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