Hemalatha Muthuganesan
Winner
What encouraged you to submit your application to the 2023 Postgraduate Research Publication of the Year?
My supervisor, Brian Corbett sent an email, encouraging PhD students in our team who had publications, to submit for 2023 Postgraduate Research Publication of the Year.
What inspired you to choose the subject of your paper?
The inspiration is from our increasing dependence on data centres and the telecommunication network in order to use the internet, video streaming etc. Integrated, low-cost, high bandwidth photodetectors are a crucial component to continue to deliver the services that people want.
What’s your paper about and how did you prepare for it? What role did research excellence play in your approach?
My paper is about integrating high-speed prefabricated photodetectors (PD) to silicon platforms using micro-transfer printing technology. These InGaAs based photodetectors employ an ultra-thin epitaxial stack less than 1 micron and a small dimension of 21 × 57 μm2. This work is the first successful demonstration of integrating the same PD into one common silicon chip via three different coupling mechanisms, namely evanescent, grating and waveguide coupling. Due to its compact size, we can obtain 1 million detectors from an InP wafer, maximizing wafer usage and saving cost.
The devices achieve high photo-responsivity, low dark current and high bandwidth at telecommunication wavelengths. In data transmission measurements, we achieve 50 Gb/s for zero on-off keying while with multilevel signalling, we accomplished transmission rates of 100 Gb/s.
Regarding preparation: The work involved the collaboration of many teams within and outside Tyndall. The photodetector was designed by myself and my supervisor. The wafer was grown in Tyndall and I completed the fabrication process. I designed the target silicon wafer which was fabricated by Cornerstone, UK. I transfer printed, integrated the detectors and then measured them. The high-speed measurements were completed by me in conjunction with the researchers in the Systems Lab in the Irish Photonic Integration Centre (IPIC), SFI Centre for Photonics at Tyndall. I received suggestions and guidance from my team (III-V materials and devices) at Tyndall National Institute.
The selection for Research Publication of the Year is extremely competitive. What is your advice for those aspiring for nomination next year?
Do not compare your work with other PhD students. I understand every person’s journey is unique and has its own pros and cons. Some might get publication in their 2nd year whereas others might get it only in their 4th year. This publication is my 1st first author journal which got accepted in my fourth-year, even though I had produced conference papers earlier. It took me a long time, to get things right, test the photodetectors and finalize the results. Till then, I had to be patient and at the same time persevere towards my goal.
Plans evolve. My PhD work started with the aim of making co-planar integration of III-V laser to SOI platform. We realised certain issues with lasers and decided to fabricate photodetectors first as optical coupling is not as crucial as with lasers. We started with only co-planar coupling idea, then decided to try evanescent and grating coupling with the results seen in the published paper. So, I realised that based on the changing circumstances, it is smart to evolve the initial plan and be ready to adapt to new ideas.
Control is an illusion. During a PhD, there are lot of things that could go wrong, some instruments might not work and take a long time to get fixed, and once fixed their process parameters changes and need optimisation or when we are dependent on other people they might go on a vacation! So, there are many things which are not in our control. All these factors, delay the estimated time to complete a work. None of this is anyone’s fault! Hence, do not be harsh on yourselves and always have a plan B, plan C etc. That way, your time is productive in achieving other tasks.
What is the single most significant support Tyndall has been able to offer you in achieving your research goals?
The guidance and support from my supervisor Brian Corbett is the most significant support. He made me independent and helped me to grow as a researcher during my PhD. It is an immense benefit that Tyndall had an epitaxy team, micro-transfer printing facility and high-speed testing capabilities, all of which ensured we could get this paper published successfully by collaborating with them. In the future, photodetectors can be designed in such a way that it can be packaged at Tyndall itself, thus achieving a fully in-house product, where epitaxial growth, design, fabrication, packaging and testing are all executed at Tyndall.
Hemalatha Muthuganesan, Enrica Mura, Shivangi Chugh, Cleitus Antony, Emanuele Pelucchi, Paul Townsend, Xingzhao Yan, Mehdi Banakar, Ying Tran, Callum Littlejohns, and Brian Corbett, ‘100 Gbps PAM4 ultra-thin photodetectors integrated on SOI platform by micro transfer printing’, Optics Express 31, 36273-36280.