Fatih Yaman

Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing.

A universal post-compensation scheme for fiber impairments in wavelength-division multiplexing (WDM) systems is proposed based on coherent detection and digital signal processing (DSP). Transmission of 10 x 10 Gbit/s binary-phase-shift-keying (BPSK) signals at a channel spacing of 20 GHz over 800 km dispersion shifted fiber (DSF) has been demonstrated numerically.

Mode-division multiplexed transmission with inline few-mode fiber amplifier

We demonstrate mode-division multiplexed WDM transmission over 50-km of few-mode fiber using the fibers LP01 and two degenerate LP11 modes. A few-mode EDFA is used to boost the power of the output signal before a few-mode coherent receiver. A 6×6 time-domain MIMO equalizer is used to recover the transmitted data. We also experimentally characterize the 50-km few-mode fiber and the few-mode EDFA.

Long distance transmission in few-mode fibers

Using multimode fibers for long-haul transmission is proposed and demonstrated experimentally. In particular few-mode fibers (FMFs) are demonstrated as a good compromise since they are sufficiently resistant to mode coupling compared to standard multimode fibers but they still can have large core diameters compared to single-mode fibers. As a result these fibers can have significantly less nonlinearity and at the same time they can have the same performance as single-mode fibers in terms of dispersion and loss. In the absence of mode coupling it is possible to use these fibers in the single-mode operation where all the data is carried in only one of the spatial modes throughout the fiber. It is shown experimentally that the single-mode operation is achieved simply by splicing single-mode fibers to both ends of a 35-km-long dual-mode fiber at 1310 nm. After 35 km of transmission, no modal dispersion or excess loss was observed. Finally the same fiber is placed in a recirculating loop and 3 WDM channels each carrying 6 Gb/s BPSK data were transmitted through 1050 km of the few-mode fiber without modal dispersion.

Efficient compensation of inter-channel nonlinear effects via digital backward propagation in WDM optical transmission

An advanced split-step method is employed for the digital backward-propagation (DBP) method using the coupled nonlinear Schrodinger equations for the compensation of inter-channel nonlinearities. Compared to the conventional DBP, cross-phase modulation (XPM) can be efficiently compensated by including the effect of the inter-channel walk-off in the nonlinear step of the split-step method (SSM). While self-phase modulation (SPM) compensation is inefficient in WDM systems, XPM compensation is able to increase the transmission reach by a factor of 2.5 for 16-QAM-modulated signals. The advanced SSM significantly relaxes the step size requirements resulting in a factor of 4 reduction in computational load.

Polarization Demultiplexing by Independent Component Analysis

Independent component analysis has been applied to polarization demultiplexing for coherent optical fiber communications. Polarization-multiplexed quadrature phase-shift keying and quadrature amplitude modulated signals were successfully demultiplexed by a tensor-based algorithm without using any knowledge of the modulation format.

Control of four-wave mixing phase-matching condition using the Brillouin slow-light effect in fibers

All-optical control of the phase-matching condition in four-wave mixing (FWM) processes is demonstrated using the Brillouin slow-light effect in optical fibers. A counterpropagating stimulated Brillouin scattering (SBS) pump has been used to control the phase velocity of the FWM pump in a wavelength conversion scheme. Both experimental results and theoretical simulations show an SBS-controlled 20 dB difference on the wavelength conversion efficiency.

Transoceanic Transmission of 40

We experimentally demonstrated transmitting 40 × 117.6 Gb/s 16 quadrature amplitude modulation with orthogonal frequency division multiplexing modulation over 10 181 km. The following techniques are applied to achieve error-free transmission: 1) hybrid large-core/ultralow-loss fibers were used for improving received optical signal-to-noise ratio while enhancing fiber nonlinearity tolerance; 2) multiband nonlinearity compensation algorithm was performed to further improve nonlinearity tolerance; 3) the forward error correction (FEC) limit of 5.3 dB provided by the concatenation of hard-decision and soft-decision FEC codes ensures to have error-free transmission after turbo equalizer with memory of three symbols, thus attaining a spectral efficiency of 4.7 b/s/Hz.

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Transmission of 117.6Gb/s optical PDM-16QAM OFDM signals over 10,181km is demonstrated at 25-GHz channel spacing with 4.7 b/s/Hz spectral efficiency. All the errors have been corrected by using 25% overhead QC-LDPC after multi-band nonlinearity compensation.

117.6 Gb/s PDM-OFDM-16QAM Over Hybrid Large-Core/Ultralow-Loss Fiber

We experimentally demonstrated long-distance transmission of 68.3 Gb/s wavelength-division multiplexing polarization division multiplexing (PDM)-orthogonal frequency division multiplexing (OFDM)-16QAM and 85.5 Gb/s PDM-OFDM-32QAM signals. The PDM-OFDM-16QAM signals have been successfully transmitted over 4242 km with a net spectral efficiency of 5.46 b/s/Hz. Furthermore, utilizing multiband digital back-propagation for nonlinearity compensation, the PDM-OFDM-32QAM signals at 6.84 b/s/Hz net SE have been successfully transmitted over the same distance. After transmission, both 16QAM and 32QAM signals surpassed the 20% soft-decision forward error correction threshold. To the best of our knowledge, these results correspond to the longest transmission distance for the PDM-OFDM-16QAM and PDM-OFDM-32QAM signals with SE higher than 5 and 6.5 b/s/Hz, respectively, by employing only erbium doped fiber amplifier amplification.

40×117.6 Gb/s PDM-16QAM OFDM transmission over 10,181 km with soft-decision LDPC coding and nonlinearity compensation

We demonstrated the first 30Tb/s (350 × 85.74Gb/s) optical transmission over 10,181km using bidirectional C/L-bands, 121.2km hybrid fiber spans, DP-QPSK modulation and EDFAs. Achieved 306Petabit/s•km capacity × distance product is the highest reported to date for WDM transmission.