Research

The research in the Optofluidics group focuses on two areas: Optical metasurfaces and Chromosome detection.
 
Template metasurface with 100 nm diameter meta-atoms
Optical metasurface: array of nano-scale meta-atoms with engineered optical properties

Optical Metasurfaces

Nano-photonics and metasurface flat optics are directly related to the fundamental understanding of optics, established by Isaac Newton in the late 17th century, that light is carrier of information - frequency dependent amplitude (color), phase, polarization - which is coded into the electromagnetic field of light when it interacts with materials. Modern nanofabrication technologies are used to create artificial, man-made materials with engineered optical properties – offering new avenues to code information into light, without being constrained by the electromagnetic response of natural materials and their chemical compounds. In particular: Optical metasurfaces are two-dimensional arrays of nanoscale elements, called meta-atoms. The meta-atoms act as individual nanoscale optical antennas, which - via their size and shape – at the nano-scale offer full control of light as it interacts with the metasurface – for example when light is transmitted through the surface. In contrast to conventional technology, optical metasurfaces can provide a required, change to the optical field – amplitude, phase, polarization – abruptly, as it propagates over distances on the scale of the wavelength of light – less than a micron. This is used to create ultra-thin, so-called metasurface flat optics, including meta-lenses. In flat optics meta-lenses, the size, shape and morphology of the meta-atoms are varied across the surface area to obtain the variation of phase change required for the desired optical function.

We laser print metasurface flat optics by laser post-writing on template optical metasurfaces. Our optical metasurfaces are based on the concepts of both localized surface plasmon resonances (LSPR) and high-index dielectrics compatible with technologies for high volume manufactured plastic products. The optical metasurfaces are formed by nanoimprinting a surface texture comprising nanoscale cylinders or holes. By subsequent deposition of a thin film of metal or high index dielectric, isolated nano-disks or -cylinders are formed with designed optical resonances. Laser post-writing can modify nano-disks and holes, and hence the optical resonances. Laser pulses induce transient local heat generation that leads to crystallization, melting, and reshaping of the initial nanostructures. This enables flexible definition and alignment of optical components on high volume manufactured plastic products. Our approach offers a printing speed of 1 ns per pixel (in raster scan), resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel.

In the European Pathfinder project ODYSSEY, we exploit our on-resonance laser printing technology, enabling mass-customization of ultra-thin – so-called flat-optics – with a wide application field, for on demand manufacture of prescription eyeglass lenses.
 

Optofluidic platform for chromosome analysis
Optofluidic platform for chromosome analysis
Working principle of optofluidic platform for chromosome analysis

Chromosome detection

Within the interdisciplinary synergy research project ChromoCapture we develop optofluidic technology capable of combined optical trapping and 3D imaging of metaphase chromosomes. The project is part of a collaboration with Prof. Ian Hickson and Prof. Eva Hoffmann at the Center for Chromosome Stability, Panum Institute, University of Copenhagen, and is funded under the NovoNordisk Foundation’s Interdisciplinary Synergy Programme.

We develop an automated multi-parameter analysis platform to investigate human chromosome abnormalities in real-time under an inverted microscope. The optofluidic platform combines three integrated sensing and actuation units (I) flow cytometry, (II) dual-beam optical tweezer, and (III) electrophoretic particle stretcher, combined with fluorescence imaging of the microscope.

The optofluidic platform comprises optical fibers aligned to a fused silica capillary microfluidic channel, assembled in a unit with external connections to microfluidic pump(s) and valves, fiber-coupled lasers and photodetectors and voltage source, and to be mounted on the microscope stage. The working principle is based on selective detection of the fluorescent light-emitting chromosomes with the flow cytometry unit before trapping at the optical tweezer region. An electric field is applied along the capillary channel for electrophoretic alignment and stretching of trapped chromosomes. Structural change of trapped and stretched chromosomes can be visualized by fluorescence microscopy.