Patent ID: 6864980

Claim:
A wavelength detector comprising: a beam splitter block having first and second surfaces, the beam splitter block receiving an input beam, tapping off first and second beams that are spatially separated from one another, the first and second beams being output from the first surface, and outputting a third beam from the second surface to proceed to an application; an optical element on the beam splitter block providing a further optical function to at least one of the first and second beams, each of the first and second surfaces of the beam splitter block providing at least one of the tapping and the further optical function to at least one of the first and second beams; a linear filter in an optical path of one of the first and second beams to form a filter beam, the one of the first and second beams not filtered by the linear filter serving as a reference beam, the linear filter having a wavelength dependent response; a first detector receiving the filter beam; and a second detector receiving the reference beam.