Recent years have witnessed rapid growth of multimedia content on the Internet, which boosts demand for higher bandwidth. “Broadband” is now one of the most frequently used words. Broadband network is the highway of the information era. People can seek for information and interact with each other on broadband network. Broadband’s high efficiency and convenience accelerate the development of our world. However, with Digital Subscriber Loop technology, traditional copper wire access network has reached its theoretical limits in bandwidth, and can not meet the increasing demand for high bandwidth. Optical access network is, without any doubt, feasible for solving the bottleneck problem of bandwidth.

The concept and consumption of optical access network(OAN) was initially raised in the early 1980s. However, insufficient demand, high cost, complicated technology stopped the OAN from any substantial progress at that time. Recent years, the increasing demand for high bandwidth, dramatic drop of cost and progress in optical network brought optical network to topic again. Especially, as network convergence goes popular today, users show increasing interests in the convergence of video network, vice network and data network. Optical access network appear as the best solution for the convergence because of its high bandwidth, capability to carry more services and flexibility to support protocols.

What is Optical Access Network? Optical Access Network is a telecommunication system that uses optical fibers as transmission media between end users and switch or terminal module, with functions like multiplex, allocation, cross connection and transmission etc, but usually without the function of switch. Compared to traditional access network, Optical Access Network features:

(1) High bandwidth and long distance transmission;

(2) Supporting more services, including narrowband service, broadband service and expansion of service for future need, and support above services simultaneously.

(3) Supporting packetized upper layer services, access layer network for next-generation network.

(4) Supports smooth evolution of access networks

Optical Access Network can be divided into Active Optical Network (AON) and Passive Optical Network (PON). Active Optical Network uses active equipment of Synchronous Digital Hierarchy (SDH), Plesiochronous Digital Hierarchy (PDH) and Ethernet as network node. The equipment need to realized the conversion of optical signal into electrical signal. Most AONs use smart devices as network nodes so they can go up or down or terminate. But building maintenance of Active Optical Network costs too much, which make is unfeasible for access network. Passive Optical Network is a optical signal only network that uses Point to multi-point technology and CWDM technology to solve the problem of bi-way signal transmission. In Passive Optical Network, Optical Line Terminal is installed closer to the core network, and Optical Distribution Network is installed closer to end users, accessing users at 1 to 16, 1 to 32 or 1 to 64 split ratio. At user’s end, Optical Network Unit is installed for the multiplexing and demultiplexing of different businesses of the user. PON is the best currently the best solution for access network due to using less optical fibers and simplicity of operation and maintenance. Presently, PON products includes APON/BPON (ATM PON/Broadband PON), EPON (Ethernet PON) and GPON (Gigabit PON). GPON recommend by International Telecommunication Union and EPON recommended by Institute of Electrical and Electronics Engineers has gone commercial. GPON is based on ATM technology and EPON is based on Ethernet technology. The deference between EPON and GPON is shown in below table:

Obviously, EPON technology, which is mature compared to GPON, has already become the top option for optical fiber access network. What worth mentioning, China as the world’s largest consumer of optical fiber, has widely applied EPON system in it’s major cities like Beijing, Hangzhou, Wuhan, etc.. EPON has now become the major form of optical access network recommended by China’s telecommunication department.