Researchers transmit RF signals through fibers
VCSELs could prove to be key components in future cellular networks. Although the devices are widely used today in fiber-optic digital communication, a Swedish team has now transmitted analog signals along fiber, in what could be a key technology for deployment of next-generation wireless networks.
The researchers from Chalmers University of Technology transmitted radio-frequency signals on an optical carrier from a VCSEL along a 500m fiber-optic link. They say that the experiment satisfied the requirements for mobile communication systems and wireless local area networks (WLANs).
The team has also carried out successful trials with Ericsson, using the VCSEL to propagate wideband code-division multiple access (WCDMA) signals for 3G systems along optical fiber.
The analog data is generated by driving a VCSEL with a RF signal. Modulation of the optical intensity follows the RF signal amplitude, so that the signal received by a photodetector bears the hallmark of the original RF signal.
The optical signals are coupled into a multimode fiber, because this is significantly easier to align than a singlemode fiber. Anders Larsson, a member of the Chalmers team, believes that this type of fiber, in combination with the directly-modulated VCSEL, should result in low-cost solutions for network infrastructure.
"We have targeted cost-sensitive applications like distributed antenna systems within buildings in mobile communication systems and WLANs," added Larsson.
The 850nm VCSEL chip was deliberately engineered to exhibit performance characteristics appropriate for analog links. According to Larsson the high power singlemode VCSELs have a relatively low resistance, lower noise, and better linearity than multimode devices, an important consideration for analog applications, since nonlinearities produce distortion.
Larsson and colleagues reported their work in the November 26 issue of New Journal of Physics .
