单项选择题
IntheOSNRmodelforEDFAamplifiers,SNROUT=1/(1/SNRIN+FhvB/PIN),whatdoesSNRINrepresent?()
A.thesignaltonoiseofthecurrentopticalamplifier
B.thesignaltonoiseofthepreviousamplifierorsource
C.thesignaltonoiseintroducedbytheopticalmultiplexer
D.theaccumulatednoisetosignalratiooftheopticalchannel