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28 August 2007


Intel demos first 40GHz hybrid InP/silicon laser

A research team led by John Bowers, a professor of electrical and computer engineering at the University of California Santa Barbara, working with Intel researcher Oded Cohen in Jerusalem, has demonstrated the first mode-locked silicon evanescent laser: an electrically pumped indium phosphide laser fabricated on silicon that produces pulses at repetition rates of up to 40GHz (B.R. Koch et al, Optics Express, Vol. 15, Issue 18 (3 September 2007), p11225).

This is the first reported achievement of such a rate on silicon and matches the rates produced by other media currently in standard use, the researchers claim.

Late last year, the team demonstrated the first hybrid silicon laser (operating in continuous-wave mode). The device integrates an indium phosphide laser diode bonded to a silicon waveguide (allowing evanescent coupling of light emitted from the InP active layer into the silicon-based laser cavity). The latest laser builds on this platform by adding elements to the laser cavity that allow it to emit highly stable ultra-short (4ps) light pulses, with low jitter and high extinction ratios (above 18dB), rivaling those of III-V mode-locked lasers (MLLs), it is claimed.

Doctoral candidate Brian Koch says that Intel is already producing experimental optical modulators, but lacked a stable silicon pulsed laser as a multi-spectrum laser light source. Now, when combined with an optical modulator to encode data onto the pulses, the mode-locked laser is suitable for all-silicon high-speed datacom and telecom transmission, multiple wavelength generation, remote sensing using LIDAR (Light Detection and Ranging), and highly accurate optical clocks.

According to the researchers, the latest development represents a step towards combining lasers and other key optical components with existing electronic capabilities in silicon, providing a practical way to integrate optical and electronic functions on a single chip and enable new types of ICs that are less expensive, lower power, and more compact.

Future designs incorporating ring structures, distributed Bragg reflector (DBR) mirrors, or deeply etched mirrors should allow for on-chip integration with other optoelectronic components, integration with CMOS electronics, and precise determination of the repetition frequency, say the researchers. The ability to transition from gain regions to low-loss passive regions should allow new possibilities for MLLs such as lower-repetition-rate integrated MLLs and single-chip optical time-division multiplexing (OTDM), wavelength division multiplexing (WDM), and optical code division multiple access (OCDMA) on silicon.

“Because our silicon laser is so powerful and its pulses so well timed, we could combine, say, four 40Gb/s lasers into a single 160Gb/s signal,” adds Koch. “One other thing we hope to do is separate all the wavelengths coming out of each pulse, to create an array of wavelengths that could be separately modulated then recombined for multi-channel communications over a single fiber."

The UCSB-Intel team’s latest advance was supported by funds from the Microsystems Technology Office of the Defense Advanced Research Projects Agency (DARPA) at the US Department of Defense.

See related item:

First electrically pumped hybrid silicon laser