Underwater optics

In visible light, red light has the longest wavelength and is more easily absorbed by water molecules; Purple light has the shortest wavelength and is more prone to scattering; The attenuation of blue-green light in water is relatively small, making it suitable as a transparent window for underwater communication. In 2020, the 11000 meter deep sea high-speed wireless blue-green optical communication project prototype developed by the Xi'an Institute of Optics and Precision Machinery, Chinese Academy of Sciences, successfully realized the world's first 10000 meter underwater TV live broadcast of the "Endeavor", marking a major breakthrough in the field of underwater communication technology in China.

The unit is designed for unsupervised public use: controls are recessed or shielded, moving parts are enclosed, and the interface is operable by a child of about six with no instruction. Where a screen is used, the language can be switched without changing the hardware, and the content can be replaced on site.

The core of underwater optics studies the propagation law, energy attenuation, and interaction of light in water bodies. Its essence is the result of the combined effect of the physical properties of light and the molecular scattering and absorption effects of water media. The core principle can be broken down into the following two parts, covering the technical logic of blue-green optical communication: 1. Basic light propagation: the "screening" and "weakening" of light by water bodies. Natural light (such as sunlight) belongs to composite light, consisting of seven monochromatic lights: red, orange, yellow, green, cyan, blue, and purple. The core difference of each monochromatic light is the wavelength - the longer the wavelength, the easier it is for energy to be absorbed by the medium; The shorter the wavelength, the stronger the penetration ability. When light enters water, two key processes, absorption and scattering, occur simultaneously, resulting in a "selective attenuation" characteristic of underwater light: 1. Absorption effect (core loss cause): Water molecules and dissolved organic matter and suspended solids in water will preferentially absorb light of specific wavelengths.