Optical amplifier integrates VCSEL to avoid distortion

TECHNOLOGY

By KATHLEEN RICHARDS

A "linear optical amplifier" (LOA) that integrates vertical-cavity surface-emitting laser (VCSEL) technology on a single chip to handle optical signals without distortion is characterized as breakthrough technology by Genoa Corp., a startup based in Fremont, CA. Introduced last month at OFC, Genoa's LOA is able to amplify optical signals, while avoiding signal distortion such as crosstalk between channels, a common problem for semiconductor optical amplifiers handling multiple wavelengths at higher data rates.

"The laser is continuously pumping photons into the amplifier, which greatly increases the power that is available out of the amplifier without distortion," explains Rick Gold, president and chief executive officer at Genoa. "It just supplies a continuous source of photons, and they are available very quickly because the relaxation time of the laser is very, very short, on the order of a picosecond, which means that it takes almost no time for an amplifier to respond to an input signal." The photons supplied by the laser counteract any variations in the gain of the amplifier, which is >15 dB, according to the preliminary specifications.

"It's like a ballast on a sailboat," says Gold. "When you get a big signal coming in just like a big puff of wind coming in to a sailboat, what happens is the big supply of photons that this laser is creating inside the chip is just like the weight in the keel of a sailboat-it is able to keep that signal coming through without distortion."

The output signals are therefore "linear," more or less faithful to the input signals-at least within required design limits, according to the company. Unlike other amplification technologies, linear optical amplification can work with unpredictable data rates and in switched networks. As such, it is well suited for DWDM applications in metropolitan-area networks.

The 1-mm square LOA chip, made of indium phosphide, is manufactured using a planar fabrication process. "We do all the fabrication ourselves; the VCSEL and the amplifier share the same gain region of the semiconductor chip, so it is all one device," says Gold. "We're fabricating that entirely in the new facility that we've built here." The first devices will be available in standard butterfly packaging.

Although pricing has not been determined, the devices are expected to offer a "10x lower installed cost than current solutions," according to the company. Power is >13 dBm, according to preliminary product specifications.

Genoa will have commercial samples by the end of the year. The first devices will operate in the C-band, with future products planned for the L- and other bands. Product plans include arrays of amplifiers on a single chip and higher-power amplifiers, with a vision toward integrated optical circuits.

The LOA is Genoa's first product. Founded in 1998, the company has obtained more than $95 million in funding and has facilities in Eindhoven, the Netherlands, in addition to its Fremont headquarters.

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