Requirements of optical fiber characteristics for all optical networks

1. To provide wider spectral bandwidth for the optical fiber of the metropolitan area Network, because the typical distance of the metropolitan network is less than 80 km, the optical amplifier is rarely used, and the group velocity dispersion of the fiber is not the primary limitation. More importantly, the metropolitan area network typically requires support for a large number of users and tends to increase frequency bandwidth and enhance management capabilities, reducing the cost of increasing business and canceling business in the fiber. One way to achieve this is to allocate the business to hundreds of wavelengths (each with a low-speed medium speed) and a full light tap, up and down wavelength. The number of wavelengths that can be transmitted by a single-mode fiber is limited by the cut-off wavelength of the fiber at the short wavelength (about 1260nm) and limited by the absorption and bending of silica material at the long wavelength end (about 1650mm). From this point of view, the ideal optical fiber should be able to hold the maximum number of wavelengths.

2. The intensity of optical power on unit area of optical fiber is small, and the characteristic of submarine optical fiber communication system is that it needs little or no upper and lower service in the thousands of km transmission, and the use of large effective area fiber can reduce the number of expensive optical amplifiers and thus save expenses. The large effective area of the optical fiber reduces the intensity of the optical power on the unit area of the fiber, allowing for greater optical power to enter the fiber. Therefore, the signal can be transmitted farther away before the need to enlarge. In addition, an optical fiber nonlinear effect, which is related to the dispersion of the optical fiber, is called modulation instability, which causes the light signal to get worse after the long sea bottom. In the actual submarine optical fiber communication system line, the large effective area fiber, the negative dispersion fiber and the dispersion non displacement optical fiber can be skillfully used to solve this problem. The dispersion of the dispersive non-displacement fiber is used to compensate the negative dispersion so as to achieve the average dispersion of the whole line close to zero.

3. For the group velocity dispersion at different wavelengths, the change should reach the wavelength of the optical fiber in the minimum terrestrial long-distance cable network, the bandwidth should be wider, and the signal at each wavelength can be transmitted at a higher rate. The variation of the group velocity dispersion at different wavelengths in the optical fiber should be minimized, as little as possible or without complex and expensive dispersion compensation devices.