Light shuttering for waveguide pupil expansion
A light shuttering device comprises a plurality of liquid crystal cells, wherein each liquid crystal cell is operable in a first optical state or a second optical state in response to a respective first or second drive signal. A drive circuit comprises a plurality of switches and a drive controller. Each switch is arranged to output the respective first or second drive signal to a respective liquid crystal cell. The drive controller is arranged to sequentially update the output of each switch during an update cycle. The drive circuit is arranged to determine the order in which the switches are sequentially updated during an update cycle based on any changes to the respective drive signals that will be made during the update.
1 . A light shuttering device comprising:
a plurality of liquid crystal cells, wherein each liquid crystal cell is operable to switch between a first optical state or a second optical state in response to a respective first or second drive signal, and wherein individual liquid crystal cells take longer to switch from the second optical state to the first optical state than from the first optical state to the second optical state;
a drive circuit comprising: (i) a plurality of switches, wherein each switch is arranged to output the respective first or second drive signal to a respective liquid crystal cell, and (ii) a drive controller arranged to sequentially update the output of each switch during an update cycle; and
wherein the drive circuit is arranged to determine an order in which the switches are sequentially updated during an update cycle based on any changes to the respective drive signals that will be made during the update where the order in which the switches are sequentially updated during an update cycle comprises updating the output of switches that will be changed from the second drive signal to the first drive signal before updating the output of any other switches.
2 . The light shuttering device of claim 1 , wherein the order in which the switches are sequentially updated during an update cycle comprises updating the output of any switches that will be changed from the first drive signal to the second drive signal after all switches that will be changed from the second drive signal to the first drive signal have been updated.
3 . The light shuttering device of claim 1 , wherein the plurality of switches comprises a plurality of digital switches, wherein each digital switch comprises a first input arranged to receive the first drive signal and a second input arranged to receive the second drive signal.
4 . The light shuttering device of claim 3 , further comprising a capacitor associated with each digital switch, wherein each capacitor is arranged to receive a signal from the drive controller during an update cycle and to provide a control input to the respective digital switch to selectively output the respective first or second drive signal to a respective liquid crystal cell, wherein the capacitor is arranged to hold the control input to the digital switch between updates.
5 . The light shuttering device of claim 1 , wherein the drive circuit further comprises a multiplexing circuit for sequentially routing control signals from the drive controller to update the output of each of the switches during an update cycle.
6 . The light shuttering device of claim 1 , wherein the liquid crystal cells are arranged in a one-dimensional array.
7 . The light shuttering device of claim 1 , wherein the light shuttering device is arranged to restrict an area of an output face of an optical replicator that is visible from a viewing plane, and wherein the optical replicator is arranged to output a plurality of replicas of a hologram.
8 . The light shuttering device of claim 1 , wherein the light shuttering device is disposed between a display device and a viewer.
9 . The light shuttering device of claim 1 , wherein at least one update cycle is completed in one of (i) less than about 100 milliseconds or (ii) less than about 200 milliseconds.
10 . The light shuttering device of claim 1 , wherein an update cycle is initiated if a change to a viewing position of a viewer is detected.