Influence Of Phase Fluctuations Research Articles

Investigation of the phase fluctuation effect on the BER performance of DPSK space downlink optical communication system on fluctuation channel

Phase fluctuation effect is an important phenomenon on bit error rate (BER) performance on fluctuation channel in space downlink optical communication system. During research process, both intensity scintillation and phase fluctuation caused by atmospheric turbulence have been considered on fluctuation channel. Through the analysis of simulation results, the influence of phase fluctuation is not sensitive for wavelength and APD gain factor at high data rate. Besides, receiving diameter and divergence angle can be adjusted properly in order to obtain optimal BER performance. This work is helpful to the research of phase fluctuation and the design of practical system.

Effect of phase fluctuations on the Fulde-Ferrell-Larkin-Ovchinnikov state in a three-dimensional Fermi gas

In ultracold Fermi gases, the effect of spin-imbalance on superfluidity has been the subject of intense study. One of the reasons for this is that spin-imbalance frustrates the Bardeen-Cooper-Schrieffer (BCS) superfluid pairing mechanism, in which fermions in different spin states combine into Cooper pairs with zero momentum. In 1964, it was proposed that an exotic superfluid state called the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in which the Cooper pairs have nonzero momentum, could exist in a spin-imbalanced Fermi gas. At the saddle-point (mean field) level, it has been shown that the FFLO state only occupies a very small sliver in the ground state phase diagram of a 3D Fermi gas. However, a question that remains to be investigated is: what is the influence of phase fluctuations around the saddle point on the FFLO state? In this work we show that phase fluctuations only lead to relatively small quantitative corrections to the presence of the FFLO state in the saddle-point phase diagram of a 3D spin-imbalanced Fermi gas. Starting from the partition function of the system, we calculate the effective action within the path-integral adiabatic approximation. The action is then expanded up to second order in the fluctuation field around the saddle point, leading to the fluctuation free energy. Using this free energy, we calculate corrections due to phase fluctuations to the BCS-FFLO transition in the saddle-point phase diagram. At temperatures at which the FFLO state exists, we find only small corrections to the size of the FFLO area. Our results suggest that fluctuations of the phase of the FFLO order parameter, which can be interpreted as an oscillation of its momentum vector, do not cause an instability of the FFLO state with respect to the BCS state.

基于平衡零拍时间测量的位相问题

基于平衡零拍时间测量的位相问题

Study of the influence of phase fluctuations on the characteristics of an OFDM radio-communication system

We consider the influence of phase fluctuations on the operation characteristics of an OFDM radio-communication system. We present the results of studying the effect of additional nonorthogonality noise appearing after the fast Fourier transform due to the phase noise and frequency detuning between the receiver and transmitter oscillators. Approximate analytical expressions for the power of additional nonorthogonality noise are presented for the classical Lorentzian model of the phase noise. Degradation of the signal-to-noise ratio in the OFDM radio-communication system is studied and analytical expressions are given for calculation of this quantity as a function of the frequency detuning and half-width of the spectral line of an oscillator. We present the computer simulation results con.rming the analytical evidence. Based on the obtained results, recommendations for practical choice of the parameters of an OFDM radio-communication system can be given.

Influence of Phase Drift on Optical Coherence Tomography Using a CCD Camera-Based Heterodyne Detection Technique

The performance of a two-dimensional heterodyne detection technique in optical coherence tomography (OCT) was studied. This technique, which is based on the frequency synchronous detection method, enables the use of an imager such as a charge coupled device (CCD) camera as a heterodyne sensor array, so that horizontal cross-sectional image can be acquired in real time without lateral scanning. OCT measurements of scattering media including a biological object were demonstrated. To evaluate the influence of phase fluctuations on the present technique, we measured and analyzed the statistical relative-standard-deviation of heterodyne signal intensity as a function of the random phase shifts between two consecutive CCD frames. Practical limitations in the signal stability and possible solutions are discussed.

Influence of phase fluctuation in external environment on Coulomb blockade in an array system of single tunnel junctions/Ni nanowires

Correlation of Coulomb blockade (CB) with phase fluctuation caused by mutual Coulomb interaction is reported in an array system of single tunnel junctions directly connected to disordered Ni nanowires. At the voltages lower than CB voltage, temperature dependence of the normalized resistance is classified to the following two regimes by a phase transition temperature (Tc), (1) mutual Coulomb interaction regime (T>Tc) and (2) CB regime (T<Tc). It is found that this Tc is very sensitive to a diffusion coefficient (D) of the mutual Coulomb interaction, resulting in a linear Tc vs D1/2 relation. This relation is interpreted as a result of the competition between the charging energy of the CB and the phase fluctuation energy caused by the multiple Coulomb scattering in the Ni nanowire. It is also reconfirmed by the wire diameter dependence of Tc.

Magnetoresistance in a Superconducting Single-Electron Transistor with a Multiply Connected Coulomb Island

The influence of phase fluctuation on fluxoid quantization in a small superconducting ring has been evaluated. In an isolated mesoscopic-sized superconductor, the number of Cooper pairs is fixed and the phase of the order parameter largely fluctuates due to Heisenberg's uncertainty principle. Under such conditions, it is not trivial whether the single-valuedness of the order parameter is kept and the fluxoid is quantized in the superconductor. We examined the problem experimentally using a superconducting single-electron transistor with a ring-shaped Coulomb island. We found that even when the fluctuation in the number of Cooper pairs is very small and a clear Coulomb oscillation is observed, the magnetic flux which goes through the ring is quantized.

Comparative study of critical behavior in several one-dimensionally modulated incommensurate phases by quadrupolar perturbed NMR

Abstract Critical behavior of the one-dimensionally modulated incommensurate phases of Rb2ZnCl4, Rb2ZnBr4, (NH4)2ZnCl4, and BCCD was studied by measuring the temperature dependence of the first order quadrupolar perturbation of the NMR-frequencies of suitable nuclei. In each case, results are in accordance with the non-classical critical exponents predicted by the 3d XY model, thus confirming the universality hypothesis. No deviations from the power laws as reported sometimes in literature and attributed to the influence of phase fluctuations could be observed.

Saturation effects at backward-stimulated scattering in the single-mode regime of interaction

The effects of amplitude modulation of interacting waves at stimulated Mandelstam-Brillouin scattering (SMBS) in a monomode fibre caused by the noise origin of the initial Stokes wave are investigated both theoretically and experimentally. Depending on the determined conditions, there can taken place either a smoothing of the noise amplitude modulation or its preservation in the Stokes radiation in the deep saturation regime of SMBS. Amplitude modulation with period corresponding to the double time of radiation propagation through the fibre is observed along with noise-amplitude modulation of the Stokes and pump waves. The effect of this period prolongation is discussed. The influence of phase fluctuations on amplitude modulation of interacting waves is investigated. The role of phase correlations in the feedback regime of SMBS is considered. Experimental results are in good agreement with numerical calculations.

Influence of phase fluctuations on the measurement of the frequency of a laser

We study the error introduced by phase fluctuations (spontaneous emission noise) in the spectroscopic measurement of the frequency of a laser, when the measurement time is shorter than the phase diffusion time (inverse of the natural linewidth).

The influence of phase fluctuations and phase modulation on two-photon fluorescence

In the present paper the two-photon fluorescence (TPF) quenching produced by ruby lasers in dye is calculated on the basis of an electronic energy level system adapted for the special conditions of Rhodamine 6G. The model used here takes into consideration the action of competing one-photon processes. It will be shown that the reversed profile of TPF quenching in the overlap region is produced by the superposition of pulses with a time-dependent fluctuating phase as well as with a determinate quadratically time-dependent phase.