Photonic Crystal Ring Resonators for Tailored Optical Microcombs

Dr Ewan Lucas

Research Fellow, Laboratoire Interdisciplinaire Carnot de Bourgogne

Nonlinear-wave mixing in optical microresonators offers a promising avenue for compact optical-frequency microcomb generation [1]. These microcombs have rapidly found applications across diverse fields, including optical frequency synthesis and high-capacity data communication systems. A fundamental characteristic of microcombs is their spectral profile, which is principally determined by the resonator’s dispersion. An illustrative example is the sech2 spectrum of dissipative Kerr solitons that emerges under anomalous group-velocity dispersion.

Concurrently, photonic crystal ring resonators (PhCR) have emerged as a flexible way of tailoring of optical microcavities [2]. These ring resonators introduce a corrugation to the inner wall of the waveguide, enabling precise and independent control of cavity mode resonance frequencies while preserving a high quality factor (Q). This innovative approach offers mode-by-mode frequency splitting capabilities, vastly expanding the design space for managing the nonlinear dynamics of optical states, such as Kerr solitons.

This presentation explores the advantages of this enhanced control, initially focusing on the control and generation of microcombs in the normal dispersion regime. I also demonstrate the creation of a ‘meta-dispersion’ resonator by selectively manipulating the resonance of multiple modes with a PhCR. The nonlinear modeling of these structures unveils new comb states and instabilities.
Furthermore, by embedding the governing equation of the system into a genetic algorithm, we efficiently pinpoint a dispersion profile that yields a microcomb closely aligned with a user-defined target spectrum [3].

[1] T. J. Kippenberg et al. “Dissipative Kerr solitons in optical microresonators”. Science 361.6402 (2018).
[2] S.-P. Yu et al. “Spontaneous pulse formation in edgeless photonic crystal resonators”. Nat. Phot. 15.6 (2021).
[3] E. Lucas, et al. “Tailoring microcombs with inverse-designed, meta-dispersion microresonators”. Nat. Photon. 1–8 (2023) doi:10.1038/s41566-023-01252-7.

Friday 15 December, 12:00pm, Room 314 Science III Building

Media Events News

Potential drivers of the recent large Antarctic ozone holes

Despite public perception, the Antarctic ozone hole has been remarkably massive and long-lived over the past years, and University of Otago researchers believe there are factors beyond CFCs that are contributing. In their ground breaking work just published in Nature Communications, University of Otago Physicists Hannah Kessenich, Annika Seppälä, and Craig Rodger analysed ozone levels from 2004 to 2022, and found there is much less ozone in the centre of the Antarctic ozone hole compared to 19 years ago. While overall Antarctic ozone is recovering due to the Montreal Protocol that banned the harmful ozone depleting CFCs, the slow ozone recovery is focused on the outer parts of the ozone hole.

The Otago team used 20 years of satellite data from the Microwave Limb Sounder instrument on the NASA Aura satellite ( to identify what drivers the continued ozone depletion in the ozone hole core, and their study highlights the pressing need for comprehensive and ongoing monitoring of the ozone hole due to the critical role the ozone layer plays in protecting life on earth.


2023 Hector Medal Award to Niels Kjærgaard

On November 15 The Royal Society held its Christchurch event to celebrate 2023 Research Honours. At the event Niels was awarded the Hector Medal for fundamental scientific studies on atomic collisions and light scattering using ultracold gases.

The Hector medal is an award for outstanding work in chemical, physical or mathematical and information sciences by a researcher in New Zealand, awarded annually. Niels will join a distinguished list of recipients since 1912, including Ernest Rutherford, Te Rangi Hiroa (Peter H. Buck), John Newton Dodd, Roy Patrick Kerr, Daniel Frank Walls, Paul Terence Callaghan and Richard Blaikie.

Find out more about the award at the Royal Society Media Release:

“Professor Niels Kjærgaard has been awarded the Hector Medal by Royal Society Te Apārangi for his outstanding contribution to the advancement of scientific understanding of fundamental particles, through experimental studies of atomic collisions and light-scattering using ultracold gases.”

Congratulations Niels!

Find out more about the research, visit the website for Kjærgaard Lab.


Promotions 2023

Congratulations to Annika Seppälä, Jono Squire, and Paul Muir on your successful promotions in 2023!

Media Events Seminars

2023 Dan Walls Medal Public Lecture: Maths powers black holes, the Universe and everything

Prof. David Wiltshire

University of Canterbury

Sixty years ago New Zealander Roy Kerr helped revolutionize physics, achieving what had eluded scientists for 47 years. He discovered the solution to Einstein’s equations defining space around a rotating star or black hole. He combined advanced mathematics with one key simplifying insight: All bodies collapsing under their own gravity inevitably rotate faster.

The Kerr solution became the basis for revolutions first in fundamental physics in the 1960s, in astronomy in the 1970–80s, and in cosmology in the 1990s and beyond. The discoveries of gravitational waves from colliding black holes, first in 2015, and then from colliding neutron stars in 2017, mean that decades of further scientific revolutions are just beginning.


Transient Array Radio Telescope to be adopted by Square Kilometre Array

What started as an idea in 2014 by Dr Tim Molteno to develop the world’s smallest radio telescope in his Department of Physics laboratory at the University of Otago, is now being rolled out across eight partner nations of the Square Kilometre Array project in Southern Africa! The open-source, low-cost radio telescope called the ‘Transient Array Radio Telescope’ has been chosen by the South African Radio Astronomy Observatory as the ideal technology to build radio astronomy capacity on the continent.


History of the Master Equation

Crispin Gardiner

Honorary Professor, University of Otago

Master equations, both classical and quantum, have been in use since at least 1910 as the basis for the description of random events in physics, and my career in Quantum Optics since the 1970s has been built on the foundation of the master equation description of quantum optics.

But why is it called the master equation, and who is responsible for its development into one of the major tools in the physics of randomness?  And how far can we trust the master equation?

I will track back the origin of the idea, and its importance in physics to the very beginning, with some unexpected results. I will cover kinetic theory, quantum optics, and the mathematics of stochastic processes, both quantum and classical up to the end of the 20th century.  At the same time, I will give some particular attention to the conditions necessary for the validity of the Master Equation.

Wednesday 8 November, 3.00pm
Room 314, Science III Building



An introduction to the physics of magnetic confinement fusion

Dr Toby Adkins

Post Doctoral Fellow, University of Otago

The ultimate goal of the global fusion programme is to harness a self-sustained nuclear fusion reaction as a commercially viable source of clean energy. At the high pressures required for nuclear fusion, the fuel becomes a plasma – an electromagnetically interacting gas of charged electrons and ions – which is unable to be contained by normal materials. Magnetic-confinement fusion proposes to use large external electromagnetic coils to generate a series of nested magnetic field “surfaces” that wrap around the device and help confine the plasma. In this talk, I will introduce the general concepts underlying magnetic-confinement fusion and review some of the fundamental physics challenges it faces, including magnetohydrodynamical stability, Neoclassical transport, and microscale turbulence. Within the latter strand, I show that the scaling of the turbulent heat flux with parameters of the plasma equilibrium can be constrained by an underlying symmetry (scale invariance) of the governing equations, a prediction that is borne out by numerical simulations. Finally, I will discuss the outlook of the global nuclear fusion programme in an effort to convince you that fusion is much closer than “thirty vears away”. This talk is appropriate for anyone with a basic physics background.

Friday 13th October, 12.00pm,
Room 314, Science III Building



Introduction to Astronomy (ASTR101)

We’re excited to share that we’ve moved the long-running physics paper “Introduction to Astronomy” from summer school to semester 2 for 2024. The paper, now coded ASTR 101 Introduction to Astronomy, covers the history and cutting edge of astronomy and astrophysics, including ancient astronomy and indigenous knowledge, the birth and death of stars, planetary systems, galaxies and cosmology, and searches for extraterrestrial life.

The paper is designed to be accessible to anyone, including non-science majors, and involves almost no maths. We hope that this move into semester 2 will make it more accessible for interested students to learn about the wonders of the Universe!

Jono Squire, Craig Rodger


2023 Energy Education Trust Scholarships

May Robertson (BSc 3rd year)
Heloise Hildreth (BSc 3rd year)

Congratulations to the two Otago Energy students for their success in this year’s Energy Education Trust Undergraduate Scholarship round!

The EETNZ Scholarships are available to students in year three or four pursuing a full-time bachelor’s degree in science, economics or engineering and related fields but with an interest in energy as it relates to the specific needs of Aotearoa New Zealand. More information can be found at