In a first aspect of the present invention, {HEAD ~ the apparatus} comprises {TAIL ~ an input element} for receiving an optical signal 
comprises
In a first aspect of the present invention , { HEAD ~ the apparatus } comprises { TAIL ~ an input element } for receiving an optical signal
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH