Picosecond 554 nm yellow-green fiber laser source with average power over 1 W.

We demonstrate a source of 554 nm pulses with 2.7 ps pulse duration and 1.41 W average power, at a repetition rate of 300 MHz. The yellow-green pulse train is generated from the second harmonic of a 1.11 µm fiber laser source in periodically-poled stoichiometric LiTaO3. A total fundamental power of 2.52 W was used, giving a conversion efficiency of 56%.

Water on Au sputtered films.

Transient changes in the contact angle, Δθ ∼ 10°, of water on gold (Au) reveal reversible wetting of near hydrophobic Au films. The recovery time is temperature dependent. Surface flatness is investigated using AFM and profilometery.

Long-period gratings for selective monitoring of loads on a wind turbine blade.

An optical fiber sensor based on long-period gratings (LPG) for selective measurements of flap- and edge-wise bending of a wind turbine blade is presented. Two consecutive LPGs separated by 40 mm interfere to improve resolution and reduce noise in a D-shaped fiber. The mode profile of the device was characterized experimentally to provide a model describing the mode couplings. The sensor was tested on a wind turbine blade.

Characterization of nanoscale features in tapered fractal and photonic crystal fibers.

The internal structure of nanostructured air-silica fiber probes have been characterized using a combined focused ion beam and scanning electron microscopy technique. The collapse rate of the air-holes is shown to differ substantially between a regular photonic crystal fiber (PCF) and the quasi-periodic Fractal fiber. The integrity of the Fractal fiber structure is maintained down to an outer diameter as small as 120 nm, whereas the air-holes of the regular PCF begin to collapse when the outer diameter is approximately 820 nm. The observed smallest hole diameter of 10 nm is suggested to be due to physical limits imposed by the molecular structure of silica. These results confirm structural inferences made in previous publications.

A study of regenerated gratings produced in germanosilicate fibers by high temperature annealing.

In light of recent proposals linking structural change and stresses within regenerated gratings, the details of regeneration of a seed Type-I Bragg grating written in H2 loaded germanosilicate fiber annealed at high temperatures (~900°C) are systematically explored. In particular, the influence of the strength of the grating, the effect of GeO2 doping concentration and the annealing conditions on regeneration are studied. We show that the role of dopants such as Ge and F contribute nothing to the regeneration, consistent with previous results. Rather, they may potentially be detrimental. Strongest regenerated gratings with R ~35% from a 5mm seed grating could be obtained in fibres with the lowest GeO2 concentrations such as standard telecommunications-compatible grade fibre.

Mode-locked picosecond pulse generation from an octave-spanning supercontinuum.

We generate mode-locked picosecond pulses near 1110 nm by spectrally slicing and reamplifying an octave-spanning supercontinuum source pumped at 1550 nm. The 1110 nm pulses are near transform-limited, with 1.7 ps duration over their 1.2 nm bandwidth, and exhibit high interpulse coherence. Both the supercontinuum source and the pulse synthesis system are implemented completely in fiber. The versatile source construction suggests that pulse synthesis from sliced supercontinuum may be a useful technique across the 1000 - 2000 nm wavelength range.

Metal-free scanning optical microscopy with a fractal fiber probe.

Scanning Near-field Optical Microscopy (SNOM) is the leading instrument used to image optical fields on the nanometer scale. A metal-coating is typically applied to SNOM probes to define a subwavelength aperture and minimize optical leakage, but the presence of such coatings in the near field of the sample can often cause a substantial change in the sample emission properties. For the first time, the authors demonstrate near-field imaging on a metal substrate with a metal-free probe made from a novel structured optical fiber, designed to maximize optical throughput and potentially remove the need for the metal.

White light sources based on multiple precision selective micro-filling of structured optical waveguides.

Multiple precision selective micro-filling of a structured optical fibre using three luminescent dyes enables the simultaneous capture of red, blue and green luminescence within the core to generate white light. The technology opens up a new approach to integration and superposition of the properties of multiple materials to create unique composite properties within structured waveguides.

A fractal-based fibre for ultra-high throughput optical probes.

A core component of all scanning near-field optical microscopy (SNOM) systems is the optical probe, which has evolved greatly but still represents the limiting component for the system. Here, we introduce a new type of optical probe, based on a Fractal Fibre which is a special class of photonic crystal fibre (PCF), to directly address the issue of increasing the optical throughput in SNOM probes. Optical measurements through the Fractal Fibre probes have shown superior power levels to that of conventional SNOM probes. The results presented in this paper suggest that a novel fibre design is critical in order to maximize the potential of the SNOM.

Impact of water and ice 1h formation in a photonic crystal fiber grating.

The impact of ice 1h formation inside the holes of a photonic crystal fiber Bragg grating was analyzed and discussed. As a result of the ice's expansion, a broadening of the grating spectrum was observed that corresponds to internal microbending of the fiber and after some temperature cycling leads to failure of the fiber. An analytical model with which to estimate the internal compression forces is proposed, and the calculated values are found to be in agreement with reported data.

Thermal hypersensitisation and grating evolution in Ge-doped optical fibre.

Low temperature (sub 1000 degrees C) thermal hypersensitisation is reported in germanosilicate optical waveguides. Gratings are written using a CW 266nm laser source. In contrast to laser hypersensitisation, thermal excitation is generally dispersive involving a range of specific glass sites. More complex grating profiles presenting evidence of solid-state autocatalysis and bistability at increasingly high sensitisation temperatures are observed. More specifically, at 500 degrees C, a behaviour resembling type IIA grating response is observed.

Diffraction in air-clad fibres.

The angular transmissivity of high numerical aperture air-clad fibres is measured as a function of skewness of the launched light. Within the experimental limits the measured transmissivity of skew rays is significantly lower compared to theoretical predictions for air-clad fibres with uniform cladding surfaces. The discrepancy is attributed to diffractive losses of skew rays from the periodic corrugations at the pump core-cladding air interface.

Exposure and characterization of nano-structured hole arrays in tapered photonic crystal fibers using a combined FIB/SEM technique.

This paper presents a technique to expose and characterize nano-structured hole arrays in tapered photonic crystal fibers. Hole array structures are examined with taper outer diameters ranging from 12.9 microm to 1.6 microm. A combined focused ion beam milling and scanning electron microscope system was used to expose and characterize the arrayed air-silica structures. Results from this combined technique are presented which resolve hole-to-hole pitch sizes and hole diameters in the order of 120 nm and 60 nm, respectively.

The characteristic curve and site-selective laser excitation of local relaxation in glass.

The so-called characteristic curve describing photosensitivity change is elaborated and shown to be a powerful tool for understanding and characterizing photosensitive growth both at a fundamental and practical level. It has been used successfully to diagnose when optimal hypersensitization has been achieved and the physical basis for this is explained. By way of example, previous results using 355 nm hypersensitization are re-examined. Evidence of single site-selective glass relaxation through direct laser excitation offers a new approach to accessing and studying induced relaxations.

Hydrogen loading of optical waveguides by use of host diluent gases.

Recent dramatic improvements in photosensitivity gas mixtures when very low hydrogen concentrations (as low as 0.1%) were used are shown to involve condensation of the host gas. The vapor pressure of the host determines the effective partial pressure of the hydrogen, and this accounts for the bulk of the observed enhancements.

Intermodal interference in a photonic crystal fibre.

Intermodal interference in photonic crystal fibres, single mode over long lengths, is measured over a short length. Akin to conventional fibres, this poses a potential problem for practical device utilisation of photonic crystal fibres. We note that given the existing widespread fabrication capability of this fibre and indications that some commercial use in devices will come to fruition, the need for standardising measurement techniques, analogous to ITU standards for conventional fibre, specific to photonic crystal fibres will be required.

Propagation in air by field superposition of scattered light within a Fresnel fiber.

Propagation of light at 1.5 microm with peak intensity in an air hole is achieved within an air-silica-structured Fresnel waveguide. Thus a simpler fiber design alternative to photonic crystal fibers is possible for high-peak-power propagation with reduced nonlinear interactions. Multiple foci are observed in the far field.

Retaining and characterising nano-structure within tapered air-silica structured optical fibers.

Air-silica fiber 125m in diameter has been tapered down to ~15m. At this diameter, it is commonly assumed that the nanostructured fiber holes have collapsed. Using an Atomic Force Microscope, we show this assumption to be in error, and demonstrate for the first time that structures several hundred nanometers in diameter are present, and that hole array structures are maintained. The use of Atomic Force Microscopy is shown to be an efficient way of characterising these structures.

Analysis and removal of fracture damage during and subsequent to holey fiber cleaving.

The damage caused by cleaving holey fibers is investigated as a function of cleaving force. Comparisons are made with standard optical fibers and holey fibers. Optimum cleaving forces are determined for a number of holey fiber air fractions and fiber diameters. A simple technique for removing cleave damage is also presented.