Optical Regeneration Research Articles

Coherent optical frequency transfer via 972-km fiber link

We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for. Instead of employing a phase discriminator and a phase locking loop in the conventional active phase control scheme, the passive phase noise cancellation is realized by feeding double-trip beat-note frequency to the driver of the acoustic optical modulator at the local site. This passive scheme exhibits fine robustness and reliability, making it suitable for long-distance and noisy fiber links. An optical regeneration station is used in the link for signal amplification and cascaded transmission. The phase noise cancellation and transfer instability of the 972-km link is investigated, and transfer instability of 1.1 × 10−19 at 104 s is achieved. This work provides a promising method for realizing optical frequency distribution over thousands of kilometers by using fiber links.

All-Optical Signal Processing in Ultrafast Optical Communication

Optical communication technology plays a crucial role in today's information age, as a result of the continuous advancement of social informatization. An array of nascent technologies, encompassing edge computing, the Internet of Things, big data, and artificial intelligence, have grown rapidly, leading to an increased demand for information transmission, which in turn has resulted in higher requirements for the development of optical communication technology. The emergence of ultrafast optical communication, which uses all-optical signal processing technology, has made data transmission faster and more reliable. This article introduces three basic methods for implementing all-optical signal processing (optical modulation, regeneration, and interconnection) based on all-optical and electronic signal processing. It examines the issues and difficulties that arise within particular application contexts and explores the progression of several correlated technologies in the times ahead. The field of all-optical signal processing is experiencing rapid growth and has the potential to bring revolutionary changes to various industries. Anticipated outcomes entail the attainment of ultra-long distance and ultra-high-capacity transmission, as facilitated by the ongoing advancements in hardware and all-optical signal processing technology. Meanwhile, the relentless pursuit of high-performance goals drives the continuous progress of ultrafast optical communication.

All-Optical Regeneration and Format Conversion for 4APSK Signals Based on Nonlinear Effects in HNLF

An all-optical format conversion and regeneration scheme about 4-ary amplitude and phase shift keying (4APSK) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). The input 4APSK signal is firstly converted into a regular quadrature phase shift keying (QPSK) signal by the nonlinear Mach-Zehnder interferometer (MZI) based on the self-phase modulation (SPM). Secondly, a degenerate phase-sensitive amplification (PSA) based on the four-wave mixing (FWM) is utilized to convert the regular-QPSK into two binary phase shift keying (BPSK) signals. The nonlinear MZI configuration is also used to compress the amplitude noise of BPSK. Thirdly, one phase shifter and one variable optical attenuator (VOA) are used to adjust the relative phase and power relationships of the two amplitude-regenerated BPSK signals. The regenerated 4APSK and converted QPSK signals can be generated in one 3-dB optical coupler through coherent addition of the two regenerated BPSK signals. The error-vector-magnitude (EVM) and the bit-error-rate (BER) are calculated and compared to evaluate the scheme performance. The proposed scheme can be applied as an optical regenerator or format convertor at the network gateway to increase the transmission distance or connect optical networks with different modulation formats.

Cascaded two-stage optical regenerator based on four wave mixing in highly nonlinear fiber.

This work focuses on the effectiveness of using four-wave mixing (FWM) in restoring the corrupted signal as well as the factors that affect the quality of the data. The method was based on the two-stage FWM-based optical wavelength converter designed using a OptiSystem version 18.0. The signal regeneration for both stages has taken place in the highly nonlinear fiber (HNLF) having length of 1.0 km and 0.8 km respectively. The first stage is to convert and restore a signal carrying NRZ formatted data at 1552 nm into a new wavelength of 1548 nm. While the second stage is to transfer the data back into the original wavelength of 1552 nm. It has been found that the quality of the data (Q-factor) is affected by the power of modulated signal (1552 nm) as well as the power of unmodulated pump source (1550 nm). The maximum Q-factor of 29.6 at 6 dBm signal power and of 35.7 at 16 dBm pump power have been achieved here. The wavelength spacing between those two sources also affect the quality of regenerated signal. The optimum quality value is found to be above 25 when the spacing is 1 nm regardless of the signal and pump power values.

Double Confinement Hydrogel Network Enables Continuously Regenerative Solar-to-Hydrogen Conversion.

Soft matter catalyst system allowing controllable manipulation of the organized nanostructure and surface property holds the potential for renewable energy. Here we demonstrate the construction of a continuously regenerative hydrogel photocatalyst that confines the metal-thiolate coordination induced nanocavity into robust micro-sized spongy network for water splitting. Thanks to low vaporization enthalpy and fast proton mobility of water molecules confining in nanocavities, the composite delivers outstanding photocatalytic H2 production (TOF of 4568 H2 h-1 ), nearly 4.5 times higher than that on the catalyst without confinements. Incorporating with conductive polymers, the TOF is substantially improved to 7819 H2 h-1 . Impressively, continuous regeneration is for the first time achieved with H2 production retention improved from 24 % to 72 % by regulating optically-active catalyst surfaces. This optical regeneration method provides new avenues for sustainable solar energy conversion.

Double Confinement Hydrogel Network Enables Continuously Regenerative Solar‐to‐Hydrogen Conversion

Soft matter catalyst system allowing controllable manipulation of the organized nanostructure and surface property holds the potential for renewable energy. Here we demonstrate the construction of a continuously regenerative hydrogel photocatalyst that confines the metal-thiolate coordination induced nanocavity into robust micro-sized spongy network for water splitting. Thanks to low vaporization enthalpy and fast proton mobility of water molecules confining in nanocavities, the composite delivers outstanding photocatalytic H2 production (TOF of 4568 H2 h−1), nearly 4.5 times higher than that on the catalyst without confinements. Incorporating with conductive polymers, the TOF is substantially improved to 7819 H2 h−1. Impressively, continuous regeneration is for the first time achieved with H2 production retention improved from 24 % to 72 % by regulating optically-active catalyst surfaces. This optical regeneration method provides new avenues for sustainable solar energy conversion.

Transparent vs Translucent Multi-Band Optical Networking: Capacity and Energy Analyses

Multi-band optical fiber transmission is generally proposed for capacity upgrades in optical transport networks. To comprehensively assess the potential of multi-band transmission, key metrics such as the potential capacity increase, energy consumption, and the number of required interfaces must be evaluated for different transmission scenarios. We consider progressive spectral exploitation, starting from the C-band only and up to C+L+S+U-band transmission, for both transparent and translucent solutions that exploit optical signal regeneration. By considering accurate state-of-the-art physical layer models, we derive a networking performance metric that enables the comparison of different solutions in terms of capacity allocation and energy consumption. For a translucent network design, different regenerator placement algorithms are compared, with the aim of minimizing energy consumption. The proposed network-wide numerical analysis shows that, for spectral occupations exceeding the C+L-band, translucent solutions can significantly increase network capacity, while leading to a similar energy consumption per transmitted bit as in the transparent design case, but they require the deployment of additional line interfaces. Significantly, these results provide evidence that the transparent exploitation of an additional transmission band produces a capacity increment that is at least comparable to that of a translucent solution based on already-in-use bands. Since this is attained at the expense of fewer line interfaces, it is a key finding suggesting that extending the number of bands supported is a cost-effective approach to scaling the capacity of existing fiber infrastructures.

Investigation of Different Transfer Functions for Optical Limiting Amplifier used in a 2R Burst Mode Optical Regenerator

Investigation of Different Transfer Functions for Optical Limiting Amplifier used in a 2R Burst Mode Optical Regenerator

A multi-hop free space optical link based on a regenerative relay

A multi-hop free space optical link based on all-optical relays is presented. All-optical relays are either composed of simple optical amplifiers or optical regenerators. It has been shown that after a certain number of hops, the amplifier based relay cannot extend the range of the free space optical link. Therefore, we have investigated the use of a self phase modulation based regenerator as a substitute for simple amplifier based relay. By employing the regenerative relay, a 10 Gbps optical signal having pulse width of 7 ps is transmitted over a distance of 8 km of free space optical link. The free space optical link is modeled on the basis of Gamma-Gamma channel model in the strong turbulence regime. The performance of the link is observed on the basis of bit error rate analysis. It has been shown that under strong turbulence and accumulation of amplifier noise, the range of the link can only be extended by employing an optical regenerator.

Modeling and design of enhanced all optical signal regeneration technique

Optical Signal regeneration in all-optical domain has played a vital in role for long haul optical communication systems. On contrary, the electronic regeneration systems have limitations in terms of real-time infeasibility for high data rate transmission with quality performance. The existing all-optical signal regeneration techniques remain in challenges for its complex design, testing and modeling prospective. The proposed all-optical signal regeneration technique is the new signal regeneration technique that is modeled and designed efficiently in order to regenerate high data rate signal that is degraded during transmission. The proposed all-optical signal regeneration technique is developed using single- pump Phase Sensitive Amplification, designed Optical Frequency Locked Model and noise mitigation model. The PSA performance is examined using various aspects i.e. signal power, noise figures, and phase error detection and correction. The proposed system will add a new dimension for signal regeneration schemes to develop more efficient regeneration systems with better performance analysis approach.

Histogram compensation algorithm for an efficient phase-only hologram calculation.

A fast computer-generated phase-only hologram (POH) calculation is needed to realize a holographic display. Existing iterative methods require many iterations and thus require speed improvement, and noniterative methods add constraints to the image, resulting in restrictions on quality or range of expression. In this paper, we propose an efficient iteration algorithm without using a feedback process. For the several initial iterations among the entire iteration process, the image constraint was replaced by a histogram adjusted image. This pre-iteration can compensate for the loss of bright and dark pixels in the image reconstructed by the POH, resulting in a more accurate POH. The quality of image reconstructed by the proposed method was compared with that of existing algorithms by computer simulation and optical regeneration. Compared to the previous method, a 1.17dB increase in peak signal-to-noise ratio was obtained, and the number of iterations to achieve the same image quality has been reduced by 23%. The proposed method hardly increased the amount of computation and could be used simultaneously with the existing feedback methods.

Virtualization of elastic optical networks and regenerators with traffic grooming

An elastic optical network (EON) plays an important role in transport technology for virtualization of networks. A key aspect of EONs is to establish lightpaths (virtual links) with exactly the amount of spectrum that is needed and with the possibility of grooming, the process of grouping many small traffic flows into larger units, creating a super-lightpath. Grooming eliminates the need for many guard bands between lightpaths and also saves transceivers; however, it often leads to the need to perform optical–electrical–optical conversions to multiple-data-rate optical signals at intermediate nodes. The aim of this paper is to provide a mixed-integer linear programming (MILP) formulation, as well as heuristic and meta-heuristic approaches, for the design of multiple virtual optical networks (VONs) in an elastic optical substrate network with bandwidth-variable lightpaths, modulation format constraints, and virtual elastic regenerator placement. Traffic grooming is allowed inside each VON, and a distance-adaptive modulation format technique is employed to guarantee efficiency in terms of bandwidth for a physical substrate, subject to several virtual topologies. A reduced MILP formulation without grooming capability is also proposed for comparison. The complete MILP formulation jointly solves the virtual topology design, regenerator placement, and grooming problems, as well as the routing, modulation, and spectrum assignment (RMSA) problem. The reduced MILP formulation, heuristics, and meta-heuristic, on the other hand, separate the virtual topology design problem from the RMSA problem. It is shown that the grooming approach can provide good results, since it solves the problem for a complete design when compared to the approach without grooming. Furthermore, heuristic solutions for large networks are proposed, which present good performance (in terms of saving spectrum) for the design with large instances.

Phase Sensing Technology Based Optical Signal Regeneration for 40 Gb/s Optical System

In this paper, phase sensing technology based optical signal regeneration system is designed and developed for 40 Gb/s optical system. The designed technique has achieved the low bit error rate (BER) and high Q-factor for the long haul optical system of 200 km. In comparison to the existing systems, the proposed technique have achieved the low BER and high Q-factor for long noisy fiber link. In this work, the HNLF configuration based that varies the phase sensing during the optical signal regeneration for high-speed 40 Gb/s degraded optical system is developed. The designed phase sensing based optical signal regeneration system has achieved the BER of 10−21 with high Q-factor. The designed system can be used in the existing regeneration system to provide the noiseless communication for long haul optical systems.

A novel Mach–Zehnder-interferometer regenerator for any level number of optical PAM signals using cross phase modulation of orthogonally polarized light

We propose a novel Mach–Zehnder interferometer (MZI) regenerator structure based on cross-phase modulation (XPM) effect between orthogonally polarized light. By adjusting the optical phase shifter on one arm of the MZI, the alignment of the optimal working points of the optical regenerator with the respective level powers of the degraded optical pulse-amplitude-modulated (PAM) signal can be achieved. The input-to-output power transfer function (PTF) capable of the regenerative Fourier transform, along with the optimal working points, is derived through theoretical analysis and the simulated PTFs are consistent with the theoretical results. Our research shows that the regenerative ability (RA) of the PAM regenerator increases with the input optical signal-to-noise ratio (OSNR), and the signal gain is inversely proportional to the level interval power of the input signal. The regeneration scheme proposed in the paper can theoretically be applied to the reshaping of an infinite number of regenerative levels, with a good consistency in the regeneration performance for each level. The phase preserving and bit-error rate (BER) properties of the regenerator are taken into account as well.

Performance Comparison of Dynamic Elastic Optical Networks with Optical Regeneration

We have investigated optical regeneration issues and application in elastic optical networks that are capable of providing dynamically optical paths with flexible bandwidths. We have analyzed the impact of optical regeneration in elastic optical networks and clarified various usage scenarios. We have then evaluated and compared the performance, in terms of the overall blocking probability and the total accommodated traffic volume, of three possible network scenarios with regeneration capability including (i) no regeneration, (ii) 3R regeneration, and (iii) 4R regeneration for practical network topologies. Numerical simulation proved that deployment of optical regeneration devices can exploit elastic optical networking to enhance the network performance for provisioning dynamically bandwidth-flexible lightpath services. It is also demonstrated that using re-modulation function while regenerating optical signals (4R regeneration) can further improve the network performance. However, due to the high cost of optical regeneration devices, especially all-optical ones, and more functional regenerators, the trade-off between the performance enhancement and the necessary number of regenerating devices needs to be carefully considered.

Robust network design for IP/optical backbones

Recently, Internet service providers (ISPs) have gained increased flexibility in how they configure their in-ground optical fiber into an IP network. This greater control has been made possible by improvements in optical switching technology, along with advances in software control. Traditionally, at network design time, each IP link was assigned a fixed optical path and bandwidth. Now modern colorless and directionless reconfigurable optical add/drop multiplexers (CD ROADMs) allow a remote controller to remap the IP topology to the optical underlay on the fly. Consequently, ISPs face new opportunities and challenges in the design and operation of their backbone networks [IEEE Commun. Mag.54, 129 (2016); presentation at the International Conference on Computing, Networking, and Communications, 2017; J. Opt. Commun. Netw.10, D52 (2018); Optical Fiber Communication Conference and Exposition (2018), paper Tu3H.2]. Specifically, ISPs must determine how best to design their networks to take advantage of new capabilities; they need an automated way to generate the least expensive network design that still delivers all offered traffic, even in the presence of equipment failures. This problem is difficult because of the physical constraints governing the placement of optical regenerators, a piece of optical equipment necessary to maintain an optical signal over long stretches of fiber. As a solution, we present an integer linear program (ILP) that does three specific things: It solves the equipment placement problem in network design; determines the optimal mapping of IP links to the optical infrastructure for any given failure scenario; and determines how best to route the offered traffic over the IP topology. To scale to larger networks, we also describe an efficient heuristic that finds nearly optimal network designs in a fraction of the time. Further, in our experiments our ILP offers cost savings of up to 29% compared to traditional network design techniques.

Selective amplitude-level regeneration based on blue-chirp spectral slicing using QD-SOAs.

We present a novel optical amplitude regenerator based on blue-chirp spectral slicing using a semiconductor optical amplifier (SOA). The combination of blue-chirp spectral slicing and gain competition in the SOA has a unique input/output (I/O) power-transfer function, which is controlled by the power of an input data signal injected into the SOA. The I/O power-transfer function provides selective amplitude-level regeneration of either the mark or space level of the input data signal. In this paper, we experimentally investigate the transfer function and the regeneration effect using a quantum-dot semiconductor optical amplifier. The results show that the regenerator has unique regeneration effect, specialized for either the mark or space level of a 10-Gbit/s on-off keying signal.

Optical Power Control in Translucent Flexible Optical Networks With GMPLS Control Plane

The continuously increasing traffic of Internet services (cloud services, video streaming, social networks, and recently, Internet of Things services) is leading to huge traffic growth in core optical networks. This traffic evolution is pushing network operators to efficiently exploit their infrastructures in order to postpone, as much as possible, the expensive deployment of new infrastructures. In this respect, the migration from fixed-to flex-grid optical networks was triggered in order to efficiently use optical network capacity, taking benefits from the improved spectral efficiency of flexible transponders. In our previous work [J. Opt. Commun. Netw., vol. 8, no. 8, p. 553, Aug. 2016], we demonstrated that migrating towards flexible networks while keeping in use existing optical amplifiers will cause a power saturation problem over highly loaded links due to the increase in the number of optical channels. To overcome this problem, we proposed in that work a power adaptation process that consists of converting transmission performance margins into optical power attenuation over optical links. However, the realized work considered only a transparent optical network controlled by the generalized multiprotocol label switching (GMPLS) protocol suite. In this paper, we consider the case of a translucent optical network where optical regeneration is required, and thus, the power adaptation process is adapted to this kind of network. A new routing algorithm and protocol extensions are proposed to take into account power and regeneration information in the GMPLS control plane of translucent networks.

Signal reshaping and noise suppression using photonic crystal Fano structures.

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

Optical vortex copier and regenerator in the Fourier domain

The generation and manipulation of optical vortices are of fundamental importance in a variety of promising applications. Here, we develop a nonlinear optical paradigm to implement self- and cross-convolution of optical vortex arrays, demonstrating the features of a vortex copier and regenerator. We use a phase-only spatial light modulator to prepare the 1064 nm invisible fundamental light to carry special optical vortex arrays and use a potassium titanyl phosphate crystal to perform type II second-harmonic generation in the Fourier domain to achieve 532 nm visible structured vortices. Based on pure cross-convolution, we succeed in copying arbitrary-order single vortices as well as their superposition states onto a prearranged array of fundamental Gaussian spots. Also, based on the simultaneous effect of self- and cross-convolutions, we can expand the initial vortex lattices to regenerate more vortices carrying various higher topological charges. Our presented method of realizing an optical vortex copier and regenerator could find direct applications in optical manipulation, optical imaging, optical communication, and quantum information processing with structured vortex arrays.