We present a three-dimensional (3D) imaging method employing linear increasing gain to encode flying time of photons into intensity information. This method obtains both the reflectivity and the depth of scene from only two two-dimensional (2D) images. High linear accuracy between the depth and the intensity information is independent of the laser pulse shape. We demonstrated <1 m linear depth accuracies with two different kinds of laser pulse shape and a 3D scene reconstruction with supperresolution depth mapping when the targets are 800-1100 m away.

In traditional three-dimensional (3D) active imaging methods, the detection depth range is observed to increase linearly with the detection time, and the intensity information was not fully utilized. However, by encoding the relative values into pseudovalues, the intensity information was fully utilized, and we found the maximum detection depth range increases exponentially with the detection time. Furthermore, we present a 3D imaging system capable of exponentially expanding the detection depth range. A 3D scene reconstruction was undertaken with the targets placed at a distance of 600-1100 m. Experimental results indicate that the method expands the detection depth range exponentially without distance resolution loss as compared with the conventional method.

Depth resolution is limited by the photoelectron shot noise in conventional gain-modulated active three-dimensional (3D) imaging methods. A proposed method, which is based on photon intensity correlation, is presented to overcome the depth resolution limitation. The signal photons are amplified by an imaging intensifier, and are then divided into two beams by a beam splitter. The theory shows that the shot-noise limitation is broken using the strong intensity coherence between the two beams. The experiment results show that the depth resolution of the correlated active 3D imaging method is three times better than that of the shot-noise limitation.

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