Silicon Photonics

As computing and networking performance continue on their exponential growth track, defined by Moore’s Law, the exponentially increasing communication needs will soon exceed the limits of copper wiring. Communications links, or interconnects, are the biggest bottleneck in networks and computers. For example, the next generation of Ethernet runs at 10 Gb/s, and at this speed electrical signals in copper wires can only travel a small distance before fading out completely.

Optical fiber on the other hand is the ideal medium for communications over most distances. The fiber itself is very cheap, and light travels through it for miles even when launched with tiny amounts of power. Optical fiber also has the capability to carry data at rates up to one thousand times faster than 10Gb/s. At each end of the fiber, an optical transmitter/receiver (“transceiver”) is required to interface to the computer or switch. Unfortunately, these optical transceivers currently are extremely expensive. The typical cost of data communications today runs about $100/Gb/s. As a result, optical fiber communication has been largely confined to the capital-intensive long distance telecommunications infrastructure.

Fortunately, Silicon Photonics technology shows promises of delivering low cost seamless optical connectivity from hundreds of meter distances at the network level all the way down to millimeters distances for inter and intra-chip communication. The cost of Silicon Photonics is expected to reach well under $1/Gb/s, many times cheaper than typical data communication links.
Within 10 years, the established approach of using electricity in copper wiring just won’t work, and the ideal approach of using light in optical fiber is just simply too expensive. Only low cost disruptive technology can tip the balance from copper wiring to fiber optics to allow the computing and networking performance to continue on an exponential growth path. Silicon Photonics can fulfill this role.

Since silicon is not an efficient electrically pumped laser material, most silicon photonic solutions need a steady source, or Continuous Wave (CW), of laser light to power the interconnection. This source can be a typical laser based on III-V substrates such as GaAs and InP. The data transfer from electrical to optical occurs in a modulator, in which a voltage applied to a silicon photonic modulator will change the amount of light transmitted. Similarly, data on a light stream is converted back into an electrical current in a silicon photonic detector. Electronic drivers and receivers on each end of the path help with the signal quality. Finally, for increased total data rate and lower cost, it’s best to have many communication channels combined or wavelength division multiplexed (WDM), onto one fiber or waveguide. These modulator, detector and WDM elements can be integrated together on one Si photonic chip for best performance and lowest cost.

The cost of most silicon photonic devices can be relatively low, like that of silicon electronics. Therefore, the majority of the cost of silicon photonic interconnects will be in the source lasers that must meet tough specifications. These lasers will need to emit high power with low noise at wavelengths that are transparent in Silicon, above 1.1 micrometers. Also, for increased total bandwidth and cost efficiency, a preferred solution would send multiple data channels on multiple wavelengths on one fiber, called wavelength division multiplexing, or WDM. The laser also must operate in a very harsh environment, perhaps from below 0 C to over 100 C.

Innolume’s lasers based on are uniquely qualified to address these needs for silicon photonics.