Patent ID: 7336250

Claim:
A method of statically driving a liquid-crystal optical-modulation device by applying an alternating electric field to a liquid crystal that is included in the liquid-crystal optical-modulation device and sandwiched by a common electrode and a segment electrode, the alternating electric field being produced by a drive signal that is pulse-width modulated based on modulation data, wherein the drive signal is a difference between a common signal and a segment signal that are applied to the common electrode and the segment electrode, respectively, in a first period in which the alternating electric field has a first polarity, the drive signal has a first ON-voltage and a first OFF-voltage, and in a second period in which the alternating electric field has a second polarity, the drive signal has a second ON-voltage and a second OFF-voltage that respectively differ from the first ON-voltage and the first OFF-voltage the absolute value of the first OFF-voltage and the absolute value of the second OFF-voltage are equal to an absolute value of a bias voltage that is a minimum voltage for changing a phase of light passing through the liquid crystal, a duration of the first ON-voltage and a duration of the second ON-voltage vary according to a phase shift amount of the light, the segment signal is a binary signal having a first segment voltage and a second segment voltage, and the common signal is a binary signal having a first common voltage higher than the first segment voltage by the bias voltage and a second common voltage lower than the second segment voltage by the bias voltage.