An optical fiber grating is a small segment within an optical fiber altered to act as a selective filter for light. This treated area functions like a specialized mirror, reflecting a specific wavelength of light while allowing all other wavelengths to pass through. a few millimeters or centimeters, and the period is of the order of. Diffraction gratings are optical components critical for a wide variety of applications including spectrometers, other analytical instruments, telecommunications, and laser systems.