A High‐Index Ge₂Sb₂Te₅‐Based Fabry–Perot Cavity and Its Application for Third‐Harmonic Generation

Abstract

Third-order harmonic generation (THG) plays a vital role in microscopy, optical communications, etc. Conventional methods of obtaining efficient THG in macroscopic crystals is already mature; however, they will finally limit the miniaturization and integration of on-chip laser sources. To date, THG from either photonic crystals or metamaterials provides compact photonic platforms; however, selection of materials remains elusive. Herein, a giant enhancement of THG efficiency from an air/high index Ge 2 Sb 2 Te 5 (GST)/gold multi-layered Fabry-Perot cavity is experimentally demonstrated. At cavity resonant wavelength in near-infrared regime, the efficiency of THG from a 50-nm thick amorphous GST planar film is boosted 422 times compared to that of nonresonant conditions. Interestingly, the THG efficiency has a dramatic decrease of three orders when the structural state of GST is transformed from amorphous to crystalline. These findings have a potential for achieving an ultracompact nonlinear optical source with high efficiency and switchable functionality.

Strongly Coupled Systems for Nonlinear Optics

“…For the sake of uncomplicated artificial framework and optimized performance in THG, Cao et al put forward to a simple FP cavity composed of chalcogenide alloy (GST) dielectric nanofilms, gold mirrors, and air, boosting the THG response dramatically (Figure 7C). [221] The THG efficiency of amorphous GST planar film increased by 422 times at cavity resonant wavelengths in the NIR regime compared to the non-resonant environment. Interestingly, when the structural state of GST changed from amorphous to crystalline, THG efficiency dropped sharply by three orders of magnitude, which also supply a new tactic to manipulate the efficiency of THG via switching the phase of Ge 2 Sb 2 Te 5 alloys.…”

Nonlinear Mid‐Infrared Metasurface based on a Phase‐Change Material

“…[ 14 ] Metasurfaces also provide a powerful means to engineer the nonlinear response of materials, as has been largely shown thus far at shorter wavelengths. [ 15–28 ] Indeed, the effective nonlinear polarization of metasurfaces can be tailored and boosted by resonance‐induced electromagnetic field enhancement. [ 15–19 ] Plasmonic metasurfaces made of noble metals such as gold and silver have been initially employed to enhance nonlinear processes like second‐harmonic generation, [ 20 ] third‐harmonic generation (THG), [ 21 ] and four‐wave mixing.…”

“…[ 24 ] In addition, semiconductor metasurfaces featuring second‐order nonlinearity have also been investigated for second‐harmonic generation. [ 25,26 ] A significant variety of resonance‐based approaches [ 17,23,27,28 ] have been extensively exploited to enhance nonlinear wave mixing processes in such systems.…”

Multistate Tuning of Third Harmonic Generation in Fano‐Resonant Hybrid Dielectric Metasurfaces

“…[35][36][37] A Fabry-Pèrot cavity in reflection mode based on high refractive index Ge 2 Sb 2 Te 2 (GST) has been demonstrated to achieve two-state switching (ON/OFF) of THG. [38] However, its THG conversion efficiency is only about 5.46 × 10 −9 %, which is largely attributed to the low Q-factor of the device and inherent high optical losses in the thick GST film.…”