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  • 1.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Forzati, Marco
    Scalable Passive Optical Network Architecture for Reliable Service Delivery2011In: Journal of Optical Communications and Networking, ISSN 1943-0620, E-ISSN 1943-0639, Vol. 3, no 9, p. 667-673Article in journal (Refereed)
    Abstract [en]

    A scalable and reliable architecture for both a wavelength division multiplexing passive optical network and a hybrid wavelength and time division multiplexing passive optical network with self-healing capability is presented and evaluated. Our protection scheme is compatible with a cascaded arrayed waveguide grating that can accommodate an ultra-large number of end users. A simple interconnection pattern between two adjacent optical network units (ONUs) is applied in order to provide protection for distributed fibers between a remote node and the ONUs. Therefore, the investment cost on a per-user basis can be significantly reduced. Meanwhile, the performance evaluation shows that our approach can achieve high connection availability while maintaining the support of long reach and high splitting ratio.

  • 2.
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Influence of polarization state, baud rate and PMD on non-linear impairments in WDM systems with mixed PM (D)QPSK and OOK channels2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 7, p. 8155-8160Article in journal (Refereed)
    Abstract [en]

    In this paper we numerically investigate nonlinear impairments in a WDM system with mixed PM (D)QPSK and OOK channels. First we analyze the dependence of XPM and XPolM on SOP and baud rate in absence of PMD. In this case we find that the nonlinear impairments are highly dependent on relative SOP between the PM (D)QPSK and neighbouring OOK channels. The dependence on relative SOP is more pronounced in differential detection than in coherent detection. However, with increasing values of PMD this dependence decreases, and non-linear tolerance improves

  • 3.
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101). KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Study of physical layer impairments in high speed optical networks2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work done in this thesis focuses on the impact of transmission impairments in high speed optical networks. Specifically it focuses on the impact of nonlinear impairments in long haul fiber optic data transmission. Currently deployed fiber optic transmission networks are running on NRZ OOK modulation formats with spectral efficiency of only 1 bit/symbol. To achieve spectral efficiency beyond 1 bit/symbol, fiber optic communication systems running on advanced modulation formats such as QPSK are becoming important candidates. The practical deployment of QPSK based fiber optic communication system is severely limited by Kerr-induced nonlinear distortions such as XPM and XPolM, from the neighboring NRZ OOK channels. In this thesis we focus on the impact of nonlinear impairments (XPM and XPolM) in fiber optical transmission systems running on QPSK modulation with both differential and coherent detection. The dependence of impact of nonlinear impairments on SOP, baud rate of the neighboring NRZ OOK channels and PMD in the fiber, is analyzed in detail through numerical simulations in VPItransmission Maker®. In this thesis we also analyze digital signal processing algorithms to compensate linear and nonlinear impairments in coherent fiber optic communication systems. We propose a simplification of the existing method for joint compensation of linear and nonlinear impairments called "digital back propagation". Our method is called "weighted digital back propagation". It achieves the same performance of conventional digital back propagation with up to 80% reduction in computational complexity.In the last part of the thesis we analyze the transmission performance of a newly proposed hybrid WDM/TDM protection scheme through numerical simulation in VPItransmission Maker®. The transmission performance of the hybrid WDM/TDM PON is limited by impairments from passive optical devices and fiber optical channel.

  • 4.
    Chughtai, Mohsan Niaz
    et al.
    Acreo Netlab, Kista.
    Forzati, Marco
    Acreo Netlab, Kista.
    Mårtensson, Jonas
    Acreo Netlab, Kista.
    Rafique, Danish
    Photonic Systems Group, Ireland.
    Dependence of non-linear impairments on polarization state and baud rate in WDM systems with mixed DQPSK and OOK channels2011Conference paper (Refereed)
    Abstract [en]

    In this paper, transmission of Polarization-Multiplexed (PM), RZ-DQPSK is analyzed numerically with copropagation of intensity modulated non return to zero on off keying (NRZ OOK) channels. The dependence of nonlinear crosstalk on baud rate (10 Gbaud, 28 Gbaud and 56 Gbaud) and relative state of polarization (SOPs) of PM RZ DQPSK and neighbouring NRZ OOK channels is analyzed in terms of required OSNR for the BER of 10 -3 versus launch power. From the results we observe that non-linear impairments are highly dependent on relative SOPs and less dependent on baud rates of the PM RZ DQPSK test channel.

  • 5.
    Chughtai, Mohsan Niaz
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Forzati, Marco
    AcreoNetlab, Kista.
    Mårtensson, Jonas
    AcreoNetlab, Kista.
    Tipsuwannakul, Ekawit
    Chalmers University of Technology.
    Karlsson, Magnus
    Chalmers University of Technology.
    Analysis of Non-Linear Impairments in 40 Gbaud PM DQPSK and D8PSK Transmission2010In: ICTON 2010, IEEE Press, 2010Conference paper (Refereed)
    Abstract [en]

    In this paper, 40 Gbaud transmission of single polarization (SP) and Polarization-Multiplexed (PM), RZ-DQPSK and RZ-D8PSK signals is analyzed numerically. The impact of nonlinear crosstalk arising from the presence of neighbouring intensity-modulated channels is analyzed in terms of required OSNR for the BER of 10-3versus launch power.

  • 6.
    Rafique, Danish
    et al.
    Photonics Systems Group, Tyndall National Institute and Department of Electrical Engineering/Physics, University College Cork, Dyke Parade, Prospect Row, Cork, Ireland.
    Mussolin, Marco
    Department of Information Engineering, University of Padova, Italy.
    Forzati, Macro
    Acreo AB, Network Transmission Lab..
    Mårtensson, Jonas
    Acreo AB, Network Transmission Lab..
    Chughtai, Mohsan Niaz
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Compensation of intra-channel nonlinear fibre impairments using simplified digital back-propagation algorithm2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 10, p. 9453-9460Article in journal (Refereed)
    Abstract [en]

    We investigate a digital back-propagation simplification method to enable computationally-efficient digital nonlinearity compensation for a coherently-detected 112 Gb/s polarization multiplexed quadrature phase shifted keying transmission over a 1,600 km link (20x80km) with no inline compensation. Through numerical simulation, we report up to 80% reduction in required back-propagation steps to perform nonlinear compensation, in comparison to the standard back-propagation algorithm. This method takes into account the correlation between adjacent symbols at a given instant using a weighted-average approach, and optimization of the position of nonlinear compensator stage to enable practical digital back-propagatio

  • 7.
    Rafique, Danish
    et al.
    Photonics Systems Group, Tyndall National Institute and Department of Electrical Engineering/Physics,.
    Mussolin, Marco
    Department of Information Engineering, University of Padova, Italy.
    Forzati, Marco
    Acreo AB, Network Transmission Lab..
    Mårtensson, Jonas
    Acreo AB, Network Transmission Lab..
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Modified Split-Step Fourier Method for Compensation of Nonlinear Fibre Impairments2011In: 13th International Conference on Transparent Optical Networks (ICTON), 2011, IEEE conference proceedings, 2011, p. 1-4Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate a modified split-step Fourier method to enable computationally-efficient digital nonlinearity compensation for a coherently-detected 112 Gb/s polarization multiplexed quadrature phase shifted keying transmission over a 1,600 km link (20×80 km) with no inline compensation. We report up to 80% reduction in required stages to perform nonlinear compensation, in comparison to the conventional backpropagation algorithm. This method takes into account the correlation between adjacent symbols at a given instant using a weighted-average approach to enable practical digital nonlinearity compensation.

  • 8.
    Tipsuwannakul, Ekawit
    et al.
    Dept. of Microtechnology and Nanoscience (MC2), Photonics Laboratory, Chalmers University of Technology.
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Influence of self- and cross-phase modulation on 40 Gbaud dual polarization DQPSK/D8PSK signals in 10 Gbit/s OOK WDM systems2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 23, p. 24178-24188Article in journal (Refereed)
    Abstract [en]

    This paper, for the first time, investigates the nonlinear degradation of 40 Gbaud single- and dual polarization RZ-DQPSK/D8PSK signals caused by SPM and XPM-induced crosstalk from neighboring 10 Gbit/s NRZ-OOK channels in an WDM upgrade scenario. The investigations were numerically and experimentally conducted over a 320 km transmission link with three different wavelength configurations to address the impact of the walk-off length. The paper also presents the first numerical analysis of the XPM dependence on the relative state of polarization of the D8PSK with respect to the neighbors.

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