SOA delivers 100 Gbit/s performance for all-optical networks

21 Sep 2007

CIP's nonlinear SOA allows easy integration for all-optical functions such as wavelength conversion and signal regeneration.

CIP, a UK-based developer of advanced photonic components, has introduced a semiconductor optical amplifier (SOA) that the company says can be used in all-optical networks operating at up to 100 Gbit/s. David Smith, CIP's CTO, told fibers.org that the key to the device's high-speed performance lies in its extremely fast recovery time.

"Our new SOA has a gain recovery time of just 10 ps," Smith said at the ECOC exhibition earlier this week. "We believe it is the fastest commercial SOA ever created."

SOAs are essentially laser diodes with anti-reflection design elements that prevent the amplifier from acting as a laser and a gain medium designed to minimize the polarization-dependent gain (PDG) of the packaged module. Linear SOAs have been developed as a cheaper and smaller alternative to erbium-doped fiber amplifiers (EDFAs), but despite continued development they still suffer from higher noise levels and lower saturation powers.

These issues have limited the use of SOAs to applications where they can offer greater functionality than a simple gain block. One example is the nonlinear SOA, which is being developed for all-optical signal processing functions such as all-optical switching and wavelength conversion. As a result, research has focused on using SOAs as elements for optical signal processing, wavelength conversion, clock recovery, signal demultiplexing and pattern recognition.

The tuned characteristics of CIP's new SOA make it ideal for all-optical wavelength conversion based on four-wave mixing, cross-gain modulation or cross-phase modulation effects. Its phase-change characteristics and 20 dB gain can also be exploited to regenerate optical signals, while Smith says that the device can also be used for implementing all-optical Boolean logic functions.

The SOA, which operates at 1550 nm, exploits a multiquantum well structure in indium phosphide. The device also features an internal active waveguide with a high confinement factor to optimize the device's performance. The device has a saturated PDG of just 0.2 dB.

CIP already produces a 40 Gbit/s SOA, which can be fabricated in arrays to produce highly integrated 2R regenerators. According to Smith, the new device is also easy to produce in arrays, and features unique integration features that eliminate the need for costly active alignment.

"The device's large-spot ultralow reflectivity interfaces, when combined with our unique hybrid integration technology, make it possible to build component subsystems using passive alignment," said Smith. "This is a genuine breakthrough for all-optical system building."

This hybrid integration technology exploits a low-cost planar silica motherboard to provide the interconnection fabric for components such as SOAs, filters and photodiodes. System components are mounted on daughterboards with precision-machined mating faces, and assembled by means of a push fit. This means that individual components require only minor modifications at their interface edges to be made compatible with the assembly technique.

The new SOA is provided in a butterfly package, and is currently available in small quantities to support research and development applications. Integrated versions of the device, and other packages suitable for high-volume applications, are available from CIP on request.

• Visit fibers.org for more coverage from the ECOC conference and exhibition.