Passive Optical Networks

The copper network, deployed worldwide for telephony, relies on twisted-pair copper cables. Since the 1960s, optical fiber and lasers have been developed, with their first commercial use in the 1970s. Initially, optical fibers had very high losses (∼ 1,000 dB/km), but thanks to technological advances—notably the use of semiconductor lasers (GaAs at 0.8 µm, followed by InGaAsP at 1.3 µm) and improvements in manufacturing processes—these losses were reduced to approximately 0.2 dB/km by the 1980s. Single-mode transmission, introduced in 1981, made it possible to increase the communication distance. Optical fiber thus surpassed copper, which has a loss of approximately 10 dB/km at 300 kHz, limiting bandwidth growth.

Wavelength Division Multiplexing (WDM) techniques and optical amplifiers have increased the capacity of long-distance links, with data rates now reaching 100 Gbit/s per channel thanks to advanced modulation schemes such as DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying). Fiber optics have revolutionized transmission, enabling very high data rates and extensive coverage.

The access network, or local loop, connects the operator’s connection node to customers, providing telephone, video, and Internet services. With the rise of services requiring high bandwidth—such as video games, HD (high-definition) television, UHD (ultra-high-definition) television, and 3D (three-dimensional) content—demand for bandwidth has skyrocketed. xDSL (Digital Subscriber Line) technologies have increased the capacity of copper networks, but fiber optics have become essential to meet these needs. Since the 2000s, the GPON (Gigabit Passive Optical Network) and EPON (Ethernet PON) standards have dominated, with downstream speeds of 2.5 Gbit/s and 1 Gbit/s, respectively, enabling FTTH (Fiber To The Home) services of up to 1 Gbit/s.

The evolution of networks has enabled exponential growth in Internet traffic and a diversification of services, particularly triple-play services: voice, TV (television), and Internet. Video on demand, online gaming, UHD TV, and 3D TV require continuous infrastructure upgrades. The transition to fiber is gradual, with FTTB (Fiber To The Building) architectures using xDSL or DOCSIS (Data Over Cable Service Interface Specification) technologies for the final few meters, or FTTLA (Fiber To The Last Amplifier) utilizing existing coaxial cable within buildings.

European strategies had set ambitious targets for the year 2020, including speeds exceeding 30 Mbit/s for everyone and 100 Mbit/s for half of the European population. Infrastructure sharing—through sharing or leasing—accelerates broadband deployment. The transition from copper to fiber also involves the gradual phase-out of the PSTN (Public Switched...