1. NET 436 optical Network Tutorial Lecture #2
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2. 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.
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3. 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
        
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4. Example 1
1. Calculate the number of allowed modes in a multimode step index fiber, a = 100 μm, core index of and a cladding index of at the wavelength of 850nm. Solution:
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5. Example 2
2. What should be the core radius of a single mode fiber that has the core index of and the cladding index of at the wavelength of 1.3μm. Solution:
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6. 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
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