Experimental verification of optimum filter bandwidths in direct-detection (N)RZ receivers limited by optical noise

We present measurements performed at a data rate of 10 Gb/s to experimentally verify these theoretical results. In the case of RZ coding we reached a sensitivity of 52 photons per bit (ppb) at a bit-error ratio BER = 10/sup -9/, which is about 1.4dB above the quantum limit. To the best of our knowledge, at 10Gb/s, this result is the best previously reported sensitivity for optically preamplified on-off-keying (OOK). The (N)RZ transmitter consisted of a DFB laser with an integrated electroabsorption modulator.