sensitivity of a receiver? any ideas

guys, i am performing real time measurement of sensitivity of an optical receiver.
unfortunately due to some design issues; i am observing a very noisy eye when using PRBS 2^7-1 at 622Mbps. the receiver ic was designed too function at 1.25Gbps. but the designer still wants to know the sensitivity of the receiver IC to help him in the next version.
any ideas?

i think due to the noisy eye; you cannot accurately perform BER testing or estimate sensitivity based on the eye diagram.

i experienced the same situation about a year ago.

first of all please confirm that the noise and jitter observed in the eye diagram is caused by design or layout issues and not by your test setup.

secondly; understand wat sensitivity of an optical receiver means.
sensitivity of a receiver refers to the lowest optical power signal that will produce a BER = 10-9 at the output of the receiver. usually sensitivity is described in term of current (uA) or dB

observing the eye diagram meanwhile attenuating the optical signal is also not a precise method of calculating sensitivity. it is just an estimation method.

so, another method : also a non accurate method is using s-parameter to estimate sensitivity.

this is what i did previously;
i) try to find a photodiode emulator circuit (from maxim) to replace your optical photodiode.. now you will be performing electrical testing - not accurate but estimation. if possible fabricate a new EB with the photodiode emulator. if not possible; then just desolder your gold sockets (connecting your PD); and solder a sma connector (this will be a tedious job, but has to be done)
ii) terminate all the other channels with 50ohm terminator; leaving only one single ended output unterminated.
iii) perform s21 measurements using a network analyzer - to calculate the loss experienced at the output compared to the signal applied at the input. co-work with the designer - ask him to estimate sensitivity based on loss.

well, i tried this method previously and it helped the designer estimate the sensitivity of the receiver. its not a very accurate method ; but can be used for estimation.

nathan80,
you seem to be expert
how many years experience?

i have a few questions?
what is gold socket?
what is diff. elec n opt testing?
"terminate all the other channels with 50ohm terminator; leaving only one single ended output unterminated" - what this means?
how to perform s21 measurment?

"if not possible; then just desolder your gold sockets (connecting your PD); and solder a sma connector (this will be a tedious job, but has to be done)"
what this means?