Step refractive index profile

Fig.1 Section of a planar waveguide with a step refractive index profile...

The simplest case of fibre structure is the step-index one, characterized by a constant circular refractive index profile in the core and polymer cladding of lower refractive index (Figure 3). The refractive indexes of the core and cladding depend on the materials used. The cores of these structures can be prepared from melts as well as from preforms without radial and azimutal variations of the refractive index. To obtain suitable mechanical... 

Consider a step-index dielectric waveguide with a linear refractive index profile, ni x) = ( a < a), n i ( x > a). 

Each layer has its own germanium concentration variation over its thickness, which finally results in the wave-like appearance of the interference lines. This example shows the problems that might rise if an attempt is made to approach a refractive index profile by deposition of only a few layers, even in the case of a step index profile. 

Fig. 2 Refractive index profile of a 200 nm step-index waveguide with refractive indices of = 1.5, = 2.0 and = 1.0...

Fig. 4 Graded-index and step-index waveguide refractive index profiles...

Figure 7.8 Schematic of optical guidance in a multimode step-index fiber and the corresponding refraction index profile.

Figure 7.9 Refractive index profiles of three common types of optical glass fiber multimode step index, multimode graded index, and single mode.

Step-index and graded-index fibers differ in their (radial) refractive index profiles. 

Step-index fibers are manufactured using the rod/tube or the double crucible process, in which the core and cladding glasses are melted separately from ultrapure powders and transferred into two crucibles with concentric orifices at the bottom and drawn into a fiber. To obtain a semi graded refractive index profile, a diffusion process can be applied in a curing furnace. Step index fibers with a transmission loss of < 10 dB/km at a wavelength of 0.8. pm can be obtained. 

Fig. 7. (a) OLED design (b) calculated reflectance (solid line) with the photopic curve (dash line) and the value of the luminous reflectance RD (c) refractive index profile (step) and irradiance profile inside the OLED, with the arrows showing the metal layers, and the emitting layer marked in black. 

FIGURE 5.30 Refractive index ( ) profiles of optical fiber cables (a) multi-core step index fiber (b) multi-step index fiber (c) graded index fiber. (After Knisley, J. 2002. Fiber optic lighting dries out, ecmweb.com/mag/... 

Figure 5 Subdivision of a refractive index profile into step profiles...

Up to now the only simplification is the discretization of the continuous refractive index profile. The next step is a reduction of the computational effort by using a Taylor-approximation up to the second order in the phaseshift 5 . This approximation is valid if the discrete layer thicknesses are much smaller than the wavelength of the light in other words a sufficiently high number of layers is required. 

In a GI fiber, the refractive index varies radially and hence increases the signal bandwidth. So the GI fiber is expected to be a high-speed data link optical signal transmission medium. Concerning GI plastic rods with the required quadratic refractive index profile, two-step copolymerization and photo-copolymerization techniques have been reported. The two-step copolymerization technique was usually applied for thermosetting resins such as CR-39 resin as a mother rod. It is difficult to draw this GI plastic rod into optical fibers. 

With reference to Fig. 1-2, the step-index planar waveguide has the refractive-index profile defined by... 

In Chapter 11 we discussed the fundamental properties of modes on optical waveguides. The vector fields of these modes are solutions of Maxwell s source-free equations or, equivalently, the homogeneous vector wave equations. However, we found in Chapter 12 that there are few known refractive-index profiles for which Maxwell s equations lead to exact solutions for the modal fields. Of these the step-profile is probably the only one of practical interest. Even for this relatively simple profile the derivation of the vector modal fields on a fiber is cumbersome. The objective of this chapter is to lay the foundations of an approximation method [1,2], which capitalizes on the small... 

Consider a step profile fiber of circular cross-section whose refractive index profile, , for x-polarized light is shown in Fig. 13-l(b). We assume that is sufficiently small so no higher-order modes propagate. Thus, an x-polarized source will excite the fundamental mode with field given by Eq. (13-20). To... 

The refractive-index profile (r, z) for a step-profile fiber with nonuniform core radius p(z) is everywhere expressible as... 

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