Fiber: FTTN, FTTC, FTTP/FTTH

The History of Fiber Optics

In 1966, Charles Kao (then at Standard Telephones and Cables) published a groundbreaking paper proposing that glass fibers could carry information over long distances if impurities were removed. At the time, glass attenuated light at1,000 dB/km — making long-distance transmission impossible. Kao calculated that reducing attenuation below 20 dB/km would make practical fiber communication feasible. He was awarded the Nobel Prize in Physics in 2009 for this work.

In 1970, Corning Glass Works (now Corning Incorporated) achieved the breakthrough: 17 dB/kmloss in a doped silica fiber. Today's single-mode fibers achieve 0.2 dB/km at 1550 nm — a 5,000x improvement that enables transoceanic cables spanning 10,000+ km without active repeaters.

How Fiber Works

Fiber optic cables transmit data as pulses of light through strands of glass thinner than human hair. Total internal reflection keeps the light bouncing along the fiber core, allowing transmission over hundreds of kilometers without regeneration. A laser or LED launches light into the core, and a photodiode at the receiving end converts the optical signal back to electrical.

Fiber Types and Standards

• Single-mode fiber (SMF): 8–10 μm core diameter, carries a single propagation mode. Operates at 1310 nm (zero dispersion) and 1550 nm (minimum attenuation). Reach: 100+ km without amplification. Used for long-haul, metro, and FTTH.
• Multi-mode fiber (MMF): 50 μm or 62.5 μm core, carries multiple modes. Uses 850 nm VCSEL (Vertical-Cavity Surface-Emitting Laser) light sources. Reach: 300–500m (OM3/OM4 laser-optimized). Used for data centers and enterprise LANs.
• OM3/OM4: Laser-optimized multi-mode for 10/40/100 Gbps. OM3 supports 10GbE to 300m, OM4 to 400m. OM5 adds wideband support for SWDM (Short-Wavelength Division Multiplexing) at 850–950 nm.

FTTx Architecture Explained

FTTx (Fiber To The x) describes how far fiber extends into the network:

• FTTN (Node): Fiber to neighborhood cabinet, 1–2 km copper (VDSL2/G.fast) remaining
• FTTC (Curb): Fiber to curb, 100–300m copper remaining
• FTTB (Building): Fiber to building (MDU), copper within (Cat6/Coax)
• FTTP (Premise): Fiber to premise — all-fiber to the building
• FTTH (Home): Fiber all the way to the home — the gold standard

PON: Passive Optical Networks

PON uses passive optical splitters to connect multiple homes to one fiber:

• GPON (ITU G.984, 2005): 2.5 Gbps down / 1.25 Gbps up, 1:64 split, 20 km reach. Uses 1490 nm downstream / 1310 nm upstream. Ethernet-based framing with 125 μs T-CONT frames.
• EPON (IEEE 802.3ah, 2004): 1 Gbps symmetric. Native Ethernet frames, simpler architecture. Popular in Asia (Japan, Korea, China).
• XGS-PON (ITU G.9807, 2015): 10 Gbps symmetric, 1:128 split. Uses 1577 nm / 1270 nm wavelengths. Enables symmetrical gigabit service and 5G mobile backhaul.
• NG-PON2 (ITU G.989, 2015): 40 Gbps aggregate, wavelength stacking with 4×10G pairs. Tunable ONTs auto-select wavelengths.
• 25G-PON: 25 Gbps symmetric (emerging, multi-vendor)
• 50G-PON (ITU G.9804): 50 Gbps symmetric (in development, targeting 2025+)

Wavelength Division Multiplexing

WDM packs multiple wavelengths (colors) of light onto one fiber, multiplying capacity:

• CWDM (Coarse WDM): 20 nm channel spacing, up to 18 channels (1270–1610 nm). Lower-cost lasers (uncooled DFB). Used for metro and enterprise links.
• DWDM (Dense WDM): 0.8 nm (100 GHz) or 0.4 nm (50 GHz) spacing, 40–96 channels in the C-band (1530–1565 nm). Uses temperature-stabilized DFB or tunable lasers. Combined with EDFA, enables 40×100 Gbps = 4 Tbps per fiber.
• C-band: 1530–1565 nm — lowest attenuation, EDFA-compatible, primary DWDM band
• L-band: 1565–1625 nm — extended capacity when C-band is exhausted

Modern submarine cables use 40+ channels × 200 Gbps × 8 fiber pairs = 64+ Tbpsper cable across ocean basins.

EDFA: The Amplifier That Changed Everything

The Erbium-Doped Fiber Amplifier (EDFA) was first demonstrated bySimon Poole at the University of Southampton in 1987. The EDFA works by doping the core of an optical fiber with erbium ions (Er³⁺) and pumping them with a laser at 980 nm or 1480 nm. When a signal at 1530–1565 nm (C-band) passes through the doped fiber, the excited erbium ions amplify the signal throughstimulated emission.

A single EDFA provides gain of 30–40 dB (1000–10,000× amplification) across approximately 35 nm bandwidth, amplifying dozens of DWDM channels simultaneously. This eliminated the need for expensive optoelectronic regenerators on long-haul fiber links, reducing the cost of long-distance fiber communication by orders of magnitude. Poole later founded Finisar Australia, which commercialized EDFA technology and developed the Wavelength Selectable Switch (WSS) — a component now deployed in optical networks worldwide.

Global Fiber Deployment

South Korea leads with 97% FTTH coverage. Japan, China, and Nordic countries follow. The US lags at ~35% FTTH, though regional providers like Google Fiber, AT&T, and municipal networks are expanding. The EU targets 50% 1 Gbps coverage by 2030.