Modulation Depth Optimization of High-power Photodiodes-driven-antennas Link

High-power photodiodes (PDs) driving ultrawide antennas directly arises as a promising solution for multi-band, high-efficiency and low-complexity RF front ends since bandwidth-limited electrical power amplifiers are removed. However, high-power performance of PDs is usually hardly to be exerted in a simple and low-cost directly-modulated photonic RF link, due to the terrible modulation depth of directly-modulated laser (DML). This paper proposes and demonstrates a new method to optimize modulation depth of DML for high-power photodiodes-driven-antennas link by using adaptive optical filtering. The filter is designed adaptively along with the frequency response of DML, which can realize modulation depth to be 100% corresponding to the maximum RF power output of high-power PD, and make the system frequency independent without tuning. As a result, the proposed method can ensure high power output and large instantaneous bandwidth simultaneously. A theoretical and experimental investigation is performed. About 20 dB power conversion efficiency and 20 dBm RF power output are obtained over an 18-GHz working frequency range.