. ▁ ▁G lass ▁pol ing ▁also ▁allows ▁for ▁the ▁creation ▁of ▁the ▁linear ▁electro - opt ic ▁effect ▁that ▁can ▁be ▁used ▁for ▁other ▁functions ▁like ▁light ▁mod ulation . ▁ ▁So , ▁glass ▁pol ing ▁re lies ▁on ▁recording ▁an ▁electric ▁field ▁which ▁breaks ▁the ▁original ▁symmetry ▁of ▁the ▁material . ▁Pol ing ▁of ▁glass ▁is ▁done ▁by ▁applying ▁high ▁voltage ▁to ▁the ▁medium , ▁while ▁exc iting ▁it ▁with ▁heat , ▁ult rav io let ▁light ▁or ▁some ▁other ▁source ▁of ▁energy . ▁He at ▁will ▁permit ▁the ▁charges ▁to ▁move ▁by ▁diffusion ▁and ▁the ▁high ▁voltage ▁perm its ▁to ▁give ▁a ▁direction ▁to ▁the ▁charges ▁disp lacement . ▁ ▁Opt ical ▁pol ing ▁of ▁sil ica ▁fib ers ▁allows ▁for ▁second - harm onic ▁generation ▁through ▁the ▁creation ▁of ▁a ▁ ▁self - organ ized ▁periodic ▁distribution ▁of ▁charges ▁at ▁the ▁core - cl adding ▁interface . ▁ ▁U V ▁pol ing ▁ ▁received ▁much ▁attention ▁because ▁of ▁the ▁high ▁non - linear ity ▁reported , ▁but ▁interest ▁dw ind led ▁when ▁various ▁groups ▁failed ▁to ▁reproduce ▁the ▁results . ▁ ▁Th erm al ▁pol ing ▁ ▁Str ong ▁electric ▁fields ▁are ▁created ▁by ▁thermal ▁pol ing ▁of ▁sil ica , ▁subject ing ▁the ▁glass ▁simultaneously ▁to ▁temper atures ▁in ▁the ▁range ▁of ▁ 2 8 0   ° C ▁and ▁a ▁few ▁kil ov ol ts ▁bias ▁for ▁several ▁minutes . ▁C ations ▁are ▁mobile ▁at ▁elev ated ▁temperature ▁( e . g ., ▁Na +) ▁and ▁are