Optimized threshold setting for performance enhancement of spectrum sliced WDM systems

Recently, there has been renewed interest in spectrum slicing as an economic means of achieving wavelength division multiplexed (WDM) optical transmission. This is due to the development of high power, broad spectrum optical sources based upon amplified spontaneous emission (ASE) in erbium doped fiber amplifiers. However, these sources suffer from excess noise caused by spontaneous-spontaneous ASE beat noise. Since the source is externally modulated, ASE noise affects data 'ones' but not data 'zeros' except where imperfect extinction of the modulator becomes significant. Consequently, the noise environment at the receiver can exhibit substantial signal dependence and at low error rates the ASE noise can result in an error floor. In this paper we explore and illustrate the implications of receiver decision threshold setting on the performance of spectrum sliced systems. We find that such systems exhibit marked sensitivity to decision threshold level. We show that considerable reduction in the optical bandwidth is possible if the receiver threshold is optimized and a receiver with a selected fixed threshold can exhibit rather small penalty.