Next Generation of Optical Access Network Based on Reflective-SOA

Abstract

Communication networks have evolved in order to fulfil the growing demand of our bandwidth-hungry world. First, the coaxial cable has replaced the copper cable since 1950 for longand medium-range communication networks. The Bit rate-distance product (BL) is commonly used as figure of merit for communication systems, where the B is the bit rate (bit/sec) and L is the repeater spacing (km). A suitable medium for transmission needed to be available and optical fibres were selected as the best option to guide the light (Kao & Hockham, 1966). A radical change occurred, the information was transmitted using pulses of light. Thus further increase in the BL product was possible using this new transmission medium because the physical mechanisms of the frequency-dependent losses are different for copper and optical fibres. The bit-rate was increased in the core network by the introduction of a new technique: Wavelength-Division Multiplexing (WDM). The use of WDM revolutionized the system capacity since 1992 and in 1996, they were used in the Atlantic and Pacific fibre optic cables (Otani et al., 1995). While WDM techniques were mostly used in long-haul systems employing EDFA for online amplification, access networks were using more and more bandwidth. Access network includes the infrastructures used to connect the end users (Optical Network Unit ONU) to one central office (CO). The CO is connected to the metropolitan or core network. The distance between the two network units is up to 20 km. The evolution of access network was very different from in the core network. High bit-rate transmissions are a recent need. At the beginning, it provided a maximum bandwidth of 3 kHz (digitised at 64 kbit/s) for voice transmission and was based on copper cable. Today, a wide range of services need to be carried by our access network and new technologies are introduced which allow flexible and high bandwidth connection. The access network evolution is obvious in Europe with the rapid growth of xDSL technologies (DSL: Digital Subscriber Loop). They enable a broadband connection over a copper cable and allow maintaining the telephone service for that user. In 2000, the maximum bit rate was around 512 kbit/s while today it is around 12 Mbit/s. However since 2005, new applications as video-on-demand need even more bandwidth and the xDSL technologies have reached their limits. The introduction of broadband access network based on FTTx (Fiber To The x) technology is necessary to answer to the recent explosive growth of the internet. Today, Internet service providers propose 100 Mbit/s using optical fibre. The experience from the core network evolution is a great benefit to access network. The use of WDM mature technology in access and