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.
