[Paper Review] An optical metamixer

Sheng Liu, Polina P. Vabishchevich+6 more|arXiv (Cornell University)|Oct 31, 2017

Advanced Fiber Laser Technologies40 references91 citations

TL;DR

This paper demonstrates an optical frequency mixer using a GaAs-based dielectric metasurface that concurrently generates eleven new frequencies from two femtosecond NIR pulses by leveraging multiple nonlinear processes.

ABSTRACT

A frequency mixer is a nonlinear device that combines electromagnetic waves to create waves at new frequencies. Mixers are ubiquitous components in modern radio-frequency technology and are widely used in microwave signal processing. The development of versatile frequency mixers for optical frequencies remains challenging: such devices generally rely on weak nonlinear optical processes and, thus, must satisfy phase matching conditions. In this work, we utilize a GaAs-based dielectric metasurface to demonstrate an optical frequency mixer that concurrently generates eleven new frequencies spanning the ultraviolet to near-infrared (NIR) spectral range. Our approach combines strong intrinsic material nonlinearities, enhanced electromagnetic fields, and relaxed phase-matching requirements, to allow seven different nonlinear optical processes to occur simultaneously. Specifically, when pumped by two femtosecond NIR pulses, we observe second-, third- and fourth-harmonic generation, sum-frequency generation, two-photon absorption induced photoluminescence, four-wave mixing, and six-wave mixing. Such ultracompact optical mixers may enable a plethora of applications in biology, chemistry, sensing, communications and quantum optics.

Motivation & Objective

• Demonstrate a compact optical frequency mixer at optical frequencies using a metasurface.
• Leverage strong nonlinearities and field enhancement to relax phase-matching constraints.
• Enable simultaneous occurrence of multiple nonlinear optical processes in a single device.

Proposed method

• Use a GaAs-based dielectric metasurface as the nonlinear optical medium.
• Pump the metasurface with two femtosecond near-infrared pulses to drive nonlinear processes.
• Observe and identify multiple nonlinear effects including second-, third-, and fourth-harmonic generation, sum-frequency generation, two-photon absorption induced photoluminescence, four-wave mixing, and six-wave mixing.

Experimental results

Research questions

• RQ1 Can a single GaAs metasurface-based device generate multiple new frequencies via various nonlinear processes when pumped by two femtosecond NIR pulses?
• RQ2 What nonlinear processes can be induced concurrently in an optical metamixer and how many distinct new frequencies can be produced?
• RQ3 How do the intrinsic nonlinearities, field enhancements, and relaxed phase-matching requirements contribute to multi-process frequency generation in a compact structure?

Key findings

• The metasurface concurrently supports seven different nonlinear optical processes.
• Eleven new frequencies spanning ultraviolet to near-infrared are generated.
• The setup uses strong intrinsic material nonlinearities and enhanced fields to relax phase matching, enabling ultracompact optical mixing.