A metasurface-based diamond frequency converter using plasmonic nanogap resonators

At a Glance

Metadata	Details
Publication Date	2020-09-28
Journal	Nanophotonics
Authors	Qixin Shen, Amirhassan Shams‐Ansari, Andrew M. Boyce, Nathaniel C. Wilson, Tao Cai
Institutions	Harvard University, Duke University
Citations	15
Analysis	Full AI Review Included

Metasurface-Based Diamond Frequency Conversion: Technical Analysis and 6CCVD Solutions

Executive Summary

This research demonstrates a highly efficient, metasurface-based frequency converter utilizing the unique nonlinear optical properties of diamond. The key findings and methods are summarized below:

Record Enhancement: Achieved a dramatic 1.6 x 10⁷-fold enhancement for both Third-Harmonic Generation (THG) and Second-Harmonic Generation (SHG) compared to bare diamond.
Ultra-Thin Material: The enhancement was realized using deeply subwavelength diamond films, with thicknesses down to 12 nm, integrated into plasmonic nanogap cavities.
High Efficiency: Maximum THG and SHG conversion efficiencies were estimated at 2.33 x 10^-5% and 7.59 x 10^-6%, respectively, comparable to other leading plasmonic systems.
Multifunctional Conversion: The platform simultaneously enhanced multiple nonlinear processes: THG, SHG, Sum Frequency Generation (SFG), and Four-Wave Mixing (FWM).
Methodology: Plasmonic nanogap cavities were formed by sandwiching the diamond slab between a gold substrate and EBL-fabricated gold nanoparticles transferred via a PDMS stamp.
Application Potential: This work suggests a promising approach for on-chip nonlinear devices, particularly for converting diamond color center emission (visible) to telecom wavelengths for quantum communication.

Technical Specifications

The following hard data points were extracted from the experimental results regarding the diamond material and device performance:

Parameter	Value	Unit	Context
Diamond Slab Thickness (Minimum)	12	nm	Thinnest section of the wedge-shaped film
THG/SHG Enhancement Factor	1.6 x 10⁷	fold	Compared to bare diamond on PDMS (1455 nm excitation)
FWM Enhancement Factor	3.0 x 10⁵	fold	Compared to bare diamond on PDMS
Maximum THG Conversion Efficiency	2.33 x 10^-5	%	Estimated at 5 mW excitation power
Maximum SHG Conversion Efficiency	7.59 x 10^-6	%	Estimated at 5 mW excitation power
Fundamental Cavity Resonance	1455	nm	Nanogap mode
Second-Order Cavity Resonance	840	nm	Nanogap mode
Excitation Wavelengths Used	1455, 840, 1130	nm	Matching cavity modes for simultaneous enhancement
Simulated Electric Field Enhancement	Up to 40	fold	Confined within the 12 nm diamond gap
Gold Film Thickness (Substrate)	75	nm	Evaporated gold ground plane
Nanoparticle Height	30	nm	EBL-fabricated gold nanoparticles

Key Methodologies

The experimental success relies on precise material integration and leveraging plasmonic resonance. The key steps involved in device fabrication and testing are:

Diamond Film Preparation: A wedge-shaped diamond slab was prepared, with the thinnest section reaching 12 nm, suitable for integration into the nanogap cavity.
Nanoparticle Fabrication: Gold nanoparticles (30 nm height, 220 nm side length, 440 nm pitch) were fabricated on a silicon substrate using Electron Beam Lithography (EBL).
Substrate Preparation: A 75 nm gold film was evaporated onto a separate substrate to serve as the ground plane for the nanogap cavities.
Nondisruptive Transfer: The EBL-fabricated gold nanoparticles were transferred onto the diamond slab using a Polydimethylsiloxane (PDMS) stamp.
Cavity Assembly: The diamond slab was sandwiched between the gold ground plane and the transferred nanoparticles, creating film-coupled, plasmonic nanogap cavities.
Resonance Matching: Excitation wavelengths (1455 nm and 840 nm) were selected to overlap precisely with the fundamental and second-order cavity resonance modes, maximizing electric field confinement (up to 40-fold).
Nonlinear Characterization: Power dependence measurements confirmed the cubic (THG) and quadratic (SHG) nature of the enhanced nonlinear processes.

6CCVD Solutions & Capabilities

6CCVD provides the high-purity, precision-engineered MPCVD diamond materials and customization services necessary to replicate, scale, and advance this frequency conversion research.

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Rationale and Advantage
High-Purity Diamond Film	Optical Grade Single Crystal Diamond (SCD)	SCD offers the lowest birefringence, highest thermal conductivity, and superior intrinsic third-order nonlinear susceptibility ($\chi^{ (3) }$) required for efficient frequency conversion.
Ultra-Thin Film Precursor	SCD Wafers (0.1 µm - 500 µm)	We supply high-quality SCD films suitable for subsequent thinning processes (e.g., lift-off or etching) necessary to achieve the 12 nm thickness used in the nanogap.
Quantum Integration	SCD with Controlled Nitrogen/Silicon Doping	Ideal for hosting color centers (e.g., NV, SiV) required for the proposed application of converting visible color center emission to telecom wavelengths.

Customization Potential

The complexity of integrating plasmonic structures requires highly customized material preparation. 6CCVD offers the following services to streamline device fabrication:

Precision Polishing: The paper relies on optimal coupling, which demands ultra-low surface roughness. 6CCVD guarantees Ra < 1 nm for Single Crystal Diamond (SCD) wafers, minimizing scattering losses and ensuring high-fidelity metasurface integration.
Custom Metalization: The experiment utilized a 75 nm gold film. 6CCVD offers in-house deposition of standard and custom metal stacks, including Au, Ti, Pt, Pd, W, and Cu, directly onto the diamond substrate, eliminating a fabrication step for the researcher.
Large-Scale Substrates: While the experiment used small samples, 6CCVD can provide SCD plates up to 125 mm (PCD) and substrates up to 10 mm thick, supporting the transition from proof-of-concept to scalable integrated photonics platforms.

Engineering Support

The successful demonstration of simultaneous, enhanced nonlinear processes in diamond opens new avenues for integrated quantum and classical photonics. 6CCVD’s in-house team of PhD material scientists and engineers specializes in optimizing MPCVD growth parameters to meet specific optical and structural requirements.

We offer consultation on:

Material Selection: Choosing the optimal SCD grade and orientation for maximizing nonlinear susceptibility and minimizing loss.
Thin Film Processing: Advising on suitable starting thicknesses and surface preparation for subsequent nanoscale thinning and transfer methods (like the PDMS stamp technique used here).
Integrated Quantum Projects: Assisting with material specifications for similar frequency conversion and quantum communication projects leveraging diamond color centers.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract Diamond has attracted great interest as an appealing material for various applications ranging from classical to quantum optics. To date, Raman lasers, single photon sources, quantum sensing and quantum communication have been demonstrated with integrated diamond devices. However, studies of the nonlinear optical properties of diamond have been limited, especially at the nanoscale. Here, a metasurface consisting of plasmonic nanogap cavities is used to enhance both χ (2) and χ (3) nonlinear optical processes in a wedge-shaped diamond slab with a thickness down to 12 nm. Multiple nonlinear processes were enhanced simultaneously due to the relaxation of phase-matching conditions in subwavelength plasmonic structures by matching two excitation wavelengths with the fundamental and second-order modes of the nanogap cavities. Specifically, third-harmonic generation (THG) and second-harmonic generation (SHG) are both enhanced 1.6 × 10 7 -fold, while four-wave mixing is enhanced 3.0 × 10 5 -fold compared to diamond without the metasurface. Even though diamond lacks a bulk χ (2) due to centrosymmetry, the observed SHG arises from the surface χ (2) of the diamond slab and is enhanced by the metasurface elements. The efficient, deeply subwavelength diamond frequency converter demonstrated in this work suggests an approach for conversion of color center emission to telecom wavelengths directly in diamond.

Tech Support

Original Source

DOI: https://doi.org/10.1515/nanoph-2020-0392

References

2017 - Refractory plasmonics without refractory materials [Crossref]
2017 - An integrated diamond Raman laser pumped in the near-visible
2014 - Diamond nonlinear photonics [Crossref]
2014 - Control of radiative processes using tunable plasmonic nanopatch antennas [Crossref]
2010 - Large enhancement of nonlinear optical phenomena by plasmonic nanocavity gratings [Crossref]
2017 - Refractory plasmonics without refractory materials [Crossref]
2013 - Optical Engineering of Diamond
2013 - Plasmonic waveguide modes of film-coupled metallic nanocubes [Crossref]
2018 - Comprehensive study of plasmonic materials in the visible and near-infrared: linear, refractory, and nonlinear optical properties
2020 - Electrical excitation and charge-state conversion of silicon vacancy color centers in single-crystal diamond membranes [Crossref]