Directional free-space coupling from photonic crystal waveguides.

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Planar photonic crystal (PC) waveguides offer unique light confinement properties.
• Efficiently coupling light between PC waveguides and free-space modes remains a challenge.
• Existing methods often require complex designs or fabrication processes.

Purpose of the Study:

• To present a general and efficient approach for mode coupling in PC waveguides.
• To enable selective coupling between specific PC waveguide modes and free-space modes.
• To demonstrate this approach using a W1 PC waveguide.

Main Methods:

• Introducing small, localized index perturbations to the PC waveguide.
• Designing these perturbations to selectively target and couple a specific transverse mode.
• Utilizing the "perturbative photonic crystal waveguide coupler" (PPCWC) concept.

Main Results:

• Achieved efficient interconversion between selectable propagating PC modes and free-space modes.
• Demonstrated coupling to an approximately Gaussian, slowly diverging free-space mode.
• The PPCWC approach requires minimal design perturbations to the original PC structure.

Conclusions:

• The PPCWC offers a versatile and efficient solution for PC to free-space mode coupling.
• This method allows for precise control over mode selection and light conversion.
• The technique has potential applications in integrated photonics and optical communication systems.