Epsilon-near-zero materials promise non-linear optical enhancement, light transport through arbitrary channels, wave-front shaping and control over optical emission. Typically implemented using either naturally occurring effects for example in conductive oxides or through multi-layer stacks all implementations are limited to flat-substrates that are compatible with clean room processing.
In our work published in APL Photonics, we have now demonstrated a flexible epsilon-near-zero metamaterial, consisting of a metal-polymer stack. Our material can be repeatably bent, without affecting the optical properties and can be placed on arbitrarily shaped substrates after fabrication.
This work was done together with the Synthetic Optics group and is the first paper of a very productive collaboration. Watch this space for more results from this collaboration, they will be coming soon.
Similar to microelectronic circuits, future photonic chips will include multiple layers of different materials to integrate functionality in a single circuit. One of the key challenges is to couple light between the different layers.
Together with the nanophotonics group at the Centre for Advanced Photonics and Process Analysis, we have now developed an efficient and compact coupler for vertically integrated system. We use a two-level tapered waveguide to efficiently couple light between a silicon and a silicon nitride layer.
One of the key tasks in integrated photonics is the separation or demultiplexing of multiple different wavelength channels that are transported through the same waveguide.
One way to separate different wavelength is to use refraction in a prism and the photonic crystal community has taken this further, developing superprism. A superprism is a prism, but with stronger refraction than possible from the normal refractive index difference and so it can get a better wavelength separation in a smaller footprint.
In our work, we have now demonstrated a flat-band superprism that has a particularly constant refraction. So different wavelength channels, with a fixed wavelength spacing, will exit our superprism with almost identical spacing, making subsequent collection and processing easier.
Before the beginning of the summer, the student Physics society interviewed Dr Schulz for their Insight podcast series.
The full interview is now online. Listen to it if you want to know more about Dr Schulz, living in Canada and returning to St Andrews as a Lecturer.
One problem in silicon photonics is that current integrated light sources are very sensitive to variations in the operating temperature.
Together with the Centre for Advanced Photonics & Process Analysis we have developed a hybrid laser with an external reflector based on silicon nitride gratings. The silicon nitride grating has a low thermo-optic coefficient and so our laser can operate unaffected over a large temperature range.
Our laser has a low threshold power, provides mW level output power and shows stable operation over a wide temperature range.
The full article is published in Applied Optics.
In collaboration with the Centre for Advanced Photonics and Process Analysis at the Cork Institute of Technology, we have demonstrated a low loss optical buffer based on photonic crystal cavities, demonstrating a record low loss per storage time. The delay can be tuned dynamically over a range of more than 150ps.
Scanning electron microscope image of the coupled photonic crystal cavities.
This work was published in the March 2018 edition of ACS Photonics.