Wide-angle beam refocusing using negative refraction in non-uniform photonic crystal waveguides

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Graded 2D photonic crystals offer unique light manipulation properties.
• Efficiently refocusing highly divergent beams is crucial for optical systems.
• Interface design between photonic crystals and waveguides impacts beam propagation.

Purpose of the Study:

• To investigate the use of a graded 2D photonic crystal interface for refocusing divergent Gaussian beams.
• To demonstrate efficient far-field refocusing using beam-steering and negative ray refraction.
• To determine the optimal length of the photonic crystal structure for high-efficiency refocusing.

Main Methods:

• Numerical simulations were employed to model the optical phenomena.
• The study focused on a graded 2D photonic crystal structure with plane tapered transitions.
• Gaussian beams with small spot sizes were used as input.

Main Results:

• A 14-micrometer long photonic crystal structure demonstrated efficient refocusing capabilities.
• The structure exhibited beam-steering and negative ray refraction.
• An efficiency of approximately 90% was achieved for refocusing the Gaussian beam.

Conclusions:

• Graded 2D photonic crystals can effectively refocus highly divergent Gaussian beams.
• The demonstrated photonic crystal structure provides a pathway for compact and efficient optical focusing elements.
• Beam-steering and negative ray refraction are key phenomena enabling this refocusing capability.