Researchers at the University of Santa Barbara, working with an Intel researcher in Jerusalem, have built the world's first mode-locked silicon evanescent laser, potentially a significant step toward the goal of combining lasers and other key optical components on silicon.

The approach paves the way towards integrating optical and electronic functions on a single chip, with improved cost, power consumption, and size. The work was published this week in the on-line issue of the Optical So

The integration of lasers and photonic devices on silicon would be ideal, combining digital computing power and the speed of light. The only problem -- it is extremely difficult, nearly impossible, to create a laser in silicon. 

Less than one year ago, a research team led by John Bowers at the University of California, Santa Barbara and Intel successfully created laser light from electrical current on silicon by placing a layer of indium phosphide (InP) above the silicon.

In this new study, the team demonstrated electrically-pumped lasers emitting 40 billion pulses of light per second, built on the hybrid silicon platform developed the year prior.

This is the first-ever achievement of such a rate in silicon and one that matches the rates produced by other media in standard use today. These short pulses are composed of many evenly spaced colors of laser light, which could be separated and each used to transmit different high-speed information, replacing the need for hundreds of lasers with just one.

Creating optical components in silicon will lead to optoelectronic devices that can increase the amount and speed of data transmission in computer chipsets, using existing silicon technology.

Employing existing silicon technology is a desirable goal because it would represent a potentially less expensive and easier-to-implement way of mass-producing future-generation devices that use both electrons and photons to process information, rather than just electrons as has been the case in the past.

Mode-locked evanescent lasers can deliver stable short pulses of laser light that are useful for many optical applications, including high-speed data transmission, multiple wavelength generation, remote sensing and highly accurate optical clocks. The researchers said the device could enable new silicon based integrated technologies, such as optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), and opti

The researchers demonstrated electrically pumped lasers on silicon that produce pulses at repetition rates up to 40 GHz, even without RF drive. The mode locked lasers generate 4 picosecond pulses with low jitter and extinction ratios above 18 dB, making them suitable for data and telecommunication transmitters and for clock generation and distribution. The lasers have high quality output characteristics such as low jitter and large extinction ratios, rivaling those of high performance III-V semiconductor MLLs. This makes them potential candidates for optical data transmitters when combined with an optical modulator to encode data onto the pulses. Their ability to be synchronized to low power RF signals enables applications such as OTDM and clock recovery.

Future designs incorporating ring structures, distributed Bragg reflector (DBR) mirrors, or deeply etched mirrors will allow for on-chip integration with other optoelectronic components, integration with CMOS electronics, and precise determination of the repetition frequency, according to the research paper. The ability to transition from gain regions to low loss passive regions will allow new possibilities for MLLs such as lower repetition rate integrated MLLs and single chip OTDM, WDM, and OCDMA sources on silicon.