Cladding etching

However, the applications of the phenomenon of the modal transition are not limited to the chemical sensing field. Indeed, cladding etching and an HRI layer of sputtered indium tin oxide were exploited to achieve an LPG-based tunable filter with a large tuning range and with limited reduction in the loss peak65. 

Fig. 17 Schematic drawing of the set-up for monitoring the cladding etching process, in HF solution...

Fig. 18 Change of the output power during the fiber cladding etching process...

This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

Resists. Resists are temporary, thin coatings appHed to the surface of the copper-clad laminate. After patterning, these films act as masks that are chemically resistant to the cleaning, plating, and etching solutions used to define the circuit traces of the PWB. Both nonphotosensitive and photosensitive types are used. 

Also the use of tapered long period gratings (TLPGs) is a step toward the use of structures with reduced cladding radius, which provide an additional sensitivity gain with respect to UV-written LPGs and are more robust than etched UV-LPGs66. 

Zhou, K. Liu, H. Hu, X., Tuning the resonant wavelength of long period fiber gratings by etching the fiber s cladding, Opt. Commun. 2001, 197, 295 297... 

Figure 10. Calculated variation with cladding thickness of the birefringence in a SOI ridge waveguide, for different Si02 cladding film stress values. The model waveguide is formed in a 2.2 [j,m thick Si layer and has a typical trapezoidal wet etched ridge profile, with a base width of 3.8 pm, a top width of 1.1 pm, and an etch depth or 1.47 pm.

Figure 11. Comparison of calculated and measured birefringence for different Si02 cladding thicknesses for a trapezoidal waveguide formed in a 2 im thick Si layer as shown in the inset. The ridge base width is 3.8 p,m, the top width is 1.1 pm, and the etch depth is 1.47 pm.

A variety of apertures have been used to deliver nanometer-sized spots of light. While early NSOM tips were fabricated out of etched quartz crystals and micropipettes, tapered optical fibers with tip diameters of ca. 100 nm are now typically used. A metallic thin film such as aluminum is usually applied around the sides of the tapered region of the NSOM tip to focus the light toward the sample. For optical fibers, the numerical aperature is related to the difference in the indices of refraction of the cladding and core (Eq. 2) ... 

Some items that were made were functional and used on board ship, but many were made as gifts for wives or girlfiiends back home. Typical items were pastry cutters, bobbins, and sevnng or knitting implements, made fi m whale teeth. Sometimes teeth were left whole, pictures were etched on the surfaces, and they were mounted as purely decorative objects (Fig. 3.10). The most common illustrations etched onto the teeth were sailing vessels, patriotic scenes or elegantly clad ladies copied from fashion magazines. 

When the ironing is completed to your satisfaction, take the circuit board and transfer sheet, and run it under cold water. After it has cooled down, slowly peel the transfer sheet off. You should see a perfect representation of the electrode grids in a blue color covering the parts that will remain copper clad after etching. Full directions come with each set of transfer sheets. 

Access to evanescent field, which can be exposed either by etching the optical fiber cladding or tapering the optical fiber as shown in Fig. 8a,b, and... 

The modification of the optical fiber involves two major steps, for chemical sensor application [19, 20] (1) removal of the passive cladding (fiber etching) and (2) application of active cladding (fiber coating). The etching and coating processes are explained next. An all-silica MM fiber with core/cladding/jacket dimension of 105/125/250 pm was selected for such application. 

Fig. 20 Micrographs of an optical fiber after a proper etching process has been completed (a) before the cladding was etched (140 pm in diameter), and (b) after the cladding was etched (100 pm in diameter)...

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