means for compensating, amplifying and limiting the error signal to a predetermined range, to thereby prevent {HEAD ~ the burnout} of {TAIL ~ the photo detector}, and 
means for compensating , amplifying and limiting the error signal to a predetermined range , to thereby prevent { HEAD ~ the burnout } of { TAIL ~ the photo detector } , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH 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