Y. Zhu, J. Wang, W. Xie, B. Tian, Y. Li, E. Brainis, Y. Jiao, D. van Thourhout
Optics Express, vol. 25, no. 26, pp. 33297-33304, 2017.
Publication year: 2017


Grating couplers have been widely used for coupling light between photonic chips and optical fibers. For various quantum-optics and bio-optics experiments, on the other hand, there is a need to achieve good light coupling between photonic chips and microscopy systems. Here, we propose an ultra-compact silicon nitride (SiN) grating coupler optimized for coupling light from a waveguide to a microscopy system. The grating coupler is about 4 by 2 μm2 in size and a 116 nm 1 dB bandwidth can be achieved theoretically. An optimized fabrication process was developed to realize suspended SiN waveguides integrated with these couplers on top of a highly reflective bottom mirror. Experimental results show that up to 53% (2.76 dB loss) of the power of the TE mode can be coupled from a suspended SiN waveguide to a microscopy system with a numerical aperture (NA) = 0.65. Simulations show this efficiency can increase up to 75% (1.25 dB loss) for NA = 0.95.

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