Signal Regeneration Research Articles

On Performance Gains of Flexible Regeneration and Modulation Conversion in Translucent Elastic Optical Networks With Superchannel Transmission

We study potential performance gains resulting from deliberate use of signal regeneration along with modulation and spectrum conversion in translucent elastic optical networks, realizing superchannel transmission. We analyze three alternative scenarios that differ in the way in which translucent lightpath connections are provisioned. Namely, a basic one in which the use of regenerators is minimized and two other cases that are more flexible in terms of signal regeneration and modulation conversion. To compare these scenarios, we focus on the problem of routing, spectrum, transceiver, and regeneration allocation (RSTRA). In RSTRA, in addition to classical RSA constraints, the selection of regeneration sites together with adaptation of modulation formats and assignment of transceivers to lightpaths is taken into account. To formulate the RSTRA optimization problem, we apply the integer linear programming approach, and to generate RSTRA solutions, we develop a heuristic algorithm. The results of numerical experiments show that intentional signal regeneration and adaptation of modulation formats of optical carriers can be beneficial in terms of both spectrum and transceivers utilization in long-distance networks; however, the savings are negligible in a small-distance network.

Development of New All-Optical Signal Regeneration Technique

All-optical signal regeneration have been the active research area since last decade due to evolution of nonlinear optical signal processing. Existing all-optical signal regeneration techniques are agitated in producing low Bit Error Rate (BER) of 10−10 at below than −10 dBm power received. In this paper, a new all-optical signal regeneration technique is developed by using phase sensitive amplification and designed optical phase locked signal mechanism. The developed all-optical signal regeneration technique is tested for different 10 Gb/s Differential Phase Shift Keying degraded signals. It is determined that the designed all-optical signal regeneration technique is able to provide signal regeneration with noise mitigation for degraded signals. It is analyzed that overall, for all degraded test signals, average BER of 10−13 is achieved at received power of −14 dBm. The designed technique will be helpful to enhance the performance of existing signal regeneration systems in the presence of severe noise by providing minimum BER at low received power.

Performance analysis of a highly nonlinear optical fiber with different graded refractive index profiles

In optical communication systems different types of fibers are employed for different applications. Particularly, highly nonlinear fibers are used for nonlinear signal processing such as wavelength conversion, optical switching, signal regeneration and demultiplexing. The performance parameters of these optical fibers can be altered through the refractive index (RI) profile modification during manufacturing. This paper explores the performance of a highly nonlinear fiber (HNLF) with parabolic, Gaussian and alpha power law functioned RI profile at the core instead of step index profile. The functional parameters are adjusted in order to obtain similar RI structure for these three functions. From the simulation analysis, it is concluded that HNLF with alpha power law RI profile reveals a better performance compared to the parabolic and Gaussian functions. Further by adjusting the alpha value in the design of alpha power law RI profile wide variety of dispersion curve and nonlinear coefficients are possible.

The theoretical investigation of the impact of two-photon absorption and free-carrier absorption on phase-sensitive amplification in silicon waveguides

We investigate the influence of two-photon absorption (TPA) and free-carrier absorption (FCA) on phase-sensitive amplification (PSA) process in a dispersion engineered silicon strip waveguide at the telecom wavelengths. The phase-dependent gain and phase-to-phase transfer functions as well as the phase regeneration capacity of PSA are numerically analysed. It is found that TPA and FCA will suppress the phase-sensitive extinction ratio (PER) and the efficiency of phase squeezing. Moreover, the phase regeneration capability of silicon waveguide-based PSA is investigated by comparing the regenerated signal waveforms at a different signal power with/without TPA and FCA. Our results have potential application in all-optical signal regeneration.

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>

All-optical wavelength conversion and signal regeneration of PAM-4 signal using a silicon waveguide.

We experimentally demonstrate on-chip all-optical wavelength conversion of 10-Gbit/s (9.35-Gbit/s net rate) 4-level pulse amplitude modulation (PAM-4) signal by exploiting degenerate four-wave mixing (FWM) in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalty of wavelength conversion is ~1 dB at a bit-error rate (BER) of 2 × 10-3. Moreover, the use of wavelength conversion for PAM-4 signal regeneration is also demonstrated in the experiment.

Spectral and power efficiency investigation in single- and multi-line-rate optical wavelength division multiplexed (WDM) networks

In order to tackle the increasing heterogeneous global Internet traffic, mixed-line-rate (MLR) optical wavelength division multiplexed (WDM) networks have emerged as the cost- and power-efficient solution. In MLR WDM networks, channels are structured as sub-bands, each of which consists of wavelengths operating at a similar data rate. By reducing the (1) spacing within a sub-band, or (2) spacing between sub-bands operating at different data rates, spectral efficiency can be improved. However, owing to high physical layer impairment levels, decrease in sub-band spacing adversely affects transmission reach of the channels, which results in higher power consumption due to requirement of increased signal regeneration. In this work, we compare power efficiency of various MLR and single-line-rate (SLR) solutions, and also investigate the trade-off that exists between spectral and power efficiency in a WDM network. Simulation results indicate that (1) for high transmission capacities, a combination of 100 Gbps transponders and 40 Gbps regenerators will obtain the highest power efficiency; (2) for long connection distances, a point ofmerging occurs for various SLR and MLR designs, where power consumption is independent of the frequency band distribution; and (3) for MLR systems, both spectral and power efficiency can be improved by using either shorter links with higher bandwidth assignment to 100 Gbps wavelengths, or longer links with higher bandwidth assignment to 40 Gbps wavelengths. Finally, the results indicate that focusing on spectral efficiency alone results in extra power consumption, since high quality of transmission and spectral efficiency leads to increased regeneration.

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.

Fiber Nonlinearity Compensation: Commercial Applications and Complexity Analysis

Fiber nonlinearities define the ultimate performance bound for optical communication systems. Todays 100 Gb/s commercial products employ advanced digital signal processing (DSP) algorithms, capable to adequately address linear channel impairments, leaving fiber nonlinearity compensation (NLC) as the next logical step to improve transmission performance, and consequently diminish the need for signal regeneration. Over the last few decades, several techniques have been presented to minimize or mitigate channel nonlinearities, ranging from specialized link designs in direct–detect legacy networks to advanced DSP algorithms in coherent systems. However, specifically in the coherent age, NLC has always been perceived as an extremely complex approach, allowing insignificant gains when practical implementations are considered. In this paper, we focus on the real-world commercial use cases and complexity tradeoffs for NLC, and review several application scenarios, including homogeneous and heterogeneous networks, dispersion unmanaged and dispersion managed link infrastructures, flex-grid networks, and short reach to ultra long-haul transmission applications. We establish that in various practical use cases, NLC may enable substantial performance gains, well beyond conventionally acknowledged bounds.

Impact of Wavelength and Modulation Conversion on Translucent Elastic Optical Networks Using MILP

Compared to legacy wavelength division multiplexing networks, elastic optical networks (EONs) have added flexibility to network deployment and management. EONs can include previously available functionality, such as signal regeneration and wavelength conversion, as well as new features such as finer-granularity spectrum assignment and modulation conversion. Yet each added feature adds to the cost of the network. In order to quantify the potential benefit of each functionality, we present a link-based mixed-integer linear programming (MILP) formulation to solve the optimal resource allocation problem. We then propose a recursive model in order to either augment existing network deployments (spectrum and regenerators) or speed up the resource allocation computation time for larger networks with higher traffic demand requirements than can be solved using an MILP. We show through simulation that systems equipped with signal regenerators or wavelength converters require a notably smaller total bandwidth, depending on the topology of the network. We also show that the suboptimal recursive solution speeds up the calculation and makes the running time more predictable, compared to the optimal MILP.

A two-hop equalize-and-forward relay scheme in OFDM-based wireless networks over multipath channels

Relay communications have attracted increasing research attentions as a cost-effective technique to improve spatial diversity, service coverage, and energy efficiency in wireless networks. However, existing relay schemes e.g., amplify-and-forward and decode-and-forward DF schemes still face several major challenges, particularly the accumulation of multipath channels effect in AF and long processing latency in DF. To address these issues, we propose a novel equalize-and-forward EF relay scheme to enhance the retransmission reliability while maintaining low processing delay at the relay node. In particular, the proposed EF relay estimates and equalizes the channel between source and relay to eliminate the channel accumulation effect without signal regeneration. To further reduce the relay processing time, the channel estimation and equalization in the proposed EF design are performed in parallel. The proposed equalization is realized by presetting the equalizer coefficients with the current channel response that is predicted in parallel using multiple past channel responses. Numerical results show that the proposed EF relay scheme can achieve comparable symbol error rate performance as the DF relay with much less relay latency. In addition, the EF relay exhibits low outage probability at the same data rate as compared with traditional amplify-and-forward and DF schemes. schemes. Copyright © 2015 John Wiley & Sons, Ltd

Novel Approach for Industrial Noise Cancellation in Speech Using ICA-EMD with PSO

Speech Signals have high range of variation in amplitudes and frequency. These acoustic signals with diverse properties are hard to recognize and filter if mixed with noise. To separate noise from original signal, the artifact peaks are separated from original signal and discarded. In this paper, the ICA method of signal denoising is used to differentiate the speech signal from periodic noise and Empirical Mode Decomposition method is proposed to generate the components of signal. The IMF(s) of signal is the non-linear descending order of frequency components that have been filtered for better SNR. Filtering with wiener filter has amended output but also results in loss of information. The selection of IMF(s) for signal regeneration when optimized using objective function of PSO, the information of original signal was dramatically preserved with suppressed noise. The system is tested on 4 example signals and proposed technique illustrates lower mean square error and higher SNR compared to wiener and ICA.

Efficient and accurate analytical performance models for translucent optical networks

This paper presents new analytical models for computing the blocking performance of translucent optical networks with sparsely located optical-electrical-optical regeneration nodes. Due to physical layer impairments such as noise and crosstalk, there is a maximum distance [called the transmission reach (TR)] that optical signals can travel before they have to be regenerated. Regeneration nodes that are allocated to a lightpath can also be used for wavelength conversion besides mitigating PLIs. The quality of transmission of a lightpath is satisfied if the length of each segment between two allocated regeneration nodes is less than the TR. We develop analytical models to estimate the call blocking probability for two typical regeneration node allocation policies. The first policy allocates regeneration nodes when the lightpath needs either regeneration or wavelength conversion, while the other allocation policy allocates regenerators only for signal regeneration. The analytical models strike a balance between computational complexity and prediction accuracy. The models are validated using extensive simulation results for a variety of network topologies and parameters.

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.

Fiber optical parametric amplifiers in optical communication systems.

The prospects for using fiber optical parametric amplifiers (OPAs) in optical communication systems are reviewed. Phase-insensitive amplifiers (PIAs) and phase-sensitive amplifiers (PSAs) are considered. Low-penalty amplification at/or near 1 Tb/s has been achieved, for both wavelength- and time-division multiplexed formats. High-quality mid-span spectral inversion has been demonstrated at 0.64 Tb/s, avoiding electronic dispersion compensation. All-optical amplitude regeneration of amplitude-modulated signals has been performed, while PSAs have been used to demonstrate phase regeneration of phase-modulated signals. A PSA with 1.1-dB noise figure has been demonstrated, and preliminary wavelength-division multiplexing experiments have been performed with PSAs. 512 Gb/s have been transmitted over 6,000 km by periodic phase conjugation. Simulations indicate that PIAs could reach data rate x reach products in excess of 14,000 Tb/s × km in realistic wavelength-division multiplexed long-haul networks. Technical challenges remaining to be addressed in order for fiber OPAs to become useful for long-haul communication networks are discussed.

Energy-Efficient Routing and Wavelength Assignment in Translucent Optical Networks

We study the energy-efficient routing and wavelength assignment (RWA) problem in translucent WDM networks, taking into account transmission limits of optical signals and the consequent need for signal regeneration. The problem is formulated through an integer linear programming model, and a heuristic algorithm called least regeneration first (LRF) is proposed to solve it in large networks. We first show that taking into account physical layer impairments and the consequent possible regeneration is mandatory to achieve satisfactory energy efficiency in RWA algorithms. In this respect, results show that LRF is much more efficient than ?impairment unaware? RWA algorithms. Then, we assess the energy efficiency achievable with different modulation formats using the proposed LRF algorithm in single-line-rate networks. Finally, the case of mixed-line-rate networks is also considered, and a heuristic method is proposed to efficiently decide the set of connections, at different bit rates, to be assigned to each traffic demand, with the goal of minimizing the total consumed power. Results show that this method is able to achieve power saving up to 25%.

Regeneration limit of classical Shannon capacity.

Since Shannon derived the seminal formula for the capacity of the additive linear white Gaussian noise channel, it has commonly been interpreted as the ultimate limit of error-free information transmission rate. However, the capacity above the corresponding linear channel limit can be achieved when noise is suppressed using nonlinear elements; that is, the regenerative function not available in linear systems. Regeneration is a fundamental concept that extends from biology to optical communications. All-optical regeneration of coherent signal has attracted particular attention. Surprisingly, the quantitative impact of regeneration on the Shannon capacity has remained unstudied. Here we propose a new method of designing regenerative transmission systems with capacity that is higher than the corresponding linear channel, and illustrate it by proposing application of the Fourier transform for efficient regeneration of multilevel multidimensional signals. The regenerative Shannon limit--the upper bound of regeneration efficiency--is derived.

Phase-Preserving Amplitude Noise Compression of 40 Gb/s DPSK Signals in a Single SOA

Wavelength-preserving and wavelength-converting amplitude regeneration of 40 Gb/s DPSK data in a saturated semiconductor optical amplifier (SOA) with limited excess phase noise feature is reported and investigated. By injecting simultaneously in the amplifier the noisy data and a CW beam with proper power levels, both the pass-through (PT) signal and the wavelength-converted data by four-wave-mixing (FWM) can be regenerated. The strongest regenerative effect is observed for the converted FWM data. The effect of input power variations on the regenerative performance of the device is thoroughly investigated in terms of Bit-Error Rate (BER) versus threshold margin improvement. We observe that regenerative behavior is attained for different levels of the data and CW power levels at SOA input. Experimental investigation of small-signal amplitude and phase SOA response reveals indeed the role of data/CW power balance for reducing the impact of excess phase noise from the amplifier. The analysis also confirms the stronger regenerative capability of the FWM process due to the strong amplitude-limiting SOA response at lower input data power in respect to the PT signal. The scheme offers the advantages of simplicity, compactness, and low operating power levels, making it a practical candidate for all-optical regeneration of high-speed DPSK signals.

A SOA-based all-optical regeneration of DPSK signals for satellite application

A semiconductor optical amplifier (SOA)-based regenerative amplification (SORA) of differential phase-shift keying (DPSK) signals for satellite application is presented, which has a simple frame and a large regenerative capacity to the small-power signals. The key mechanism of SORA is the discriminative gain provided by the SOA for the marks and spaces colliding in it. Simulation shows that, by using the SORA, the Q-factor improvement of degraded DPSK signals is about 0.7dB, but it is significantly influenced by both optical confinement factor and gain relaxation time. Considering the satellite vibration, the bit error rate (BER) for the case of SORA can improve more than one order of magnitude compared with the case of no SORA.

Research progress of hemodynamic signal and liver regeneration

Liver has great ability in regeneration,and liver regeneration is closely related to the prognosis of patients who received liver surgeries.The mechanisms of liver regeneration include biochemical theory and hemodynamic theory.Portal perfusion with moderate pressure is an important factor for starting liver regeneration.Hepatic artery buffer response,fluid shear stress and gasotransmitter play important roles in the liver regeneration.Learning the mechanisms of hemodynamic signal is of great importance for the treatment of liver diseases. Key words: Liver diseases ; Liver regeneration; Hepatectomy; Shear stress; Hepatic arterial buffer response