3,288 research outputs found

    MMI Devices with Weak Guiding Designed in Three Dimensions Using a Genetic Algorithm

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    We discuss the design of weakly guided multimode interference (MMI) devices using a genetic algorithm. For devices exhibiting a nonnegligible vertical waveguide offset, such as those produced using ion exchange in glass, three-dimensional modeling is required to properly evaluate the device performance. A combination of semivectorial finite difference modeling in two transverse dimensions and mode propagation analysis (MPA) in the propagation direction is used to evaluate the merit of each trial design. An example is provided of a 1 x 4 power splitter designed for ion exchange, which shows considerable improvement over that obtained by self-imaging theory

    Determination of Ion Exchange Parameters by a Genetic Algorithm

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    Modeling the process of ion exchange in glass requires accurate knowledge of the self-diffusion coefficients of the incoming and outgoing ions. Furthermore, correlating the concentration profile of the incoming ions to a change in refractive index requires knowledge of the correlation coefficient. We present a method by which these three parameters can be quickly determined experimentally, using a genetic algorithm. Comparison with published data is presented

    Properties of the Quarter-Wave Bragg Reflection Waveguide: Theory

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    The Bragg reflection waveguide (BRW), or one-dimensional photonic crystal waveguide, has recently been proposed for a wide spectrum of applications ranging from particle acceleration to nonlinear frequency conversion. Here, we conduct a thorough analytical investigation of the quarter-wave BRW, in which the layers of the resonant cladding have a thickness corresponding to one quarter of the transverse wavelength of a desired guided mode. An analytical solution to the mode dispersion equation is derived, and it is shown that the quarter-wave BRW is polarization degenerate, although the TE and TM mode profiles differ significantly as the external Brewster’s angle condition in the cladding is approached. Analytical expressions for waveguide properties such as the modal normalization constants, propagation loss, and overlap factors between the mode and each waveguide layer are derived, as are dispersion and tuning curves

    Transfer Matrix Analysis of the Unidirectional Grating-Assisted Codirectional Coupler

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    The unidirectional grating-assisted codirectional coupler (U-GACC) has recently been proposed. This unique structure permits irreversible coupling between orthogonal waveguide eigenmodes by means of simultaneous modulation of both the real and imaginary parts of the refractive index in the coupling region. Analysis of the U-GACC has until now relied on coupled mode theory, which can be restrictive in its application as a design tool. We analyze the U-GACC by the transfer matrix method, which demonstrates in a simple fashion why the device operates in a unidirectional manner. In addition, we show that for all practical designs, there is a limit to the minimum cross talk between outputs, a phenomenon that has not been previously identified

    Dispersion Tailoring of the Quarter-Wave Bragg Reflection Waveguide

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    We present analytical formulae for the polarization dependent first- and second-order dispersion of a quarter-wave Bragg reflection waveguide (QtW-BRW). Using these formulae, we develop several qualitative properties of the QtW-BRW. In particular, we show that the birefringence of these waveguides changes sign at the QtW wavelength. Regimes of total dispersion corresponding to predominantly materialdominated and waveguide-dominated dispersion are identified. Using this concept, it is shown that the QtW-BRW can be designed so as to provide anomalous group velocity dispersion of large magnitude, or very small GVD of either sign, simply by an appropriate chose of layer thicknesses. Implications on nonlinear optical devices in compound semiconductors are discussed

    Ion-Exchanged Glass Waveguide Technology: A Review

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    We review the history and current status of ion exchanged glass waveguide technology. The background of ion exchange in glass and key developments in the first years of research are briefly described. An overview of fabrication, characterization and modeling of waveguides is given and the most important waveguide devices and their applications are discussed. Ion exchanged waveguide technology has served as an available platform for studies of general waveguide properties, integrated optics structures and devices, as well as applications. It is also a commercial fabrication technology for both passive and active waveguide components

    Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

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    Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation

    Test for a learned drinking response : support for appetitive preparedness

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    Seligman, Ives, Ames and Mineka (1970a) have suggested that by the nature of the stimulus-response association in appetitive states a prepared mechanism using mild deprivation cues exists which will activate an appetitional resolution. Pairing of a neutral stimulus with this prepared mechanism results in a conditioned stimulus capable of electing the drinking response. Contrary to this hypothesis, Mowrer (1956) posited that a water deprived state induces an emotional reaction or thirst fear. It is assumed that reduction of this stimulus may be accomplished by means of alleviating the deprived state. A conditioned external stimulus can therefore elicit the drinking response by the mediational stress stimulus. Rates demonstrated increased water intake at zero hours water deprived in the presence of an external stimulus previously paired with an increasing motive state, one-half hour through 23 hours water deprivation. A hi motive state associated cue, 23 hours through 23-1/2 hours water deprived, failed to elicit a greater drinking response in zero hour deprived animals. Intake monitored at quarter hour segments for two hours revealed that lo to hi drive associated stimulus does not effect overall intake but induces differentiation in drinking patterns causing a significant enhancement and then a reduction in intake amounts. These results are in agree with Seligman et al. (1970a) suggesting that elicitation of the prepared mechanism will evoke a drinking response but that water regulation controls do not allow prolonged hyperdipsia
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