An Optimization Framework for Silicon Photonic Evanescent-Field Biosensors Using Sub-Wavelength Gratings

Abstract

Silicon photonic (SiP) evanescent-field biosensors aim to combine the information-rich readouts offered by lab-scale diagnostics, at a significantly lower cost, and with the portability and rapid time to result offered by paper-based assays. While SiP biosensors fabricated with conventional strip waveguides can offer good sensitivity for label-free detection in some applications, there is still opportunity for improvement. Efforts have been made to design higher-sensitivity SiP sensors with alternative waveguide geometries, including sub-wavelength gratings (SWGs). However, SWG-based devices are fragile and prone to damage, limiting their suitability for scalable and portable sensing. Here, we investigate SiP microring resonator sensors designed with SWG waveguides that contain a “fishbone” and highlight the improved robustness offered by this design. We present a framework for optimizing fishbone-style SWG waveguide geometries based on numerical simulations, then experimentally measure the performance of ring resonator sensors fabricated with the optimized waveguides, targeting operation in the O-band and C-band. For the O-band and C-band devices, we report bulk sensitivities up to 349 nm/RIU and 438 nm/RIU, respectively, and intrinsic limits of detection as low as 5.1 × 10−4 RIU and 7.1 × 10−4 RIU, respectively. This performance is comparable to the state of the art in SWG-based sensors, positioning fishbone SWG resonators as an attractive, more robust, alternative to conventional SWG designs.

Dielectric Waveguide-Based Sensors with Enhanced Evanescent Field: Unveiling the Dynamic Interaction with the Ambient Medium for Biosensing and Gas-Sensing Applications—A Review

“…The sensitivity of these sensors is governed by the overlay of the E-field with the analyte, which can be enhanced by increasing this overlap [95]. Given the high index contrast of Si/SiO 2 , most of the E-field is narrowed to the core of the WG for TE polarized light.…”

Crown ether decorated silicon photonics for safeguarding against lead poisoning

“…In the reference arm, slot waveguides with identical dimensions are also implemented. This is to normalize waveguide propagation losses on the sensing and reference arms, and the power ratio of the asymmetrical adiabatic tapered splitters are designed according to H 2 O absorption 47 (designed losses) in the sensing region. The lightwave from the sensing and reference arms recombines at the asymmetrical adiabatic tapered splitter, forming the MZI interferometric spectrum.…”

“…H 2 O poses significant water absorption at the C-band 47 . Yet, the length of the sensing region increases the surface sensitivity; which forces an inherent tradeoff between the fringe visibility (extinction ratio) and sensitivity 44 .…”

High-Resolved Near-Field Sensing by Means of Dielectric Grating With a Box-Like Resonance Shape

“…High-resolved near-field sensing by means of dielectric grating with a box-like resonance shape their suitability for portable sensing [10]. To overcome this limit and exploit the resonant behavior, ring resonator sensors with SWG waveguides consisting of a "fishbone" structure have been proposed to solve this downside [11]. Bulk sensitivities up to 349 nm/RIU and 438 nm/RIU have been achieved at 1,310 nm and 1,550 nm, respectively, and intrinsic LODs as low as 5.1•10 −4 RIU and 7.1•10 −4 RIU [11].…”