With the rapid demand for underwater optical communication (UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of “the aperture-averaged scintillation index” (SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time, signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system’s performance. Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.

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Diffraction image technology is an updated technology. It has more potential for developing the larger aperture and lightweight telescope than the conventional refractive and reflective optics. In order to develop a large aperture diffractive telescope, the key is to solve the problem of large aperture lens stitching. Different stitching patterns have different effects on the image quality. However, the stitching pattern for diffractive telescope is different from the conventional refractive and reflective telescope. This paper, for the first time, studies the theory of stitching pattern for diffractive telescope.On the basis of theoretical analysis, a long-wavelength infrared diffractive telescope of segmented-lens is designed and for the first time, good results through stitching experiments have been achieved.According to theoretical analysis and experiment verification, the paper gives the best stitching pattern on diffractive telescope.

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