Direct light-coupling to thin-film waveguides using a grating-structured GRIN lens.

Area of Science:

• Optoelectronics
• Nanophotonics
• Biomedical Engineering

Background:

• Efficient light coupling is crucial for integrated photonic devices, particularly in biosensing.
• Conventional methods often employ internal grating couplers, which can be difficult to fabricate and integrate.
• There is a need for external, reusable, and efficient coupling solutions for planar waveguides.

Purpose of the Study:

• To introduce and validate a novel external optical coupling scheme.
• To demonstrate the use of a gradient-index (GRIN) lens with a high-frequency grating for light coupling.
• To compare the performance of this new external coupler with existing internal grating couplers.

Main Methods:

• Finite Element Method (FEM) simulations were performed to model the optical coupling.
• Experimental characterization of the novel coupling scheme was conducted.
• Coupling efficiency was measured and compared between the external coupler and conventional internal gratings.

Main Results:

• The novel external coupler achieved comparable coupling efficiencies to standard internal grating couplers.
• The proposed method enables direct light coupling from single-mode optical fibers to thin-film waveguides.
• The external coupler demonstrated reusability, offering a practical advantage over integrated solutions.

Conclusions:

• The developed GRIN lens-based external coupler provides an efficient and reusable alternative for light coupling into planar waveguides.
• This technique is suitable for applications requiring efficient fluorescence excitation, such as in biosensor platforms.
• The findings suggest a potential shift towards external coupling solutions in integrated photonics.