The concept of the beam propagation factor M2 is extended for chromatic laser beams. The definition of the beam propagation factor can be generalized with the weighted effectivewavelength.
The six — wavelengths pyrometers with six interference filters for effectivewavelength defined and with optical fibers for beam split were developed by the U. S. and CEC scientists inl980's.
Its objective is trying to offer the best balance among delay, load and the cost of wavelength conversion in addition to improving the effectivewavelength utilization and failure restoring rate.