Intermodulation distortion in high dynamic range microwave fiber-optic links with linearized modulators

Abstract

Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier.