The present invention relates to an optical waveguide type grating element and
others in structure for decreasing absolute values of chromatic dispersion occurring
in selective reflection of each of signal channels in a reflection band. The optical
waveguide type grating element is provided with an optical waveguide in which signal
light containing a plurality of signal channels spaced at a channel spacing i
propagates, and a grating which is an index modulation formed over a predetermined
range of the optical waveguide. Particularly, the optical waveguide type grating
element has a transmittance of -;20 dB or less for each of the signal channels
in the reflection band, and has a reflectance of -;20 dB or less for each of signal
channels outside the reflection band. Furthermore, a deviation of a group delay
time of each of the signal channels in the reflection band, which is caused by
reflection in the grating, is 10 ps or less in a wavelength range of (CH-;i0.375/2)
or more but (CH+i0.375/2) or less, where
CH is a center wavelength of each signal channel.
