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.
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.