Abstract

The use of coherent transceivers with higher-order quadrature-amplitude modulation (QAM) is expected to solve the capacity limit imposed in current short-haul transmission systems based on non-coherent transceivers. However, coherent transceivers are more costly than non-coherent transceivers. Indeed, most existing short-haul communication systems adopt non-coherent transceivers. To lower the cost of coherent transceivers, it is desirable to use low-cost lasers and eliminate costly booster erbium-doped fibre amplifiers (EDFAs). However, the use of low-cost lasers induces severe phase noise while the elimination of EDFAs causes SNR degradation due to modulation loss; these problems hinder the effective use of higher-order QAM signals.

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