Fabrication of a single mode laser by UV-writing in neodymium doped silica-on-silicon

We describe the fabrication of a waveguide laser by UV-writing in neodymium doped silica-on-silicon. The substrate is fabricated by Flame Hydrolysis Deposition and solution doping techniques. Lasing at 1048-1056nm was observed with a slope efficiency of 33% and threshold of 4mW for the transition. Lasing was also observed at 1356nm

Are we teaching our students what they need to know about ageing? Results from the National Survey of Undergraduate Teaching in Ageing and Geriatric Medicine

Introduction - Learning about ageing and the appropriate management of older patients is important for all doctors. This survey set out to evaluate what medical undergraduates in the UK are taught about ageing and geriatric medicine and how this teaching is delivered. Methods – An electronic questionnaire was developed and sent to the 28/31 UK medical schools which agreed to participate. Results – Full responses were received from 17 schools. 8/21 learning objectives were recorded as taught, and none were examined, across every school surveyed. Elder abuse and terminology and classification of health were taught in only 8/17 and 2/17 schools respectively. Pressure ulcers were taught about in 14/17 schools but taught formally in only 7 of these and examined in only 9. With regard to bio- and socio- gerontology, only 9/17 schools reported teaching in social ageing, 7/17 in cellular ageing and 9/17 in the physiology of ageing. Discussion – Even allowing for the suboptimal response rate, this study presents significant cause for concern with UK undergraduate education related to ageing. The failure to teach comprehensively on elder abuse and pressure sores, in particular, may be significantly to the detriment of older patients

Ultra-wide planar Bragg grating detuning and 2D channel waveguide integration through direct grating writing

We present a technique for defining 20 channel waveguide structures with internal Bragg gratings in photosensitive germanosilica-on-silicon using two interfering focussed UV beams. Grating detuning across the S, C, and L bands is demonstrated

Planar waveguide water state sensor allowing detection of supercooling

A sensor believed to be the first truly integrated optical sensor demonstrating the detection of the liquid-solid phase transition of water is presented. The condensation, freezing, melting and evaporation of water are all detected with a planar silica Bragg grating operating in the 1.5 micron telecommunications window. Additionally, use of the sensor allows recognition of supercooled liquid at temperatures below the melting point of water. The device is fabricated by direct UV writing with simultaneous definition of the grating, a method inherently suited to integration with other technologies. The Bragg grating is exposed and water is allowed to condense over it. Interaction with the evanescent field causes small changes in effective index (5x10-6) which can be detected, a sufficient sensitivity to identify the phase transitions of water clearly

Direct UV writing for channel definition on FHD silica-on-silicon

Direct UV Writing (DUW) is a relatively new technique used to define channels on photosensitive planar substrates and relies on a photosensitive reaction of the substrate material to UV light irradiation. Photosensitivity refers to the permanent (but reversible) change in the index of refraction of the waveguide core when exposed to light with characteristic wavelength and intensity that depends on the core material. A laser with an emission around the 240nm absorption window is focussed down to a circular spot about 4µm in diameter and the sample is then translated relative to this writing spot, with the path of translation defining the channel waveguide structure. The more advanced Direct Grating Writing (DGW) technique involves utilising interference pattern generated by crossed UV beams and allows the simultaneous definition of channel waveguides and grating structures. The UV interference pattern is generated by intersecting two tightly focussed coherent UV beams at a fixed point in space. A photosensitive sample is then aligned with this interference spot and translated relative to it. Both of the techniques require no clean room facility and involve no etching processes. UV writing is particularly attractive for researching crossed waveguides as it is does not require etching and allows a smooth and continuous merging and splitting of channels. Characterisation of direct UV written straight channels, s-bends and crossed waveguides are presented in this manuscript. The structures were defined on 3-layer photosensitive silica-on-silicon (SiO2:Si) samples fabricated via flame hydrolysis deposition (FHD), involving the production of silica soot through the injection of halide reagents into a hydrogen/oxygen (H2/O2) flame. Straight channels written at various fluences show a saturation effect, possibly due to the sample reaching its upper limit of photosensitivity level whereas the s-bends display the reduction in excess loss with increase of bend radius as expected

Single-step fabrication of raised index X-couplers via direct UV writing

X-couplers having low polarization and wavelength dependency with 1.9-95% coupling ratios were fabricated in a single step via direct UV writing, exhibiting typical excess loss of 1.0dB. First experimental validation of analytical and BPM modeling is also presented

Fabrication of directly UV-written channel waveguides with simultaneously defined integral Bragg gratings

A new technique for UV direct writing of Bragg gratings in planar silica is presented. In this method the Bragg gratings and the channels are defined simultaneously, conferring advantages in flexibility of design and grating performance. Photosensitive Germanium doped silica-on-silicon produced by Flame Hydrolysis Deposition was used

Single step writing of equalised bandwidth Bragg gratings within planar light-wave circuits

We demonstrate single-step writing of waveguide circuits with Bragg gratings between 1227nm and 1687nm and for the first time show that the grating bandwidth can be normalised over this large wavelength range

Direct UV writing of channel waveguides and Bragg grating structures

Direct UV writing is a dynamic planar lightwave circuit fabrication technique offering great potential as a means of rapid prototyping and small/medium batch fabrication. The technique is based on the refractive index increase of photosensitive glasses through exposure to ultraviolet light. In this case, a beam is tightly focused to create a writing spot in the order of microns and is translated relative to the sample. It is this translation over a 2-d plane that defines the channel waveguide structures; there is no need for a photolithographic mask or subsequent processing. This process has previously been shown to be a versatile system producing good quality, low loss waveguides compatible with existing silica based telecom fibres