We investigate the effects of low cut-off frequency of optical receiver on the performance of lightwave systems. The results show that we can reduce the tone-induced power penalty by similar to 0.8 dB (tone frequency=1 MHz) using a high-pass filter in the optical receiver. In addition, our calculation shows that the power penalty can be negligible (<0.1 dB) even when the low cut-off frequency of the 10 Gb/s optical receiver is increased up to similar to 10 MHz. (C) 2005 Elsevier B.V. All rights reserved.