Ge₂ Sb₂ Te₅ -Based Tunable Perfect Absorber Cavity with Phase Singularity at Visible Frequencies

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Asymmetric Fabry-Perot (F-P) cavities with metal-dielectric stacks offer lithography-free, cost-effective perfect absorption from visible to infrared.
• Tunable absorption and phase singularity are key for advanced photonic devices.

Purpose of the Study:

• To experimentally demonstrate an asymmetric F-P cavity system for tunable wide-angle perfect absorption and phase singularity.
• To investigate the effect of a phase-change material (Ge2Sb2Te5 - GST) on absorption properties.

Main Methods:

• Fabrication of an asymmetric F-P cavity system incorporating an ultrathin layer of Ge2Sb2Te5 (GST).
• Experimental characterization of absorption spectra under varying incident angles and polarization states.
• Validation of experimental results using a transfer matrix method simulation.

Main Results:

• Achieved tunable multiband perfect absorption (up to 99.8%) in the visible spectrum.
• Observed blueshift and broadening of absorption bands upon switching GST from amorphous to crystalline phase.
• Demonstrated tunable phase singularity at the reflection-less point.

Conclusions:

• The proposed asymmetric F-P cavity with GST enables tunable perfect absorption and phase singularity.
• The phase-change properties of GST are critical for achieving tunable optical responses.
• Potential applications include phase-sensitive biosensors and absorption filters.