question about optical transceiver

I design a optical transceiver , the circuit board of transmitter and receiver is separately,when I add the voltage to the LA of the receiver,the signal all disappear, only a lot noise, and very stange, the circuit signal that drives the laser also becomes very bad, a lot noise in it , and I donnot kown the reason, can someone to help me?
Thanks

do you add the isolator in the optical link?

yeh i need to know what does an opto isolator d
o?