Ultra Wideband Multibeam Optical Coherent Transient Radar

In this paper, we present an electro-optic radar receiver for wide bandwidth, high time-bandwidth-product radar returns that simultaneously performs parallel beamforming across arrays with thousands of antenna elements. This analog technique allows for correlation times of approximately 10 mus across 30 GHz of bandwidth without the use of extremely fast digitizing circuits or digital processors. To perform this technique, we upconvert the return waveforms from the antenna array onto an array of optical fibers by using an array of electro-optic modulators. From here, we can use a single lens as a Fourier optical beamformer. The frequency scaled beams are formed into a optical coherent transient (OCT) crystal along with an optically upconverted copy of the transmitted waveform. The OCT crystal correlates the return with the reference signal across all squinted beams. A chirped readout laser probes the spectrum of the correlation at each frequency bin across all beams while a synchronized zoom lens compensates for the frequency scaled location of the beams. The resulting beam spectra is Fourier transformed across time to generate the correlation peaks of the return signal. Pulse-to-pulse correlation peaks can be achieved using spatial multiplexing within the crystal or temporal multiplexing of the readout of the signal. We motivate such a system by calculating the digital processor requirements of a similar system, followed by a detailed description of the architecture