RF photonics

We have collaborated with Profs. Kelvin Wagner (ECE) and Dana Anderson (physics, JILA) on how to use optical signals to control microwave circuits (thesis, James Vian) and to process microwave signals from antenna arrays (Stefania Romisch, Darko Popović, Paul Smith, Edeline Fotheringham). In the first area, we have demonstrated very efficient optical switching between transmit and receive functions in a T/R array: for 2.4 ns switching speed, the switch requires only about 10 pJ of optical energy. The specific switch that was demonstrated had over 36 dB isolation and about 0.3 dB loss from 7 to 15 GHz. The optical power is a separate control parameter which affects only the switching speed. Multimode fibers with extremely inexpensive manufacturing are used and they do not affect the microwave fields.

Photograph of active part of a T/R array (left) and control optical circuit mount (right) (James Vian). To accomplish optical processing of microwave antenna array signals, we have demonstrated Principal Component Extraction on a 2-channel prototype. This means that any two dynamical signals in a possibly mobile and multipath environment can be separated adaptively. The 130-MHz signals are on a 10-GHz carrier, and the output of the system is an electrical signal as well (e.g. audio). The entire system consumes less than 50W of power (less than most light bulbs) and is packaged in a standard size briefcase with a single power plug. The free-space nonlinear optical holographic processor is integrated on a glass coin the size of a USD quarter. The work is now being extended to Independent Component Analysis (ICA).