Nathaniel Groothoff

Bragg gratings in air-silica structured fibers.

We report on grating writing in air-silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

Water-core Fresnel fiber

A water core photonic crystal Fresnel fiber exploiting a hole distribution on zone plates of a cylindrical waveguide was developed and characterized. This fiber has similar guiding properties as the pristine air-hole guiding fiber although a large loss edge ~900nm is observed indicating that the bandgap associated with Fresnel guidance has shifted to longer wavelengths. The absorption bands of the water in the region of the NIR were observed. The application to biosensing is discussed.

Strain and temperature characterization of photonic crystal fiber Bragg gratings.

A Bragg grating in a photonic crystal fiber was written and its dependence with temperature and strain analyzed. The two observed Bragg wavelengths correspond to a fundamental and a higher-order mode in the optical fiber. The temperature and strain calibration curves for both modes are measured and found to be distinct. The general properties of gratings in these fibers, and their implications, are enunciated.

Enhanced type IIA gratings for high-temperature operation

The inscription of type IIA fiber Bragg gratings in standard boron-codoped germanosilicate fiber has been demonstrated to show marked differences from that reported in the literature. These gratings were subjected to high temperatures, and their decay behavior was evaluated. Gratings resistant to heat up to 800 degrees C for a moderate length of time are demonstrated.

Micromachining structured optical fibers using focused ion beam milling

A focused ion beam is used to mill side holes in air-silica structured fibers. By way of example, side holes are introduced in two types of air-structured fiber, (1) a photonic crystal four-ring fiber and (2) a six-hole single-ring step-index structured fiber.

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.

Optical loss mechanisms in femtosecond laser-written point-by-point fibre Bragg gratings

Fibre Bragg gratings inscribed with the point-by-point method using a Ti-sapphire femtosecond laser operating at 800 nm are shown to display strong increasing attenuation towards shorter wavelengths with a large and spectrally sharp recovery observed below 400 nm. The origin of this loss is shown to be Mie scattering, and the sharp recovery in the transmission results from wavelength dependent scattering within the numerical aperture of the core. The permanent losses from these Type II gratings have implications for high temperature sensors and fibre lasers.

Gratings in Structured Optical Fibres

Grating writing in structured optical fibres and their properties and applications are reviewed. To date, most gratings have been written in a straightforward manner into structured fibres containing a photosensitive germanosilicate step-index core. However, gratings have also been written directly into single material, structured silica fibres and into air-clad cores using two and higher-photon processes with both UV and near IR pulsed (nanosecond-femtosecond) light. Given the intrinsic-added functionality possible within a structured optical fibre, structured fibre gratings offer further capabilities for sensors, diagnostics, lasers, and devices.

Distributed feedback photonic crystal fibre (DFB-PCF) laser

A distributed feedback laser is fabricated in Er3+-doped photonic crystal fibre. Preferential single-mode lasing is obtained with no special consideration of polarisation issues. The results demonstrate practical implementation of a multi-photon writing process for complex structures in these optical fibres. No hydrogen loading and no germanium are involved.

Refractive index measurement within a photonic crystal fibre based on short wavelength diffraction

A new class of refractive index sensors using solid PCF is demonstrated. Refractive indices of water and ice are measured during the ice lh formation inside of the fibre holes.