Designing an Electro-Optical Tunable Racetrack Microring Resonator on a Diamond–Lithium Niobate Thin-Film Hybrid Platform

At a Glance

Metadata	Details
Publication Date	2023-11-11
Journal	Electronics
Authors	Fan Yang, Yuhao Wu, Changlong Cai, Hong Fang
Institutions	Xi’an Technological University, Shenzhen Technology University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond-Lithium Niobate Hybrid Microring Resonators

6CCVD Material Analysis Reference: Yang et al., Designing an Electro-Optical Tunable Racetrack Microring Resonator on a Diamond-Lithium Niobate Thin-Film Hybrid Platform, Electronics 2023, 12, 4616.

Executive Summary

This study validates the design and performance of an Electro-Optical (E-O) tunable racetrack microring resonator built on a diamond waveguide integrated with an x-cut Lithium Niobate on Insulator (LNOI) platform. This hybrid approach is highly relevant for next-generation integrated photonics and quantum information systems.

Hybrid Platform Validation: Successfully combines the exceptional optical properties of diamond (high index, low loss, wide bandgap) with the strong linear E-O effect of Lithium Niobate (LN).
High Performance Metrics: Achieved a high Quality Factor (Q-factor) of approximately 6100 and a coupling efficiency of ~95% for the Transverse Electric (TE) mode.
Telecommunication Relevance: Optimized for operation at the critical 1.55 µm telecommunication wavelength (C-band).
E-O Tunability: Demonstrated a resonant tunability coefficient of 1.84 pm/V, enabling compact, voltage-controlled wavelength selection.
Optimal Dimensions: Determined precise diamond waveguide dimensions (1.1 µm thickness, 1.1 µm width) required for stable fundamental TE single-mode operation.
Integrated Optics Advancement: Provides a robust pathway for integrating quantum emitters (diamond color centers) and classical optical components on a single chip with low operating voltage.

Technical Specifications

The following hard data points were extracted from the simulation and optimization results for the diamond racetrack microring resonator:

Parameter	Value	Unit	Context
Operating Wavelength (λ)	1.55	µm	C-band telecommunication
Diamond Refractive Index (n)	2.38	N/A	At 1.55 µm
Diamond Bandgap	5.5	eV	Wide bandgap property
Diamond Waveguide Thickness (h)	1.1	µm	Optimized for single-mode TE operation
Diamond Waveguide Width (w)	1.1	µm	Optimized for single-mode TE operation
Microring Radius (R)	30	µm	Optimized device parameter
Racetrack Length (L)	150	µm	Optimized device parameter
Optimal Gap Size	0.45	µm	Balance of Q-factor and coupling efficiency
Electrode Separation (D)	1.5	µm	Minimizes surface plasmon resonance loss
Achieved Q-Factor	~6100	N/A	For TE mode at 0.45 µm gap
Coupling Efficiency	~95	%	Achieved with 0.45 µm gap
E-O Tunability Coefficient	1.84	pm/V	Rate of wavelength shift vs. electric field
Maximum Wavelength Shift (at 15 V/µm)	27.6	pm	Achieved at 1.1 µm diamond thickness
Free Spectral Range (FSR)	4.99	nm	At L = 150 µm
LN Linear E-O Coefficient (r₃₃)	31.2	pm/V	Used for E-O effect calculation

Key Methodologies

The design and optimization relied heavily on advanced numerical simulation techniques to ensure single-mode operation and maximize coupling efficiency and Q-factor.

Platform Selection: The hybrid structure utilized a diamond waveguide on an x-cut Lithium Niobate on Insulator (LNOI) substrate, chosen specifically to maximize the linear E-O coefficient (r₃₃) via the Transverse Electric (TE) mode.
Waveguide Optimization (FDE): The Finite-Difference Eigenmode (FDE) method was used to systematically examine single-mode conditions, transmission losses, and waveguide dispersion. This determined the optimal diamond thickness (h = 1.1 µm) and width (w = 1.1 µm) to suppress higher-order modes (TE₁, TM₁).
Loss Minimization: FDE analysis was used to optimize the electrode separation distance (D) to 1.5 µm, ensuring the waveguide mode field interaction with the Au electrodes was minimized, thereby reducing propagation loss below 10^-2 dB/cm.
Resonator Simulation (3D-FDTD): The three-dimensional Finite-Difference Time-Domain (3D-FDTD) method was employed to simulate the coupling gap, bending radius (R=30 µm), and racetrack length (L=150 µm) to achieve the optimal balance between high Q-factor and high coupling efficiency.
E-O Effect Modeling: The change in the extraordinary refractive index (Δn_e) of the LN layer due to the applied electric field (E_z) was calculated using the linear E-O coefficient (r₃₃), which was then correlated with the resulting resonant wavelength shift (Δλ_TE) of the hybrid waveguide.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, dimensionally precise diamond materials and advanced integration services. 6CCVD is uniquely positioned to supply the necessary materials and fabrication support to replicate and advance this E-O tunable hybrid platform.

Applicable Materials

To achieve the low-loss, high-index waveguide required for this high-Q resonator, the following 6CCVD material is essential:

Optical Grade Single Crystal Diamond (SCD): Required for the active waveguide layer. SCD provides the necessary high refractive index (n ≈ 2.38) and wide bandgap (5.5 eV) for low-loss propagation and potential integration of quantum color centers (e.g., NV centers).
Precision Thickness Control: The paper specifies a critical thickness of 1.1 µm. 6CCVD specializes in delivering ultra-thin SCD films with thickness control ranging from 0.1 µm up to 500 µm, ensuring the precise single-mode cutoff conditions required by the FDE optimization are met.

Customization Potential

The successful fabrication of this device relies on tight dimensional control and specific metal integration. 6CCVD offers comprehensive services to meet these requirements:

Research Requirement	6CCVD Customization Capability	Impact on Research Replication
Specific Waveguide Dimensions	Custom Laser Cutting and Etching Support	We provide SCD plates and wafers up to 125mm (PCD) and custom-sized SCD substrates, allowing researchers to define the exact 1.1 µm x 1.1 µm cross-section and R=30 µm racetrack geometry.
Integrated Au Electrodes	In-House Custom Metalization Services	We offer internal deposition of Au, Pt, Pd, Ti, W, and Cu. We can apply the necessary Ti/Au adhesion and electrode layers directly onto the diamond surface or substrate interface, streamlining the hybrid integration process.
Ultra-Low Loss Surface	Advanced Polishing Services	Achieving the high Q-factor (~6100) requires minimizing scattering loss. 6CCVD guarantees surface roughness (Ra) of < 1 nm for SCD and < 5 nm for inch-size PCD, critical for high-performance microring resonators.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science and engineering of MPCVD diamond for advanced photonic and electronic applications. We can assist researchers with:

Material Selection: Consulting on the optimal SCD grade and thickness for specific E-O tunable microring resonator designs or similar integrated quantum photonics projects.
Integration Guidance: Providing technical specifications for diamond films compatible with standard LNOI bonding and etching processes.
Dispersion Engineering: Assisting in selecting diamond parameters to achieve specific normal or anomalous dispersion characteristics required for nonlinear frequency conversion or comb generation.

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

View Original Abstract

This study proposes and simulates a numerical analysis of a diamond racetrack microring resonator on a lithium niobate thin film, operating at a 1.55 µm wavelength. The single-mode conditions, transmission losses, and waveguide dispersions are systematically examined. The microring resonator’s radius and gap size are computed and optimized. The designed racetrack microring resonator exhibits a high quality factor (Q-factor) and a high coupling efficiency of approximately 6100 and 95%, respectively, for the transverse TE mode in the C-band. This study achieves a resonant tunability of 1.84 pm/V near the 1.55 μm wavelength by harnessing the electro-optical effect of lithium niobate.

Tech Support

Original Source

DOI: https://doi.org/10.3390/electronics12224616

References

2014 - Diamond nonlinear photonics [Crossref]
2011 - Resonant enhancement of the zero-phonon emission from a colour centre in a diamond cavity [Crossref]
2005 - Transflectance Spectra of Faceted Diamonds Acquired by Infrared Microscopy [Crossref]
2018 - Photon-mediated interactions between quantum emitters in a diamond nanocavity [Crossref]
2022 - Diamond Integrated Quantum Nanophotonics: Spins, Photons and Phonons [Crossref]
2022 - A Wideband Balun-Based Microwave Device for Quantum Information Processing with Nitrogen-Vacancy Centers in Diamond [Crossref]
2016 - Microwave-free magnetometry with nitrogen-vacancy centers in diamond [Crossref]
2011 - Diamond photonics [Crossref]
2013 - Nonlinear optical properties of detonation nanodiamond in the near infrared: Effects of concentration and size distribution [Crossref]
1974 - Dispersion of the nonlinear optical susceptibility tensor in centrosymmetric media [Crossref]