Calibration of a spatial light modulator

Abstract

A method for calibrating a spatial light modulator comprising an array of channels includes selecting a plurality of channel sets; operating each of the channel sets to provide corresponding output radiation; providing a detector for measuring the output radiation; determining a plurality of intensity values, each representing an intensity of the output radiation provided by a different one of the channel sets; providing a correction factor for each of the channels sets, wherein each correction factor remains constant during a subsequent recalibration of the spatial light modulator; modifying each determined intensity value in accordance with a corresponding one of the correction factors; determining a difference between one of the modified intensity values and a target intensity value; and reducing the determined difference by adjusting a control level of at least one channel in the channel set corresponding to the one of the modified intensity values.

1 . A method for calibrating a spatial light modulator comprising an array of individually addressable channels, the method comprising:
 selecting a plurality of channel sets from the array of channels;   operating each of the channel sets to provide corresponding output radiation;   providing a detector for measuring the output radiation provided by each of the channels sets;   determining a plurality of intensity values, wherein each intensity value is a single value representing an intensity of the output radiation provided by a different one of the channel sets;   providing a correction factor for each of the channels sets, wherein each correction factor remains constant during a subsequent recalibration of the spatial light modulator;   modifying each determined intensity value in accordance with a corresponding one of the correction factors;   determining a difference between one of the modified intensity values and a target intensity value; and   reducing the determined difference by adjusting a control level of at least one channel in the channel set corresponding to the one of the modified intensity values.   
     
     
         2 . A method according to  claim 1 , wherein each correction factor corrects a systematic error associated with a measurement made by the detector of the output radiation provided by each of the channel sets. 
     
     
         3 . A method according to  claim 1 , wherein the detector is a single-value detector. 
     
     
         4 . A method according to  claim 1 , wherein each of the channel sets comprises a plurality of channels, and operating each of the channel sets to provide corresponding output radiation comprises operating all the channels in each channel set to provide corresponding output radiation. 
     
     
         5 . A method according to  claim 4 , comprising separately operating each of the channels sets to provide corresponding output radiation. 
     
     
         6 . A method according to  claim 1 , wherein the target intensity value is equal to a second one of the modified intensity levels. 
     
     
         7 . A method according to  claim 1 , wherein the target intensity value is determined by a distribution of the modified intensity values. 
     
     
         8 . A method for calibrating a spatial light modulator comprising an array of individually addressable channels, the method comprising:
 selecting a plurality of channel sets from the array of channels, each channel set comprising a plurality of channels;   operating each of the channel sets to provide corresponding first output radiation;   determining a plurality of intensity values, each of the intensity values corresponding to the first output radiation provided by a different one of the channel sets;   selecting a first intensity value from the plurality of intensity values, wherein the first intensity value corresponds to a first channel set in the plurality of channel sets;   determining a difference between the first intensity value and a first target intensity value;   performing a channel set adjustment, the channel set adjustment comprising adjusting a control level of each channel in the first channel set to reduce the determined difference between the first intensity value and the first target intensity value;   selecting a plurality of channel subsets from the first channel set;   providing a correction factor for each channel subset; and   performing a channel subset adjustment, the channel subset adjustment comprising adjusting a control level of at least one channel in each of at least one of the channel subsets in accordance with a corresponding one of the correction factors.   
     
     
         9 . A method according to  claim 8 , wherein the channel subset adjustment is performed after performing the channel set adjustment. 
     
     
         10 . A method according to  claim 9 , comprising employing each of the correction factors in a subsequent recalibration of the spatial light modulator, wherein each correction factor remains unaltered during the subsequent recalibration of the spatial light modulator. 
     
     
         11 . A method according to  claim 10 , wherein the channel subset adjustment is performed without performing the channel set adjustment during the subsequent recalibration of the spatial light modulator. 
     
     
         12 . A method according to  claim 8 , wherein the channel subset adjustment comprises:
 selecting a first channel subset from the plurality of channel subsets;   operating the first channel subset to emit second output radiation;   determining a second intensity value for the second output radiation;   modifying the second intensity value in accordance with the correction factor corresponding to the first channel subset;   determining a difference between the modified second intensity value and a second target intensity value; and   performing the channel subset adjustment on the first channel subset to reduce the determined difference between the modified second intensity value and the second target intensity value.   
     
     
         13 . A method according to  claim 12 , wherein the first target intensity value is equal to one of the plurality of intensity values other than the first intensity value. 
     
     
         14 . A method according to  claim 12 , wherein the first target intensity value is determined by a distribution of the plurality of intensity values. 
     
     
         15 . A method according to  claim 12 , wherein the second target intensity value is equal to the first target intensity value. 
     
     
         16 . A method according to  claim 8 , wherein each of the channel sets is operated separately to provide corresponding first output radiation. 
     
     
         17 . A method for calibrating a spatial light modulator comprising an array of individually addressable channels, the method comprising:
 selecting a plurality of first channel sets from the array of channels, each of the first channel sets comprising X channels;   operating each of the first channel sets to provide first output radiation;   determining a plurality of first intensity values, wherein each first intensity value is determined for the first output radiation provided by a different one of the first channel sets;   reducing a difference between one of the first intensity values and a first target intensity value by adjusting control levels of a group of the channels in the array of channels;   selecting a plurality of second channel sets from the array of channels, each of the second channel sets comprising Y channels, wherein Y is less than X;   operating each of the second channel sets to provide second output radiation, wherein at least one of the operated second channel sets comprises a portion of the group of the channels operated with the adjusted control levels;   determining a plurality of second intensity values, wherein each second intensity value is determined for the second output radiation provided by a different one of the second channel sets;   determining a correction factor for each of the second channel sets;   modifying each second intensity value in accordance with the correction factor determined for the second channel set corresponding to the second intensity value; and   reducing a difference between at least one of the modified second intensity values and a second target intensity value by adjusting a control level of at least one channel in each of the second channel sets corresponding to each of the at least one of the modified second intensity values.   
     
     
         18 . A method according to  claim 17 , wherein each correction factor is determined based at least on an average of all the second intensity values. 
     
     
         19 . A method according to  claim 18 , wherein each correction factor is determined based at least on the second intensity value corresponding to the second channel set associated with the correction factor. 
     
     
         20 . A method according to  claim 19 , wherein each correction factor is determined based at least on a value derived by dividing the second intensity value corresponding to the second channel set associated with the correction factor by the average of all the second intensity values. 
     
     
         21 . A method according to  claim 17 , comprising normalizing each second intensity value to the average of all the second intensity values. 
     
     
         22 . A method according to  claim 21 , comprising fitting a mathematical curve to the normalized second intensity values, wherein each correction factor is determined based at least on the mathematical curve. 
     
     
         23 . A method according to  claim 22 , wherein modifying each second intensity value comprises dividing each second intensity value by the correction factor determined for the second channel set corresponding to the second intensity value. 
     
     
         24 . A method according to  claim 17 , comprising providing a detector for measuring each second output radiation, wherein each correction factor is determined for correcting a systematic error associated with a measurement made by the detector. 
     
     
         25 . A method according to  claim 17 , comprising employing each of the correction factors in one or more subsequent recalibrations of the spatial light modulator, wherein each correction factor remains constant during each of the one or more subsequent recalibrations of the spatial light modulator. 
     
     
         26 . A method according to  claim 17 , wherein each of the first channel sets comprises one or more of the second channel sets. 
     
     
         27 . A method according to  claim 17 , wherein the group of channels includes the first channel set corresponding to the one of the first intensity values. 
     
     
         28 . A method according to  claim 17 , wherein adjusting the control levels of the group of the channels comprises adjusting a control level of each channel in the first channel set corresponding to the one of the first intensity values by a same amount. 
     
     
         29 . A method according to  claim 17 , wherein operating each of the first channel sets to provide first output radiation comprises separately operating each of the first channel sets. 
     
     
         30 . A method according to  claim 17 , wherein operating each of the second channel sets to provide second output radiation comprises separately operating each of the second channel sets. 
     
     
         31 . A method according to  claim 17 , wherein each second channel set of two of the operated second channel sets includes at least one common channel and at least one different channel.