INDEX deposit profiles

This technology also allows the control of refractive index profiles by doping. AH vapor-phase techniques use a vapor stream of volatile haUdes such as SiCl, GeCl, BCl, or POCl, and gases such as CI2 or O2. The reactants are oxidized and deposited onto a substrate to produce a soHd glass preform which is then drawn into a fiber. The variations of the technique differ in the way the reactants are oxidized (16). 

Figure 10-11. The sample is a 290 nm thin film of LPPP deposited on a BK7 substrate. A planar waveguide glass/polymer/air is formed since the polymer film has the highest index of refraction. The resulting intensity profile of the guided TE waveguide mode for the sample is shown on the right hand side. Only one guided mode is supported.

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. 

Figure 14b displays a graded index profile which was produced by the deposition of 2000 layers. Because of the thinness of the layers they can no longer be detected individually. For both preforms the germanium depletion in the center is obvious from the circular interference lines. 

Since the reaction zone in the plasma process is capable of high speed, a large number of layers can be deposited per unit time. This allows smooth approximation of a desired index profile. Figure 19 shows the impulse response of a fiber23 with... 

Figure 31.2 Mg 2p spectra from depth profiles showing Mg migration into the oxide layer due to heating during extended plasma pretreatments the three samples are a) the native acetone cleaned surface, b) alkaline cleaned and deoxidized, and c) alkaline cleaned and deoxidized followed by 10 min of Ar + H2 plasma treatment and 10 min of N2 plasma treatment prior to deposition of a plasma polymer from TMS + N2, the arrow indicates the evolution as a function of sputtering time, but spacing between spectra is not linear but rather a spectral index, the lines mark the different regions on the samples, as obtained from spectra of the other constituent elements.

Figure 5.4 Ellipsometric profiles of a PDMS microdroplet. Right The PDMS chain whose viscosity = 420 cP (Mp = 16 kg/mole), polydispersity index. Ip = 1.20 (fractionated sample], and surface tension, y = 21.1 mN/m. Substrate Silicon wafer grafted with hexamethyldisilazane critical surface tension close to 21.5 mN/m. Vertical scale. Angstrom horizontal scale, mm baseline, silica layer lateral resolution, 30 pm. Profiles recorded at 18 h, 44 h, and 95 h after drop deposition. Each step is a flat, compact monolayer of PDMS chains at 2D (right]. (Adapted from N. Fraysse ].

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