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