Low Loss 18GHz Fiber Optic Link

Currently, wide bandwidth, microwave fiber optic links suffer from excessive loss due to the poor conversion efficiency of laser drive current to photodectector signal current. An additional disadvantage of this high loss is a relatively poor noise figure for the microwave link. These fiber optic links would be more easily used in many applications if this link loss could be significantly reduced. Several methods have been proposed to more effectively couple the RF input power to the laser diode mar microwave frequencies over wide bandwidth, both passively and actively, but none have been demonstrated. In this work we will design a passive, wide bandwidth matching network that combines a microstrip transformer along with a lumped element transformer to match a 50ohm system to a 4ohm laser diode. Improvement in electrical link loss is expected to be 10dB. Additionally, we will study the feasibility of developing wide bandwidth active matching circuits to further reduce electrical link loss. This study will include both lumped and distributed amplifier techniques. The anticipated link loss improvement will be 20dB over resistive matching to the laser diode. The expected bandwidth is 6 to 18 GHz.