Efficient Thermo-Optic Switching and Modulating in Nonlocal Metasurfaces.

Area of Science:

• Photonics
• Metasurfaces
• Nanophotonics

Background:

• High-Q optical resonances in nonlocal metasurfaces enable strong light-matter interactions.
• Quasi-guided modes (QGMs) offer potential for efficient optical modulation.
• Photonic crystal slabs (PCS) are versatile platforms for optical phenomena.

Purpose of the Study:

• To achieve efficient optical switching and modulation using QGMs in a PCS nonlocal metasurface.
• To investigate the thermo-optic response of the metasurface under weak optical pumping.

Main Methods:

• Fabrication of a silicon PCS with shifted air holes to support QGMs.
• Experimental measurement of Q-factor for the realized QGMs (∼2200).
• Application of a 532 nm continuous-wave pump laser to induce photothermal heating and observe spectral shifts.

Main Results:

• Achieved QGMs with a Q-factor of approximately 2200.
• Observed a pronounced spectral shift of the QGM resonance around 1550 nm.
• Demonstrated a modulation depth exceeding 55% at low illumination intensity (< 4.0 W/cm²).
• Attributed the effect to the thermo-optic response caused by photothermal heating.

Conclusions:

• The study successfully demonstrates efficient optical switching/modulation in nonlocal metasurfaces.
• Leveraging high-Q QGMs in PCS structures provides a simple and effective method for light control.
• The thermo-optic effect triggered by weak optical pumping is a viable mechanism for optical modulation.