Fault management is a challenging task in all-optical wavelength division multiplexing (WDM) networks. However, fast fault localization for shared risk link groups (SRLGs) with multiple links is essential for building a fully survival and functional transparent all-optical mesh network. Monitoring trail (m-trail) technology is an effective approach to achieve the goal, whereby a set of m-trails are derived for unambiguous fault localization (UFL). However, an m-trail traverses through a link by utilizing a dedicated wavelength channel (WL), causing a significant amount of resource consumption. In addition, existing m-trail methods incur long and variable alarm dissemination delay. We introduce a novel framework of real-time fault localization in all-optical WDM mesh networks, called the monitoring-burst (m-burst), which aims at initiating a balanced trade-off between consumed monitoring resources and fault localization latency. The m-burst framework has a single monitoring node (MN) and requires one WL in each unidirectional link if the link is traversed by any m-trail. The MN launches short duration optical bursts periodically along each m-trail to probe the links of the m-trail. Bursts along different m-trails are kept non-overlapping through each unidirectional link by scheduling burst launching times from the MN and multiplexing multiple bursts, if any, traversing the link. Thus, the MN can unambiguously localize the failed links by identifying the lost bursts without incurring any alarm dissemination delay. We have proposed several novel m-trail allocation, burst launching time scheduling, and node switch fabric configuration schemes. Numerical results show that the schemes, when deployed in the m-burst framework, are able to localize single-link and multi-link SRLG faults unambiguously, with reasonable fault localization latency, by using at most one WL in each unidirectional link. To reduce the fault localization latency further, we also introduce a novel methodology called nested m-trails. At first, mesh networks are decomposed into cycles and trails. Each cycle (trail) is realized as an independent virtual ring (linear) network using a separate pair of WLs (one WL in each direction) in each undirected link traversed by the cycle (trail). Then, sets of m-trails, i.e., nested m-trails, derived in each virtual network are deployed independently in the m-burst framework for ring (linear) networks. As a result, the fault localization latency is reduced significantly. Moreover, the application of nested m-trails in adaptive probing also reduces the number of sequential probes significantly. Therefore, practical deployment of adaptive probing is now possible. However, the WL consumption of the nested m-trail technique is not limited by one WL per unidirectional link. Thus, further investigation is needed to reduce the WL consumption of the technique.

Microwave signal processing in the optical domain is investigated in this thesis. Two signal processors including an all-optical fractional Hilbert transformer and an all-optical microwave differentiator are investigated and experimentally demonstrated. Specifically, the photonic-assisted fractional Hilbert transformer with tunable fractional order is implemented based on a temporal pulse shaping system incorporating a phase modulator. By applying a step function to the phase modulator to introduce a phase jump, a real-time fractional Hilbert transformer with a tunable fractional order is achieved. The microwave bandpass differentiator is implemented based on a finite impulse response (FIR) photonic microwave delay-line filter with nonuniformly-spaced taps. A microwave bandpass differentiator based on a six-tap nonuniformly-spaced photonic microwave delay-line filter with all- positive coefficients is designed, simulated, and experimentally demonstrated. The reconfigurability of the microwave bandpass differentiator is experimentally investigated. The employment of the differentiator to perform differentiation of a bandpass microwave signal is also experimentally demonstrated.

Pour des applications technologiques d’enregistrement magnétique de l’information à haute densité et vitesse d’écriture et de lecture ultra-rapide, les chercheurs se sont penchés vers des méthodes de manipulation de l’aimantation sans application de champ magnétique externe. Il a été découvert qu’il était possible de renverser de manière déterministe l’aimantation de plusieurs matériaux ferri- et ferro-magnétiques à l’aide uniquement d’impulsions laser ultracourtes polarisées circulairement. Ce retournement tout-optique s’est avéré être un processus cumulatif nécessitant plusieurs impulsions ultracourtes dans les matériaux ferromagnétiques. Notamment dans les multicouches (Co/Pt), le retournement tout-optique se fait en deux étapes : une désaimantation indépendamment de l’hélicité suivie d’une ré-aimantation dans une direction ou l’autre selon l’hélicité. Pour autant, le mécanisme à l’origine du rétablissement de l’ordre magnétique n’a pas été étudié jusqu’à présent. Dans cette thèse, nous avons étudié le mécanisme de renversement de l’aimantation dans les couches ferromagnétiques résultant de l’excitation par impulsions laser ultracourtes polarisées circulairement. Pour cela, nous étions intéressé par la réponse d’une paroi de domaine dans les couches minces de Pt/Co/Pt à la suite d’une excitation laser et en fonction de la polarisation de la lumière. Nous avons démontré la possibilité d’induire un déplacement tout-optique et déterministe d’une paroi de domaine. Nous montrons que la propagation de la paroi résulte de la compétition entre trois contributions : le gradient de température dû aux effets de chauffage par le laser, l’effet de l’hélicité de la lumière et les effets de piégeages de la paroi. Par ailleurs, par mesures expérimentales du dichroïsme circulaire, nous excluons un mécanisme purement thermique du déplacement de paroi. Ainsi nous confirmons que le retournement tout-optique des couches ferromagnétiques se fait par une nucléation suivie d’une ré-aimantation par propagation déterministe des parois de domaines selon l’hélicité. De plus, nous avons exploré la possibilité d’utiliser le retournement tout-optique dans des dispositifs spintroniques pour l’enregistrement de l’information à haute densité. Pour se faire, il est nécessaire d’étudier les effets de tailles du retournement lorsque le matériau est structuré en îlots à l’échelle du micro- ou nanomètre. Nous avons montré qu’un plus grand nombre d’impulsions laser est nécessaire afin de renverser l’aimantation de micro-disques comparés à la couche continue ferromagnétique. Il en résulte que le champ dipolaire aide le renversement de l’aimantation dans les couches continues rendant ainsi le retournement tout-optique énergétiquement plus favorable / Over the past decade, the demand for an even higher capacity to store data has been gradually increasing. To achieve ultrafast and ultrahigh density magnetic data storage, low-power methods to manipulate the magnetization without applying an external magnetic field has attracted growing attention. The possibility to deterministically reverse the magnetization with only circularly polarized light was evidenced in multiple ferri- and ferro-magnetic materials. This phenomenon was called helicity-dependent all-optical switching (HD-AOS). In ferromagnets, it was demonstrated that HD-AOS was a cumulative and multishot process with a helicity-independent demagnetization followed by a helicity-dependent magnetization recovery. Yet, the microscopic mechanism of this helicity-dependent remagnetization remained highly debated. In this thesis, we investigated the magnetization reversal mechanism of all-optical switching in ferromagnetic materials. To explore a potential switching process through domain nucleation and domain wall (DW) propagation, we studied the response of a DW upon femto- or pico-second laser irradiation in Co/Pt thin films that exhibit HD-AOS. We reported helicity-dependent all-optical domain wall motion. We demonstrated that it results from the balance of three contributions: the temperature gradient due to the laser heating, the helicity effect and the pinning effects. By measuring the magnetic circular dichroism, a purely thermal mechanism of the laser-induced DW motion appears to be excluded. Furthermore, we examined the size effects in AOS in Co/Pt films patterned into microdots with a diameter between 10 and 3 μm. This allowed us to explore the role of the dipolar field in the switching mechanism. We discovered that a larger number of laser pulses was required to reverse the magnetization of a microdot compared to the continuous film. This indicated that the dipolar field actually eases the magnetization reversal in the full film. Thus, AOS is less energy-efficient in patterned films, hence making Pt/Co/Pt multilayers not an ideal candidate for integrating AOS in spintronic devices

MENEZES, José Wally Mendonça. Implementação de porta lógicas ópticas com acoplador direcional não linear triplo planar simétrico de fíbras ópticas. 2006. 111 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2006. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-25T22:18:49Z No. of bitstreams: 1 2006_dis_jwmmenezes.pdf: 2170108 bytes, checksum: 0615686d0a317fa8d05e85006ca06e1b (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-27T18:52:06Z (GMT) No. of bitstreams: 1 2006_dis_jwmmenezes.pdf: 2170108 bytes, checksum: 0615686d0a317fa8d05e85006ca06e1b (MD5) / Made available in DSpace on 2015-05-27T18:52:06Z (GMT). No. of bitstreams: 1 2006_dis_jwmmenezes.pdf: 2170108 bytes, checksum: 0615686d0a317fa8d05e85006ca06e1b (MD5) Previous issue date: 2006 / In this work, optical logical gates are proposed starting from the use of a symmetric three-core nonlinear directional coupler (NLDC) of fiber optic and with one of the guides operating as control. For such end, we obtain the characteristics of transmission of the coupler and, soon afterwards, we made an analysis of the extinction ratio and of the compression factor. Initially, we investigated the acting of the proposed coupler operating in the regime CW and later using ultra short pulses, type sóliton with 2ps of width. With the model proposed for the device, we got to execute logical gates AND, NAND, OR, XOR and NOT for a group of applied phases to the control pulse. The logical gates generated with the device operating with signs CW, they came more efficient than the same gates generated with soliton pulses. / Neste trabalho, portas lógicas ópticas são propostas a partir da utilização de um acoplador direcional não linear (NLDC) triplo planar simétrico de fibra óptica e com um dos guias operando como controle. Para tal fim, obtemos as características de transmissão do acoplador e, em seguida, fizemos uma análise do coeficiente de extinção e do fator de compressão. Inicialmente, investigamos o desempenho do acoplador proposto operando no regime CW e posteriormente utilizando pulsos ultracurtos, tipo sóliton com 2ps de largura. Com o modelo proposto para o dispositivo, conseguimos efetivar portas lógicas AND, NAND, OR, XOR e NOT para um conjunto de fases aplicadas ao pulso de controle. As portas lógicas geradas com o dispositivo operando com sinais CW, apresentaram-se mais eficientes que as mesmas portas geradas com sinais pulsados.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Neste trabalho, portas lÃgicas Ãpticas sÃo propostas a partir da utilizaÃÃo de um acoplador direcional nÃo linear (NLDC) triplo planar simÃtrico de fibra Ãptica e com um dos guias operando como controle. Para tal fim, obtemos as caracterÃsticas de transmissÃo do acoplador e, em seguida, fizemos uma anÃlise do coeficiente de extinÃÃo e do fator de compressÃo. Inicialmente, investigamos o desempenho do acoplador proposto operando no regime CW e posteriormente utilizando pulsos ultracurtos, tipo sÃliton com 2ps de largura. Com o modelo proposto para o dispositivo, conseguimos efetivar portas lÃgicas AND, NAND, OR, XOR e NOT para um conjunto de fases aplicadas ao pulso de controle. As portas lÃgicas geradas com o dispositivo operando com sinais CW, apresentaram-se mais eficientes que as mesmas portas geradas com sinais pulsados. / In this work, optical logical gates are proposed starting from the use of a symmetric three-core nonlinear directional coupler (NLDC) of fiber optic and with one of the guides operating as control. For such end, we obtain the characteristics of transmission of the coupler and, soon afterwards, we made an analysis of the extinction ratio and of the compression factor. Initially, we investigated the acting of the proposed coupler operating in the regime CW and later using ultra short pulses, type sÃliton with 2ps of width. With the model proposed for the device, we got to execute logical gates AND, NAND, OR, XOR and NOT for a group of applied phases to the control pulse. The logical gates generated with the device operating with signs CW, they came more efficient than the same gates generated with soliton pulses.

Orientadores: Edson Moschim, Luiz Henrique Bonani do Nascimento / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-21T20:14:55Z (GMT). No. of bitstreams: 1 Galdino_Lidia_D.pdf: 15165913 bytes, checksum: b0a79c7ac69b13cce3baf82b480c99fc (MD5) Previous issue date: 2012 / Resumo: A exigência crescente de se atingir maiores taxas de bits para satisfazer a demanda por largura de banda na internet tem motivado a investigação de dispositivos totalmente ópticos que viabilizem o desenvolvimento de redes ópticas transparentes (TON). O intuito dessas redes é manter o fluxo de dados sempre no domínio óptico, eliminando o gargalo no processamento das conversões óptico-elétricas e eletro-ópticas existentes nos atuais sistemas de comunicações ópticas. Neste trabalho foram investigadas, por meio de experimentos e simulações computacionais, técnicas de processamento óptico de sinais. Estas técnicas utilizam o fenômeno da mistura de quatro ondas (FWM) para multiplexar as informações de dois sinais em um único sinal. Em especial, foram investigadas duas novas técnicas para codificação e regeneração totalmente óptica do sinal não coerente de multiplexação por divisão de códigos ópticos no acesso (OCDMA). Estas técnicas convertem e regeneram no domínio totalmente óptico o sinal modulado em intensidade on-off keying (OOK) e o sinal modulado pelo chaveamento por desvio de fase diferencial (DPSK) no sinal OCDMA. Os resultados obtidos comprovaram que ambas as técnicas propostas funcionam corretamente. O sinal de saída OCDMA apresentou ganho na potência de regeneração de 1,69 dB em relação ao sinal de entrada OOK ou DPSK. A aplicação das técnicas de conversão e regeneração totalmente ópticas propostas, deu origem ao estudo da tecnologia híbrida de multiplexação por divisão de comprimentos de onda com a multiplexação por divisão de códigos ópticos (WDM/OCDM) na camada de transporte de uma rede TON. Heurísticas para atribuição de códigos ópticos e comprimentos de onda, bem como arquiteturas de conversão de códigos ópticos e comprimentos de onda foram propostas. Dos resultados, comprovou-se que a heurística Random-Random apresenta um melhor desempenho quando analisada a probabilidade de bloqueio. Ainda, a arquitetura de conversão esparsa parcial de códigos ópticos e comprimentos de onda (SPOCC/SPWC) melhora a utilização de recursos de rede, diminuindo o custo de implementação da rede / Abstract: The growing demand to achieve higher bit rates to satisfy the bandwidth in the internet has motivated the investigation of all optical devices that enable the development of transparent optical networks (TON). The idea is that the data stream always remains in the optical domain, eliminating the bottleneck in the processing of electro-optical conversion that existing in current optical communication systems. In this work new all-optical signal processing techniques are investigated through computer simulations and experiments. These techniques utilize the four wave mixing effect to multiplex information of two input signals into a single one. In particular, two new all-optical techniques for coding and regeneration incoherently optical code division multiple access (OCDMA) signals were investigated. These all optical techniques convert and regenerate the optical signal modulated in intensity, on-off keying (OOK) and / or the optical signal modulated in differential phase shift (DPSK) on OCDMA signal. The results showed that both techniques worked properly. The output OCDMA signal presented an improved in the optical power regeneration of 1,69 dB. The application of all optical conversion technique with simultaneous signals regeneration led to the study of hybrid wavelength division multiplexing with optical code division multiplexing (WDM/OCDM) technology at the transport layer in a TON network. Heuristics for assigning optical codes and wavelengths as well as optical codes and wavelengths conversion architectures were proposed. From the results, it was shown that Random-Random heuristic has a better performance when analyzing the blocking probability. Still, the sparse partial optical code and wavelength conversion (SPOCC/SPWC) architecture improves the utilization of network resources, reducing the deployment cost of network / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

A unique all-optical 1x2 self-routed switch is introduced. This switch routes an optical packet from one input to one of two possible outputs. The header and payload are transmitted separately in the system, and the header bits are processed in parallel thus increasing the switching speed as well as reducing the amount of buffering required for the payload. A 1x2 switching operation is analysed and a switching ratio of up to 14dB is obtained. The objective of the research was to investigate a unique all-optical switch. The switch works by processing the optical bits in a header packet which contains the destination address for a payload packet. After the destination address is processed the optical payload packet gets switched to one of two outputs depending on the result of the optical header processing. All-optical packet switching in the optical time domain was accomplished by making use of all-optical parallel processing of an optical packet header. This was demonstrated in experiments in which a three bit parallel processing all-optical switching node was designed, simulated and used to successfully demonstrate the concept. The measure of success that was used in the simulated experiments was the output switching ratio, which is the ratio between the peak optical power of a high bit at the first output and the peak optical power of a high bit at the second output. In all experimental results the worst case scenario was looked at, which means that if there was any discrepancy in the peak value of the output power then the measurement’s minimum/maximum value was used that resulted in a minimum value for the switching ratio. The research resulted in an optical processing technique which took an optical bit sequence and delivered a single output result which was then used to switch an optical payload packet. The packet switch node had two optical fibre inputs and two optical fibre outputs. The one input fibre carried the header packet and the other input fibre carried the payload packet. The aim was to switch the payload packet to one of the two output fibres depending on the bit sequence within the header packet. Also only one unique address (header bit sequence) caused the payload packet to exit via one of the outputs and all the other possible addresses caused the payload packet to exit via the other output. The physical configuration of the all-optical switches in the parallel processing structure of the switching node determined for which unique address the payload packet would exit via a different output than when the address was any of the other possible combinations of sequences. Only three Gaussian shaped bits were used in the header packet at a data rate of 10 Gbps and three Gaussian shaped bits in the payload packet at a data rate of 40 Gbps, but in theory more bits can be used in the payload packet at a decreased bit length to increase throughput. More bits can also be used in the header packet to increase the number of addresses that can be reached. In the simulated experiments it was found that the payload packet would under most circumstances exit both outputs, and at one output it would be much larger than at the other output (where it was normally found to be suppressed when compared to the other output’s optical power). The biggest advantage of this method of packet-switching is that it occurs all-optically, meaning that there is no optical to electronic back to optical conversions taking place in order to do header processing. All of the header processing is done optically. One of the disadvantages is that the current proposed structure of the all-optical switching node uses a Cross-Gain Modulator (XGM) switch which is rather expensive because of the Semiconductor Optical Amplifier (SOA). In this method of packet-switching the length of the payload packet cannot exceed the length of one bit of the header packet. This is because the header processing output is only one header bit length long and this output is used to switch the payload packet. Thus any section of the payload packet that is outside this header processing output window will not be switched correctly / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / unrestricted

Microwave signal processing in the optical domain is investigated in this thesis. Two signal processors including an all-optical fractional Hilbert transformer and an all-optical microwave differentiator are investigated and experimentally demonstrated. Specifically, the photonic-assisted fractional Hilbert transformer with tunable fractional order is implemented based on a temporal pulse shaping system incorporating a phase modulator. By applying a step function to the phase modulator to introduce a phase jump, a real-time fractional Hilbert transformer with a tunable fractional order is achieved. The microwave bandpass differentiator is implemented based on a finite impulse response (FIR) photonic microwave delay-line filter with nonuniformly-spaced taps. A microwave bandpass differentiator based on a six-tap nonuniformly-spaced photonic microwave delay-line filter with all- positive coefficients is designed, simulated, and experimentally demonstrated. The reconfigurability of the microwave bandpass differentiator is experimentally investigated. The employment of the differentiator to perform differentiation of a bandpass microwave signal is also experimentally demonstrated.

All-optical signal processing has grown over the last decade due to the demand for high-speed and high-bandwidth data processing. The main objective of all-optical signal processing is to avoid signal conversions from the optical domain to electrical domain and then back to optical, which introduces noise and bottlenecks data transmission speeds. These conversions can be avoided by manipulating light using an optical medium, e.g. an optical fiber, and taking advantage of the nonlinear response of the medium's dipoles to an external electric field. Nonlinear effects arising from the third-order nonlinearities, such as the Kerr effect, allow for an intense light beam to modify the refractive index of a medium through which it propagates. As a consequence, the phase of the light beam changes as it propagates and new frequencies are generated; this phenomenon is referred to as self-phase modulation (SPM). Light's ability to modify not only its own properties but also the properties of other co-propagating beams has been widely applied in telecommunications to create integrated all-optical data regenerators. While optical fibers are mainly utilized to transmit data at extreme speeds, they can also act as sensors when considering the reflected signal as opposed to the transmitted signal. Surprisingly, most of the fiber sensing field relies on electrically-driven components for manipulating light and does not take advantage of all-optical signal processing capabilities. In this thesis, we demonstrate the use of the nonlinear Kerr effect to improve aspects of both fiber point and distributed sensing. These sensing scenarios respectively refer to the use of a fiber as a single sensing element, and to the detection of external perturbations continuously along the entire length of the fiber. The sensing improvement are obtained by first inducing a sinusoidal modulation on the light before it experiences self-phase modulation in a nonlinear medium, leading to the generation of optical sidebands. By judiciously adjusting the peak power of the light and extracting a specific sideband, multiple all-optical signal processing functions are achieved. First, high extinction ratio pulses can be generated by extracting a higher-order sideband, which allows for extending the sensing distance of distributed fiber-based sensors. The extinction ratio refers to the ratio between the pulse peak and pedestal powers. To quantify the generated extinction ratios, we develop a measurement technique based on a single-photon counter and measure a pulse exhibiting a 120 dB extinction ratio, which was originally created by an electro-optic modulator with a 20-dB extinction ratio. Second, all-optical peak power stabilization can be achieved by extracting the first-order SPM-generated sideband. We utilize this technique to stabilize the peak power of an optical pulse sent to a distributed fiber sensor. We demonstrate that this stabilization technique allows for the detection of applied vibrations that would otherwise remain buried in the background noise. Third, we demonstrate an all-optical scheme, based on sinusoidally-modulated light experiencing SPM, that enables the magnification of fluctuations in the peak power intensity of a pulsed signal. The light's peak power at the entrance of the nonlinear medium is adjusted to reach a power regime yielding a magnification factor of 2m+1, when extracting the mth-order SPM-generated sideband. Finally, we propose a new sensing scheme composed of two all-optical signal processing steps to allow for the detection of environmental perturbations previously too small to be detected by a given intensity-based fiber sensor.

All-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase-preserving amplitude regeneration, phase regeneration, and phase-regenerative wavelength conversion are analyzed and demonstrated experimentally. The single-pump phase-conjugation process was used to regenerate RZ-DPSK pulse amplitudes with different input noise distributions, and the impact on output phase characteristics was studied. Experiments revealed a limited range over which amplitude noise could effectively be suppressed without introduction of phase noise, particularly for signals with intensity pattern effects. Phase regeneration requires use of phase-sensitive amplification (PSA), which occurs in nonlinear interferometers when the pump and signal frequencies are degenerate (NI-PSA), or in fiber directly through single-stage (degenerate) or cascaded (non-degenerate) FWM processes. A PSA based on a Sagnac interferometer provided the first experimental demonstration of DPSK phase and amplitude regeneration. The phase-regenerative capabilities of the NI-PSA are limited in practice by intrinsic noise conversion (amplitude to phase noise) and to a lesser extent by the requirement to modulate the pump wave to suppress stimulated Brillouin scattering (SBS). These limitations are relaxed in novel materials with higher SBS thresholds and nonlinearities. Degenerate FWM provides PSA in a traveling-wave configuration that intrinsically suppresses the noise conversion affecting the NI-PSA, while providing stronger phase-matched gain. Experiments confirmed superior phase-regenerative behavior to the NI-PSA with simultaneous reduction of amplitude noise for NRZ-DPSK signals. Phase-regenerative wavelength conversion (PR-WC) provides the regenerative properties of PSA at a new wavelength, and was proposed and demonstrated for the first time in this research. The parallel implementation of two FWM processes, phase-conjugation and frequency conversion, provides two idlers which exhibit interesting and useful regenerative properties. These were investigated theoretically and experimentally. Ideal phase-regenerative behavior is predicted when the contributing FWM processes are equally phase-matched, which can be maintained over any interaction length or wavelength shift provided the pump powers are properly adjusted. Depleted-pump regime PR-WC provides simultaneous phase and amplitude regeneration. Experiments confirmed regenerative behavior for wavelength shifts of the idlers up to 5 nm. Two techniques for phase regeneration of 4-level PSK signals were developed and evaluated. The first is based on parallel operation of PSAs suitable for processing 2-level PSK signals, where phase projection and regeneration are combined to recover the input data. Analysis of this scheme outlined the conditions required for effective phase regeneration and for practical implementation using known PSAs. A novel process based on FWM (parallel phase-conjugation followed by PSA) was developed and analyzed, and demonstrated using numerical simulations. These studies provide a basis for further work in this area.