The optical signal passing out of {HEAD ~ the second end} of {TAIL ~ the nontransparent hollow tube} is optically coupled onto an OEC 
of
The optical signal passing out of { HEAD ~ the second end } of { TAIL ~ the nontransparent hollow tube } is optically coupled onto an OEC
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH