The Theory And Design Of Novel Optical And Acoustical Absorption Systems

Metamaterial, as a new research orientation, has a very broad application prospect in the optical and acoustic fields and has attracted continual attentions all over the word due to its unique physical properties. With the rapid development of the electromagnetic and acoustic metamaterial, its absorption properties also aroused tremendous interest of researchers. The concept of coherent perfect absorber(CPA) has been realized in the field of optical and acoustic because metamaterial has unique feature of exhibiting almost arbitrary effective parameters. The principle of CPA is to utilize the interference effect of coherent light within the absorber, which is the inverse process of laser. Such an absorber exhibits perfect(100%) absorption of the incident waves. CPA, or time-reversed laser,absorbs all of the light that strikes it, give just the right conditions. This process is completely run in reverse with laser. Recently, the concept of CPA laser has been proposed in parity-time(PT) symmetric systems by the loss and gain medium, it can switch the functionality of CPA to lasing by tuning the phase of the incident wave.This dissertation start from the strict coherence requirement of incident wave phase which is necessary condition of CPA. Then studied its limitation in practical applications and propose the concept of multi-channel coherent perfect absorbers(MCPs), which can be realized by two different schemes. MCPs are much more robust in achieving high absorption efficiency under “incoherent” incident waves with random wave fronts. In the other hand, we introduce a unique type of “energy-balanced” media and realized the so-called “CPA lasing” by energy-balanced zero index media(EB-ZIM). The dissertation is organized as follows:In the chapter one, we review the background and progress about our project. we also introduce the investigation progress and physical properties of electromagnetic and acoustic metamaterials. Through the theoretical derivations and numerical simulations, the CPA can be realized by utilizing metamaterials in fields of optical and acoustic.In the chapter two, we investigate the MCPAs. The absorption efficiency of CPA is usually dependent on the phase coherence of the incident waves on the surfaces. So, we present two schemes, a multilayer structure and a cluster of coherent perfect absorbers, to create MCPAs so as to reduce the requirement of phase coherence and achieve high absorption efficiency under “incoherent” incident waves with random wave fronts.In the chapter three, we investigate the MCPAs in acoustic. Analogous to the optical MCPA, we realize the acoustic MCPA by using a multilayer structure.In the chapter four, we study the EB-ZIM and the progress of realizing CPA lasing.Firstly, we introduce a unique type of “energy-balanced” media, whose effective permittivity and permeability are both complex values, but the imaginary part with opposite signs and the refractive index is real, indicating the coexistence and balance of loss and gain. Through the analysis of the condition of CPA and lasing, we find when the loss and gain share the same magnitude, the so-called “CPA lasing”, which was previously proposed in parity-time(PT) symmetric systems, can be realized by EB-ZIM.