| 摘要 |
PROBLEM TO BE SOLVED: To provide a refractive index grating which is accompanied by a photosensitive profile including at least one 'adjustment area' in a core of a waveguide, in a single mode inclined grating within an optical waveguide. SOLUTION: When the photosensitive profile of the waveguide is suitably selected, a result bringing 'supernal' in a coupling from LP01,f to LP01,b is obtained. That is, the angular range of an inclined angleθthat a core mode coupling is substantially zero (that is, smaller than -30 dB) is larger than 0.1 deg., or is larger than 0.2 deg. or 0.5 deg. and is largely increased compared to an angular range obtained when the 'adjustment area' does not exist within the core of the waveguide. When the angular range is increased, the manufacture of the grating is more facilitated. In a favorable embodiment, the grating is provided with a large cladding loss (larger than 20 dB) and a band width (larger than 20 nm). A method for trimming the grating is also disclosed.
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