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. Military and emergency personel use heat imagers that work at these wavelengths, allowing them to locate 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.

"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.