单项选择题

IntheOSNRmodelforEDFAamplifiers,SNROUT=1/(1/SNRIN+FhvB/PIN),whatdoesSNRINrepresent?()

A.thesignaltonoiseofthecurrentopticalamplifier
B.thesignaltonoiseofthepreviousamplifierorsource
C.thesignaltonoiseintroducedbytheopticalmultiplexer
D.theaccumulatednoisetosignalratiooftheopticalchannel