Optimization of Silicon Nitride Waveguide Platform for On-Chip Virus Detection

Abstract

This work presents a rigorous and generic sensitivity analysis of silicon nitride on silicon dioxide strip waveguide for virus detection. In general, by functionalizing the waveguide surface with a specific antibodies layer, we make the optical sensor sensitive only to a particular virus. Unlike conventional virus detection methods such as polymerase chain reaction (PCR), integrated refractive index (RI) optical sensors offer cheap and mass-scale fabrication of compact devices for fast and straightforward detection with high sensitivity and selectivity. Our numerical analysis includes a wide range of wavelengths from visible to mid-infrared. We determined the strip waveguide’s single-mode dimensions and the optimum dimensions that maximize the sensitivity to the virus layer attached to its surface at each wavelength using finite difference eigenmode (FDE) solver. We also compared the strip waveguide with the widely used slot waveguide. Our theoretical study shows that silicon nitride strip waveguide working at lower wavelengths is the optimum choice for virus detection as it maximizes both the waveguide sensitivity (Swg) and the figure of merit (FOM) of the sensor. The optimized waveguides are well suited for a range of viruses with different sizes and refractive indices. Balanced Mach–Zehnder interferometer (MZI) sensors were designed using FDE solver and photonic circuit simulator at different wavelengths. The designed sensors show high FOM at λ = 450 nm ranging from 500 RIU−1 up to 1231 RIU−1 with LMZI = 500 µm. Different MZI configurations were also studied and compared. Finally, edge coupling from the fiber to the sensor was designed, showing insertion loss (IL) at λ = 450 nm of 4.1 dB for the design with FOM = 500 RIU−1. The obtained coupling efficiencies are higher than recently proposed fiber couplers.

Demonstration of a Single-Mode Expanded-Beam Connectorized Module for Photonic Integrated Circuits

“…An important feature of the SiN platform, besides being transparent at visible wavelength (which expands the range of possible applications of SiN photonic chips), is smaller refractive index contrast between the waveguide and air as compared to silicon on insulator (SOI) waveguide devices (~2:1 contrast as opposed to 3.4:1) [14]. Since the majority of optical adhesives have refractive indices in the range of 1.45-1.6, the lower contrast between the waveguide effective index and the adhesive index reduces the reflections at the interface and prevents optical cavity effects.…”

Mirror-terminated Mach-Zehnder interferometer based on SiNOI slot and strip waveguides for sensing applications using visible light

“…The TM mode exhibits field discontinuity at the core edges in the y direction; as a result, reducing the width over thickness ratio will increase the amount of the evanescent field and, consequently, the sensitivity. Thus, for inexpensive and manufacturable big-feature size sensors, TM mode is better (El Shamy et al, 2022). The coupling losses between the modes are challenging due to the optical mode mismatch between the slot and strip waveguides as shown in Figure 4.…”

Silicon-based, fractal metamaterial structure for IR broadband absorption

“…One of the approaches is using structures having multiple resonators to couple different absorption peaks; however, these structures have large fingerprints due to incorporating several components [1 -3]. Furthermore, other structures with high absorption were proposed based on metallic plasmonics [4][5][6][7], Silicon nanowires, and porous silicon; but they have some drawbacks such as instability, high cost, and high thickness [8,9].…”