Comparison of ACO-OFDM, DCO-OFDM and ADO-OFDM in IM/DD Systems

TLDR

The study compares three OFDM variants—ACO‑OFDM, DCO‑OFDM, and ADO‑OFDM—for intensity‑modulated/direct‑detection optical systems. ADO‑OFDM transmits ACO‑OFDM on odd subcarriers and DCO‑OFDM on even subcarriers, with odd subcarriers demodulated conventionally and even subcarriers demodulated via interference cancellation. ADO‑OFDM achieves higher optical power efficiency than ACO‑OFDM and DCO‑OFDM at certain bit‑rate/normalized‑bandwidth settings, and its efficiency can be tuned by adjusting power split, DC bias, and constellation choices.

Abstract

In this paper, three forms of orthogonal frequency division multiplexing (OFDM) designed for intensity modulated/direct detection (IM/DD) optical systems are compared. These are asymmetrically clipped optical OFDM (ACO-OFDM), DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped DC biased optical OFDM (ADO-OFDM). ADO-OFDM is a new technique that combines aspects of ACO-OFDM and DCO-OFDM by simultaneously transmitting ACO-OFDM on the odd subcarriers and DCO-OFDM on the even subcarriers. The odd subcarriers are demodulated as in a conventional ACO-OFDM receiver and the even subcarriers are demodulated using a form of interference cancellation. ADO-OFDM is shown to be more optically power efficient than conventional ACO-OFDM and DCO-OFDM, for some bit rate/normalized bandwidths. It is also shown that by varying the proportion of optical power on the ACO-OFDM component, the DC bias level of DCO-OFDM and the constellations sent on the odd and even subcarriers, the optical power efficiency of ADO-OFDM can be changed.