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Optical amplifier tech aimed to reach >40km

Posted: 01 Nov 2011 ?? ?Print Version ?Bookmark and Share

Keywords:optical aggregation network? optical amplifier? optical access system?

Fujitsu Limited and Fujitsu Laboratories Limited today have begun the development of optical amplifier technology that can have 128 terminal-equipment connections, with distances of more than 40km, the companies said. They added that it is designed for optical access systems that link subscribers to central offices and features four times the splitting number and twice the transmission distance.

The use of optical aggregation networks has been proposed as one way to reduce the constantly growing amount of electrical power consumed by networking equipments. Although passive optical networks (PONs) that increase transmission speeds in both downstream and upstream from the prevailing speed of 1Gbit/s-10Gbit/s are now starting to be deployed commercially, there are constraints in using them for optical aggregation networks. This is because the number of optical network terminals (ONTs) for the most commonly used PON is typically limited to 32 connections and its transmission distance is also limited to about 20km.

Optical access system

Increased splitting number and transmission distance in optical access system using this technology.

To solve these constraints, especially in upstream bursts, Fujitsu and Fujitsu Laboratories have developed a burst-mode optical amplifier technology with a semiconductor optical amplifier (SOA), an integrated SOA-array module fabrication technology, and an SOA chip fabrication technology enabling uncooled operation. These three technologies, used together, make it possible to quadruple the splitting number in an optical access system and double the transmission distance between the central office equipment and the terminal equipment.

This makes it possible for a next-generation optical access system to be used as an optical aggregation network at low cost and with low power consumption requirements, paving the way for cloud infrastructure. The research results achieved by the Commissioned Research of National Institute of Information and Communications Technology (NICT) have been applied to portion of this work.

Burst-mode optical amplification
One method that has been considered for increasing the number of ONTs is the installation of optical amplifiers in remote nodes that lie between OLT and ONT that would compensate for fiber and splitting losses. The technology announced here is for an amplifier that detects an incoming upstream burst and rapidly switches its 'off'-state to 'on'-state for amplification. Whereas, conventionally, there would be multiple continuous 'on'-state optical amplifiers installed, with a proportionate amount of noise making the optical signal-to-noise ration worse, the new technology turns on only the optical amplifier with an incoming upstream burst. This means, for example, that even with four optical amplifiers installed in the remote node (where each optical amplifier equipped to 32-way split), up to 128-way split can be supported with the same amount of the optical signal-to-noise ratio as 32.

Integrated SOA-array module fabrication
In an industry first, integrated four semiconductor optical amplifiers are fabricated into a single module. The newly-developed optical coupling scheme simultaneously couples four SOAs with four single mode fibers with high efficiency, which reduces cost and footprint per piece, stated the companies.

SOA chip fabrication enabling uncooled operation for small footprint and power-saving
An aluminum composite material is deployed in the active layer of the semiconductor optical amplifier to obtain high gain, even at high temperatures, eliminating the temperature control of SOA. This dramatically contributes to the reduction of the module volume to one-fifth and one-sixth the power compared with a conventional cooled SOA module. It operates at temperatures of up to 85C, so it can be installed outdoors on utility poles or in street gutters, allowing for remote nodes that need to operate under harsh conditions.

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