Abstract

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.¹ 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.² The consequence of intermodulation distortion (IMD)³ resulting from the low-biasing technique is considered.

© 1996 Optical Society of America