We report a five-step processing algorithm for photon counting depth imaging under strong background noise environment, and experimentally verified that this method can realize single photon counting 3D imaging under signalto-noise ratio (SNR) less than 1. In order to accurately locate the target position when the ambient flux is high, a computational pile-up correction is performed to recover the underlying signal photons, then performing an adaptively full-pixel target position locating. After the target position is determined, the signal and noise photons are separated pixel-wisely using a cluster method. Pixels which have no arrival photons are filled by using the information from neighborhood. At last, by using total variation spatial regularization, the depth images are reconstructed accurately. To validate the proposed method, a single photon counting 3D imaging system is established and experiments at different noise levels are carried out. Experimental results show that accurate depth imaging can be reconstructed with the SNR as low as 0.41. This approach is suitable for depth imaging under high background noise and also very suitable for the noncooperative target imaging with no prior knowledge of the target distance for its adaptive range gating.
We report the quantum-enhanced metal target detection based on quantum illumination, and experimentally verified that quantum illumination still helps low-reflectivity target detection in photon loss scenarios. The results show that the signal-to-noise ratio and target recognition ability of the quantum detection system are more than 10 times stronger than those of the classical detection under the same thermal noise conditions. We believe that the photon-counting based QI protocol, for its robustness to noise and losses, has a huge potentiality to promote the usage of quantum correlated light in real environments.
Using the entangled photons generated by the spontaneous parametric down conversion as a light source, we demonstrate the first quantum ghost imaging system with a modified compressive sensing technique based on the spatial correlation of sensing matrix (SCCS). The ghost image is achieved at 16.27% sampling ratio of raster scanning and 0.65 photons/pixel at each measurement on average. Our results show that image quality and photon-utilization efficiency are remarkably enhanced in comparison with the traditional compressive imaging technique, due to the sensing matrix and noise-free measurement vector rebuilt by SCCS technique. It suggests the great potential of SCCS technique applied in quantum imaging and other quantum optics fields, such as quantum charactering and quantum state tomography to use the information loaded in each photon with high efficiency.
We presented three-dimensional image including reflectivity and depth image of a target with two traditional optical imaging systems based on time-correlated single photon counting technique (TCSPC), when it was illuminated by a MHz repetition rate pulsed laser source. The first one is bi-static system of which transmitted and received beams path are separated. Another one called mono-static system of which transmit and receive channels are coaxial, so it was also named by transceiver system. Experimental results produced by both systems showed that the mono-static system had more advantages of less noise from ambient light and no limitation about field area of view. While in practical applications, the target was far away leading to there were few photons return which was prejudicial to build 3D images with traditional imaging system. Thus an advanced one named first photon system was presented. This one was also a mono-static system on hardware system structure, but the control system structure was different with traditional transceiver system described in this paper. The difference was that the first return photon per pixel was recorded across system with first photon system, instead of overall return photons per pixel. That’s to say only one detected return photon is needed for per pixel of this system to rebuild 3D images of target with less energy and time.
Based on previous researches, we construct a pseudo-thermal light ghost imaging system suited for remote imaging applications. By using pulsed pseudo-thermal light, the transmitted power is improved to ghost imaging long distant targets. By using imaging lens system, the path lengths of reference and signal light need not keep equal, as in lensless ghost imaging system, thus the transmitter, receiver, and correlator circuit can be integrated and keep compact. Furthermore, the revolution is improved by reducing the sizes of speckles. And the number of imaging frames is decreased (thus reduced the image-reconstruct time) and the signal-noise-ratio of ghost image is improved by compressed sensing. Based on the constructed experimental system, we implemented ghost imaging of a target at about 30m range.