Use of SiGe Photo-Transistor in RoF links based on VCSEL and standard single mode fiber for low cost LTE applications

This paper presents for the first time the transmission of LTE signal based-on Radio-over-Fiber (RoF) scheme by using SiGe Hetero-junction Photo-Transistor as photo-receiver. The photo-transistor is fabricated based-on the commercial bipolar transistor technology. An 850 nm single mode Vertical Cavity Surface Emitting Lasers (VCSELs) and Standard Single Mode Fiber (SSMF) are used to complete the link so that makes the total cost of the system very low. The transmission of 20 MHz bandwidth LTE signal with high modulation format is achieved. The performance of the system is evaluated through the measurement of Error Vector Magnitude (EVM) under different operation conditions of the photo-transistor (in photodiode mode, photo-transistor mode and two terminals mode). We reach an EVM below 8% for the input power of -25 dBm to -2 dBm when the photo-transistor operates under two terminals condition. This EVM value fulfills the requirements of the LTE standard for 64-QAM modulation. The stability of the system with regard temperature variation and modal noise is also presented.