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Online ISSN 1751-8598 Print ISSN 1751-858X

IET Circuits, Devices & Systems

Volume 5, Issue 2, March 2011

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Volume 5, Issue 2

March 2011

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  • Optical computing circuits, devices and systems

    • Editorial: Optical computing circuits, devices and systems
      Optical logic elementary circuits
      • Author(s): A. Bogoni ; L. Potì ; A.E. Willner ; P. Ghelfi ; C. Porzi ; M. Scaffardi ; G. Meloni ; G. Berrettini ; F. Fresi ; E. Lazzeri ; X. Wu
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 76 –83
      • DOI:  10.1049/iet-cds.2010.0105
      • Type: Article
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      • p. 76 –83 (8)
        Elementary blocks, performing logic operations, are the building elements for more complex subsystems implementing all-optical digital processing. They can potentially enable next generation optical networks and optical computing, overcoming the limitations of the electronics bandwidth, also guaranteeing scalability, transparency, easy reconfigurability and modularity. Finally, integrated technologies can reduce power consumption, footprint and cost.
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      Low-power nanophotonic devices based on photonic crystals towards dense photonic network on chip
      • Author(s): M. Notomi ; A. Shinya ; K. Nozaki ; T. Tanabe ; S. Matsuo ; E. Kuramochi ; T. Sato ; H. Taniyama ; H. Sumikura
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 84 –93
      • DOI:  10.1049/iet-cds.2010.0159
      • Type: Article
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      • p. 84 –93 (10)
        The authors review their recent studies on various nanophotonic devices including all-optical switches, optical memories, electro-optic modulators, photo-detectors and lasers, all of which are based on photonic crystal (PhC) nanocavities. The strong light confinement achieved in PhC nanocavities has enabled these devices with ultrasmall footprint and ultralow power/energy consumption. These characteristics are ideally suited for constructing dense photonic network on chip, which will overcome the limitation of future CMOS chips in terms of high-speed operation with less energy consumption and heat generation.
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      Integrated waveguide circuits for optical quantum computing
      • Author(s): M.G. Thompson ; A. Politi ; J.C.F. Matthews ; J.L. O'Brien
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 94 –102
      • DOI:  10.1049/iet-cds.2010.0108
      • Type: Article
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      • p. 94 –102 (9)
        Although practical realisation of a fully functioning quantum computer is still a long way off, recent progress both experimentally and theoretically is paving the way for possible implementations. One of the leading approaches is quantum optics, where photons are used as carriers of quantum information, and are manipulated in both linear and non-linear optical circuits. More recently, advances in integrated quantum photonics are enabling the realisation of compact and stable quantum gates and circuits. This approach provides routes to enhancing the complexity of quantum optic experiments, and ultimately towards the development of advanced quantum technologies. This study presents an overview of recent developments in the field of integrated waveguide quantum circuits. Key building blocks required for the realisation of quantum circuits are presented, and a rudimentary version of Shor's quantum factoring algorithm is demonstrated. Planar waveguide quantum circuits provide a high-performance platform from which quantum technologies and experimental quantum physics using single photons can be developed, and a new generation of quantum information and computing devices can be monolithically integrated onto a single optical chip.
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      Nanoparticles with logic and numeracy: towards ‘computer-on-a-particle’ optoelectronic devices
      • Author(s): A.K. Podborska ; M.F. Oszajca ; S.A. Gawe˛da ; K.T. Szaciłowski
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 103 –114
      • DOI:  10.1049/iet-cds.2010.0068
      • Type: Article
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      • p. 103 –114 (12)
        The review focuses on semiconductor nanoparticles and hybrid materials obtained by immobilisation of various molecular species on nanoparticulate semiconductors. These materials constitute unique systems combining collective properties of solids with structural diversity of molecules which show distinctive photoelectrochemical properties. Theoretical models of electronic interactions between molecules and semiconductor surfaces have been presented. Additionally, the review summarises the idea of small particles that can work as electronic devices. These devices are able to sense the environment and communicate with other devices and with the user. The devices are based on surface modified wide-band gap semiconductors and the photoelectrochemical photocurrent switching effect. This effect has created a new platform for novel chemical switches, logic gates and other information processing devices. The mechanism of photocurrent switching is discussed with respect to the type of surface complex-support interaction. Photoelectrochemical properties of multicomponent photoelectrodes based on wide band gap nanocrystaline semiconductors modified with various molecules were investigated. The review presents some examples of hybrid materials working as logic devices, including reconfigurable ones and simple arithmetic systems together with mechanistic problems related to nanoscale information processing.
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      All-optical logic gate in silicon nanowire optical waveguides
      • Author(s): M. Khorasaninejad  and  S.S. Saini
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 115 –122
      • DOI:  10.1049/iet-cds.2010.0142
      • Type: Article
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      • p. 115 –122 (8)
        In this study, the authors propose a novel optical waveguide consisting of arrays of silicon nanowires (SiNWs) in close proximity for applications to all-optical logic operations. The logic operations are based on two non-linear phenomena, stimulated Raman scattering (SRS) and free carrier absorption (FCA). Since, the SRS coefficient is increased in the nanowire regime, the performance of the optical logic gates in terms of optical power required can be improved by a factor of at least 7 using our proposed waveguides. The advantage of the proposed waveguide is that it allows for increased photon-carrier interactions while keeping the optical confinement factor high even when the individual nanowire diameters are less than 100 nm. We analyse the waveguides using the finite-difference time domain method and show that the radiation loss is less than 0.034 cm−1. Further, the waveguide allows for optical guidance even when the nanowires are randomly arranged. We also show a maskless etch method to create SiNWs with dimensions required to create our proposed waveguide structure.
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      All-optical binary to Gray code and Gray to binary code conversion scheme with the help of semiconductor optical amplifier-assisted Sagnac switch
      • Author(s): D.K. Gayen ; T. Chattopadhyay ; M.K. Das ; J.N. Roy ; R.K. Pal
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 123 –131
      • DOI:  10.1049/iet-cds.2010.0069
      • Type: Article
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      • p. 123 –131 (9)
        Gray codes are widely used to facilitate error correction in digital communications. An all-optical four-bit binary to Gray code and Gray to binary code converter with the help of semiconductor optical amplifier-assisted Sagnac switch is proposed and described. This study describes all-optical conversion scheme using a set of all-optical switches. The new method promises both higher processing speed and accuracy. Numerical simulation result confirming the described methods and conclusion are given here.
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      Interferometric switch based all optical scheme for conversion of binary number to its quaternary-signed digit form
      • Author(s): T. Chattopadhyay ; M.K. Das ; J.N. Roy ; A.K. Chakraborty ; D.K. Gayen
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 132 –142
      • DOI:  10.1049/iet-cds.2010.0056
      • Type: Article
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      • p. 132 –142 (11)
        Multi-valued logic (with radix>2) can be viewed as an alternative approach to solve many problems in transmission, storage and processing of large amount of information in digital signal processing. In arithmetical operation signed digit number is very essential for carry free computation. To achieve the parallelism in computation, a suitable number system and an efficient encoding/decoding scheme for handling the data are very much essential. In radix-4 system negative number is represented by quaternary-signed digit (QSD). In this study a conversion from 3-bit binary number (2's complement representation) to its equivalent single-digit QSD is reported. The technique for conversion of QSD to its binary equivalent form is also presented. All-optical circuits are designed with non-linear material-based interferometric switches such as terahertz optical asymmetric demultiplexer in optical tree architecture, where the numbers are represented by different discrete polarised state of light. Device-based simulation of the proposed optical circuit is used to verify the operation of the optical converter.
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      Computer-aided design model for a quantum-cascade laser
      • Author(s): S. Tankiz ; F.V. Çelebi ; R. Yildirim
      • Source: IET Circuits, Devices & Systems, Volume 5, Issue 2, p. 143 –147
      • DOI:  10.1049/iet-cds.2010.0100
      • Type: Article
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      • p. 143 –147 (5)
        This study presents a simple, single and an accurate computer-aided design model for quantum-cascade laser based on multi-layer perceptrons. Each critical quantity (optical gain, differential refractive index change, linewidth enhancement factor) that is used in the model requires long mathematical calculations with a strong background knowledge. In addition to that, these quantities use different theories, estimations and assumptions of some parameter values. The model tremendously decreases the computational time in the order of microseconds and is in very good agreement with previously published results.
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