Arrayed waveguide grating (AWG) is very attractive device for the all optical networks. This paper is devoted to the principle of AWG, the advantages and drawbacks of AWG.The problems of AWG were described and the decisions of these problems are resulted as well.

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Polarization measurements of two-phonon absorption spectra in TlSe and TlInSe,, and of the second-order Raman scattering spectrum in TlSe are carried out in the range of overtone and combination frequencies a t room temperature. The observed peaks in the absorption and scattering spectra are interpreted by the selection rules for two-phonon processes obtained for crystals of TlSe type (space group D: : ) .The peaks which cannot be described by the phonon combination from the centre of the Brillouin zone, are successfully interpreted by selection rules involving the phonons from T and N points of the Brillouin zone.