Sydney Terahertz Laboratory Upgrades!

Delighted to report two important new upgrades to the Sydney THz Lab!

First, we have tweaked our Menlo THz fiber-coupled system to emit and detect with Protemics near field probes! Special thanks to visiting PhD student Kseniia Lezhennikova from the Institute Fresnel (Marseilles) and the ALPhA collaboration.

Secondly, our closed cycle cryostat attoDRY800xs was just installed, and I’m very excited to try it out.

Please get in touch if you think this setup can be useful for your research!

Wrapping up 2022: invited talks and papers

Taking the chance to share some good news before heading for my end-of-year break. A new invited contribution was just published in the Sensors special issue  Plasmonic Optical Fiber Sensors: Technology and Applications, titled “Plasmonic Sensors beyond the Phase Matching Condition: A Simplified Approach”. Anyone working on plasmonic sensing designs in fibers and waveguides will probably find this useful, so please take a look and share it with your colleagues. We present an easy approach for device-level plasmonic sensor designs (using coupled mode theory), which only needs mode calculations (no overlap integrals!), giving meaningful information for first design steps. It also ships with code!



Thank you Alex Song, Giuseppe Della Valle and Martijn de Sterke for the collaboration!

Last week I also presented one invited and one contributed talk at the big AIP/ANZCOP/WSOF conference in Adelaide. It was great to finally be able to see my friends and colleagues face-to-face after many years. It felt like I was seeing three years of concentrated research in one week, happy to be a part of this new start. The plenaries were certainly a highlight. Photos below!

Functionalizing waveguides with 2D materials

Concept schematic of the MoS2 crystal (green) grown over a Si waveguide structure (pink) via the CVD process. Reproduced from licensed under the Creative Commons Attribution 4.0 International License.

New paper published this week! Congratulations to the talented lead author Athira Kuppadakkath, a collaboration with Falk Eilenberger’s group at Fraunhofer IOF (Jena).

2D materials can be used to to functionalize optical waveguides and nanostructures, but getting the materials on there normally requires manual transfer. In this paper we showed that crystalline monolayer MoS2 can grow directly on photonic nanostructures with good quality in a scalable process, and what to pay attention to when doing so, and ensure they continue performing as you’d want.

This work emerged from a visit to Falk way back in 2019, and I clearly remember discussing the first results when COVID lockdown started! I also did some of the calculations and some follow-up experiments at the Nanoplasmonics Lab at the University of Sydney.

Terahertz light cages!

New paper from our Sydney Terahertz Lab! Light cages can provide diffractionless propagation in free space, so we 3D printed a few modules with various materials (stiff and flexible resins, ceramics) and tested out what they can do.

We took some near-field images of the straight and bent waveguides with our new fiber-coupled microprobes, and I was stoked to see the conformal map model of bent waveguides come to life. We heated up a ceramic light cage beyond what polymers can withstand, and showed direct-in-core sensing. We also introduced two new Figures of Merit which compare light cages with free space Gaussian beams (our fiercest competitor in the terahertz range).

Thank you Alessio Stefani, Boris Kuhlmey, Mohammad Mirkhalaf, and Hala Zreiqat for the collaboration. This work couldn’t have been possible without our talented students Benjamin Davies and Zizhen Ding, and the amazing Justin Digweed from ANFF NSW.

For those without access, I include the pre-edited version here (please do not redistribute, and cite the ACS Photonics version):


And to top it all off, a cool near field measurement of the bent waveguide can be seen below, compared with COMSOL simulations:

ABC Elevator Pitch: what is light?

Fun video for the ABC, doing my best to explain what light is – but in a single elevator ride.

As a side note, this is a textbook example of an insufficient explanation for the particle nature of light! (But how to do it in just a fraction of an elevator ride!!!???) As my quantum photonics friends keep telling me, I am cheating by assuming I know the answer. For anyone interested in this fascinating topic, I recommend getting your hands on first few chapters of this wonderful book:

The Quantum Challenge: Modern Research on the Foundations of Quantum Mechanics, by George Greenstein and Arthur G. Zajonc (Jones and Bartlett, 2006)

Plasmonic sensing in waveguides: a non-Hermitian perspective

New paper just published in Photonics Research! Should be useful for anyone working on sensing with plasmonic waveguides and fibers. We discuss in detail what to expect from the experimental spectra of plasmonic waveguide sensors in various regimes.

Because this is a non-Hermitian system, things can be a bit confusing. It’s quite tempting to infer everything from just mode dispersions, but sometimes the propagation constants cross, sometimes they anti-cross. So what to make of it, and how does it all affect an actual sensor? That’s what we discuss here. And the exceptional point.

I put up my “rawest” Python Notebook on github, that reproduces a few key plots, in case anyone wants to adapt it to their own sensor design.

I like to call this my “Sydney lockdown” paper – thanks to Boris Kuhlmey and Markus Schmidt for the collaboration.

Bend losses in polyurethane fibers

Happy to announce that the first experimental paper from our revamped Sydney Terahertz Lab has been published in Optics Express.

Our talented Denison Student Jonathan Skelton had the opportunity to study the world-famous polyurethane fibers of our friend and colleague Alessio Stefani during the summer earlier this year, way back when Sydney was not in lockdown mode. To enable this, we built a fast terahertz 2D imaging setup based on our fiber-coupled Menlo Systems TERAK15. This system makes it very easy to study bend losses in waveguides.

We took a close look at bend losses in two hollow core THz fibers, which are really flexible despite being quite thick. It’s not common to be able to bend terahertz waveguides of this size by this much, and it was interesting to weigh the pros and cons of these kinds of structures. What we learned: in terms of bend losses, these simple tubes are not so bad, unless you bend them a lot. Vice versa: structured tubes are better if you the fibers a lot! Otherwise, you couple to tube cladding modes…

Download the paper for more information:

A. Stefani, J. Skelton, A. Tuniz, “Bend losses in flexible polyurethane antiresonant terahertz waveguides”, Optics Express 29 28692-28703 (2021)

Imaging in Hyperbolic Media: Python Code

In response to an out-of-the-blue email asking for help, I recently dug up my Jupyter Notebook code for reproducing the results of a paper written with Boris Kuhlmey in 2015, “Two-dimensional imaging in hyperbolic media–the role of field components and ordinary waves“.

With a bit of extra love, this can be adapted to reproduce every figure! The beauty of this approach compared to brute-force methods such as FEM and FDTD is that it allows quite rapid calculations via analytical formulae. I seem to remember that, for comparison, COMSOL sometimes struggled to converge, and that the huge slabs considered towards the end of the paper would have impossibly large meshes. However, this code is slowed down by the need for arbitrary-precision computations, which stems from large exponentials that appear when considering fine spatial features… Please cite the paper if you use this code for your research!

Code is here: