**2.2 Ring and open loop topologies**

The ring topology means, that all stages are connected to one another in the shape of a closed loop, so that each stage is connected directly to two others, one on either side of it. The ring or loop network topologies are set up in a circular fashion in which data travels around the ring in one direction and each unit on the right acts as a repeater to keep the signal strong as it travels. Each stage incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The open loop topology is not closed; it is similar to bus topology, where each node is connected to a single fibre.

Fig.4. shows a loop topology for signal distribution in a RoF system. In the network the transmission frequencies are fixed and the reception frequencies are different at each node. A control unit provides information for the nodes concerning the subcarrier frequency to be received. In the ring type version of the network a single fiber is used at each node both for transmission and reception of the information. The ring structure enables each node to communicate with any other one. In the open loop version of a network the optical fiber collects the information of the nodes and then it is routed back to make possible the reception of the collected information. Applying that folded back construction each node can communicate with any other one. However, the distance between the nodes is limited by the fiber loss and the available power.

Fig. 4. Loop topology with traditional Electrical-to-Optical (E/O) and Optical-to-Electrical (O/E) converters

In Fig.5. the open loop version of a WDM-RoF network is shown. In the combined WDM-RoF network every node has a fix optical carrier instead of electrical subcarrier. In this way, the transmission capacity is extended. The multifunctional SOA can operate as a transparent unidirectional add-drop node with potential applications in photonic ring, loop or open loop networks, whose main feature is the possibility of adding new nodes and/or increasing the bit-rate for the required nodes without reconfiguring the whole network. The concept of the complete system is based on the cascaded SOA chain approach which produces simultaneous modulation and amplification. Furthermore, such read-write nodes need a minimum amount of external electronics, therefore reducing network cost and complexity. The Optical Add Drop Multiplexers (OADMs) select the dedicated optical carriers for the transceivers. The multifunctional SOA detects the information from the downlink optical carrier and modulates the uplink optical carrier with the information received from the antenna.

The ring topology means, that all stages are connected to one another in the shape of a closed loop, so that each stage is connected directly to two others, one on either side of it. The ring or loop network topologies are set up in a circular fashion in which data travels around the ring in one direction and each unit on the right acts as a repeater to keep the signal strong as it travels. Each stage incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The open loop topology is not

Fig.4. shows a loop topology for signal distribution in a RoF system. In the network the transmission frequencies are fixed and the reception frequencies are different at each node. A control unit provides information for the nodes concerning the subcarrier frequency to be received. In the ring type version of the network a single fiber is used at each node both for transmission and reception of the information. The ring structure enables each node to communicate with any other one. In the open loop version of a network the optical fiber collects the information of the nodes and then it is routed back to make possible the reception of the collected information. Applying that folded back construction each node can communicate with any other one. However, the distance between the nodes is limited

closed; it is similar to bus topology, where each node is connected to a single fibre.

**T R SM**

**OR OR OR**

**OS EAM**

**OM**

**OM OM**

Fig. 4. Loop topology with traditional Electrical-to-Optical (E/O) and Optical-to-Electrical

In Fig.5. the open loop version of a WDM-RoF network is shown. In the combined WDM-RoF network every node has a fix optical carrier instead of electrical subcarrier. In this way, the transmission capacity is extended. The multifunctional SOA can operate as a transparent unidirectional add-drop node with potential applications in photonic ring, loop or open loop networks, whose main feature is the possibility of adding new nodes and/or increasing the bit-rate for the required nodes without reconfiguring the whole network. The concept of the complete system is based on the cascaded SOA chain approach which produces simultaneous modulation and amplification. Furthermore, such read-write nodes need a minimum amount of external electronics, therefore reducing network cost and complexity. The Optical Add Drop Multiplexers (OADMs) select the dedicated optical carriers for the transceivers. The multifunctional SOA detects the information from the downlink optical carrier and modulates the uplink optical carrier with the information received from the

**OM = optical modulator OR = optical receiver OC = optical coupler**

**TERMINALS T R T R • • • T R** **CONTROL**

**OC**

**SOA**

**OM**

**OR**

**T R SM**

**OC**

**TERMINALS T R T R • • • T R**

 **OS = optical source EAM= electro-absorption modulator SOA = semiconductor optical amplifier**

**ROOM N**

**FIBER**

**FIBER**

**RADIO NODE**

**UNIT**

**ROOM 2**

**EAM SOA**

**RADIO**

**NODE <sup>T</sup> <sup>R</sup>**

**OC OC**

**2.2 Ring and open loop topologies** 

by the fiber loss and the available power.

**SM**

 **T = radio transmitter R = radio receiver SM = shift mixer**

**TERMINALS T R T R • • • T R**

**ROOM 1**

**RADIO NODE**

(O/E) converters

antenna.

Fig. 5. WDM - RoF open loop concept with SOA transceivers
