Laser illumination system with reduced speckle

Abstract

A despeckling device and method in which an optical path difference staircase element is disposed between a fly's eye lens array and the image plane in a position near the focus position of the fly's eye lens array, and a laser generating unit generates and transmits pulsed laser beams to the optical path difference staircase element, wherein the pulsed laser beams are driven at a very short pulsed rate.

1 . A despeckle unit, comprising:
 a first transparent element comprising a plurality of microlenses to receive collimated light having a coherence length and to output a beamlet from each of the microlenses; and   a second transparent element comprising a plurality of steps having a one-to-one correspondence with the plurality of microlenses, wherein each of the steps receives one of the beamlets and outputs the beamlet to an image plane, where a height of each step of at least two of the steps is configured to produce an optical path difference of the beamlet longer than the coherence length,   wherein the second transparent element is disposed approximately at a foci of the beamlets output from the first transparent element.   
     
     
         2 . The despeckle unit according to  claim 1 , wherein the collimated light comprises pulsed laser beams driven by a pulse of less than 10 nanoseconds. 
     
     
         3 . The despeckle unit according to  claim 2 , wherein the pulse reduces a coherence of the laser beam and the steps are configured to further reduce the coherence of the laser beam not reduced by the pulse, to substantially despeckle the pulsed laser beam. 
     
     
         4 . The despeckle unit according to  claim 1 , wherein the at least two of the steps are configured as a one-dimensional staircase and the microlenses are configured as a one-dimensional array of microlenses. 
     
     
         5 . The despeckle unit according to  claim 1 , wherein:
 the collimated light is linearly polarized with a polarization direction;   the second transparent element comprises at least one physical step, comprising:
 an optical wave plate disposed on a first portion of the at least one physical step which is configured to change the polarization direction of the collimated light, and 
 a second portion of the at least one physical step which does not include the optical wave plate; and 
   the optical waveplate and the second portion each comprise one of the steps having the one-to-one correspondence with the microlenses.   
     
     
         6 . The despeckle unit according to  claim 1 , wherein:
 the collimated light is linearly polarized with a polarization direction;   the second transparent element comprises at least one physical step, comprising:
 a first optical wave plate disposed on a first portion of the at least one physical step which is configured to change the linearly polarized light to right circular polarized light, and 
 a second optical wave plated disposed on a second portion of the at least one physical step which is configured to change the linearly polarized light to left circular polarized light; and 
   the first optical wave plate and the second optical wave plate each comprise one of the steps having the one-to-one correspondence with the microlenses.   
     
     
         7 . A despeckle unit, comprising:
 a first transparent element comprising a plurality of microlenses to receive collimated light having a coherence length and to output a beamlet from each of the microlenses; and   a second transparent element comprising a plurality of steps having a one-to-one correspondence with the plurality of microlenses, wherein each of the steps receives one of the beamlets and outputs the beamlet to an image plane, wherein a height of each step of at least two of the steps is configured to produce an optical path difference of the collimated light longer than the coherence length,   wherein the second transparent element is disposed in a location relative to the first transparent element such that edges of the second transparent element parallel to an optical path of the beamlets exiting the second transparent element do not diffract the beamlets.   
     
     
         8 . The despeckle unit according to  claim 7 , wherein the collimated light comprises pulsed laser beams driven by a pulse of less than 10 nanoseconds. 
     
     
         9 . A despeckling laser unit to despeckle a laser beam, comprising:
 a laser generating unit to generate a pulsed laser beam having a coherence length;   a first transparent element comprising a plurality of microlenses to receive the pulsed laser beam and to output a beamlet from each of the microlenses; and   a second transparent element comprising a plurality of steps corresponding to the plurality of microlenses, wherein each of the steps receives one of the beamlets and outputs the beamlet to an image plane, wherein a height of each step of at least two of the steps is configured to produce an optical path difference of the pulsed laser beam longer than the coherence length;   wherein the second transparent element is disposed approximately at the foci of the beamlets output from the first transparent element.   
     
     
         10 . The despeckling laser unit of  claim 9 ,
 wherein the pulsed laser beams are driven by a pulse of less than 10 nanoseconds.   
     
     
         11 . The despeckling laser unit of  claim 9 , further comprising:
 a collimator disposed between the laser generating unit and the first transparent element to receive the pulsed laser beam and output a collimated laser beam; and   a field lens to receive the beamlets output from the second transparent element and focus the received beamlets on the image plane.   
     
     
         12 . The despeckle unit according to  claim 9 , wherein the at least two of the steps are configured as a one-dimensional staircase and the microlenses are configured as a one-dimensional array of microlenses. 
     
     
         13 . The despeckle unit according to  claim 9 , wherein:
 the pulsed laser beam is linearly polarized with a polarization direction;   the second transparent element comprises at least one physical step, comprising:
 an optical wave plate disposed on a first portion of the at least one physical step which is configured to change the polarization direction of the pulsed laser beam, and 
 a second portion of the at least one physical step which does not include the optical wave plate; and 
   the optical waveplate and the second portion each comprise one of the steps having the one-to-one correspondence with the microlenses.   
     
     
         14 . The despeckle unit according to  claim 9 , wherein:
 the pulsed laser beam is linearly polarized with a polarization direction;   the second transparent element comprises at least one physical step, comprising:
 a first optical wave plate disposed on a first portion of the at least one physical step which is configured to change the linearly polarized light to right circular polarized light, and 
 a second optical wave plated disposed on a second portion of the at least one physical step which is configured to change the linearly polarized light to left circular polarized light; and 
   the first optical wave plate and the second optical wave plate each comprise one of the steps having the one-to-one correspondence with the microlenses.   
     
     
         15 . The despeckling laser unit of  claim 9 , further comprising a third transparent element comprising another plurality of microlenses disposed after the second transparent element and corresponding to the plurality of microlenses in one-to-one correspondence with the plurality of microlenses. 
     
     
         16 . A despeckling laser array, comprising:
 a plurality of the despeckling laser units according to  claim 9 ; and   a single field lens to focus the beamlets output from each of the plurality of despeckling laser units onto the image plane.   
     
     
         17 . A despeckling laser assembly, comprising:
 the despeckling laser array according to  claim 16 ;   a base plate to support the despeckling laser array;   a circuit board attached to one end of the despeckling laser array; and   at least one driver integrated circuit mounted on the circuit board to drive the laser generating units of the despeckling laser array.   
     
     
         18 . An annealing system to anneal a substrate, comprising:
 a plurality of the despeckling laser assemblies according to  claim 17  disposed above a front surface of the substrate, such that each of the despeckling laser assemblies is configured to focus the beamlets on the substrate,   wherein each of the despeckling laser assemblies is movable to enable the annealing system to anneal the front surface of the substrate.   
     
     
         19 . The annealing system of  claim 18 , wherein the substrate comprises amorphous silicon for organic LED displays. 
     
     
         20 . A one-dimensional crossed despeckling unit, comprising:
 a first transparent element comprising:
 a first surface having a first plurality of first microlenses to receive collimated light having a coherence length, and output a first plurality of first beamlets corresponding to the first plurality of microlenses, and 
 a second surface having a second plurality of second microlenses to receive the collimated light, and output a second plurality of second beamlets corresponding to the second plurality of microlenses; and 
   a second transparent element comprising:
 a first plurality of first steps oriented such that at least one of the first steps corresponds to at least one of the first beamlets; and 
 a second plurality of second steps oriented such that at least one of the second steps corresponds to at least one of the second beamlets, 
   wherein:   a height of each step of at least two steps from among the first steps and the second steps is configured to produce an optical path difference of the pulsed laser beam longer than the coherence length, and   the second transparent element is disposed approximately at a foci of the first beamlets and the second beamlets output from the first transparent element.   
     
     
         21 . The one-dimensional crossed despeckle unit according to  claim 20 , wherein the collimated light comprises pulsed laser beams driven by a pulse of less than 10 nanoseconds. 
     
     
         22 . The one-dimensional crossed despeckle unit according to  claim 21 , wherein the pulse reduces a coherence of the laser beam and the steps are configured to further reduce the coherence of the laser beam not reduced by the pulse, to substantially despeckle the pulsed laser beam. 
     
     
         23 . The one-dimensional crossed despeckling unit according to  claim 20 , wherein the first transparent element comprises a one-dimensional crossed microlens array, and the second transparent element comprises a combination of a first staircase element having the first plurality of steps and a second staircase element having the second plurality of steps. 
     
     
         24 . The one-dimensional crossed despeckling unit according to  claim 23 , wherein the first steps each have the same first height, the second steps each have the same second height, and the first height is different from the second height. 
     
     
         25 . The one-dimensional crossed despeckling unit according to  claim 24 , wherein the first staircase is provided in plural. 
     
     
         26 . A laser module, comprising:
 a housing;   a plurality of laser diodes disposed at one end of the housing to generate respective pulsed laser beams having respective coherence lengths;   a first transparent element, disposed after the plurality of laser diodes in the direction of travel of the laser beams, comprising a plurality of microlenses to receive the pulsed laser beams and to output a beamlet from each of the microlenses; and   the one-dimensional crossed despeckling unit according to  claim 25  disposed after the first transparent element in the direction of travel of the laser beams,   wherein each of the first staircases corresponds to at least one of the laser diodes.   
     
     
         27 . The laser module of  claim 26 , wherein:
 the laser diodes are arranged in an M×N grid, where M an N are positive integers respectively representing a number of laser diodes in columns and rows of the grid;   the plurality of first staircases comprise M first staircases, and   each one of the M first staircases corresponds to a respective one of the M columns.   
     
     
         28 . The laser module of  claim 27 , wherein:
 M>N,   N≧1,   M≧2;   a beam shaping axis is arranged in a direction corresponding to the N laser diodes; and   each one of the M×N laser diodes generates approximately 0.2 watts (W) of output power.   
     
     
         29 . A method to despeckle a laser beam, comprising:
 generating a pulsed laser beam having a coherence length;   transmitting the pulsed laser beam through a first transparent element comprising a plurality of microlenses so that the pulsed laser beam is output as a beamlet from each of the microlenses; and   transmitting each one of the beamlets through a respective step included in a second transparent element comprising a plurality of the steps having a one-to-one correspondence with the plurality of microlenses, to an image plane, wherein a height of each step of at least two of the steps is configured to produce an optical path difference of the beamlets longer than the coherence length,   wherein the second transparent element is disposed approximately at the foci of the beamlets output from the first transparent element.   
     
     
         30 . The method according to  claim 29 ,
 wherein the generating of the pulsed laser beam comprises driving the pulsed laser beam using a pulse of less than 10 nanoseconds.   
     
     
         31 . The method according to  claim 29 , further comprising:
 collimating the generated pulsed laser beam and outputting the collimated generated pulsed laser beam to the first transparent element; and   focusing the received beamlets transmitted through the respective steps by the second transparent element on the image plane using a field lens.   
     
     
         32 . The method according to  claim 29 , wherein the at least two of the steps are configured as a one-dimensional staircase and the microlenses are configured as a one-dimensional array of microlenses. 
     
     
         33 . The method according to  claim 29 , further comprising:
 polarizing the pulsed laser beam with a linear polarization having a polarization direction; and   changing the polarization direction of the pulsed laser beam by passing the pulsed laser beam through an optical wave plate comprising one of the steps of the second transparent element.   
     
     
         34 . The method according to  claim 29 , further comprising:
 polarizing the pulsed laser beam with a linear polarization; and   changing the linear polarization of the pulsed laser beam to right and left circular polarization by passing the pulsed laser beam through corresponding first and second optical wave plates each comprising one of the steps of the second transparent element.   
     
     
         35 . The method according to  claim 29 , further comprising transmitting each one of the beamlets output from the second transparent element through a third transparent element comprising another plurality of microlenses in one-to-one correspondence with the plurality of the microlenses. 
     
     
         36 . A two-dimensional despeckling unit, comprising:
 a first transparent element comprising:
 a surface having a plurality of microlenses to receive collimated light having a coherence length from a pulsed laser beam, each of the microlenses configured to output a beamlet which is shaped in two-dimensions; and 
   a second transparent element comprising:
 a light incident surface forming a two-dimensional area comprising two first boundaries and two second boundaries perpendicular to and connecting the two first boundaries; and 
 a plurality of steps protruding out from the light incident surface and arranged in rows, wherein the steps in each row are configured to increase in height along a first direction parallel to the first boundaries, and the rows increase in height along a second direction parallel to the second boundaries, each of the steps having a different height from each other, and each of the steps being configured to receive a corresponding one of the beamlets; 
   wherein:   the height of each step is configured to produce an optical path difference longer than the coherence length, and   the light incident surface is disposed approximately at a foci of the beamlets output from the first transparent element.