METHOD FOR FORMING REFRACTIVE INDEX PERTURBATION AND METHOD FOR FORMING GRATING PATTERN

摘要

PROBLEM TO BE SOLVED: To form a grating having a space dependent period which can specify a wide range of function forms as a space dependency. SOLUTION: Beams which are not on two same parallel straight lines of electromagnetic radiation having a photochemistry wavelengthλare generated, and a periodic interference pattern is generated in the axial direction by irradiating a part of medium with the beams so that the beams intersect at an angleϕ. The irradiated portion of an interference pattern is displaced in the axial direction with respect to the medium so that the local coherence of the interference pattern is stored in the space. A productλ×0.5 csc (ϕ/2) is changed in the space so that a grating pattern has a period which is quasiperiodic and changes spatially.