James E. Leight

Analog Signal Splitting and Amplification for Optically-Controlled Phased-Array Antennas

In this work, multimode interference in a semiconductor optical amplifier is used to simultaneously split (× 10) and amplify a RF signal on an optical carrier.

Broadband high-power photodetector arrays for photonically implemented phased-array antenna architectures

The authors present a monolithically integrated photodetector array combiner approach that operates over an extremely wide RF bandwidth. These arrays are suitable for coherent RF signal combining applications such as optically controlled phased array radar. The approach consisted of a monolithically integrated array of high-power, wideband photodetectors distributed along an RF transmission line resulting in a low power consumption, broadband, high power handling optical-to-RF combiner, The authors demonstrated a 4-element photodetector array with a small-signal 3dB bandwidth of 34 GHz. RF models were developed and calibrated to the measured results to predict the performance of larger arrays. The models predict than an 8-, 16-, and 48-element array would have a small-signal 3dB bandwidth of 25 Ghz, 15.7GHz, and 5.8GHz respectively. These arrays showed a reasonable amount of robustness to variations and/or errors in the time delays of the input optical feed network suggesting that implementation outside the laboratory should be practical.

Photonic correlation for wideband processing in MMW imaging systems

In recent years, many examples have been cited where photonic signal procesors have the potential of enabling the deployment of wideband RF sensor systems whose data rates would otherwise overwhelm the capabilities of traditional digital signal processors. Passive, synthetic aperture millimeter-wave (MMW) imaging arrays are one such class of sensor system that offers a solution to the need for a passive, all-weather look-down sensor for critical DoD and environmental missions. A photonic method of correlating the signals received by the various elements of the array offers a highly efficient, exceptionally wideband capability, exploiting a powerful new technology for aperture- synthesis imaging. Our trade study has helped to establish that a photonically based interferometric imager can significantly reduce the weight and power consumption of the system relative to an all-digital- electronics approach. In addition, the ability of an airborne or space based system to process multi-gigahertz bandwidths offers the first real-time MMW imager operating at video rates. Previous demonstrations of optical correlators have used discrete components, and generate only the real part of the correlation. Using integrated optical waveguide technology developed in part fof the telecommunications industry, we have developed an approach for computing complex correlations over wide bandwidths and in such a way to allow video rate imaging for passive MMW systems. We will describe a general processing architecture, its capability, and our trade study results to provide a motivation for the future development of these types of systems.