Silicon optical modulator exceeds 1GHz bandwidth
Silicon’s success in electronics may be about to repeat itself in the world of optoelectronics. In this week’s issue of Nature, scientists at the microelectronics giant Intel report the first silicon-based optical modulator that has a bandwidth exceeding 1 GHz -- 50 times faster than previous efforts. (Nature 427 615)
Although the prototype device’s performance is still far below that of commercial products based on materials such as lithium niobate (LiNbO3) and III-V semiconductors, the development suggests that silicon, the basis of cheap yet powerful computer chips, could also make high-speed optical switches.
It raises the possibility that both optical and electronic functions could be combined on low-cost silicon chips.
“Breakthrough developments such as this fast silicon modulator suggest that a low-cost silicon optical superchip could soon be a reality,” commented Graham Reed, a semiconductor scientist from the University of Surrey, UK, in an accompanying review of the breakthrough in Nature. “It [silicon] is already the world’s favorite electronic material and could yet come to dominate the photonics industry as well.”
The silicon-waveguide modulator is based on a so-called Mach-Zehnder interferometer design. A silicon waveguide is split into two arms which recombine a short distance later. Applying a voltage to one of the arms causes a small change in the refractive index of the silicon and, through optical interference, controls the amount of light leaving the device.
Intel’s prototype operates at the all-important telecoms wavelength of 1.5 microns and requires a drive voltage of about 8 V to achieve an extinction ratio of around 16 dB. However, it currently suffers from a large insertion loss of 15.3 dB.
In contrast, commercial modulators have an insertion loss that is about ten times smaller (5 dB) and can operate at least ten times faster (>10 GHz). However, the Intel team is confident that it can significantly improve device performance by tweaking the design.
Author
Oliver Graydon is Editor of Optics.org and Opto & Laser Europe magazine.
