Provided is {HEAD ~ a means} for applying potentials to the first and second photodiodes to reverse bias the first and second photodiodes to produce {TAIL ~ a dark current} in flowing through each photodiode 
Provided is { HEAD ~ a means } for applying potentials to the first and second photodiodes to reverse bias the first and second photodiodes to produce { TAIL ~ a dark current } in flowing through each photodiode
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH