Inverse photonic design of functional elements that focus Bloch surface waves

Area of Science:

• Photonics
• Materials Science
• Nanotechnology

Background:

• Bloch surface waves (BSWs) propagate at the interface of dielectric photonic crystals and ambient materials.
• BSW propagation is controlled by spatially structured device layers that alter the effective refractive index.
• Existing focusing elements are limited by low index contrast (Δn≈0.1), hindering efficient sub-wavelength focusing.

Purpose of the Study:

• To develop novel functional elements for efficient Bloch surface wave focusing.
• To overcome the limitations of low index contrast in conventional BSW focusing devices.
• To enable sub-wavelength focusing of BSWs for advanced photonic applications.

Main Methods:

• Utilized an inverse photonic design strategy to create functional focusing elements.
• Fabricated selected inverse design elements.
• Experimentally verified focusing capabilities using scanning near-field optical microscopy to measure field distributions.

Main Results:

• Achieved efficient focusing of Bloch surface waves into spatial domains smaller than half the wavelength.
• Demonstrated the effectiveness of inverse design elements in overcoming low index contrast limitations.
• Experimental verification confirmed the predicted focusing performance of the fabricated elements.

Conclusions:

• Inverse photonic design provides a powerful strategy for creating efficient BSW focusing elements.
• The developed focusing elements are suitable for integrated photonic devices and lab-on-chip sensing applications.
• This work advances the development of next-generation photonic devices leveraging Bloch surface waves.