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