Радиофизика UDC 535.5: 537.87 Nonlinear Coherent Perfect Absorption K. Nireekshan Reddy, S. Dutta Gupta School of Physics University of Hyderabad Hyderabad, India, 500046 We review some of the recent concepts and their realization exploiting the perfect destructive interference of light in micro and nano structures. <...> One refers to optical structures where the effective absorption can be controlled and maximized to perfect absorption. <...> Achieved with a single (two or more) incident plane wave (waves) the effect carries the name of critical coupling (coherent perfect absorption). <...> Thus in a system supporting critical coupling (CC) or coherent perfect absorption (CPA) all the incident radiation can be absorbed leading to null scattering. <...> In particular all the incident light energy can be channeled into a specified mode of a multimodal structure if such modes are supported by the system. <...> Next we review our work on the nonlinear extensions of CC and CPA where one or more of the layered media could be nonlinear with Kerr-type nonlinearity. <...> Further we show that the nonlinear periodic structure can support gap solitons which absorbs all the incident energy and do not scatter any light outside the hetero-guide. <...> Key words and phrases: interference effects, optical periodic structures, optical nonlinearity. 1. <...> There were several reports on planar geometries using absorptive polymers or metal dielectric composites on such systems, wherein, all the incident radiation is absorbed by the structure [6, 7]. <...> Gap solitons in the context of CPA in a nonlinear periodic structure are studied in Section. 5. <...> Critical Coupling Critical coupling (CC)refers to a case when all the incident radiation on micro- or nano- surfaces is completely absorbed without any scattering. <...> The coupling of optical power between micro-resonators and dielectric waveguides was considered by Yariv theoretically [4]. <...> Later, this was extended to a planar geometry with the help of layered stratified media [6]. <...> As shown in Fig. 1, the planar geometry consisted of a very thin (5 nm) absorbingmedium (organic dye), spacer layer and a distributed Bragg reflector (DBR). <...> Schematics of the critical coupling structure in planar geometry and illumination wavelength of incident (at normal incidence <...>