Question

Explain what is meant by the Weakly Guided Approximation for glass core/cladding fiber.

Answer 1

In a weakly guided fiber, the difference between the refractive indices of the core and the cladding is very small. Due to this, the light guiding capacity of the fiber is weaker.

Mathematically, this weakly guided approximation is essentially written as

As the index profile of such a fiber is different from the regular fiber, the guidance parameter tends to zero thus reducing the number of modes in the fiber. For such fibers, all the modes which have same cut-off V-number degenerate. These modes are linearly polarized modes.