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Overview

ASK-ASK Configuration for RSOA-based WDM-PON

Description

The use of reflective SOA (RSOA) to implement the Optical Network Unit (ONU) in WDM-PONs has been established as a promising device attributable to its simultaneous amplification and modulation capabilities.
In RSOA-based ONUs, the seed-light is generated at the central office and injected towards the ONUs. It can be either a continuous wave or a modulated signal. At each of the ONUs, the seed-light is modulated with the corresponding data and sent back in upstream direction to the central office. As light is exposed twice to link loss, amplification is required at each ONU, ideally coming directly from the RSOA [1]. In this application example we show a full-duplex re-modulating scheme.

Typical Results

The schematic is represented in Figure 1. The downlink signal, modulated in amplitude (ASK) is divided by an optical coupler into two parts at the ONU side. The upper branch is used for downstream data detection. At the bottom branch the signal enters into the RSOA, where it is modulated with the upstream data, and reflected back in upstream direction. The optical amplifier operates in saturation and thus, the two levels of the incoming signal can be equalized. However, the impact of the downstream signal cannot be fully cancelled out and induces amplitude ripple on the upstream signal, which leads to a system penalty.
The eye diagram of the optical signal generated by the RSOA is displayed in Figure 2, where the residual modulation of the downstream data channel can be observed. In order to see the influence of the extinction ratio of the downstream signal on the re-modulated data, the amplitude of the driver of the Mach-Zehnder modulator at the central office has been varied. It can be observed in Figure 3 that the bit error rate of the downstream signal is degraded when decreasing the driver amplitude (as a consequence of the lower extinction ratio). The opposite trend is observed in Figure 4 for the upstream signal (reduced impact of the downstream signal).

Keywords

Amplitude Shift Keying (ASK), re-modulation, Reflective Semiconductor Optical Amplifier (RSOA), WDM-PON