Femtometer resolution optical wavelength meter

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 high-resolution 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.