Equal Channel Spacing Research Articles

Unequal channel spacing 8×5Gbps optical system utilizing different signal representations.

Data representations are important to communication networks; they convert the data bits into a signal form, which affects the system capacity, maximum bit rate, transmission distance, and different linear and nonlinear impairments. In this paper, we propose non-return-to-zero (NRZ), chirped NRZ, duobinary, and duobinary return-to-zero (DRZ) data representations with eight dense wavelength division multiplexing channels for transmitting a 5Gbps data rate through a 250km fiber length. The results of the simulation design are calculated at different equal and unequal channel spacings, and the quality factor is measured over a wide range of optical power. For equal channel spacing, the DRZ has a preferable performance with a 28.40 quality factor at 18dBm threshold power, and the chirped NRZ has a preferable performance with a 26.06 quality factor at 12dBm threshold power. For unequal channel spacing, the DRZ has a 25.76 quality factor at 17dBm threshold power, and the NRZ has a 25.06 quality factor at 10dBm threshold power.

FWM crosstalk reduction and performance investigation of SC-DWDM system employing ML techniques

This article presents a comprehensive approach towards mitigation of four-wave mixing (FWM) induced crosstalk for a super-combined dense wavelength division multiplexing (SC-DWDM) system with in-line erbium-ytterbium doped fiber amplifier (EYDFA) + Raman hybrid optical amplifier (HOA). The performance of modified duo-binary return to zero (MDRZ) and differential phase-shift keying (DPSK) modulation formats employed on alternate channels of the 40-channel system have been compared considering equal (ECSA) and unequal channel spacing allocation (UECSA) schemes at a data rate of 40 Gbps. In the case of the UECSA scheme, the DPSK modulated channels have shown a reduction of FWM crosstalk components and intensities of up to 80% and 40 dB, respectively at a low bit error rate (BER) of 2.5 × 10−14. Different artificial neural network (ANN) techniques have been compared for gain spectrum estimation of HOA has been carried out based on input features of channel spacing, the number of channels and wavelength. Levenberg-Marquardt's (LM) model proves to be the best fit as compared to other ANN techniques. The k-nearest neighbours (KNN), support vector machine (SVM) and decision tree (DT) algorithms have been applied for the estimation of impairments based on root mean square error (RMSE) and coefficient of determination (R2) values as performance metrics. The best-performing model results applying an ANN approach with predicted R2 values of quality - factor (Q-factor) and noise figure (NF) of 0.74 and 0.56, respectively.

FSO Communication: Benefits, Challenges and Its Analysis in DWDM Communication System

Free-space optical (FSO) communication is one of the choice of researchers for most of the bandwidth hungry applications in evolving networks where the deployment of optical fiber is not directly possible as a transmission medium. In this research article, benefits, challenges, applications and role of FSO is discussed in detail for evolving networks. Further, performance of FSO communication system is tested using four channels of dense wavelength division multiplexing (DWDM). Various simulations are performed on FSO including different weather conditions, that directly affect the link performance. Many important parameters such as distance, data rate, bit error rate, amplifier gain, transmitter power, and attenuation under different weather conditions are tested in this research work. The operation of FSO communication system is carried out in the range 760-850 nm where equal channel spacing is considered for the working of DWDM communication system. Moreover, a fair comparison of proposed system is also presented for its operation in two more bands i.e. C and L-band, to show which one offers better performance. Simulation are performed in licensed version of Optisystem 14.0 and MATLAB. For the analysis of proposed system, results are presented in the form of BER and Q-factor plots.

Performance Evaluation of DPSK System with Different Combination of Hybrid Optical Amplifiers by Using Equal and Unequal Channel Spacing

AbstractThis article investigates the performance of differential phase shift key system with different hybrid optical amplifiers with equal and unequal channel spacing. The differential phase shift key signals are transmitted with equal channel spacing of 0.1 THz and unequal channel spacing of 0.05, 0.075, 0.1 and 0.15 THz at 96×20 Gbps bit rate. The maximum transmission distance of 230 km is achieved with unequal channel spacing. It is observed that the interference between adjacent channels decreases due to unequal channel spacing and gives better results than equal channel spacing in terms of bit error rate and quality factor. It is found that the maximum distance of 220 km is achieved with equal channel spacing using Raman-erbium-doped fiber amplifier hybrid amplifier.

Performance Analysis of Hybrid PON (WDM-TDM) with Equal and Unequal Channel Spacing

AbstractIn this hybrid WDM-TDM PON has been evaluated and compared the downstream wavelengths with equal and unequal channel spacing at 5 Gbit/s per wavelength in the scenario of triple play services with 128 optical network units (ONUs). The triple play services: data, voice and video signals are transmitted up to 50 km distance having Q factor of 6.68 and BER of 3.64e-012 with unequal channel spacing and 45 km distance having Q factor of 6.33 and BER of 2.40e-011 with equal channel spacing in downstream direction. It has been observed that downstream wavelengths with unequal channel spacing provide better results than equal channel spacing.

Performance Comparison of 8x10Gbps WDM System Using RZ and NRZ Format

In this paper, the performance analysis of 8X10 Gbps WDM system for different data formats has been done. The performance is analyzed for Non return-to-zero (NRZ) and Return-to-Zero (RZ) modulation formats to find maximum transmission distance for 80Gbps WDM system. It has been found that for NRZ the system travel transmission distance of 962 km and for RZ the system travel transmission distance of 1203 km. The total of eight channels with data rate of 10Gbps and equal channel spacing of 300 GHZ has been taken.

Investigation on four wave mixing effect in various optical Fibers for different spectral efficient orthogonal modulation Formats

The paper analyzes the four wave mixing (FWM) effect in different spectral efficient orthognal modulation formats at equal channel spacing of 100GHz and 50GHz to design long haul wavelength division multiplexing (WDM) optical system. Further, the comparison of reduction of FWM for existing and proposed modulation format have been analyzed by varying the laser input power from −10dBm to 10dBm.

Enhancing performance of multiwavelength Brillouin-Raman fiber laser by capturing residual pump power.

We demonstrate a simple design to enhance the performance of a multiwavelength Brillouin-Raman fiber laser by capturing the residual Raman pump power (RPP) from the laser cavity using a wavelength-selective coupler. The performance parameters of the laser system are investigated and compared with the conventional design under the same input design parameters. Both laser systems at a RPP of 375mW can generate up to 33 Stokes lines with an equal channel spacing of 0.08nm; however, the tunability of the laser without injection of residual RPP is 25% higher than the conventional laser structure. In addition, for a laser system without residual RPP injection, increasing the RPP improves the laser performance and generates up to 42 Stokes lines with a tunability of 24.5nm, from 1570 to 1594.5nm, at 475mW. In contrast, the laser system with a residual RPP has the worst performance as the pump power is increased, and generates only nine Stokes lines with a tuning range of 5nm at the same RPP of 475mW.

Performance improvement on OVSB based WDM RoF-EPON link using SOA with DCF and FBG

Performance of four channel WDM RoF-EPON link based on OVSB transmission using SOA is enhanced by compensating dispersion and FWM with DCF and FBG by 10.95% for equal channel spacing and further improvement has been shown up to 23.61% by using unequal spacing for the same transmission link. The performance enhancement by using DCF and FBG is ascertained by evaluating Q factor and eye opening.

Simulative Investigation of Laser Line-width and Channel Spacing for Realization of DWDM Systems under the Impact of Four Wave Mixing

This work is focused on how to implement 4- and 8-channel dense wavelength division multiplexing (DWDM) system, with each channel of 10 Gbps over an optical span of 100 km in the presence of four wave mixing (FWM) under the impact of unequal-channel spacing and laser line-width. In this proposed work, we have evaluated electrical power, Q-factor and average eye opening of 4- and 8-channel dense wavelength division multiplexing in the presence of FWM under the impact of equal channel spacing of 0.24 nm and 0.27 nm at 100 kHz, 10 MHz and 100 MHz laser line-widths. The comparison of parameters in the terms of electrical power, Q-factor and average eye opening has been observed at different laser line-widths.

Investigation of 40Gbps Dispersion Compensated DWDM System Incorporating Different Optical Pulses

The focus of this paper is to report a detailed investigation of dispersion compensated DWDM system with equal channel spacing incorporating pre-, post- and symmetrical- dispersion compensation techniques (DCF) with different optical pulses. The proposed high speed DWDM system is demonstrated with dispersive standard single-mode fiber (SSMF), which is compensated with proportionate length of DCF fiber under different DCF compensation schemes. Further, a performance comparison of pre-, post- and symmetrical- DCF schemes is reported by computing Q-parameter, and required optical power at receiver sensitivity at varied values of laser linewidth to underscore the best possible performance. A connection among the attributes like laser line-width, different optical pulses and different DCF schemes is reported at 10Gbps.

Impact of Laser Line-width in 40 Gbit/s DWDM Transmission System in the Presence of FWM Incorporating Equal Channel Spacing

The focus of this paper is to investigate a 40 Gbit/s DWDM system over the optical span of 100 km in the presence of Four Wave Mixing (FWM) under the impact of equal channel spacing at varied values of laser line-width. In this proposed work, the performance of DWDM system is carried out by evaluating received electrical power, Q-factor and average eye opening at varied values of equal channel spacing of 0.26 nm and 0.24 nm at laser line-widths of 100 kHz, 10 MHz and 100 MHz under the impact of fiber dispersion.

Equal channel spacing Sagnac filter using high-birefringent photonic crystal fibers

An equal channel spacing Sagnac filter is proposed using a high-birefringent photonic crystal fiber (PCF) with birefringence square to the operation wavelength. A PCF with four smaller central air holes surrounded by larger air holes is applied in a Sagnac filter with optimized parameters to achieve equal channel spacing of 0.8 nm. Given that the birefringence of this PCF is square to the operation wavelength, the channel spacing of the proposed filter changes by only 0.03 nm within a wavelength range from 1400 to 1650 nm; this is about one order of magnitude less than that constructed with conventional high-birefringent fibers.

Investigation on modified FWM suppression methods in DWDM optical communication system

The focus of this paper is to investigate the methods for Four Wave Mixing (FWM) suppression. Modified techniques equal and unequal-channel spacing with polarization, equal channel spacing with alternate channel delay, optical coupling and varied laser power have been proposed to reduce the impact of FWM on Dense Wave Length Division Multiplexing (DWDM) optical communication system. Further the comparison of reduction of FWM for existing and proposed techniques has been discussed by varying the dispersion of fiber from 0 to 16 ps/nm/km. It has been observed that the suggested techniques are simpler to design optical communication system and superior to the existing methods.

Multichannel Photonic Crystal Wavelength Filter Array for Near-Infrared Wavelengths

Multichannel wavelength filters consisting of 2-D photonic crystal (PhC) for the near-infrared wavelength region (~800 nm) are demonstrated. The filter is a thin-film wavy multilayer structure and is fabricated by the autocloning method, which is based on a radio frequency bias sputtering process. Twelve long-pass-type filter regions are integrated on a common silica substrate. Sharp cutoff characteristics and almost equal channel spacing are experimentally verified. To precisely control the effective lattice constant of PhC, a modulated lattice structure on the substrate is utilized

Bandwidth-Flexible WDM System Based on Homodyne Detection and Power Splitting Configuration

Conventional WDM systems multiplex channels with different signal bandwidths using fixed and equal channel spacing. As a result, their spectral efficiency is rather poor. If the wavelength and the bandwidth of each channel in a WDM system could be freely changed as needed, a variety of services with different signal bandwidths could be accommodated efficiently. This is expected to yield high spectral efficiency. For this purpose, this paper proposes a WDM optically amplified system that combines optical power splitting with homodyne detection; its use in three configurations, point to point, ring (center to remote nodes), and peer to peer, is described. Coherent optical systems generally need a frequency stable local light source in addition to a sending light source in each WDM channel. We improve cost effectiveness by proposing that the output of one light source be divided to yield the local light for frequency selection by homodyne detection and the sending light source whose output is externally modulated by transmission signal. In this configuration, the local light level is low to permit high levels of sending power. The key problem is how to get high SNR with limited low-level local lights. This paper derives the optimum receiving loss condition that can maximize the SNR with local light levels as low as -20 dBm for the point to point configuration. For the ring configuration, the system overcomes the optical power loss created by splitting numbers over 1,000 even if the local lights are as low as OdBm. The ring configuration can, therefore, flexibly accommodate many users and services. We also elucidate the relation between SNR and BER for DPSK homodyne detection in a bandwidth-flexible system.

Effective Channel Allocation to Reduce Inband FWM Crosstalk in DWDM Transmission Systems

An accurate analysis of the four-wave mixing (FWM) impact on dense wavelength-division multiplexing optical systems is carried out for different types of fibers. Particular channel allocations on the ITU grid are studied to reduce the inband FWM crosstalk and guarantee high performances in different types of optical fiber. These schemes, with respect to the other known channel allocations, allow one to find an optimum tradeoff between the required bandwidth expansion and the maximum inband FWM crosstalk. A comparison between the system spectral occupation and the signal-to-crosstalk ratio (SXR) versus the channel input power for the equal channel spacing and the proposed channel allocations validates the proposed solutions in the case of single-mode, nonzero dispersion-shifted, and dispersion-shifted fiber. For a 32-channel system, SXR improvements up to 4 dB without bandwidth expansion, and bandwidth savings up to 15 nm with a guaranteed minimum SXR of 25 dB, are obtained with respect to an equally spaced channel allocation.

Relative intensity noise enhancement due to out-of-band dispersion in cascaded fibre Bragg gratings

We analyse the relative intensity noise (RIN) induced in a transmitted channel by the out-of-band dispersion from cascaded fibre Bragg gratings used for dropping the adjacent channels. For wavelength-division-multiplexed systems having equal channel spacing, the RIN enhancement is due to the net out-of-band dispersion slope of the cascaded gratings and is considerably more significant than that due to propagation in fibre at the zero first-order dispersion wavelength.

A generalized suboptimum unequally spaced channel allocation technique. II. In coherent WDM systems

For pt.I see ibid., vol.46, no.8, p.1027-37 (1998). Four-wave mixing (FWM) in dispersion-shifted optical fiber is a major problem associated with low optical input power levels in optical wavelength-division multiplexed (WDM) systems. To reduce the crosstalk caused by FWM, a generalized suboptimum unequally spaced channel allocation (S-BISCA) technique has been proposed. While the S-USCA technique reduces the PWM power substantially, it also reduces the minimum channel spacing compared to conventional equal channel spacing (ECS) systems when the same number of carrier channels are accommodated in a fixed optical bandwidth. This results in more interchannel interference (ICI) when employing the S-USCA scheme. The power penalty of the ECS and the S-USCA systems caused by crosstalk and frequency drift are investigated and compared in this paper. The superior system performance region, where S-USCA systems out perform ECS systems, is also quantified. For 20-channel systems using an amplitude-shift keying (ASK) heterodyne detection scheme, for instance, results show that the S-USCA technique pays less power penalty up to bit rates of 5.5, 7.5, and 9.5 Gb/s, when all channels have identical states of polarization and the launched input power per channel P/sub in/, equals to -6, -3, and 0 dBm, respectively.

Allowable fibre input power for installed dispersion-shiftedfibre in equal/unequal channel spaced WDM transmission systems

The authors experimentally investigated the allowable fibre input power for installed DSF in WDM transmission systems with both equal and unequal channel spacing allocation. The allowable input powers for both equal and unequal channel spacing systems were higher than the values given by numerical analyses which assumed that there was no fluctuation in the zero-dispersion wavelength of the installed DSF.