FORMATION OF OPTICAL WAVEGUIDE TYPE DIFFRACTION GRATING AND FORMING DEVICE THEREFOR

摘要

PURPOSE: To provide a forming device for optical waveguide type diffraction gratings having a reflection characteristic of good wavelength selectivity. CONSTITUTION: An optical fiber 1 has a core added with Ge and the refractive index of its core part increases when the core part is irradiate with light of a wavelength about 240nm. A UV laser beam 2 having such wavelength is bisected by a beam splitter 3 and the flank of the optical fiber 1 is irradiated with the respective beams via a mask 8 from mirrors 4, 5. The bisected laser beams interfere with each other in the core part of the optical fiber 1. The core part is irradiated with the interference fringes. The transmittance of the mask 8 is large in the middle and is smaller toward both sides and, therefore, the interference fringes formed in the core part of the optical fiber 1 have a gentle light intensity distribution. The changes in the refractive index are induced in the patterns meeting the same and the diffraction gratings are formed on the core.