Intensity Difference Fluctuation Research Articles

Intensity Equalization of Bidirectional Fiber Laser Based on a Non-Reciprocal Optical Attenuator.

The application of a bidirectional laser requires the laser intensity in both directions to be balanced. However, the CW and CCW light intensities in current bidirectional erbium-doped fiber laser experiments differ due to the gain competition effect. There is no report on equalizing the intensity in the CW and CCW directions. This paper proposes a bidirectional non-reciprocal optical attenuator using the Faraday optical rotation effect. Continuous attenuation adjustment is realized by changing the angle between the polarizer's transmission axis and the linear polarized light. In this study, we analyzed the influence of different parameters on the device's performance, built a non-reciprocal attenuator, and tested the bidirectional attenuation curve, which was consistent with the simulation results. The device was integrated into a bidirectional fiber laser, and the light intensity in both directions was balanced through non-reciprocal adjustment. Combined with closed-loop control, the average intensity difference fluctuation between the two directions was controlled at 0.28% relative to the average power, realizing stable long-term bidirectional fiber laser intensity equalization.

Enhanced Squeezing and Entanglement in Nondegenerate Three-Level Laser Coupled to Squeezed Vacuum Reservoir

Squeezing and entanglement of a two-mode cascade laser, produced by a three-level atom which is initially prepared by a coherent superposition of the top and bottom levels then injected into a cavity coupled to a two-mode squeezed vacuum reservoir is discussed. I obtain stochastic differential equations associated with the normal ordering using the pertinent master equation. Making use of the solutions of the resulting differential equations, we determined the mean photon number for the cavity mode and their correlation, EPR variables, smallest eigenvalue of the symplectic matrix, intensity difference fluctuation, and photon number correlation. It is found that the squeezed vacuum reservoir increases the degree of the statistical and nonclassical features of light produced by the system. Furthermore, using the criteria developed by logarithm negativity and Hillery-Zubairy criteria, the quantum entanglement of the cavity mode is quantified. It is found that the degree of the entanglement for the system under consideration increases with the squeezing parameter of the squeezed vacuum reservoir.

V-type Three-Level Laser Coupled to Squeezed Vacuum Reservoir

The squeezing, entanglement, and statistical properties of cavity modes produced by V-type three-level laser coupled to squeezed vacuum reservoir were studied employing the steady state solutions of the expectation values of the cavity mode operators. The study showed that a light in squeezing state can be produced by the system under consideration under the condition that the cavity decay constant is larger than linear gain coefficient and the squeezing occurs in the plus-quadrature. The cavity modes do not exhibit entanglement properties. It is also observed that the degree of squeezing increases with the linear gain coefficient and squeezing parameter. We also determined the mean and variance of the photon number, intensity difference fluctuations, and the second order correlation function of the two modes. The mean and variance of the photon number as well as the correlation function of two modes decrease as the difference of the probability of the two states at initial time increases. The photons have super-poissionian statistics. The point, η, at which the maximum intensity difference fluctuation occurred depends on linear gain coefficient but not squeezing parameter. The result shows that the correlation of the two modes decreases as η the linear gain coefficient and squeezing parameter.

A Bright Entanglement and Squeezing Generated by an External Pumping Radiation in a Correlated Emission Laser

The quantum and statistical properties of light generated by an external classical field in a correlated emission laser with a parametric amplifier and coupled to a squeezed vacuum reservoir are investigated using the combination of the master and stochastic differential equations. First, the solutions of the cavity-mode variables and correlation properties of noise forces associated to the normal ordering are obtained. Next, applying the resulting solutions, the mean photon number of the separate cavity modes and their crosscorrelation, smallest eigenvalue of the symplectic matrix, mean photon number, intensity difference fluctuation, photon number variance, and intensity correlation are derived for the cavity-mode radiation. The entanglement produced is studied employing the logarithmic negativity criterion. It is found that pumping atoms from the lower energy state to excited state, introducing the nonlinear crystal into the cavity and coupling the system to a biased noise fluctuation, generate a bright and strong squeezing and entanglement with enhanced statistical properties although the atoms are initially in the ground state.

Enhanced squeezing and entanglement in a non-degenerate three-level cascade laser with injected squeezed light

We consider a non-degenerate three-level cascade laser coupled to a two-mode squeezed vacuum reservoir via the lossy single-port mirror. Applying the pertinent master equation, we analyze the effects of the injected squeezed light on the quadrature squeezing, entanglement and normalized intensity difference fluctuations. We show that the injected squeezed light considerably enhances the degree of squeezing and entanglement in the two-mode light for certain initial conditions. Moreover, the injected squeezed light increases the mean photon number where the squeezing and entanglement is significant. We also show that the presence of the injected squeezed light greatly reduces the noise in the intensity difference.

Observation of noise reduction in spatially coupled microchip lasers

We report on the observation of noise-correlated light beams emitted from a pair of spatially coupled microchip lasers. We study in particular, both experimentally and theoretically, the noise reduction induced in the intensity difference fluctuations, by examining the spectral density ratio between the difference and the sum of the two laser intensities in different frequency domains. The noise in the intensity difference is strongly reduced in the spectral domain of the relaxation oscillations of the coupled lasers. The agreement between experiment and the theoretical model findings is very good. d between the two lasers, ~ii! their relative frequency detun- ing D5d 22d 1 ~expressed in Hz!, with d 1 and d 2 the indi- vidual laser cavity detunings, and ~iii! the normalized pump- ing rates of the two lasers M 1 and M 2. Fine adjustments of one of these two latter parameters allow us to vary the rela- tive frequency detuning D. Typically we observe a 20 MHz shift for a pumping rate variation equal to 0.01 @4#. The other relevant parameters will be defined throughout the text. The dependence of the noise reduction on these parameters is studied and a detailed comparison of the experimental results with the extended theoretical model @5# is given. In order to observe the synchronization of the noise- driven fluctuations in the intensities of the two lasers and the consequent noise reduction effect, we first analyzed the time evolution of the intensity of each laser for different values of the distance d in the region of phase locking @3-5#, keeping the system close to resonance, because far from resonance the two microlasers are weakly coupled and the noise corre- lation effects are greatly reduced, as will be shown later. All experiments were performed in nearly identical conditions ~same pump and laser beam waist, and same region of the crystal!, except for the pumping rates M 1 and M 2, which were adjusted in order to achieve the phase locking. The values of the pumping rates remain very close and their variations are moderate ( M 153.060.6 and M 253.360.3). Table I shows the values corresponding to the series of ex- periments performed for D'0.

Application of an all-solid-state, frequency-doubled Nd:YAP laser to the generation of twin beams at 1080 nm.

A laser-diode-pumped intracavity frequency-doubled Nd:YAP/KTP laser is presented. Over 110 mw of TEM00 single-frequency output power at 540-nm wavelength was obtained. The output green laser was employed to pump a semimonolithic nondegenerate optical parametric oscillator to produce intensity quantum correlated twin beams at 1080 nm, and the maximum quantum noise squeezing of 74% (5.9dB) on the intensity difference fluctuation between the twin beams is observed. The threshold was reduced and the stability was increased significantly when compared with similar lamp-pumped systems.

Theoretical analysis and experimental scheme of QND measurement for intensity difference fluctuations

A feasible experimental scheme of QND measurement for intensity difference fluctuations is presented, in which a nondegenerate optical parametric amplifier is used as the nonlinear coupling device. Optimum behavior is obtained by appropriately choosing the operating parameters, which can provide design references for the measurement.

Experimental Realization of a Quantum Measurement for Intensity Difference Fluctuation Using a Beam Splitter

A new quantum measurement scheme of intensity difference fluctuation between two light beams of equal mean intensity is presented. In this system a beam splitter is used as the coupling device and the twin beams with high quantum correlation are injected into its dark port as the input meter wave instead of the usual vacuum field. A measurement satisfying all the quantum nondemolition criteria is experimentally achieved. The measured sum of the transfer coefficients and the conditional variance are, respectively, ${T}_{s}{+T}_{m}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.31$ and ${V}_{s/m}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2.1\mathrm{dB}$.

QND measurement of intensity difference fluctuations

We present a QND scheme for measuring the intensity difference fluctuations between two light beams of equal mean intensity. The scheme involves a nondegenerate parametric oscillator, with the fields on either side of the cavity being the signal and probe fields. Optimum behaviour is obtained above threshold with a highly reflecting signal mirror and a lossy probe mirror.

The effect of loss asymmetry on the nonclassical properties of nondegenerate parametric devices

The effect of linear absoption loss asymmetry on two-mode squeezing in nondegenerate parametric oscillation and amplification is analysed. The interbeam correlations show time-displaced maxima, which we have analytically identified. The analysis of the intensity difference fluctuations shows that the essential factor governing noise reduction is the proper balancing of the system which, in some cases, may be enhanced by increasing the total losses. Finally, an interesting interplay between loss asymmetry and twin beam frequency splitting arises in the analysis of two-mode quadrature squeezing by means of heterodyne detection. Though no perfect squeezing is possible, we have identified optimal squeezing parameter regions and local minima.