High-capacity undersea long-haul systems

The present paper proposes the optimal transmission parameters for non-return-to-zero (NRZ), return-to-zero differential phase shift keying (RZ-DPSK), carrier-suppressed RZ-DPSK (CSRZ-DPSK) and duobinary (DB) modulation formats in 16-channel 10 Gbit/s wavelength division multiplexed passive optical network (WDM-PON) transmission system. The paper investigates influence of laser output power, length of dispersion compensating fiber (DCF) and application of erbium-doped fiber amplifiers (EDFA), as well as impact of optical components configuration on received signal quality. It compares demand of these modulation formats for amplification and dispersion compensation with the increase of transmission distance, determining the optimal conditions for achieving maximal network reach for each of them. It is shown, that DB is the most resistant to chromatic dispersion (CD) and is able to achieve the longest transmission distance (100 km) without dispersion compensation. Whereas RZ-DPSK and CSRZ-DPSK modulation formats demonstrated maximal achievable reach (180 km) using DCF and EDFA.

In this article optical minimum-shift keying (MSK) modulation format in 9×40 Gbit/s wavelength-division multiplexing (WDM) spacing of 100 GHz transmission systems is investigated and compared with return-to-zero differential phase-shift keying (RZ-DPSK) and return-to-zero (RZ). The performance of optical MSK in presence of amplification noise, chromatic dispersion and nonlinear effects is analytically determined. Operations over a wide range of parameters, such as span input power, precompensation value, and chromatic dispersion parameter are performed; experimental results show that optical MSK demonstrates special performance in transmission distance, nonlinear effects, and dispersion tolerance.

The authors compare analytical and numerical estimates, showing that the nonlinear phase noise of short optical pulses associated with the coupling between amplified spontaneous emission noise and fiber nonlinearity may be controlled by adjusting the duty cycle of the return-to-zero (RZ) signal modulation format. The impact of this effect in the optimization of the performance of 10-Gb/s dispersion-managed wavelength division multiplexed (WDM) systems using RZ-differential phase-shift keying (DPSK) modulation is discussed. By extensive numerical simulations, it is shown that the transmission quality of ultradense WDM systems using the RZ-DPSK modulation format may be significantly enhanced by optimizing the duty cycle of the RZ pulses.

We proposed an arrayed waveguide granting (AWG) based 10 Gbps full duplex wavelength division multiplexing passive optical network (WDM-PON) utilizing a return-to-zero differential phase shift keying (RZDPSK) modulation technique for down-link direction and then re-modulation of the downlink (DL) signal for the uplink (UL) direction using intensity modulation technique (OOK) with a data rate of 10 Gbps per channel. A successful cost effective colorless WDM-PON full duplex transmission operation for a data rate of 10 Gbps per channel, with a channel spacing of 60 GHz over a distance of 25 km without any optical amplification and dispersion compensation is achieved within low power penalty.

This paper proposes an ultra-high capacity free space optical communication (FSO) system, employing optical dual polarization quadrature phase shift keying (DP-QPSK) modulation format. It is a 16-channel dense wavelength division multiplexing (DWDM) system with 120 Gbps/channel bit rate. The FSO system is analyzed with three optical advanced modulation schemes; such as 4-quadrature amplitude modulation (4-QAM), quadrature phase shift keying (QPSK) and DP-QPSK. The main focus of the projected system is to improve the FSO setup performance in terms of eye diagram, bit error rate (BER), high received power and Q-factor. The center channel wavelength used for the proposed system is 1550 nm. In the present wireless communication world, the proposed system will be highly helpful as an ultrahigh capacity wireless system.

Wavelength division multiplexing (WDM) systems are widely deployed in high-capacity long-haul transmission systems. They can provide cost-effective additional capacity on fibers overloaded by the increase in data traffic. Current WDM systems are used mainly for point-to-point transmission links. Next generation WDM technologies are expected to provide full functionality at both the system and network levels. Next generation WDM system will require many optical components, including optical filters, add/drop multiplexers, circuit switches and wavelength converters. Optical components using planar lightwave circuits (PLCs) are now widely used in WDM systems. Arrayed waveguide gratings (AWGs), in particular, play an important role in current WDM systems. In the next generation system, optical components using PLCs are expected to provide many functions that counterparts cannot. In this paper, we will describe the current and future WDM components using PLCs, focusing on AWGs and switchable add/drop filters.

We propose and experimentally demonstrate the generation of various modulation formats using a directly modulated chirp-managed laser (CML), including phase-shaped binary transmission (PSBT), inverse-return-to-zero duobinary (IRZ-duobinary), Manchester-duobinary, return-to-zero differential phase shift keying (RZ-DPSK) and return-to-zero differential quadrature phase-shift-keying (RZ-DQPSK). The CML-based modulation formats improved dispersion tolerance and their corresponding transmitters have the features of compactness, low power consumption and cost-effectiveness, which are desired in metro/access networks. System applications of such formats are also studied.

WDM Network Issues: QOT Impairments, Dynamic Bandwidth Allocation, Modeling and Monitoring Schemes based on ML

Choice of modulation format plays a critical role in the design and performance of fiber optic communication systems. We discuss the basic physics of electro-optic phase and amplitude modulation and derive model transfer functions for ideal and non-ideal Mach-Zehnder modulators. We describe the generation and characteristics of the standard nonreturn-to-zero (NRZ) modulation format, as well as advanced formats such as return-to-zero (RZ), carrier-suppressed RZ (CSRZ), duobinary, modified duobinary, differential phase-shift keyed (DPSK), and return-to-zero DPSK (RZ-DPSK). Finally, we discuss the relative merits of these formats with respect to a variety of system impairments.KeywordsFiber opticsModulation formatsOptical communication systemModeling

Performance of linear avalanche photodiode-based balanced homodyne receiver (APD BHD) is examined and compared to reference BHD based on PIN photodiodes, in terms of common mode rejection ratio (CMRR), quantum-to-classical noise clearance (QCNR) and sensitivity in coherent reception of quadrature phase shift keying (QPSK) modulation format. NIST randomness validation was performed on sampled data for quantum random number generator (QRNG). Achieved CMRR values were 50 dB and 30 dB at 100 MHz and 1 GHz, respectively. QCNR of 20 dB at low input power of −20 dBm was demonstrated. Optical sensitivity of APD BHD coherent receiver compared to its PIN BHD counterpart can be improved by 3 dB at low local oscillator (LO) powers, whereas for high LO powers the sensitivity of APD BHD approaches the values for PIN BHD.

This paper describes the performance improvement of 10-Gb/s four-channel WDM dispersion-supported transmission systems by using broadened passband arrayed-waveguide grating demultiplexers. Multimode interference couplers are assumed to be used to broaden the passaband of these demultiplexers. Performance Improvement of 40-Gb/s Capacity Four-Channel WDM Dispersion-Supported Transmission by Using Broadened Passband Arrayed-waveguide Grating Demultiplexers Mario M. Freire Department of Mathematics and Computer Science, University of Beira Interior Rua Marques d'Avila e Bolama, P-6200 Covilha, Portugal Telephone: +351 75 3101700, Fax: +351 75 26198, E-mail: mfreire@ alpha.ubi.pt Henrique J. A. da Silva Department of Electrical Engineering, Pole II of University of Coimbra Pinhal de Marrocos, P-3030 Coimbra, Portugal Telephone: +351 39 7006248, Fax: +351 39 7006247, E-mail: hjas@ci.uc.pt Summary Integrated N×N wavelength multiplexers based on arrayed-waveguide gratings (AWG) are being developed for wavelength division multiplexing (WDM) systems and networks, since they can offer four basic functions: multiplexing, demultiplexing, add/drop multiplexing, and N×N full-interconnection [1]. The use of this technology for demultiplexing in high density WDM systems may impose very stringent requirements on the alignment of signal wavelengths and demultiplexers due to their peaked (Gaussian-like) spectral passband. However, the passband of these demultiplexers may be broadened by the use of multimode interference couplers (MMI), as proposed and demonstrated in [2]. In this paper, we describe the performance improvement due to the use of broadened passband AWG demultiplexers in 40-Gb/s capacity four-channel WDM dispersion-supported transmission (DST) systems with 0.5 nm channel spacing. The block diagram of the simulated 10-Gb/s four-channel WDM-DST system is shown in Fig. 1. The system model is broadly similar to the one reported in [3] and includes a rate equation model for quantum-well lasers, and the frequency responses of a PIN photodiode and of a standard singlemode fiber (SMF) with chromatic dispersion of 17 ps/(nm.km) at 1532 nm. The frequency response of the AWG filter is assumed to be Gaussian and the frequency response of the broadened passband AWG filter is modeled by the double Gaussian approximation [2] with r = 2 , which is the ratio between the peak separation and the FWHM of each simple Gaussian profile. The optical amplifiers (EDFAs) have been considered as linear with a noise figure of 6 dB and an equivalent noise bandwidth of 1 THz. A RC lowpass filter was used to provide the 3-dB bandwidth required by the DST method [4]. The receiver sensitivity was estimated taking into account the signal-ASE and ASE-ASE beat noises, the thermal and shot noises, as well as the contribution due to frequency-to-intensity conversion of laser phase noise after propagation via dispersive fibers [5]. Fig. 2 shows the receiver sensitivity for channel 2 versus fiber length for single-channel DST, without optical filters, and for four-channel WDM-DST using an arrayed-waveguide grating demultiplexer with (BP-AWG) and without (AWG) broadened passband. For comparison purposes, the receiver sensitivity of four-channel WDM-DST using a three-mirror Fabry-Perot demultiplexer (TMF) is also shown. For distances larger than 80 km, the performance of four-channel WDM-DST systems using three-mirror Fabry-Perot demultiplexers is close to the performance of single-channel DST systems without optical filters. Compared with the performance of single-channel DST without optical filters, the use of conventional arrayed-waveguide grating filters as demultiplexers in four-channel WDMDST degrades the system performance at least 0.6 dB for link lengths larger than 11 km. However, the use of broadened passband AWG demultiplexers instead of the conventional AWG demultiplexers improves the performance of the four-channel WDM-DST system at least 1.5 dB, for link lengths larger than 11 km (see Fig. 2). Detailed BER characteristics for channel 2 are displayed in Fig. 3 for four-channel WDM-DST via 204 and 253 km SMF. For the 204 km transmission simulation, sensitivities of -23.886, -23.169 and -24.827 dBm have been estimated for TMF, AWG and BP-AWG demultiplexers, respectively. The BER curves for 253 km clearly indicate an error floor due to laser phase noise. In conclusion, the use of broadened passband AWG demultiplexers improves the performance of four-channel WDM-DST systems with 0.5 nm channel spacing, while conventional AWG demultiplexers are less suitable to operate at this channel spacing.

Along with the emergence and maturity of 100Gbit/s technologies, numbers of trial and commercial 100Gbit/s Wavelength Division Multiplexing (WDM) systems have been established worldwide. The research-oriented lab tests of 100Gbit/s WDM systems were done by China Unicom in 2012. The 100Gbit/s technologies of polarization multiplex-quadrature phase shift keying with coherent detection from multiple vendors have been studied. There are some further issues to be specified before the commercial application of 100Gbit/s WDM system is implemented in large scale in backbone network, including optical performance parameters, optical performance monitoring of 100Gbit/s system, protection mechanism, selection of client interface and comprehensive Operation, Administration and Maintenance (OAM).

This paper is demonstrating the simulative comparisons and investigation of free-space optical fiber optic (FSO/FO) hybrid link under the effects of clear sky, haze and light rain weather conditions by using phase shift keying (PSK) modulation format with a data rate 40 GB/s at 1550 nm wavelength. An optical amplifier with 40 dB gain is placed before the FSO transmitter to boost the amplitude of a weak signal. A combination of multiple FSO transmitters, erbium-doped fiber (EDF) 3 m and bidirectional dispersion compensating fiber (DCF) 3.2 km are employed to overcome the effect of attenuation in the propagating channel. The performance of the system is evaluated in terms of BER, SNR, Q factor and eye diagrams. It has been observed that the performance of dual-channel hybrid FSO/FO is very robust as compared to conventional FSO/FO systems. While the communication distance with the hybrid link is escalated up to 54 km, 11 km and 5.5 km in a clear sky, haze and light rain climate conditions correspondingly. The satisfying values of BER have been observed as 10−14, 10−11, and 10−13 for clear, haze and light rain weather conditions, respectively.

This paper compares the efficiency of on-off Keying (OOK) modulation formats non-return-to-zero (NRZ) and return-to-zero (RZ) in both electrical and optical chromatic dispersion compensation. While In electrical compensator feed forward-decision feedback equalizer (FFE-DFE) method was applied, Dispersion Compensation Fiber (DCF) was chosen to evaluate the effect of modulation format on them. Transmission distance, subsequently are varied in both systems with mentioned compensation systems to evaluate the Bit Error Rate (BER) regarding to mentioned modulation techniques.

Experimental demonstration of underwater wireless optical OFDM communication system with a single SPAD receiver