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In this work we present a new method to optically obtain the convolution / correlation between two functions. The technique is based on obtaining higher powers of a properly designed phase-only hologram. The approach combines some of the advantages of the classical 4f and the JFTC correlator systems. These higher powers of the hologram transmission function can be obtained easily using a spatial light modulator (SLM) with an extended phase modulation of various cycles of 2π radians. SLMs with such extended phase modulation present useful unusual diffraction properties that can be exploited to surpass some limits of SLM technology. In this case we exploit them to obtain higher order optical correlation terms. Computational simulations and experimental results agree with theory.

We propose a novel approach for demodulating Brillouin Optical Correlation Domain Analysis (BOCDA) signals using digital dual-phase lock-in detection scheme, which enables simultaneous multi-point sensing.

We demonstrate the suppression of errors caused by the AM-FM phase delay of light source in the Brillouin optical correlation domain analysis. With an injection-locked DFB-LD the maximum error is suppressed by over 70 %.

Optical correlation measurements catch interference in coherent light from a Young’s double-slit interferometer system.

We present the state-of-the-art and future challenges of Brillouin optical correlation-domain reflectometry, which is the only fiber-optic distributed sensing technique that can simultaneously achieve single-end-access operation, high spatial resolution, random accessibility, and cost efficiency.

Semiconductor lasers are notoriously sensitive to optical feedback, and their dynamics and coherence can be significantly modified through optical reinjection. We concentrate on the dynamical properties of a very small (i.e., microscale) Vertical Cavity Surface Emitting Laser (VCSEL) operated in the low coherence region between the emission of (partially) coherent pulses and ending below the accepted macroscopic lasing threshold, with the double objectives of: 1) studying the feedback influence in a regime of very low energy consumption and 2) using the micro-VCSEL as a surrogate for nanolasers, where measurements can only be based on photon statistics. The experimental investigation is based on time traces and radiofrequency spectra (common for macroscale devices) and correlation functions (required at the nanoscale). Comparison of these results confirms the ability of correlation functions to satisfactorily characterize the action of feedback on the laser dynamics. Numerical predictions obtained from a previously developed, fully stochastic modeling technique provide very close agreement with the experimental observations, thus, supporting the possible extension of our observations to the nanoscale.

We investigate Airy-soliton interaction in a nonlinear fiber with Raman effect. We find that Airy solitons may fuse upon interaction at a position that can be controlled by a proper engineering of the Airy tail direction. This control allows us to generate Airy solitons with varying deceleration. At variance with the case of two solitons interaction, Raman-induced soliton self-frequency shift (SSFS) is strongly enhanced when the leading soliton is replaced with the accelerating Airy pulse and slightly suppressed for the decelerating one. These notable features are ascribed to the unique properties of asymmetrical Airy pulses with a switchable direction of the oscillatory tails. We show the way these processes are uncovered unambiguously by cross-correlation frequency resolved optical gating. We also investigate the impact of chirp imposed on the input pulse on the SSFS dynamics. Our results not only provide a new way to manipulate the SSFS, but may help to improve the control of soliton fusion events during supercontinuum generation, optical rogue waves and giant dispersive waves formation. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We represent the optical fiber output beam as linear superposition of orbital angular momentum (OAM) modes to quantify its purity. Through controlled experiments, we observe good agreement between the experimentally measured OAM and simulated spectrum.

We present a polarization imaging method to image through highly turbid water based on the dependence of light scattering and the optical correlation theory. Experiments demonstrate its contribution to make “can’t see” into “can see”.

A method of all-optical correlation is proposed using the nonlinear phenomena Four Wave Mixing (FWM) of two different signals. The method shows a serial solution where correlation of an ultrafast real-time serialized broadband source is demonstrated using a Highly Non-Linear Fibre (HNLF) with correlation rate reaching 200MHz.

Brillouin scattering mechanism and Young modulus variations in optical fiber distributed sensing systems are directly affected by ambient temperature and thermal strain formations. Generally, in such sensing systems where temperature and strain formations are detected and measured simultaneously, Brillouin frequency shift and Brillouin power changes of backscattered optical signal are used due to their temperature and strain dependencies. In this research, a different point of view has been developed and effects of Young modulus variations of the sensing fiber core on the Brillouin power and the Brillouin frequency shift changes have been analyzed. In this study, positioning five heating units at different locations along a 1000 m G.652 type single-mode fiber operating at 1550 nm, a sensing system model has been constructed. On this model, simulations related to Young modulus variations along the sensing fiber depending on temperature fluctuations generated by heating units have been performed using Matlab 2010 and results have been obtained for 1000 different points with a spatial resolution of 1 m. For 40 degrees C- 47 degrees C operating temperature range of the sensing fiber, the Young modulus of the fiber core changes from 73.205 GPa to 73.283 GPa. Furthermore, using the analytical method, linear formula between the Young modulus and Brillouin parameters, i.e. Brillouin power and Brillouin frequency shift changes, of the backscattered optical signal have been derived. Thus, for the system model constructed, Matlab simulations analyzing relations between Young modulus variations and Brillouin parameter changes have been performed under specified operating conditions. For Young modulus variations in 73.205 GPa - 73.283 GPa range, values of Brillouin power and Brillouin frequency shift changes have been obtained in ranges of 13.950 % - 16.273 % and 69.00 MHz - 85.72 MHz, respectively. Moreover, temperature and thermal strain resolutions along the sensing fiber have been acquired as similar to 0.7 degrees C and similar to 40 mu epsilon, respectively.

We develop a simplified configuration for optical correlation-domain reflectometry (OCDR) without an explicit reference path. Instead, the Fresnel-reflected light generated at the distal open end of the sensing fiber is exploited as a reference light. After the fundamental demonstration, the optimal incident power is found to be approximately 8 dBm. We also show that the loss near the distal end should not be applied, unlike in the case of Brillouin-based OCDR.

In the second part of this study, we compare both the wind speed and turbulence given by the Sodars with independent sets of measurements. In the case of the wind speed we compare the lowest Sodar data bin with a sonic anemometer located on a 7-m tower. The agreement between the two instruments was convincing with a regression slope near unity. The integrated turbulence measurements of the Sodars are compared with those obtained with a combined multi-aperture scintillation sensor and differential image motion monitor (MASS/DIMM) unit. It was found that the Sodars are indeed capable of quantitatively measuring optical turbulence, and agree with the MASS/DIMM measurements with a correlation coefficient of approximately 80% and a regression slope within 10% of unity. Additional acoustic noise in the Sodar data was identified using this comparison and removed from the data. © 2011 Springer Science+Business Media B.V.

The modified Becke-Johnson exchange potential proposed by Tran and Blaha (TB-mBJ) is useful for accurate calculations of electronic band structures of solids. In this view, we used such potential together with spin–orbit coupling to calculate the electronic and optical correlation effects in bulk gold (Au) via first principle DFT. Inclusion of the relativistic effects in the simulation were found to play vital role on the optical properties of bulk Au. Furthermore, the imaginary part of the dielectric function of Au disclosed good agreement with the experimental results. Disclosure of good agreement between simulation and experimental results (up to Fermi level) was due to the improvement in the band structure of bulk Au achieved by incorporating spin–orbit coupling.

This paper propose a method to enlarge the measurement range for Brillouin optical correlation domain analysis (BOCDA) system simplified with time-division pump-probe generation scheme. In this sys...

This feature issue of Applied Optics contains a series of selected papers reflecting recent progress of correlation optics and illustrating current trends in vector singular optics, internal energy flows at light fields, optical science of materials, and new biomedical applications of lasers. (C) 2016 Optical Society of America

A novel optical correlation domain reflectometry technique utilizing artificially-generated low-coherence light is proposed for long-range measurement with high resolution. We successfully demonstrate the selection of one correlation peak of a laser at an arbitrary delay for a fibre under test.

A fluorescence correlation spectrometer is developed that is suitable for use in advanced laboratory courses. The instrument is simple to build and understand and can be constructed at a small fraction of the cost of a commercial or research-grade instrument. We demonstrate its surprisingly high performance with a simple biophysics application, the study of the binding of two complementary DNA strands. The instrument will be useful in areas of physics where precise measurements of the dynamics of fluorescent (or fluorescently labeled) molecules or nanoparticles in solution are of interest.

We propose a novel multiple pilot-carriers assisted direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) superchannel transmission scheme. With the proposed scheme, a 432-Gb/s transmission over 3040-km standard single mode fiber (SSMF) is successfully demonstrated. The nonlinear effect of correlated/uncorrelated sub-band loading is also investigated.

Correlation properties of light scattered by a moving diffuser are determined by studying the spectral characteristics of the light that emerges from two pinholes placed after the diffuser. These properties are used to determine the correlation functions of the heights of diffuser surface and the speed of the diffuser. The phase of the light on the two pinholes after it has passed through the moving diffuser, is also determined.

A new strategy of pulse shaping based on the quasi-direct space-to-time (QDST) conversion principle has been recently proposed theoretically [Mnguez-Vega , Opt. Express 16, 16993 (2008)]. In this letter, the working principle of this pulse shaper has been experimentally verified by using a simple second order cross-correlation setup with spatial resolution. The QDST conversion principle is evidenced through the experimental measurement of the parabolic dependence of the time delay on the focal plane versus the radii of the components of the spatial profile in the far field.

The use of optical cross correlations for characterizing timing jitter is investigated. Applications, limitations, and correspondence to radio frequency measurements are presented and clarified. The probability density function of the timing jitter of semiconductor mode-locked lasers is deconvolved from the cross-correlation measurements with the aid of pulse characterization techniques.

Nous presentons la premiere source solide monomode de photons uniques, constituee par une boite quantique semiconductrice placee dans une microcavite optique. Cette source exploite la forte interaction coulombienne entre porteurs pieges pour controler le nombre de photons, et l'effet Purcell pour collecter et preparer dans un etat donne (meme mode spatial, meme polarisation) les photons emis. Nous discutons plus particulierement les performances et l'interet potentiel de cette nouvelle source dans le contexte de la distribution de clefs quantiques.

An optical coherent transient signal correlator with variable true time delay is experimentally demonstrated. Storage of a pattern waveform in a spectral-spatial population grating is achieved by interfering it with two chirped pulses instead of a single brief reference pulse. Correlative signal processing results when a data waveform probes that grating, stimulating an emitted coherent output signal after the appropriate time delay. The signal is the result of a six-wave mixing process that can be as efficient as the traditional four-wave mixing process using a single brief reference pulse. Frequency shifting of the two chirped pulses enables programming of a variable time delay in the grating without changing the timing of the programming pulses. This concept is experimentally demonstrated with variable time delays over 448 ns (offset by greater than 1 μs) for the auto-correlation of a code with an experimentally limited bandwidth of 40 MHz. Processing bandwidths exceeding 10 GHz are achievable in materials such as Tm 3+ :YAG (0.1 at%).

Quantum mechanics allows quantum nondemolition (QND) variables to be measured without being changed. This requires QND variables to be initially in an eigenstate and measurement backaction noise to be directed into conjugate variables. Experimental demonstrations thus require two measurements: the first to collapse variables toward an eigenstate and the second to show results identical to the first. Here, we report results from two successive soliton-collision QND measurements that optical correlation measurements show to be nearly identical.

We present an experimental realization of optical correlation for real-time rotational-invariance pattern recognition by means of a photorefractive joint transform correlator. Single and multiple circular harmonic components have been used to form correlation filters. The correlator operates with a liquid crystal television as the input images and a photorefractive crystal Bi 12 SiO 20 (BSO) as the recording medium. Suitable pre-processing of the references at the object plane makes up for the lack of light transmission. The properties of circular harmonic phase-only filter and circular harmonic matched filter have been compared. Also the noise robustness of these filters has been tested by tracking an object against a non-overlapping noise background. Analysis and experimental results are presented.

In the past triple correlation has been used successfully as an algorithmic tool for image processing. Here, we consider triple correlation of a wavefield as a new kind of a wavefield with its own wave equation and consequences thereof, such as free space propagation and spatial filtering.

We report the design of limited sections of polarization-mode dispersion and polarization-dependent loss (PMD-PDL) emulators that lead to the lowest averaged frequency interchannel correlation in the wavelength-division-multiplexed systems. We show that emulators with the elements with the minimum PMD and PDL values at the end of the emulator setting with respect to the light propagation have the lowest averaged frequency autocorrelation in the neighboring channels, therefore, the lowest averaged frequency interchannel correlation. Both experiments and simulations are performed to confirm the design principle

We report on the measurements of state of polarization (SOP) and differential group delay (DGD) in submarine fibers. The experimental autocorrelation function shows the fastest change in both SOP and DGD is faster than 15 s, which is limited by the measurement speed. The Fourier transform is utilized to study ocean-wave-induced vibrations on submarine fibers.

This chapter aims to provide a simple introduction to the application of optical correlation methods in colloidal science. In particular, the basic concepts of temporal and spatial coherence are used to provide firm bases for the understanding of dynamic light scattering measurements and to develop a consistent theory of microscope imaging. Finally, I show that a full appraisal of the intimate relation between light scattering and microscopy allows to design novel investigation techniques that combine their powers. Among them, photon correlation imaging, differential dynamic microscopy, and ghost particle velocimetry offer novel opportunities to investigate the local dynamics of colloidal structures and their flow in microfluidic devices.

In this paper, we demonstrate dynamic strain measurement at arbitrary points by a basic BOCDA system with 500 points/s random access speed. This is the highest speed of the random accessibility reported so far.

The coarsely discrete structure of polarization-mode dispersion (PMD) emulators can artificially correlate the PMD affecting different wavelength-division-multiplexed channels. We present a model that predicts the background autocorrelation of concatenated-section emulators with independently rotatable elements, and show how emulators with low interchannel correlation can be designed.

By monitoring stage drift via the normalized cross-correlation of an image of a stuck bead, obtained in real-time, with an out-of-focus “template” image of a similar immobile bead, stored in memory, we implement a simple approach to actively stabilize drift in all three dimensions for existing video microscopy setups. We demonstrate stability to 0.0062 nm along the Z-axis and 0.0031 nm along the X- and Y-axes for long (100 s) timescales.

We investigate the propagation of pre-existing quantum correlations through a fast-light medium with an experiment based on two successive four-wave mixing processes in rubidium vapour.

We report full characterization of the intensity and phase of /spl sim/10-fs optical pulses using second-harmonic-generation frequency-resolved-optical-gating (SHG FROG). We summarize the subtleties in such measurements, compare these measurements with predicted pulse shapes, and describe the implications of these measurements for the creation of even shorter pulses. We also discuss the problem of validating these measurements. Previous measurements of such short pulses using techniques such as autocorrelation have been difficult to validate because at best incomplete information is obtained and internal self-consistency checks are lacking. FROG measurements of these pulses, in contrast, can be validated, for several reasons. First, the complete pulse-shape information provided by FROG allows significantly better comparison of experimental data with theoretical models than do measurements of the autocorrelation trace of a pulse. Second, there exist internal self-consistency checks in FROG that are not present in other pulse-measurement techniques. Indeed, we show how to correct a FROG trace with systematic error using one of these checks.

A local speckle correlation method is proposed for vibration studies. A brief analysis of the technique and some experimental results on a vibrating plate are presented.

International audience; Underwater target detection is investigated by combining active polarization imaging and optical correlation-based approaches. Experiments were conducted in a glass tank filled with tap water with diluted milk or seawater and containing targets of arbitrary polarimetric responses. We found that target estimation obtained by imaging with two orthogonal polarization states always improves detection performances when correlation is used as detection criterion. This experimentally study illustrates the potential of polarization imaging for underwater target detection and opens interesting perspectives for the development of underwater imaging systems.

Brillouin optical correlation domain analysis (BOCDA) in linear configuration is demonstrated newly based on differential lock-in detection. Three-fold enhancement in the spatial resolution is achieved compared to the former system based on beat-lock-in detection, as well as the simpler configuration for the signal processing. Distributed strain measurement over a 57-m test fiber with a 10-cm spatial resolution is presented as a proof-of concept.

Brillouin optical correlation-domain analysis (B-OCDA) allows for distributed measurements of strain and temperature with sub-cm resolution. Time-multiplexing techniques have previously extended B-OCDA to the monitoring of many km of fiber and two million resolution points. Thus far, however, the number of scans of correlation peaks positions, necessary to cover the fiber under test, was restricted to the order of 100 or more. In this work we report a B-OCDA protocol that is able to address an entire fiber using only 11 pairs of position scans per choice of frequency. The measurements protocol relies on a merger between B-OCDA principles and double-pulse-pair analysis, previously incorporated in time-domain Brillouin sensors. Phase coding of the pump and signal waves with a repeating, short and high-rate code stimulates Brillouin interactions in a large number of narrow correlation peaks, with substantial temporal overlap. Unambiguous measurements are achieved by repeating each experiment twice, using a pair of pump pulses of different durations, and subtracting the two output traces. The principle is demonstrated in the analysis of a 43 m-long fiber with 2.7 cm resolution. Several local hot-spots are properly identified in the measurements. The experimental uncertainty in the measurement of the local Brillouin frequency shift is estimated as ± 1.9 MHz. The proposed method requires broader detection bandwidth and a larger number of averages than those of previous time-gated B-OCDA setups. Hence the overall number of measurements is similar to that of previous setups.