Depolarizing homogenizer

Abstract

A depolarizing homogenizer including one or more lenslet arrays, for providing a plurality of beamlets associated with different respective parts of a received beam. The depolarizing homogenizer includes a depolarizer comprising different areas which affect polarization differently, the depolarizer being positioned to cause alteration of the polarization characteristics of at least some of the plurality of beamlets. A lens is arranged to at least partially overlap the beamlets having the altered polarization characteristics.

1 . A depolarizing homogenizer, comprising:
 one or more lenslet arrays, adapted for providing a plurality of beamlets associated with different respective parts of a received beam;   a depolarizer comprising different areas which affect polarization differently, wherein the depolarizer is positioned to cause alteration of the polarization characteristics of at least some of said plurality of beamlets; and   a lens arranged to at least partially overlap the said beamlets having said altered polarization characteristics, to provide an output beam.   
     
     
         2 . A depolarizing homogenizer according to  claim 1 , wherein the depolarizer is positioned to receive said plurality of beamlets, wherein at least some of said beamlets pass through respective different areas of the depolarizer, thereby to alter the polarization characteristics of said at least some beamlets. 
     
     
         3 . A depolarizing homogenizer according to  claim 1  or  claim 2 , wherein the depolarizer is located between at least one of the one or more lenslet arrays and the lens. 
     
     
         4 . A depolarizing homogenizer according to  claim 1  or  claim 2 , wherein the lens is located between at least one of the one or more lenslet arrays and the depolarizer. 
     
     
         5 . A depolarizing homogenizer according to  claim 1 , wherein the depolarizer is configured to depolarise light before the light passes through the one or more lenslet arrays to form said plurality of beamlets, thereby to cause alteration of the polarization characteristics of at least some of said plurality of beamlets. 
     
     
         6 . A depolarizing homogenizer according to  claim 1  or  claim 5 , wherein said one or more lenslet arrays is located between the depolarizer and the lens. 
     
     
         7 . A depolarizing homogenizer according to any one of the preceding claims, wherein the depolarizer comprises a liquid crystal polymer or a quartz crystal wedge depolarizer. 
     
     
         8 . A depolarizing homogenizer according to any one of the preceding claims, wherein the depolarizer comprises a first depolarizing element having a first optic axis and a second depolarizing element have a second optic axis, wherein the first and second depolarizing elements are oriented such that the first and second optic axes are at an angle to one another, wherein optionally the first and second depolarizing elements are oriented such that the first and second optic axes are perpendicular to one another. 
     
     
         9 . A depolarizing homogenizer according to any one of the preceding claims, further comprising a fibre bundle, wherein the fibre bundle includes a plurality of optical fibres for guiding light, wherein the depolarizer is located between an output of the fibre bundle and an image plane of the lens. 
     
     
         10 . A depolarizing homogenizer as claimed in  claim 9 , further comprising a collimating lens to receive light from the fibre bundle and to collimate the received light, wherein the one or more lenslet arrays are arranged to receive light which has been collimated by the collimating lens. 
     
     
         11 . A depolarizing homogenizer as claimed in any one of the preceding claims, wherein the one or more lenslet arrays comprise a plurality of lenslets shaped to cause the output beam to have a flat intensity beam profile in an image plane of the lens. 
     
     
         12 . A depolarizing homogenizer as claimed in any one of the preceding claims, wherein the one or more lenslet arrays comprise a plurality of lenslets shaped to cause the output beam to have a square or rectangular beam profile. 
     
     
         13 . A depolarizing homogenizer as claimed in any one of the preceding claims, wherein the one or more lenslet arrays comprise a first lenslet array and a second lenslet array, wherein the first and second lenslet arrays are oriented perpendicularly with respect to one another. 
     
     
         14 . A depolarizing homogenizer as claimed in any preceding claim, wherein the depolarizer comprises an electronically controlled liquid crystal depolarizer. 
     
     
         15 . A light source comprising a depolarizing homogenizer according to any one of the preceding claims. 
     
     
         16 . A light source as claimed in  claim 15 , wherein the light source includes a linearly polarized or partially linearly polarized source, wherein the beam received by the one or more lenslet arrays of the depolarizing homogenizer is derived from said linearly polarized or partially linearly polarized source. 
     
     
         17 . A light source as claimed in  claim 15  or  claim 16 , wherein the light source includes a supercontinuum source configured to generate a supercontinuum, wherein the beam received by the one or more lenslet arrays of the depolarizing homogenizer is derived from said supercontinuum source. 
     
     
         18 . A light source as claimed in  claim 17 , wherein the supercontinuum includes the wavelength range 375 nm to 1200 nm. 
     
     
         19 . A light source as claimed in  claim 17  or  claim 18 , wherein the supercontinuum includes the wavelength range 375 nm to 2400 nm. 
     
     
         20 . A light source as claimed in any one of  claims 17  to  19 , wherein the supercontinuum includes the wavelength range 1100 nm to 4200 nm. 
     
     
         21 . A light source according to any one of  claims 17  to  20 , wherein the light source further comprises a wavelength selector to select one or more wavelengths from the supercontinuum. 
     
     
         22 . A light source according to any one of  claims 15  to  21 , wherein the output beam has a polarization extinction ratio of 1 dB or less, 0.5 dB or less, 0.1 dB or less, or 0.05 dB or less. 
     
     
         23 . A depolarization method, comprising:
 dividing received light into a plurality of beamlets;   causing alteration of the polarization characteristics of at least some of said plurality of beamlets;   providing a depolarized output beam by at least partially overlapping the beamlets having said altered polarization characteristics.   
     
     
         24 . The depolarization method as claimed in  claim 23 , comprising altering the polarization characteristics of at least some of said plurality of beamlets after said plurality of beamlets have been divided from said received light. 
     
     
         25 . A depolarization method as claimed in  claim 23 , comprising depolarizing the received light before it is divided, thereby altering the polarization characteristics of at least some of said plurality of beamlets. 
     
     
         26 . A depolarization method as claimed in any one of  claims 23  to  25 , wherein the depolarized output beam has a flat top beam profile. 
     
     
         27 . A depolarization method as claimed in any one of  claims 23  to  26 , wherein the depolarized output beam has a square beam profile. 
     
     
         28 . A depolarization method as claimed in any one of  claims 23  to  27 , wherein the depolarized output beam has a polarization extinction ratio of idB or less, 0.5 dB or less, 0.1 dB or less, or 0.05 dB or less. 
     
     
         29 . A light source, comprising:
 a supercontinuum source for generating a supercontinuum;   a wavelength selector for selecting light at one or more wavelengths from the supercontinuum;   a fibre bundle comprising a plurality of optical fibres arranged to guide light selected by the wavelength selector, and to output light at the one or more selected wavelengths;   a depolarizing homogenizer configured to receive light which has been output by the fibre bundle, wherein the depolarizing homogenizer comprises:
 one or more lenslet arrays, for providing a plurality of beamlets associated with different respective parts of a beam received at the one or more lenslet arrays; 
 a depolarizer comprising different areas which affect polarization differently, wherein the depolarizer is positioned to cause alteration of the polarization characteristics of at least some of said plurality of beamlets; and 
 a lens arranged to at least partially overlap the said beamlets having said altered polarization characteristics, to provide an output beam. 
   
     
     
         30 . A light source as claimed in  claim 29 , wherein the supercontinuum includes the wavelength range 375 nm to 1200 nm. 
     
     
         31 . A light source as claimed in  claim 29  or  claim 30 , wherein the supercontinuum includes the wavelength range 375 nm to 2400 nm. 
     
     
         32 . A light source as claimed in any one of  claims 29  to  31 , wherein the supercontinuum includes the wavelength range 1100 nm to 4200 nm.