Traveling-wave amplification of a lambda = 1.53 microm signal with +22-dB gain is achieved at 295 K in an Er(3+)-doped single-mode fiber using a lambda = 514.5 nm pump source. The optimum fiber length for maximum gain is determined experimentally. A limit in signal-to-noise ratio that is due to concurrent amplification of spontaneous emission is observed. By cooling the fiber to 77 K, the amplifier gain is increased to +29 dB as a result of depopulation of the lower laser level.

High-gain erbium-doped traveling-wave fiber amplifier

A novel WDM optical network architecture based on a physical ring topology is proposed and demonstrated. The architecture does not require in-line channel filters, is immune to recirculating ASE noise and permits prompt traffic restoration in the event of fibre and node failures. The results obtained from a prototype network have been most encouraging.

Flexible bus: a self-restoring optical ADM ring architecture

This thesis describes an optical fibre network that uses a bus topology and Code Division Multiple Access (CDMA). Various potential configurations are analysed and compared and it is shown that a serious limitation of optical CDMA schemes using incoherent correlators is the effect of optical beating due to the presence of multiple incoherent optical signals at the receiver photodiode. The network proposed and analysed in this thesis avoids beating between multiple optical fields because it only uses a single, shared, optical source. It does this through the SLIM (Single Light-source with In-line Modulation) configuration in which there is a continuously-operating light source at the head-end of a folded bus, and modulators at the nodes to impose signals on the optical field in the form of pulses of darkness which propagate along the otherwise continuously bright bus. Optical CDMA can use optical-fibre delay-line correlators as matched filters, and these may be operated either coherently or incoherently.Coherent operation is significantly more complex than incoherent operation, but incoherent correlators introduce further beating even in a SLIM network. A new design of optical delay-line correlator, the hybrid correlator, is therefore proposed, analysed and demonstrated. It is shown to eliminate beating. A model of a complete network predicts that a SLIMbus using optical CDMA with hybrid correlators can be operated at TeraBaud rates with the number of simultaneous users limited by multiple access interference (MAI), determined only by the combinatorics of the code set.

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Dark signalling and code division multiple access in an optical fibre LAN with a bus topology

In this paper, based on bidirectional optical amplifiers and n couplers, we propose a bidirectional transparent (BTL) network configuration Compared to the MPL and SLB schemes, the BTL structure can save much optical fiber and optical filters

Bidirectional transparent optical networks

Based on π couplers and optical amplifiers of two-way amplifications, we propose a Bidirectional Active Bus (BAB) structure for fiber networks which support two-way communications. The BAB structure at least saves half amount of bus fiber and optical amplifiers than the Dual Active Bus scheme [1, 2]. The structure applies to both single-optical-carrier and optical FDM/WDM fiber networks. In expanding/interconnecting fiber networks, the proposed BAB structure is free of Signal Circulation (SC) [3, 4] and Multipath Propagation (MP) [5] problems and independent of constellation of sub networks, and it uses less amount of fiber and optical filters than the MPL and SLB schemes [3, 4]. Star-BAB structure is suggested for large networks. The BAB structure has potential good survivability.

Bidirectional Active Bus and its Applications in Fiber Networks

This paper proposes a new method of expanding a local area optical FDM/WDM star network by m times with the help of m optical amplifiers (OAs) and m optical bandstop filters (BSFs). Instead of parallelly connecting m star couplers to an extra (m + 1) x (m + 1) star coupler and forming a Multiple Parallel Loop (MPL) topology [1], we suggest to cascade the star couplers one after another by active fibers and finally connect the last coupler to the first one to form a Single Loop Bus (SLB) topology. Compared with the MPL network, our SLB network needs (m + 1) times smaller OA gain, half optical filters, and no (m + 1) x (m + 1) star coupler. Moreover, SLB configuration is more proper to be used in interconnecting far separated star network since it decreases fiber consumption. A network classification error in [1] is corrected.

Expansion/interconnection of local area FDM/WDM star networks using active loop bus topology

Based on a modified two-level Er 3+ lasing model and its numerical solution, power evolution, gain saturation, optimal EDF length, and noise characteristic in a bidirectional EDFA (BiEDFA) with balanced input pumps and signals are discussed and compared with that in forward and backward pumped EDFAs. Larger gain and less noise are given by BiEDFA than the other two kinds of EDFAs with the same pumps and signals. In addition, bidirectional semiconductor light amplifiers are considered.

Zhong Cao

Papers

Bidirectional Active Bus and its Applications in Fiber Networks

Expansion/interconnection of local area FDM/WDM star networks using active loop bus topology

Bidirectional Amplification in an EDFA with Balanced Input Signals and Pumps

Bidirectional transparent optical networks

Noise limitations in solid state photodetectors: comment