Coupler structures

In orange dyes of the haloheterocyclic type, the reactive system is invariably attached via the nitrogen of the ] acid coupler. In vinylsulphone dyes, on the other hand, it is normally more convenient to use as diazo component an intermediate such as 7.38 or 7.39 bearing the precursor grouping together with an N-acetylated derivative of ] acid or y acid as coupler, structure 7.93 being typical. 

Figure 14. Intensity distribution for light at wavelength X = 1550 nm propagating through a SiOxNy GRIN coupler structure composed of a 0.5 im Si3N4 waveguide with a 3.5 im SiO Ny GRIN layer.

Figure 15. (a) Index profile for one, two and three layer GRIN waveguide coupler structures and (b) corresponding coupling efficiencies. 

Examples of some coupler structures are shown in Figure 29. 

Figure 29. Some coupler structures , position at which coupling with CD-ox occurs.

Usually, there are two ways of optical excitation to achieve the resonant condition total refiection in prism-coupler structures [12] and diffraction at diffraction gratings [13]. The most commonly used is the first one due to its simplicity, and it is called the Kretschmann configuration, already shown in Fig. 5.5a. 

Monostatic antennas use the same focussing mechanism for the transmitted and the received signals, with the signal channels being separated electronically. Direction-sensitive decoupling between the transmitted and the received signals is required for the FMCW radar. As indicated in Fig. 7.7.3, this can be achieved with a circulator or with suitable directional coupler structures. Fig. 7.7.4 is a photograph of the Bosch 77 GHz sensor. 

Kreuwel H.J.M., Lambeck P.V., Beltman J.M.M., Popma T.J.A., Mode coupling in multilayered structures applied to a chemical sensor and a wavelength selective directional coupler, ProcECIO 87, Glasgow, UK, 1987,217-220. 

The operating principles of the reviewed interferometers are well studied. However, by no means these devices are matured. For example, a mode-selective, wavelength-independent and environmental-resistant 3-dB core-cladding mode coupler is yet to be found to construct an ideal CCMI. As technology advances and research continues, we expect that more device structures will be explored and new methods will be investigated to fabricate these devices. Although the applications of these two types of sensors are yet to be explored, it is almost certain that they will find their way into real-world applications in the future. 

Many of the premetallised direct dyes are symmetrical structures in the form of bis-1 1 complexes with two copper(II) ions per disazo dye molecule. Scheme 5.12 illustrates conversion of the important unmetallised royal blue Cl Direct Blue 15 (5.43), derived from tetrazotised dianisidine coupled with two moles of H acid, to its much greener copper-complex Blue 218 (5.44) with demethylation of the methoxy groups as described above. Important symmetrical red disazo structures of high light fastness, such as Cl Direct Red 83 (5.45), contain two J acid residues linked via their imino groups. Unsymmetrical disazo blues derived from dianisidine often contain a J acid residue as one ligand and a different coupler as the other, such as Oxy Koch acid in Cl Direct Blue 77 (5.46), for example. 

Not all homobifunctional reactive dyes that react with cellulose by the nucleophilic addition mechanism are marketed as sulphatoethylsulphones. Thus the bluish red structure 7.74 contains two chloroethylsulphone precursor groups attached via a diethylamine residue and an activated chlorotriazine grouping to the H acid coupling component. The azopyrazolone yellow structure 7.75 depends for its reactivity on sulpha toe thylsulphonamide precursor groups located separately at the diazo and coupler extremities of the molecule. 

These dyes are invariably monoazo compounds with the reactive system attached to the diazo component, owing to the ready availability of monosulphonated phenylenediamine intermediates. Pyrazolone couplers are most commonly used, as in structure 7.82 (where Z is the reactive grouping), and this is particularly the case for greenish yellow vinylsulphone dyes. Catalytic wet fading by phthalocyanine or triphenodioxazine blues is a characteristic weakness of azopyrazolone yellows (section 3.3.4). Pyridones (7.83), barbituric acid (7.84) and acetoacetarylide (7.85 Ar = aryl) coupling components are also represented in this sector, with the same type of diazo component to carry the reactive function. 

These are reddish blue 1 1 copper-complex monoazo dyes derived from a 2-naphthylamine-or 2-aminonaphtholsulphonate as diazo component and another aminonaphtholsulphonate as coupler. Often such dyes are more easily prepared using a 2-naphthylaminesulphonate and oxidatively coppering the resulting monoazo dye (section 5.5.3). In orthodox structures the imino link of H acid carries the reactive system (7.99), but in other instances the naphthylamine diazo component provides the site of attachment of a haloheterocyclic (7.100) or sulphatoethylsulphone (7.101) grouping. 

Figure 19. (a) Cross-sectional view of the calculated field distribution in a total internal reflection (TIR) coupler in a 2 pm SOI waveguide, and (b) an etched TIR structure in SOI. 

R. W. ZioUcowski and T. Liang, Design and characterization of a grating-assisted coupler enhanced by a photonic-band-gap structure for effective wavelength-division demultiplexing. Opt. Lett. 22, 1033-1035 (1997). 

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