Incoherent optical sensors based simply on the measurement of the amplitude of light transmitted by the sensor head are subject to errors unless care is taken to ensure the stability of light sources and detectors, the constancy of launch conditions and freedom from unintentional fibre microbending losses and variations in connector coupling. Sensors based on spectral filtering techniques, however, make use of wavelength-dependent variations in transmission, reflection or scattering processes which greatly exceed the normal spectral variations of transmission which may normally occur in optical fibre and connectors. This paper reviews the types of spectral filtering sensors which have been developed with classification into analogue and digital sensors.
J P Dakin,
"Analogue And Digital Extrinsic Optical Fibre Sensors Based On Spectral Filtering Techniques", Proc. SPIE 0468, Fibre Optics '84, (15 August 1984); doi: 10.1117/12.941675; https://doi.org/10.1117/12.941675