Low-biasing the cascaded downconverting fiber-optic link

Summary form only given. The downconversion of microwave signals using fiber-optic links is of interest because it enables the use of low-speed photodetectors, which have much higher power saturation thresholds than high-speed photodetectors, leading to improved conversion loss. A downconverter containing two cascaded modulators was recently demonstrated, which showed excellent potential for application in sensor systems. The modulators were biased at quadrature, and the system used optical amplification along with two electrically combined photodetectors to achieve -20 dB conversion loss. In this paper we use the same arrangement and examine the benefits of low-biasing one of the modulators to further improve conversion loss, exploiting a technique that has been shown to improve dynamic range in other systems.