The applications of semiconductor optical devices for ultra-fast passive optical networks

Abstract

Global telecommunications industry in the past decade has maintained a stable growth trend. As a mainstream fixed broadband technology, fiber-to-the-home (FTTH) technology is promising for the next-generation fixed access networks. Because of its potential in transmitting data in higher bandwidth, larger optical splitting ratio and longer distance, Wavelength-division multiplexing passive optical network (WDM-PON) is an extremely attracting solution for the next-generation fiber-to-the-x (FTTx) systems. Due to its tree topology, there is no direct physical connection between users in WDM-PONs. A virtual private network (VPN) is needed for users to communicate with each other. In contrast to the conventional optical-electrical-optical conversion, all-optical virtual private networks are proposed in order to reduce electronic processing burden at central office and bypass the electronic bottleneck. An all-optical VPN in PONs needs to have simple structure, convenient reconfiguration, high data rate and high power efficiency. In this thesis, a reconfigurable all-optical VPN is proposed. The proposed scheme is based on mutually injection-locked Fabry-Perot laser diodes (FP-LDs) at central office in WDM-PONs. At the Optical Line Terminal (OLT), the VPN signal transmitted from one Optical Network Unit (ONU) at its upstream wavelength is converted by the mutually injection-locked FP-LD to the upstream wavelength of another ONU. Injection locking of FP-LD allows low injected power from ONUs. Moreover, the proposed all-optical VPN scheme is reconfigurable because of the multi-mode characteristics of FP-LDs. As a result, our proposal is more power efficient with more convenient reconfiguration compared to previous solutions. Another obstacle to the popularization of WDM-PONs is that the usage of different wavelength yields a high cost of devices at the user end. Recently, the optical loopback technology with RSOAs has received lots of research attention. In the second part of this thesis, we focus on the important issue that the limited modulation bandwidth of current commercial RSOA affects the data rate of the uplink transmission in the RSOA-based PONs. We try to establish high-speed modulation for RSOAs with limited bandwidth by using high-order modulation formats and differential interferometers. Experimental results show a reliable 20-km transmission when using 20-Gbps 4-level Pulse Amplitude Modulation (PAM4) format in RSOA-based WDM-PON.