Wavelength Division Multiplexing Optical Systems Research Articles

A Comprehensive Study on EDFA Gain Flattening for WDM Transmission using Cascaded Fiber Bragg Gratings

The gain flattening of optical amplifiers plays a crucial role in optical Wavelength Division Multiplexing (WDM) communication systems, ensuring uniform amplification across all channels. This study focuses on investigating the gain flattening characteristics of Erbium-Doped Fiber Amplifiers (EDFAs) using cascaded Fiber Bragg Gratings (FBGs) in the C-band wavelength range. A comparative analysis of various optical amplifiers revealed that EDFA exhibited the highest gain variation, making it an optimal choice for gain flattening. The key parameters to achieve optimal EDFA gain flattening include the wavelengths of the channels, EDFA length, noise figure (NF), and the number of cascaded FBGs. Simulation experiments are conducted using Optisystem software (ver. 14.2) and the obtained results reveal that EDFA gain flatness can be achieved within the wavelength range of 1531 to 1533 nm, utilizing an EDFA length of 6 m and 12 cascaded FBGs. These findings contribute to the advancement of gain flattening techniques in optical WDM systems, enhancing their performance and reliability.

Nature-Inspired Hybrid Multi-objective Optimization Algorithms in Search of Near-OGRs to Eliminate FWM Noise Signals in Optical WDM Systems and their Performance Comparison

Nowadays, the multi-objective optimizing algorithms which are inspired by nature are widely used in solving the many objectives of NP-complete engineering and industrial design problems. To eliminate one of the prevailing nonlinear optical noise mechanisms, i.e., four-wave mixing noise signals in the optical wavelength division multiplexing (WDM) systems, several unequally spaced channel-allocation algorithms were found that require increased bandwidth than the equally spaced channel-allocation. One of the bandwidths efficient, a USCA algorithm can be designed by considering the optimal Golomb rulers (OGRs) in optical WDM systems. Two nature-inspired multi-objective optimization algorithms (MOAs), namely multi-objective big bang–big crunch (MOBB-BC) optimization algorithm and multi-objective firefly optimization algorithm (MOFA), to solve NP-complete OGR problem in an optical WDM system are proposed here. Additionally, the algorithms MOBB-BC and MOFA are hybridized by introducing differential evolution (DE) based mutation and random walk features in their standard forms. These two features have the potential to explore new search space for MOAs to search for OGRs in a reasonable time. The algorithms presented here solve the two objectives in optical WDM systems, one is the occupied length by the ruler, and the other is total channel bandwidth obtained by OGRs. The obtained results suggest that the considered nature-inspired MOAs are computationally better than the other algorithms to search near-OGRs. To assert the improvement in the MOAs further, the non-parametric Friedman statistical analysis test is employed. The results conclude that for large mark values, the hybridization of MOFA with both DE mutation and Levy-flight strategies potentially performs better than the MOBB-BC and its hybrid forms to search OGR sequences. The hybrid algorithm MOBB-BC can explore OGRs up to 8-marks and near-OGRs for 9 to 20-marks with a maximum computation time of 27 h, whereas hybrid MOFA can examine up to 16-mark OGRs, but finds 17 to 20-mark near-OGRs with the maximum computation time of 20 h. The success rate of the proposed hybrid MOFA to search best OGRs up to 20-marks is 80%, whereas for hybrid algorithm MOBB-BC is 40%.

Mathematical modeling of optical impairments in DSP based WDM coherent system

Abstract Optical transmission impairments are most critical reason to reduce both capacity and achievable transmission distance in optical communication system. Advanced modulation formats are important keys to reduce optical transmission impairments in digital signal processing (DSP) based coherent wavelength division multiplexed (WDM) system. These formats are more robust to non-linearity of optical fiber and results in increasing both spectral efficiency and bandwidth. Coherent detection technique increases sensitivity of receiver up to 30 dB in comparison of direct detection. Simulink seems to be the best cost-effective platform for analyzing mathematical modeling of optical coherent system. In this paper, mathematical model has been developed to analyze the optical transmission impairments by employing the advanced polarization multiplexed QPSK modulation in DSP based WDM coherent system. The simulation results have shown bit error rate (BER) improvement up to 10−6 and enhanced transmission distance to 150 km. These values have seen to be in close proximity with experimental results. The developed mathematical model seems to be more useful for extending the existing WDM optical system for longer distances with acceptable BER.

Performance comparison of five metaheuristic nature-inspired algorithms to find near-OGRs for WDM systems

The metaheuristic approaches inspired by the nature are becoming powerful optimizing algorithms for solving NP-complete problems. This paper presents five nature-inspired metaheuristic optimization algorithms to find near-optimal Golomb ruler (OGR) sequences in a reasonable time. In order to improve the search space and further improve the convergence speed and optimization precision of the metaheuristic algorithms, the improved algorithms based on mutation strategy and Levy-flight search distribution are proposed. These two strategies help the metaheuristic algorithms to jump out of the local optimum, improve the global search ability so as to maintain the good population diversity. The OGRs found their potential application in channel-allocation method to suppress the four-wave mixing crosstalk in optical wavelength division multiplexing systems. The results conclude that the proposed algorithms are superior to the existing conventional computing algorithms i.e. extended quadratic congruence and search algorithm and nature-inspired optimization algorithms i.e. genetic algorithms, biogeography based optimization and simple big bang–big crunch to find near-OGRs in terms of ruler length, total optical channel bandwidth and computation time. The idea of computational complexity for the proposed algorithms is represented through the Big O notation. In order to validate the proposed algorithms, the non-parametric statistical Wilcoxon analysis is being considered.

Accumulation of nonlinear interference noise in probabilistically shaped 64-quadrature amplitude modulation systems

An efficient procedure is presented for evaluating the effects of modulation format on the accumulation of nonlinear interference noise (NLIN) in probabilistically shaped 28 Gbaud 64-quadrature amplitude modulation (QAM) wavelength division multiplexed (WDM) systems. The shaped symbol sequences are generated by the rate adaptive scheme concatenating a constant composition distribution matcher and a systematic forward error correction encoder. A shaping distribution based on the Maxwell–Boltzmann and the uniform distribution with the same net bit rate is considered. The NLIN variance is emulated using the accurate enhanced modulation-dependent Gaussian noise model. Accounting for the impact of higher-order standardized moments of the modulation, the dependence of NLIN variance on probabilistic shaping is determined using the proposed procedure. In addition, an increase in NLIN variance for shaping over uniform input is demonstrated. For a dual polarization (DP) fully loaded C-band WDM optical fiber system with a channel spacing of 37.5 GHz, probabilistic shaping leads to a reduction of 0.036 in the ratio of intrachannel and interchannel contributions to nonlinear noise over uniform 64-QAM for a 1500-km distance. Finally, for nine channels with DP probabilistically shaped 64-QAM input over 1500-km transmission, distributed amplification enables a reduction of 2.54 dB in the accumulation of normalized NLIN power compared to lumped amplification.

Comparison of Nonlinear Compensation Techniques for 400-Gb/s Coherent Multi-Band OFDM Super-Channels

The last few years, many studies have been published on the 3rd-order inverse Volterra series transfer function nonlinear equalizer (IVSTF-NLE) in long-haul optical communication systems. Nonetheless, no experimental work has been published on investigating the potential of the 3rd-order IVSTF-NLE for the compensation of Kerr nonlinearities in a long-haul wavelength division multiplexing (WDM) system consisting of high-bit rate super-channels, as high as 400 Gb/s. In this paper, we study experimentally the performance of a 3rd-order IVSTF-NLE in a coherent optical WDM system, with a central, 400-Gb/s, 4-band, dual-polarization (DP), 16-ary quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) super-channel. We compare its performance against the performance of the digital back-propagation split-step Fourier (DBP-SSF) method for the compensation of nonlinearities after 10 × 100 km of ITU-T G.652 standard single mode fiber (SSMF). In the second part of this paper, we compare, via Monte Carlo simulations, the performance of the 3rd-order IVSTF-NLE and the DBP-SSF method, in terms of reach extension and computational complexity, after propagation through ITU-T G.652 SSMF and a ITU-T G.655 large effective area fiber (LEAF). By means of both experimental evaluation and simulations, we show that, in the presence of strong nonlinear effects, the 3rd-order IVSTF-NLE, which uses a single step per span, performs similarly with the two-steps-per-span DBP-SSF, whereas the eight-steps-per-span DBP-SSF is only marginally better but at the vast expense of computational complexity.

Coherent optical WDM systems for 1.6 Tb/s Ethernet over 40 km of single-mode fiber

Abstract Two 1.6 Tb/s coherent optical wavelength division multiplexed (WDM) systems targeting inter-data center links of up to 40-km reach over conventional single-mode fiber (CSMF) on C-band are proposed and numerically analyzed: a DP-QPSK-based 16 × 112 Gb/s system and a DP-16-QAM-based 8 × 224 Gb/s system. To satisfy the metro access space, noise and power transceiver characteristics are optimized, avoiding the use of any type of optical amplification or forward-error correction (FEC) scheme. Accordingly to the current Ethernet standard, feasibility of both 28 GBd architectures is hence numerically demonstrated at a very low bit-error-ratio (BER) threshold of 1 × 10−13, uncovering power sensitivities of −26.0 and −13.5 dBm and optical signal-to-noise ratio (OSNR) sensitivities of 35 and 40 dB for the first and second architectures, respectively. Negligible transmission OSNR and power penalties with respect to the back-to-back (BtB) case are calculated, thus demonstrating the effectiveness of the utilized DSP algorithms. Our simulation work also confirms that the 16-QAM-based scheme is more demanding in terms of OSNR and transmission power specifications than the 16-channel one, requiring approximately 12 dB more power and 5 dB more OSNR level at the transmitter laser outputs, with similar requirements at the receiver end. It is also demonstrated that laser linewidths of at most 1 MHz should be specified in both architectures, that the transmitter laser characteristics play a more appreciable role than those of the receiver laser, and that the frequency offset between these two lasers should be kept below 3 GHz. Our research work leverages the use of optical coherent technology at metro network level and claims for a necessary technological upgrade to such schemes for a forthcoming 1.6 Tb/s Ethernet standard to be feasible.

Threshold-Based Multiple Optical Signal Selection Scheme for Free-Space Optical Wavelength Division Multiplexing Systems

We propose a threshold-based multiple optical signal selection scheme (TMOS) for free-space optical wavelength division multiplexing systems. With this scheme, we can obtain higher spectral efficiency while reducing the possible complexity of implementation caused by the beam-selection scheme and without a considerable performance loss. To characterize the performance of our scheme, we statistically analyze the operation characteristics under conventional detection conditions (i.e., heterodyne detection and intensity modulation/direct detection techniques) with log-normal turbulence while taking into consideration the impact of pointing error. More specifically, we derive exact closed-form expressions for the outage probability, the average bit error rate, and the average spectral efficiency while adopting an adaptive modulation. Some selected results show that TMOS increases the average spectral efficiency while maintaining a minimum average bit error rate requirement.

Nature–inspired metaheuristic algorithms to find near–OGR sequences for WDM channel allocation and their performance comparison

Abstract Nowadays, nature–inspired metaheuristic algorithms are most powerful optimizing algorithms for solving the NP–complete problems. This paper proposes three approaches to find near–optimal Golomb ruler sequences based on nature–inspired algorithms in a reasonable time. The optimal Golomb ruler (OGR) sequences found their application in channel–allocation method that allows suppression of the crosstalk due to four–wave mixing in optical wavelength division multiplexing systems. The simulation results conclude that the proposed nature–inspired metaheuristic optimization algorithms are superior to the existing conventional and nature–inspired algorithms to find near–OGRs in terms of ruler length, total optical channel bandwidth, computation time, and computational complexity. Based on the simulation results, the performance of proposed different nature–inspired metaheuristic algorithms are being compared by using statistical tests. The statistical test results conclude the superiority of the proposed nature–inspired optimization algorithms.

(Invited) Heterogeneous Photonic Integration by Direct Wafer Bonding

The silicon photonics platform has emerged as a promising integration technique for use in many applications, particularly datacenter communications, which is expected to produce demand for large numbers of low cost photonic integrated circuits (PICs). Silicon-based PICs are almost universally based on silicon-on-insulator (SOI) wafers, which are enabled by wafer bonding technology. Silicon (Si) is useful as a waveguide material due to its high index contrast, low intrinsic absorption, and mature manufacturing infrastructure. However, it does not strongly interact with light in wavelength ranges of interest for data transmission. Heterogeneous integration of InP-based materials with Si using wafer bonding technology is able to overcome this limitation and has allowed the realization of a wide range of photonic devices on Si1. Beyond integration of InP with Si, wafer bonding enables complex vertical integration with of a wide variety of materials, such as silicon nitride (Si3N4) ultra-low loss waveguides, and magnetic and nonlinear materials. A crystalline Si layer transferred to an ultra-low loss Si3N4 waveguide wafer by bonding allows for integration of highly confined Si photonic waveguide with low-loss passive components in Si3N4. Any device that can be realized on an SOI wafer can be integrated with the Si3N4 waveguide. Multiple die bonding of InP chips on the Si layer can add lasers, amplifiers, modulators, and photodetectors to the circuit. Lateral tapers of the waveguides allows coupling between the layers with loss below 0.5 dB. This technology was used to combine a Si3N4 arrayed waveguide grating (AWG) wavelength multiplexer with high-speed 50 Gb/s heterogeneous Si/InP photodetectors to form a 400 Gb/s wavelength division multiplexing (WDM) receiver2. A cross section of the photodetector is shown in Figure 1. Bonding technology can allow the introduction of additional circuit functions that are unavailable using common semiconductor materials. One such device is an optical isolator, which allows light to experience loss that is dependent on the direction of optical propagation. This optical nonreciprocity can be achieved by bonding a magneto-optic material such as cerium substituted yttrium iron garnet (Ce:YIG) on Si waveguides, and applying a magnetic field through the material. Using this phenomenon, it is possible to fabricate optical isolators as well as circulators for use in optical sensors, amplifiers, and WDM systems. Our design consists of a Si microring with a bonded Ce:YIG die on top, shown schematically in Figure 2. A metallic microstrip is deposited on the backside of the bonded die following substrate removal. By applying a current through this microstrip, we generate a magnetic field, which causes a resonance split between the forward and backwards propagating light. Thus, optical isolators with up to 32 dB of isolation have been demonstrated3. Lithium niobate (LN) is a material of paramount importance for nonlinear optics, thanks to its large nonlinear coefficient and broad transparent window (0.4-5.0 µm)4. It has attracted attention for use in PICs, because the compact scale of integrated waveguides results in high photon densities that effectively enhance nonlinear interaction. Recently, the LN-on-insulator (LNOI) technology has been successfully demonstrated by ion injection and heterogeneous bonding. This allows the implementation of LN thin films with submicron thickness on various material platforms5. We present here a quasi-phase matched, ultra-low-loss S3N4-LN platform, which reduces the loss of integrated LN waveguides down to a value comparable with best results of bulk LN waveguides 6 (Figure 3). Bonding of LN to silicon is also possible, allowing integration of LN-based devices with SOI photonics. Wafer bonding technology allows the realization of complex and highly integrated photonic devices. The ability to combine multiple materials such as multiple-die bonding for integration of lasers, modulators, and detectors enables PICs with a wide variety of functions. Vertical integration through bonding of high-quality thin films, such as silicon nitride, lithium niobate, crystalline silicon, and thermal silicon dioxide can be used to construct integrated waveguides with useful properties and high performance. 1. M. J. R. Heck et al., IEEE J. Sel. Top. Quantum Electron. 19, 6100117 (2013). 2. M. Piels, J. F. Bauters, M. L. Davenport, M. J. R. Heck, and J. E. Bowers, J. Light. Technol. 32, 817–823 (2014). 3. D. Huang et al., Optical Fiber Communications (2016). 4. G. D. Boyd, R. C. Miller, K. Nassau, W. L. Bond, and A. Savage, Appl. Phys. Lett. 5, 234–236 (1964). 5. L. Chen, Q. Xu, M. G. Wood, and R. M. Reano, Optica 1, 112 (2014). 6. K. R. Parameswaran et al., Opt. Lett. 27, 179–181 (2002). Figure 1

Optimal Golomb Ruler Sequences Generation for Optical WDM Systems: A Novel Parallel Hybrid Multi-objective Bat Algorithm

In real-life, multi-objective engineering design problems are very tough and time consuming optimization problems due to their high degree of nonlinearities, complexities and inhomogeneity. Nature-inspired based multi-objective optimization algorithms are now becoming popular for solving multi-objective engineering design problems. This paper proposes original multi-objective Bat algorithm (MOBA) and its extended form, namely, novel parallel hybrid multi-objective Bat algorithm (PHMOBA) to generate shortest length Golomb ruler called optimal Golomb ruler (OGR) sequences at a reasonable computation time. The OGRs found their application in optical wavelength division multiplexing (WDM) systems as channel-allocation algorithm to reduce the four-wave mixing (FWM) crosstalk. The performances of both the proposed algorithms to generate OGRs as optical WDM channel-allocation is compared with other existing classical computing and nature-inspired algorithms, including extended quadratic congruence (EQC), search algorithm (SA), genetic algorithms (GAs), biogeography based optimization (BBO) and big bang-big crunch (BB-BC) optimization algorithms. Simulations conclude that the proposed parallel hybrid multi-objective Bat algorithm works efficiently as compared to original multi-objective Bat algorithm and other existing algorithms to generate OGRs for optical WDM systems. The algorithm PHMOBA to generate OGRs, has higher convergence and success rate than original MOBA. The efficiency improvement of proposed PHMOBA to generate OGRs up to 20-marks, in terms of ruler length and total optical channel bandwidth (TBW) is 100 %, whereas for original MOBA is 85 %. Finally the implications for further research are also discussed.

A flexible decision-aided maximum likelihood phase estimation in hybrid QPSK/OOK coherent optical WDM systems

Although decision-aided (DA) maximum likelihood (ML) phase estimation (PE) algorithm has been investigated intensively, block length effect impacts system performance and leads to the increasing of hardware complexity. In this paper, a flexible DA-ML algorithm is proposed in hybrid QPSK/OOK coherent optical wavelength division multiplexed (WDM) systems. We present a general cross phase modulation (XPM) model based on Volterra series transfer function (VSTF) method to describe XPM effects induced by OOK channels at the end of dispersion management (DM) fiber links. Based on our model, the weighted factors obtained from maximum likelihood method are introduced to eliminate the block length effect. We derive the analytical expression of phase error variance for the performance prediction of coherent receiver with the flexible DA-ML algorithm. Bit error ratio (BER) performance is evaluated and compared through both theoretical derivation and Monte Carlo (MC) simulation. The results show that our flexible DA-ML algorithm has significant improvement in performance compared with the conventional DA-ML algorithm as block length is a fixed value. Compared with the conventional DA-ML with optimum block length, our flexible DA-ML can obtain better system performance. It means our flexible DA-ML algorithm is more effective for mitigating phase noise than conventional DA-ML algorithm.

Investigation of EDFA based 32 Channel C-Band Optical WDM System for Different Pumping Techniques

With the rise in demand for channel capacity, Wavelength Division Multiplexing (WDM) technique is employed in optical communication networks. Gain Flattened Erbium Doped Fiber Amplifier (EDFA) is used in optical WDM system to obtain a uniform output power level. The performance of EDFA depends on various parameters such as fiber length, pump power, pumping wavelength and pumping technique. The objective of this paper is to analyze the performance of EDFA for different pumping techniques namely co-propagating, counter-propagating and bidirectional propagating in a 32 channel C-band optical WDM transmission system at different levels of pump power and different fiber lengths. The system has been analyzed on the basis of received power, BER, gain, noise figure and Q- Factor in the wavelength range of 1528nm to 1562nm at 25dBm transmission power and 0.5nm channel spacing. The results obtained using different pumping techniques are compared to find an appropriate pumping technique which optimizes the performance of the optical WDM transmission system.

Decision-aided maximum likelihood phase estimation with optimum block length in hybrid QPSK/16QAM coherent optical WDM systems

We propose a general model to entirely describe XPM effects induced by 16QAM channels in hybrid QPSK/16QAM wavelength division multiplexed (WDM) systems. A power spectral density (PSD) formula is presented to predict the statistical properties of XPM effects at the end of dispersion management (DM) fiber links. We derive the analytical expression of phase error variance for optimizing block length of QPSK channel coherent receiver with decision-aided (DA) maximum-likelihood (ML) phase estimation (PE). With our theoretical analysis, the optimum block length can be employed to improve the performance of coherent receiver. Bit error rate (BER) performance in QPSK channel is evaluated and compared through both theoretical derivation and Monte Carlo simulation. The results show that by using the DA-ML with optimum block length, bit signal-to-noise ratio (SNR) improvement over DA-ML with fixed block length of 10, 20 and 40 at BER of 10−3 is 0.18dB, 0.46dB and 0.65dB, respectively, when in-line residual dispersion is 0ps/nm.

An overview of fiber dispersion and nonlinearity compensation techniques in optical orthogonal frequency division multiplexing systems

Optical fiber based transmission network is the key technology to support high capacity backhaul needs for future wireless communication standards. Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO) transreception, Carrier Aggregation (CA), Co-operative Multi-Point (Co MP) and Wavelength Division Multiplexing (WDM) for backhaul/backbone are all, state of the art techniques used in most of these standards. The successful implementation of all these technologies requires modification of the network architecture which leads to challenges on backhaul design in terms of capacity and latency requirements. The optical fiber networks implemented in the form of analogue Radio over Fiber (RoF) or digital RoF offers a prospective solution. The performance of analogue RoF suffers from noise and linearity issues and digital RoF is degraded by fiber dispersion and nonlinearity due to high rate of transmission. Dispersion and nonlinearity compensation becomes essential to make the optical fiber backhaul supportive of the emerging wireless technologies. This paper reviews and compares various techniques proposed in the literature for compensating fiber dispersion and nonlinearity. A comprehensive comparison of fiber dispersion and nonlinear effects are summarized. Further, the selection criteria for choosing a particular compensating technique in Optical OFDM and WDM systems have been presented in this work.

Conditions for a Monotonic Channel Capacity

Motivated by results in optical communications, where the performance can degrade dramatically if the transmit power is sufficiently increased, the channel capacity is characterized for various kinds of memoryless vector channels. It is proved that for all static point-to-point channels, the channel capacity under an equal-power constraint is a nondecreasing function of power. As a consequence, maximizing the mutual information over all input distributions with a certain power is for such channels equivalent to maximizing it over the larger set of input distributions with upperbounded power. The channel coding theorem is formally proved for an equal-power constraint. For interference channels such as optical wavelength-division multiplexing systems, the primary channel capacity is always nondecreasing with power if all interferers transmit with identical distributions as the primary user. Also, if all input distributions in an interference channel are optimized jointly, then the achievable sum-rate capacity is again nondecreasing. The results generalize to the channel capacity as a function of a wide class of costs, not only power.

Spectral Shaping in Long Haul Optical Coherent Systems With High Spectral Efficiency

One of the main obstacles faced when decreasing channel spacing in optical wavelength division multiplexing (WDM) systems is the linear crosstalk resulting from spectral overlap between neighboring channels. Methods of reducing channel bandwidth and corresponding crosstalk using optical pre-filtering are reviewed along with the limitations of these techniques. High speed transmitter side digital signal processing (DSP) and digital-to-analog converters enable the use of more powerful techniques that precisely shape and limit the bandwidth of the transmitted optical signal. These techniques allow channel spacing to be reduced to nearly the theoretical minimum Nyquist spacing with only negligible crosstalk penalty. We review well known principles of linear modulation theory and apply them to coherent optical transmission systems to describe the desired channel transmit spectra along with the associated transmit and receive DSP. The implementation issues of a typical optical transmitter, which uses these techniques, are discussed. Experimental results of a laboratory long-haul WDM optical system using spectrally shaped PDM-16-QAM type modulation are presented demonstrating near Nyquist channel spacing on a trans-pacific length system with more than 44 terabits of capacity. We also present an additional application of these spectral shaping techniques, which can carefully expand the bandwidth of the transmitted channels to reduce non-linear transmission penalties. Experimental results show the advantages of these spectral broadening techniques and their ability to trade spectral efficiency for increased reach.

Simulative Investigation and Comparison of 8 x 40 Gbps WDM system Using Different Dispersion Compensation Techniques Based On DCF

Wavelength division multiplexing (WDM) technology allows several channels to be routed through the same fiber cable with different wavelengths. In WDM systems dispersion , loss , attenuation , and non-linear effects are the issues that degrade its performance. Dispersion is a main limiting factor in high speed optical WDM system. In this paper 8 channel WDM system at 40Gbps and 125km length of optical fiber with 25 km length of DCF has been investigated for three dispersion compensation techniques i.e. pre , post and symmetric using DCF. All three methods are compared in terms of different parameters such as Q-factor, BER by using OptiSystem simulator .It has been observed that the set-up requires appropriate matching between EDFA gain and length of optical fiber for best performance.

Reconfigurable silicon filter with continuous bandwidth tunability

We present the design and the fabrication of compact tunable silicon-on-insulator bandpass filters based on the integration of a Mach-Zehnder interferometer with ring resonators and activated via thermo-optic phase shifters. The proposed architecture provides wide filter bandwidth tunability from 10% to 90% of the free spectral range preserving the filter off-band rejection. Possible applications are channel subset selection in wavelength division multiplexing optical systems, adaptive filtering to signal bandwidth, and reconfigurable filters for gridless networking.

Design and optimization of high-performance microring-based uni-traveling carrier photodiode for WDM optical systems

This paper presents the design principles of a novel optimized microring-based uni-traveling carrier photodiode (MR-UTC-PD), for wavelength division multiplexing (WDM) optical systems. The fundamental parameters for output characteristics such as quantum efficiency and 3-dB bandwidth of MR-UTC-PD are discussed. We analyze the effects of basic parameters as effective ring radius, definite coupling condition and the suitable cross section on the MR-UTC-PD main characteristics for high performance of the device. It is shown that the maximum quantum efficiency and most efficient performance of the device can be obtained at critical coupling condition. We show that the maximum 3-dB bandwidth and an efficient approach for high bandwidth-efficiency product can be achieved at overcoupling condition. In this regard, some design curves are presented for the optimized MR-UTC-PD.