Optical waveguide diffraction grating device, method for fabricating optical waveguide diffraction grating device, multiplexing/demultiplexing module, and optical transmission system

A diffraction grating device in which a diffraction grating based on perturbation of refractive index is formed through a predetermined range in a light guide direction in an optical waveguide and in which said diffraction grating selectively reflects light in a reflection band out of light guided through the optical waveguide,

• wherein, where a first band is defined as a wavelength band with a maximum bandwidth out of continuous wavelength bands for which the transmittance is not more than T0 (in units of dB) and where a second band is defined as a wavelength band between a maximum wavelength and a minimum wavelength out of wavelengths for which the reflectance is R0 (in units of dB),
• the perturbation of refractive index of said diffraction grating is of antero-posterior symmetry with respect to the center on a center position of said predetermined range,
• T0 is not more than −20 dB,
• R0 is not more than −20 dB,
• a ratio (B1/B2) of a width B1, of said first band (in units of nm) to a width B2 of said second band (in units of nm) is not less than 0.3, and
• a maximum group delay difference (in units of ps) caused by reflection of light in said first band by said diffraction grating is not more than 0.011×exp(7.86×B1/B2−0.045×R0)/B1.