The German Agenda "Optical Technologies for the 21st Century" describes optical
technologies as enabling technologies for other technical fields and their applica-
tions in the future which has just recently been confirmed by a study of the
German Ministry of Education and Research (Bundesministerium flir Bildung
und Forschung, BMBF, [2]). Already at the very beginning of this twenty-first
century, optical sensors play a vital role in virtually every technical application:
from simple light barriers to complicated white-light interferometers, from auto-
motive rain sensors to high-resolution scanning near-field optical microscopes,
there are sensors to measure a wide variety of measurement properties.
Optical sensors offer various advantages over their electronic and/or mechanical
counterparts. Apart from their wide dynamic range and lower noise levels, optical
sensors react on any change in the measurement properties literally with the speed
of light. Also, the noncontact nature of the optical measurement avoids all system-
atic errors that come with tactile techniques. Consider the measurement of brake
path lengths in vehicle testing: a well-established technique employs a combina-
tion of a so-called fifth wheel with an incremental encoder. To calculate the
measurement result with sufficient measurement uncertainty, the wheel diameter
must be known with the same precision. Here, the wheel slip will introduce sys-
tematic measurement errors. This is why the majority of automobile manufactur-
ers relies on sensors that determine dynamic measurement properties from the
optical cross-correlation between an image of the road surface and an optical
grating 13].