Any angle measured from the longitudinal center line up to the maximum acceptance angle of an incident ray that will be accepted by the waveguide. The maximum acceptance angle is dependent on the indices of refraction of the two mediums. A contoured exposure to UV light to eliminate the side lobes.
Light is reflected.
More than one grating in a length of fiber. In optical waveguides it is primarily due to absorption losses and scattering losses. Reject a broad band of light. Made by combining chirped or apodized gratings with mode coupling gratings. Potential information-carrying capacity, the amount of information that can be sent over a communication channel, increases with the frequency.