scheme, 9.5 W average output power of infrared supercontinuum and more than 60% conversion efficiency can be obtained from a 1 m long tellurite fiber with a large mode area of 500µm2.

We investigate theoretically and experimentally the possibility of electrostatic actuation of nanomechanical optical fibers with integrated electrodes. The fiber has two optically guiding cores suspended in air by thin flexible membranes. This fiber structure allows for control of the optical properties via nanometer-range mechanical core movements. The electrostatic actuation of the fiber is generated by electrically charged electrodes embedded in the fiber cladding. Fiber designs with one to four electrodes are analyzed and, in particular, a quadrupole geometry is shown to allow for all-fiber optical switching in a 10cm fiber with an operating voltage of 25 - 30V. A multi-material fiber draw technique is demonstrated to fabricate a fiber with well-defined dual core structure in the middle and four continuous metal electrodes in the cladding. The fabricated fiber is analyzed and compared with the modeled requirements for electrostatic actuation.

An optical fiber with nano-electromechanical functionality is presented. The fiber exhibits a suspended dual-core structure that allows for control of the optical properties via nanometer-range mechanical movements. We investigate electrostatic actuation achieved by applying a voltage to specially designed electrodes integrated in the cladding. Numerical and analytical calculations are preformed to optimize the fiber and electrode design. Based on this geometry an all-fiber optical switch is investigated; we find that optical switching of light between the two cores can be achieved in a 10 cm fiber with an operating voltage of 35 V.

The theoretical model of the Faraday rotation in the low birefringence optical fiber is proposed to serve as a convenient tool for the determination of the birefringence upper limit allowed to retain current sensor sensitivity. The measurement technique offers a fast and efficient determination of the ultra-low linear birefringence when other techniques are not sensitive enough or they are difficult to implement. A temperature dependence of the Faraday rotation and its causes are investigated.

We have developed the nanomechanical optical fibre, which contains two cores that not only transmit light also can be continuously tuned by mechanical actuation. We will review the process of fabrication and options for actuation.

Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to saturate the optical absorption, we observed an abrupt transition between reaction- and diffusion- limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ~ 0.2 per encounter. This represents the first experimental observation of a crossover between classical and critical kinetics in a 1D coalescing random walk, which is a paradigm for the study of non- equilibrium systems., Accepted for Physical Review Letters. Title changed, and "exciton fusion" replaced by "exciton-exciton recombination". Present address of Prof Tom Brown added. 12 pages plus 3 figures

International audience; We report the fabrication of new dehydrated halo-tellurite glass fibers with low OH content (1ppm in weight) and low OH-induced attenuation of 10dB/m in 3-4 μm region. It shows halo-tellurite glass fibers a promising candidate for nonlinear applications in 2-5μm region.

Optical fibers are an excellent transmission medium for light and underpin the infrastructure of the Internet, but generally after fabrication their optical properties cannot be easily modified. Here, we explore the concept of nanomechanical optical fibers where, in addition to the fiber transmission capability, the internal core structure of the fiber can also be controlled through sub-micron mechanical movements. The nanomechanical functionality of such fibers is demonstrated in the form of dual core optical fibers, in which the cores are independently suspended within the fiber. The movement-based optical change is large compared with traditional electro-optical effects and we show that optical switching of light from one core to the other is achieved through moving one core by just 8 nm.

A nanomechanical optical fibre with a mechanically adjustable dual-core structure has been demonstrated recently. The realisation of equivalent systems with an electric actuation would allow for low-loss all-fibre reconfigurable optical networks. Here, the feasibility of nanoelectromechanical actuation of the dual-core fibre is investigated. Such optical systems with mechanically adjustable or controllable components are well known in the form of silicon micro- and nanoelectromechanical systems (MEMS and NEMS) and are widely used in various optoelectronic devices, for example 2-D optical switches and reconfigurable optical add-drop multiplexers.

We demonstrate using a sheet-stacking method to fabricate nanomechanical optical fibres with long and thin spokes. This approach shows great advantage for manufacturing complex multi-material speciality optical fibres with novel photonic and nanomechanical functionalities.

We report a highly nonlinear soft-glass Er-doped fiber with a flattened anomalous dispersion around 1540 nm. We demonstrate continuum generation by seeding the fiber with ps-pulses at 1550 nm and pumping at 1480 nm.

Recent years have seen the development of a range of promising optical fibre technologies emerge, enabled by advances in materials and fabrication techniques. We describe 3 emerging areas in optical fibre developments: nanomechanical optical fibres, microstructured hollow core silica fibres for high peak optical power and/or extended infrared transmission, and chalcogenide glasses and fibres for mid-IR applications.

We propose a chip-based optical buffer that is continuously tunable by microelectromechanical actuation. The device consists of two identical semiconductor waveguides with a mechanically variable gap in-between, allowing for a change of group delay of over 100% and for extremely broadband operation.

We report for the first time the fabrication of a novel glass ribbon fibre with laser-induced single (or quasi-single) crystalline (La,Yb)BGeO5 optical waveguide.

We propose a design for an optical buffer that comprises two coupled silicon waveguides, which is capable of generating a large continuously tunable change in the propagation delay time. The optical delay can be varied by more than 100% through varying the spacing between the waveguides.

A 2.2m long sample of lead-silicate W-index profile fiber with nonlinear coefficient of 820W−1km−1 and exhibiting low and flat dispersion across the C-band is used in an all-optical 160-to-40Gbit/s demultiplexing scheme based on four-wave-mixing.

We report arc fusion splicing of highly nonlinear soft glass fibre with a flattened, near-zero dispersion profile at 1.55μm to conventional silica fibre. Reasonable splice loss values and watt-level power handling are demonstrated.

We report flat, broadband supercontinuum generation at low pump pulse energies (69pJ 740fs pulses at 1540nm) in a lead-silicate fibre providing a unique combination of high nonlinearity (820W−1km−1) and a flat near-zero dispersion profile.

We propose a new technique for making optical fiber preforms in order to realize complex structured optical fibers. The preforms are fabricated by rolling up custom-patterned flat glass sheets, and the resulting cylindrical structure drawn into optical fibers.

We demonstrate the generation of a 1.1–1.7µm supercontinuum in a 1.3m long airsuspended- core tellurite holey-fiber with a nominal zero-dispersion wavelength of ∼1.38µm. The fiber is pumped at 1.06µm with a 20ps pulsed fiber laser. The high Raman gain-coefficient of tellurite glass is attributed a key role in the supercontinuum generation.

We review our recent progress in the design and fabrication of lead silicate glass fibers with high nonlinearity and tailored near-zero dispersion at telecommunication wavelengths. We have explored a range of different fiber structures, including suspended core fibers, holey fibers, all-solid microstructured and conventional W-type profiled fibers. The optical properties of the fabricated fibers are assessed both experimentally and through accurate numerical simulations. The relative merits of each fiber design are discussed and the significant potential of lead silicate highly nonlinear fibers for all-optical signal processing at telecommunication wavelengths is shown through reference to a number of key experimental demonstrators.

The generation of ultrastable optical pulses beyond 160GHz is demonstrated based on two injection-locked CW lasers through nonlinear temporal compression in a high SBS threshold highly nonlinear dispersion tailored compound glass W-type fibre.

Recent advances in optical fibre technology, most notably in the area of micro structured optical fibres (MOFs), offer a host of new opportunities within future high speed communication systems. Herein we review how our recent progress on the implementation of lead silicate fibre designs, allowing both flexible dispersion control and a high effective nonlinearity, can be integrated into various all-optical signal processing devices for high speed optical communication systems. Highly nonlinear lead silicate fibres have already proven to be well suited for achieving efficient four-wave mixing (FWM) due to their high effective nonlinear coefficient, low dispersion profile and short length.

We experimentally demonstrate the wavelength conversion of three wavelength multiplexed 40 Gbit/s Differential Phase Shift Keyed (DPSK) signals in a 2.2m length of highly nonlinear, dispersion tailored W-type lead-silicate optical fibre.

We review our recent progress in the development of lead silicate glass fibers with high nonlinearity and tailored near-zero dispersion at telecommunication wavelengths, encompassing holey, all-solid microstructured and W-type fiber designs. The fabrication techniques and relative merits of each fiber design are described in detail. The optical properties of the fabricated fibers are assessed both experimentally and through accurate numerical simulations. The significant potential of lead silicate highly nonlinear fibers for all-optical signal processing at telecommunication wavelengths is shown via a number of key experimental demonstrators.

Photodarkening in samarium doped germanosilicate fiber and laser by downconversion is studied. Appreciable photodarkening occurs in the fiber and we attribute the effect to color centres which are both related to Sm 2 O 3 and GeO 2 . An energy level scheme has been illustrated to explain the photodarkening mechanism.

The delayed self-heterodyne interferometric technique, first proposed in the context of semiconductor lasers, has been commonly used for over 20 years in the determination of the optical linewidth of lasers. We examine this technique in the light of recent work on fiber lasers, and point out further constraints in the applicability of these measurements. An approximate but simple and intuitive expression is provided for assessing the self-heterodyne technique when applied to fiber lasers.

In this study, we discuss the influence of DNA strand length on DNA wrapping of single-walled carbon nanotubes under high-shear sonication and find that different strand length results in changed DNA-nanotube interaction, which is sensitively probed by the upshift extent of the Raman radial breathing mode bands of nanotubes due to DNA wrapping. The difference in the interaction between nanotubes and DNA strands of various length results in apparently different degrees of wrapping compactness, revealed by atomic force microscopy observations, and nanotube selectivity in wrapping, indicated by both Raman and photoluminescence spectroscopy results. The above findings can be utilized to precisely control the nanotube diameter distribution and modulate the physicochemical properties of the nanotube wrapped by DNA without any direct functionalization of nanotubes. This finding is of considerable interest from both theoretical and practical standpoints.

We report the fabrication of a large mode area tellurite holey fiber from an extruded preform, with a mode area of 3000microm(2). Robust single-mode guidance at 1.55microm was confirmed by both optical measurement and numerical simulation. The propagation loss was measured as 2.9dB/m at 1.55microm. A broad and flat supercontinuum from 0.9 to 2.5microm with 6mW output was obtained with a 9cm length of this fiber.

We demonstrate simultaneous lasing at 17 wavelengths in a miniature 2mm long erbium:ytterbium fiber Fabry-Perot laser. The wavelengths are separated by 0.4nm (50GHz) corresponding to the free spectral range of the laser cavity

The anomalous linewidth behavior in a DFB fiber laser is investigated. It is shown that not only does the linewidth deviate drastically from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration used. These results have potentially important implications for the design and operation of such fiber lasers.

We report on the first fabrication of a glass fiber based laser-induced crystalline waveguide. The glass and crystal are based on the stoichiometric composition of (La,Yb)BGeO(5). A laser induced waveguide has been fabricated on the surface of a ribbon glass fiber using milliwatt-level continuous wave UV laser radiation at a fast scanning speed. Evidence of crystallinity in the created structure was observed using micro-Raman spectroscopy and scanning electron microscopy. Preliminary investigations on the waveguiding behavior and the nonlinear performance in the crystalline waveguide are reported.

We experimentally demonstrate phase regeneration of a 40-Gb/s differential phase shift keying (DPSK) signal in a 1.7-m long highly nonlinear lead silicate W-type fiber using a degenerate two-pump phase-sensitive amplifier (PSA). Results show an improvement in the Error Vector Magnitude (EVM) and a reduction of almost a factor of 2 in the phase noise of the signal after regeneration for various noise levels at the input.

We experimentally demonstrate phase-sensitive amplification in a highly nonlinear and low-dispersion lead-silicate W-type fiber. A phase-sensitive gain variation of 6 dB was observed in a 1.56-m sample of the fiber for a total input pump power of 27.7 dBm.

We investigate a novel approach to obtain highly nonlinear fibers with a tailored group velocity dispersion around a desired wavelength region of interest. Rather than exploiting longitudinal holes to control the average refractive index of the cladding and hence the fiber's waveguide dispersion, as in holey fibers, we propose using an all-solid cladding with a suitably chosen refractive index difference relative to the core. We demonstrate numerically that this solution allows a large freedom in the manipulation of the overall fiber dispersive properties, while enabling, in practice, a much more accurate control of the fiber's structural properties during fabrication. Effectively single mode guidance over a broad wavelength range can be achieved through the use of a second outer cladding forming a W-type index profile. We derive simple design rules for dispersion controlled fibers, based on which an algorithm for the automatic dispersion optimization is proposed, implemented and used to design various nonlinear fibers for all-optical processing and supercontinuum generation. Fabrication of a lead silicate fiber with flattened dispersion at telecoms wavelengths confirms the potential of these new fibers.

We report the design, fabrication and characterization of a lead silicate glass highly nonlinear W-type fiber with a flattened and near-zero dispersion profile in the 1.55 µm region. The fiber was composed of three types of commercial lead silicate glasses. Effectively single-mode guidance was observed in the fiber at 1550nm. The nonlinear coefficient and the propagation loss at this wavelength were measured to be 820 W-1km-1 and 2.1dB/m, respectively. Investigations of the Brillouin threshold revealed no evidence of stimulated Brillouin scattering for continuous wave signal powers up to 29dBm in a 2m sample of the fiber. A broadband dispersion measurement confirmed the near-zero dispersion values and the flat dispersion profile around 1550nm, in good agreement with our simulations. Efficient four-wave-mixing, tunable across the whole C-band, was demonstrated in a 2.2m length of the fiber.

We report the fabrication of an all-solid highly nonlinear microstructured optical fiber. The structured preform was made by glass extrusion using two types of commercial lead silicate glasses that provide high index-contrast. Effectively single-moded guidance was observed in the fiber at 1.55 microm. The effective nonlinearity and the propagation loss at this wavelength were measured to be 120 W(-1)km(-1) and 0.8 dB/m, respectively. Numerical simulations indicate that the fiber is dispersion-shifted with a zero-dispersion-wavelength of 1475 nm and a dispersion slope of 0.16 ps/nm(2)/km respectively at 1.55 microm. These predictions are consistent with the experimentally determined dispersion of + 12.5 ps/nm/km at 1.55 microm. Tunable and efficient four-wave-mixing based wavelength conversion was demonstrated at wavelengths around 1.55 microm using a 1.5m-length of the fiber.

We comment on the recent paper by Zhou et al. [Appl. Opt.45, 4433 (2006)APOPAI0003-693510.1364/AO.45.004433], in which transmission losses of 0.2-0.3 dB/m were claimed across the wavelength range 420-900 nm in a high-index (n(d)=1.80518 at 587.6 nm) SF6 glass-based photonic crystal fiber fabricated by novel die-cast technique. If confirmed, these losses are at least 1 order of magnitude lower than previous reported losses of SF6 photonic crystal fibers from other fabrication approaches. Here we present a statistic survey on the relationship between the refractive index and the bulk material attenuation, based on a large number of commercial Schott optical glasses with the n(d) ranging between 1.40 and 2.05. It shows that the loss of a high-index (n(d)=1.80) glass optical fiber should be at the levels of 10-50 dB/m at 420 nm and 1-10 dB/m at 500 nm, respectively. Moreover, the material attenuation of such a high-index glass fiber should intrinsically show a large decay, from 10-50 dB/m at 420 nm to the level of 1 dB/m at 700 nm, which arises from the tail on the UV absorption edge of the high-index glass extending to the visible region. Therefore, we conclude that: (1) the low loss of 0.2-0.3 dB/m reported in the cited paper is abnormally one or two magnitudes lower than the material attenuation that a high-index (n(d)=1.80) glass optical fiber should have in the range between 420 and 500 nm and that (2) the flat loss curve between 420 and 700 nm in the cited paper deviates greatly from the intrinsic behavior of a high-index (n(d)=1.80) glass fiber.

The lifetime of Er3+ in silicon-rich silicon oxide has been reported with quite widely varying values ranging from 9 ms to 2 ms. In this work, we consider the direct impact of silicon nanoclusters on the erbium radiative lifetime, and show that it is a function of the silicon nanocluster size, and also the erbium proximity to the nanocluster.