Nanoscale displacement sensor

The ability to measure very precise alignments and displacements is a key requirement for many steps in semiconductor fabrication and manufacturing, for example, during lithography or wafer bonding. Using small nanoparticles, exhibiting a Huygens dipole coupled to crossed Photonic crystal waveguides we have now shown that light can be used to measure displacements of a few nm, beyond the accuracy of many current alignment systems.

Scanning electron microscope image of the displacement sensor. The insets show b the Photonic crystal waveguide, c the nanoparticle placed on the waveguide crossing and d the outcoupling interface used to redirect the light to a camera above the sensor. The figure is taken from the paper in Nature Communications.


Together with our colleagues from the Max Planck Institute for the Science of Light in Erlangen, we developed a three-way waveguides crossing with a nanoparticle on its centre. If there is a displacement between the centre of an optical beam and the nanoparticle, then the light will couple into the waveguides with a directionality which we can measure using the same objective used to excite the Huygens dipole. By measuring the different optical power output from each end of the waveguides we can work out the displacement between the nanoparticle and the axis of the incident beam.

The work has now been published in Nature Communications. Here is a link to the full article.

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Nanoantennas demonstrating weak superradiance

Dicke superradiance is a phenomenon where multiple closely spaced emitters can enter a collective excited state with a much shorter lifetime than the excited states of the individual emitters.

Together with collaborators at the Universities of Rochester, Ottawa, Toronto, British Columbia and the Technológico de Monterrey, we have now demonstrated that a similar phenomenon, termed weak superradiance exists for plasmonic nanoantennas. If N-antennas are contained within a circle with radius equal to the resonance wavelength of the antennas, then the extinction linewidth of the system is broadened by a factor N compared to the linewidth of the individual antennas.

As the antenna spacing is reduced the linewidth is broadened as more and more antennas are contained within a single wavelength radius.

This work is now published in the October edition of Physical Review A.

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Flexible epsilon-near-zero metamaterials highlighted by Nature Photonics

Our recent APL Photonics paper on flexible epsilon-near-zero metamaterials has been highlighted in the News & Views section of the July Issue of Nature Photonics. Congratulations to everyone involved.

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Flexible metasurface patches for mm-wave applications

In this work, we present a flexible metasurface that operates in the mm-wavelength region. A major problem in modern technology is that many systems, e.g. antennas, are designed for specific functionality. If new functionality is needed, then a new antenna needs to be made and installed, a wasteful and costly process.


Pictures of a) a conventional metasurface on silicon and b) our flexible metasurface.

But using metasurfaces we can create artificial materials with custom properties that could be used to add new functionality to existing systems or to improve upon existing technology, e.g. by correcting antenna aberrations. However, a key question is “How do we get our metasurface onto a pre-existing object?”

Together with the Synthetic Optics and mm-Wave groups here in St Andrews, we have demonstrated flexible metasurfaces for the mm-wave wavelength range. These metasurfaces can realize the broad functionality or conventional, rigid, metasurfaces, but are designed so that they can be used as patches on existing objects.

The work is published in Applied Physics Letters.

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Flexible epsilon-near-zero metamaterials

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.

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Vertical couplers for multi-layer photonic integrated circuits

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.


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Sebastian Schulz awarded best presentation price at BICOP 2018

Last week Sebastian Schulz attended the inaugeral IEEE British and Irish Conference on Optics and Photonics (BICOP) held at the Royal Society in London. He presented a poster on our work on overcoming the delay-bandwidth limit using nonreciprocity, as well as a talk on Nonlinear metasurfaces based on epsilon-bear-zero materials. For the latter presentation he won the best paper award.

A good ending to an exciting and productive year.

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Flat-band superprism in photonic crystals

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.

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Dr Schulz awarded a Royal Society Research Grant

Good news everyone: Dr Schulz has been awarded a Royal Society research grant for his proposal “Tuneable, dielectric metasurfaces on epsilon-near-zero films”. Stay tuned for progress updates. And if you are interested in learning more about our work on metasurfaces incorporating epsilon-near-zero materials, why not visit the description of our research activities, read some of our previous papers on this topic (M. Z. Alam et al. Nature Photon 2018, S. A. Schulz et al. PRA 2016) or visit our friends from the synthetic optics group and learn about their work on epsilon-near-zero materials.

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Student Physics Society interview of Dr Schulz

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.

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