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Optical fibers
Published in Matthew N. O. Sadiku, Optical and Wireless Communications, 2018
Graded-index fibers have a higher data rate than do step-index fibers. In fact, almost all multimode fibers used today are graded-index fibers. For graded-index fibers, the refractive index profile of the core varies with the radial distance ρ, while that of the cladding is constant. The most common form of refractive index is given by () n(ρ)={n1[1−Δ(p/a)α],forρ<an1(1−Δ)=n2,forρ≥a
Optical Fibers and Lightwave Propagation
Published in Jerry D. Gibson, The Communications Handbook, 2018
This picture of the underlying mechanism for multimode dispersion suggests an equalization scheme aimed at slowing down the low-order modes that are concentrated near the axis, while speeding up the high-order ones that spiral around as they progress and are to be found primarily near the core-cladding interface, farther from the axis. This is achieved by varying the index of refraction of the core gradually, from a high value (for slower speed) near the axis to a lower one (for higher speed) near the cladding. Fibers so fabricated are termed graded-index (or GRIN) fibers. It is found that a refractive index profile that varies approximately (but not precisely) quadratically with radius can be effective in reducing multimode dispersion dramatically by equalizing the speeds of propagation of various modes of that fiber. Figure 45.6 illustrates the radial variation of the refractive index n(r) for both a step-index fiber and a GRIN fiber.
Biomedical Fiber Optics
Published in María L. Calvo, Vasudevan Lakshminarayanan, Optical Waveguides, 2018
There are two main types: the step-index type and the graded-index type. While the refractive index profile is a step function of a step-index fiber, it generally varies along the core radius for the graded-index fiber. These fibers are also classified as single mode and multimode with respect to guides. Only one mode is guided through the single mode fibers whereas many modes are transmitted through multimode fibers, thus satisfying the general V-number equation [6]. Attenuation is a factor that is difficult to avoid when one deals with solid core fibers. It generally depends on waveguide (fiber) dimensions. It increases when the fiber length increases or when the inner radius decreases [7]. The research leading to subduing these attenuation mechanisms in solid and hollow core fibers has led to the development of multilayer waveguides (generally known as photonic crystals) [8].
Sound reception system by an acoustic meta-lens
Published in Journal of International Maritime Safety, Environmental Affairs, and Shipping, 2021
Sang-Hoon Kim, Byeong-Won Ahn, Kyung-Min Park, Gung Su Lim, Mukunda P. Das
A main feature of the Luneburg meta-lens is its multi-focusing property as shown in Figure 2 (Smolyaninova et al. 2015). The focusing region come from the geometry of the lens depends on the frequency. The refractive index of the ALL depends on the density of the medium. We designed and fabricated an ALL using the common gradient index lens method (Torrent and Sanchez-Dehesa 2007; Climente, Torrent, and Sanchez-Dehesa 2010; Kim S.-H., 2014). It is a direct geometric application of transformation optics. The refractive index profile of the Luneburg lens is given as, . Where R is the radius of the lens and . It was derived from Fermat’s principle and the calculus of variation (Luneburg 1944; Gutman 1954; Morgan 1958). The refractive index of ALL can be rewritten in the discrete form as , where N is the number of layers inside the lens and i =0,1, 2, …, N-1.
Electronic structure, mechanical and optical properties of ternary semiconductors Si1-xGexC (X = 0, 0.25, 0.50, 0.75, 1)
Published in Philosophical Magazine, 2019
M. Manikandan, A. Amudhavalli, R. Rajeswarapalanichamy, K. Iyakutti
The refractive index profile of cubic carbides is shown in Figure 10. In Figure 10, all the sharp peaks are due to the excitonic transitions at the energy band gap edge which are allowed in the infrared spectrum. The refractive index n (0) is given in Table 6 and frequency dependent refractive index n (ω) is listed in Table 7. The static refractive index n (0) of SiC, Si0.75Ge0.25C, Si0.5Ge0.5C, Si0.25Ge0.75C and GeC is found to be 2.6477, 2.6858, 2.8313, 2.7839 and 4.0139 and it reaches the maximum value of 6.453, 5.857, 5.289, 5.930 and 5.784 respectively. The refractive index values are found to be above unity. It shows that the incident photons are slowed down, when they interact with electrons. The refractive index of the material is high, when more photons are slowed down [43]. The results show that n(ω) decreases from SiC to GeC, This is due to the decrease in cation size of ‘Si to Ge’ atom. The refractive index of all these carbides corresponds to low energy region. It is observed that the refractive index decreases with the increase in the photon energy.