Multiplexed fiber-optic Fabry-Pérot cavities for refractive index and temperature sensing fabricated using diamond-blade dicing
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | EPJ Web of Conferences |
| Authors | Ivonne Pfalzgraf, Sergiy Suntsov, Kore Hasse, Detlef Kip |
| Institutions | Helmut Schmidt University |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Diamond-Blade Diced Fabry-Pérot Sensors
Section titled “Technical Documentation & Analysis: Diamond-Blade Diced Fabry-Pérot Sensors”Executive Summary
Section titled “Executive Summary”This document analyzes the fabrication and performance of multiplexed fiber-optic Fabry-Pérot (FP) sensors, highlighting the critical role of precision diamond processing and identifying opportunities for 6CCVD’s advanced MPCVD diamond materials.
- Core Achievement: Successful multiplexing of up to four open FP micro-cavities within a single-mode optical fiber for spatially resolved sensing.
- Fabrication Method: Precision micro-machining achieved using a diamond-blade dicing saw to create smooth, rectangular slots through the fiber core.
- High Accuracy Sensing: Demonstrated ultra-high refractive index (RI) measurement accuracy down to $6 \times 10^{-6}$ RIU after temperature compensation.
- Temperature Compensation: Achieved using either solid fiber core sections or a high thermo-optic coefficient Si inlay glued into one of the cavities.
- Reflectivity Enhancement: Dielectric coatings (Ta2O5) were applied to the cavity sidewalls to increase reflectivity and optimize sensor response.
- Application Potential: The compact, multiplexed design is highly suitable for “lab-on-a-fiber” systems and small-volume biomedical applications.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results, demonstrating the high performance of the fabricated sensors.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Wavelength Range | 1460 - 1620 | nm | Interrogation System |
| Refractive Index (RI) Sensitivity (Coated) | ~1185 | nm/RIU | Average for all four FP sensors |
| RI Measurement Accuracy (Compensated) | 2 x 10-5 | RIU | Using Si inlay for temperature compensation |
| RI Cross-Sensitivity Accuracy | 6 x 10-6 | RIU | Deviation from expected Δnm = 0 |
| Temperature Sensitivity (Si Inlay) | 79 | pm/°C | High sensitivity due to Si thermo-optic coefficient |
| Temperature Sensitivity (Solid Fiber Core) | 19.33 - 20 | pm/°C | Used for temperature compensation (FPR5, FPR6, FPR7) |
| Temperature Measurement Accuracy | 0.01 | °C | Achieved using solid core sections |
| Ta2O5 Refractive Index | 2.07 | N/A | At 1550 nm wavelength |
| Si Thermo-Optic Coefficient | 1.7 x 10-4 | K-1 | High value enables effective temperature sensing |
Key Methodologies
Section titled “Key Methodologies”The fabrication relies heavily on high-precision micro-machining, a process where the quality of the diamond tooling is paramount.
- Fiber Stabilization: The single-mode optical fiber is glued into a quartz ferrule to ensure mechanical stability during processing.
- Precision Dicing: Slots of varying widths are cut through the fiber core using a Disco DAD322 wafer saw equipped with resin-based diamond blades of very fine grit.
- Surface Quality Control: Blade conditioning with a special dresser board ensures all cuts have a nearly rectangular shape and smooth surfaces, critical for high-reflectivity FP cavities.
- Optional Inlay Preparation: A thin Si rectangular plate is prepared using the dicing saw, placed inside one of the open cavities, and secured with NOA61 glue for temperature sensing.
- Reflectivity Enhancement: Single high-index Ta2O5 dielectric layers (n = 2.07 at 1550 nm) are evaporated onto both sidewalls of the open cavities to increase reflectance.
- Interrogation: Phase tracking of the essential fast Fourier transform (FFT) components is used to extract small changes in optical length (Lo) induced by temperature or RI changes.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research demonstrates the necessity of ultra-precise diamond micro-machining for advanced fiber-optic sensors. 6CCVD provides the foundational MPCVD diamond materials and customization services required to replicate this work, enhance sensor robustness, and extend its functionality.
Applicable Materials
Section titled “Applicable Materials”| Material | 6CCVD Recommendation | Application in Research Context |
|---|---|---|
| Optical Grade SCD | High Purity, Polished (Ra < 1 nm) | Ideal for high-power optical windows, lenses, or substrates requiring superior thermal management and transparency in the 1460-1620 nm range. |
| Polished PCD | Inch-size wafers (up to 125 mm), Ra < 5 nm | Provides a robust, large-area platform for non-fiber-based FP sensor arrays or for manufacturing the high-quality diamond dicing blades used in the fabrication process. |
| Boron-Doped Diamond (BDD) | Heavy Doping (Conductive) | Extends the sensor’s capability beyond RI/Temperature. BDD can be integrated as an electrode for simultaneous electrochemical sensing (e.g., pH, trace substances), leveraging its stability and inertness. |
Customization Potential
Section titled “Customization Potential”6CCVD’s in-house capabilities directly address the complex material requirements demonstrated in this paper, offering superior alternatives to standard silica or Si components.
- Precision Dicing & Shaping: While the paper used diamond blades to cut fiber, 6CCVD utilizes advanced laser cutting and micro-machining to shape diamond substrates (SCD/PCD) into custom geometries (e.g., micro-lenses, prisms, or custom FP cavity structures) up to 125 mm in diameter.
- Advanced Metalization Services: The paper used Ta2O5 for reflectivity enhancement. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu). We can deposit custom multi-layer stacks (e.g., Ti/Pt/Au) directly onto diamond substrates, providing highly reflective, robust, and chemically inert mirrors for FP cavities, potentially replacing the less stable Ta2O5/NOA61 system.
- Custom Substrates: We can supply SCD or PCD substrates up to 500 µm thick, polished to Ra < 1 nm (SCD), allowing researchers to transition from fragile fiber-based sensors to robust, high-thermal-conductivity diamond platforms for extreme environments.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in the application of MPCVD diamond for high-precision optical and sensing projects. We offer consultation on:
- Material Selection: Optimizing diamond grade (SCD vs. PCD) and doping level (BDD) based on specific application requirements (e.g., high temperature, chemical inertness, or electrochemical integration).
- Thermal Management: Designing diamond components to leverage diamond’s superior thermal conductivity, crucial for minimizing temperature cross-talk in sensing applications.
- Surface Preparation: Ensuring the required surface finish (Ra < 1 nm) for high-reflectivity optical interfaces, critical for maximizing the finesse of FP resonators.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures timely delivery of specialized diamond materials worldwide.
View Original Abstract
We report on multiplexing several Fabry-Pérot (FP) cavities in single-mode optical fibers for highprecision spatially resolved sensing of refractive indices (RI) of liquids. Resonators are fabricated by cutting small slots into fibers using a diamond-blade dicing saw and additional coating with thin Ta 2 O 5 layers to increase cavity reflectance. Temperature compensation of RI measurements is achieved either by evaluating the reflection signals resulting from the solid core parts between different open-cavity sensor elements, or by using a thin Si inlay glued into one of the open cavities. The multiplexing performance and accuracy of the fabricated sensors with up to four open cavities were tested on sucrose solutions over a range of temperatures.