OPTICAL SYSTEM AND OPTICAL DEVICE USING LONG FREQUENCY SPECTRUM MOLDING DEVICE

摘要

PURPOSE: To remove unused excitation energy in a fiber amplifier by providing a long-period spectrum forming device which shifts light of unnecessary wavelength from a guided mode to a non-guided mode. CONSTITUTION: An optical fiber 10 has a core 11 enclosed with a clad 12 having a low refractive index. The core 11 includes one or more long-period gratings 13, and each grating includes plural refractive index perturbations 14 which are separated by a period distance Λ and have a width (w). These perturbations are formed in the glass core of the fiber and, preferably form an angle θ(2 deg.<=θ<=90 deg.) to the major axis of the fiber. This fiber is so designed that wide band light with about λ as the center wavelength is transmitted. The interval Λof these perturbations shifts transmitted light in the area of a selected wavelength λp from the guided mode to the non-guided mode, and as the result, the intensity of light in the band with the wavelength λp as the center is reduced.