With the development in communications of dense
wavelength-division-multiplexed (DWDM) systems, there is an increasing
need to determine the wavelength of lasers to a very high
resolution. The Fabry-Perot interferometer offers potentially highresolution
wavelength measurement; however, it suffers from an
ambiguity in resolving different fringe orders. We present here a
novel method that solves this ambiguity using the wavelength dependence
of the Brillouin shift in optical fibers. This technique is
shown to measure the wavelength of light with a resolution to as
fine as 12 fm. The new method is also ideally suited to measuring
the wavelength of pulsed light as a pulse travelling down an optical
fiber generates a continuous stream of backscattered light that may
be readily analyzed