2R Regeneration Research Articles

Correction to "EDFA-Free All-Optical 2R Regeneration Using a Compact Self-Seeded Fabry–PÉrot Laser Diode"

This study presents an erbium-doped fiber amplifier (EDFA)-free all-optical 2R (reamplification and reshaping) regeneration scheme based on a compact self-seeded Fabry-Perot laser diode. The proposed 2R regenerator achieves a straight line transmission at 10 Gb/s over 76 km without either the EDFA or the external probe laser, both of which are traditionally re- quired. Additionally, device characteristics such as data-rate transparency, input dynamic range, amplified gain, and 2R regen- eration performance are investigated experimentally. Index Terms—Fabry-Perot (FP), reamplification and reshaping (2R) regeneration.

Optical bistability in vertical-cavity semiconductor optical amplifiers

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.

All-optical wavelength-path service with quality assurance by multilayer integration system

In the future all-optical network controlled by generalized multiprotocol label switching (GMPLS), the wavelength path between end nodes will change dynamically. This inevitably means that the fiber parameters along the wavelength path will also vary. This variation in fiber parameters influences the signal quality of high-speed-transmission system (bit rates over 40 Gb/s). Therefore, at a path setup, the fiber-parameter effect should be adequately compensated. Moreover, the path setup must be completed fast enough to meet the network-application demands. To realize the rapid setup of adequate paths, a multilayer integration system for all-optical wavelength-path quality assurance is proposed. This multilayer integration system is evaluated in a field trial. In the trial, the GMPLS control plane, measurement plane, and data plane coordinated to maintain the quality of a 40-Gb/s wavelength path that would otherwise be degraded by the influence of chromatic dispersion. It is also demonstrated that the multilayer integration system can assure the signal quality in the face of not only chromatic dispersion but also degradation in the optical signal-to-noise ratio by the use of a 2R regeneration system. Our experiments confirm that the proposed multilayer integration system is an essential part of future all-optical networks.

A study on the wavelength conversion and all-optical 3R regeneration using cross-absorption modulation in a bulk electroabsorption modulator

A 40-Gb/s 3R regenerator with a two-ring injection mode-locked fiber laser as the clock recovery and an electroabsorption modulator (EAM) as the reshaping optical decision gate is proposed and demonstrated. The cross-absorption modulation effect in a bulk EAM was also numerically modeled. Using this model, both the shape and the extinction ratio of the optical decision gate are optimized. The model is also employed to investigate the tolerance of the timing jitter, the chromatic dispersion, and the polarization mode dispersion of an all-optical 3R regenerator based on a bulk EAM decision gate. The operation margin of the 3R regenerator is presented. The theoretical results agree well with the experimental results

101-hop cascaded operation of an optical-label switching router with all-optical clock recovery and 3R regeneration

This paper experimentally demonstrates the cascaded operation of an optical-label switching router for up to 101hops with 3R regeneration (reamplification, reshaping, and retiming). A semiconductor optical amplifier-based Mach-Zehnder interferometer wavelength converter performs the reshaping. A Fabry-Peacuterot filter all-optically recovers the clock from the incoming packets. Synchronous modulation by a LiNbO3 modulator using the recovered clock performs the retiming. The 3R regeneration maintains good signal quality in the cascaded operation, which is important for scalable optical networking

Modeling of All-Optical-Signal Processing Devices Based on Two-Mode Injection-Locked Vertical-Cavity Surface-Emitting Laser

We proposed all-optical signal processing devices based on a two-mode injection locking scheme. The operating principle is based on an all-optical inverter using transverse mode switching of an injection-locked vertical-cavity surface-emitting laser (VCSEL). Injection-locking with CW assist light enables us to increase the operating speed and to stabilize the fixed polarization state. Also, it provides a nonlinear transfer function in input–output characteristics, which will be useful for signal re-shaping, re-amplification. The polarization state of an output signal can be strictly controlled by two-mode optical injection scheme. Thus, the polarization state of an inverted signal can be fixed for randomly polarized input light. In addition, all-optical 3R regeneration and NRZ–RZ format conversion can be achieved with an electrically driven clock signal. The proposed scheme gives rise to novel functions such as all-optical 3R regeneration with an optical re-polarization function, which is called 4R regeneration. In addition, NRZ–RZ format conversion can be supported. We carried out the modeling based on a multi-transverse-mode rate equation analysis, which includes two orthogonal polarization modes, exhibiting a potential for high-speed 4R regeneration and format conversion at 10 Gbps.

The characterization of all-optical 3R regeneration based on InP-related semiconductor optical devices

We report characterization and experimental realization of recent InP-related semiconductor optical devices for all-optical 3R regeneration. A Mach-Zehnder interferometric wavelength converter (MZ IWC) with preamplifiers gives an extinction ratio (ER) improvement and a negative power penalty for all-optical reamplification and reshaping (2R) of pseudorandom bit sequence (PRBS) nonreturn-to-zero (NRZ) data at 10 Gb/s. In addition, we briefly describe the mechanism for injection locking of the multisection laser diode with a distributed feedback (DFB) reflector. Using this device, we demonstrate clock recovery from PRBS return-to-zero (RZ) and NRZ data. The achieved rms timing jitter is less than 1 ps for the input of 11.727 Gb/s PRBS RZ and NRZ. All-optical 3R regeneration leads to a good performance using the MZ IWC and multisection DFB LD. The combination of these functions provides all-optical 3R regeneration with NRZ to RZ conversion. For the realization of a small and compact 3R regeneration module, we propose the hybrid module packaging process, which is composed of 2R and 1R semiconductor chip in single butterfly-type module

Optical networks research at UCL

New dynamic optical switching technologies and adaptive transmission techniques will allow increased capacity and flexibility in future core and metro networks. The Optical Networks Group at UCL has carried out research focused on these areas, in collaboration with industry and other university research groups, for over a decade. In this paper, the technical challenges to be overcome in implementing dynamic, high-capacity networks are discussed, and recent results of the group's work are presented. New network architectures based on wavelength-routing and optical burst switching have been proposed and analysed, and the experimental demonstration of burst switching using fast wavelength-tunable lasers is described. High-capacity dense wavelength division multiplexed transmission systems, using advanced regeneration and equalisation techniques, have been studied, both theoretically, and experimentally using a dynamically reconfigurable recirculating fibre loop. Research results on advanced optical signal formats, all-optical 3R regeneration at 40 Gbit/s channel rates, adaptive analogue and digital electronic processing techniques and optical finite impulse response equalisation are presented. Finally, the development of optical performance monitoring technology, a key component of future all-optical networks, is described. The paper concludes with a prediction of future trends in optical communications research.

2R optical regeneration: an all-optical solution for BER improvement

We show both theoretically and experimentally that signal re-amplifying and reshaping (2R) optical regenerator based on self-phase-modulation (SPM)-induced spectral broadening followed by optical filtering has significant advantages over conventional 2R regenerators. By discriminating amplified spontaneous emission noise from a pulsed signal, the SPM-based regenerator is able to selectively attenuate noise more than the pulsed signal. This unique feature results in a direct improvement in bit-error ratio (BER) of a noisy pulsed signal, whereas conventional 2R regenerators can only prevent BER degradation-not actually improve it. We compare the two classes of regenerator and highlight their fundamental differences. We also demonstrate the BER improvement of a noisy signal filtered with an SPM-based regenerator that utilizes a highly nonlinear silica fiber, and present a compact version by exploiting a short length of As/sub 2/Se/sub 3/ chalcogenide glass fiber.

Design of Raman-Based Nonlinear Loop Mirror for All-Optical 2R Regeneration of Differential Phase-Shift-Keying Transmission

We present a concept for all-optical regeneration of signals modulated in phase-sensitive modulation formats, which is based on a new design of Raman amplified nonlinear optical loop mirror (RA-NOLM). We demonstrate simultaneous amplitude-shape regeneration and phase-noise reduction in high-speed differential phase-shift-keying transmission systems by use of the RA-NOLM combined with spectral filtering

Output performance investigation of self-phase-modulation-based 2R regenerator using bismuth oxide nonlinear fiber

We investigate the feasibility of the use of 1-m length of our fabricated bismuth oxide-based nonlinear fiber (Bi-NLF) for the implementation of a Mamyshev-type 2R regenerator that is based on self-phase-modulation-induced spectral broadening followed by spectral filtering, and evaluate the regeneration performance in both experimental and theoretical ways from a perspective of system application. Owing to the excellent dispersion and /spl chi//sup (3)/ nonlinearity characteristics of our 1-m-long Bi-NLF, a nonlinear S-shape power transfer curve is readily obtained. A Q-factor improvement of a noisy 10-Gb/s return-to-zero signal by 1.2 dB is achieved by use of the regenerator.

An all-optical 2R regenerator using a compact self-seeded Fabry-Pe/spl acute/rot laser diode incorporated in a bidirectional EDFA

An all-optical 2R regenerator, based on a compact self-seeded Fabry-Peacuterot laser diode with a 10-mm-long embedded fiber Bragg grating cavity, and a bidirectional erbium-doped fiber amplifier, is proposed and experimentally demonstrated to execute all-optical 2R regeneration at 10 Gb/s. Compared with the conventional 1R regeneration, the proposed scheme has achieved significant 6.4-dB improvement of power penalty at bit-error ratio =10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> in the transmission experiment over 100-km standard single-mode fiber

Cascadability assessment of a 2R regenerator based on a saturable absorber and a semiconductor optical amplifier in a path switchable recirculating loop

We assess a new 2R regenerator based on a microcavity saturable absorber and a semiconductor optical amplifier. Cascadability is demonstrated and the impact of regeneration span is studied in a 10-Gb/s two-path recirculating loop. A wavelength study demonstrates the tunability of the device over 13 nm

EDFA-free all-optical 2R regeneration using a compact self-seeded Fabry-Pe/spl acute/rot laser diode

This study presents an erbium-doped fiber amplifier (EDFA)-free all-optical 2R (reamplification and reshaping) regeneration scheme based on a compact self-seeded Fabry-Pe/spl acute/rot laser diode. The proposed 2R regenerator achieves a straight line transmission at 10 Gb/s over 76 km without either the EDFA or the external probe laser, both of which are traditionally required. Additionally, device characteristics such as data-rate transparency, input dynamic range, amplified gain, and 2R regeneration performance are investigated experimentally.

Optical 2R regeneration using cascaded fiber four-wave mixing with suppressed spectral spread

A fiber four-wave mixing (FWM)-based all-optical reshaping and reamplifying (2R) regeneration technique with near-ideal step-like transfer function and suppressed spectral spread is proposed. By setting proper phase modulation conditions and wavelength relations in a two-stage cascaded FWM approach, we succeeded in nearly spectral-spread free 2R regeneration, and demonstration of improved performance for 10-Gb/s nonreturn-to-zero pseudorandom binary sequence data transmission.

Nanosecond guard time packet-by-packet burst-mode optical 3R regeneration in an optical-label switching router

This letter discusses an experimental demonstration of 10-Gb/s packet-by-packet burst-mode optical 3R regeneration in an optical-label switching router. A monolithically integrated Mach-Zehnder interferometer with semiconductor optical amplifiers provides the all-optical 2R regeneration. Synchronous modulation with the use of Fabry-Pe/spl acute/rot filter-based clock recovery performs the burst-mode retiming function necessary for 3R regeneration. The clock recovery works successfully despite a clock phase discontinuity between adjacent packets. The optical 3R regenerator shows bit-error rates below 1/spl times/10/sup -10/ and sensitivity variations less than 1.5 dB over a wide range of guard times from 3 to 1000 ns.

Steep and adjustable transfer functions of monolithic SOA-EA 2R regenerators

Measurements and numerical modeling of a reamplification and reshaping (2R) regenerator demonstrate a steep power transfer function with adjustable threshold. The threshold can be adjusted more than 6 dB by simple control of the reverse bias voltage of the absorber section. The device consists of a semiconductor waveguide with alternating amplifier and absorber sections using quantum-well active material. The steep nonlinearity of the transfer function is achieved by concatenating several sections. We identify the saturation properties of the absorbing media, as dictated by the band-filling and field screening, as important for the observed transfer functions. The relation of the saturation powers of the gain and absorption sections is important for design optimization.

Self-phase modulation-based integrated optical regeneration in chalcogenide waveguides

We demonstrate integrated all-optical 2R regenerators based on Kerr optical nonlinearities (subpicosecond response) in chalcogenide glass waveguides with integrated Bragg grating filters. By combining a low loss As/sub 2/S/sub 3/ rib waveguide with an in-waveguide photo-written Bragg grating filter, we realize an integrated all-optical 2R signal regenerator with the potential to process bit rates in excess of 1 Tb/s. The device operates using a combination of self phase modulation induced spectral broadening followed by a linear filter offset from the input center wavelength. A nonlinear power transfer curve is demonstrated using 1.4 ps pulses, sufficient for suppressing noise in an amplified transmission link. We investigate the role of dispersion on the device transfer characteristics, and discuss future avenues to realizing a device capable of operation at subwatt peak power levels.

Optical 40-gb/s 3R regenerator with a combination of the SPM and XAM effects for all-optical networks

An all-optical 3R regenerator with a combination of self-phase modulation (SPM) and cross-absorption modulation (XAM) effects is proposed and investigated. Principle performances of the proposed all-optical 3R regenerator were experimentally investigated at a signal bit rate of 40 Gb/s. The all-optical 3R regenerator, which is located at the midpoint of a 1080-km transmission line, successfully provided an approximately 3-dB improvement of the Q-factor both just after regeneration and after totally 1080-km transmission. The chromatic dispersion tolerance of the proposed 3R regenerator was also investigated and successfully enhanced to about twice as wide by introducing a predistortion block configuration including a highly nonlinear fiber (HNLF). It was confirmed that the proposed all-optical 3R regenerator can become one of the strong candidates for the actual deployment of the all-optical network

10 000-hop cascaded in-line all-optical 3R regeneration to achieve 1 250 000-km 10-Gb/s transmission

We demonstrate 1 250 000-km 10-Gb/s return-to-zero transmission over 10 000 stages of in-line all-optical reamplification, reshaping, and retiming (3R) regeneration spaced every 125 km. The all-optical 3R regenerator incorporates a 10-GHz all-optical clock recovery module including a Fabry-Pe/spl acute/rot filter and a semiconductor optical amplifier in a cascaded configuration for fast and stable response. Bit-error-rate (BER) performance measurements show less than 0.7-dB power penalty at the BER of 10/sup -9/ between 1 250 000- (Lap 10 000) and 125-km (Lap 1) transmission using pseudorandom bit sequence 2/sup 23/-1.