ABSTRACT
When photographing objects underwater, it is important to utilize an optical window to isolate the imaging device from the water. The properties of the entire imaging system will change, and the imaging quality will decrease due to the refraction impact of the water and the window. The theoretical calculation method for air imaging is no longer relevant in this context. To analyze the unique rule, this research derives the formulas for key parameters of underwater imaging systems under paraxial circumstances. First, the optical window is modeled, then the formula for the optical window's focal length in the underwater environment is derived, and the change rule for the focal length of various window forms underwater is condensed. For the ideal imaging system using a domed optical window, the equivalent two-optical group model of the imaging system is established, and the formula for calculating the focal length, working distance, and depth of field of the underwater imaging system is derived through paraxial ray tracing. The accuracy of the formula is verified through the comparative analysis of the formula calculation results and the Zemax modeling simulation results. It provides an important theoretical basis for the in-depth study of underwater imaging technology.
ABSTRACT
Due to the advantages of its low cost and high utilization rate of light energy and no moving parts, Hadamard transform spectrometer with DMD has become a focus in the research of spectrometer. In order to solve the reduction of spectral resolution caused by the spectral curvature of Hadamard transform spectrometer with DMD (Digital Micro-mirror Device), the spectral aliasing in the spectrometer was investigated. Firstly, the mathematical relationship of spectral aliasing to radius of spectral curvature was deduced. Then, two procedures were proposed to solve the spectral aliasing. One is making the DMD encoded spectral band accordant with the standard spectral band as far as possible by adjusting the DMD-encoded stripe, and another is correcting remaining spectral aliasing by means of data processing. Finally, by analyzing and correcting spectral curvature in six situations of the curvature radius of 15.8 x 104, 7.8 x 104, 9.7 x 104 µm and etc, we fit out the relationship of spectral aliasing and spectrum correction effect of spectral-curvature to the curvature radius. The simulation indicates that the spectral resolution increases to the resolution of optical system. It shows that the proposed methods are universal, simple and effective in the improvement of spectral resolution.
ABSTRACT
We develop an interferometer which has high spectral sensitivity based on the dispersive property of the semiconductor GaAs in the near-infrared region. Our experiment demonstrates that the spectral sensitivity could be greatly enhanced by adding a slow light medium into the interferometer and is proportional to the group index of the material. Subsequently the factors which influence the spectral sensitivity of the interferometer are analyzed. Moreover, we provide potential applications of such interferometers using the dispersive property of semiconductor in whole infrared region.
