光ファイバ通信についての誤解

概要

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Three misunderstandings about optical fiber communications are described. The first misunderstanding is, "because optical fibers transmit light, which speeds through wires faster than electricity, they enable high-speed communication." Electrical signals through wires and space also transfer at the speed of light. The light speed is not directly contributed to the data rate. The frequency of light is extremely high and the bandwidth is large. The wide bandwidth is essential to high-speed communications. The second is about mode in fiber. The mode is sometimes explained by using a ray-tracing method. However, the mode is a feature of waves. The single mode and multi mode should be understood based on the wave analysis. The third is about coherent light and shot noise. It is a classical view that the coherent light has a uniform phase. The phase of coherent state can not be fixed. Quantum mechanics shows that the coherent state consists of many states with different numbers of quantum. The shot noise originates from the coherent state.
沼津工業高等専門学校の論文
2010-01-31