Fundamental limit of detection of photonic biosensors with coherent phase read-out

Abstract

Photonic biosensors offer label-free detection of biomolecules for applications rangingfromclinicaldiagnosistofoodqualitymonitoring. BothsensorsbasedonMach-Zehnder interferometers and ring resonators are widely used, but are usually read-out using different schemes, making a direct comparison of their fundamental limit of detection challenging. A coherent detection scheme, adapted from optical communication systems, has been recently showntoachieveexcellentdetectionlimits,usingasimplefixed-wavelengthsource. Herewe present, for the first time, a theoretical model to determine the fundamental limit of detection of suchacoherentread-outsystem,forbothinterferometricandresonantsensors. Basedonthis analysis,weprovideguidelinesforsensoroptimizationinthepresenceofopticallossesandshow thatinterferometricsensorsarepreferableoverresonantstructureswhenthesensorsizeisnot limited bythe available samplevolume.