In the calibration with a fibre, a single-mode fibre or a multimode fibre may be used. A singlemode
fibre may be advantageous because of its reproducible beam characteristics, but may
not be available for all wavelengths. If a multimode fibre is used, then full excitation is
preferred because this excitation can be more easily reproduced. A launching device may be
necessary to create the appropriate excitation. Note that multimode fibres will emit irregular
beam patterns (speckle patterns) when driven by a laser diode; this will result in an increased
calibration uncertainty. Optical power in the cladding (cladding modes) should be removed with
an appropriate mode stripper or launching device, if necessary.