Investigations on fiber bragg gratings for fiber optic communication systems

Abstract

This thesis presents the Investigations on Fiber Bragg Gratings for Fiber Optic Communication Systems. A Fiber Bragg Grating (FBG) is a periodic or aperiodic perturbation of the effective absorption coefficient or the effective refractive index of an optical waveguide. A Bragg Grating can reflect a predetermined narrow or broad range of wavelengths of light incident on the grating, while passing all other wavelengths of the light. FBG can be fabricated by exposing a photosensitized fiber with an intensive pattern of excimer laser radiation. Fiber Bragg Gratings have emerged as important components in a variety of applications. Their unique filtering properties and versatility as in-fiber devices is illustrated by their use in Wavelength-Stabilized Lasers, Fiber Lasers, Remotely Pump Amplifiers, Raman Amplifiers, Phase Conjugators, Wavelength Converters, Passive Optical Networks, Wavelength Division Multiplexers (WDM s), Demultiplexers, Add/drop Multiplexers, Dispersion Compensators, and Gain Equalizers. They are also stimulating growth in fiber optic applications outside of telecommunications, such as nonlinear frequency conversion, spectroscopy, and remote sensing. Since the output of a Bragg grating sensor is present in the wavelength domain it requires sophisticated circuits to measure wavelength shift. One way of interrogating a Bragg grating sensor is to use a tunable filter. One option is the Fabry Perot interferometer with a cavity length controlled by a piezoelectric actuator. Although this approach has a good resolution and is independent of light intensity variations, it is relatively slow and expensive. Chirped Fiber Bragg Grating (CFBG) can also be used as the wavelength-sensitive component. A chirped Bragg grating can be used as a device that converts wavelength into delay. By measuring this delay, the wavelength of light corresponding to the delay can be found. Very fast electronic circuitry is required for resolving this delay and it proves to be very expensive.