Integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy: design, fabrication and performance demonstration

Gyllion B Loozen; Arnica Karuna; Mohammad M R Fanood; Erik Schreuder; Jacob Caro

doi:10.3762/bjnano.11.68

Integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy: design, fabrication and performance demonstration

Beilstein J Nanotechnol. 2020 May 27:11:829-842. doi: 10.3762/bjnano.11.68. eCollection 2020.

Authors

Gyllion B Loozen¹, Arnica Karuna^{1

2}, Mohammad M R Fanood¹, Erik Schreuder³, Jacob Caro¹

Affiliations

¹ Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
² present address: Institute of Physical Chemistry, Friedrich Schiller University Jena, 07737 Jena, Germany.
³ LioniX International B.V., P.O. Box 456, 7500 AL, Enschede, Netherlands.

Abstract

We realized integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy of particles in a fluid. In these devices, multiple beams directed towards the device center lead to a local field enhancement around this center and thus counteract the effect of light concentration near the facets, which is a disadvantage of dual-waveguide traps. Thus, a trapping region is created around the center, where a single particle of a size in a wide range can be trapped and studied spectroscopically, free from the influence of surfaces. We report the design (including simulations), fabrication and performance demonstration for multi-waveguide devices, using our Si₃N₄ waveguiding platform as the basis. The designed ridge waveguides, optimized for trapping and Raman spectroscopy, emit narrow beams. Multiple waveguides arranged around the central microbath result from fanning out of a single input waveguide using Y-splitters. A second waveguiding layer is implemented for detection of light scattered by the trapped particle. For reliable filling of the device with sample fluid, microfluidic considerations lead to side channels of the microbath, to exploit capillary forces. The interference of the multiple beams produces an array of hot spots around the bath center, each forming a local trap. This property is clearly confirmed in the experiments and is registered in videos. We demonstrate the performance of a 2-waveguide and a 16-waveguide device, using 1 and 3 μm polystyrene beads. Study of the confined Brownian motion of the trapped beads yields experimental values of the normalized trap stiffness for the in-plane directions. The stiffness values for the 16-waveguide device are comparable to those of tightly focused Gaussian beam traps and are confirmed by our own simulations. The Raman spectra of the beads (in this work measured via an objective) show clear peaks that are characteristic of polystyrene. In the low-wavenumber range, the spectra have a background that most likely originates from the Si₃N₄ waveguides.

Keywords: Brownian motion; Raman spectroscopy; integrated optics devices; lab-on-a-chip; nanofabrication; optical trapping; ridge waveguides.

Grants and funding

The authors acknowledge the Dutch Organization for Scientific Research (NWO) (14197) for funding and NWO Physical Sciences (15316) for making available Supercomputer Cartesius for simulations.