Power-efficient schemes using directly modulated lasers for intensity modulation and direct detection OFDM-PONs.

The intensity modulation and direct detection (IM/DD) passive optical network (PON) has been demonstrated as a cost-effective solution for a long-reach ( $$>\!80\,\hbox {km}$$ ) access system because it can be easily installed and maintained with low cost and complexity. Meanwhile, orthogonal frequency division multiplexing (OFDM) has been widely used in PONs due to its high spectral efficiency and strong resistance to dispersion impairments. So, the IM/DD OFDM-PON emerged. The power efficiency has attracted great research interests in IM/DD OFDM-PONs. The previous works achieved power savings from the perspective of MAC-layer or hardware-level optimization, but they neglected designing appropriative algorithms, and the long-reach transmission performance cannot be guaranteed. In this paper, we propose an improved Hughes-Hartogs algorithm (IHHA) to adjust the number of bits and power level allocated for each subcarrier, with the objective to minimize the electrical transmitting power of all subcarriers. The OFDM signal is generated according to the bit/power allocation result of IHHA, and we conduct extensive simulations to verify the long-reach transmission performance of our system. Simulation results show that our system has high power efficiency by using IHHA, and bit error rate satisfies the forward error correction limitation after 100 km single-mode fiber transmission. [ABSTRACT FROM AUTHOR]