Spatial light modulator and a method for driving the same

A driving method for a spatial light modulator,

• wherein said spatial light modulator includes a pair of facing transparent electrodes, and a light-modulating layer and a photoconductive layer provided between said transparent electrodes, said light-modulating layer having different optical states depending on an applied charge amount, said light-modulating layer having:
• a first optical state when said applied charge amount is a first threshold charge amount or more;
• a second optical state then said applied charge amount is a second threshold charge amount or less;
• and a spatially uniform intermediate state between said first optical state and said second optical state depending on said applied charge amount,
• wherein said photoconductive layer has rectification, and generates, when said photoconductive layer is in a reversed bias condition, a photoelectric current having a magnitude depending on an intensity of writing light incident on said photoconductive layer,
• wherein one period of a waveform of a driving voltage includes an erasure period in which the photoconductive layer is in a forward bias condition and a charge amount larger than said first threshold charge amount is applied, and a writing period in which the photoconductive layer is in a reversed bias condition so as to generate a photoelectric current having a magnitude depending on an intensity of writing light, and
• wherein said method includes a step of applying said driving voltage to said two transparent electrodes, so that in said writing period, said applied charge amount to said light-modulating layer is kept in the range of said first threshold charge amount or more when the intensity of said writing light is a first threshold light intensity or lower, and said applied charge amount to said light-modulating layer is reduced to said second threshold charge amount or less when the intensity of said writing light is a second threshold light intensity of higher.

A driving method for a spatial light modulator,

• wherein said spatial light modulator includes a pair of facing transparent electrodes, and a light-modulating layer and a photoconductive layer provided between said transparent electrodes, said light-modulating layer having different optical states depending on an applied charge amount, said light-modulating layer having:
• a first optical state when said applied charge amount is a first threshold charge amount or more;
• a second optical state when said applied charge amount is a second threshold charge amount or less;
• and a spatially uniform intermediate state between said first optical state and said second optical state depending on said applied charge amount, and
• wherein said driving method includes the steps of:
• applying a driving voltage to said two transparent electrodes;
• irradiating said spatial light modulator with writing light;
• measuring an output light intensity of said spatial light modulator with respect to at least one writing light intensity;
• detecting a change of the output light intensity as a function of time;
• and
• performing a feedback to at least one of the writing light intensity and the driving voltage, in accordance with the detected change of the output light intensity, in order to keep a ratio of writing light intensity to output light intensity approximately constant.

A spatial light modulating apparatus comprising:

• a spatial light modulator including a light-modulating layer and a photoconductive layer provided between two facing transparent electrodes, said light-modulating layer having different optical states depending on an applied charge amount, said light-modulating layer having:
• a first optical state when said applied charge amount is a first threshold charge amount or more;
• a second optical state when said applied charge amount is a second threshold charge amount or less;
• and a spatially uniform intermediate state between said first optical state and said second optical state depending on said applied charge amount;
• means for applying a driving voltage to said two transparent electrodes;
• means for irradiating said spatial light modulator with writing light;
• means for measuring an output light intensity of said spatial light modulator with respect to at least one writing light intensity;
• means for detecting a change of the output light intensity as a function of time with respect to said at least one writing light intensity;
• and
• means for performing a feedback to at least one of the writing light intensity and the driving voltage in accordance with the detected change of the output light intensity in order to keep a ratio of writing light intensity to output light intensity approximately constant.