NET 436 optical Network Tutorial Lecture #2 Networks and Communication Department

Fiber Modes The V number is a normalized frequency parameter, which determines the number of modes of a step-index fiber. It is defined as:               where λ is the wavelength, a is the radius of the fiber core. Networks and Communication Department

Fiber Modes For V values below ≈ 2.405, a fiber supports only single-mode fibers. Multimode fibers can have much higher V numbers. For large values, the number of supported modes of a step-index fiber can be calculated approximately as M=0.5V^2 And the number of supported modes of Graded index fibers can be calculated approximately as M=0.25V^2          Networks and Communication Department

Example 1 1. Calculate the number of allowed modes in a multimode step index fiber, a = 100 μm, core index of 1.468 and a cladding index of 1.447 at the wavelength of 850nm. Solution: Networks and Communication Department

Example 2 2. What should be the core radius of a single mode fiber that has the core index of 1.468 and the cladding index of 1.447 at the wavelength of 1.3μm. Solution: Networks and Communication Department

Mode field diameter (MFD) In fiber optics, the mode field diameter (MFD) is an expression of distribution of the irradiance, i.e., the optical power per unit area, across the end face of a single-mode fiber. 7-Dec-18 Networks and Communication Department