2R Regeneration Research Articles

All-Fiberized Dispersion-Managed Multichannel Regeneration at 43 Gb/s

We report on the simultaneous 2R regeneration of up to three 42.7-Gb/s wavelength-division-multiplexing channels in a simple dispersion-managed fiber section with signal quality improvements higher than 1.7 dB. The regenerator relies on self-phase modulation-induced spectral broadening of the optical channels inside the fiber section and subsequent bandpass filtering at shifted wavelengths, and it is experimentally investigated in single-, dual-, and three-channel operation using optical pulses of 33% duty cycle.

Investigation of Four-Wavelength Regenerator Using Polarization- and Direction-Multiplexing

We demonstrate a four-channel extension to the Mamyshev regenerator and investigate its potential for the simultaneous processing of 4 times 10 Gb/s return-to-zero wavelength division-multiplexed channels. Mitigation of the interchannel nonlinearities is achieved through the rapid walkoff induced by both the large differential group delay of a specially developed polarization maintaining highly nonlinear fiber and a bidirectional architecture. Numerical and experimental results demonstrate the reduction of interchannel crosstalk as well as the potential of the scheme for 2R regeneration.

DPSK signal regeneration using a fiber-based amplitude regenerator

An experiment of an all-optical DPSK-signal regeneration is reported. In the regenerator, incoming DPSK signals are first demodulated to on-off-keying signals, then amplitude-regenerated by a 2R regenerator, and subsequently used as control pulses for phase remodulation of clock pulses in an all-optical phase modulator. Penalty-free operation with reduced amplitude noise is demonstrated by the use of a two-stage fiberbased cascaded 2R amplitude regenerator in bidirectional configuration.

Characterisation of an optical clock recovery method based on a mode-locked laser diode using spectrographic pulse measurement

As channels rates in optical networks are expected to exceed 100 Gb/s in the near future, new optical techniques for clock recovery will have to be developed for optical regeneration. This paper describes an optical clock recovery method based on a mode-locked laser diode. Experimental results show that a 42 GHz high quality optical clock can be retrieved from a 170 Gb/s OTDM data signal. Chirp transfer between the incident signal and the recovered clock signal is investigated using the SHG-FROG method. Results demonstrate that this clock recovery technique is invariant to input dispersion varying between +/-75 ps/nm, making it ideal for use in 3R regenerators.

Four-Channel All-Fiber Dispersion-Managed 2R Regenerator

We experimentally investigate a dispersion-managed four-channel 2R regenerator that relies on self-phase modulation-induced spectral broadening and offset filtering at four shifted wavelengths. The device consists of several alternating sections of dispersion-compensating fibers and single-mode fibers. Due to this arrangement and the use of low duty-cycle return-to-zero pulses, nonlinear interchannel effects are sufficiently mitigated resulting in almost no additional degradation compared to the single-channel case.

Operation properties of a reconfigurable photonic logic gate based on cross phase modulation in highly nonlinear fibers

The operation features of a 160 Gb / s reconfigurable all-optical logic gate based on cross phase modulation in highly nonlinear fibers are numerically investigated for six logic functions (XOR, OR, NAND, NOR, NOT, and AND). High bit rate operation is numerically demonstrated for a wide input signal wavelength range ( > 20 nm ). Performance enhancement of the proposed setup operating at 160 Gb / s for different signal wavelengths is exhibited by using a 2R regenerator based on the self-phase modulation effect in highly nonlinear fibers at the gate's output. The operation of the multi-functional logic gate is investigated considering either a pulsed or a continuous wave probe.

Jitter and Amplitude Noise Accumulations in Cascaded All-Optical Regenerators

This paper proposes and demonstrates a simulation model to systematically investigate jitter accumulations in cascaded all-optical 2R regenerators. The simulation results indicate that when the pattern dependence from the memory effect is minimized, the jitter accumulation depends critically on the degree of the regenerative nonlinearity. Studies of tradeoffs between the jitter from bandwidth limitation and the signal-to-noise-ratio degradation help identify the optimized regenerator bandwidth for various degrees of regenerative nonlinearity. The simulation then considers the pattern dependence from the memory effect and finds that it can severely degrade the cascadability of an optical 2R regenerator and can make it worse than that of a linear optical amplifier (optical 1R). The simulation results show good matches to the experimental results of an optical 2R regenerator based on a semiconductor optical amplifier based Mach-Zehnder interferometer. To overcome the jitter accumulation associated with the optical 2R regeneration, we experimentally demonstrate an optical 3R regenerator for optical nonreturn-to-zero signals with all-optical clock recovery. The experiments achieve more than 1000-hop cascadability for pseudorandom binary sequence 231-1 inputs with a 100-km recirculation loop using lab fiber. Field trial experiments then demonstrate a more than 1000-hop cascadability for a 3R spacing of 66 km and a 100-hop cascadability for a 3R spacing of 264 km.

All‐optical 3R regeneration based on the XPM effect of semiconductor optical amplifier

AbstractWe propose a 40 Gb/s all optical 3R regeneration system. A high Finesse Fabry‐Perot (F‐P) filter (FSR = 40 GHz, finesse = 1012) and a gain‐saturated SOA are used to extract 40 GHz clock. Before the clock extraction, 40 Gb/s RZ optical signals are converted into a stable wavelength after noninverted wavelength conversion based on the XPM of a single SOA. In the all optical decision, dual SOAs in series were used to lengthen active region of SOA. The 40 Gb/s degraded RZ signals are regenerated based on the XPM of dual SOAs in series, when a 0.26‐nm OBPF is blue shifted with respect to the wavelength of extracted clock. The experimental results show better eye opening, the decreased timing jitter from 5 to 1.4 ps and the 15 dB improved optical signal to noise ratio (OSNR). © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1807–1810, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23473

MZI‐SOA‐based 2R regeneration of OCDMA signals with multiaccess interference noise

AbstractIn this work, we present 2R regeneration of coherent optical code division multiple access (OCDMA) signals with distortion provoked by multiple access interference. The regeneration scheme is based on a Mach‐Zehnder interferometer exploiting cross phase modulation in semiconductor optical amplifiers. Experimental regeneration of an 8 Chip 10 Gb/s OCDMA signal is demonstrated with improvements in the required optical signal‐to‐noise ratio and elimination of bit error rate floor. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1521–1523, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23412

Nonlinear loop mirror-based all-optical signal processing in fiber-optic communications

All-optical data processing is expected to play a major role in future optical communications. The fiber nonlinear optical loop mirror (NOLM) is a valuable tool in optical signal processing applications. This paper presents an overview of our recent advances in developing NOLM-based all-optical processing techniques for application in fiber-optic communications. The use of in-line NOLMs as a general technique for all-optical passive 2R (reamplification, reshaping) regeneration of return-to-zero (RZ) on–off keyed signals in both high-speed, ultralong-distance transmission systems and terrestrial photonic networks is reviewed. In this context, a theoretical model enabling the description of the stable propagation of carrier pulses with periodic all-optical self-regeneration in fiber systems with in-line deployment of nonlinear optical devices is presented. A novel, simple pulse processing scheme using nonlinear broadening in normal dispersion fiber and loop mirror intensity filtering is described, and its employment is demonstrated as an optical decision element at a RZ receiver as well as an in-line device to realize a transmission technique of periodic all-optical RZ-nonreturn-to-zero-like format conversion. The important issue of phase-preserving regeneration of phase-encoded signals is also addressed by presenting a new design of NOLM based on distributed Raman amplification in the loop fiber.

Investigation of Simultaneous 2R Regeneration of Two 40-Gb/s Channels in a Single Optical Fiber

We experimentally investigate the simultaneous all-optical signal processing of two 40-Gb/s wavelength-division-multiplexing optical streams spaced by 5 nm using self-phase modulation and offset filtering in a single highly nonlinear fiber to achieve a 2R optical regeneration. Using a bidirectional configuration, we demonstrate efficient mitigation of the interchannel crosstalk. We experimentally observe no degradation of the regenerator performance arising from the presence of the second channel as compared to the single-channel case.

SOA Nonlinear Polarization Rotation With Linear Polarization Maintenance: Characterization and Applications

We present characterization and applications of the nonlinear polarization rotation (NPR) with linear polarization maintenance arising in polarization-insensitive semiconductor optical amplifiers (SOAs). The NPR with linear polarization maintenance is characterized in terms of probe and pump power, bias current, pump polarization, as well as wavelength. The NPR with linear polarization maintenance is then exploited for simultaneous inverted and noninverted polarization-insensitive wavelength conversions (WCs) with 2R regeneration using a single polarization beam splitter (PBS). WC of 10 Gb/s with 2R regeneration is experimentally demonstrated in the whole C-band with a power penalty reduction of 1.2 dB for the inverted WC and 0.8 dB for the noninverted WC. The NPR with linear polarization maintenance is also applied to perform on-off-keying (OOK) to polarization-shift-keying (PolSK) format conversion in conjunction with WC function, where the power fluctuation caused by the SOA cross gain modulation (XGM) is successfully mitigated using two cascaded SOAs. The power fluctuation of the converted PolSK signal is reduced to less than 0.6 dB, while the extinction ratio (ER) of polarization modulation is maintained at larger than 30 dB.

Introduction to the Special Issue on Nonlinear-Optical Signal Processing

The 11 invited and 37 contributed papers in this special issue focus on nonlinear-optical signal processing. Topics covered include: nonlinear pulse shaping; 2R and 3R regeneration; all-optical clock recovery; optical limiting; optical bistability; all-optical switching/gating; optical data format conversion; wavelength conversion; phase conjugation; phase-sensitive amplification; optical delay lines; optical burst/packet switching; all-optical OTDM multiplexing/demultiplexing; and micro- and nano-scale nonlinear-optical devices.

Optical Network Design for a Multiline-Rate Carrier-Grade Ethernet Under Transmission-Range Constraints

Ethernet is a success story in local area networks (LAN). Efforts for extending its boundaries beyond LAN to the carriers' backbone networks are in progress. We study the problem of designing reliable and cost-efficient high-rate (100 Gbit/s) carrier-grade Ethernet in a multiline-rate optical network under signal transmission-range constraints. Reliability is achieved using shared-path protection at the connection level (Ethernet tunnel in this study). We construct an auxiliary graph, called mixed topology (MT), using which it is possible to: 1) identify traffic grooming possibilities; 2) select a path which requires the minimum amount of 3R regeneration; and 3) effectively choose the data rate of the channel to be established. Our algorithms, tested on the 17-node German network, resulted in lower network cost and higher resource utilization compared with other schemes.

Polarization Independent All-Optical 3R Regeneration Based on the Kerr Effect in Highly Nonlinear Fiber and Offset Spectral Slicing

A detailed experimental characterization of a polarization-independent all-optical 3R regenerator is presented. The regenerator is comprised of a self-pulsating distributed feedback laser for clock recovery, cross-phase modulation in a highly nonlinear fiber (HNLF) and offset spectral slicing for retiming, and self-phase modulation in an HNLF and offset spectral slicing for reshaping. A key feature of the regenerator is that polarization-independent operation is achieved without additional complexity as compared to a conventional polarization-dependent implementation. The regenerator performance is assessed for important properties of the input signal, including the optical signal-to-noise ratio, waveform distortion due to residual group velocity dispersion and polarization mode dispersion, state-of-polarization, power, and wavelength. With careful attention to key design parameters, excellent performance is achieved.

Phase-preserving amplitude regeneration for a WDM RZ-DPSK signal using a nonlinear amplifying loop mirror

We propose a modified nonlinear amplifying loop mirror (NALM) for phase-preserving 2R regeneration of wavelength division multiplexed (WDM) return-to-zero differential phase-shift-keyed signals. As proof of principle the regeneration capability of this NALM setup has been investigated experimentally for two 10 Gbit/s wavelength channels. A significant eye-opening improvement and a negative power penalty of 1.2 dB have been observed in both channels.

40 Gbit/s all-optical clock recovery based on the injection mode-locked fiber ring laser

All-optical clock recovery is a key technology in all-optical 3R (Re-timing, Re-shaping, Re-amplifying) regeneration. In this paper, we demonstrate an all-optical clock recovery circuit based on injection mode-locked fiber laser. We have successfully extracted 40 GHz optical clock pulse from 40 Gb/s pseudorandom signal. Before the injected signal goes into the ring cavity, we make it pass a Mach–Zender interferometer (MZI) firstly. And thereby the clock component in the injected signal has been increased relatively, which is benefit to the clock recovery. We obtain firstly 10 GHz clock signal with perfect waveform from 10 Gb/s pseudorandom data stream, and then we extract 40 GHz clock signal from 40 Gb/s pseudorandom signal.

40 Gbps All-Optical 3R Regeneration and Format Conversion with Related InP-Based Semiconductor Devices

We report an experimental demonstration of 40 Gbps all-optical 3R regeneration with all-optical clock recovery based on InP semiconductor devices. We also obtain alloptical non-return-to-zero to return-to-zero (NRZ-to-RZ) format conversion using the recovered clock signal at 10 Gbps and 40 Gbps. It leads to a good performance using a Mach-Zehnder interferometric wavelength converter and a self-pulsating laser diode (LD). The self-pulsating LD serves a recovered clock, which has an rms timing jitter as low as sub-picosecond. In the case of 3R regeneration of RZ data, we achieve a 1.0 dB power penalty at 10 -9 BER after demultiplexing 40 Gbps to 10 Gbps with an eletroabsorption modulator. The regenerated 3R data shows stable error-free operation with no BER floor for all channels. The combination of these functional devices provides all-optical 3R regeneration with NRZ-to-RZ conversion.

Hybrid Link/Path-Based Design for Translucent Photonic Network Dimensioning

The advancement of ultralong-haul transmission technology has dramatically enhanced the all-optical reaches. However, the actual situations of installed fiber and sites for terrestrial network often prevent implementing a purely transparent network, and thus, opaque reshaping retiming regenerating (3R) regeneration is required to guarantee optical signal reachability. Since 3R regenerators based on optical/electrical/optical conversion tend to dominate the total network costs, an efficient network design method that allocates a minimum number of 3R regenerators to optimum locations is essential to build a cost-effective photonic network. In this paper, we propose such a network-dimensioning method by combining the advantages of link-based and path-based design approaches. It first guarantees optical signal reachability for any possible traffic demand in each segmented linear link. After combining all the links, excessive regenerators are eliminated based on the optical signal quality check with -factor calculation for each wavelength path. A trial design of a large-scale mesh network demonstrated a significant cost savings of more than 30% in comparison with a conventional link-based design. In the trial, the impact of fiber loss coefficient over the total network cost was investigated quantitatively, addressing the importance of such quantitative modeling and analysis.

Simulation of Multiwavelength Regeneration Based on QD Semiconductor Optical Amplifiers

In this letter, we examine the performance of a multiwavelength 2R regenerator based on the cross-gain modulation effect in quantum-dot semiconductor optical amplifiers. Extensive numerical simulations have been performed to investigate the device parameters and operating conditions of the proposed subsystem. All-optical regeneration of two input channels at 40 and 160 Gb/s are illustrated.