Noise suppression of incoherent light using a gain-saturated SOA: implications for spectrum-sliced WDM systems

Abstract

Abstract-In this paper, we present an experimental and numerical study of semiconductor optical amplifier (SOA)-based noise suppression and its relevance to high-channel-density spectrumsliced wavelength-division-multiplexed systems. We show that the improvement in signal quality is accompanied by spectral distortion, which renders it susceptible to deterioration in the presence of subsequent optical filtering. This phenomenon originates from the loss of intensity correlation between spectral components of the SOA output when the signal spectrum is altered. As a consequence, a design tradeoff is introduced between intensity noise and crosstalk in high-channel-density systems. These adverse effects can be overcome by optimized SOA design, resulting in a significant improvement in signal quality.Index Terms-Optical noise, semiconductor optical amplifier (SOA), spectrum slicing, wavelength-division multiplexing(WDM).

Feasibility Study of SOA-Based Noise Suppression for Spectral Amplitude Coded OCDMA

“…Despite the benefits listed above, in the course of our research, we found that the superior signal quality offered by the saturated SOA was noticeably degraded by subsequent optical filtering, leading to a tangential investigation into these effects [13]. Spectral filtering at the receiver is an unavoidable part of SAC and thus places severe limits on the partnership of the two technologies.…”

“…The gain compression that occurs in saturation acts across the entire gain bandwidth of the SOA and introduces correlations between the intensity noise of the various spectral components propagating through the amplifier. We have shown both experimentally and via simulations [13] that in distinct contrast to thermal light (e.g., the SOA-input light), anticorrelations exist between the intensity noise of different spectral components, which in turn yield reduced fluctuations in the total output intensity (i.e., noise suppression). Subsequent optical filtering removes frequency components that contribute to the intensity smoothing, thereby counteracting the noise suppression introduced by the saturated SOA.…”

“…RIN measurements on the CW signal also show the same trend. A comprehensive study into post-SOA spectral filtering effects is given in [13].…”

“…In a practical multichannel SAC OCDMA system, the total noise contribution from the many interfering channels would outweigh the improvement to the matched channel, minimizing the advantage of this approach. Furthermore, any phenomenon that alters the correlations between the spectral components of the intensity-smoothed light (e.g., dispersion) can also lead to additional signal degradation [13], [17].…”

“…Nevertheless, it is worth noting that the number of SOAs required per-chip approaches that required by the SOA per-channel system for large channel counts (assuming chips could be shared between channels), and that the cost of a single SOA or optical integrated circuit is ultimately a question of market volume. Using lower linewidth enhancement (i.e., α-factor) amplifiers as discussed in [13], would also give additional performance advantages for SOA per-chip systems; however, SOA per-code systems would not have appreciable benefits even in this case.…”