Amr Ragheb

Performance analysis of next generation-PON (NG-PON) architectures

Next generation passive optical networks (NG-PONs) is the natural development of PONs toward achieving higher data rates, larger counts of wavelength channels, and longer fiber ranges. NG-PON can be implemented as high speed time division multiplexing (TDM), wavelength division multiplexing (WDM), Hybrid TDM/WDM, optical code division multiplexing (OCDM) PON. Many enhancements and adaptations are occurring in order to offer higher bandwidths with higher number of subscribers. This includes coverage area that is increasing to reach of 100km and more, e.g. the LR-PON. In addition, the wireless access network is gradually going to be integrated with PON systems, e.g. FiWi network. In this paper, we examine the different promising architectures for NG-PON. A comparison between key network specifications such as data rates and power budget has been reported. Moreover, we study different state-of-the-art technologies that will potentially be used for NG-PONs. We discuss the different characteristics of NG-PON showing the important contributions and challenges of various NG-PON demonstrations.

Experimental demonstration of outdoor 2.2 Tbps super-channel FSO transmission system

Free space optic (FSO) is a wireless technology that promises high speed data rate with low deployment cost. Next generation wireless networks require more bandwidth which is not supported by todays wireless techniques. FSO can be a potential candidate for last mile bottle neck in wireless network and for many other applications. In this paper, we experimentally demonstrate a high speed FSO system using super-channel source and multi-format transmitter. The FSO system was installed outdoor on the building roof over 11.5 m distance and built using off-the-shelf components. We designed a comb source capable of generating multi-subcarriers with flexible spacing. Also we designed a multi-format transmitter capable of generating different complex modulation schemes. For single carrier transmission, we were able to transmit a 23 Gbaud 16-QAM signal over FSO link, achieving 320 Gbps with 6 b/s/Hz spectral efficiency. Then using our super-channel system, 12 equal gain subcarriers are generated and modulated by a DP-16QAM signal with different symbol rates. We achieved maximum symbol rate of 23 Gbaud (i.e. 2.2 Tbps) and spectral efficiency of 7.2 b/s/Hz.

Candidate modulation schemes for next generation-passive optical networks (NG-PONs)

Various approaches have been developed for next generation passive optical networks (NG-PONs) in order to achieve higher data rates, larger counts of wavelength channels, and longer fiber ranges. Several modulation formats together with electronic based digital signal processing (DSP) implementations have been investigated in order to optimally design an access optical network. Besides increasing data rates, this new trend also plays a major role in reducing the cost and increasing the flexibility of NG-PON. In this paper, we survey the main promising modulations and DSP technologies for NG-PON. This includes modulation and optical OFDM schemes enumerate QPSK, MQAM, MSK, and multilevel based OFDM schemes. We discuss the different characteristics of these technologies showing most important contributions and challenges toward high performance cost-effective next generation access networks.

Up to 64 QAM/32 Gbaud flexible dual polarization transmitter for future elastic optical networks

Abstract. Next generation elastic optical networks will very likely require dual polarization (DP) optical transmitter with inherent flexibility to dynamically change its baud rate and/or modulation format. We develop a prototype of compact flexible DP M-ary quadrature amplitude modulation (MQAM) optical transmitter and demonstrate its reconfigurability to accommodate baud rates ranging from 8 to 32  Gbaud/s using the same hardware. The prototype has another advantage in that the modulation format can also be dynamically changed from binary phase shift keying up to 64 quadrature amplitude modulation (QAM) for single and DPs, all over a single optical carrier. This allows the generation of variable data rate up to 384-Gb/s over a single wavelength. Experimental results show that for the most challenging setting of DP-64 QAM/32 Gbaud, the worst case values of error vector magnitude and bit error rate are 6.7 and 3×10−2, respectively. For less stringent settings, i.e., lower baud rate and/or lower modulation format, forward error correction limit error free transmission is easily obtained. Further results are also reported to demonstrate transmitter flexibility and software definability, by measuring symbol streams showing instantaneous swapping between modulation schemes with a swapping time less than 10 symbols duration, i.e., 0.3 ns.

Enhanced Blind Equalization for Optical DP-QAM in Finite Precision Hardware

In this letter, we apply the inverse QR decomposition-constant modulus algorithm (IQRD-CMA), blind equalization technique, for impaired 14 GBd DP-16 quadratic-amplitude modulation optical modulated signal. The IQRD-CMA is considered here to mitigate the effect of residual chromatic dispersion (CD) and polarization mode dispersion (PMD). We evaluate the performance of the proposed inverse QR decomposition in terms of convergence rate, steady-state/residual mean square error (MSE), and bit error rate (BER), in comparison with standard blind constant modulus algorithm (CMA) and recursive least squares (RLS-CMA). Assuming infinite precision, the IQRD-CMA and RLS-CMA achieve similar performance and induce the same computational complexity; however, both largely outperform standard CMA for wide ranges of CD and PMD. However, for finite precision hardware, compared with RLS-CMA, the proposed blind IQRD-CMA clearly achieves one order of BER magnitude at 8- and 10-b resolutions, and further reduces the steady-state MSE by 3 dB. Moreover, results show that IQRD-CMA maintains the system stability at acceptable number of bits resolutions. In addition, this letter addresses the tradeoff between the complexity and the performance of all these equalizers for several precision settings.

Far L-band Single Channel High Speed Downstream Transmission using Injection-locked Quantum-dash Laser for WDM-PON

We demonstrate an externally modulated single channel 64 Gbit/s DP-QPSK transmission based on injectionlocked Fabry-Pérot broadband quantum-dash laser at far L-band ~1621 nm wavelength. A receiver sensitivity of -16.7 dBm has been observed after 10 km SMF transmission, with power penalty of ~2 dB, under the FEC threshold. We also propose that these novel quantum-dash laser diode could be a route towards next generation 100Gbit-PONs as a unified upstream and downstream transmitters.

Optimizing OSSB Generation Using Semiconductor Optical Amplifier (SOA) for 5G Millimeter Wave Switching

Millimeter waves (MMWs), operating at 30–300 GHz band, are very promising to the next-generation 5G wireless communication systems, enabling data rates of multi Gbps per user. Photonic technology is increasingly considered to play a key role in a wide range of MMW devices, modules, and subsystems that are essential to successfully build next generation MMW-based 5G networks. This work considers the switching function of MMWs exploiting nonlinearity in photonic devices. In this paper, we perform a systematic investigation of the optimum operating conditions that enable an optical single sideband wavelength conversion, by exploiting the nonlinear effects in a semiconductor optical amplifier (SOA). This principle of switching carefully exploits SOA’s four-wave mixing, cross-gain modulation in addition to self-phase modulation effects. The key parameters under investigation include the injection current, the wavelength spacing between the probe and the pump signals in addition to their respective powers. We experimentally determine the optimal operating conditions that maximize the sideband suppression ratio and simultaneously reduce the useless left sideband signal intensity, leading to a dispersion free transmission in optical fiber. Further, we experimentally demonstrate a photonic-based MMW switch of MMW signals having 30 GHz frequency and carrying 3 Gbaud/QPSK modulated signals. A 14-dB sideband suppression ratio of modulated signal is reported.

Performance investigation of CMA and RLS based equalization for next generation long reach passive optical networks

Digital coherent receivers (DCR) exploiting advanced digital signal processing (DSP) have shown major impact, in terms of increasing receiver sensitivity and spectral efficiency, on optical communication for long haul transmission. Recently coherent receivers started to be employed in metro/access networks. In this paper, we investigate the performance of DCR in next generation long reach passive optical networks (NG-LRPON). Constant modulus algorithm (CMA) and recursive least squares (RLS) equalizers are used to blindly mitigate fiber chromatic dispersion (CD) and polarization mode dispersion (PMD) for different signal speeds and modulation schemes. For low signal speed, our simulation results show that CMA achieves same steady state as RLS however with low complexity. For high baud rate signals such as 5 and 10Gbaud, RLS achieves 50% faster convergence rate in terms of number of symbols.

Inverse QR decomposition (IQRD) blind equalizer for QAM coherent optical systems

Advanced digital signal processing techniques have a vital role in the development of emerging and next generation ultrahigh speed optical networks. These techniques highly contribute to the improvement of system spectral efficiency. Blind equalizers have recently been used to compensate for linear fiber impairments. In this paper we apply the inverse QR decomposition (IQRD), algorithm for blind equalization in 14Gbaud-16QAM coherent receiver. IQRD is widely used in wireless communications and known for its inherent stability in finite precision environment. We compare its performance with the standard Constant Modulus Algorithm (CMA) and Recursive Least Squares (RLS) algorithm in terms of convergence rate (CR) and bit error rate (BER). Our simulation results show that IQRD algorithm achieves similar CR and BER performance as those of standard RLS algorithm. However, in finite precision environment, which is more appropriate for practical implementation, and results in lower system power consumption (human friendly or Green solution), IQRD completely outperforms the RLS technique. A substantial reduction in BER of two orders of magnitude at 14 bit resolution is achieved for the optical system under consideration.

Demonstration of Millimeter Wave 5G Setup Employing High-Gain Vivaldi Array

We present a 4 × 4 slot-coupled Vivaldi antenna (SCVA) array unit cell, which offers wide bandwidth and high gain (~23 dBi) at the millimeter wave (mmW) frequencies of 28 GHz and 38 GHz. A single SCVA element is first presented, which has a bandwidth of 25–40 GHz with an average gain of ~13 dBi at the frequencies of interest. This antenna element is then used to design a 1 × 4 linear SCVA array matched to a 50 Ω impedance via a modified Wilkinson power divider (WPD). Next, the 1 × 4 linear array is used to construct a 4 × 4 antenna array unit cell. The proposed 4 × 4 antenna array unit cell is fabricated, and the characteristics of its elements (i.e., the single SCVA, 1 × 4 linear array, and WPD) are thoroughly investigated. Further, the 4 × 4 array is tested for signal reception of various digital modulation formats at lab environment using high-speed digital signal oscilloscope. In particular, a 2.5 Gbps data rate is successfully transmitted achieving receiver sensitivity of −50 dBm at 2 × 10−3 bit error rate (BER) for 32 quadrature amplitude modulation (QAM) with a system baud rate of 500 MHz. The wide bandwidth and high gain along with the excellent performance of the proposed 4 × 4 antenna array unit cell makes it an excellent candidate for future 5G wireless communication applications.