Midway Optical Phase Conjugation Research Articles

Dispersion-Managed Optical Links Combined with Asymmetrical Optical Phase Conjugation for Compensating for Distorted WDM Signals

The combination of dispersion management (DM) and midway optical phase conjugation (OPC) is one of the promising techniques for compensating for optical signal distortion due to group velocity dispersion and nonlinear fiber effects. However, in this combination technique, midway OPC restricts the flexible optical link configuration. Therefore, the possibility of implementing the flexible optical link configuration with non-midway OPC applied to complete inline DM links is investigated in this study. It is confirmed that although the compensation using non-midway OPC for the distorted WDM channels is less effective than that using midway OPC, when non-midway OPC is placed at positions closer to the transmitters, the deployment of precompensation (i.e., the sequence of DCF + SMF)–OPC–postcompensation (i.e., the sequence of SMF + DCF) is more advantageous for the compensation. On the other hand, inverse deployment with respect to OPC (i.e., postcompensation–OPC–precompensation) is more advantageous when non-midway OPC is placed at positions closer to the receivers.

Simultaneous Cancellation of Fiber Loss, Dispersion, and Kerr Effect in Ultralong-Haul Optical Fiber Transmission by Midway Optical Phase Conjugation Incorporated With Distributed Raman Amplification

An alternative application of distributed Raman amplification (DRA) for ultralong-haul optical fiber transmission is proposed. In our study, the DRA is employed in a transmission system using midway optical phase conjugation (OPC) for amplifying an optical signal and, at the same time, for constructing signal power evolution, which is symmetrical with respect to the midpoint of the system where the OPC is performed. Then, the nonlinear signal waveform distortions that are caused by the Kerr effect, as well as fiber dispersion, are almost completely compensated by the OPC, whereas the fiber loss is compensated by the DRA. Three possible symmetrical signal power maps - a power map that has a reverse sign of the power map that is caused by lump amplification, a flat signal power map, and an arbitrary symmetrical signal power map - are numerically designed by using appropriate Raman pump powers. We show that the flat power map exhibits smaller difference from the target and a higher optical signal-to-noise ratio and requires lower pump power than the other two power maps. Numerical simulation results demonstrate that, by employing the flat power maps with a span of 40 km, a single-wavelength signal whose data rate is 160 Gb/s can be successfully transmitted over 5000 km, and the Kerr effect is sufficiently suppressed near limitation due to the nonlinear accumulation of noise. Finally, we study the feasibility of expanding our method to wavelength-division-multiplexed signal transmission by designing a DRA gain with multiple-wavelength pumping to simultaneously obtain a flat power map and a wide-and-flat gain bandwidth. By using four-wavelength Raman pumps while carefully choosing pump wavelengths and their powers, we achieve the DRA gain that simultaneously gives a fluctuation of the signal power of only 3.5%, a gain ripple of only 5.3%, and, at the same time, a gain bandwidth of as wide as 46 nm.

Simultaneous dispersion and non-linearity compensation with mid-span optical phase conjugation and distributed Raman amplifier for a sub-carrier multiplexed optical transmission link

Optical phase conjugation (OPC) and distributed Raman amplifier (DRA) combination (OPC–DRA) is demonstrated as a potential enabling solution for simultaneous reduction of fiber non-linearities and dispersion compensation of a sub-carrier multiplexed (SCM) optical transmission link. The present work is focused on the use of OPC–DRA combination for system performance improvement in terms of composite second order distortion (CSO) and carrier to noise ratio (CNR) of the SCM link. The analysis further shows that, introduction of DRA with proper pumping scheme significantly reduce fiber non-linearity resulting in improvement of the system performance in terms of CNR, compared to the situation where only mid-way optical phase conjugation is used.

Suppressing modulation instability in midway optical phase conjugation systems by using dispersion compensation

Modulation instability (MI) limits the transmission capacity of fiber systems using optical phase conjugation (OPC). A midway OPC system with periodic dispersion compensation (DC) where fiber parameters and the local path-averaged power are distributed symmetrically with respect to the position of OPC, is proposed to cope with the MI effect. The analytical solution for evaluating the effect of MI shows that the MI effect can be suppressed considerably in such an OPC system with a strong DC configuration. The improvement of the system performance is confirmed by numerical simulations.

Simultaneous suppression of third-order dispersion and sideband instability in single-channel optical fiber transmission by midway optical phase conjugation employing higher order dispersion management

In optical phase conjugation (OPC) systems, the third-order dispersion (TOD) of optical fibers and the nonlinear resonance at well-defined signal sideband frequencies called sideband instability (SI) mainly limit the transmission performance. We propose, for the first time, a scheme for simultaneous suppression of both TOD and SI in OPC systems using a periodic higher order dispersion-managed link consisting of standard single-mode fibers (SMFs) and reverse dispersion fibers (RDFs). Computer simulation results demonstrate the possibility of 200-Gb/s data transmission over 10 000 km in the higher order dispersion-managed OPC system, where the dispersion map is optimized by our system design strategies.

Feasibility of 100-Gb/s 10000-km single-channel optical transmission by midway optical phase conjugation incorporated with third-order dispersion compensation

In optical phase conjugation systems, the third-order dispersion of fibers almost linearly accumulates along the transmission distance, and the distortion induced from the third-order dispersion can be perfectly compensated by using a linear third-order dispersion compensator placed at any point of the system. We demonstrate by numerical simulations that 100-Gb/s single-channel transmission can be achieved over a 10000-km distance in midway optical phase conjugation transmission systems by compensating the third-order dispersion.

Subpicosecond pulse transmission over 144 km using midway optical phase conjugation via a cascaded second-order process in a LiNbO3waveguide

We demonstrate for the first time the feasibility of 600-fs pulse transmission over 144 km using midway optical phase conjugation via a cascaded second-order process in a periodically poled LiNbO/sub 3/ waveguide. The output pulses are negligibly distorted and broadened to 680 fs. This result could not be obtained without complete compensation for fourth-order dispersion performed by midway optical phase conjugation.

Effects of asymmetric power change on BER performanceusing midway optical phase conjugation for fadingcancellation in 60 GHz millimetre-wave optical DSB signaltransmission over 100 km non-dispersion-shifted fibre

An experimental observation is reported on the effects of an asymmetric power change along an optical fibre with respect to the optical phase conjugator position on the bit error rate (BER) performance in a midway optical phase conjugation (OPC) system. The system is applied to received RF power fading cancellation in 60 GHz subcarrier multiplexed (SCM) optical double sideband (DSB) signal transmission system over 100 km of non-dispersion-shifted fibre.

Cancellation of the signal fading for 60 GHz subcarrier multiplexed optical DSB signal transmission in nondispersion shifted fiber using midway optical phase conjugation

In millimeter-wave (mm-wave) optical double sideband (DSB) signal transmission systems, the received radio frequency (RF) power fades periodically because of the group velocity dispersion (GVD) and the self-phase modulation (SPM) of optical fibers. In this paper, cancellation of the signal fading by using midway optical phase conjugation in mm-wave subcarrier multiplexed (SCM) optical DSB signal is analyzed. Fading-free 60 GHz mm-wave optical DSB signal transmission over 100 km-long nondispersion shifted single-mode fiber at 1550 nm by using a semiconductor optical amplifier (SOA) optical phase conjugator (OPC) in the midway of optical link is experimentally demonstrated for the first time. Finally, the degradation factor of the OPC system is also discussed.

Design theory of long-distance optical transmission systems using midway optical phase conjugation

This paper describes the basic system principle, the residual waveform distortion, the optimal design method, the ultimate transmission capacity, and its future improvement of the long-distance optical fiber transmission system using midway optical phase conjugation. We show that the periodic power variation in an optical amplifier chain and the dispersion value fluctuation from span to span along the system cause imperfect compensation for waveform distortion in the midway optical phase conjugation system. The optimal design method for suppressing the residual waveform distortion is proposed and confirmed by using computer simulations.

Extending Transmission Distance Limitation for a 40 Gb/s Signal over Standard Fiber Using Optical Phase-Conjugation

40 Gb/s signal transmission over up to more than 3000 km standard fiber by use of midway optical phase conjugation is predicted with a power penalty of below 5 dB and an eye closure of below 1 dB. This suggests that optical phase conjugation seems to be a very attractive technique in compensating for signal distortion for high speed long-haul standard fiber transmission systems.

Design of long-distance optical transmission systems using midway optical phase conjugation

We present the method for designing long-distance optical transmission systems with midway optical phase conjugation. The main cause of the waveform distortion in this type of system is found to be the sideband instability that is induced by the periodic signal power variation along the fiber link. It is shown that the effective waveform distortion compensation can be achieved by properly designing the amplifier spacing and the fiber dispersion to minimize the effect of the sideband instability. >

Effect of residual dispersion in the phase-conjugation fiber on dispersion compensation in optical communication systems

A simple analytic formula is obtained for calculating the output pulse shape and spectrum in a dispersion-compensation system where the midway optical phase conjugation (OPC) is realized by nondegenerate four-wave mixing in a dispersion-shifted fiber. The nonlinearity and residual dispersion of the OPC fiber are included in our model, and their effects on the OPC process are discussed. The third-order dispersion in the OPC fiber contributes to the total third-order dispersion of the system while the second-order dispersion (group velocity dispersion) and fourth-order dispersion introduce spectral filtering. The design issues such as the bandwidth limits of the input signal, maximum frequency spacing between the signal and the pump, and optimal location of the OPC fiber are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cancellation of four-wave mixing in a single-mode fiber by midway optical phase conjugation

Cancellation of waves generated by four-wave mixing (FWM) in a single-mode fiber by use of midway optical phase conjugation is proposed and analyzed, and the possible power reduction is estimated. Effective cancellation of FWM is demonstrated with phase-conjugate waves generated by forward FWM in a zero-dispersion single-mode fiber, and a power reduction ratio of -13.9 dB is achieved in experimental three-channel transmission along a 40-km dispersion-shifted fiber.

Cancellation of four-wave mixing in multichannelfibre transmissionby midway optical phase conjugation

The cancellation of waves generated by four-wave mixing (FWM) in multichannel optical fibre transmission is demonstrated using midway optical phase conjugation. An FWM reduction ratio of –10.6 dB is achieved in an experimental three-channel transmission experiment along a 40 km dispersion-shifted fibre.