Integrated holographic filters for flat passband optical multiplexers

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Integrated Optics

Background:

• Volume holographic filters are crucial for optical multiplexing.
• Existing grating-based devices often lack single-mode compatibility and exhibit high loss.
• Coarse wave-division multiplexing (CWDM) requires efficient and integrated filtering solutions.

Purpose of the Study:

• To demonstrate lithographically fabricated, slab-waveguide-based volume holographic filters.
• To achieve fully integrated, single-mode compatible, flat-topped, and low-loss filtering.
• To enable wide bandwidth multiplexing for applications like CWDM.

Main Methods:

• Fabrication of slab-waveguide-based volume holographic filters using lithography.
• Implementation of multi-path interference for filtering, mimicking thin-film filter operation.
• Utilizing flexible apodization via binary etch for steep passband falloff.
• Employing a tailored dual-core waveguide geometry for mode concentration.

Main Results:

• Demonstrated fabrication and testing of functional volume holographic filters.
• Achieved single-mode compatibility by avoiding angular dispersion.
• Obtained flat-topped passbands with low insertion loss and wide bandwidth.
• Successfully implemented steep passband falloff using binary etch apodization.

Conclusions:

• Lithographically rendered, slab-waveguide volume holographic filters are viable for integrated optical systems.
• These filters offer superior performance for CWDM and similar wide bandwidth multiplexing applications.
• The demonstrated technology provides a path towards highly integrated and efficient optical communication components.