{HEAD ~ Some part} of the incident laser beam is reflected by the optical member and then returned to {TAIL ~ the beam splitter} to be focused on an optical disc 
is returned to
{ HEAD ~ Some part } of the incident laser beam is reflected by the optical member and then returned to { TAIL ~ the beam splitter } to be focused on an optical disc
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH