One-Bit Time-Resolved Imaging.

Spatial resolution is one of the fundamental bottlenecks in the area of time-resolved imaging. Since each pixel measures a scene-dependent time profile, there is a technological limit on the size of pixel arrays that can be simultaneously used to perform measurements. To overcome this barrier, in this paper, we propose a low-complexity, one-bit sensing scheme. On the data capture front, the time-resolved measurements are mapped to a sequence of +1 and -1. This leads to an extremely simple implementation and at the same time poses a new form of information loss. On the image recovery front, our one-bit time-resolved imaging scheme is complemented with a non-iterative recovery algorithm that can handle the case of single and multiple light paths. Extensive computer simulations and physical experiments benchmarked against conventional Time-of-Flight imaging data corroborate our theoretical framework. Thus, our low-complexity alternative to time-resolved imaging can indeed potentially lead to a new imaging methodology.

Threefold rotational symmetry in hexagonally shaped core-shell (In,Ga)As/GaAs nanowires revealed by coherent X-ray diffraction imaging.

Coherent X-ray diffraction imaging at symmetric hhh Bragg reflections was used to resolve the structure of GaAs/In0.15Ga0.85As/GaAs core-shell-shell nanowires grown on a silicon (111) substrate. Diffraction amplitudes in the vicinity of GaAs 111 and GaAs 333 reflections were used to reconstruct the lost phase information. It is demonstrated that the structure of the core-shell-shell nanowire can be identified by means of phase contrast. Interestingly, it is found that both scattered intensity in the (111) plane and the reconstructed scattering phase show an additional threefold symmetry superimposed with the shape function of the investigated hexagonal nanowires. In order to find the origin of this threefold symmetry, elasticity calculations were performed using the finite element method and subsequent kinematic diffraction simulations. These suggest that a non-hexagonal (In,Ga)As shell covering the hexagonal GaAs core might be responsible for the observation.

Development and investigation of a long-range time-of-flight and color imaging system.

Time-of-flight (Tof) imaging based on the photonic mixer device (PMD) or similar ToF imaging solutions has been limited to short distances in the past, due to limited lighting devices and low sensitivity of ToF imaging chips. Long-range distance measurements are typically the domain of laser scanning systems. In this paper, PMD based medium- and long-range lighting devices working together with a 2-D/3-D camera are presented and several measurement results are discussed. The proposed imaging systems suffer from two systematic limitations in addition to problems due to wind and insufficient lighting: a low lateral resolution of the depth imaging chip and ambiguities in the distance measurements. In order to provide a robust and flexible system, we introduce algorithms to obtain unambiguous depth values (phase unwrapping) and to perform a joint motion compensation and super-resolution. Several experiments were conducted in order to evaluate the components of the multimodal imaging system.

Angular motion estimation using dynamic models in a gyro-free inertial measurement unit.

In this paper, we summarize the results of using dynamic models borrowed from tracking theory in describing the time evolution of the state vector to have an estimate of the angular motion in a gyro-free inertial measurement unit (GF-IMU). The GF-IMU is a special type inertial measurement unit (IMU) that uses only a set of accelerometers in inferring the angular motion. Using distributed accelerometers, we get an angular information vector (AIV) composed of angular acceleration and quadratic angular velocity terms. We use a Kalman filter approach to estimate the angular velocity vector since it is not expressed explicitly within the AIV. The bias parameters inherent in the accelerometers measurements' produce a biased AIV and hence the AIV bias parameters are estimated within an augmented state vector. Using dynamic models, the appended bias parameters of the AIV become observable and hence we can have unbiased angular motion estimate. Moreover, a good model is required to extract the maximum amount of information from the observation. Observability analysis is done to determine the conditions for having an observable state space model. For higher grades of accelerometers and under relatively higher sampling frequency, the error of accelerometer measurements is dominated by the noise error. Consequently, simulations are conducted on two models, one has bias parameters appended in the state space model and the other is a reduced model without bias parameters.