Performance and Noise Analysis of VCSEL ROF Using Spherical-ended Multimode Fiber Coupling

A low cost radio-over-fiber (ROF) transmitter has been built based on extremely low cost 850 nm vertical-cavity surface-emitting laser (VCSEL) diode using spherical-ended multimode fiber (MMF) coupling technique. This technique has been shown to deliver excellent light launching characteristics for VCSEL lasers in short haul ROF applications. Transmission distance of more than 600 m has been demonstrated experimentally with consistent performance highly desired for transmitting WLAN RF signals in both 2.45 and 5.25 GHz in a directly modulated MMF VCSEL short haul ROF link. Various coupling methods and the bonding process of mating the VCSEL to MM fiber have been investigated to optimize the optical power coupling for cost reduction and low complexity. The results show that the transmitter coupled by spherical-ended MMF provides 30% more optical coupling efficiency and enhanced noise figure performance than the lens-less flat cleaved alternative