Plug-and-Play Optical Node Architectures and Their Built-in Optical Fiber Characterization Techniques

Cost-effective plug-and-play optical (PPO) nodes may enable a new generation of self-configuring and simple-to-deploy optical networks. Three possible PPO node architectures are discussed in the paper along with their built-in opitcal fiber characterization techniques. Introduction The deployment of optical networks is in part delayed by two factors: the excessive cost of optical node equipment and the highly complex procedure of design, installation and maintenance of the overall network. To circumvent the cost and complexity burden of extant optical networks, the authors proposed to design ad-hoc optical networks that use cost-effective self-configurable optical nodes [4]. Such nodes will look like today's fast Ethernet hubs and switches, providing however, several orders of magnitude higher bandwidth, and larger geographical network coverage. Any user will be able to connect such nodes with existing fibers by a simple plug-andplay operation. Once connected, the plug-and-play optical (PPO) nodes will be able to communicate with one another, finding the characteristics of surrounding optical links and looking for cost-effective ways to provide reliable and optimized optical circuits to the end user's applications and interfaces. This selfconfiguring property of the PPO nodes will be essential to make the node installation procedure easy, and to adjust the optical data flows to both varying traffic patterns and changing conditions of the optical physical layer, e.g., introduction and removal of PPO nodes, aging of optical components and soft failure of network elements. This paper discusses three possible PPO node architectures and their builtin techniques to characterize some linear and nonlinear properties of the input/output optical fiber pairs. Three node architectures and their functionalities A PPO node requires simplicity of configuration and integratibility of its components. On the other hand, in order to self-determine the network connectivity and transmission characteristics, a PPO node needs to provide sufficient functionalities. The tradeoff between the PPO node complexity, cost, and functionalities is discussed using three possible architectures. PPO node 1. The simplest PPO node makes use of a low-cost and low-speed optical transceiver at each input/output fiber pair. The transceivers can establish and verify connections between the PPO node and its neighboring nodes. Identification information will be carried by the optical signal shared between the connected nodes. By regulating the optical output power of each transmitter, the loss of each fiber pair can be evaluated through the measurement of the received optical power at the other end. PPO node 2. A more sophisticated PPO node makes use of both a superluminescent LED (SLED) at the transmitter and a tunable optical filter at the receiver. The wide spectrum SLED is modulated by a sinusoid signal. At the receiver, the relative RF phase shift of the sinusoid is detected at multiple wavelengths selected by the tunable filter. Chromatic dispersion of the optical fiber can then be evaluated using conventional techniques. Thanks to its tunable filter, PPO node 2 can also evaluate the optical signal-tonoise-ratio (OSNR) of the link when the fiber pair involves optical amplifiers. PPO node 3. Another possible PPO node architecture (shown in Fig.1) makes use of a tunable laser diode and employs coherent detection to determine chromatic dispersion, nonlinearity and PMD of the fiber pairs. Depending on the state of the 1x2 optical switch, the tunable laser can be used as either transmitter or local oscillator of the coherent detection at the receiver. The PPO node identification and channel information is modulated into the optical signal and sent to the receiving PPO nodes. At the receiving PPO nodes, each input fiber port has a low cost and low speed receiver. These receivers will monitor the optical signal connectivity between PPO nodes. Fig.1, PPO node using a tunable laser diode 1 x N sw itc h Tunable laser M od ul at or 1 x N sw itc h 1 x 2 switch PPO node & channel identification Switch control