Wavelength monitoring in fiber-optic sensors using a tunable optical waveguide filter

In sensor systems that are based on optical fiber Bragg gratings, the center wavelength of the grating reflection must be determined with a precision on the order of hundredths of a nm over an operating range of several nm. Systems have been reported using interference filters, long-pass transmission filters and Mach-Zehnder interferometers to provide the required wavelength discrimination. With these there is a trade-off to be made between the conflicting requirements of a large filtering slope (in %/nm) and a wide range of operating wavelengths. This paper reports on the use of a GaAs/AlGaAs multiple quantum well optical waveguide modulator to serve as a sharp-edged filter that can be voltage tuned over several nm.