Worldwide Universities Networks

During my recent trip to China I had the opportunity to meet with researchers in my field of integrated photonics. Through Chaotan Sima, an alumni of my research group in the Optoelectronics Research Centre, I was introduced to Professor Huilian Ma, of Zhejiang University’s Laboratory of Micro-Optic Gyroscopes in the school of Aeronautics and Astronautics. The research centre has approximately 40 research students and 10 professors. I had the pleasure of meeting Prof. Ma’s group, including my PhD student-counterpart Jianjie Zhang. I am extremely grateful for the kind and generous reception of my hosts, who made me discover Hangzhou food and helped me settle in after an eventful travel. Credit goes to them too for all the pictures in the post!

A warm reception to Hangzhou, with Prof. H Ma's research group and Chaotan Sima, to my right.
A warm reception to Hangzhou, with (left to right) Lu Ying, Lin Yi, Ma Huilian, Sima Chaotan, Posner 马修 (me!), Zhang Jianjie, Ye Sen and Li Hanzhao. In Chinese, it’s first surname, then given name!

The visit was a great opportunity to learn about how photonics integrated circuits can be used as optical gyroscopes. Gyroscopes are used to stabilise position of navigation systems or automatic pilots independent of their movement of rotation. It is important for space applications, such as in satellites orbiting around the earth, where the ability to accurately determine position is of the utmost importance. Normally gyroscopes have moving (mechanical) parts, so can be delicate to package and send safely up to the space! The integration of these devices leads to more stable, smaller and scalable technologies.

Prof. Ma’s group at Zhejiang University is developing integrated optical gyroscopes on chips the size of a large stamp. They design and test prototypes on a silica-(glass)-on-silicon platform. These devices must maintain a very high signal-to-noise ratio to be efficient sensors. A well-known problem for optical gyroscopes is that the signal can be degraded by imperfect polarisations of the laser source used with these systems. In Southampton I had been researching ways to create on-chip polarisation filters compatible with silica technology, which could improve the performance of these devices. In the months leading up to this trip I had received some prototypes to test the suitability of the Southampton Direct UV Writing laser system to make polarizing filters using tilted gratings in waveguides, using the fabrication techniques I’ve discussed previously. The visit gave me the opportunity to present the work I’ve conducted to date and understand the testing methods. It’s been extremely worthwhile discussing the project directly with the people involved, and I’m looking forward to further experimental work that will arise from these discussions.

Professor Huilian Ma, I, and ORC alumni Chaotan Sima discussing preliminary test results of the integrated optical gyroscopes.
Professor Ma Huilian, Sima Chaotan and I discussing preliminary test results of the integrated optical gyroscopes, with some refreshing seasonal fruits.

Integrated Photonics Research

Eureka. I made an experiment, and then made it better.

In my PhD I am building integrated optical circuits. The devices I have been making act as polarising filters: they split a light signal into 2 signals that have different amounts of polarisation in each of them. It’s a bit like with polarised sunglasses, where held one way (say horizontally) the light coming through looks strong, and when turned at a right angle, the light looks weak. My devices have the same effect, and I want to quantify this contrast in the strengths of the polarised light with physical quantities.

So this is how I did it

Integrated photonics experiments are delicate
My integrated photonics experiment

Now the tricky thing with this experiment is that am trying to measure the polarisation contrast within a tiny ray of light that is very close to a huge sun that is a source of unwanted noise. The higher the noise the harder it is to measure a high level of polarisation contrast at the device output. It works on a scale of 1 to 100 (in dBs for those familiar with logarithmic scales). Said differently, without taking care, my device looks like it’s on level 5. If I collect the data by filtering out the noise then I can show a higher level of contrast. I used a combination of fibre optics, microscope objectives, highly precise mechanical stages and filters to try and make it better.

It’s a bit like playing Pokemon. I was at level 17 initially, worked hard to improve an experiment and after some time got to level 28. That’s a 10 billion (10^10!) fold improvement in contrast. Next step is level 30; at that point my device evolves from a research product to a device worthy of industrial interest.