Effect of gain saturation on receiver sensitivity in 1 Gb/s multichannel FSK direct-detection systems using erbium-doped fiber preamplifiers

The effects of gain saturation on receiver sensitivity were studied theoretically and experimentally when using an erbium-doped fiber amplifier (EDFA) in a frequency-shift-keyed direct-detection system. It was found that when the amplifier undergoes a 6-dB gain compression due to saturation by a strong adjacent signal, the power penalty at 10/sup 9/ bit-error-rate (BER) is less than 1.5 dB. This power penalty increases rapidly when saturation is greater than 6 dB. Such a penalty increase with EDFA gain saturation is explained by the observed changes in the spontaneous emission noise factor and in the relative contribution of the circuit noise and is closely predicted by the theoretical analysis. These results demonstrate the possibility of using a saturated EDFA preamplifier while accommodating as many as several hundred optical channels or potential network users without incurring significant BER degradation.<>