Long-Reach and High-Splitting-Ratio WDM/TDM-PON Systems Using Burst-Mode Automatic Gain Controlled SOAs

This paper presents novel burst-mode automatic gain controlled semiconductor optical amplifiers (AGC-SOAs) that are utilized as one upstream channel of a repeater in long-reach time- and wavelength-division multiplexed passive optical networks (WDM/TDM-PONs). Two SOAs are cascaded in the AGC-SOAs to achieve high gain. Two-stage gain switching with a fast feed forward (FF) control circuit is applied to the first SOA and the second SOA equalizes output burst frame powers regardless of input powers; the combination plays a key role in expanding the system operating range of long-reach systems. The first SOA with the simple gain control scheme can be also utilized as a preamplifier, which is useful to realize high-splitting-ratio systems without facing any electric supply issues. Unlike conventional burst frame power equalizers which change the gain of a single SOA through an FF control circuit and so do not provide a wide enough input dynamic range for PON applications, our gain control scheme successfully overcomes this issue. It improves the accuracy of output power equalization by reducing the input power range to the second SOA. We develop a prototype that implements this scheme and experimentally confirm that it can expand the system operating range of both long-reach and high-splitting-ratio systems. Although we have only one prototype at this time, experiments and discussions that consider the presence of neighbouring WDM channels support the possibility of WDM operations.