Dr Krishna Coimbatore Balram Associate Professor in Photonic Quantum Engineering, University of Bristol (in conjunction with PhD student Ankur Khurana)

CORNERSTONE’s work with Krishna’s research group at the University of Bristol could lead to his group bidding for EPSRC funding to further develop MEMS-based low power large scale photonic integrated circuits.

Why did you get in contact with CORNERSTONE?

My research group was interested in extending the capabilities of standard photonics foundry platforms. These hybrid platforms allow the scale and complexity that foundries provide to be combined with novel device architectures and potentially enable new solutions. 

One of the key challenges facing linear optic implementations of quantum photonics is low-power phase shifters operating in a cryogenic environment, limiting the scale of photonic circuits that can be run at low temperatures.  We wanted to overcome this restriction by exploring the use of MEMS-based phase shifters that have zero static power dissipation and provide cryogenic operation. By demonstrating that these devices can be built as part of standard silicon photonics foundry processes, combined with in-house post-processing, we could show the scale and complexity that could be achieved with the MEMS devices was comparable to that of traditional heaters. 

CORNERSTONE was able to provide us with the ability to pull chips out at different steps of the process based on our user requirements which enabled us to carry out our research. 

How did CORNERSTONE help you with this work?

CORNERSTONE carried out the standard multi-project-wafer (MPW) passive photonics runs to implement the designs. As our designs required postprocessing, it was critical to account for the MPW design rules in order to facilitate the release steps. CORNERSTONE Coordinator Callum Littlejohns gave us some very useful feedback during our early designs. He picked up on a couple of errors where we had missed a design rule and misinterpreted the mask tones. If the design had been fabricated like this, it wouldn’t have worked. So thanks to CORNERSTONE we could sort out these issues before fabrication.

CORNERSTONE was also very flexible with our requests for modifying certain fabrication steps. They were also very prompt in responding to our feedback and generously provided us with a new set of chips. By getting the photonic backbone fabricated through the MPW, we could focus on the MEMS bits in our fabrication, which saved us a lot of time.

How will the work with CORNERSTONE help you in the future?

Currently, we are in the process of characterising our devices. We have some exciting preliminary results but we need to do more work to fully understand our system. We hope our work with CORNERSTONE will act as a springboard for an Engineering and Physical Sciences Research Council (EPSRC) standard mode grant on MEMS-based low power large scale photonic integrated circuits.

We also hope to use the suspended-Si platform that CORNERSTONE is developing to fabricate our devices without the need for post-processing.