Michael Holtmannspoetter

Optimized digital backward propagation for phase modulated signals in mixed-optical fiber transmission link

The parametric optimization of Digital Backward Propagation (DBP) algorithm for mitigating fiber transmission impairments is proposed and numerically demonstrated for phase modulated signals in mixed-optical fiber transmission link. The optimization of parameters i.e. dispersion (D) and non-linear coefficient (γ) offer improved eye-opening (EO). We investigate the optimization of iterative and non-iterative symmetric split-step Fourier method (S-SSFM) for solving the inverse non-linear Schrödinger equation (NLSE). Optimized DBP algorithm, with step-size equal to fiber module length i.e. one calculation step per fiber span for obtaining higher computational efficiency, is implemented at the receiver as a digital signal processing (DSP) module. The system performance is evaluated by EO-improvement for diverse in-line compensation schemes. Using computationally efficient non-iterative symmetric split-step Fourier method (NIS-SSFM) upto 3.6 dB referenced EO-improvement can be obtained at 6 dBm signal launch power by optimizing and modifying DBP algorithm parameters, based on the characterization of the individual fiber types, in mixed-optical fiber transmission link.

Compensation of transmission impairments by digital backward propagation for different link designs

We investigate the performance of digital backward-propagation (DBP) in single-channel phase-encoded transmission systems for various in-line compensation schemes and depending on the parameters of DBP. A modified non-iterative DBP setup improves the eye opening by 3.5dB.

Logarithmic step-size based digital backward propagation in N-channel 112Gbit/s/ch DP-QPSK transmission

We propose and numerically investigate logarithmic step-size distribution for implementing efficient digital backward propagation (DBP) algorithm using split-step Fourier method (SSFM). DBP is implemented in N-channel 112Gbit/s/ch dual-polarization quadrature-phase-shift-keying (DP-QPSK) transmission over 2000km standard single mode fiber (SMF) with no in-line optical dispersion compensation. This algorithm is compared with constant step-size modified DBP (M-SSFM) algorithm in terms of efficiency, complexity and computational time. Furthermore, we investigate the same-capacity and same-bandwidth-efficiency transmission systems with 28GBaud and 56GBaud per-channel rates. The logarithmic step-size based DBP algorithm depicts efficient mitigation of chromatic dispersion (CD) and non-linear (NL) impairments. Benefit of the logarithmic step-size is the reduced complexity and computational time for higher baud rates.

Evaluation of correlative coding and DP-16QAM n-channel 112Gbit/s coherent transmission: digital non-linear compensation perspective

We report on the complexity reduction of digital backward propagation (DBP) by utilizing correlative encoded transmission over 1640km fiber link. Comparative system performance w.r.t DP-16QAM transmission can be achieved with 60% less computations and with a step-size of 205km.

Low-complexity logarithmic step-size-based filtered digital backward propagation algorithm for compensating fiber transmission impairments

We have investigated a new method to reduce the complexity of the digital backward propagation algorithm (DBP). A logarithmic step-size based split-step Fourier method (SSFM) is investigated in this paper to compensate fiber transmission impairments i.e. chromatic dispersion (CD) and non-linearities (NL) in dual-polarization quadrature phase shift keying (DP-QPSK) system. The algorithm is numerically investigated for coherently-detected multiple channel DP-QPSK system over 2000km (25 spans) standard single mode fiber (SMF-28) with un-compensated transmission link. The algorithm is numerically evaluated for: (a) 20 channel 56Gbit/s (14GBaud) with 25GHz channel spacing; (b) 10 channel 112Gbit/s (28GBaud) with 50GHz channel spacing and (c) 5 channel 224Gbit/s (56GBaud) with 100GHz channel spacing. Each simulation configuration has the bandwidth occupancy of 500GHz and a total transmission capacity of 1.12Tbit/s. The logarithmic DBP algorithm (L-DBP) shows efficient results as compared to the conventional DBP method based on modified SSFM (M-DBP). The results depict efficient mitigation of CD and NL, therefore improving the non-linear threshold point (NLT) upto 4dB. Furthermore by implementing a low-pass-filter (LPF) in each SSFM step, the required number of DBP stages to compensate fiber transmission impairments can be significantly reduced (multi-span DBP) by 75% as compared to L-DBP and by 50% as compared to M-DBP. The results delineate improved system performance of logarithmic step size based filtered DBP (FL-DBP) both in terms of efficiency and complexity which will be helpful in future deployment of DBP algorithm with real-time signal processing modules for non-linear compensation.

Electronic mitigation of fiber transmission impairments in 100Gbit/s WDM phase encoded transmission with optical add-drop multiplexers

Digital Backward Propagation (DBP) algorithm for mitigating fiber dispersion and non-linearities based on modified non-iterative symmetric split-step Fourier method (M-SSFM) is implemented and numerically evaluated. The algorithm is modified by shifting the calculation point of non-linear operator (r) together with the optimization of dispersion (D) and non-linear coefficient (γ) to get the optimum system performance. DBP is evaluated for 10x10Gbit/s wavelength division multiplexed (WDM) system (a total transmission capacity of 100Gbit/s) with RZ-DQPSK encoded signals over a transmission length of 1600km standard single mode fiber (SMF) with no in-line optical dispersion compensation. Furthermore, we quantify the impact of optical add-drop multiplexers (OADMs) in the transmission link. Modification of DBP parameters and bandwidth of optical filters associated with OADMs give significant improvement in the system performance.

Compensation of signal distortion by optimized digital backward propagation in DQPSK transmission

We optimize digital backward-propagation (DBP) to compensate signal distortions for various launch powers and bit rates. By optimizing transmission parameters and nonlinear phase calculating point, multi-span DBP gives significant improvement.

Evaluation of correlative coding and DP-16QAM N-channel 112Gbit/s coherent transmission: Digital non-linear compensation perspective

We report on the complexity reduction of digital backward propagation (DBP) by utilizing correlative encoded transmission over 1640km fiber link. Comparative system performance w.r.t DP-16QAM transmission can be achieved with 60% less computations and with a step-size of 205km.

Dynamic model of spectral hole burning for EDFAs with 980-nm-pumping

Spectral hole burning (SHB) in the gain spectrum of EDFAs influences the dynamic response of EDFAs and their electronic control. A 3-level-model incorporating SHB has been derived and numerically investigated. Conclusions for EDFA-control are drawn.

Use of Fiber Nonlinearities for Signal Improvement in Optical Transmission Systems

Optical data signals suffer from signal distortion and noise accumulation during transmission over long distances. In this paper we report on the usage of nonlinear fiber effects for improvement of the signal quality in two examples. On the one hand side we describe our work on the regeneration of phase encoded signals using nonlinear optical loop mirror setups. On the other hand side Raman effect based optical attenuators for the suppression of power transient caused by changes in channel numbers are discussed. Index Terms – Nonlinear optical effects, Optical regeneration, Optical power transient