Patent ID: 7257292

Claim:
A variable dispersion compensator comprising: a first variable dispersion-compensating unit having, as wavelength dispersion characteristics, a frequency period FSR 1 , a frequency band W 1 approximated with a straight line of a gradient “a 1 ” in the FSR 1 , and a gradient “a 2 ” of a line segment connecting a maximum point and minimum point of a wavelength dispersion characteristics curve in a band W 2 adjacent to the band W 1 in the FSR 1 , and a variable dispersion control function for shifting the wavelength dispersion characteristics in a frequency axis; and a second variable dispersion-compensating unit having, as wavelength dispersion characteristics, a frequency period FSR 2 , a frequency band W 3 approximated with a straight line of a gradient “a 3 ” in the FSR 2 , and a variable dispersion control function for shifting the wavelength dispersion characteristics in the frequency axis; wherein: the band W 1 is greater than W 2 , an absolute value of the gradient “a 2 ” of the line segment connecting the maximum point and minimum point of the wavelength dispersion characteristics curve in the band W 2 is larger than an absolute value of the gradient “a 1 ”; the gradients “a 1 ,” and “a 3 ” are opposite to each other in sign and essentially equal to each other in absolute value; the first variable dispersion-compensating unit and the second variable dispersion-compensating unit are cascade-connected to each other; a range of variable dispersion quantities in a plus direction is asymmetrical with respect to a range of variable dispersion quantities in a minus direction; and wavelength dispersion is assigned to one optical signal or to plural optical signals with different wavelengths.