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