“Silicon Photonics is a critical part of tera-Scale computing as we need the ability to move massive amounts of data on and off these very high performance chips” - Justin Rattner, Intel Chief Technology Officer
Research Breakthrough: Hybrid Silicon Laser
Intel and the University of California Santa Barbara (UCSB) announced the demonstration of the world's first electrically driven Hybrid Silicon Laser. This device successfully integrates the light-emitting capabilities of Indium Phosphide with the light-routing and low cost advantages of silicon. The researchers believe that with this development, silicon photonic chips containing dozens or even hundreds of hybrid silicon lasers could someday be built using standard high-volume, low-cost silicon manufacturing techniques. This development addresses one of the last hurdles to producing low-cost, highly integrated silicon photonic chips for use inside and around PCs, Servers, and data centers.
The hybrid silicon laser is a key enabler for silicon photonics, and will be integrated into silicon photonic chips that could enable the creation of optical “data pipes” carrying terabits of information. These terabit optical connections will be needed to meet the bandwidth and distance requirements of future servers and data centers powered by hundreds of processors.
The demonstration of the first electrically pumped hybrid silicon laser overcomes one of the last remaining obstacles of integrated silicon photonics; namely, developing a low-cost light source on silicon. Previously, getting laser light from a silicon photonic chip was done using one of two approaches: attach and align individual pre-fabricated lasers directly to a silicon waveguide or have a high-powered external laser source off the chip and then route the light into the silicon chip using an optical fiber. Both approaches are expensive and not practical for high-volume production. This new laser is termed “hybrid” because it combines two materials: Silicon and an Indium Phosphide based material The Indium Phosphide based material is a compound semiconductor that is widely used today to produce commercial communication lasers.
When voltage is applied to the contacts, current flows, and the electrons (-) and holes (+) recombine in the center and generate light.
There are two key aspects to this development.
- A novel design that uses an Indium Phosphide based material for light generation and amplification bonded to a silicon waveguide that forms the laser cavity and determines the laser's performance.
- A unique manufacturing process which create a “glass-glue” which “fuses” these two materials together. This glass-glue is a mere 25 atoms thick.
In this process, the Indium Phosphide based wafer is bonded directly to a pre-patterned silicon photonic chip. This bonding does not require alignment of the indium phosphide based material to the silicon waveguide chip. When a voltage is applied to the bonded chip the light generated from the Indium Phosphide based material couples directly into the silicon waveguide creating a hybrid silicon laser.
This bonding technique can be performed at the wafer or die level, depending on the application, and could provide a solution for large scale optical integration onto a silicon platform.
Silicon Photonics Research
Silicon is the principal material used in semiconductor manufacturing today, because it has many desirable properties. For example, silicon is plentiful, inexpensive, easy to work with, and well understood by the semiconductor industry. Intel, in particular, has developed some of the most advanced silicon fabrication technology available today. Due to the company's leadership in this area, it has long invested in research to “siliconize” other technologies, such as optical communications. The resulting field-known as silicon photonics-aims to provide inexpensive silicon building blocks that can be integrated together to produce optical products that solve real communication problems for consumers.
Silicon is an especially useful material for photonics components due to one key property: it is transparent at the infrared wavelengths at which optical communication operates. Therefore, while silicon is opaque to the human eye, it appears clear as glass to a laser operating at infrared wavelengths.
The hybrid silicon laser announcement builds on Intel's other accomplishments in its long-term research program to “siliconize” photonics using silicon and silicon manufacturing processes. In 2004, Intel researchers were the first to demonstrate a silicon-based optical modulator with a bandwidth in excess of 1GHz. A year later in 2005, researchers demonstrated data transmission at 10Gb/s using a silicon modulator. Also in 2005, Intel researchers were the first to demonstrate that silicon could be used to amplify light and produced a continuous wave laser-on-a-chip based on the “Raman” effect. In 2006, Intel researchers demonstrated world-class performance in silicon-germanium photo-detectors.
Benefits and Potential Applications
The principal benefit of the hybrid silicon laser is that silicon photonics components no longer need to rely on aligning and attaching discrete lasers to generate light into a silicon photonic chip. In addition, dozens and maybe even hundreds of lasers can be created with a single bonding step. This has several advantages:
- The laser is compact so it allows many lasers to be integrated on a single chip. The first demonstration hybrid silicon laser is only ~800 microns long. Future generations will be significantly smaller.
- Each of these lasers can have a different output wavelength by simply modifying the silicon waveguide properties without having to modify the Indium phosphide based material.
- The materials are bonded with no alignment and are manufactured using high volume, low cost manufacturing processes.
- Easy to integrate with other silicon photonic devices to produce highly integrated silicon photonic chips. An example of this is shown below
Concept image of a future integrated terabit silicon optical transmitter containing 25 hybrid silicon lasers, each emitting at a different wavelength, coupled into 25 silicon modulators, all multiplexed together into one output fiber.
With this highly integrated silicon photonic transceiver, it is possible to imagine a future world in which most computing devices are endowed with high-bandwidth optical connectivity. Be they servers, desktops, or smaller client devices, all devices will have access to substantially greater bandwidth at a lower cost.
Intel is actively continuing its research work in silicon photonics, in the hope of building smaller, faster, and less expensive optical components that fulfill the goal of universal, ubiquitous, low cost, high-volume optical communications.
The announcement from UCSB and Intel demonstrating the first electrically powered hybrid silicon laser is another example demonstrating progress towards this overarching goal. The research collaboration has been able to successfully combine the light-emitting capabilities of Indium Phosphide based materials and the light-routing capabilities of silicon.
Researchers believe that with this development , silicon photonic chips containing dozens or even hundreds of hybrid silicon lasers could someday be built using standard high-volume, low-cost silicon manufacturing techniques. This development addresses one of the key hurdles to producing low-cost, highly integrated silicon photonic chips for use inside and around PCs, Servers, and future data centers.