INDEX distribution

The spatially periodic temperature distribution produces the corresponding relxactive index distribution, which acts as an optical phase grating for the low-power probing laser beam of the nonabsorbed wavelength in the sample. The thermal diffusivity is determined by detecting the temporal decay of the first-order diffracted probing beam [°o exp(-2t/x)] expressed by... 

It is known that the complete electromagnetic field in each slice s can be expressed in terms of Hertz electric and magnetic vectors rf and rf that are both parallel with the x coordinate axis. (It is a consequence of the invariance of the refractive index distribution of the slice with respect of the coordinates y and x). The field components in the slice s are given by the expressions... 

Figure 1. Schematic view of the one-dimensional layered structure. The vertical lines denote discontinuities of refractive index distribution. The monochromatic plane wave is incident in the y direction with the electric field amplitude The amplitudes of reflected and transmitted waves are ref and, respectively.

Starting from Maxwell s equations with the ansatz of monochromatic, z-propagating fields, E, H Qx i k- co t)), transversal and longitudinal components get decoupled if the refractive index distribution is z-independent. Two physically equivalently meaningful equations for the transversal electric and the transversal magnetic field. 

One special topic for field propagation techniques in general is the minimization of the effect of the transversal boundaries. Uncared, they correspond to abrupt changes of the refractive index distribution, and back-reflections from the boundary into the computational domain do occur. After the obvious ansatz of absorbing BC, TBC " and PML indicate the major improvements so far, which eliminate the problem almost completely. 

Fig. 11 2D model structure of empty channels inside a material with refractive index, n = 1.5. The refractive index distribution (a) and the corresponding near-field pattern of light intensity distribution was calculated by the FDTD technique. The arrow marks the direction of the plane wave (0,1,0) incidence, d is thickness of the sample. The square in b marks the region of the TFSF source used in the calculations... 

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

Ellipsometry measures the relative attenuation and phase shift of polarized light reflected from a polymer-coated surface. The Drude equations (Drude, 1889a,b, 1890 Stromberg et ai, 1963 McCrackin and Colson, 1964) relate the attenuation and phase shift to the average refractive index and thickness tel of an equivalent homogeneous film. Interpretation of fel in terms of the actual refractive index distribution or the polymer distribution [Pg.189]

A two-dimensional guide need not have a rectangular cross section or sharp boundaries. Glass fibers in which the refractive index decreases approximately in proportion to the square of the distance from the axis of the fiber are currently being developed for use in communication systems (14). Graded refractive-index distributions are used for this application because they... 

As described in Section 16.4.5, the detection of refractive-index change between two isomers in a photochromic material is the most promising technique for nondestructive readout.It is necessary to develop a readout system that is sensitive to refractive-index distribution. For this purpose, several methods, such as phase-contrast microscope, differential phase-contrast microscope, and reflection confocal microscope configurations have been proposed. 

Interferometric images are processed online to obtain phase information on the refractive index distribution in the flow... 

Although the principle and applications of the TL technique is very similar to that of the TG method, the time window of the TL method is generally submicroseconds to seconds, which is about three orders of magnitude shifted to the longer scale compared with that of the TG method (see below). The difference comes from the different characteristic length of the refractive index modulation. While the TG signal comes from the spatial modulation of the refractive index in an order of 100-0.1 fim, the TL method detects the spatial shape of the refractive index distribution created by the focused laser beam, whose radius is usually 100-10 /an. [If the Temp.G component is compared with the corresponding temperature lens component (TL due to (dn/dT) [24,62], the difference becomes less clear, particularly for the fast time limit. The TL as well as the TG method can be used for dynamics up to a few picoseconds [62, 63],... 

Viscosity Index Distributions in Base Stocks Use of Thermal Diffusion... 

Figure 1 also shows a typical example of refractive index distribution in the GI POFA preform rod measured by an interferometric technique (10, 11), where Uq and n mean the refractive indices at the center axis and at distance r, respectively. As shown in the curve of Figure 1, the preform rod has a cladding region coming from the PMMA tube and a quadratic index profile in the core region. The normalized refractive index distribution of the GI POFA was almost the same as that of this preform rod (12),... 

Figure 1. Dye density and refractive index distributions of Rhodamine B-doped GI POFA preform rod prepared from MMA solution of 20 ppm-Rhodamine B. Plots and solid line denote the dye density and refractive index values, respectively.

The optimum refractive-index distribution of the high bandwidth graded-index polymer optical fiber (GI POP) was clarified by consideration of both modal and material dispersions. The ultimate bandwidth achieved by the POP is investigated by a quantitative estimation of the material dispersion as well as the modal dispersion. 

The results indicated that even if the refractive-index distribution is tightly controlled, the bandwidth of the poly (methyl methacrylate) (PM )-base GI POP was dominated by the material dispersion when the required bit rate becomes larger than 4 Gb/s for 100-m transmission. It was also confirmed that the material dispersion strongly depends on the matrix polymer and that the fluorinated polymer whose material dispersion (-0.078 ns/nm km) is lower than that of poly methyl methacrylate (-0.305 ns/nm-km) allows for a 10 Gb/s transmission rate in 100 m link. 

It is well known that the dispersion in the optical fibers is divided into three parts, modal dispersion, material dispersion, and waveguide dispersion. In the case of the SI POF, the modal dispersion is so large that the other two dispersions can be approximated to be almost zero. However, the quadratic refractive-index distribution in the GI POF can dramatically decrease the modal dispersion. We have succeeded in controlling the refractive-index profile of the GI POF to be almost a quadratic distribution by the interfacial-gel polymerization technique (2). Therefore, in order to analyze the ultimate bandwidth characteristics of the GI POF in this paper the optimum refractive index profile is investigated by taking into account not only the modal dispersion but also the material dispersion. 

Gradient-index (GRIN) polymer fibers with a quadratic distribution of the refractive index are prepared by a novel closed extrusion process. The effects of the die geometry and the length of the diffusion zone on the refractive index distribution of the polymer fibers are studied. The results show that the non-quadratic refractive index portion of the GRIN polymer fiber can be removed by a coreshell separation die design. Also, the spatial refractive index... 

Control of the Refractive Index Distribution of GRIN Polymer Fibers. 

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