Design for Distributed Feedback Laser Biosensors Based on the Active Grating Model.

Yi Zhou,Zhihe Guo,Bowen Wang,Xiang Wu

doi:10.3390/s19112569

Abstract

The distributed feedback (DFB) laser is widely used in sensing because of its portable size, simple fabrication and high sensitivity. Most theoretical design models are based on passive Bragg gratings. However, passive grating models cannot be used to predict sensor performance using the important indicator of figure of merit (FOM) through theoretical calculations. To solve this problem, we replaced the passive grating with an active grating by using the imaginary part of the coupling constant that represents the value of the gain. As a comparison, the influence of the full width at half maximum (FWHM) and sensitivity were analyzed for different grating duty cycles and depths in the passive grating sensors. To obtain a higher FOM in the active grating sensors, we systematically investigated the effects of duty cycle and gain value through numerical simulations. We found that the redshift caused by a duty cycle increase can improve the sensitivity of biomolecule detection by 1.7 times.

Highlights

Optical biosensors based on the distributed feedback (DFB) laser, with their advantages of small and portable size, simple fabrication, low cost and high sensitivity, have attracted increasing attention and represent one of the most important tools for drug screening, diagnostic testing, nucleic acid detecting, food safety and environmental monitoring [1,2,3,4]
For a DFB laser sensor, the resonant wavelength is described by the Bragg equation [6]: mλ = 2Λne f f where m is the order of diffraction, λ is the wavelength of the laser, neff is the mode’s effective refractive index, which for a specific mode is a function of the refractive index of the surrounding medium [7], and Λ is the grating period
The RSoft product based on rigorous coupled-wave analysis (RCWA) [28] was used to simulate the effect of the grating duty cycle (DC) and dg on the sensors’ sensitivity, full width at half maximum (FWHM) and figure of merit (FOM)

Summary

Introduction

Optical biosensors based on the distributed feedback (DFB) laser, with their advantages of small and portable size, simple fabrication, low cost and high sensitivity, have attracted increasing attention and represent one of the most important tools for drug screening, diagnostic testing, nucleic acid detecting, food safety and environmental monitoring [1,2,3,4]. Due to the dependency of neff on the surrounding medium, any adsorption and binding of bio or chemical analyte to the sensor changes the effective refractive index, causing a shift in the wavelength of the resonant mode. This change in the resonant condition can be determined using a spectrograph. To more accurately simulate the performance of DFB laser sensors, we replaced the passive grating with an active grating and obtained the relationships between the gain value, relative intensity and FWHM. The variation of the laser intensity with the thickness of the biomolecule layer (dbl ) was observed

Simulation Results and Discussion

The Effect of DC and dg on Passive Grating Sensors

Active Grating for High FOMs of Sensors

Sensors with Active Gratings for Biomolecule Detection

Conclusions