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