MESA+ University of Twente
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Jonathan Bradley (promotion date: 17 September 2009)

Al2O3:Er3+ as a gain platform for integrated optics

Promotion date: 17. September 2009

Promotor: Prof. Dr. Markus Pollnau

The goal of integration is to reduce the size and cost of devices by realizing many functions on a single chip. There is still a need for active devices, such as amplifiers and lasers.

Amorphous erbium-doped aluminium oxide is investigated and optimized, as a promising optically-pumped gain medium. Deposition of thin films using RF co-sputtering was explored, a new structuring procedure using reactive ion etching was developed also.

Channel waveguide amplifiers with varying Er-concentrations were fabricated and characterized. Various novel on-chip devices were realized: a zero-loss optical power splitter, a high bit-rate amplifier and a ring laser.

Why did you choose for erbium-doped aluminium oxide, as main material for your thesis project?

Erbium-doped aluminium oxide glass is known as a very promising optically-pumped gain medium, already used in large-scale optical fibres, due to its high transparency, refractive index and broad emission spectrum. For chip-like devices the results were not good enough, yet.

We achieved low losses in the high transparent films, using a new deposition method. Instead of conventional direct current (DC) methods we used radiofrequency (RF) sputtering, to bring in Er-ions in well-defined concentrations, with very good results on different parameters. The second step was to create micro-structures for guiding light, which was done using reactive ion etching (RIE). We also achieved excellent results with the micro-structuring, allowing a lot of design flexibility.

It required a lot of systematic investigations to come to a consistent process, using the two fabrication steps. I mainly focussed on the etching techniques, a colleague was more involved in film growth.

Will the project be continued within Mesa+?

It certainly will, for example with respect to the usability in sensor devices and laser applications. In this project we succeeded in demonstrating a ring-laser, usable at different wavelengths and easily tuneable.

Was this project a Mesa+ type of research?

First of all, it was team-work of the Integrated Optics MicroSystems Group, working together with PhD’s, post-docs and several technicians of the cleanroom.

Due to Mesa+ I was exposed to a lot of different equipment. It was necessary in this project to try some different things, to solve upcoming problems together with other experts, and eventually to choose the most feasible combination of techniques.

As a researcher I found that the planning part of the process is really important in scientific research. You have to have multiple options in case things go wrong, in order to continue working and make progress.

What else is important, besides the cleanroom facilities, for Mesa+ in the future, in your opinion?

In this project we worked together, in some degree, with the Telecommunication Engineering group. This cooperation has started because people met, while talking about research activities.

In my opinion a lot could be gained if familiar groups meet on a more regular basis, for example in group-seminars every two months. Something like that. For example, for a long time I had no idea what the Optical Science group was working on, though their research activities are very similar to ours. It would be very interesting to hear some researchers of this group, talking about their work.

What are your future plans?

First of all, I am having a holiday. I experience a great sense of freedom, after four years of working on one subject, being able to choose something new for the upcoming years.

Right now, I am applying for a job, favourably in a smaller or medium sized company. I like to have an overview of the activities happening within one company, so I can think along actively and strategically.

I already spoke to a spin-off company of Twente University, acting in the optical-electronic field. Above all, I am applying in my home country, Canada, in the Toronto area.