Intermodulation distortion in high dynamic range microwave fiber-optic links with linearized modulators

Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier

A search for inverse magnetic catalysis in thermal quark-meson models

We explore the parameter space of the two-flavor thermal quark-meson model and its Polyakov loop-extended version under the influence of a constant external magnetic field $B$. We investigate the behavior of the pseudo critical temperature for chiral symmetry breaking taking into account the likely dependence of two parameters on the magnetic field: the Yukawa quark-meson coupling and the parameter $T_0$ of the Polyakov loop potential. Under the constraints that magnetic catalysis is realized at zero temperature and the chiral transition at $B=0$ is a crossover, we find that the quark-meson model leads to thermal magnetic catalysis for the whole allowed parameter space, in contrast to the present picture stemming from lattice QCD.Comment: 8 pages, 5figure

Antenna-coupled millimeter-wave LiNbO_3 electro-optic modulator

The phase-velocity mismatch due to material dispersion in traveling-wave LiNbO_3 optical waveguide modulators may be greatly reduced by breaking the modulation transmission line into short segments and connecting each segment to its own surface antenna. The array of antennas is then illuminated by the modulation signal at an angle which produces a delay from antenna to antenna to match the optical waveguide's delay

60 GHz and 94 GHz antenna-coupled LiNbO_3 electrooptic modulators

Antenna-coupled LiBbO_3 electrooptic modulators can overcome the material dispersion which would otherwise prevent sensitive high-frequency operation. The authors previously demonstrated the concept with a phase modulator at X-band. They have extended this demonstration to a narrowband 60-GHz phase modulator and broadband amplitude modulator designs at 60 and 94 GHz, respectively

Novel Millimeter-Wave Electro-optic Modulator

A waveguide LiNbO_3 electro-optic modulator has been demonstrated with a novel wave-coupling technique which greatly reduces phase-velocity mismatch. An 8-12 GHz version produces 48° phase modulation with 126 mW of drive power. A 60 GHz version is being built

Energy dynamics in a simulation of LAPD turbulence

Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Inst. 62, 2875 (1991)] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flute-like ($k_\parallel = 0$) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to $k_\parallel \ne 0$ fluctuations, the nonlinear instability accesses the adiabatic response, which provides the requisite energy transfer channel from density to potential fluctuations as well as the phase shift that causes instability. The turbulence characteristics in the simulations agree remarkably well with experiment. When the nonlinear instability is artificially removed from the system through suppressing $k_\parallel=0$ modes, the turbulence develops a coherent frequency spectrum which is inconsistent with experimental data

Possible Signatures Of Dissipation From Time-Series Analysis Techniques Using A Turbulent Laboratory Magnetohydrodynamic Plasma

The frequency spectrum of magnetic fluctuations as measured on the Swarthmore Spheromak Experiment is broadband and exhibits a nearly Kolmogorov 5/3 scaling. It features a steepening region which is indicative of dissipation of magnetic fluctuation energy similar to that observed in fluid and magnetohydrodynamic turbulence systems. Two non-spectrum based time-series analysis techniques are implemented on this data set in order to seek other possible signatures of turbulent dissipation beyond just the steepening of fluctuation spectra. Presented here are results for the flatness, permutation entropy, and statistical complexity, each of which exhibits a particular character at spectral steepening scales which can then be compared to the behavior of the frequency spectrum

On thermal nucleation of quark matter in compact stars

The possibility of a hadron-quark phase transition in extreme astrophysical phenomena such as the collapse of a supernova is not discarded by the modern knowledge of the high-energy nuclear and quark-matter equations of state. Both the density and the temperature attainable in such extreme processes are possibly high enough to trigger a chiral phase transition. However, the time scales involved are an important issue. Even if the physical conditions for the phase transition are favorable (for a system in equilibrium), there may not be enough time for the dynamical process of phase conversion to be completed. We analyze the relevant time scales for the phase conversion via thermal nucleation of bubbles of quark matter and compare them to the typical astrophysical time scale, in order to verify the feasibility of the scenario of hadron-quark phase conversion during, for example, the core-collapse of a supernova.Comment: 6 pages, 4 figures, talk given at the International Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200