The interference fringes of an atomic Ramsey interferometer may be narrowed if the two separated fields have different frequencies and their phase difference is controlled. For spatially separated fields, their width depends inversely on the free flight time of ground state atoms before entering the first field region in addition to the time between the fields. The narrowing effect is stable with respect to velocity fluctuations and for realistic mode functions. We also show that systematic phase shifts and phase fluctuations do not aggravate the frequency offset of the standard (one-frequency) Ramsey method.

The radiation field can be regarded as a collection of independent harmonic oscillators and, as such, constitutes a heat bath. Moreover, the known form of its interaction with charged particles provides a "rosetta stone" for deciding on and interpreting the correct interaction for the more general case of a quantum particle in an external potential and coupled to an arbitrary heat bath. In particular, combining QED with the machinery of stochastic physics, enables the usual scope of applications to be widened. We discuss blackbody radiation effects on: the equation of motion of a radiating electron (obtaining an equation of motion which is free from runaway solutions), anomalous diffusion, the spreading of a Gaussian wave packet, and decoherence effects due to zero-point oscillations. In addition, utilizing a formula we obtained for the free energy of an oscillator in a heat bath, enables us to determine all the quantum thermodynamic functions of interest (particularly in the areas of quantum information and nanophysics where small systems are involved) and from which we obtain temperature dependent Lamb shifts, quantum effects on the entropy at low temperature and implications for Nernst's law.

Different physical processes using strong laser fields with intensities likely available in the near future are studied. We focus on the possibility of probing experimentally the nonlinear properties of the quantum vacuum that arise due to the existence of the so-called "quantum vacuum fluctuations", as predicted by quantum electrodynamics (QED). In particular, we consider the laser-assisted photon-photon scattering process and the diffractive effects arising during the interaction between an x-ray probe and a strong, focused optical standing wave. Also, the enhancement of vacuum polarization effects due to the presence of a cold relativistic plasma is pointed out. Finally, direct nuclear excitation by an intense, high-frequency laser field is studied.

High time-bandwidth product waveforms have long been used in radar systems to achieve high-resolution ranging at high signal-to-noise ratio under a peak power constraint on the radar transmitter. We consider a laser radar system in which a series of N-photon entangled-state pulses are prepared with only one photon from each pulse being used to interrogate the target while the others are detected within the radar itself. This send-one-detectall protocol (SODAP) achieves high time-bandwidth product pulse compression in a cryptographic quantum manner, i.e., the entanglement precludes any passive receiver from performing pulse compression on the target return.

Several proposed quantum optics approaches to single-molecule imaging will be discussed. These include magnetic resonance, light shift, and Doppleron techniques. They will be compared in terms of resolution and signal to noise ratio.

This short review contains description of distinctive features of the one-dimensional classical harmonic and nonlinear oscillator with additive and multiplicative noises. In addition to the old articles considered at great details in the recently appeared book,¹ we consider some new articles appeared after 2005.

The validity of the few-level approximation is investigated in a system of two dipole-dipole interacting four-level atoms. Each atom is modelled by two complete sets of angular momentum multiplets. We provide two independent arguments demonstrating that the few-level approximation in general leads to incorrect predictions if it is applied to the Zeeman sublevels of the atomic level scheme. First, we show that the artificial omission of sublevels generally leads to incorrect eigenenergies of the system. The second counterexample involves an external laser field and illustrates that the relevant states in each atom are not only determined by the laser field polarization, but also by the orientation of the atomic separation vector. As the physical origin of this outcome, we identify the dipole-dipole interaction between orthogonal dipole transitions of different atoms. Our interpretation enables us to identify conditions on the atomic level structure as well as special geometries in which (partial) few-level approximations are valid.

We propose an imaging scheme based on the quantum spatial correlation of twin beams generated by PDC, and we show that it provides a substantial enhancement of the signal-to-noise ratio with respect to classical schemes.

The NE flank of Stromboli volcano referred to as Sciara del Fuoco (SdF), due to its slope instability and the strombolian type activity is subject to landslides. Analysis performed on ground displacements measured at the SdF by an automatic monitoring system referred to as THEODOROS (THEOdolite and Distancemeter Robot Observatory of Stromboli), have shown that the recorded cumulative probability of displacements are power-law distributed. The volcano flank seems affected by movements that could be explained using a mechanical model. The proposed model consists of a slider mass driven-noise placed on an inclined plane with the same incline angle of the SdF (θ=36.8°). The aim of our study is to investigate the effects of noise on the cumulative size distribution of the proposed model. In particular we show that appropriately choosing the range of variation for the intensity of a Gaussian distributed noise source with zero mean it is possible to model the observed displacements. This is an example of noise-induced critical phenomena.

Nowadays, also thanks to the modernization of the Global Navigation Satellite Systems (GNSS), the number of applications based on the user position is increasing very quickly. Since for many of those applications the accuracy level is one of the core requirements, the monitoring of the interference produced by other telecommunication systems has a fundamental role in the design of GNSS receivers. In fact, because of the useful signal reaches the receiver antenna characterized by a very low power level, the interference from other electromagnetic sources can become one of the main causes of the signal degradation. Moreover it is well known that the frequency spectrum appears very busy and the characteristics of the signals that can interfere with the GNSS one are very different from each other.¹ For this reason the algorithms able to detect or mitigate the effect of an interference should be precisely designed for each different interference source. The presented technique is suitable for non-stationary signals and it develops into two different steps: the detection of the presence of the interference and the characterization of it. During the second phase the technique is able to estimate the time and frequency characteristics of the undesired source. The algorithm is based on the analysis of the auto-correlation function of the received signal, which is composed by the GNSS signal, the noise and the interference, and it exploits the particular characteristics of the auto-correlation of the noise and of the GNSS signals. In the paper the performance of the algorithm are shown for its application to pulsed signals. Moreover the paper shows the benefits obtained by introducing an algorithm based on the modal analysis during the detection phase.

Broadband services require data rates that can only be achieved by using relatively high spectrum frequencies. At such high frequencies, the DSL (Digital Subscriber Line) signal is more susceptible to external noise sources, such as radio frequency interference and impulsive noise. This paper aims to characterize how the impulsive noise impacts on services and applications for a broadband system using an ADSL2+ loop. The first approach was to use the impulsive noise defined in the standards G.996.1 (Test Procedures for DSL Transceivers) from ITU-T and TR-048 (ADSL Interoperability Test Plan) from DSL Forum. In this approach we have also used a HDSL (High Bit Rate DSL) and white noise disturbers on the line. The impulsive noises c1 and c2 (defined in G.996.1) are injected into the circuit at the CO (Central Office) end and CPE (Customer Premises Equipment) end of the loop simulator. Additionally, it was analyzed the spikes of noise's impact on the ADSL2+ line. In this case, pre-defined models of NEXT (Near-end crosstalk) and white noise are injected on CO and CPE side, simultaneously. Metrics like packet rate, lost packet count, bandwidth, short-term average transfer delay, and errored seconds are used to characterize the DSL loop under the noise impairments.

In Shannon's information theory, noise is mathematically identical to entropy. The point of this comment is to highlight the role of noise suppression in the ribosome transition state (TS) reaction. When the rRNA of the ribosome peptidyl transfer center (PTC) is considered along with the reactants which pass through it, enthalpy but also, noise suppression, contributes to the catalysis of the TS reaction.

Vertical-cavity surface-emitting lasers (VCSELs) are widely used as low-cost coherent sources in optical communication systems because they offer many advantages over edge-emitting lasers. However, because of their circular transverse geometry, they often present polarization instabilities. When VCSELs start to lase they emit a linear polarization, and as the injection current is increased, a switching to the orthogonal polarization often occurs. Here I study the influence of spontaneous emission noise on the value of the injection current at which the polarization switching (PS) occurs, when the injection current is sweep in time, starting below the lasing threshold and brought above the PS point and back. I analyze the cases of type I PS, from the high-frequency to the low-frequency polarization, and of type II PS, and from the low-frequency to the high-frequency polarization, and discuss the dependence of the PS point on the noise strength and on the injection current sweep rate.

We address the problem of efficient resolution, detection and estimation of weak tones in a potentially massive amount of data. Our goal is to produce a relatively small reduced data set characterizing the signals in the environment in time and frequency. The requirements for this problem are that the process must be computationally efficient, high gain and able to resolve signals and efficiently compress the signal information into a form that may be easily displayed and further processed. To meet these requirements, we propose a concentrated peak representation (CPR) in which the spectral energy is concentrated in spectral peaks, and only the magnitudes and locations of the peaks are retained. We base our process on the cross spectral representation we have previously applied to other problems. In selecting this method, we have considered other representations and estimation methods such as the Wigner distribution and Welch's method. We compare our method to these methods. The spectral estimation method we propose is a variation of Welch's method and the cross-power spectral (CPS) estimator which was first applied to signal estimation and detection in the mid 1980's. The CPS algorithm and the method we present here are based on the principles first described by Kodera et al.

Typically, entropy is used as a number indicating the amount of uncertainty or information of a source. That means that noise can not be distinguished from information by simply measuring entropy. Nevertheless, the Rényi entropy can be used to calculate the entropy in a pixel-wise basis. When the source of information is a digital image, a value of entropy can be assigned to each pixel of the image. Consequently, entropy histograms of images can be obtained. Entropy histograms give information about the image information contents in a similar way as image histograms give information about the distribution of gray-levels. Hence, histograms of entropy can be used to quantify differences in the information contents of images. In this paper, the behavior of entropy histograms of noisy images has been analyzed and results have been applied to define an index that measures the noise contents of natural images. The pixel-wise entropy of digital images has been calculated through the use of a spatial/spatial-frequency distribution. The generalized Rényi entropy and a normalized windowed pseudo-Wigner distribution (PWD) have been selected to define particular pixel-wise entropy. In this way, a histogram of entropy values has been derived. The shape of such a distribution of entropy indicates the amount of noise present in the image. Some examples are presented and discussed.

New methods in optical communications rely on the quantum properties of photons to assure link security and data privacy. However, optical quantum communications make several assumptions, among them that the quantum properties of photons are preserved over many-kilometer long continuous fiber, which additionally is free from absorbing and scattering centers. In this paper we review quantum communication methods based on photon polarization, single and entangled, and we investigate the impact of noise sources on quantum signal propagation.

We define the transient spectrum as the time-frequency spectrum of a random system undergoing a transient behavior. We show that the transient spectrum approaches the classical frequency spectrum when time goes to infinity. We prove that it is always possible to decompose the transient spectrum into the sum of a stationary spectrum and a decaying spectrum. The stationary spectrum is, up to a constant, the classical power spectrum, while the decaying spectrum accounts for the nonstationary behavior of the transient. All the results are valid for random LTI systems defined by stochastic differential equations of n-th order. The Langevin equation is studied as an example.

We discuss a method that analyzes time series generated by point processes to detect possible non stationarity in the data. We interpret each observation as the first passage time of a stochastic process through a deterministic boundary and we concentrate the effect of different dynamics on the boundary shape. We propose an estimator for the boundary and we compute its confidence intervals. Applying the Inverse First Passage Time Algorithm we then recognize the evolution in the dynamics of the time series by means of a comparison of the boundary shapes. This is performed using a suitable time window fragmentation on the observed data.

We explore the application of a quantum algorithm to optimisation problems over a structured space. For example, problems in automated planning can be represented as automata. These automata are shown to posses algebraic structure that can be exploited by a quantum period finding algorithm. The fact that the quantum walk also provides exponential speed-up over these same structures is of particular interest and results of our investigation will be presented.

The first general analytic solutions for the one-dimensional quantum walk in position and momentum space are derived. These solutions reveal new symmetry features of quantum walk probability densities and insight into the behaviour of their moments. The analytic expressions for the quantum walk probability distributions provide a means of modelling quantum phenomena that is analogous to that provided by random walks in the classical domain.

In this paper we consider feedback control algorithms for the deterministic purification of a bipartite state consisting of two qubits, when the observer has access to only one of the qubits. We show that Hamiltonian feedback control can be used to produce deterministic evolution of the purity of either qubit individually, or both together.

In this paper we address the quantum random walk on the real line. Specifically, we utilize a dynamical system formulation of the walk, which leads to a momentum space expression of the probability amplitude that is a function of only the initial condition. Our focus is, for the most part, limited to the Hadamard walk. As such, this closed form expression is not as general as that given by [1]. This lack of generality is offset by the ease with which we obtain the expression, and the insight offered by it. Our closed form expression allows us to easily compute the walk pdf, hence the cdf (cumulative distribution function). It is shown that the cdf converges to its limiting form relatively quickly. We push the simple mathematics in an to attempt to obtain a closed form expression for this form. But it becomes too involved to take it to completion in this paper, without running the risk of losing appreciation for the simplicity of our approach.

The Global Positioning System (GPS) is an extremely effective satellite-based system that broadcasts sufficient information for a user to determine time and position from any location on or near the Earth. The fundamental GPS measurement is the corrected time of the satellite clock relative to the receiver clock. This paper uses publicly available information to present a statistical analysis of the underlying timescale and clock performance, which can be largely presented without recourse to the many significant and interesting scientific corrections and parameterized models that could or must be applied to the data.

The Bureau International des Poids et Mesures (BIPM), is on charge of computing and publishing international reference time scale. A practical scale of time for world-wide use has two essential elements: a realization of the unit of time and a continuous temporal reference. The reference used is International Atomic Time (TAI), a time scale calculated at the BIPM using data from some three hundred atomic clocks in over fifty national laboratories. TAI is a uniform scale. The Coordinated Universal Time (UTC) is obtained by adding to TAI leap seconds due to slightly irregular rotation of the Earth. The contributing clocks located around the world, mostly in hemisphere north, are compared by different satellite time transfer techniques. Clocks and transfer techniques are affected by various types of noise. This paper briefly reports the impact of these noises on the computation of TAI.

Noise is generally considered a disturbance in understanding systems dynamics and large efforts are devoted to filter its presence in observed data. In many instances the filtering helps the comprehension of involved phenomena but this cleaning can result in a distruction of important information. A set of examples, extracted from existing mathematical and applied literature, illustrate instances where the noise plays a positive role in determining the final dynamics of the system or allowing optimum values for signal detection. In this paper we will specifically focus on possible roles of noise when the underlining system presents non-linearities. Some of the discussed examples are toy examples useful to explain some unexpected result but we also consider the mathematical problem of determining the first passage times of stochastic processes through boundaries. These times have an immediate role in reliability theory, when alarms are tuned to prevent crashes. The fact that their behavior is highly determined by a positive role of the noise can suggest improvements for some measurement device.

Atomic clocks are ultra-precise time references, and because of this fact in the past 20 years they have found a fundamental application in navigation problems. The error in the localization of the user is highly dependent on the clock stability: variations of few nanoseconds in the clock phase result in an increase of the localization error by a factor of meters. Unfortunately atomic clocks are nonstationary, and their stability changes with time. We have recently proposed the DAVAR, or dynamic Allan variance, a representation of the instantaneous stability of an atomic clock. In this paper we will discuss the definition of the DAVAR and we will apply it to simulated nonstationary data, to prove its validity in clock noise characterization.

In this paper, the problem of detecting anomalies in the behavior of atomic clocks is addressed by means of statistical fault detection techniques. In particular, a method based on a generalized likely hood ratio test (GLRT), which allows the detection of a fault and the estimate of the time at which fault has occurred, is analyzed and characterized by means of both synthesized and experimental data obtained from a Rubidium frequency standards. The effectiveness of the method has been already compared with standard tools such as the Allan variance. In this paper, the characterization of the detection technique is deeply analyzed and information are used for designing a practical fault detection method for revealing atomic clock failures.

Accreting binaries containing a black hole are stellar systems composed of a normal star and a black hole. Because of the strong gravitational pull of the black hole, matter is removed from the companion star and falls into the compact object. In falling, it forms an accretion disk of gas that spirals towards the center, heating up and emitting in X rays. The physics of such a structure is extremely complex and can be studied through observations with X-ray satellites. The time series derived from X-ray observations of bright black-hole binaries in the Galaxy show a complex phenomenology. Broad noise components with a variability of up to ~40% are observed, as well as quasi-periodic features on time scales from 100 seconds down to a few milliseconds. The characteristic frequencies of the di.erent components can change on very short time scales. However, some of these signals are elusive as they are very weak and are drowned in intrinsic and instrumental noise. The physical nature of these signals is still largely unknown, but it is clear that they originate from gas orbiting a few kilometers from the central black hole and accreting onto it. In addition of being important for the study of the accretion of matter onto a black hole, these observational properties constitute a unique probe for testing General Relativity in the strong field regime. I review the current observational status as well as the techniques used to study these signals.

The past twelve years have seen the discovery, with NASA's Rossi X-ray Timing Explorer (RXTE), of several long-predicted phenomena associated with the accretion of matter onto a neutron star in a binary (double) star system. These phenomena are observed in the strong X-ray emission produced by these neutron stars, at luminosities up to several 100,000 Solar luminosities, and take place at the dynamical time scale of the strong field gravity region surrounding a neutron star (~0.001 sec). Physical models for these millisecond phenomena include the neutron star spin, thermonuclear burning and release of gravitational energy at the neutron star surface, and general relativistic orbital and epicyclic motions in the accreting plasma. The detection and characterization of these phenomena (some of which are themselves best modeled as noise phenomena, others of which have a more deterministic nature but always involve random-process aspects) is done by the estimation of the Fourier power spectrum of the intrinsic millisecond time variations in the X-ray luminosity in the presence of dominant photon counting statistics noise which can be characterized as Poisson noise modified by instrumental deadtime effects. To a large extent these methods work well: they give astronomers the quantitative answers they need. I discuss some of the methodological challenges as well as some of the main results in this field.

The fluctuating brightness of cosmic X-ray sources, particularly accreting black holes and neutron star systems, has enabled enormous progress in understanding the physics of turbulent accretion flows, the behaviour of matter on the surfaces of neutron stars and improving the evidence for black holes. Most of this progress has been made by analysing and modelling time series data in terms of their power and cross spectra, as will be discussed in other articles in this volume. Recently, attempts have been made to make use of other aspects of the data, by testing for non-linearity, non-Gaussianity, time asymmetry and by examination of higher order Fourier spectra. These projects, which have been made possible by the vast increase in data quality and quantity over the past decade, are the subject of this article.

We present a brief review of time-varying spectral analysis and we discuss the applicability of the methods to the case of x-ray bursts where it is known that there are time-varying frequency components. A preliminary analysis is done on x-ray burst the experimental data. Two methods are presented to estimat the instanteous frequency and both methods give approximately the same results.

Quantum entanglement has the potential to revolutionize the entire field of interferometric sensing by providing many orders of magnitude improvement in interferometer sensitivity. The quantum-entangled particle interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/√N N, where N is the number of particles passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of √N to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. This effect can translate into a tremendous science pay-off for space missions. For example, one application of this new effect is to fiber optical gyroscopes for deep-space inertial guidance and tests of General Relativity (Gravity Probe B). Another application is to ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively. Other applications are to Satellite-to-Satellite laser Interferometry (SSI) proposed for the next generation Gravity Recovery And Climate Experiment (GRACE II).

Three-mode (tripartite) squeezed light is important for continuous variable quantum information tasks such as quantum teleportation, state sharing, and generating tripartite continuous variable entangled states, and furthermore is the first nontrivial step towards multipartite squeezed states. In such cases just one two-mode squeezer is used, and the squeezed light is distributed across multiple channels by passive optical elements. Here we show that these three-mode squeezed states are produced by optical networks that can be described as SU(1, 1) transformations, which enables relatively straightforward and elegant calculations of any output state from such squeezing networks for any input state.

We demonstrate, using an all-optical setup, the difference between local and global dynamics of entangled quantum systems coupled to independent environments. Even when the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear.

We review the measurement of entanglement in the above-threshold optical parametric oscillator, an experimental challenge that lasted 17 years. The challenge was in part technical, owing to the difficulty of measuring phase noise, but also related to unexpected noise features that remain unexplained. We describe the experimental strategies used to measure phase noise and to circumvent the "extra" noise. The theoretical prediction of a higher order of entanglement is presented, as well as measurements of bright three-color quantum correlations.

We consider an optical cavity made by two moving mirrors and driven by an intense classical laser field. We determine the steady state of he optomechanical system and show that two vibrational modes of the mirrors, with effective mass of the order of micrograms, can be entangled thanks to the effect of radiation pressure. The resulting entanglement is however quite fragile with respect to temperature.

Light scattered by a regular structure of atoms exhibits spatial interference signatures, similar to Young's classical double-slit experiment. The first-order interferences, however, are known to vanish for strong light intensities, where the incoherently fluctuating part of the emitted light dominates. Here, we show how to overcome these limitations to quantum interference in stronger laser fields, and how to recover the first-order interference in strong fields by a tailored electromagnetic vacuum with a suitable frequency dependence. We also discuss higher-order correlation functions of the scattered light, with applications, e.g., to lithography. In the second part, we study light propagation of a probe field pulse in closed-loop atomic systems. The closed interaction loop induces a sensitivity to the relative driving field phase, but in general prohibits a stationary steady state. In particular, the finite frequency width of the short probe pulse requires a time-dependent analysis beyond the so-called multiphoton resonance assumption. Using a Floquet decomposition, we identify the different contributions to the medium response, and demonstrate sub- and superluminal light propagation with small absorption or even gain, where a coupling field Rabi frequency allows to switch between sub- and superluminal light propagation.

We have studied the nonlinear Faraday effect of intense linear polarized light in an optically thick atomic rubidium vapor. We have shown that the polarization rotatation rate (rotation angle per unit magnetic field, in the limit of low field) reaches a saturation value as the intensity and density are increased.

In this paper, we present influence of optical mixing of microwave signals on conversion of the noise power spectral density (NPSD), using a directly modulated semiconductor laser and an interferometer to convert frequency modulation into intensity modulation. The results show the influence of the modulation index and modulation frequency in an optical link by considering optical mixing.

The authors experimentally demonstrate stable pulse generation from a rational harmonic mode-locked fiber ring laser that employs carrier-suppressed return-to-zero (CS-RZ) format as a modulation waveform. We obtain the CS-RZ format by tuning the bias voltage of the LN intensity modulator and the RF driving amplitude. The rational mode-locking is realized by detuning the modulation frequency in the laser system. We have observed the rational harmonic mode-locking of up to the fifth order. The most stable pulses are generated at the rational harmonic order of two, where the stability of the output pulses is evaluated by the sum of the normalized standard deviation of the voltage and that of the time of the pulse leading edge.

In a digital camera, several factors cause signal-dependency of additive noise. Many denoising methods have been proposed, but unfortunately most of them do not work well for the actual signal-dependent noise. To solve the problem of removing the signal-dependent noise of a digital camera, this paper presents a denoising approach via the nonlinear image-decomposition. In the nonlinear decomposition-and-denoising approach, at the first nonlinear image-decomposition stage, multiplicative image-decomposition is performed, and a noisy image is represented as a product of its two components so that its structural component corresponding to a cartoon approximation of the noisy image may not be corrupted by the noise and its texture component may collect almost all the noise. At the successive nonlinear denoising stage, intensity of the separated structural component is utilized instead of the unknown true signal value, to adapt the soft-thresholding-type denoising manipulation of the texture component to the signal dependency of the noise. At the final image-synthesis stage, the separated structure component is combined with the denoised texture component, and thus a sharpness-preserved denoised image is reproduced. The nonlinear decomposition-and-denoising approach selectively removes the signal-dependent noise of a digital camera without not only blurring sharp edges but also destroying visually important textures.

In this paper we propose to employ an instability that occurs in bistable devices as a control signal at the reception stage to generate the clock signal. One of the adopted configurations is composed of two semiconductor optical amplifiers arranged in a cascaded structure. This configuration has an output equivalent to that obtained from Self-Electrooptic Effect Devices (SEEDs), and it can implement the main Boolean functions of two binary inputs. These outputs, obtained from the addition of two binary signals, show a short spike in the transition from "1" to "2" in the internal processing. A similar result is obtained for a simple semiconductor amplifier with bistable behavior. The paper will show how these structures may help recover clock signals in any optical transmission system.

A sensitive technique to measure the relative intensity noise of a laser is described. Such experiment is a useful tool for laser characterizations, allowing direct measurement of physical parameters like relaxation oscillation frequencies and damping factor. Examples of determination of such parameters are given.

Nonlinear Optical Loop Mirrors have been considered as nonlinear compressors for high input power optical pulses. The present work proposes a NOLM scheme that compresses and reshapes low power picosecond optical pulses in the miliwatts range. This scheme is based on a Semiconductor Optical Amplifier and the use of highly nonlinear Photonic Crystal fibers. The attention of this study is the amplitude noise and timing jitter behavior of this scheme.

This paper deals with photodetected noise processes occuring in co-propagative DRA (Distributed Raman Amplifiers) such as beat noises. We develop here numerical modelisations and experimental set-ups in order to confront theory and measurements for each excess noise source. Our measurements demonstrate that the Raman ASE process, which gives rise to the DRA "background" noise, is poissonian, in spite of a super-poissonian pumping power, and how this statistics is disturbed by pump excess noise.

Noise and fluctuations are of fundamental importance in all aspects of laser systems, especially in laser amplifiers. We present the results that not only enhance the signal seed sources to the maximum amplification, but also produced single amplified signal source. The outputs of the complete high intensity ultra-short pulse UV laser system are presented and characterized.

This paper deals with the study of the various excess noises in copropagative distributed Raman Amplifiers. We study the influence of the biasing system on the laser sources through three simple home-made curent sources. A second step consists in studying the polarization multiplexer noise contribution. Finally, the impact of these noise exces on the amplifier background noise is studied.

This paper deals with noise and noise correlation experimental results in copropagative distributed Raman Amplifiers. Each stage of the whole amplifier is studied, focusing on the pumping system influence. This work finally leads to the background ASE noise excess noise due to pumping system RIN.

We present high precision intensity noise measurements of Quantum Dot Superluminescent LEDs and lasers emitting at 1.3μm. For the QD-SLEDs we investigate the intensity noise behavior and identify the relevant noise parameters by comparing the experimental results to theoretical calculations. We find an Excess Noise behavior due to amplified spontaneous emission, the dominant origin of noise. The investigation of the spectrally resolved emission enables further characterization of the noise properties. The influence of a resonator on the noise behavior is discussed for QD-Lasers. The noise of the laser is compared to the SLED's, and shows strong deviation from the Excess Noise character above threshold.

The intensity fluctuations of focused general-type beams in weakly turbulent atmospheric links are formulated and numerically evaluated. Focused general-type beams in general cover very large range of beams, however in this work we concentrate specifically on the focused sinusoidal-Gaussian, annular and flat-topped beams. The behavior of the scintillations for these beams is examined versus the focusing distance, wavelength of operation and the source size. In our formulation, atmospheric turbulence is introduced through the Rytov method where the free space field (i.e., in the absence of turbulence) at the receiver plane for the general-type focused beam is found by utilizing the Huygens-Fresnel principle. Figures are presented showing the scintillation index for focused general-type beams and collimated general-type beams. To find out the source and medium parameters that will yield favourable scintillation levels, the intensity fluctuations of the focused sinusoidal-Gaussian, annular and flat-topped beams are compared. Within the range of selected source and medium parameters, our observations indicate that the intensity fluctuations in weak turbulence tend to be the smallest for the focused flat-topped Gaussian beams and the largest for the focused cos-Gaussian beams. Gaussian, cosh-Gaussian and annular beams experience interim level fluctuations. The comparison of the scintillation levels for the mentioned types of focused beams follow the same tendency for all the propagation distances. Also, the intensity fluctuations of the focused general-type beams in turbulence are compared with their collimated counterparts. Such a comparison reveals that for all the beams at a selected source size, the scintillations are nearly the same for both the focused and the collimated cases at all the propagation distances, except for the flat-topped Gaussian beams. When focused flat-topped Gaussian beams are employed, the intensity fluctuations seem to be lower as compared to the equivalent collimated flat-topped Gaussian beam at shorter link lengths.

We study the role of noise during the growth process of opal-based photonic crystals, and demonstrate that noise significantly improves their structural properties. We observe a stochastic resonance-like behaviour, where the ordering of the resulting structure improves up to a certain optimal noise level and then deteriorates for larger noise volumes. This demonstrates that noise can have a nontrivial effect when applied during a non-equilibrium pattern forming process.

Atomic Force Microscopy (AFM) gives a possibility to study and control the surface structure at submicron spatial scales. The essential problem in studying the surfaces is their adequate parameterization. It is necessary to extract information from the surface roughness profiles h(x) and h(y) along coordinates x and y. These profiles contain regular (resonant) components as well as chaotic (noisy) components with "long memory". The main questions are how to extract useful information about the surface state and study the effect of various external factors on it by analyzing the spatial series h(x) and h(y) and separate out the information contents of chaotic and resonant components. These problems can be solved by using Flicker-Noise Spectroscopy (FNS) approach. According to FNS, the information hidden in chaotic surface profiles is represented by correlation links in sequences of different types of irregularities: spikes, jumps, and discontinuities in derivatives of different orders at all spatial hierarchical levels of the systems. In this paper, the FNS is used to parameterize AFM images of sufficiently homogeneous structures obtained for surfaces of lithium fluoride single crystals as well as two dendritic (treelike) structures formed on mica surface from solutions of surfactant copolymers.

In an open-air setting, one source of fluctuations in a T-ray (THz) pulsed signal is attributed to water vapor. Fluctuations of this type are generally undesired, and so the water vapor is commonly removed in a closed chamber. Yet, in some applications a closed chamber is not feasible. This paper presents a preliminary study on a computational means to address the problem. Initially, the complex frequency response of water vapor is modeled from spectral line data. Using a deconvolution technique, together with fine tuning of the line strength at each frequency, the response is partially removed from a measured T-ray pulse, with minimal signal distortion.

We study the impact of Amplified Spontaneous Emission (ASE) noise on a Semiconductor Optical Amplifier (SOA)-based optical pulse delay discriminator and SOA-based distance ranger. Our experiments show that ASE reduces the sensitivity of these SOA-based devices and we confirm this finding by carrying out extensive simulations by modeling the ASE response of SOAs. The simulation results, obtained by numerical integration of these equations in MATLAB^TM using the NIMROD^TM portal, are in qualitative agreement with experimental results.

In this paper the theory of the joint neutron-gamma photon distributions emitted from fissile samples with an intrinsic neutron source, i.e. spontaneous fission, is described. In a sample of finite size short fission chains will develop for each initial source event, thereby changing the number distributions (multiplicities) of the emitted neutrons and gamma photons as compared to the elementary source events. Although in the fission process the neutrons and the gamma photons are generated independently of each other, since new gamma photons are also generated in the fission chain, the number of total emitted neutrons and gamma photons will develop correlations which increase with increasing sample mass. In the paper the general theory of the joint distributions is derived through master equations for the generating functions. The first few joint factorial moments are calculated explicitly, including the covariance between the neutron and gamma photon numbers.

The analysis of the dynamics of lateral couple diode lasers is a key issue on the study and understanding of these devices. In this work a detailed study of the different nonlinear regimes observed in these devices is made. By the observation of both the RIN spectrum and the filtered optical spectrum, a clear identification of the different regimes dependence with the relative bias was achieved.

The quantum Zeno effect predicts that the decay of an unstable system can be slowed down by measuring the system frequently enough. In some systems, however, an enhancement of the decay due to frequent measurements, namely the anti-Zeno effect, may occur. In this paper we study the Zeno-anti-Zeno crossover for quantum Brownian motion. Moreover, we propose a way to manipulate the decay of the system and to observe a controlled continuous passage from decay suppression to decay acceleration by using reservoir engineering techniques.

In modern WDM telecommunications, optical signals undergo an evolutionary degradation as a result of ultra-high data rates (>10Gbps), very long fiber links (800 km), attenuation, non-linear photon-matter interactions, noise and jitter. BER, Q-factor, SNR, NF and optical power level are among the key parameters that determine channel performance. Typical channel performance relies on EDC codes, which have a limited error detection capability and require several frames to estimate BER (only); EDCs detect up to sixteen errors and correct up to eight within a block of information. We present a method, which is based on statistical estimation of synchronous data sampling to construct two virtual statistical distributions from which all performance parameters (not BER only) and signal power levels are estimated in real-time and without service interruption.

The chaotic behavior of on external-cavity semiconductor laser (ECSL) working in a regime of low-frequency fluctuations (LFFs) can be controlled by external electro-optical phase or intensity current modulation. It is shown by numerical simulation that, for specific values of the modulating frequency and amplitude, the phase difference between the laser power drop-out and the modulator remains constant in time leading to phase-synchronized states, steady LFFs, so called m:n phase synchronization. The degree of stabilization is determined by calculating Shannon's entropy and by the analyzing the stability of the phase locking. The synchronization regions are mapped and zones of low and high amplitude chaos are identified. The light emission can be stabilized from a regime of large amplitude chaotic oscillations corresponding to LFFs to one of low-amplitude chaotic or even periodic oscillations. The dynamics of the laser can be controlled when the period of the modulating signal is comparable with the laser itinerancy time between consecutive external-cavity modes.

Fluctuations of optical and electronic noise, as well as other non-linear phenomena, affects the performance of optical channels in fiber-optic communication networks. Estimating and tracking channel performance at the receiver in real-time is a critical function to the integrity of communications service. This is realized when the receiver is equipped with mechanisms that perform in-service, in-real time and at low cost. In addition, another mechanism must be employed that reassigns non-performing channels to others for uninterrupted service. In this paper, we evaluate the noise and performance degrading mechanisms in optical links; we describe a method for in-service performance estimation, and performance tracking. In addition, we adopt a supercontinuum source to cost-efficiently generate a comb of twenty optical channels and we simulate it. Finally, we develop a protocol for remedial actions such as multiple-channel equalization and proactive single or multiple switch-to-protection channel.

We describe a scheme capable of localizing an ensemble of interacting two-level atoms. The atoms are assumed to be bunched together in a volume much smaller than an emission wavelength, and they interact with a standing wave laser field. Due to the laser-pumping of the atomic sample, it collectively emits fluorescence light with properties depending on the ensemble position in the standing wave. This relation can be described by a fluorescence intensity profile, which depends on the standing wave field parameters, the ensemble properties, and which is modified due to collective effects in the ensemble of nearby particles. We demonstrate that the intensity profile can be tailored to suit different localization setups.

We present an experiment where the motion of a silicon micro-mechanical resonator is optically monitored with a very high-finesse optical cavity, down to a quantum-limited sensitivity at the 10-¹⁹m/√Hz level. We have observed the thermal noise of the resonator at room temperature over a wide frequency range, and fully characterized its optomechanical behaviour, in good agreement with theoretical models. We have also demonstrated a direct effect of intracavity radiation pressure upon the dynamics of the micro-resonator in a detuned high-finesse optical cavity: depending on the sign of the detuning, we have obtained both cooling and heating, with an effective temperature ranging from 10 to 2000 K. We have also observed a related radiation-pressure induced instability of the resonator. This experiment opens the way to radiation pressure-driven quantum optics effects, with silicon resonators offering high resonance frequencies, low effective masses, and a high displacement sensitivity. Possible experiments include QND measurement of light intensity or optomechanical squeezing of the optical field, as well as the optical observation of the quantum ground state of a macroscopic oscillator.

We have developed an experiment of ultrasensitive interferometric measurement of small displacements based on a high-finesse Fabry-Perot cavity. We describe recent progress in our experimental setup in order to reach a sensitivity better than 10^-20 m/√Hz. This unique sensitivity is a step towards the first observation of radiation pressure effects and the resulting standard quantum limit in interferometric measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes, and we already report the first experimental demonstration of a back-action noise cancellation. Using a classical radiation-pressure noise to mimic the quantum noise of light, we have observed a drastic improvement of sensitivity either in position or force measurements.

Various Monte Carlo methods allow the simulation of the dynamics of open quantum systems. We highlight the central features a commonly used method for Markovian systems, i.e., Monte Carlo Wave Function method and another one used for non-Markovian systems, i.e., the doubled Hilbert space method. One of the open problems in the field has been the lack of the existence of Monte Carlo method with quantum jumps for non-Markovian systems. We characterize the key problems that should be solved in this context and give indications for the way towards the development of quantum jump method without auxiliary states for non-Markovian systems.

In ground based interferometric observations, fringe stabilization over long integration times is a mandatory task in order to achieve useful performances even on faint sources. This is done by dedicated instruments which search the maximum of the fringe envelope and consequently correct the optical path of the interfering beams. Localization of the fringe maximum position is corrupted by noise coming both from turbulent atmosphere and instruments. Atmospheric fluctuations are corrected at telescope level, but high frequency disturbance, as well as inter-telescope one, still remain. These residuals must be recognized and separated from the source signal, in order to properly model the instrument behaviour. Moreover, algorithms for fringe tracking must be strong enough to tolerate residual noise and instrument model inaccuracy. We provide some examples of noise performance of both calibration and fringe maximum localization based on laboratory experiments.

We are proposing a new method for the denoising of speech in dedicated single channel speech communication systems. Dedicated speech communication systems are optimized for the use by a dedicated speaker. Our procedure employs a speech production model that combines a fixed (but speaker dependent) glottal excitation process with an adaptive autoregressive filter. Denoising is performed in two steps: 1) model parameter estimation and 2) signal resynthesis from the proposed model. Our parameter estimation procedure is inspired by a maximum likelihood approach that utilizes learned parameter statistics from a training process. The procedure produces improvements that are perceptually comparable to improvements obtained by adaptive Wiener filtering and spectral subtraction. Performance validation was performed with speech signals from the VOICES database and noise signals from the NOISEX database.

This PDF file contains the front matter associated with SPIE Proceedings Volume 6603, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.