Browsing by Subject "Phase difference"
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Item Open Access Asymmetric chiral metamaterial circular polarizer based on four U-shaped split ring resonators(Optical Society of America, 2011-04-28) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, EkmelAn asymmetric chiral metamaterial structure is constructed by using four double-layered U-shaped split ring resonators, which are each rotated by 90° with respect to their neighbors. The peculiarity of the suggested design is that the sizes of the electrically and magnetically excited rings are different, which allows for equalizing the orthogonal components of the electric field at the output interface with a 90° phase difference when the periodic structure is illuminated by an x-polarized wave. As a result, left-hand circular polarization and right-hand circular polarization are obtained in transmission at 5:1 GHz and 6:4 GHz, respectively. The experiment results are in good agreement with the numerical results.Item Open Access Broadband circular polarizer based on high-contrast gratings(Optical Society of America, 2012-05-30) Mutlu, M.; Akosman, A. E.; Özbay, EkmelA circular polarizer, which is composed of periodic and two-dimensional dielectric high-contrast gratings, is designed theoretically such that a unity conversion efficiency is achieved at λ0 = 1.55 μm. The operation is obtained by the achievement of the simultaneous unity transmission of transverse magnetic and transverse electric waves with a phase difference of π/2, meaning that an optimized geometrical anisotropy is accomplished. By the utilization of the rigorous coupled-wave analysis and finite-difference time-domain methods, it is shown that a percent bandwidth of ∼50% can be achieved when the operation bandwidth is defined as the wavelengths for which the conversion efficiency exceeds 0.9.Item Open Access Large bandwidth mode order converter by differential waveguides(Optical Society of American (OSA), 2015) Oner, B.B.; Üstün, K.; Kurt H.; Okyay, Ali Kemal; Turhan-Sayan G.In this article, we propose a large bandwidth mode-order converter design by dielectric waveguides with equal lengths but different cross-sectional areas. The efficient conversion between even and odd modes is verified by inducing required phase difference between the equal length waveguides of different widths. Y-junctions are composed of both tapered mode splitter and combiner to connect mono-mode waveguide to multi-mode waveguide. The converted mode profiles at the output port show that the device operates successfully at designed wavelengths with wide bandwidth. This study provides a novel technique to implement compact mode order converters and direction selective/sensitive photonic structures. © 2015 Optical Society of America.Item Open Access Observation of soliton molecules with independently evolving phase in a mode-locked fiber laser(2010) Ortaç, B.; Zaviyalov, A.; Nielsen, C.K.; Egorov O.; Iliew, R.; Limpert J.; Lederer F.; Tünnermann, A.We report the experimental generation of two-soliton molecules in an all-polarization-maintaining ytterbium-doped fiber laser operating in the normal dispersion regime. These molecules exhibit an independently evolving phase and are characterized by a regular spectral modulation pattern with a modulation depth of 80% measured as an averaged value. Moreover, the numerical modeling confirms that the limited modulation depth of the spectrum is caused by the evolution of the phase difference between the pulses. © 2010 Optical Society of America.Item Open Access Stability of phase difference trajectories of networks of kuramoto oscillators with time-varying couplings and intrinsic frequencies(Society for Industrial and Applied Mathematics Publications, 2018) Lu, W.; Atay, Fatihcan M.We study dynamics of phase differences (PDs) of coupled oscillators where both the intrinsic frequencies and the couplings vary in time. In the case the coupling coefficients are all nonnegative, we prove that the PDs are asymptotically stable if there exists T > 0 such that the aggregation of the time-varying graphs across any time interval of length T has a spanning tree. We also consider the situation that the coupling coefficients may be negative and provide sufficient conditions for the asymptotic stability of the PD dynamics. Due to time variations, the PDs are asymptotic to time-varying patterns rather than constant values. Hence, the PD dynamics can be regarded as a generalization of the well-known phase-locking phenomena. We explicitly investigate several particular cases of time-varying graph structures, including asymptotically periodic PDs due to periodic coupling coefficients and intrinsic frequencies, small perturbations, and fast-switching near constant coupling and frequencies, which lead to PD dynamics close to a phase-locked one. Numerical examples are provided to illustrate the theoretical results.Item Open Access Using phase relations in microstrip directional couplers to achieve high directivity(2013) Tas, V.; Atalar, AbdullahWe analyze the microstrip directional couplers with a special focus on the phase difference between the coupled and isolated ports. The analysis uses the even-odd mode decomposition technique and network theory. The results show that the phase difference between the signals at the coupled port and the isolated port is close to \pi in a very wide band. This property can be used to achieve a broadband directivity by inducing a voltage cancellation at the isolated port of the couplers. Two different cancellation methods are investigated. Analytical formulas for the required component values of both methods are given. Higher directivity can be obtained at the expense of reduced bandwidth.