Abir Hraghi

Optimization of Optical Flat Comb Source based on Dual-Arm Mach-Zehnder modulator for flexgrid terabit superchannel WDM-Nyquist systems

In this paper, we investigate the generation of ultra-flat Optical Flat Comb Source (OFCS) using an asymmetrically driven Dual Arm Mach-Zehnder modulator (DA-MZM). A modified simulated annealing-based optimization method is applied to derive the necessary ranges for which the comb source is ultra-flat (less than 1 dB ripple) over 2, 4, 8, 16 and 32 carriers where the driving signals are well within the nominal operational range of a typical LiNbO3 MZM, and an acceptable output optical power is reached.

Automatic modulation format recognition for the next generation optical communication networks using artificial neural networks

A new technique for Automatic Modulation Format Recognition (AMFR) in next generation optical communication networks is presented. This technique uses the Artificial Neural Network (ANN) in conjunction with the features of Linear Optical Sampling (LOS) of the detected signal at high bit rates using direct detection or coherent detection. The use of LOS method for this purpose mainly driven by the increase of bit rates which enables the measurement of eye diagrams. The efficiency of this technique is demonstrated under different transmission impairments such as chromatic dispersion (CD) in the range of -500 to 500 ps/nm, differential group delay (DGD) in the range of 0-15 ps and the optical signal tonoise ratio (OSNR) in the range of 10-30 dB. The results of numerical simulation for various modulation formats demonstrate successful recognition from a known bit rates with a higher estimation accuracy, which exceeds 99.8%.

One Tbps superchannel generated by Optical Flat Comb Source WDM-Nyquist and OFDM system simulative investigation

In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using WDM-Nyquist and OFDM approaches with new flex-grid channel spacing. The new flex-grid defines WDM channel spacing having a multiple of 12.5 GHz. We compare through simulation the performance of two techniques for generating Dual Polarization-Quadrature Amplitude Modulation based on 16 (DP-16QAM), 64 (DP-64QAM) and 128 (DP-128QAM). We first study the performance of WDM-Nyquist and OFDM super-channels implementing DP- 16QAM, DP-64QAM and DP-128QAM in back-to-back scenarios in terms of receiver sensitivity and Optical Signal-to- Noise Ratio (OSNR) requirement with 12.5 GHz flex-grid spacing. We find that DP-16QAM has the best receiver sensitivity and the lower OSNR penalty compared to the other modulation formats in WDM-Nyquist system. With DP- 128QAM sensitivity as reference, we can observe a benefit of 10 dB for DP-16QAM with a BER equal to 3.8 10-3. In addition, we can observe a benefit of 12.4 dB in OSNR for DP-16QAM compared to DP-128QAM for a BER equal to 3.8 10-3. Also, we study the impact of the optical and electrical shaping filters. Finally, we investigate the performance of WDM-Nyquist and OFDM terabit system with 12.5 GHz flex-grid spacing over long-haul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that DP-16QAM is the suitable modulation format in dispersion compensated WDM-Nyquist systems using SSMF fiber. In addition, we prove that the use of Raman amplification improve the maximum reach of the super-channel by increasing the span distance between the amplifier module. Indeed, using the Raman amplification the maximum reach increase from 812 km to 955 km in a WDM-Nyquist system based on DP-16QAM with 12.5 GHz flex-grid spacing.

Transmission impairments study of 160 Gb/s generated thought a flat comb source

In this paper, we investigate an optical multicarrier source to achieve 160 Gb/s by wavelength using Polarization Multiplexing-Differential Quadrature Phase Shift Keying (POLMUX-DQPSK) and Dual Carrier-Differential Quadrature Phase Shift Keying (DC-DQPSK) with 33RZ (Return-to-Zero) pulse carving and coherent detection. The optical multicarrier source is generated by the means of a Dual-arm Mach-Zehnder Modulator (MZM) fed by a sinusoidal signal in order to generate an Optical Flat Comb Source (OFCS) spaced by the driven sinusoidal frequency. We compare the performance of the both configurations to the conventional single polarization 33RZ-DQPSK and Non-Return-to-Zero-On Off Keying (NRZ-OOK). We discuss their back-to-back receiver sensitivity and required Optical-to-Noise Signal Ratio (OSNR) for 10-9 Bit Error Rate (BER). We find, in back-to-back configuration, that 33RZ-POLMUX-DQPSK has the best receiver sensitivity and the least penalized format in terms of OSNR. We study also the robustness of these optical modulation formats against the optical fibre impairment. We find that 33RZ-DC-DQPSK has the best behaviour.

A performance comparison between 33RZ-POMUX-DQPSK and 33RZ-DC-DQPSK using coherent detection for 1.6 Tb/s (16×100 Gb/s) over 1200 km

In this paper, we compare the performance of Polarization Multiplexing-Differential Quadrature Phase Shift Keying (POLMUX-DQPSK) and Dual Carrier-Differential Quadrature Phase Shift Keying (DC-DQPSK) with RZ (Return-to- Zero) carving and duty cycle of 33% in 100 Gb/s transmission systems. These formats appear to be the most promising technology for long-haul with coherent detection. POLMUX-DQPSK use the polarization dimension of the optical signal to transmit the information. DC-DQPSK uses two wavelengths to transmit the information. We discuss their back-toback receiver sensitivity and required Optical-to-Noise Signal Ratio (OSNR) for a Bit Error Rate (BER) equal to 10-9. We find that 33RZ-POLMUX-DQPSK has the best receiver sensitivity and lower OSNR penalty compared to 33RZ-DCDQPSK. For 33RZ-POLMUX-DQPSK sensitivity as reference, we can observe a benefit of 1.5 dB for 33RZ-DCDQPSK. Also, we can observe a benefit of 2.3 dB in OSNR for 33RZ-POLMUX-DQPSK compared to 33RZ-DCDQPSK. We study the robustness of these two optical modulation formats for transmission of 1.6 Tb/s (16×100 Gb/s) over 1200 km in dispersion compensated Wavelength Division Multiplexing (WDM) systems with 100 GHz channel spacing using two types of fibers Standard Single Mode Fiber (SSMF) and Non-Zero Dispersion Shifted Fiber (NZDSF). We find that 33RZ-DC-DQPSK is a suitable modulation formats in dispersion compensated WDM systems with 100 Gb/s channel spacing using NZDSF fiber. We simulate the nonlinear tolerance of optical 33RZ-POLMUX-DQPSK and 33RZ-DC-DQPSK formats. 33RZ-DC-DQPSK modulation format has the best robustness against the nonlinear fiber effects in NZDSF fiber.

Polarization mode dispersion monitoring in the presence of XPM effect for high speed WDM communication systems

WDM optical systems and nonlinear effects are experiencing last years a huge investigation for performance evaluation. In this paper, and for high speed phase modulated WDM Nyquist systems, a novel method of PMD and first-order PMD (DGD) monitoring using cross phase modulation effect is presented. This technique demonstrate that in the presence of XPM effect, the states of polarization changes and the group-velocity mismatch operates effectively to evaluate the performance of the proposed method. The results are extended to show the output power variation when the number of WDM channels increase for a giving DGD values.

Comb source generation by dual-tone excitation of a dual-arm MZM

A novel way to generate asymmetric optical comb sources is presented. Optical comb sources are an essential component of Terabit orthogonal frequency-division multiplexing (OFDM) and wavelength division multiplexing-Nyquist (WDM-Nyquist) systems. Each arm of the modulator is excited with the linear combination of two sine waves. An asymmetric output spectrum characterized by a flat region, where spectral ripple less than 1dB and which width ranges from 4 to 32 sub-carriers. The simulated annealing optimization algorithm was used to speed up the search for the aforementioned flat regions. The search results for the entire possibility space are interpolated.

Robust modulation formats recognition technique using wavelet transform for high speed optical networks

There is a need, for high speed optical communication networks, in the monitoring process, to determine the modulation format type of a received signal. In this paper, we present a new achievement of modulation format recognition technique, where we proposed the use of wavelet transform of the detected signal in conjunction with the artificial neural network (ANN) algorithm. Besides, wavelet transform is one of the most popular candidates of the time-frequency transformations, where the wavelets are generated from a basic wavelet function by dilations and translations. We proved that this technique is capable of recognizing the multi-carriers modulation scheme with high accuracy under different transmission impairments such as chromatic dispersion (CD), differential group delay (DGD) and accumulated amplified spontaneous emission (ASE) noise with different ranges. Both the theoretical analysis and the simulation results showed that the wavelet transform not only can be used for modulation identification of optical communication signals, but also has a better classification accuracies under appropriate OSNR (optical signal-to-noise ratio) values.

Investigation of receiver contraints on the transmission performance of 1 Tbps WDM-Nyquist and CO-OFDM signals

In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using Wavelength Division Multiplexing-Nyquist (WDM-Nyquist) and Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) approaches with 12.5 GHz channel spacing. We evaluate through simulation the performance of the two techniques for generating Dual Polarization Quadrature-Amplitude Modulation based on 16 (DP-16QAM). We first study the robustness of CO-OFDM system to the receiver constraints such as Analog-to-Digital Converters (ADCs) speed and the receiver bandwidth in Back-to-Back link (Optical Signal-to- Noise Ratio (OSNR)) and over longhaul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that CO-OFDM requires 6 Samples per Symbol (SpS) with a large receiver bandwidth (2.25× Baud rate) to achieve the same performance of WDM-Nyquist system in terms of SNR. However, the CO-OFDM system needs more than 6 SpS to achieve the same distances as WDM-Nyquist. We also study the impact of the input power level in terms of OSNR for CO-OFDM and WDM-Nyquist systems in order to evaluate the robustness of both systems to the nonlinear effects.

A performance evaluation of WDM-Nyquist systems generated by optical flat comb source and based on POLMUX-QPSK, POLMUX-DQPSK, POLMUX-16QAM and POLMUX-64QAM

In this paper, we implement a WDM-Nyquist transmission system with 12.5 GHz channel spacing generated through an Optical Flat Comb Source (OFCS). Each channel could carry one of four different modulation format as Polarization Multiplexing-Quadrature Phase Shift Keying (POLMUX-QPSK), Polarization Multiplexing-Differential Quadrature Phase Shift Keying (POLMUX-DQPSK), Polarization Multiplexing-Quadrature Amplitude Modulation based on 16 (POLMUX-16QAM) and 64 (POLMUX-64QAM) with Return-to-Zero (RZ) pulse carving and 33% duty cycle. Numerical simulations of 1 Tbit/s superchannel have been carried out, in order to evaluate the performances of the different modulation format using appropriate metrics. We discuss their back-to-back receiver sensitivity and the required Optical-to-Noise Signal Ratio (OSNR) for 3.8•10-3 and 10-9 Bit Error Rate (BER). We find that POLMUXQPSK has the best receiver sensitivity and the lower OSNR penalty compared to the other modulation formats. With POLMUX-QPSK sensitivity as reference, we can observe a power penalty of 13.4 dB (for a BER equal to 3.8•10-3) for POLMUX-64QAM. In addition, we can observe an OSNR penalty of 21 dB in OSNR for POLMUX-64QAM compared to POLMUX-QPSK modulation format for a BER equal to 3.8•10-3. However, it is important to mention that POLMUX- 64QAM presents higher Spectral Efficiency (SE). We study also the robustness of these four optical modulation formats for transmission of 1 Tbit/s in dispersion compensated WDM-Nyquist systems using two kinds of transmission fibers: SMF (Single Mode Fiber) and NZDSF (Non-Zero Dispersion Shifted Fiber). We find that POLMUX-QPSK is the suitable modulation format in dispersion compensated WDM-Nyquist systems using NZDSF fiber. We simulate the nonlinear effect tolerance by considering self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM) for the different modulation format. We observe that POLMUX-QPSK has the best robustness against the cited nonlinear fiber effects in NZDSF fiber.