Photon counting, chirped AM LADAR (LIDAR) systems and methods

A laser radar (LADAR) system that utilizes diode laser transmitters, enabling very compact, low-power, eye-safe, and/or long-range LADARs with low-cost, low-bandwidth readout integrated circuits for foliage and camouflage penetration, target ID, manned and unmanned ground and air vehicle navigation, three-dimensional face recognition, battle damage assessment, and change detection.


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Photon counting chirped AM LADAR architecture

This patent describes a method of using Geiger-mode avalanche photodiode (GM-APD) photon counting detectors in ARL’s chirped amplitude modulation (AM) LADAR receiver to yield sensitivities approaching the shot noise limit. In fact, it increases sensitivity by four orders-of-magnitude over the sensitivities of the currently used unity-gain, opto-electronic mixing metal-semiconductor-metal detectors.

Diode lasers cost significantly less than solid-state lasers and are more electrically efficient. Pulsed diode lasers have limited peak power capability due to damage at the output laser facet that, in a typical pulse operation, limits the amount of total energy that can be focused onto a target. Low-cost, continuous waveform (CW) laser diodes, however, with optical power levels in the low Watts level, are available commercially. In this architecture, the transmitter is based on a semi-conductor diode laser that is intensity-modulated with a linear frequency-modulated (FM), CW. Light reflected from the target impinges on a detector where it is mixed with the same linear FM waveform to create a current whose frequency is proportional to range. This technique is commonly used in FM radar to extract target range and velocity, while simultaneously utilizing the high-frequency of the optical fields to achieve high-angular resolution. As such, RF waveforms and signal processing techniques developed over the past 50 years for FM/CW radar systems can all be applied directly, or with only slight modification, to the LADAR architecture.

The Army invention incorporates a chirped AM architecture, low-cost CW semiconductor diode lasers and range-Doppler processing to measure both the range and velocity of a moving target. It features a significant increase in sensitivity (10^4) which can be used to obtain LADAR operation with some combination of longer range, lower laser power, and/or smaller receiver aperture area.

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