Grating couplers fabricated by e-beam lithography for long-range surface plasmon waveguides embedded in a...

Area of Science:

• Photonics and Nanophotonics
• Optoelectronics
• Plasmonics

Background:

• Surface plasmon polariton (SPP) waveguides are crucial for miniaturized optical devices.
• Efficiently coupling light into SPP modes without high-quality facets is a significant challenge.
• Existing coupling methods often involve complex alignments and can suffer from high background light.

Purpose of the Study:

• To propose and experimentally demonstrate long-range surface plasmon polariton waveguides with integrated grating couplers.
• To investigate the efficiency and characteristics of broadside coupling using grating couplers.
• To evaluate the potential of this coupling scheme for biosensing applications.

Main Methods:

• Fabrication of gold (Au) stripe waveguides embedded in Cytop claddings with integrated grating couplers.
• Experimental demonstration of light coupling using cleaved bow-tie and lensed fibers.
• Measurement of grating coupling efficiencies across a broad wavelength range.
• Comparison of experimental results with theoretical models accounting for fabrication imperfections.

Main Results:

• Grating couplers enable efficient broadside coupling with low background light.
• The proposed scheme eliminates the need for high-quality edge facets, simplifying optical alignment.
• Lensed fiber coupling shows superior performance with better mode overlap and minimal background light.
• Experimental measurements align well with theoretical predictions, considering fabrication-induced curvature.

Conclusions:

• The demonstrated grating coupler scheme provides an efficient and simplified method for exciting long-range SPP modes.
• The lensed fiber approach offers optimal coupling efficiency and low background noise.
• This integrated waveguide and coupling design holds significant potential for developing advanced biosensors.