A variable optical fiber grating is provided which is compact, and in which an
amount of chromatic dispersion can be effectively varied without changing an operating
center wavelength. Also provided is a dispersion compensator, which uses this variable
optical fiber grating. The fixing member is formed by providing an outer cylinder
2 comprising a material with a lower coefficient of linear expansion around
an inner cylinder 1 comprising a material with a higher coefficient of linear
expansion, and an optical fiber grating is fixed in a groove 3 formed on
the inner cylinder 1. By adjusting the fixing position of the optical fiber
grating, an expansion coefficient and contraction coefficient of the optical fiber
grating which follows the expansion and contraction of the material with the higher
coefficient of linear expansion, differ along the longitudinal direction of the
optical fiber grating, so that an amount of chromatic dispersion is controlled.
