Active Waveguide fabrication using PLD and Sol-gel

Component producers have always strived to produce the smallest and most efficient devices. In the same way that electrical wires were replaced by integrated circuits, optical fibres and standalone devices are now being replaced by Photonic Integrated Circuits (PICs). One major breakthrough that allowed high bandwidth, large distance optical data links was the advent of the Erbium Doped Fibre Amplifier (EDFA). The PIC version of the EDFA, the Erbium Doped Wavguide Amplifier (EDWA), has attracted much research interest over the last decade resulting in EDWAs with small signal gains of over 20dB across the entire C band (1530-1565 nm). Unfortunately, the processes by which these EDWAs are produced have low deposition rates and low yield due to difficulties in ensuring the uniformity of the thickness and refractive index in each layer of the waveguide structure. Other routes for producing high gain EDWAs through sol-gel and pulsed laser deposition (PLD) technologies may be possible. In short, the aim of our research is to investigate the production of high gain EDWAs using new manufacturing techniques.

Unlike other EDWA technologies such as flame hydrolysis deposition (FHD), chemical vapour deposition (CVD), sputtering, ion exchange, ion implantation and E-beam deposition, sol-gel is a chemical process. Due to the chemical nature of the sol-gel process, good homogeneity of the distribution of the erbium should be achieved therefore avoiding clustering effects. Clustering effects are thought to be a major gain limiting factor in high erbium concentration waveguides.

Green fluorescence due to upconversion clearly visible in a EDWA sample

In addition to our research on sol-gel EDWAs, we are also investigating the use of Pulsed Laser Deposition (PLD) for the production of EDWAs. PLD is of interest because it preserves the stoicheometry of the target between bulk and film. This allows complex glasses to be constructed in bulk that can then be deposited onto a substrate for patterning.

Pulsed laser deposition process, conducted at Universita de Lecce. Inset: bulk erbium doped glass target in target holder