Fujitsu develops 4-V optical modulator for 40G optical transmission systems

MARCH 27, 2007 -- Fujitsu Limited (search for Fujitsu) has developed what the company says is the world's lowest drive-voltage differential quadrature phase-shift keying (DQPSK) LN optical modulator for 40-Gbit/sec optical transmission systems. The product -- which Fujitsu says will make possible the construction of commercial systems with greater reliability, low power consumption, and high transmission quality -- will be available starting June 1, 2007.

Dramatic increases in data transmission traffic have resulted in the increasing deployment of 40-Gbit core optical network systems. While many optical transmission signal encoding methods are under consideration, DQPSK transmission technology is becoming essential due to its strength against signal distortions resulting from transmission fibers and relay nodes, as well as its superior bandwidth efficiency.

There has been growing demand for low drive voltage and broadband optical modulators required for the construction of commercial optical transmission systems. However, achieving both low drive voltage and broadband capabilities has been a major challenge for DQPSK-compatible modulators, due in part to their complicated structures.

Conventional LN modulators have required 20-Gbit/sec high-speed electric signals of 10 V or more in order to generate 40-Gbit/sec DQPSK signals, and reducing the size and power consumption of drive circuits while maintaining reliability has been a challenge In order to generate high-quality DQPSK signals, it is necessary to expand the bandwidth of optical frequency response.

Using technology similar to that employed in previously commercialized 40-Gbit/sec LN moderators, a 25-GHz bandwidth has been achieved. Fujitsu's new LN modulator achieves a drive voltage of 4 V, which is thought to be the lowest in the world, making it a practical optical modulator for use in commercial systems.

Positioning multiple high-speed electrical signal input terminals close together on one side of the modulator enables generation of DQPSK signals without the need to adjust for electrical signal lag on the drive circuit. Furthermore, employing separate input terminals for the high-speed electrical signals and the DC bias signals for controlling the modulator eliminates the need for an external electrical circuit to combine them.

Fujitsu will have samples of the new LN optical modulator on exhibit at OFC/NFOEC 2007 in Anaheim, CA, from March 27-29.

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