BACKGROUND:  Currently, microwave mixers perform downconversion for remote applications such as antenna remoting. Photonic downconversion provides a means to reduce the complexity of receiver stations. However current photonic solutions often require two fibers which must be equalized to maintain phase matching and multiple discrete well-tuned photodiodes to maintain amplitude matching. Matching phase and amplitude is challenging with discrete components.

INNOVATION:  A device is created whereby optical signals travel over a single optical fiber arrive at the invention and split into 2 identical paths via a 1x2 multimode interferer. A local oscillator drives the balanced electroabsorption modulator (B-EAM) by push pull modulation to downconvert the incoming high frequency or RF signals to an IF, while the balanced photodetector (B-PD) performs balanced detection. The B-EAM and B-PD are electrically isolated form each other. Due to the balanced scheme, common mode noises such as laser RIM and ASE noise are cancelled, leaving shot noise and thermal noise. The B-EAM has the unique ability to maintain balanced outputs independent of the operating bias point, while the balanced architecture effectively linearizes the frequency translation process by canceling all even-order distortions generated by the B-EAM.

The invention provides highly linear frequency translation and wideband robust common mode noise rejection. Monolithic integration ensures broadband phase matching and higher common mode noise rejection compared to balanced links build from discrete components. Finally, integration reduces packaging costs.

The invention may be used to frequency translate ultra-wideband RF signals or an ultra-large number of subcarrier multiplexed RF channels without sacrificing noise or spurious free dynamic range. Applications include fiber radio, wireless distribution networks, cable television, antenna remoting and radar systems.

DEVELOPMENT TO DATE:  A theoretical model is complete for predicting performance of a frequency translating fiber link. Also a shot noise-limited balanced downconverting link was demonstrated by employing discrete components: a cross couple Mach-Zehnder photonic mixer, an EDFA, discrete photodiodes wired for balanced detection and mujltiple optical paths.

Reference: UCLA Case No. 2003-040