Optical Regeneration Research Articles

Nonlinear Pulse Shaping in Fibres for Pulse Generation and Optical Processing

The development of new all-optical technologies for data processing and signal manipulation is a field of growing importance with a strong potential for numerous applications in diverse areas of modern science. Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored, potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses and on the applications of advanced pulse shapes in all-optical signal processing. Amongst other topics, we will discuss ultrahigh repetition rate pulse sources, the generation of parabolic shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion.

Enhanced multi-hop operation using hybrid optoelectronic router with time-to-live-based selective forward error correction

Multi-hop operation is demonstrated with a prototype hybrid optoelectronic router for optical packet switched networks. The router is realized by combining key optical/optoelectronic device/sub-system technologies and complementary metal-oxide-semiconductor electronics. Using the hop count monitored via the time-to-live field in the packet label, the optoelectronic buffer of the router performs buffering with forward error correction selectively for packets degraded due to multiple hopping every N hops. Experimental results for 10-Gb/s optical packets confirm that the scheme can expand the number of hops while keeping the bit error rate low without the need for optical 3R regenerators at each node.

Wide range operation of regenerative optical parametric wavelength converter using ASE-degraded 43-Gb/s RZ-DPSK signals

For sustainable growth of the Internet, wavelength-tunable optical regeneration is the key to scaling up high energy-efficiency dynamic optical path networks while keeping the flexibility of the network. Wavelength-tunable optical parametric regenerator (T-OPR) based on the gain saturation effect of parametric amplification in a highly nonlinear fiber is promising for noise reduction in phase-shift keying signals. In this paper, we experimentally evaluated the T-OPR performance for ASE-degraded 43-Gb/s RZ-DPSK signals over a 20-nm input wavelength range between 1527 nm and 1547 nm. As a result, we achieved improved power penalty performance for the regenerated idler with a proper pump power range.

Regenerator Placement Strategies for Translucent OBS Networks

Most research works in optical burst switching (OBS) networks do not take into account the impact of physical layer impairments (PLIs) either by considering fully transparent (i.e., with optical 3R regeneration) or opaque (i.e., with electrical 3R regeneration) networks. However, both solutions are not feasible due to the technological requirements of the former and the high cost of the latter. In this paper, we deal with a translucent OBS (TL-OBS) network architecture that aims at bridging the gap between the transparent and opaque solutions. In order to evaluate its performance, a formulation of the routing and regenerator placement and dimensioning problem (RRPD) is presented. Since such formulation results in a complex problem, we also propose two alternative strategies. In particular, we evaluate the tradeoff between optimality and execution times provided by these methods. Finally, we conduct a series of simulation experiments that prove that the TL-OBS network model proposed effectively deals with burst losses caused by the impact of PLIs and ensures that the overall network performance remains unaffected.

Optical signal processing based on semiconductor optical amplifier and tunable delay interferometer

In this paper, several applications in all-optical signal processing based on a semiconductor optical amplifier (SOA) and variable delayed interferometers (DIs) have been experimentally demonstrated. Wavelength converter based on a nonlinear polarization switch (NPS) and a DI is proposed and presented for the wavelength conversion of nonreturn-to-zero (NRZ) signals. An all-optical nonreturn-to-zero to return-to-zero (NRZ-to-RZ) format converter with tunable duty cycles is achieved by the DI with variable delays. The 40 Gb/s reconfigurable optical OR/NOR gate in a single SOA, followed a tunable optical bandpass filter (OBF) and a DI, optical 2R regeneration using an SOA-DI are investigated. It is found that this combinative realization of filters has been endowed with great flexibility and quality for 40 Gb/s optical logic and 2R regeneration.

Offline Routing and Regenerator Placement and Dimensioning for Translucent OBS Networks

The deployment of translucent optical networks is considered the most promising short term solution to decrease costs and energy consumption in optical backbone networks. In fact, translucent wavelength switched optical networks (WSONs) have recently received great attention from the research community due to their technological maturity. However, the inflexibility and coarse granularity of WSONs is (re-)fostering research interest in sub-wavelength switching technologies such as optical burst switching (OBS). In OBS, however, the majority of research works neglect the impact of physical layer impairments by considering either fully transparent (i.e., with optical 3R regeneration) or opaque (i.e., with electrical 3R regeneration) networks. For this very reason, in this paper we present a translucent OBS (T-OBS) network architecture which aims at bridging the gap between the transparent and opaque solutions. In the T-OBS network the problem of routing and regenerator placement and dimensioning (RRPD) emerges. Joint RRPD is a complex problem and, in order to approach it, we propose to decompose it into the routing and RPD subproblems. As a consequence, we provide a mixed integer linear programming formulation of the routing problem and several heuristic strategies for the RPD problem. Illustrative numerical results prove the effectiveness of these methods at minimizing the number of electrical 3R regenerators deployed in the network. Considering a broad range of network topologies, we show that the proposed RPD heuristics ensure a proper quality of transmission performance whilst at the same time providing a cost-effective T-OBS network architecture.

All-optical signal processing based on semiconductor optical amplifiers

In this paper, we review the recent progress in the optical signal processing based on the nonlinearity of semiconductor optical amplifiers (SOAs). The four important optical signal processing functional blocks in optical switching are presented, i.e., optical wavelength conversion, optical regeneration, optical logic, and optical format conversion. We present a brief overview of optical wavelength conversion, and focus on various schemes to suppress the slow gain recovery of the SOA and improve the operating speed of the SOA-based optical switches. Optical regeneration including re-amplification, re-shaping and re-timing is also presented. Optical clock recovery that is essential for optical regeneration is reviewed. We also report the recent advances in optical logic and optical format conversion, respectively. After reviewing the four important optical signal processing functional blocks, the review concludes with the future research directions and photonic integration.

43-Gb/s Operation of Wavelength-Tunable Optical Parametric Regenerator

We have investigated a wavelength-tunable optical parametric regenerator (T-OPR) using a 43-Gb/s return-to-zero on-off-keying (RZ-OOK) signal and evaluated its performance. A 5.1-dB Q-factor improvement was achieved using a degraded signal with a 3.2-dB Q -factor. The power penalty occurring between the back-to-back condition and the regeneration was about 0.2 dB at the 10-9 bit error rate, as the best case using a degraded signal with a 6.1-dB Q-factor. The wavelength tunable range covers over 20 nm.

Analytical Investigation of an All-Optical T-Type Flip-Flop Using a Semiconductor Optical Amplifier Mach–Zehnder Interferometer with Push–Pull Configuration

To achieve an optical regenerator for a differential phase-shift keying signal based on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI), we need an all-optical T-type flip-flop (T-FF) for encoding. We propose an all-optical T-FF consisting of an SOA-MZI with push–pull configuration and a feedback mirror to overcome the speed limitation of the previously proposed counter-faced configuration. Numerical simulation reveals its possibility of stable operation in 10 Gbps with a 27 - 1 pseudo random binary sequence (PRBS) signal even by using a conventional SOA with a slow carrier recovery of 100 ps, and the possibility of 40 Gbps operation is also investigated.

Novel synchronous DPSK optical regenerator based on a feed-forward based carrier extraction scheme

We experimentally demonstrate a novel synchronous 10.66 Gbit/s DPSK OEO regenerator which uses a feed-forward carrier extraction scheme with an injection-locked laser to synchronize the regenerated signal wavelength to the incoming signal wavelength. After injection-locking, a low-cost DFB laser used at the regenerator exhibited the same linewidth characteristics as the narrow line-width transmitter laser. The phase regeneration properties of the regenerator were evaluated by emulating random Gaussian phase noise applied to the DPSK signal before the regenerator using a phase modulator driven by an arbitrary waveform generator. The overall performance was evaluated in terms of electrical eye-diagrams, BER measurements, and constellation diagrams.

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Ultrafast relaxation dynamics of photogenerated carriers in nanostructure based saturable absorber (SA) are investigated using a degenerate cross-polarized pump–probe experiment at 1.55 µm operating wavelength. Single-walled carbon nanotubes (SWNT) encased in micelles are studied and compared to bundled ones as well as to iron doped InGaAs/InP multiple quantum wells (MQW). SA parameters for all optical signal regeneration (AOSR) are extracted from the normalized differential transmission. Although all samples show the same order of recombination time, SWNT in micelles present a much higher contrast ratio associated to a lower level of saturation fluence as compared to their bundled and MQW counterparts.

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Power Assigning Method for Increasing the Number of Users in Time-spreading Optical CDMA Systems

Abstract In this paper, a method for increasing the number of supportable users in a time-spreading Optical code division multiple access (OCDMA) system is proposed. In the presented technique, a unique codeword is assigned to a couple of users instead of just one. Different optical powers are employed for such users in order to distinguish them from each other. Other methods use the frequency or the polarization of the optical signals as an additional coding dimension to increase the number of codewords and hence the number of users in the network. It is proposed to employ nonlinear optical regenerators for separating optical pulses with different powers. A comprehensive design algorithm for such regenerators is presented. In order to evaluate the performance of the designed regenerators a TS-OCDMA system is simulated using OptiSystem software. Results indicate an error free transmission in the system employing the proposed technique.

Fiber optic loop buffer switch incorporating 3R regeneration

In this paper, an all-optical regenerator based, photonic packet switch architecture, which consists of fiber loop for the storage of the contending packets, is proposed. In the loop buffer, the available buffer space may not be fully utilized due to the re-circulation limit (maximum number of re-circulations that data can take before it can be correctly received at the output). The re-circulation limit arises due to the accumulated ASE (amplified spontaneous emission) noise of the optical amplifier and crosstalk of the optical components. This limit can be counteract by placing a pool of regenerators inside the buffer, which regenerates the signal after some fixed number of re-circulations. As optical regenerators are costly devices, hence they should be placed optimally in the buffer. To do so, in this paper an expression is presented to evaluate the minimum number of required regenerators, to be placed optimally in the buffer for different buffer configurations (B) and re-circulation limits (K), such that full buffer capacity can be utilized without any re-circulation constraints. The simulation results in terms of packet loss probability are presented by considering the detrimental effect of re-circulation limits. Finally, advantages gain due to the regenerator placement inside the buffer are shown.

Wavelength Assignment in Multi-Carrier Distributed Optical Ring Networks With Wavelength Reuse

This paper investigates the problem of wavelength assignment in wavelength reusable multi-carrier distributed (WRMD) wavelength-division-multiplexing (WDM) ring networks. In conventional WDM ring networks, each edge node (EN) has its own light sources, and optical channels, called lightpaths, are established by using optical carriers generated from laser diodes (LDs) at the source EN. However, such networks will suffer from the need for complicated wavelength management (e.g., monitoring LDs, avoiding wavelength collision) in the future since each EN requires a large number of LDs to deal with the exponential increase in traffic. On the other hand, a WRMD ring network overcomes this problem. In this network, lightpaths between source and destination ENs are established by using carriers generated from a centralized multi-carrier light source. Moreover, the carrier regeneration technique is applied for the purpose of reducing the number of wavelengths used for lightpath establishment. Although optical carrier regeneration reduces the number of wavelengths, the quality of the regenerated carrier is slightly degraded after carrier regeneration. Therefore, in the WRMD network, the allowable number of carrier regenerations per wavelength must be limited in order to avoid communication error. This paper formulates the wavelength assignment problem, minimizing the number of wavelengths needed to establish all requested lightpaths, as the vertex coloring problem, and then an integer linear programming (ILP) solution is provided. Since ILP problems are non-deterministic polynomial-time- (NP-) complete, a heuristic algorithm is developed. Numerical results indicate that our developed algorithm performs well in our test cases. It is observed that one and two carrier regenerations per wavelength reduce the number of wavelengths for lightpath establishment by approximately 50% and 60%, respectively, compared to that without carrier regeneration. The results also show that regenerating carriers more than two times per wavelength has little effect on the required number of wavelengths regardless of the number of ENs.

All-Optical Regeneration Based on Phase-Sensitive Nondegenerate Four-Wave Mixing in Optical Fibers

An optical regeneration scheme based on nondegenerate phase-sensitive amplification in highly nonlinear fibers is numerically investigated. The proposed regenerator exhibits significant amplitude and phase noise suppression properties and eliminates the need for precise phase and frequency locking with the input return-to-zero differential phase-shift keying signal.

Tb/s Transmission and Routing Systems Using Integrated Micro-Photonic Components

Abstract —Recent advances in the development of photonic switching and transmission systems that exploit high and low index contrast integration materials are reported. Micro-ring resonators, delayed interferometers and all-optical wavelength converters integrated in Si3N4-SiO2 and silica-on-silicon substrates are used for the regeneration and wavelength routing of amplitude and phase modulated optical signals. Micro-photonics is the key for elegantly squeezing terabits into a few mm 2 with optimum yield and at a low development cost. Index Terms —high-speed transmission, optical regeneration, photonic routing, all-optical wavelength conversion, photonic integration I. I NTRODUCTION Today we are witnessing a resurgence of the growth and increasing customer demand for capacity in optical networks. A major factor for this growth is an unprecedented deployment of optical access networks worldwide for providing ample bandwidth to the end-user in the >50Mb/s region. In this rationale, the growth rates of end-users take new meaning, compared to those in 2000. Before the telecom bubble, penetration rates in excess of 100% reported, fuelled massive technology investments in the core network. However, these growth rates always translated to new users with bandwidth of a few kb/s, since the access network was just not ready. Moreover, broadband applications were still in their infancy and the telecom world was still searching for the “killer application”. The situation is very different today, with each new data connection translating to fast internet with combined voice and video. These new developments in the access networks are now exerting pressure on the metro and core networks that inevitably will always be “out-of-step” with the access networks, given that the genuine and sustainable market drivers for bandwidth are originating from the end-users. Photonic integrated circuits are expected to play a central role in the development of new hardware to be included in next generation telecommunication systems.

Wavelength-tunable optical parametric regenerator

We designed a wavelength-tunable optical parametric regenerator, where functions of reamplification, reshaping, and wavelength conversion are incorporated into a highly nonlinear fiber component. The uniform power transfer functions and negative penalties over a 20nm input wavelength range are experimentally demonstrated.

Multichannel Optical Signal Processing in NRZ Systems Based on a Frequency-Doubling Optoelectronic Oscillator

Optical signal processing, including clock recovery, nonreturn-to-zero (NRZ) to return-to-zero (RZ) or to carrier-suppressed return-to-zero (CSRZ) format conversions, serial-to-parallel conversion, and optical regeneration in NRZ systems using a frequency-doubling optoelectronic oscillator (OEO) is investigated. The key device in the OEO is a dual-output intensity modulator (IM), which is implemented using a polarization modulator (PolM). If a continuous-wave (CW) probe along with a multichannel NRZ signal is injected into the OEO, an electrical clock at half the data rate of the NRZ signal will be generated. When the electrical clock is fed back into the PolM-based IM, it will modulate the later injected CW probe and the NRZ signal, thus carving the NRZ signal to be an RZ/CSRZ signal at the same data rate or an RZ signal at half the data rate of the NRZ signal. Meanwhile, the CW probe is also carved to be an optical pulse train with a frequency equal to the data rate or half the data rate of the NRZ signal. Multichannel line-rate and prescaled clock recovery, NRZ-to-RZ/CSRZ conversion, 1:2 serial-to-parallel conversion, and synchronous-modulation-based regeneration are thus realized. An experiment is performed with all the aforementioned signal processing functions verified.

All-Optical 2R Regeneration Using the Hysteresis in a Distributed Feedback Laser Diode

A broadband optical 2R regenerator based on a single distributed feedback laser is demonstrated for nonreturn to zero signals at a bitrate of 10 Gb/s. A semi-analytical approach for the influence of hysteresis on the transfer function of a 2R regenerator is shown.