INTERVIEW Silicon lasers: the fi nal frontier

People have been trying to get silicon to lase since the fi rst semiconductor laser in the 1960s. Thanks to recent breakthroughs, silicon lasers are fi nally beginning to take fl ight. Amber Jenkins spoke to Haisheng Rong, Victor Krutul and Manny Vara at Intel to fi nd out more.

Silicon photonics is all the rage right now. Where next for your silicon laser? Why the interest in silicon lasers? In the short term, we need to address Optical communication has changed our interface issues — how to get light in or out of lives. By hooking a laser up to a transatlantic the chip more effi ciently. It’s very challenging cable, you can drive an optical signal for to keep losses within the waveguide small thousands of kilometres and transmit a lot when you shrink it to tiny proportions, but of data with very low loss. Th e problem is we can overcome this. In the longer term, that conventional communication lasers are we want to make the laser cavity more made from exotic semiconductor materials tunable. With the proper design one can that are not produced in bulk, so they are envisage shift ing the emitted wavelength to too expensive for interconnects or to put the mid-infrared range and creating a room- into computers or servers where we cost temperature mid-infrared laser. Th is would things in ‘pennies per pin’. open up a lot of applications. Today most optical functions can be performed in silicon using components such What kinds of applications are in store for as waveguides and modulators, but the laser the silicon laser? is really the fi nal frontier. We make hundreds Historically Raman lasers have been less of millions of silicon chips per year; if we can INTEL popular than their traditional counterparts, use existing CMOS manufacturing facilities but they can cover spectral gaps not accessible to make silicon lasers, we can drive the price Pioneers of silicon lasers. From left to right: Shengbo Xu, to conventional lasers. In biomedicine, a down and open up mass-market applications Simon Ayotte, Haisheng Rong and Jonathan Doylend. silicon Raman laser could be important for to optical technology. detecting specifi c molecular transitions. Alternatively, doctors and dentists could use a What was the impact of your fi rst Raman laser that emits several wavelengths for continuous-wave silicon Raman laser? off on a normal runway. We’ve boosted the diff erent purposes: one wavelength for tooth When we started working on the silicon laser’s power output by fi ve times to more ablation, say, and another for tissue incisions. laser two years ago, we took a diff erent than 50 mW, decreased its lasing threshold by route. Most people had attempted to create ten times and scaled down its size from 5 cm How will silicon lasers aff ect people’s lives? a laser based on stimulated emission, but we to 1.5 cm. Using a ring cavity, we’ve integrated Th e killer application for silicon lasers is used stimulated Raman scattering instead. the entire cavity onto a chip — crucial for information — delivering huge amounts of Demonstrating the fi rst continuous-wave connecting it to other components. More data, and fast. In the future we can imagine Raman laser in silicon was a technological importantly, we no longer need an external some form of silicon lasers sitting alongside breakthrough. More importantly, it was a power supply to achieve lasing. Th e device processors inside high-performance servers psychological breakthrough. Up to that point, has become 100% optical and can be used in around the world, helping to transmit data people didn’t believe that a practical laser applications that don’t have access to external from one computer to another in record time. could be made using silicon. Our work said power, such as remote sensing, You might be able to download the entire to the fi eld: “Th ere is hope aft er all.” content of a fi lm in a couple of seconds rather How has the environment at Intel shaped than the half a day it can take at present. How have things progressed since then? this progress? But aside from computers, by siliconizing Our fi rst silicon laser was really a proof-of- As photonics researchers, we are very photonics we can take optics to places no- concept demonstration, a bit like the fi rst lucky to work closely with fabrication- one thought possible, infl uencing optical fl ight taken by the Wright brothers when they process engineers. Th ey give us valuable communications, wireless technology, sensing, invented the aeroplane — we showed it was insights into the manufacturing techniques lab-on-a-chip research and even healthcare. possible, but there were still lots of practical that enable us to get optical functions Th ese things will profoundly aff ect people. issues. It was a simple construction — a out of the chip. Working in a company Th e silicon laser is a key part of this vision. silicon waveguide and a linear laser cavity. such as Intel, which makes silicon But the cavity design did not enable chips for a living and makes them very Amber Jenkins is an associate editor of Nature integration with other photonics components well, we have that entire infrastructure Photonics and is based in San Francicso. on chip, and the laser required relatively high behind us. It’s a nice combination to e-mail: [email protected] power to operate [about 200 mW]. have and helps us to translate research Since then we’ve put wheels on the plane, and development into high-volume, Rong and his co-workers have an article on and built a stronger engine so that it can take low-cost end products more quickly. Raman silicon lasers on p232 of this issue.

240 nature photonics | VOL 1 | APRIL 2007 | www.nature.com/naturephotonics