High sensitivity and low detection limit sensor based on a slotted nanobeam cavity
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-09-30 |
| Journal | Photonics Letters of Poland |
| Authors | Mohannad AlâHmoud, Rasha Alyahyan |
| Institutions | Imam Mohammad ibn Saud Islamic University |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the design and simulated performance of a highly sensitive refractive index sensor utilizing a slotted Photonic Crystal Nanobeam Cavity (NPCC) fabricated in silicon.
- Ultra-High Performance: The sensor achieves an exceptionally high Quality factor (Q) of 2.0 x 106 and a high sensitivity (S) of 325 nm/RIU when optimized for a water environment.
- Low Detection Limit (DL): The calculated detection limit is 2.4 x 10-7 RIU, positioning this device as a promising candidate for applications requiring the detection of extremely small refractive index changes, potentially enabling single-particle sensing.
- Slotted Design Advantage: The introduction of a central air slot forces the electric field to be strongly confined within the low-index (analyte) region, maximizing the light-matter interaction essential for high sensitivity.
- Optimization Mechanism: The high Q-factor is achieved through careful geometric optimization (tapering holes, adjusting cavity length) based on impedance matching between the waveguide mode and the Bloch mode, drastically reducing radiation losses.
- Material System: The device is based on a standard silicon platform (n=3.48), making it compatible with existing CMOS fabrication processes for mass production and integration.
- Target Wavelength: The design centers the Photonic Band Gap (PBG) around the telecom wavelength (~1550 nm), suitable for integration with existing fiber optic infrastructure.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Quality Factor (Q) | 2.0 x 106 | Dimensionless | Optimized in water background (n=1.333) |
| Sensitivity (S) | 325 | nm/RIU | Performance metric in water |
| Detection Limit (DL) | 2.4 x 10-7 | RIU | Calculated minimum measurable RI change |
| Resonant Wavelength (λ0) | 1568.37 to 1569.33 | nm | Range observed during seawater testing |
| Lattice Constant (a) | 510 | nm | Photonic crystal periodicity |
| Waveguide Thickness (t) | 220 | nm | Silicon layer thickness |
| Waveguide Width (w) | 550 | nm | Optimized width |
| Slot Width | 40 | nm | Central air slot dimension |
| Optimal Cavity Length (l) | 235 | nm | Optimized for water background |
| Silicon Refractive Index (nSi) | 3.48 | Dimensionless | Dielectric material property |
| Effective Mode Volume (Veff) | ~0.01(λ/n)3 | Dimensionless | Ultra-small confinement volume |
| PBG Range | 1270 to 1750 | nm | Calculated Photonic Band Gap |
Key Methodologies
Section titled âKey MethodologiesâThe sensor design and performance analysis relied exclusively on computational modeling using the 3D Finite-Difference Time-Domain (3D-FDTD) method.
- Initial Design Parameters: The unperturbed 1D nanobeam photonic crystal was defined with a lattice constant (a) of 510 nm, air hole radius (r) of 0.365a, and thickness (t) of 220 nm (Silicon n=3.48).
- Band Structure Calculation: The PBS was calculated to confirm the PBG extended from 1270 nm to 1750 nm, centering the fundamental mode near the 1550 nm telecom window.
- Slotted Cavity Geometry: A 40 nm air slot was introduced at the center of the waveguide (w=550 nm, t=220 nm) to maximize electric field confinement in the analyte region.
- Mirror Optimization (Air): To minimize radiation loss, 15 pairs of air holes were used as mirrors. The five holes closest to the cavity were linearly tapered in both radius and spacing down to 67% of their value in the mirror region.
- Q-Factor Tuning (Air): The cavity length (l) was scanned (481 nm to 492 nm) to find the optimal length (l = 486 nm) that maximized the Q-factor (6.6 x 105) by achieving impedance matching.
- Water Environment Re-optimization: The entire structure was simulated with a water background (n=1.333). The cavity length was re-optimized, yielding a new maximum Q-factor (2.0 x 106) at l = 235 nm.
- Sensitivity Measurement: The resonant wavelength shift (Îλ) was calculated for four different seawater salinity concentrations (0, 10, 20, and 30 g/mole). The resulting linear relationship between Îλ and the refractive index change (În) was used to determine the sensitivity (S = Îλ/În).
Commercial Applications
Section titled âCommercial ApplicationsâThe high sensitivity and ultra-low detection limit of this slotted nanobeam cavity sensor make it highly valuable for integrated photonics and advanced sensing applications.
- Optofluidic Systems: Integration into microfluidic chips for real-time, high-throughput analysis of chemical reactions or fluid composition in small volumes.
- Biosensing and Diagnostics: Used in Point-of-Care (POC) devices for detecting low concentrations of biomarkers, viruses, or proteins, leveraging the potential for single-molecule detection due to the small mode volume.
- Environmental Monitoring: Highly accurate monitoring of water quality, including salinity, heavy metal contamination, or pollutant levels in aquatic environments.
- Pharmaceutical Research: High-precision refractive index measurement for monitoring binding kinetics, concentration changes, and purity in drug discovery and development processes.
- Integrated Photonics: Serving as a fundamental building block for highly sensitive, compact, and scalable sensor arrays within silicon-on-insulator (SOI) platforms.
View Original Abstract
In this work, the three-dimensional finite-difference time-domain (3D-FDTD) method is used to design and analyze a refractive index sensor based on a slotted photonic crystal nanobeam cavity. These type of cavities support a high quality-factor and a small volume, and therefore is attractive for optical sensing. We demonstrate that when immersing our proposed sensor in water it can possess a high-quality factor of 2.0Ă10^6, high sensitivity of 325 nm/RIU, and a detection limit of 2.4Ă10^(-7) RIU. We believe that our proposed sensor is a promising candidate for potential applications sensing like in optofluidic- and bio-sensing. Full Text: PDF ReferencesE. Chow, A. Grot, L. Mirkarimi, M. Sigalas, G. Girolami, âUltracompact biochemical sensor built with two-dimensional photonic crystal microcavityâ, OSA Trends Opt. Photonics Ser. 97 909 (2004). CrossRef S. Kim, H-M. Kim, Y-H. Lee, âSingle nanobeam optical sensor with a high Q-factor and high sensitivityâ, Opt. Lett. 40 5351 (2015). CrossRef D-Q, Yang, B Duan, X, Liu, A-Q, Wang, X-G, Li, Y-F, Ji, âPhotonic Crystal Nanobeam Cavities for Nanoscale Optical Sensing: A Reviewâ, Micromachines 11 (2020). CrossRef P.B. Deotare, M.W. McCutcheon, I.W. Frank, M. Khan, M. LonÄar, âHigh quality factor photonic crystal nanobeam cavitiesâ, Appl. Phys. Lett. 94 121106 (2009). CrossRef P. Seidler, K. Lister, U. Drechsler, J. Hofrichter, T. Stöferle, âSlotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratioâ, Opt. Express 21 32468 (2013). CrossRef H. Choi, M. Heuck, D. Englund, âSelf-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearitiesâ, Phys. Rev. Lett. 118 223605 (2017). CrossRef M. Al-Hmoud, S. Bougouffa, âSimultaneous high Q/V-ratio and optimized far-field emission pattern in diamond slot-bridge nanobeam cavityâ, Results Phys. 26 104314 (2021). CrossRef Q. Quan (2014). CrossRef M.A. Butt, C. Tyszkiewicz, P. KarasiĆski, M. ZiÄba, D. Hlushchenko, T. Baraniecki, A. KaĆșmierczak, R. Piramidowicz, M. Guzik, A. Bachmatiuk, âDevelopment of a low-cost silica-titania optical platform for integrated photonics applicationsâ, Opt. Express 30 23678 (2022). CrossRef D-Q. Yang, B. Duan, X. Liu, A-Q. Wang, X-G. Li, Y-F. Ji, ""Photonic Crystal Nanobeam Cavities for Nanoscale Optical Sensing: A Reviewâ, Micromachines 72, 11 (2020). CrossRef Y.N. Zhang, Y. Zhao, R.Q Lv, âA review for optical sensors based on photonic crystal cavitiesâ, Sens. Actuators A: Phys. 233 374 (2015). CrossRef P. Lalanne, S. Mias, and J.P. Hugonin, âTwo physical mechanisms for boosting the quality factor to cavity volume ratio of photonic crystal microcavitiesâ, Opt. Express 12 458 (2004). CrossRef C. Sauvan, G. Lecamp, P. Lalanne, J.P Hugonin, âModal-reflectivity enhancement by geometry tuning in Photonic Crystal microcavitiesâ, Opt. Express 13 245 (2005). CrossRef J.T. Robinson, C. Manolatou, L. Chen, M. Lipson, âUltrasmall Mode Volumes in Dielectric Optical Microcavitiesâ, Phys. Rev. Lett. 95 143901 (2005). CrossRef S. Olyaee, M. Seifouri, R. Karami, A. Mohebzadeh-Bahabady, âDesigning low power and high contrast ratio all-optical NOT logic gate for using in optical integrated circuitsâ, Opt. Quantum Electron. 51 1 (2019). CrossRef