{HEAD ~ sensors} for identifying types of the installed optical parts which have been installed in {TAIL ~ the main equipment}; and 
{ HEAD ~ sensors } for identifying types of the installed optical parts which have been installed in { TAIL ~ the main equipment } ; and
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH