Passive Optical Network (PON) elements such as Optical Line Terminal (OLT) and Optical Network Units (ONUs) are currently managed by inflexible legacy network management systems. Software-Defined Networking (SDN) is a new networking paradigm that improves the operation and management of networks. In this paper, we propose a novel architecture, based on the SDN concept, for Ethernet Passive Optical Networks (EPON) that includes the Service Interoperability standard (SIEPON). In our proposal, the OLT is partially virtualized and some of its functionalities are allocated to the core network management system, while the OLT itself is replaced by an OpenFlow (OF) switch. A new MultiPoint MAC Control (MPMC) sublayer extension based on the OpenFlow protocol is presented. This would allow the SDN controller to manage and enhance the resource utilization, flow monitoring, bandwidth assignment, quality-of-service (QoS) guarantees, and energy management of the optical network access, to name a few possibilities. The OpenFlow switch is extended with synchronous ports to retain the time-critical nature of the EPON network. OpenFlow messages are also extended with new functionalities to implement the concept of EPON Service Paths (ESPs). Our simulation-based results demonstrate the effectiveness of the new architecture, while retaining a similar (or improved) performance in terms of delay and throughput when compared to legacy PONs.
We report a new scheme to support, cost efficiently, ultra-dense wavelength division multiplexing (UDWDM) for optical access networks. As validating experiment, we apply phase modulation of a reflective semiconductor optical amplifier (RSOA) at the ONU with a single DEB, and simplified coherent receiver at OFT for upstream. We extend the limited 3-dB modulation bandwidth of available uncooled To-can packaged RSOA (similar to 400 MHz) and operate it at 3.125 Gb/s with the optimal performance for phase modulation using small and large signal measurement characteristics. The optimal condition is selected at input power of 0 dBm, with 70 rnA bias condition. The sensitivities at 3.125 Gbis (at BER=10(-3)) for heterodyne and intradyne detection reach -34.3 dBm and -38.8 dBm, respectively.
Staliunas, K.; VALCARCEL, G.; Martínez-Quesada, M.; Gilliland, S.; González-Segura, A.; Múñoz-Matutano, G.; Cascante-Vindas, J.; Marqués-Hueso, J.; Torres-Peiró, S. Optics communications Vol. 268, p. 160-168 Data de publicació: 2006-01 Article en revista
Conservation of the orbital angular momentum (OAM) of light in photon downconversion has been observed experimentally in nearly collinear phase-matching geometries, where the pump, signal and idler photons propagate along almost the same direction [Nature 412 (2001) 313]. However, here we predict that such paraxial measurements conducted with entangled photons in noncollinear geometries are not expected to comply with OAM conservation in the above sense. Under proper conditions, the strength of such apparent anomaly approaches 100%. We discuss the physical origin of the effect and suggest experimental schemes where it can be verified.
We analyze the self-action of light waves mediated by cascaded optical rectification in a quadratic nonlinear crystal in the framework of the full local-field equations and show that the process can lead to a rich variety of self-effects. We put forward a general scheme to calculate the full nonlinear response mediated by the self-generated rectified fields and thus show that acting on the shape, the polarization of the light beam and the geometric arrangement of the nonlinear crystal allows tuning the sign, the strength, and the type of the induced nonlinearities, opening the door to the exploration of a variety of self- and cross-phase modulations, and solitary-waves. We also show configurations where even though the macroscopic rectified field vanishes, the macroscopic self-effects do not.
We report on a scheme which might make it practically possible to engineer the effective competing nonlinearities that on average govern the light propagation in quasi-phase-matching (QPM) gratings. Modulation of the QPM period with a second longer period, introduces an extra degree of freedom, which can be used to engineer the effective quadratic and induced cubic nonlinearity. However, in contrast to former work here we use a simple phase-reversal grating for the modulation, which is practically realizable and has already been fabricated. Furthermore, we develop the theory for arbitrary relative lengths of the two periods and we consider the effect on solitons and the bandwidth for their generation. We derive an expression for the bandwidth of multicolor soliton generation in two-period QPM samples and we predict and confirm numerically that the bandwidth is broader in the two-period QPM sample than in homogeneous structures.
In this paper, an optical pattern recognition system with adjustable sensitivity to shape distortions and texture changes of the objects is presented. Application to a recognition task where the information of texture is the most decisive feature for a given object to be detected is provided. We apply the dual nonlinear correlation (DNC) model along with a support function acting in the frequency domain. This support function performs as an additional nonlinearity that enhances the information of some selected frequency bands related to the textural content of the target. A mathematical analysis allows the authors to show the usefulness of the proposed support function in the frame of the DNC model. The recognition system is applied to accomplish different recognition tasks involving model and real textured objects. The proposed optoelectronic correlator has been used to obtain successful experimental optical results, which are in accordance with the simulated results also provided.
Torner, L.; Carrasco, S.; Juan P. Torres; Crasovan, L.; Mihalache, D. Optics communications Vol. 199, num. 1, p. 277-281 DOI: 10.1016/S0030-4018(01)01573-5 Data de publicació: 2001-11 Article en revista
We put forward a novel strategy to achieve formation of fully three-dimensional light bullets. The new scheme is based on tandem structures where nonlinearity and group-velocity dispersion required for the self-trapping of light are spatially distributed, opening the door for the possibility that they are not necessarily contributed by the same crystal. We show that multicolor light bullets do exist for a variety of tandems with feasible domain lengths.
The impact of temporal effects to the generation of multiple wave quadratic spatial solitons with pulsed light is shown. We examine soliton formation under conditions of second-harmonic generation but our conclusions are relevant to soliton formation in all parametric processes. It is shown how group-velocity mismatch between the multiple interacting signals prevents spatial soliton formation with too short pulses. Illustrative examples of the minimum pulse width allowed for soliton generation in lithium niobate (LiNbO3), potassium titanyl phosphate (KTiOPO4), and lithium triborate (LiB3O5) are discussed.
We find the walk-off acceptance for multicolor soliton formation in second-harmonic generation schemes with single-frequency pump light. It is revealed that even though soliton families exist, outside the allowed band of walk-off values they are not actually excited. However, we predict that inside the allowed band the soliton content of the input signals can be almost flat. We also show how the acceptance bandwidth can be adjusted through the mismatch. Direct implications to the experimental observation of temporal quadratic solitons with tilted pulse techniques in phase-matched ß-BaB2O4 and LiIO3 are discussed.
This paper shows, theoretically and experimentally, how a polarization scrambler increases the response stability of a fiber Mach–Zehnder interferometer. We have studied the situation when the scrambler is placed in one of the interferometer branches and also when it is placed at the interferometer input. The measurements carried out using a scrambler based on the Faraday effect, agree with the simulation results.
We address the robustness of quadratic solitons with periodic non-conservative perturbations. We find the evolution equations for guiding-center solitons under conditions for second-harmonic generation in the presence of periodic multi-band loss and gain. Under proper conditions, a robust guiding-center soliton formation is revealed.
This paper illustrates that remote fault localisation in all-optical links with concatenated fibre amplifiers can be performed by simple monitoring of the signal and the accumulated ASE noise powers at the receiver end. The method is first presented in ideal operating conditions, and second, the effect of the spontaneous emission factor variation and the EDFA non-linear behaviour are taken into account. From the analysis, the requirements of the link design for proper supervision accuracy are derived. The presented supervisory method is a simple solution for links where a fibre break or an amplifier fault is to be detected and located with the granularity of an amplifier section without local supervisory elements within the transmission sections.
A selfsplitting of the beams entering a waveguide made of a quadratic nonlinear material is observed numerically. Relative p phase differences between harmonics as positively contributing to linear diffraction are shown to trigger the effect. Formation of solitons out of this energy so that a Y-branched structure is nonlinearly induced, is shown to be dependent on input and material parameters. Simple setups should provide the means for experimental observation of the predicted phenomena.
A selfsplitting of the beams entering a waveguide made of a quadratic nonlinear material is observed numerically. Relative π phase differences between harmonics as positively contributing to linear diffraction are shown to trigger the effect. Formation of solitons out of this energy so that a Y-branched structure is nonlinearly induced, is shown to be dependent on input and material parameters. Simple setups should provide the means for experimental observation of the predicted phenomena.
Two-parameter families of chirped stationary two-dimensional light bullets, in the form of localized spatio-temporal solitons in dispersive-diffractive quadratically nonlinear optical media under conditions for the Type I second-harmonic generation, are constructed in the presence of the temporal walkoff. One of the two parameters is the velocity of the soliton's walk relative to its carrier waves. Basic features of the walking light bullets, including a comprehensive consideration of their dynamical stability, are studied in the general case of unequal group-velocity dispersions at the fundamental and second-harmonic frequencies. The transverse shapes of the walking light bullets exhibit a spatio-temporal asymmetry. It is concluded that, when propagated in two-dimensional geometries, most of the two-dimensional walking light bullets are dynamically stable, hence they may be observed in an experiment.
Summary form only given. Quadratic solitons, that form through cascading in materials with second-order nonlinearities, are a topic of current intense investigation. Solitons have been observed in second harmonic generation (SHG) and in parametric amplification schemes, and many of their basic properties are well established. In particular, families of spatial and temporal solitons existing in waveguides and in bulk geometries are known, including those existing in settings with a small Poynting vector walk-off and/or temporal group-velocity mismatch. Under conditions where modulational instabilities can not grow, such families of solitons are stable under propagation and robust against several perturbations.
We study the dynamics of the soliton–radiation interaction in the process of soliton excitation in quadratic nonlinear media. The focus is on the dynamics of initial signals that are not weakly perturbed exact solitons. We use a combination of numerical experiments and analytical tools based on the integral conserved quantities of the wave evolution. We show the rate of convergence of representative, experimentally relevant inputs, to the asymptotic soliton states. A measure of soliton content of arbitrary input signals is introduced and evaluated in several representative examples. The dynamic evolution of oscillating solitons is studied using generalized Stokes parameters.
We investigate the evolution of vortex wave front dislocations in multiple-wave second-harmonic generation processes in quadratic nonlinear media. Vortices nested in finite-size host beams are shown to nucleate and to annihilate in pairs, and to move across the transverse wave front during the beam evolution. A closed-form model that holds under conditions of negligible-depletion of the pump beam is developed to describe the vortex dynamics in order to predict the number of vortices present in the wave fronts of the beams at any instance of the propagation. Results are compared with numerical simulations of the full governing equations and with experimental observations. Limitations of the model are outlined.
The discrimination capability requirements of pattern recognition systems may vary from one given purpose to another. In this work a recognition system with variable and selective discrimination capability is obtained by applying a dual non-linear correlation (DNC) model to a joint-transform correlator. DNC is obtained by means of two non-linear operators that are applied to both the reference and input channels. A particular DNC is given by the values taken by two real control parameters that determine the non-linear operators. In comparison with conventional filtering methods, an increased and variable discrimination capability is achieved by varying the parameters values. Thus, variable tolerances are introduced in the recognition process. Specifically, tolerances to slight shape variations and intensity variations of the objects (alphabetic characters) are analysed in this work. Ranges for the two control parameters are found in each case in order to achieve either an increase or a relaxation in the system's discrimination capability. The developed application is extended to colour pattern recognition by multichannel correlation. In this case, four further applications with selective discrimination capability are developed: pattern recognition with high discrimination capability for shape variations and some tolerance to colour variations and, vice versa, pattern recognition with high discrimination capability for colour variations and some tolerance to slight shape variations; pattern recognition with high discrimination for both shape and colour, and, finally, a tolerance to slight variations in both shape and colour.
We address the existence and properties of three-dimensional solitons localized in space and time, or light bullets, in bulk dispersive quadratic nonlinear media under conditions for Type I second-harmonic generation, with emphasis on the general case of different group-velocity dispersions at the fundamental and second-harmonic frequencies. We find families of three-dimensional light bullets and study their features in detail, including their stability on propagation. Most of the three-dimensional spatio-temporal solitons are shown to be stable.
We address the existence and instability of bright vortex solitary waves in quadratic non-linear media under conditions for Type II second-harmonic generation and study in detail the effects introduced by the presence of power imbalancing at the fundamental frequency. We find the families of solitary-wave solutions with different combinations of topological charges of the nested vortices and show their spontaneous azimuthal instability. The growth rates of the azimuthal perturbations are calculated as a function of the imbalancing. Experimental consequences are stressed and discussed.
Amplification of spatial solitons in quadratic nonlinear media under conditions for second-harmonic generation is
addressed. Under the action of gain at a given frequency band the energy has to be redistributed among the multiple-frequency
waves that form the solitons, which ought to reshape accordingly. It is shown that solitons in quadratic nonlinear media
appear to be well suited for such purpose. Practical implementation conditions are discussed.
We find exact one-parameter families of stationary two-dimensional light bullets in the form of solitons localized in
space and time in diffractive and dispersive nonlinear media under conditions for second-harmonic generation. We study the
shape and various features of the solitons, including their stability during propagation, with emphasis on the general case of
unequal group-velocity dispersions for the fundamental and second-harmonic waves when the transverse spatio-temporal
shape of the solitons is asymmetric. It is shown that, when propagating in two-dimensional geometries, most of the
spatio-temporal solitons are dynamically stable. q 1998 Elsevier Science B.V. All rights reserved
We find families of optical bright, vortex solitary waves in bulk quadratic nonlinear media under conditions for type II second-harmonic generation. We study the main properties of the families of solitary waves, including their stability. The vortex solitary waves are found to be azimuthally unstable and their decay into sets of stable spatial solitons is shown. We calculate the growth rates of the possible azimuthal perturbations with different azimuthal index and show how those affect the pattern of output light. Numerical simulations to check the predictions of the stability analysis are also reported.
We address the effect of quintic nonlinearities in the propagation of optical solitons in cubic nonlinear media. Our focus is on the decay of higher-order solitons in the presence of self-defocusing quintic perturbations. We show that, in spite of the fact that the governing evolution equations are symmetric, the quintic nonlinearity produces the asymmetrical self-splitting of the solitons. We study in detail the self-splitting process and compare the results with the soliton evolution with self-focusing quintic perturbations.
We investigate pulse propagation in birefringent optical fibers under conditions where both the walk-off length and the birefringence beat length between the linearly polarized modes of the fiber are comparable to the nonlinear scale length. We find numerically families of stationary vector solitons that propagate with a common group velocity. These solitons constitute a two-parameter family of solutions. We study the shape and chirp of the solitons and the fraction of energy carried by each polarization as a function of the soliton energy and velocity.
Passive fiber ring resonators synchronously pumped by cw trains of ultrashort pulses are shown to exhibit polarization symmetry breaking. Application of this feature to all-optical storage is considered. The proposed storage device operates in the flip-flop mode which makes possible all-optical writing and erasing operations on individual bits. Numerical simulations suggest that a storage capacity of the order of thousand bits could be attainable at bit rates of hundreds of Gb/s with a maximum information processing rate of several Gb/s
We study the mutual trapping of fundamental and second-harmonic light beams propagating in bulk quadratic nonlinear media in the presence of Poynting vector beam walk-off. We show numerically the existence of a two-parameter family of (2 + 1)-dimensional stationary, spatial walking solitons. We have found that the solitons exist at various values of material parameters with different wave intensities and soliton velocities. We discuss the differences between (2 + 1) and (1 + 1)-dimensional walking solitons and between walking and non-walking solitons.
We investigate the interaction between one-dimensional bright solitary waves in quadratic nonlinear media. We use a perturbational approach via collective coordinates to reduce the full evolution equations to a set of coupled ordinary differential equations which provides a simple qualitative picture of the soliton interactions. We use the scheme to calculate the collision distance between equal amplitude solitons and compare the results with the outcome of direct numerical solution of the evolution equations. A good agreement is found.
A new method to select colour channels in colour pattern recognition systems is presented to improve the chromatic discrimination capability. Instead of using the conventional RGB decomposition, we propose to use other narrow-band channels that can show more variations of the objects of a scene. This method exploits the spectral information of the objects and is useful in discriminating objects with similar colour. Simulated and experimental optical correlation results, for scenes with objects of similar colours, are presented and discussed. Model and natural objects are considered and a variety of ranges are studied.
The three-waveguide nonlinear directional coupler switching characteristic is studied using the eigenmodes of the structure (i.e. supermodes). This model, which is more exact than the one used in previous works, has allowed to confirm the three waveguide configuration as an alternative to the two waveguide nonlinear coupler. Moreover, an analytical expression for the critical power at which the switching between the output branches occurs has been found.
The dynamics of a semiconductor laser with optical feedback is studied numerically for increasing time delay. Although the dimension of the attractors generally increases with the delay time, i.e., for short external cavities the attractor is a fixed point or a limit cycle, while for longer external cavities the attractor is a complicated torus or a chaotic attractor, special behavior is found when the external cavity length is chosen such that the product of the delay time t with the relaxation oscillation frequency of the laser frsol yields a number close to integer. For these values of the time delay, the attractors become topologically simpler, i.e., in the regions where the attractor is a limit cycle, for tfrsol ˜ n it becomes a fixed point, in the regions where is a two-torus, it becomes a limit cycle. Also, Lyapunov analysis indicates that in the resonance regions, the stability of the attractors changes strongly. The effects of the resonances are strong for short external cavities but become difficult to detect as the delay time increases.
Torner, L.; Mihalache, D.; Mazilu, D.; Wright, E.; Torruellas, W.; Stegeman, G. Optics communications Vol. 121, num. 6, p. 149-155 DOI: 10.1016/0030-4018(95)00568-2 Data de publicació: 1995-12 Article en revista
The mutual trapping of fundamental and second harmonic, continuous-wave light beams propagating in bulk second-order nonlinear media is studied. We find numerically families of stationary, radially symmetric solitary waves. The transverse profiles of the trapped beams, their scaling properties, and their stability under propagation are investigated as a function of the total power and the linear wavevector-mismatch between the waves. We show that at phase-matching mutually trapped solitary waves exist for any total wave power, whereas they exist only above a threshold power for both positive and negative phase-mismatches.