Direct UV-written waveguide devices
This thesis describes a series of experimental studies concerning waveguide structures based on the direct UV and direct grating writing fabrication techniques. The latter approach allows simultaneous definition of waveguide structures and Bragg gratings. The first result of this work describes the fabrication and characterisation of small angle X-couplers that exhibit low polarisation and wavelength dependence. Maximum and minimum coupling ratios of 95% (±0.8%) and 1.9% (±1%) respectively with typical excess loss of 1.0dB (±0.5dB) were recorded. Device modelling using Beam Propagation Method (BPM) and an analytical model showed good agreement with experimental results over a broad crossing angle and wavelength range. By introducing refractive index asymmetry in 2° X-couplers, it was possible to tune the response to give a 50:50 coupling ratio. Multiple UV exposure experiments investigated the 'proximity effect' and provided further proof of the ability of UV writing to produce raised waist index X-couplers. A first order Bragg grating electrically tunable via liquid crystal index modification with a maximum tunability of 141 GHz at 1562nm (TM polarised) and 114 GHZ at 1561.8nm (TE polarised) using electro-patterned ITO-coated glass electrodes is also presented. The 141GHz tuning range effectively covers up to five 25 GHz WDM channel spacing and was achieved with 170Vpp sinusoidal 1 kHz supply voltage. Hysteretic behaviour of the tuning curves was observed and is believed to be related to the dynamics of the disclination line formed along the waveguide axis with increase or decrease in supply voltage. Finally, a description of the successful demonstration of UV-written single channels, y-splitters, and Bragg gratings into a novel flat fibre substrate is provided. Utilising a series of Bragg gratings enabled assessment of the core layer uniformity and birefringence.