A wideband wavelength discriminator using 3/spl times/3 directional coupler

Fiber interferometers have been widely used as wavelength discriminators of fiber Bragg grating sensors. The positive and negative slopes of the interferometer's transfer function can be used as an effective sensors wavelength discriminator, which convert Bragg wavelength shift to variations of the transmitted optical intensity. However due to its periodicity, the dynamic range of measurement is limited by the quasi-linear range in the slopes. The fluctuating phase bias, which is temperature dependent, is also a limiting factor of interferometric measurement because it leads to the variation in the system sensitivity. To solve the problems while maintaining high-resolution, a newly developed quadrature signal processing is applied to the photodetector signals.