Long-haul DWDM transmission systems employing optical phase conjugation

Abstract

Abstract-In this paper, we review the recent progress in transmission experiments by employing optical phase conjugation (OPC) for the compensation of chromatic dispersion and nonlinear impairments. OPC is realized with difference frequency generation (DFG) in a periodically poled lithium-niobate (PPLN) waveguide, for transparent wavelength-division multiplexed (WDM) operation with high conversion efficiency. We discuss extensively the principle behind optical phase conjugation and the realization of a polarization independent OPC subsystem. Using OPC for chromatic dispersion compensation WDM 40-Gb/s long-haul transmission is described. As well, transmission employing both mixed data rates and mixed modulation formats is discussed. No significant nonlinear impairments are observed from the nonperiodic dispersion map used in these experiments. The compensation of intrachannel nonlinear impairments by OPC is described for WDM carrier-suppressed return-to-zero (CSRZ) transmission. In this experiment, a 50% increase in transmission reach is obtained by adding an OPC unit to a transmission line using dispersion compensating fiber (DCF) for dispersion compensation. Furthermore, the compensation of impairments due to nonlinear phase noise is reviewed. An in-depth analysis is conducted on what performance improvement is to be expected for various OPC configurations and a proof-of-principle experiment is described showing over 4-dB improvement in Q-factor due to compensation of nonlinear impairments resulting from nonlinear phase noise. Finally, an ultralong-haul WDM transmission of 22 × 20-Gb/s return-tozero differential quadrature phase-shift keying (RZ-DQPSK) is discussed showing that OPC can compensate for chromatic dispersion, as well as self-phase modulation (SPM) induced nonlinear impairments, such as nonlinear phase noise. Compared to a "conventional" transmission link using DCF for dispersion compensation, a 44% increase in transmission reach is obtained when OPC is employed. In this experiment, we show the feasibility of using only one polarization-independent PPLN subsystem to compensate for an accumulated chromatic dispersion of over 160 000 ps/nm. Index Terms-Dispersion compensation, differential phaseshift keying (DPSK), differential quadrature phase-shift keying (DQPSK), duobinary, fiber-optics communications, nonlinear phase noise, phase conjugation, phase-shift keying, periodically poled lithium niobate (PPLN), spectral inversion.

Dispersion Managed Optical Links with Optical Phase Conjugator Placed at the Various Positions

“…It is well known that dispersion management (DM) and optical phase conjugation are the available mitigation techniques, which compensate for the optical signal distortion due to GVD and nonlinear effects [5,6].…”

“…This technique offers unique advantages over other competitive methods such as data rate and modulation format transparency, ultra-fast responses, and simultaneous multi-channel compensation. It is independent of the transmission fiber's dispersion property as long as the same type of fiber is used for both halves of the transmission link with respect to OPC [6].…”

Extending the Neural Model to Study the Impact of Effective Area of Optical Fiber on Laser Intensity

“…Moreover, the fiber non-linearity could cause more restrictions on the limits of the fundamental Shannon capacity [4][5][6]. Compensation of the nonlinear distortion may be probably accomplished, if nonlinear pre-distortion as well as OPC transmitter are utilized [7].…”

114Tb/s DP-QPSK WDM polarization-diverse optical phase conjugation

“…Within telecoms applications, the conjugating element is typically a nonlinear optical waveguide which can support three-wave mixing via the χ 2 susceptibility [2] and/or four-wave mixing via the χ 3 susceptibility [3]. Specific examples of OPC elements range from discrete semiconductor optical amplifiers/lasers [4,5] to periodically-poled lithium niobate crystals (PPLN) [6] and specialty optical fibers such as highly nonlinear fiber (HNLF) [7]. In particular, HNLF offers numerous advantages as a passive medium which is easily spliced to standard single mode transmission fiber with low loss.…”

“…This can be achieved in various ways by e.g. using two discrete orthogonal pumps [15], placing the nonlinear element in a loop with counter-propagating orthogonal pump/signal polarizations [6,7,11] or by employing a reflective Faraday rotator [9]. However, to the best of our knowledge these schemes have not been shown to be compatible with the semi-standardized format of dual-polarization (DP)-QPSK modulation.…”