Friedrich-Alexander-Universität Erlangen-Nürnberg

Digital Backward Propagation to Compensate Fiber Transmission Impairments in Coherent Transmission Systems with Advanced Modulation Formats

Digital Backward Propagation to Compensate Fiber Transmission Impairments in Coherent Transmission Systems with Advanced Modulation Formats

Principle Investigator: Prof. Dr.-Ing. Bernhard Schmauss

Doctoral Candidtaes: Dipl.-Ing. Michael Holtmannspoetter, M.Sc. Chien-Yu  Lin, M.Sc. Rameez Asif

The digital non-linear distortion compensation i.e. backward propagation algorithm (DBP) is a topic of high interest, to improve the non-linear tolerance of the optical communication systems. With higher baud-rates and advanced modulation formats, channel capacity is limited by the signal degradation due to fiber non-linearity, as it increases with signal input power. The DBP algorithm allows joint compensation of chromatic dispersion (CD) and nonlinearities (NL) along with the coherent receiver. It can be implemented by inversely solving the nonlinear Schrodinger equation (NLSE) using split-step Fourier methods (SSFM).

The main focus of our research is to investigate efficient numerical methods to implement DBP algorithm in order to make it more efficient for the compensation of chromatic dispersion (CD) and non-linear (NL) impairments and also to explore methods to improve the computational efficiency in order to facilitate its future implementation in real-time optical communication systems.

Numerical Implementation of Transmission System and Digital Signal Processing Module:

The block diagram illustrates the numerical model of a single-channel 112Gbit/s 16-QAM coherent transmission system with the digital signal processing module. The signals are transmitted over 2000km (20*80km) of standard single mode fiber by means of a recirculating loop. The fiber losses are compensated by Erbium doped fiber amplifier (EDFA) with a noise figure of 4.5dB. At the receiver an ideal laser source, as local oscillator, combined with an optical hybrid is used to convert the received optical signal down to base-band electrical signal and separate the in-phase and quadrature-phase components. The homodyne coherent receiver is followed by a digital signal processing (DSP) module which is implemented in Matlab. The base-band electrical signal is sampled at 2 symbol rate by analog-to-digital converters (ADCs). As the signal distortion is fully compensated by DBP compensation, no extra finite-impulse-response (FIR) filter is needed for chromatic dispersion compensation. The DBP algorithms are implemented based on step-size distribution as constant step-size and logarithmic step-size based DBP.

Comparison of the Transmission Performance based on the Criteria of Step-Size Selection to Implement DBP:

Figure 1. BER of all SSFM algorithms with varying number of steps per DBP stage for (a)3dBm, and (b) 6dBm.
Figure 2. Constellation diagrams of received 16-QAM signals at 3dBm after DBP compensation with (a) constant step- size and (b) logarithmic step-size methods.

Selected Publications:

 

  1. C.Y Lin, M. Holtmannspoetter, R. Asif and B. Schmauss, “Compensation of Transmission Impairments by Digital Backward Propagation for Different Link Designs”, In Proceedings of 36th European Conference and Exhibition on Optical Communication (ECOC), P3.16, Torino Italy, Sept 2010.
  2. R. Asif, C.Y Lin, M. Holtmannspoetter and B. Schmauss, “Optimized Digital Backward Propagation for Phase Modulated Signals in Mixed-Optical Fiber Transmission Link”, OSA Optics Express 18, 22796-22807, 2010.
  3. R. Asif, C.Y Lin and B. Schmauss, “Impact of Channel Baud-Rate on Logarithmic Digital Backward Propagation in DP-QPSK System with Un-compensated Transmission Links”, Optics Communications, Volume 284, Issue 24, Pages 5673-5677, December 2011.
  4. R. Asif, C.Y Lin, M. Holtmannspoetter and B. Schmauss, “Multi-Span Digital Non-Linear Compensation for Dual-Polarization Quadrature Phase Shift Keying Long-Haul Communication Systems”, D.O.I: 10.1016/j.optcom.2011.11.120, Optics Communications, 2012.
  5. C.Y Lin, R. Asif, M. Holtmannspoetter and B. Schmauss, “Step-Size Selection for Split-Step Based Nonlinear Compensation with Coherent Detection in 112Gbit/s 16-QAM Transmission”, OSA Chinese Optics Letters , Feb 2012.
  6. B. Schmauss, R. Asif and Chien-Yu Lin, “Recent Advances in Digital Backward Propagation Algorithm for Coherent Transmission Systems with Higher Order Modulation Formats ”,  Paper 8284-23, SPIE Photonics West, 21-26th January 2012, San Francisco, California, USA. (Invited Talk)
  7. R. Asif,  C.Y Lin, M. Usman and B. Schmauss, “400Gbit/s DP-RZ-QPSK Transmission over 1200Km SMF-28 Employing Digital Backward Propagation ”, Paper 8284-26, SPIE Photonics West, 21-26th January 2012, San Francisco, California, USA.
  8. R. Asif, C.Y Lin, M. Holtmannspoetter and B. Schmauss, “Low Complexity based Logarithmic Step-Size based Filtered Digital Backward Propagation for Compensating Fiber Transmission Impairments ”, Paper 8284-25, SPIE Photonics West, 21-26th January 2012, San Francisco, California, USA.

Mission

SAOT provides an interdisciplinary research and education program of excellence within a broad international network of distinguished experts to promote innovation and leadership in the areas

Optical Metrology
Optical Material Processing
Optics in Medicine
Optics in Communication and Information Technology
Optical Materials and Systems
and Computational Optics.