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Why do short wavelength single-mode cables have higher insertion loss then longer wavelength cables?

April 26, 2017cables insertion longer loss short single-mode

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Why do short wavelength single-mode cables have higher insertion loss then longer wavelength cables?

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The shorter the wavelength of light the smaller the mode field diameter (MFD) of the fiber. Fiber for a 400nm purple laser has a 3.5um MFD while a 1550nm laser requires a fiber with a 10.5um MFD. The 400nm fiber is 1/3 the diameter and 1/9 the area of the 15510nm fiber. If both fibers are misaligned by 1um the 1550nm fiber will have approximately 0.16dB (3.5%) loss while the 400nm fiber will have approximately 1.5dB (30%) loss.