Optical Regeneration Research Articles

Scalable WDM phase regeneration in a single phase-sensitive amplifier through optical time lenses

Optical data regeneration is attractive, due to its potential to increase transmission reach and data throughput in communication systems, and several interesting proposals have been made. However, efficient and scalable solutions for regeneration of multiple parallel wavelength channels have been elusive, constituting a key challenge, which must be overcome for optical regeneration to have any prospect of being adapted in actual communication systems. Here we report a scalable wavelength-division multiplexing (WDM) regeneration scheme for phase only regeneration, which satisfies the multichannel requirement, using a set of optical time-lens-based Fourier processors combined with a single phase-sensitive amplifier (PSA). We describe the concept theoretically, and experimentally demonstrate simultaneous regeneration of 16 WDM channels with 50-GHz spacing, each carrying 10-Gbit/s DPSK phase-modulated data. The proposed scheme relies on ultrafast broadband optical processing and is inherently scalable in modulation speed and channel number.

Simultaneous wavelength exchange and 2R regeneration for two optical time division multiplexing signals by a single highly nonlinear fiber

The simultaneous wavelength exchange and 2R regeneration between two degraded optical time division multiplexing (OTDM) signals is experimentally demonstrated. By exploiting the self-phase modulation effect and offset filtering in a single highly nonlinear fiber (HNLF), it achieves 2R optical regeneration. Meanwhile, it realizes wavelength exchange using a bidirectional configuration. Optical wavelength exchange and 2R of 20- and 50-Gbit/s OOK signals at 1557.3 and 1552.3 nm is implemented with a power penalty of ∼0.5 dB at a bit-error rate of 10−9. The results show that the crosstalk is negligible for both channels in opposite directions. This bidirectional configuration exhibits excellent performance for simultaneous wavelength exchange and 2R regeneration between two degraded OTDM signals with different wavelengths.

Multichannel phase-sensitive amplification in a low-loss CMOS-compatible spiral waveguide.

We investigate single-channel and multichannel phase-sensitive amplification (PSA) in a highly nonlinear, CMOS-compatible spiral waveguide with ultralow linear and negligible nonlinear losses. We achieve a net gain of 10.4dB and an extinction ratio of 24.6dB for single-channel operation, as well as a 5dB gain and a 15dB extinction ratio spanning over a bandwidth of 24nm for multiple-channel operation. In addition, we derive a simple analytic solution that enables calculating the maximum phase-sensitive gain in any Kerr medium featuring linear and nonlinear losses. These results not only give a clear guideline for designing PSA-based amplifiers but also show that it is possible to implement both optical regeneration and amplification in a single on-chip device.

Effect of a timebase mismatch in two-way optical frequency transfer

Two-way frequency transfer on optical fibers is a powerful technique for the comparison of distant clocks over long and ultra-long hauls. In contrast to traditional Doppler noise cancellation, it is capable of sustaining higher link attenuation, mitigating the need of optical amplification and regeneration and thus reducing the setup complexity. We investigate the ultimate limitations of the two-way approach on a 300 km multiplexed fiber haul, considering fully independent setups and acquisition systems at the two link ends. We derive a theoretical model to predict the performance deterioration due to a bad synchronisation of the measurements, which is confirmed by experimental results. This study demonstrates that two-way optical frequency transfer is a reliable and performing technique, capable of sustaining remote clocks comparisons at the resolution, and is relevant for the development of a fiber network of continental scale for frequency metrology in Europe.

Performance analysis of 2R optical regeneration by cross gain compression using multiple quantum well semiconductor optical amplifiers

Este artículo presenta el análisis de prestaciones de una configuración para la regeneración óptica 2R (re-amplificación y re-formado de onda) mediante Compresión de Ganancia Cruzada (XGC) y Modulación de Ganancia Cruzada (XGM) sobre un Amplificador Óptico de Semiconductor de Múltiples Pozos Cuánticos (MQW-SOA). Se desarrolló un modelo logarítmico y se configuró en un simulador de eventos discretos. Los resultados de simulación muestran que con XGC se puede lograr satisfactoriamente la regeneración óptica 2R pero también muestra deficiencias cuando se usa en nodos en cascada debido a la existencia de diferentes niveles de amplificación en los bits procesados.

Widely tunable microwave photonic filter based on self-adaptive optical carrier regeneration

In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplification. The MPF system features with a single microwave passband as the result of the processed signal sideband beating with the regenerated optical carrier. Since the Brillouin-laser optical carrier and the SBS amplification are generated from one laser source, the optical carrier regeneration process of the proposed MPF is self-adaptive and carrier-frequency independent. Moreover, by simply varying the wavelength spacing between the optical carrier and the optical filter, the central passband of the MPF can be continuously tuned from 6 to 32 GHz, which is limited by the bandwidth of the modulator and the photodetector. The 3 dB bandwidth and the out-of-band suppression ratio of the MPF can reach 640 MHz and 21 dB, respectively.

Impact of amplitude jitter and signal-to-noise ratio on the nonlinear spectral compression in optical fibres

We numerically study the effects of amplitude fluctuations and signal-to-noise ratio degradation of the seed pulses on the spectral compression process arising from nonlinear propagation in an optical fibre. The unveiled quite good stability of the process against these pulse degradation factors is assessed in the context of optical regeneration of intensity-modulated signals, by combining nonlinear spectral compression with centered bandpass optical filtering. The results show that the proposed nonlinear processing scheme indeed achieves mitigation of the signal's amplitude noise. However, in the presence of a jitter of the temporal duration of the pulses, the performance of the device deteriorates.© 2016 Elsevier

100-Gb/s 3R Regeneration With Cross Gain Compression in Semiconductor Optical Amplifiers

All optical 3R regeneration of 100-Gb/s return-to-zero on-off-keying (OOK) signal based on cross gain compression effect using semiconductor optical amplifiers is experimentally demonstrated for the first time. The shape of optical filters and signal powers are carefully adjusted to obtain the regenerative result. Bit error rate (BER) measurement is performed, and the receiving sensitivity is improved by 2 to 3 dB in the regenerative signal, compared with the degraded signal. Regenerative capability for different degrees of degradation has been studied.

A New All-Optical Signal Regeneration Technique for 10 GB/S DPSK Transmission System

<p>The transmission of high power inside the optical fiber, produce amplitude noise, phase noise and other transmission impairments that degrade the performance of optical communication system. The signal regeneration techniques are used to mitigate these nonlinear impairments in the electrical or in the optical domain. All-optical signal regeneration techniques are one of the solutions to mitigate these nonlinear transmission impairments in the optical domain without converting the signal from optical to electrical domain. The existing techniques are not capable enough to attain the Bit Error Rate (BER) less than 10<sup>-10</sup> with the power penalty less than – 9dBm. In this paper, a new all-optical signal regeneration technique is developed that mitigate amplitude and phase noises in the optical domain. The new optical signal regeneration technique is developed by combining the two existing technique one is 3R (Reshaping, Reamplification and Retiming) regeneration and other is Phase Sensitive Amplification (PSA). The 10Gb/s Differential Phase shift Keying (DPSK) noisy transmission system is used to verify the features of developed technique. The developed technique successfully mitigates the nonlinear impairments from the noisy DPSK system with significant improvement in BER at low power penalty with the additional feature of high Q-factor and an eye open response for the regenerated signal. It is determined that BER of 10<sup>-12</sup> is achieved at the power penalty of -14 dBm with Q-factor of 42 and an eye opened response. The developed technique in the DPSK system is realized using commercial software package Optisystem. The designed technique will be helpful to enhance the performance existing high-speed optical communication by achieving the minimum BER at low power penalty.</p>

Simultaneous Phase Regeneration of MDM Signals Utilizing a Multimode Silicon Waveguide

Mode-division multiplexing (MDM) is an effective technique to enlarge the transmission capacity. In order to extend the transmission distance and increase the transparency of the phase-encoded MDM communication system, all optical phase regeneration (PR) for MDM signals is much in demand. However, the PR of the MDM signals has been rarely reported. In this paper, the simultaneous PR of the MDM signals is proposed and theoretically demonstrated. The PR performance relies on the dispersion engineering of a multimode nonlinear waveguide, obtaining strong intramode phase sensitive amplifications (PSAs), where the involved pumps and the MDM signal component are carried on the same mode. On the other hand, the weak PSA/four wave mixing interaction is ensured among different modes, owing to the large phase mismatch or weak nonlinear coupling. Detailed characteristics are investigated to further optimize the PR performance. Results show an effective phase squeezing for the degraded 20 Gbit/s MDM differential phase-shift keying signals, and the error vector magnitudes of the regenerated signals on dual modes are improved from 10.7% and 11.5% to 4.9% and 3.7%, respectively.

All optical wavelength multicaster and regenerator based on four-mode phase-sensitive parametric mixer.

Four-mode phase-sensitive (4MPS) process has been employed in a parametric mixer based wavelength multicaster, enhancing the multicasting conversion efficiency and signal-to-noise ratio. In addition, the 4MPS parametric multicaster is an outstanding candidate for all-optical regeneration, owing to its inherent capabilities to clamp amplitude fluctuations by the saturated parametric effect and to squeeze phase distortions by the phase sensitive process. The investigation in this paper focuses on the 4MPS multicaster operated in the saturation gain regime, including theoretical simulations and experimental demonstrations on amplitude and phase noise regeneration over 20 multicasting signal copies.

InP Microdisk Lasers Integrated on Si for Optical Interconnects

We review recent theoretical and experimental work on InP membrane microdisk lasers heterogeneously integrated on SOI and coupled to a Si bus waveguide. The lasers can now be fabricated with very high yield, have typical threshold currents of 0.5 mA and output powers of tens of μW, while the total power consumption is restricted to 5 mW. First, we describe various improvements in the fabrication technology and interesting results on the uniformity in device characteristics. In a second part, unidirectional behaviour and reflection sensitivity are briefly discussed. The third part is focused on optical signal regeneration with microdisk lasers. The last part contains a brief summary of optical interconnects based on heterogeneously integrated microdisk lasers and heterogeneously integrated photodetectors.

All Regeneration for Optical Communication Network Using Optical 3R Regeneration and Phase Sensitive Amplifier

Nonlinear optical effects in fibers occur via ultrafast Kerr nonlinearity, offers a flexible framework within which numerous signal-processing functions can be accomplished. When high power launched in optical fiber, several nonlinear transmission impairment such as amplitude noise, phase noise, power spectral losses, that degrades the performance of optical communication system. All optical regeneration is one of the solution to mitigate transmission impairments instead of optical to electrical conversion. In this paper, all optical regeneration is demonstrated for 10Gb/s DPSK system using 3R regeneration and Phase sensitive amplification to mitigate amplitude and nonlinear phase noise form 10G noisy DPSK transmission system. Bit error rate of 10-11 is achieved at power penalty of 6 dB. The system is developed and tested using optisystem. The developed all optical regeneration system is very demanding for long distance transmission in high-speed communication systems.

Energy-Efficient Cascaded Bit-Interleaved Converged Optical Access/In-Building Network Protocol

This paper proposes the cascaded bitinterleaved optical network protocol, an energy-efficient solution aiming at low power consumption in converged optical access/in-building networks while providing high data rates to end users, and a novel network architecture for optical access/in-building networks. In the proposed network architecture, optical–electrical–optical (OEO) regeneration is employed at the interface between access and in-building networks. The downstream frames are generated in the central office using a two-stage bitinterleaving scheme. In the downstream direction, the network nodes only process the data destined for them at a lower clock rate than that of the aggregate passive optical network (PON). In the upstream direction, no word alignment or decoding is performed in the intermediate nodes. Simulation and experimental results show that significant reduction in the power consumption of access/in-building networks can be achieved when the proposed cascaded bit-interleaved protocol is employed in conjunction with the proposed network architecture.

Nonlinear photonic waveguides for on-chip optical pulse compression

All-optical signal processing on nonlinear photonic chips is a burgeoning field. These processes include light generation, optical regeneration and pulse metrology. Nonlinear photonic chips offer the benefits of small footprints, significantly larger nonlinear parameters and flexibility in generating dispersion. The nonlinear compression of optical pulses relies on a delicate balance of a material's nonlinearity and optical dispersion. Recent developments in dispersion engineering on a chip are proving to be key enablers of high-efficiency integrated optical pulse compression. We review the recent advances made in optical pulse compression based on nonlinear photonic chips, as well as the future outlook and challenges that remain to be solved.

Impact of IP Layer Routing Policy on Multilayer Design [Invited

In this work we, first, investigate multilayer network planning approaches with different levels of integration by extending a commercial planning tool that accurately models the IP network. The different levels of integration are defined with respect to the degree to which information from the optical layer is considered in the optimization of the IP layer. The impact of traffic demand and topology size is evaluated in terms of the obtained cost savings. Case study results indicate cost savings reaching 25% by holistic multilayer network planning. We then proceed to evaluate the impact of the IP layer routing policy, expressed by the IP link weights, on the cost and latency of a holistic multilayer network design. As many network operators prefer to assign IP link weights based on simple rules that are unaffected by the network conditions, we focus on two weight setting policies that are agnostic to the network conditions: the hop-based policy and the distance-based policy. We find that different IP layer policies may lead to different optimized IP topologies for the same traffic and optical layer topology. It is shown that the optical network's regeneration requirements affect the optimal policy.

Genetic Approach for Optimizing the Placement of All-Optical Regenerators in WSON

In wavelength switched optical networks (WSONs), the placement of opto-electronic regenerators has always been optimized to keep the cost and power consumption contained, while ensuring the quality of transmission (QoT) for the optical signals. Nowadays, with the increase of the transmission rates and the spectral efficiency of the modulation formats, optical signal regeneration is still relevant for ensuring QoT. The progress in integrated photonics makes possible the realization of integrated optical regenerators that can replace the traditional opto-electronic regenerators. All-optical regenerators enable a reduction of size and energy consumption. However, differently from opto-electronic regenerators, recently fabricated integrated optical regenerators neither perform wavelength conversion nor regenerate multiple lightpaths at the same wavelength. Thus, novel constraints and limitations are introduced to the conventional regenerator placement problem, which has been well studied in the past for opto-electronic regenerators. This paper addresses the all-optical regenerator placement (ORP) problem in WSONs with guaranteed QoT. A genetic algorithm (GA) is proposed for optimizing the ORP while jointly solving the routing and wavelength assignment problem. GA results are compared with the optimal solutions found by solving a binary linear programming (BLP) formulation. When properly tuned, GA is able to quickly achieve the optimal solutions found by the BLP solver. The performance analysis indicates that the additional constraints have a negligible impact on the overall number of regenerators, compared to the case with opto-electronic regenerators.

Analysis of Self-Pulsating Sources Based on Cascaded Regeneration and Soliton Self-Frequency Shifting

We characterize the operation of self-pulsating sources made of two optical regenerators in cascade, namely a first regenerator of the type self-phase modulation spectral broadening and offset filtering, followed by a second regenerator of the type supercontinuum generation and offset filtering. The range of operation of this laser is explored as the wavelength and bandwidths of the band-pass filters are adjusted. We also provide experimental evidence that soliton self-frequency shift emanating from modulation instability triggers bursts of pulses at the repetition rate of the cavity. The stochastic nature of sources based on this concept leads to shot-to-shot pulse fluctuations in the cavity, which on average result in a flat supercontinuum extending beyond 1900 nm. Finally, a seed pulse can be sustained efficiently via this laser architecture, and the cavity consequently generates subpicosecond pulses at one of its output.

Tunable Optical Parametric Regenerator Assessment in a 43 Gb/s RZ-DPSK Signal Transmission Link

We study a wavelength-tunable optical parametric regenerator (OPR) demonstrated experimentally by assessing numerically its performance as an inline component of a 43-Gb/s return-to-zero differential phase-shift keying transmission system. The device features wide input wavelength range operation and regenerative wavelength conversion. The improvement in the transmission reach that it provides is predicted by simulations benchmarked against the experimental data. An up to fourfold improvement at a bit error ratio of ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> is estimated for a 360-km long regeneration span. We show that the improvement is achieved by a combination of the amplitude regeneration capabilities with the phase noise blocking character of the OPR, despite of the small amount of phase fluctuations induced by the regenerator itself.

Chalcogenide glass square photonic crystal fibre with large negative dispersion and high non-linearity

We propose a square structure, square lattice photonic crystal fibre (PCF) with square air-holes in its cladding. We consider chalcogenide (As2Se3) glass as the material of PCF. Chalcogenide glass has a large refractive index and high non-linearity compared to silica glass. A large negative dispersion of around -5473.7 ps/(nm-km) at 0.85 mum is obtained. A high non-linearity of 4813.5 W-1km-1, at telecom wavelength of 1.55 mum is observed. This PCF can be used for dispersion compensation as well as non-linear applications such as non-linear switching, optical regeneration, wavelength division multiplexing, frequency conversion, super-continuum, etc.