  Coating Brownian noise is the dominant noise term, in a frequency band from a
few tens to a few hundreds Hz, for all Earth-bound detectors of gravitational
waves. Minimizing such noise is mandatory to increase the visibility distance
of these instruments, and eventually reach their quantum limit. Several
strategies are possible to achieve this goal. Layer thickness optimization is
the simplest option, yielding a sensible noise reduction with limited
technological challenges. Experimental results confirm the accuracy of the
underlying theory, and the robustness of the design.
