High-resolution microwave-photonic and laser ranging

Abstract:  High resolution ranging systems are of great importance for both civilian and military applications. Both radio frequency (RF) waveforms and optical waveforms (LADAR) are used for range detection purposes. In both techniques, high range resolution can be obtained using short and intense pulses. However, the transmission and processing of such pulses is difficult and potentially unsafe. Instead, temporally extended waveforms or sequences, in conjunction with proper compression techniques at the receiver end, may be used. The instantaneous power of the extended waveforms can be orders-of-magnitude lower, making them safer and simpler to generate in a real-world system and more difficult to intercept by an adversary.

In this work, I propose and demonstrate two distinct schemes for high resolution ranging measurements. The first proposition is a microwave-photonic, ultra-wideband (UWB) noise RADAR system. The system makes use of the amplified spontaneous emission (ASE) of optical amplifiers to generate random 'physical noise' that is later converted to the RF domain. The system comprised of a central unit and remote end unit that were separated by 10 km of fiber. A range resolution of 10 cm was achieved using this system.

The second technique is a LADAR system, employing an encoded sequence of pulses and a proper post-processing to obtain high resolution ranging measurements with low sidelobes. A novel compression scheme, previously proposed by Prof. Nadav Levanon of Tel-Aviv Univ., was employed in the experiment. The method achieved the sidelobe suppression of complex coherent receivers, even though a simple direct detector was employed. A ranging resolution of 3 cm was obtained.