Star pattern recognition and attitude determination accuracy is highly dependent on star spot location accuracy for the star tracker. A star spot location estimation approach with the Kalman filter for a star tracker has been proposed, which consists of three steps. In the proposed approach, the approximate locations of the star spots in successive frames are predicted first; then the measurement star spot locations are achieved by defining a series of small windows around each predictive star spot location. Finally, the star spot locations are updated by the designed Kalman filter. To confirm the proposed star spot location estimation approach, the simulations based on the orbit data of the CHAMP satellite and the real guide star catalog are performed. The simulation results indicate that the proposed approach can filter out noises from the measurements remarkably if the sampling frequency is sufficient.

A practical direct-view scheme for generating arbitrary high-order cylindrical vector (HCV) beams by cascading vortex half-wave plates (VHPs) is presented. The combination of odd number 2n-1 VHPs for n≥1 can realize (m_2n-1-m_2n-2+…+m₁)-order CV beams, in which m is the order number of VHP and the corresponding subscript 2n-1 represents the arrangement number of VHPs, and the cascading of even number 2n ones can obtain (m_2n-m_2n-1+…+m₂-m₁)-order CV beams. All 1-12 order CV beams, including the high-order anti-vortex CV (ACV) beams, are generated only by selectively cascading the VHPs with m=1, 3 and 8. The polarization properties of the generated HCV beams are investigated by measuring the corresponding Stokes parameters. It is experimentally demonstrated that arbitrary HCV beams are effectively achieved by the proposed method. The order numbers of CV beams can be greatly expanded by cascading limited types of VHPs.

Target images recorded with range-gated laser imaging systems and conventional passive imaging systems through rapidly changing turbid mediums inevitably suffer from inhomogeneous degradations. Consequently, this makes the images partly or entirely different from their true targets and eventually has adverse effects on target identification. To date, the inhomogeneous degradations are still not finely eliminable despite utilizing adaptive optical methods and pure mathematical signal improvement techniques. Herein, we demonstrate an image restoration method involving intrinsic physical evolution of light beams based on the backscattering images of a turbid medium. The corresponding mathematical signal processing algorithms are applied for restoring the true target images in the presence of rapidly changing inhomogeneous degradations. This technique would benefit target imaging through moving cloud/mist in air and flowing muddy masses under water.

We report coherent imaging of objects behind opaque scattering media with only one piece of the power spectrum pattern. We solve the unique solution and improve algorithm speed for the inverse problem. Based on the proposed scattering-disturbance model, with only one piece of the Fourier transform power spectrum pattern under coherent illumination, we successfully reconstruct clear images of the objects fully hidden by an opaque diffuser. The experimental results demonstrate the feasibility of the reconstruction method and the scattering-disturbance model. Our method makes it possible to carry out snapshot coherent imaging of the objects obscured by scattering media, which extends the methodology of x-ray crystallography to visible-light scattering imaging for underwater and living biomedical imaging.

A method for generating vector beams with higher-order states of polarization based on a setup with a one phase-only liquid crystal spatial light modulator is proposed. The polarization properties and double-slit interference of the higher-order vector beams were investigated in detail. The cross section intensity distributions were flower-like for higher-order vector beams when passing through a linear polarizer. Misplacements appeared in the double-slit interference fringes, which divided each fringe into several discrete parts, i.e., $2P-1$ for $P\ge 2$, and 3 for $P=1$, where $P$ is the polarization order number. When associated with optical petal orientations analysis of the beam spots behind a linear polarizer, the double-slit interference can be used to detect and analyze higher-order vector beams.

We demonstrate the evolution of picosecond pulses in silicon nanowire waveguides by sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) and nonlinear Schrödinger equation (NLSE) modeling. Due to the unambiguous temporal direction and ultrahigh sensitivity of the SFG-XFROG, which enable observation of the pulse accelerations, the captured pulses' temporal and spectral characteristics showed remarkable agreement with NLSE predictions. The temporal intensity redistribution of the pulses through the silicon nanowire waveguide for various input pulse energies is analyzed experimentally and numerically to demonstrate the nonlinear contributions of self-phase modulation, two-photon absorption, and free carriers. It indicates that free carrier absorption dominates the pulse acceleration. The model for pulse evolution during propagation through arbitrary lengths of silicon nanowire waveguides is established by NLSE, in support of chip-scale optical interconnects and signal processing.