Tracking moving targets behind a scattering medium is a challenge, and it has many important applications in various fields. Owing to the multiple scattering, instead of the object image, only a random speckle pattern can be received on the camera when light is passing through highly scattering layers. Significantly, an important feature of a speckle pattern has been found, and it showed the target information can be derived from the speckle correlation. In this work, inspired by the notions used in computer vision and deformation detection, by specific simulations and experiments, we demonstrate a simple object tracking method, in which by using the speckle correlation, the movement of a hidden object can be tracked in the lateral direction and axial direction. In addition, the rotation state of the moving target can also be recognized by utilizing the autocorrelation of a speckle. This work will be beneficial for biomedical applications in the fields of quantitative analysis of the working mechanisms of a micro-object and the acquisition of dynamical information of the micro-object motion.

A robust method for efficient spatial separation optical imaging through scattering media regardless of the three-dimensional (3D) optical memory effect is proposed. In this method, the problems of imaging dealiasing, decomposition, and separation of speckle patterns are solved by employing independent component analysis. Multitarget imaging behind a scattering layer with diverse spatial positions is observed experimentally, for the first time, to the best of our knowledge. In this work, we demonstrate that, by knowing the number of targets and keeping each subtargets’ size in the optical memory effect range while isolating them beyond this range without overlap in the axial direction, speckle dealiasing and multitarget imaging are solved effectively. The strategy provides a potentially useful means for incoherent imaging through scattering media in a wide class of fields such as optical microscopy, biomedical imaging, and astronomical imaging.

We propose a thin-film Ge-on-Si-on-insulator (Ge-on-SOI) photodetector with enhanced performance by exploiting induced guided mode resonance (GMR) employing Ge/SiO₂ grating on Si-on-insulator (SOI). Numerically calculated results and theoretical analysis demonstrate that normal-incidence light can be coupled to the GMR and partly be converted into the spatial resonance mode which propagates along the whole properly designed grating structure. A notable absorption efficiency of higher than 70% is obtained in the photodetector with only 280 nm-thick Ge/SiO₂ grating, which is about 35 times larger than that of the counterpart without the designed grating structure. Remarkable enhanced light absorption can be achieved in the device with very few grating periods, which significantly promotes a theoretical 3-dB bandwidth-efficiency product of ∼66 GHz. The result is promising for a compact Ge-on-Si photodetector design with low dark current, high-bandwidth, and high-responsivity.