1 NET 436 OPTICAL NETWORK TUTORIAL LECTURE 2

1 NET 436 OPTICAL NETWORK TUTORIAL LECTURE #2 Networks and Communication Department

Fiber Modes 2 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 3 • For V values below ≈ 2. 405, a fiber supports only singlemode fibers. • Multimode fibers can have much higher V numbers. • For large values, the number of supported modes of a stepindex fiber can be calculated approximately as M=0. 5 V^2 And the number of supported modes of Graded index fibers can be calculated approximately as M=0. 25 V^2 Networks and Communication Department

Example 1 4 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 850 nm. Solution: Networks and Communication Department

Example 2 5 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) 6 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. 22 -Nov-20 Networks and Communication Department