IBM crafts silicon optical amplifier

    

PORTLAND, Ore. -- Optical amplifiers used in applications like telecommunication links must be made with materials such as indium gallium arsenide phosphide. IBM researchers said they have been able to do the same thing for other applications using a much less expensive standard silicon process.

Fabricated at its Yorktown Heights, N.Y., pilot line using the same silicon photonic waveguides used for telecommunications optical interconnects, the new silicon optical amplifier targets the mid-infrared band used by heat sensors, medical imagers and industrial process monitors.

"Our group has been able to get enough optical amplification to compensate for all the losses on the chip and coupling to the fibers and still have substantial net off-chip gain," claimed IBM researcher William Green. IBM reported 13-dB gain for its all-optical amplifier.

The telecommunications industry today uses the 1,500-nm wavelength, the near-infrared band, but sensors use the mid-infrared wavelengths starting at 2,200 nm. The U.S. military uses mid-infrared wavelengths for sensors in heat-seeking missiles. Mid-infrared also is used to track environmental heat sources.


Heat sensors detect a faint environmental source of heat, convert it to an electrical signal, then amplifies the signal. The process also amplifies the noise of conversion. IBM's all-optical amplifier, however, used four-way mixing to amplify the optical signal before it is converted.

Scanning electron microscope image of IBM's silicon nanophotonic waveguide for mid-infrared wavelengths. (Source: IBM Corp.)

"If you try to use this technique in the telecom band, you run into difficulties. But moving to the mid-infrared allows you to build a very good optical amplifer that takes silicon photonics into a new application space," said Green.

IBM researchers next want to add other optical components on the amplifier chip, including a feedback loop that could create an optical resonator. The resonator could generate many wavelengths at the same time, "sort of a broadband source which is essentially a laser in the mid-infrared," said Green.