OPTICAL FIBER DIFFRACTION GRATING HAVING INTERNAL GAP CLADDING FOR LESSENING SHORT-WAVELENGTH CLADDING MODE LOSS

摘要

PROBLEM TO BE SOLVED: To provide an optical fiber Bragg diffraction grating provided with a ring consisting of gap regions (gaps) extending in a longitudinal direction apart spacings around a core in order to lessen short-wavelength cladding mode loss. SOLUTION: This invention is based on the finding that the internal gap claddings formed to necessary dimensions apart the suitable spacings substantially lessen the short-wavelength cladding mode loss in the fiber Bragg diffraction grating. The fiber Bragg diffraction grating is provided with the ring consisting of the gap regions extending in the longitudinal direction apart the proximate spacings in the glass enclosing the periphery of the core. The gaps are formed to the spacings parted by thin glass webs having a thickness below the wavelength of the light to be transmitted and are arranged around the core at distances of 1 to 10 wavelengths from the center of the core. The thin webs limit the passage of the light between the gaps. The combinations of the webs and the gaps act as the internal thin claddings to support the cladding mode fewer than the conventional glass claddings and considerably provide the increase of the wavelength intervals between the Bragg resonance and the first cladding mode resonance.