{TAIL ~ Prior art devices} wherein the thickness of the layers was not calculated to optimize light efficiency had a product of {HEAD ~ phase factors} ξ1 and ξ2 of less than 80% 
{ TAIL ~ Prior art devices } wherein the thickness of the layers was not calculated to optimize light efficiency had a product of { HEAD ~ phase factors } ξ1 and ξ2 of less than 80 %
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH