Photonics applications: optical computing

Nanoscale structures such as inverse opals have fascinating photonic properties related to Natural nanostructures with potential applications in optical computing. 

The application potential of the effects dealt with in this chapter covers a broad field extending from specific electro-optical devices to the all-optical computer. For many applications, polymeric materials have proven appropriate and equivalent to inorganic materials. This section is focused on two aspects, the electro-optical (EO) or Pockels effect and two-photon absorption, which have been exploited extensively. Technical developments relating to polymeric modulators operating on the basis of the Pockels effect have reached the stage of commercialization [5]. 

The linear and nonlinear optical (L NLO) properties are of great importance, because they allow to understand a large number of physical effects (e.g. Kerr-effect, intermolecular forces, solvatochromism)[l, 2]. In addition they are key properties for the design and study of novel photonic materials, which have several significant applications (e.g. optical processing of information and optical computing etc.) [3,4]. The static NLO properties have, in general, two important contributions the electronic and the vibrational. Here we shall mainly review some of our recent work on these properties, but for completeness we shall also present some of the recently published articles by other teams. 

Two main aspects of the present contribution can be generalized and formulated as follows. Firstly, we compute both electronic (Sect. 3.2.2) and vibrational (Sect. 3.2.4) contributions to (hyper)polarizability. Thus, we explore the limitations of the currently available computational procedures. Secondly, we associate the linear and nonlinear optical properties of investigated organofullerenes with their electronic structure (Sect. 3.2.3). The purpose of the analysis of the relations between NLO properties and structure of organofullerenes is to make a basis for further rational design of new [60]fullerene derivatives suitable for photonic applications. 

Losses still occur in the fibres developed for commercial use. Nonetheless, these have been reduced to a point where transmission over kilometres is possible. Along with transmission of information in telephone systems and similar applications, it has been suggested that optical devices may replace conventional electronics in more advanced applications such as computers. For such applications, it will be necessary to develop optical switches, amplifiers, and so on. In the last two decades, new materials have been developed that may form the basis of integrated optical circuits. These materials are photonic crystals. 

Table 2 summarizes different possible applications of photoswitchable biomaterials, while detailing the nature of the biomaterial, the area of application, and, when possible, specific examples. Reversible light-induced activation and deactivation of redox proteins (enzymes) corresponds to write - read - erase functions. The photonic activation of the biomaterial corresponds to the write function, whereas the amperometric transduction of the recorded optical information represents the read function of the systems. Switching off of the redox functions of the proteins erases the stored photonic information and regenerates the photosensory biomaterial. These integrated, photoswitchable redox enzyme electrode assemblies mimic logic functions of computers, and may be considered as first step into the era of biocomputers. 

Although FCS has now been invoked in about 3,000 scientific publications, now at 400 per year, its use before about 1990 was limited by severe technological barriers involving instability of laser light sources, poor sensitivity of photon detectors, noisy electronics, and insufficient computer capacities for the correlation computations. These problems inhibited application of FCS, until suddenly about 1990 the electro-optical and computational technologies advanced so that it became feasible. These advances occurred in synchrony with our creation of Multiphoton Laser Scanning Microscopy, which has enabled effective research on the molecular dynamics of life in living tissues and animals [14]. 

To summarize, we have studied the interaction of two weak quantum fields with an optically dense medium of coherently driven four-level atoms in tripod configuration. We have presented a detailed semiclassical as well as quantum analysis of the system. The main conclusion that has emerged from this study is that optically dense vapors of tripod atoms are capable of realizing a novel regime of symmetric, extremely efficient nonlinear interaction of two multimode single-photon pulses, whereby the combined state of the system acquires a large conditional phase shift that can easily exceed 1r. Thus our scheme may pave the way to photon-based quantum information applications, such as deterministic all-optical quantum computation, dense coding and teleportation [Nielsen 2000]. We have also analyzed the behavior of the multimode coherent state and shown that the restriction on the classical correspondence of the coherent states severely limits their usefulness for QI applications. 

Baev et al. review a theoretical framework which can be useful for simulations, design and characterization of multi-photon absorption-based materials which are useful for optical applications. This methodology involves quantum chemistry techniques, for the computation of electronic properties and cross-sections, as well as classical Maxwell s theory in order to study the interaction of electromagnetic fields with matter and the related properties. The authors note that their dynamical method, which is based on the density matrix formalism, can be useful for both fundamental and applied problems of non-linear optics (e.g. self-focusing, white light generation etc). 

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