Reflective leaky waveguide gratings (LWGs) with internal referencing for sensing

Ruchi Gupta,Nicholas J Goddard

doi:10.1039/d1sd00061f

Abstract

Current transmission grating sensors are unsuitable for use in typical samples that absorb and scatter light.

Highlights

To address the above limitations, we report leaky waveguide gratings (LWGs), which operate in reflective mode
As LWGs were fabricated by exposing chitosan films with PCbiotin to interference fringes of the interference lithography (IL) set-up, the expected grating pitch (Λexp) is given by eqn (1).[41,42]
Absolute shifts in peak positions of first diffracted orders of LWG strips without and with streptavidin were comparable at equilibrium, their transient responses were different as suggested by the presence of dips/peaks in differential responses as solutions were changed

Summary

Introduction

High RI evanescent wave sensors such as RWGs and other grating-based guided mode resonance structures need to enhance the evanescent field to increase sensitivity as the guiding layer is non-porous to analytes. Goddard et al showed theoretically and experimentally that porous, low RI LWs (anti-resonant reflecting optical waveguides, ARROW) gave higher sensitivity, by a factor of about 3, than a resonant mirror (RM) evanescent sensor using a high RI silicon nitride guiding layer.[32]. The narrower strips are not visible as independent LWs, but instead give a diffraction pattern at resonance angles where the reflected light is undergoing a rapid 2π phase shift. Light reflected from LW strips without and with REs do not interfere with each other Interference fringes at resonance angles of LWs. No visible diffraction pattern Chitosan films without and with strips of REs on glass substrates Sensing with internal referencing

Experimental

Results and discussion

Conclusions