Patent ID: 7251410

Claim:
A variable optical attenuator comprising: an input and output unit that inputs light from outside and that outputs light to outside; a polarization rotator element that includes a liquid crystal, sandwiched between a pair of electrodes, and rotates a polarizing direction of a light traveling therethrough by controlling a voltage applied to the liquid crystal through the electrodes; and an optical-path-length correction plate that is arranged between the input and output unit and the polarization rotator element, and that separates the light input from the input and output unit into p-polarized light and s-polarized light to be output to the polarization rotator element, and combines the p-polarized light and the s-polarized light reflected from the polarization rotator element into light to be output to the input and output unit, wherein the p-polarized light and the s-polarized light travel through the optical-path-length correction plate along different optical paths of substantially equal length, and an amount of light output from the input and output unit is determined by a birefringence characteristic of the liquid crystal that is determined by the voltage applied to the liquid crystal through the electrodes.