Single-mode optical waveguides on native high-refractive-index substrates
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-08-01 |
| Journal | APL Photonics |
| Authors | Richard R. Grote, Lee C. Bassett |
| Institutions | University of Pennsylvania |
| Citations | 17 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation for 6CCVD
Section titled âTechnical Analysis and Documentation for 6CCVDâExecutive Summary
Section titled âExecutive SummaryâThis paper introduces a disruptive waveguide architecture that allows for the monolithic integration of Photonic Integrated Circuits (PICs) on native, high-refractive-index substrates, specifically Diamond and Silicon Carbide (SiC). This approach is critically important for next-generation quantum and nonlinear optical systems.
- Key Innovation: A high-aspect-ratio âfin waveguideâ geometry utilizing stacked dielectrics ($\text{SiO}{2}/\text{Si}{3}\text{N}_{4}$) to achieve tight optical confinement, eliminating the need for traditional, thick buried low-index layers (e.g., buried oxide or InGaAsP).
- Integration Advantage: Solves the major co-integration challenge in silicon photonics by removing the thick buried oxide layer that is incompatible with standard VLSI electronics, enabling large-area, scalable PICs.
- Diamond Focus: Design is specifically optimized for emerging platforms like Single Crystal Diamond (SCD) at $\lambda = 637\text{ nm}$, corresponding to the Nitrogen-Vacancy (NV) center zero phonon line.
- Performance Metrics: The optimized diamond fin structure achieves ultratight confinement ($A_{min}$ at $w_{symm}$), leading to very low substrate leakage loss (< 0.15 dB/cm) and high quality factors (unloaded Q > 30,000) suitable for quantum information processing and nonlinear optics.
- Manufacturing Compatibility: The design uses conventional top-down fabrication techniques, including dry etching and standard dielectric deposition, aligning perfectly with 6CCVDâs precision MPCVD material and processing services.
Technical Specifications
Section titled âTechnical SpecificationsâDesign parameters and performance metrics for the Single-Mode Optical Waveguides on Diamond and Silicon, extracted from numerical simulations.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material | Diamond (SCD) | --- | High-index substrate |
| Target Wavelength ($\lambda$) | 637 | nm | NV Center Zero Phonon Line |
| Diamond Refractive Index ($n_{f}$) | 2.41 | None | At $\lambda = 637\text{ nm}$ (Guiding Fin) |
| Confinement Index ($n_{H}$) | 2.01 | None | $\text{Si}{3}\text{N}{4}$ at $\lambda = 637\text{ nm}$ |
| Buffer Index ($n_{L}$) | 1.46 | None | $\text{SiO}_{2}$ at $\lambda = 637\text{ nm}$ |
| $\text{Si}{3}\text{N}{4}$ Confinement Layer Thickness | 200 | nm | Conformal layer design (Fig. 4a) |
| Buffer Layer Thickness ($t_b$) Requirement | > 1.0 | ”m | Minimum required for low loss |
| Calculated Substrate Leakage Loss | < 0.15 | dB/cm | For $t_b$ > 1.0 ”m (Diamond fin) |
| Calculated Bending Loss (R=10 ”m) | < 0.06 | dB per 90° bend | For $t_b = 2.5$ ”m (Diamond fin) |
| Unloaded Q Factor (Ring Resonator) | > 30,000 | None | For 20 ”m diameter ring (Diamond fin) |
| Material | Silicon (Si) | --- | High-index substrate |
| Target Wavelength ($\lambda$) | 1.55 | ”m | Telecommunications Band |
| Si Refractive Index ($n_{f}$) | 3.48 | None | At $\lambda = 1.55$ ”m |
| Si${3}\text{N}{4}$ Refractive Index ($n_{H}$) | 1.98 | None | At $\lambda = 1.55$ ”m |
| $\text{SiO}{2}$ Refractive Index ($n{L}$) | 1.44 | None | At $\lambda = 1.55$ ”m |
| Unloaded Q Factor (Ring Resonator) | > 10,000 | None | Achieved for optimized Si design |
Key Methodologies
Section titled âKey MethodologiesâThe experimental design relies on rigorous modeling and proposes fabrication methods that require precision material engineering.
- Material Stack Selection: Utilized $\text{SiO}{2}$ as the low-index buffer layer ($n{L}$) and $\text{Si}{3}\text{N}{4}$ as the medium-index confinement layer ($n_{H}$), stacked on the high-index SCD substrate ($n_{f}$). Alternative material pairs ($\text{Al}{3}\text{O}{2}/\text{AIN}$ or polymers/chalcogenides) were identified as possible substitutes.
- Waveguide Geometry Optimization: The fin structure width ($w$) and height ($h$) were optimized based on normalized dispersion curves ($w/\lambda$ and $h/\lambda$). Optimization focused on achieving the tightest possible confinement ($A_{min}$), which occurs at the specific geometric condition defined as $w = w_{symm}$.
- Numerical Modeling: Mode dispersion, effective index ($n_{eff}$), mode area ($A_{eff}$), and confinement factor ($\Gamma$) were calculated using both the analytical Effective Index Method (EIM) and verified using rigorous Full-Vectorial Finite Difference Method (FDM) simulations.
- Loss Calculation:
- Substrate Leakage: Calculated using two methods: (1) Coupled-Mode Theory (CMT) via an overlap integral, and (2) FDM incorporating Perfectly Matched Layers (PML) boundary conditions.
- Bending Loss: Calculated using FDM specifically in cylindrical coordinates, determining the loss per 90° bend and the resulting bending-loss-limited Q factor for ring resonators.
- Fabrication Proposal: The high-aspect ratio diamond fins are intended to be realized via highly anisotropic dry etching processes, followed by standard dielectric deposition (CVD/PECVD) and planarization techniques.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the foundational high-purity materials and advanced fabrication services required to replicate and advance the research outlined in this paper, particularly the critical diamond platform.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and ExtensionâTo achieve the targeted high Q-factors and low loss for quantum applications (NV centers), high-purity diamond is essential. 6CCVD provides:
- Single Crystal Diamond (SCD): Required for the fin waveguide core. We supply Optical Grade SCD with ultra-low nitrogen incorporation necessary for achieving long spin coherence times and high-quality NV center formation referenced in the source paper [21, 22].
- Custom Thickness: We provide SCD substrates and thick plates required for the high-aspect-ratio fin structures, with thicknesses ranging from $0.1\text{ ”m}$ up to $500\text{ ”m}$ (SCD) and large substrates up to $10\text{ mm}$ (Substrates).
Customization Potential
Section titled âCustomization PotentialâSuccessfully translating this design into a functioning PIC requires precision surface preparation and dimensional controlâkey specialties of 6CCVD.
| Required Service | 6CCVD Capability | Research Link / Application |
|---|---|---|
| Surface Quality | Polishing to Ra < 1 nm (SCD) | Critical for minimizing scattering loss and achieving the calculated Q factors (> 30,000). |
| Custom Dimensions | Plates/wafers up to $125\text{ mm}$ (PCD) | Enables the âlarge-area, scalable PICsâ goal mentioned in the paper. |
| High-Aspect Ratio Processing | Precision laser cutting and shaping services | Essential for defining the intricate fin geometries and achieving optimized $w_{symm}$ dimensions. |
| Dielectric Stack Integration | Custom dielectric deposition (Internal capability) | While the paper uses $\text{SiO}{2}/\text{Si}{3}\text{N}{4}$, 6CCVD can integrate additional layers (e.g., $\text{Al}{2}\text{O}_{3}$) or subsequent layers used in active device integration. |
| Electrical Integration | Metalization Services (Au, Pt, Ti, W, Cu) | For future integration of active devices (e.g., p-i-n junctions [28]) or electrical contacts required for spin manipulation. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team provides authoritative support for advanced photonic projects. We can assist researchers in:
- Material Selection: Determining the optimal growth parameters and nitrogen concentration (PPM levels) in SCD necessary to maximize NV center yield and coherence for integrated quantum information processing.
- Design Consultation: Advising on material parameters (like BDD doping) or customized polishing techniques to reduce interface losses and meet the stringent optical requirements defined by this fin waveguide architecture for similar quantum optics or nonlinear optics projects.
- Global Logistics: We ensure reliable delivery of sensitive materials globally, providing DDU (default) and DDP shipping options to streamline the acquisition process for international research labs.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
High-refractive-index semiconductor optical waveguides form the basis for modern photonic integrated circuits (PICs). However, conventional methods for achieving optical confinement require a thick lower-refractive-index support layer that impedes large-scale co-integration with electronics and limits the materials on which PICs can be fabricated. To address this challenge, we present a general architecture for single-mode waveguides that confine light in a high-refractive-index material on a native substrate. The waveguide consists of a high-aspect-ratio fin of the guiding material surrounded by lower-refractive-index dielectrics and is compatible with standard top-down fabrication techniques. This letter describes a physically intuitive, semi-analytical, effective index model for designing fin waveguides, which is confirmed with fully vectorial numerical simulations. Design examples are presented for diamond and silicon at visible and telecommunications wavelengths, respectively, along with calculations of propagation loss due to bending, scattering, and substrate leakage. Potential methods of fabrication are also discussed. The proposed waveguide geometry allows PICs to be fabricated alongside silicon CMOS electronics on the same wafer, removes the need for heteroepitaxy in III-V PICs, and will enable wafer-scale photonic integration on emerging material platforms such as diamond and SiC.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2008 - Silicon Photonics: The State of the Art [Crossref]