History of Passive Optical Networking

The concept of using light to communicate has been around for hundreds of years. Alexander Graham Bell even patented a concept for an optical telephone system in 1880 and called it the Photophone. Various mechanisms for bending and channeling light were created in the latter part of the 19th century and on into the early 20th century. These light pipes were used for a variety of applications including ornamental applications and even illuminating body cavities in medical studies.

It wasnt until 1930 that Heinrich Lamm become the first person to transmit an image of a light bulb filament through a bundle of optical fibers. The 1950's saw various patents and capabilities developed around the concept of coating glass or plastic fibers with a cladding designed to reduce the loss of signal along the fiber. In 1958, the first laser was developed which led to many optical technology developments over the next 10 years. Then, in 1970, Corning Glass Works developed a titanium doped single mode fiber that presented low attenuation (less than 20dB/km). Up to this point this optical power-versus-distance challenge was impeding the proliferation of optical communications networks. In that same year, Bell Laboratories, produced a semiconductor diode laser which was suitable for transmitting and receiving high speed optical communications. In 1975, after lightning destroyed the Dorset, UK police communications system, the first optical fiber communications link was put into service. In 1977 the first telephone traffic began to flow through fiber optic cables in Long Beach, California. By the early 1980's extensive fiber optic long distance voice deployments had signaled that the optical communications age had arrived.

The concept of a passive optical network has been around for longer than one might think. In fact one of the first fiber to the home deployments occurred in the southwest of France in 1986 where 1500 homes were connected to an early switched broadband system in the town of Biarritz. That same year, the erbium doped fiber amplifier or EDFA was invented which allowed optical signals to be amplified without first converting them to electronic signals and back again.

It wasn't until 1995 when the first ITU standards were being developed that the concept of PON began to take shape as a true replacement for legacy TDM technologies. During that time PON technology was based upon ATM (asynchronous transfer mode) and was referred to as APON. Later, as DSL speeds increased and carriers required more security, BPON arose and those standards were established by the ITU in 1998. At the same time the IEEE was establishing its standards for EPON.

Both APON and BPON are similar in their approach but the newer BPON standard is much more prevalent. BPON is characterized by a 622 Mbps downstream and 155 Mbps upstream bit rate. BPON initially included a scrambling mechanism for security rather than true encryption. At the same time EPON (Ethernet PON) was rapidly developing and has since become the most prevalent PON standard in the world today. Deployed mostly in Asia/Pacific regions, EPON is characterized by a 1.25 Gbps symmetrical bit rate although the newer IEEE 802.3av standard includes an asymmetrical 10 Gpbs downstream/1.25 Gbps upstream bit rate. GPON (or Gigabit PON) is an ITU standard (G.984) and is characterized by a 2.5 Gpbs downstream and a 1.25 Gbps upstream bit rate. GPON has become the most popular standard implemented in North America with AT&T's U-verse and Verizon's FiOS service offering being the most well known GPON services.

Note that early in the development of EPON, the technology was known as Gigabit Passive Optical Networking (GPON) however, as the ITU began gaining ground with its standard, the GPON name came to be more associated with the ITU implmentation than the IEEE. Now the IEEE version is simply referred to as EPON (Ethernet PON) or alternatively, GEPON (Gigabit Ethernet PON).