Flat nonlinear optics with intersubband polaritonic metasurfaces

Area of Science:

• Optics and Photonics
• Condensed Matter Physics
• Materials Science

Background:

• Nonlinear optical responses are crucial for optical signal processing and frequency conversion.
• Existing nonlinear optical materials often require thick films and high intensities.
• Metasurfaces offer a platform for novel optical functionalities due to engineered nanostructures.

Purpose of the Study:

• To review the state-of-the-art in nonlinear intersubband polaritonic metasurfaces.
• To highlight their strong nonlinear optical responses at infrared frequencies.
• To discuss applications in second-harmonic generation, saturable absorption, and optical power limiting.

Main Methods:

• Fabrication of metasurfaces as 2D arrays of nanoresonators from multi-quantum-well semiconductor heterostructures.
• Optimizing coupling between optical modes and intersubband transitions.
• Co-optimization of quantum engineering of electron states and photonic engineering of nanoresonators.

Main Results:

• Achieved record second- and third-order nonlinear optical responses in condensed matter.
• Demonstrated significant nonlinear conversion efficiencies (>0.1%) in subwavelength films with modest pumping intensities (10-100 kW/cm²).
• Showcased tunable nonlinear response amplitude and phase via quantum/photonic engineering and applied voltage.

Conclusions:

• Nonlinear intersubband polaritonic metasurfaces are promising for efficient, compact nonlinear optical devices.
• Subwavelength design overcomes phase-matching limitations of bulk crystals.
• Voltage-tunability offers dynamic control over nonlinear optical properties.