Fujitsu Labs touts small 25-Gbps per channel optical transceivers

Fujitsu Laboratories Ltd. says its researchers have developed a compact, cost-effective optical transceiver capable of transmitting 25 Gbps per channel. The development aims to meet the needs of next-generation high-speed servers.

Improved driver IC circuit and module packaging structures enable the 25 Gbps per channel performance, Fujitsu Labs says.

Current optical transceivers for server interconnect typically range between 10 and 14 Gbps, the lab notes. These devices also are bulky, making it difficult to place near CPUs or other devices.

To overcome these challenges, Fujitsu Laboratories says it was able to increase IC circuit speeds by making optical waveforms rise and fall more steeply, even in inexpensive optical devices with insufficiently fast response times. It also used circuit technology that suppresses multiple reflections that degrade the electrical signal's waveform. The two techniques increased data rates from the current 10-14 Gbps to 25 Gbps per channel.

Meanwhile, it also addressed optical coupling issues. A typical optical coupling unit comprises a lens component and an optical connector. However, the size of the lens component often is large and expensive, the lab states. Fujitsu’s approach consists of an opto-electric converter with a flexible printed circuit board that has been equipped with optical devices and ICs. The result is a more compact optical transceiver. The labs also developed a cost-effective film-type lens sheet that is stacked on the underside of the flexible PCB.

Fujitsu Labs says it used these technologies to create a prototype of a 4x25-Gbps opto-electric converter. With a size of 22x9x0.86 mm (including on-board electrical components and optical waveguide), the lens component is less than one-tenth the size of conventional lens components in opto-electric converters, while the overall unit is less than one-third the conventional size, Fujitsu asserts. Taking advantage of the thin size, Fujitsu Laboratories developed optical transceivers with the prototype opto-electric converters placed on both sides. Transmitters and receivers both utilized eight channels with a size of 47.8x16x 21.6 mm, enabling adjacent devices such as the CPU on the printed circuit board to occupy a smaller area.

Fujitsu Laboratories says R&D will continue to apply this technology to high-performance servers, with the goal of practical use in servers within three years. It also plans to extend this technology more widely to increase the performance of information and communications equipment.