Entrelaçamento de comprimentos de onda em redes DWDM-PON

Abstract

The new emerging technologies and services have increased their requirements such as high transmission speed and large bandwidth. In this context, passive optical networks, or PON, have been an adopted solution to answer these demands. PON networks can successfully exploit the use of multiple wavelengths with the use of WDM techniques, with advantages in terms of higher data rate, easy configuration, flexibility in signal routing and network protection as well. WDMsystems consider the wavelength ITU-T standard allocation and spacing (50 GHz and 100 GHz), which considers a reservation of spectrum for downstream transmission and another to upstream transmission. This wavelength allocation strategy results in inefficient use of the available spectrum. Furthermore, on the point of view of operators, the coexistance of PON standards already implemented with new ones are extremely desirable. This facilitates the progressive migration of subscribers to new services in accordance with the demand. As might be expected, with each generation of PON, available channels for spectrum allocation tends to decrease. In 2010, the Full Service Access Network (FSAN) working group, formed by major telecommunications service providers and system vendors initiated the development of the Next Generation PON stage 2. FSAN concluded ITU-T G.989 standard, in 2013, which defined Time and Wavelength Division Multiplexing (TWDM) technology for 40 Gbits/s transmission in downstream transmission and 10 or 40 Gbits/s in the upstream path, using 20 km and 40 km fiber distances and 64 subscribers. ITU-T 989.x Amd1, in 2015, increased the bit rate to 80 Gbits/s in a symmetric path for the same fiber distances and subscriber numbers. For future PON generations there will be the necessity for high spectral efficiency systems, with high speed data and number of subscribers. In this work, a proposal of interleaved wavelengths for access networks with direct detection and without digital signal processing techniques, named FI-DWDM-PON (Frequency Interleaved Dense Wavelength Division Multiplexing PON), is presented as a solution to improve spectral efficiency and ensure coexistence with already implemented PON. The proposed concept is based on the tree topology, where each OLT connects to at least one passive splitter/combiner device, providing services at most 256 ONUs. Furthermore, an optical comb source using a recirculation technique, is responsible to create the downstream and upstream optical carriers. The multiplexing and demultiplexing operation, in downstream and upstream transmission, is processed by the use of cascade Mach-Zehnder interferometers, as a way to decrease the crosstalk between wavelengths.Simulation results performed in Matlab, for 20 km and 40 km single mode fiber, considering different optical modulation formats show the viability of this technique for 50 Gbits/s and 100 Gbits/s DWDM-PON networks with higher spectral efficiency in comparison with existing PON standards.