  In modern particle physics experiments wavelength-shifting and scintillating
fibres based on plastic polymers are used for tracking and calorimetry. In this
review the role of photon trapping efficiencies, transmission functions and
signal response times for common multimode active fibres is discussed.
Numerical simulations involving three dimensional tracking of skew rays through
curved fibres demonstrate the characteristics of trapped light. Of practical
interest are the parametrisations of transmission functions and the minimum
permissible radius of curvature. These are of great importance in today's
experiments where high count rates and small numbers of photoelectrons are
encountered. Special emphasis has been placed on the timing resolution of fibre
detectors and its limitation due to variations in the path length of generated
photons.
