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%.

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.

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.

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.

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.

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.

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.

Stability of thermally hypersensitised phosphosilicate waveguides and the characteristic growth curve.

Low temperature (80 0 C) hypersensitised hydrogen-loaded phosphosilicate optical fibre is found to be unstable, decaying progressively at room temperature. However, the hypersensitisation process linearises the grating growth characteristic curve. Further, a negative index contribution is inferred at low fluence in the presence of hydrogen.

Bending-induced colouring in a photonic crystal fibre.

A photonic crystal fibre has been fabricated with a photonic crystal that is surrounded by a number of silica cores. Bending of the fibre induces an interaction between the core and photonic crystal areas, resulting in a highly wavelength-dependent loss of the core modes. White-light transmission experiments are presented which show that the colour of the transmitted light changes as a function of the fibre-bending radius. We compare the results to a simple model and find agreement.

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.

All-fibre photonic crystal distributed Bragg reflector (PC-DBR) fibre laser.

We describe an Er3+-doped aluminosilicate core photonic crystal fibre laser incorporating distributed Bragg reflectors written by two-photon 193nm irradiation through an optical phase mask as the feedback elements. The laser is diode pumped at 980nm and evidence of dual linewidth laser operation close to threshold is observed. However, at higher pumping levels gain competition preferentially selects one laser line.

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.

The scrotal hitch for hemostasis and edema prevention in scrotal surgery.

Postoperative hematoma, edema, and echymosis are the most common complications in scrotal surgery. Without proper hemostasis intraoperatively or appropriate scrotal compression postoperatively, significant morbidity, including re-exploration and prolonged convalescence, can occur. The scrotal hitch provides hemostasis, minimizes edema and hematomas, and reaffirms other clinicians' findings.

Exsanguinating hemorrhage from urinary ileal conduit in patient with portal hypertension.

A patient with an ileal conduit diversion after cystectomy for carcinoma of the bladder is seen with cirrhosis and portal hypertension. Massive bleeding from the peristomal varices developed. Our experiences with conservative treatment is outlined.

Positive bethanechol supersensitivity test in neurologically normal patients.

A positive bethanechol supersensitivity test (BST) usually indicates neuropathic detrusor areflexia and warrants neurologic correlation. Seven females, average age thirty-three years, with straining to void and high residual urines, had detrusor areflexia, with a borderline or positive BST, ranging from 19 cm water to 55 cm H2O change in intravesical pressure after 5 mg of subcutaneous bethanechol. However, all patients had a normal neurologic workup, even though 2 patients had insignificant spina bifida occulta. Two of the patients also had prior pelvic surgery, 1 of whom was azotemic, and 4 of the patients had psychosocial problems; factors reported to be associated with a false positive BST. The positive BST is not diagnostic of neurogenic detrusor areflexia because of the many variables that can influence the test. Therefore, the bethanechol supersensitivity test should be interrupted in light of the complete neurourologic evaluation.