[Paper Review] Giant Enhancement of Third Harmonic Generation from Ge2Sb2Te5 based Fabry-Perot Cavity

Tun Cao, Kuan Liu+4 more|arXiv (Cornell University)|Jan 25, 2019

Photonic and Optical Devices42 references4 citations

TL;DR

This study demonstrates a 422-fold enhancement in third harmonic generation (THG) efficiency using a Fabry-Perot cavity incorporating an amorphous Ge2Sb2Te5 (GST225) film, leveraging resonant cavity engineering in the near-infrared regime. The enhancement vanishes upon crystallization of GST225, enabling switchable, ultra-compact nonlinear optical sources with high efficiency.

ABSTRACT

Third-order harmonic generation (THG) plays a vital role in microscopy, optical communications etc. Conventional methods of obtaining efficient THG in macroscopic crystal 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 provide compact photonic platforms, however selection of materials remains elusive. Herein, we experimentally demonstrate a giant enhancement of THG efficiency from an air/high index Ge2Sb2Te5 (GST225) /gold multi-layered Fabry-Perot cavity. At cavity resonant wavelength in near-infrared regime, the efficiency of THG from a 50 nm thick amorphous GST225 planar film is boosted by 422 times compared to that of nonresonant conditions. Interestingly, the THG efficiency has a dramatic decrease of three orders when the structural state of GST225 is transformed from amorphous to crystalline. Our findings have a potential for achieving ultra-compact nonlinear optical source with high efficiency and switchable functionality.

Motivation & Objective

• To overcome the miniaturization and integration limits of conventional macroscopic third harmonic generation (THG) materials.
• To explore alternative compact platforms for efficient THG beyond photonic crystals and metamaterials.
• To investigate the role of phase-change materials like Ge2Sb2Te5 in enhancing nonlinear optical responses.
• To demonstrate a switchable, high-efficiency on-chip THG source using structural phase transitions.

Proposed method

• Fabrication of an air/GST225/air multilayered Fabry-Perot cavity with a 50 nm amorphous GST225 film as the nonlinear medium.
• Utilization of cavity resonance in the near-infrared range to enhance the local electric field and thus boost third harmonic generation efficiency.
• Employment of a gold mirror to form a high-Q cavity structure, increasing photon confinement and nonlinear interaction.
• Measurement of THG efficiency under resonant and nonresonant conditions to quantify enhancement.
• Controlled phase transition from amorphous to crystalline GST225 to study its impact on THG performance.
• Use of a pump laser at 1550 nm to excite the cavity and detect the third harmonic at 516.7 nm.

Experimental results

Research questions

• RQ1 Can a Fabry-Perot cavity with amorphous Ge2Sb2Te5 significantly enhance third harmonic generation efficiency?
• RQ2 How does the phase state of GST225 (amorphous vs. crystalline) affect the THG efficiency in a resonant cavity?
• RQ3 What is the maximum achievable enhancement factor of THG in a compact, planar GST225-based cavity?
• RQ4 Can the THG response be electrically or thermally switched via phase transition in GST225?
• RQ5 Is the enhancement mechanism primarily due to field localization and cavity resonance or intrinsic material nonlinearity?

Key findings

• The THG efficiency of a 50 nm amorphous GST225 film is enhanced by 422 times at the cavity resonant wavelength compared to nonresonant conditions.
• The THG efficiency drops by three orders of magnitude when the GST225 film is transformed from amorphous to crystalline phase.
• The enhancement is attributed to resonant field confinement in the Fabry-Perot cavity, which amplifies the effective nonlinear interaction.
• The observed enhancement is highly sensitive to the structural phase of GST225, enabling active switching of the nonlinear response.
• The system demonstrates a compact, switchable, and highly efficient platform for on-chip third harmonic generation.