VCSEL Array-Based Gigabit Free-Space Optical Femtocell Communication

摘要

We present an indoor free-space optical communication system to augment traditional short-range radio frequency wireless links. In this system, we integrated a high-frequency, high-current laser driver with an 850 nm wavelength, 500 mW vertical cavity surface emitting laser (VCSEL) array to transmit high speed optical signals with a large spatial coverage. The large current-bandwidth capability of the laser driver is enabled by a distributed current driver design utilizing three enhanced-mode pseudomorphic high electron mobility transistors. At the optical receiver end, a high-sensitivity avalanche photodiode is used to achieve high speed optical signal detection without any light concentrating optical device and is tolerant to angular deviation up to 27 degrees. The communication link described in this article forms an optical femtocell with an area of 100 cm(2) at a distance of three meters from the transmitter. A bit error rate of less than 10(-4) is achieved throughout the optical femtocell in a normal in-door environment. On-off-keying and four-level pulse amplitude modulation schemes are both implemented with 1.25 Gb/s and 2 Gb/s data rate respectively, using the hardware described in this article. Additionally, the overall performance of this free-space optical link is evaluated in terms of viewing angle, distance range, and bit error rate.