{HEAD ~ The structure} 2 wherein {TAIL ~ the index} of refraction of the guiding core is smaller than the index of refraction of the surrounding distributed gratings 
{ HEAD ~ The structure } 2 wherein { TAIL ~ the index } of refraction of the guiding core is smaller than the index of refraction of the surrounding distributed gratings
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH