Octave-spanning coherent perfect absorption in a thin silicon film

Area of Science:

• Photonics
• Materials Science
• Optics

Background:

• Optical absorption is a fundamental material property.
• Coherent perfect absorption (CPA) achieves 100% light absorption but is typically limited to narrow bandwidths and requires multiple coherent light sources.
• Existing CPA methods often rely on specific phase relationships between laser beams.

Purpose of the Study:

• To demonstrate CPA in a thin film using a single, incoherent light beam.
• To eliminate bandwidth restrictions associated with traditional CPA.
• To engineer a material's photonic environment to decouple effective absorption from intrinsic absorption.

Main Methods:

• Fabrication of thin aperiodic dielectric mirrors.
• Utilizing a 2 μm thick film of polycrystalline silicon.
• Demonstrating CPA across a spectrally flat, octave-spanning near-infrared spectrum (≈800-1600 nm).
• Designing mirrors with wavelength-dependent reflectivity.

Main Results:

• Achieved coherent perfect absorption in a polycrystalline silicon thin film.
• Demonstrated CPA using a single, incoherent light beam.
• Overcame narrow bandwidth limitations, achieving absorption across a broad spectrum.
• Showcased the decoupling of effective absorption from intrinsic material absorption through photonic environment engineering.

Conclusions:

• Engineering the photonic environment of a thin film can enable broadband coherent perfect absorption.
• Aperiodic dielectric mirrors with tailored reflectivity are key to overcoming intrinsic material absorption limitations.
• This approach offers a pathway to highly efficient light absorption devices across wide spectral ranges.