Patent ID: 6130973
Filing Date: 2000-10-10
Classification: G02B

Abstract:
A method to photoinduce a modulated refractive index change in a length of an optical medium, the optical medium being photosensitive and having at least one waveguiding axis, the modulated refractive index change having a variable intensity profile and a controlled average value along the waveguiding axis, the method comprising steps of:performing consecutive writing steps, each of the writing steps having an exposure time selected to generate the controlled average value of the modulated refractive index change, each writing step comprising substeps of:a) exposing for the entire exposure time a segment of the optical medium to a writing radiation beam having an angle of incidence on the segment of the optical medium that is generally perpendicular to the waveguiding axis, the writing radiation beam also having an interference pattern generated therein to produce the modulated refractive index change; andb) dithering the angle of incidence of the writing radiation beam for a fraction less than 1 of the exposure time to blur the interference pattern and partially replace the modulated refractive index change by a DC refractive index change, the fraction of the exposure time being selected for each writing step to define the variable intensity profile of the modulated refractive index change;translating the optical medium along the waveguiding axis between each writing step to expose a different segment of the optical medium at each writing step; andperforming a sufficient number of writing steps and translating steps to cover the length of the optical medium.