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Optofluidics

An overview of the group's research into optofluidics with hollow-core photonic crystal fibres.

Optofluidic hollow-core photonic crystal fibre (HC-PCF) allows light to be guided at the centre of a microfluidic channel, maximizing its interaction with liquids and particles. This system offers unique opportunities to study photochemical reactions and in advanced optical trapping experiments.

optofluidic microreactors
The maximized overlap between light and sub-µL samples enables highly-efficient photochemistry at optical powers a million times less than in conventional systems [1]. The system also allows sensitive in-situ reaction monitoring, which is also of great importance in catalytically active fibre [2]. In a continuous flow arrangement, photoproducts can be analysed in parallel by mass-spectrometry, which is particularly important in the development of novel light-activatable anticancer drugs.

optothermal trapping in air-filled HC-PCF
Radiation pressure resulting from the fundamental mode of a HC-PCF can keep a microparticle trapped at the centre of the core, while propelling it along the fibre. Our experiments in which light scattered by the particle creates a temperature gradient along the fibre, have led to the discovery of an opto-thermal trapping mechanism that is the result of a competition between optical forces and viscous drag caused by a thermally-driven air flow [3]. 

optical conveyor belt
Wavefront shaping techniques make it possible to selectively excite higher-order spatial modes of a HC-PCF [4]. We recently showed that microparticles can be moved over long distances and precisely positioned in a low-loss air-filled hollow-core photonic crystal fibre by exciting coherent superpositions of spatial modes. The beat pattern allows trapped microparticles to be moved and exquisitely positioned along the fibre by tuning the relative phase between the modes [5].

flying particle sensor
We recently introduced a new kind of fibre optic sensor, based on a 'flying-particle' optically trapped and moved to and fro inside a HC-PCF. The transverse displacement of a charged microparticle can be detected by changes in the transmitted light signal, and is used to map electric field patterns near the surface of a multi-element electrode with high spatial resolution. We believe such flying-particle sensors open up a plethora of new opportunities, potentially allowing multiple physical quantities to be mapped with very high positional accuracy over km distances [6].

collaborations

This research was initiated in the group of Philip Russell at the Max Planck institute for the Science of Light in Erlangen, Germany. Our work over the past years builds on several successful collaborations including:  

- Peter Sadler, University of Warwick (photomedicine)
- Anita Jones, University of Edinburgh (photoswitching, fluorescence)
- Bastian Etzold, Peter Wasserscheid, University of Erlangen-Nuremberg (catalysis)
- Graeme Whyte, Heriot Watt University (wavefront shaping)

With state-of-the-art labs in the new Maxwell Centre for the Physical Sciences, the Optofluidics group in NanoPhotonics establishes strong links with expertise in catalytic chemistry, microfluidics, particle technology, and spectroscopy, both within NanoPhotonics and across the School of Physical Sciences.

References

[1] "Photonic crystal fibres for chemical sensing and photochemistry", A. M. Cubillas, S. Unterkofler, T. G. Euser, B. J. M. Etzold, A. C. Jones, P. J. Sadler, P. Wasserscheid, and P. St.J. Russell. Chem. Soc. Rev. 42, 8629 (2013). Highlighted on front cover.

[2] "Chemical and (Photo)-Catalytical Transformations in Photonic Crystal Fibers", M. Schmidt, A. M. Cubillas, N. Taccardi, T. G. Euser, T. Cremer, F. Maier, H. P. Steinrueck, P. St.J. Russell, P. Wasserscheid, and B. J. M. Etzold. Chem. Cat. Chem. 5, 641 (2013).  Highlighted on front cover.

[3] "Reconfigurable optothermal microparticle trap in air-filled hollow-core photonic crystal fiber", O. A. Schmidt, M. K. Garbos, T. G. Euser, and P. St. J. Russell, Phys. Rev. Lett. 109, 024502 (2012).

[4] T. G. Euser, G. Whyte, M. Scharrer, J. S. Y. Chen, A. Abdolvand, J. Nold, C. F. Kaminski, and P. St.J. Russell, Dynamic control of higher-order modes in hollow-core photonic crystal fibers, Opt. Express 16, pp. 17972-17981 (2008).

[5] O. A. Schmidt, T. G. Euser, and P. St.J. Russell, Mode-based microparticle conveyor belt in air-filled hollow-core photonic crystal fiber, Opt. Express 21, pp. 29383-29391 (2013).

[6] "Flying particle sensors in hollow-core photonic crystal fibre", D. Bykov. O. A. Schmidt, Tijmen G. Euser, and Philip St.J. Russell. Nature Photonics 9, 461 (2015).

Further references can be found on:
http://www.researcherid.com/rid/A-2876-2014

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