Fiber Optic Tutorials

This is a continuation from the previous tutorial - weakly guiding fibers. In a graded-index fiber, the index profile, n(r), in the core of the fiber is a function of the radial distance, r, from the center of the fiber, as shown in figure 7 below. Figure 7  Graded-index fiber with a core radius a It starts at a value of n(0) = n1 at the center of the fiber and gradually decreases to a value of n(a) = n2 at the boundary between the core and the cladding. The fiber V number defined in (1) [refer to the step-index...

This tutorial is a continuation from the step-index fibers tutorial. Most optical fibers for practical applications are weakly guiding fibers that have a small index step, Δn, between the core and the cladding: \[\tag{48}\Delta=\frac{\Delta n}{n_1}=\frac{n_1-n_2}{n_1}\ll1\] The mathematics for the modes of a weakly guiding fiber can be greatly simplified by taking proper approximations. For example, the cutoff Vc for the HEmn modes with m ≥ 2 of a weakly guiding fiber can be approximated by the nth nonzero root of the equation \[\tag{49}J_{m-2}(x)=0\] which is obtained from (45) [refer to the step-index fibers tutorial] under the condition of (48). Meanwhile, for the modes of...

This is a continuation from the channel waveguides tutorial. An optical fiber is basically a cylindrical dielectric waveguide with a circular cross section where a high-index waveguiding core is surrounded by a low-index cladding. Optical fibers are usually made of silica (SiO2) glass. The index step and profile are controlled by the concentration and distribution of dopants. For example, the core can be doped with germania (GeO2) or alumina (Al2O3) or other oxides, such as P2O5 or TiO2, for a slightly higher index than that of a silica cladding. Alternatively, to take advantage of low-loss pure silica, the cladding can be...

This is a continuation from the previous tutorial - graded-index planar waveguides. So far we have discussed the characteristics of planar waveguides. In practice, most waveguides used in device applications are nonplanar waveguides. For a nonplanar waveguide, the index profile n(x, y) is a function of both transverse coordinates x and y. There are many different types of nonplanar waveguides that are differentiated by the distinctive features of their index profiles. One very unique group is the circular optical fibers discussed in the next tutorial. Another important group of nonplanar waveguides is the channel waveguides, which include the buried channel...

This is a continuation from the previous tutorial - Symmetric Slab Waveguides. In the previous two tutorials, we have considered slab waveguides that have step-index profiles. In this tutorial, we consider graded-index planar waveguides, which do not have the piecewise-constant index profiles of step-index waveguides. Two types of graded-index planar waveguides, shown in figure 12 below, are of practical interest. One is the smooth graded-index waveguide, which has a smooth index profile across its entire structure in the x direction, as shown in figure 12(a). The other is the step-bounded graded-index waveguide, which has a graded-index profile on one side...