Dense Wavelength Division Multiplexing Transmission System Research Articles

Design and implementation of DP-DQPSK DWDM transmission system by using direct detection

Designing a system that guarantees both the lower cost implantation, lower complexity on the receiver station side and higher data rate was an essential topic for several researchers recently, in which several methods and approaches were proposed to handle these problems individually and with the best overall outcome. In this work, these problems would be considered by designing and analyzing a novel system based on the combination of Dual Polarization Differential Quadrature Phase Shift Keying (DP-DQPSK) and Dense Wavelength Division Multiplexing (DWDM) technique and by using the Direct Detection (DD) technique. The system was designed with Optisystem software 18 and consist of 64 channels and each channel could transmit 14 Gbps of data rate. The channels 1,6,12,18,24,30,36,42,48,54,60 and 64 were selected as samples among all channels to be investigated and analyzed. Additionally, the proposed system was investigated based on different distances and different parameters of Quality Factor (QF) and Bit Error Rate (BER). The significant contribution of the proposed system is that using the DD would result in a no-required for reference wave and that will result in a less complex system and easier to implement. Results obtained indicate higher quality QF for the sampled channel and lower BER values. For instance, the average QF obtained were in the range of 6.75-8.36 dBm and 6.77-8.35 dBm for data 1 and 2 respectively, which indicates the reliability and efficiency of the proposed system by considering all results obtained from distance variation were above the minimum threshold

Decreasing base units-unequally spaced channel allocation algorithm for dense wavelength division multiplexed transmission systems

We propose an unequally spaced channel allocation algorithm, i.e., decreasing base units-unequally spaced (DBU-US) algorithm tested for high-capacity dense wavelength division multiplexed (DWDM) transmission systems. The new scheme decides upon the number of base units (BUs) covering the entire bandwidth and the allocation of different number of channels in the BUs. Starting from BUi = 0, the number of channels in each subsequent BU(BUi = 1 , 2 , 3 ) reduces by a factor of 2, “i” being the index of the BUs. The BUi , BUi + 1 , … have even and odd slot frequency allocations, which creates a substantial degree of unequal channel spacing, which virtually proves to reduce the four wave mixing (FWM) products effectively for any number of transmitted channels. When compared with existing unequal channel allocation schemes of unequally spaced repeated unequally spaced (URUS), alternately paired URUS (APRUS), a reduction of 6.25% and 13.7% in bandwidth is observed, respectively. Similarly, a reduction of FWM products by 45.5%, 41.3%, and 31.7% is observed, when compared with URUS, paired URUS, and APRUS, respectively. The FWM intensities generated by DBU-US are reported to be 5 dBm lesser when compared to widely accepted URUS scheme. Therefore, it is concluded that DBU-US is superior and is considered suitable for DWDM transmission systems.

Design of a Hybrid Optical amplifier for 64 DWDM Channels network by using EDFA and Raman Amplifier

In this paper a hybrid amplifier EDFA-RAMAN DWDM transmission system is proposed and demonstrated. A new hybrid two-stage optical fiber amplifier for dense wavelength division multiplexing (DWDM) network is observed. The hybrid amplifier is cascaded erbium- doped fiber amplifiers (EDFA) & Raman amplifier which provide a nearly flat gain over 80 nm. The hybrid amplifier has been modeled using an Optic-System version 14 on a DWDM transmission. In this paper we compare Q-factor at different input power i.e. at 0db and at 10 db. Here two different types of apodized function (Uniform & Gaussian) are selected as fiber Bragg grating parameters and system performance is analyzed. Performance of the system is analyzed by using BER analyzer.

Evaluating the Impact of QAM Constellation Subset Selection on the Achievable Information Rates of Multidimensional Formats in Fully Loaded Systems

An efficient procedure is presented for evaluating the performance of multidimensional modulation formats in terms of the achievable information rate (AIR). It allows the explicit properties of signal constellations to be captured and is applicable to fully loaded dense wavelength-division multiplexed transmission systems. The efficiency of the procedure facilitates formulating multidimensional quadrature amplitude modulation (QAM) constellation subset selection as a combinatorial optimization problem. The attained solutions for the quadrature phase shift keying (QPSK) 8D constellation subset selection suggest that a known 8D power and polarization balanced constellation (PPB constellation, 4 bits/8D symbol) and its different variations are the closest 8D QPSK subsets to the Shannon limit at 4 bits/8D symbol. 8D constellation subset selection of a QPSK constellation at 6 bits/8D symbol allows obtaining an 8D polarization balanced version of polarization-switched QPSK (PB-PS-QPSK). Using the proposed procedure, the performance of these constellations and their nonpolarization balanced counter parts, i.e., dual polarization binary phase shift keying (DP-BPSK) and PS-QPSK, is assessed in terms of the estimated AIR. The results exhibit good agreement with those of full system simulations for a single channel and five channels. Moreover, the impact of QAM constellation subset selection on the system performance is evaluated by comparing the reduction in information rate for a symbol rate of 35 Gbaud as a function of the number of channels. For 41 channels, the PPB constellation outperforms DP-BPSK by 2 Gb/s in information rate for a 12,000 km dispersion-managed (DM) link due to the improved linear and nonlinear constellation properties. Finally, PB-PS-QPSK enables an increase of 1.5 Gb/s in information rate compared to PS-QPSK for a 10,000 km DM link.

Investigation of Dispersion and Performance Based on Ring Cavity by Birefringent Interleaver for DWDM Transmission Systems

We theoretically investigate a 25 GHz multichannel filter based on ring cavity birefringent optical interleaver for dense wavelength division multiplexing (DWDM) transmission systems. The simulation tool used in this work is the Advanced System Analysis Program (ASAP) optical modeling software. We improve the dispersion performance by employingλ/6 andλ/4 wave plates as birefringent compensators for interleavers. The new structure exhibits a high performance with nearly zero ripple, a channel isolation greater than 102 dB, and a passband utilization of 86% within the C-band. The research results illustrate that our modified scheme can improve the dispersion of more than 76.6% in comparison with the previous studies of optical interleaver with birefringent crystal and ring cavity structures.

High raman gain of dispersion compensation fiber using RZ‐DPSK format for long‐haul DWDM transmission system

AbstractWe investigated the transport of a 16 channels 40 Gb/s dense wavelength division multiplexing (DWDM) system which uses high Raman gain of dispersion compensation fiber (DCF) for long‐haul DWDM transmission. Using the return to zero differential phase shift keying (RZ‐DPSK) modulation format with an optimized dispersion compensation format, we demonstrate DWDM transmission with a capacity of 640 Gb/s with 0.4 nm channel spacing over 4500 km of transmission fiber. The transmission system structure uses 120 km single mode fiber and 30 km DCF for thirty spans in the C band wavelength range and a Raman Amplifier with high Raman gain to achieve long‐haul transmission. We also used enhanced forward error correction for high capacity transmission over several thousand kilometers with the RZ‐DPSK modulation format. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2548–2551, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25552

Impact of fibre nonlinearities in optical DWDM transmission systems at different data rates

The impact of major fibre nonlinearities, like stimulated Raman scattering (SRS) and four wave mixing (FWM), in cascaded amplifier dense wavelength division multiplexing (DWDM) transmission system, has been studied at different data rates. SRS has been calculated considering pulse walk off effect. Analysis has been carried out to evaluate signal to noise ratio (SNR) considering the combined effect of SRS and FWM in the presence of amplified spontaneous emission (ASE) noise to achieve minimum noise at different data rates.

Employing a Novel Series Optical Carrier Suppressed and Separation Technology in DWDM Transmission System

In this paper, we propose and demonstrate a novel type for Serial Optical Carrier Suppressed and Separation (SOCSS) structure in Dense Wavelength Division Multiplexing (DWDM) transmission system. The proposed SOCSS technology in DWDM transmission system, the laser source of transmitter using SOCSS technology that the original 20 laser sources to spread 80 channels Dense Wavelength Division Multiplexing (DWDM) wavelength and channel spacing 0.4 nm. The proposed 80 channels of SOCSS technology that power flatness ±0.38 dB and using Single-mode Fiber (SMF) and Reverse Dispersion Fiber (RDF) for transmission scheme, combined Raman Amplifier (RA) in C and L band wavelength ranges. The proposed SOCSS technology in 80×10 Gbit/s DWDM scheme using Non-return to Zero (NRZ) modulation to transmission 20 spans total 1540-km long―haul length which can maintain Q factor should be greater than 6 dB excellent transmission performance.

Investigations on the Effects of Limiting Factors in Optical DWDM Transmission Systems

The current generation of light wave systems benefit from increased transmission distance by using optical amplification and increased capacity by using dense wavelength division multiplexing (DWDM) technology. The reach of present systems is limited by the noise contributed by the used amplifiers, combined with nonlinear effects from transmission. The nature and extent of degradations in the optical DWDM systems due to these limiting factors have been discussed in this paper. Methods to minimize the degradations due to these factors have been proposed.

A Novel Dispersion-Free Interleaver for Bidirectional DWDM Transmission Systems

We propose a novel dispersion-free interleaver using optical delay lines by accurately locating the zeros in the transfer function. It has been implemented with the design of interleaver pairs with the same amplitude responses but opposite phase responses for bidirectional dense wavelength-division multiplexed (DWDM) transmission systems. The measured results are consistent with device simulation. We have further modified the original three-port design using unidirectional amplification, and a fourport interleaver has been built and demonstrated to achieve bidirectional DWDM transmission. In this paper, we fully studied and verified the applications of our four-port interleavers in bidirectional transmission. We demonstrated a bidirectional strain-line system over 210 km and a recirculating loop transmission over a 500-km standard single-mode fiber using 10-Gb/s on-off keying signals. Furthermore, we also demonstrated return-to-zero differential phase-shift keying (DPSK) and nonreturn-to-zero DPSK modulation formats for more than 230 km of transmission. For comparison, the different amplification functions, such as the erbium-doped fiber amplifier and the semiconductor optical amplifier, have also been probed in this paper. The experimental results have clearly illustrated the desirable functions of this novel bidirectional amplifier in this dispersion-free interleaver.

Efficient Transmission Scheme for AWG-Based DWDM Millimeter-Wave Fiber-Radio Systems

We propose and demonstrate an upstream transmission scheme using a semiconductor optical amplifier (SOA) for arrayed waveguide grating (AWG)-based dense wavelength-division-multiplexed (DWDM) millimeter-wave fiber-radio systems and show improved link performance. In our scheme, unused optical carriers from the cyclic AWG in the downlink (DL) are tapped for uplink (UL) transmission. An SOA in conjunction with the AWG simultaneously amplifies the DL RF subcarriers and UL optical carrier, thus improving carrier-to-sideband ratio in the DL while also yielding an improved power budget for the UL. Our experimental results show that the proposed scheme can be a practical solution for future bidirectional wavelength interleaved DWDM transmission systems

Investigation of chirped return-to-zero differential phase-shift keying (DPSK) modulation format and its performance comparison with return-to-zero DPSK in <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>40</mn><mo>×</mo><mn>40</mn></mrow></math></inline-formula>-Gbit/s dense wavelength-division multiplexing transmission systems

Chirped return-to-zero differential phase-shift keying (CRZ-DPSK) modulation format under different channel spacings is investigated and compared with RZ-DPSK in 40×40-Gbit/s dense wavelength-division multiplexing transmission systems. An optimization operation over a wide range of parameters, such as span input power, precompensation percent, and chirp parameter (only for CRZ-DPSK), is performed in the simulation. Simulation results show that CRZ-DPSK demonstrates better performance in transmission distance, nonlinear, and dispersion tolerance with wider channel spacing of 100 GHz. When the channel spacing is reduced to 75 GHz, a slight degradation is observed for CRZ-DPSK and the performances of both formats are acceptable. But when it is reduced from 75 GHz to 50 GHz, a clear degradation of the CRZ-DPSK performance is measured, but RZ-DPSK demonstrates no significant degradation.

Theoretical and experimental analysis of the effect of stimulated Raman scattering on pilot-tone detection technique in dense wavelength-division multiplexing transmission system

A math model that can describe the effect of stimulated Raman scattering (SRS) on a pilot-tone detection technique is developed. Through numerical simulation, it is shown that the effect of SRS could produce ghost tones. The power of the ghost tone is larger for the channels separated farther from the real tone. The experiment results show that this model can evaluate the effect accurately. The power ratio between real tone and ghost tone increases linearly with the increase of transmission length when wavelengths transmit longer than 300 km.

Merits of low-density WDM line systems for long-haul networks

Conventional wisdom claims that the higher the number of wavelengths supported by a dense wavelength-division multiplexing transmission system's line system the better, since the high costs of amplifiers are split among more revenue-generating entities. For example, a 20/spl lambda/ link must cost less than 25% of the cost of an 80/spl lambda/ link to compete at full (80/spl lambda/) fill, assuming four 20/spl lambda/ links need to be deployed in parallel. We show that this is not necessarily the case if network considerations and technology evolution are taken into account. In particular, we show that a 20/spl lambda/ link can cost as high as 64-79% of the cost of an 80/spl lambda/ link and still be competitive at full fill, while providing much lower initial cost. This is because of the cost reduction of technology over time, economic considerations (net present value), nonuniform capacity needs in real networks, and how network maintenance can be achieved. We also reason why such lower end systems can indeed achieve the required cost reduction.

Analytical model for the performance evaluation of DWDM transmission systems

We present a novel analytical model to assess the signal quality in nonlinear dense wavelength-division-multiplexed (DWDM) transmission. The nonlinear impairment dependence on various system parameters is reported. The good agreement with numerical simulations indicates that the proposed model can be of significant value in the search for optimized DWDM systems.

Optimized filtering for 40-gb/s/ch-based DWDM transmission systems over standard single-mode fiber

We show that the optimized optical filtering at the transmitter and receiver side is the key technology for the achievement of higher spectral efficiencies in 40-Gb/s-based dense wavelength-division-multiplexing (DWDM) systems. Through the improved filtering, the spectral efficiency of 0.8 b/s/Hz can be realized in DWDM systems independently on the used modulation format.

A study on the relationship between DWDM transmission performance and chromatic dispersion

In this letter, we numerically study the relationship between 40-Gb/s-based dense wavelength-division-multiplexing (DWDM) transmission performance and chromatic dispersion in two different transmission lines. We show that the optimum chromatic dispersion region for improving the DWDM transmission performance varies with the type of transmission line. We also show that a hybrid transmission line has a greater potential to resist any change in the dispersion slope compensation characteristics than a single fiber transmission line with a dispersion compensation fiber module. Finally, we show that chromatic dispersion of more than 12 ps/nm/km in a hybrid transmission line is optimum for a 40-Gb/s-based DWDM transmission system by taking the design of a dispersion compensating fiber into account.