Availability analysis and comparison of different WDM systems

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.

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).

Development of an OADM to reduce the incoherent crosstalk in WDM system

The authors have studied the possibilities to obtain the maximum spectral efficiency for a combined wavelength division multiplexing (WDM) system by minimizing the channel spacing. The fiber optic transmission systems under study can be considered in the context of next generation optical networks and is offered as a model for designing the future backbone networks. In the case of different telecom operators' optical networks merging, in the nearest future the necessity may arise to transmit variously modulated optical signals over a single optical fiber (even with different per channel bitrates). In this paper the authors show an optimal combined WDM system configuration that provides the least bit-error-rate values for the signals detected in system's channels. It is found that the minimal channel spacing for differently modulated optical signals in the investigated mixed data rates WDM system is 75 GHz if these signals are transmitted with 10 Gbit/s and 40 Gbit/s per channel bitrates. It is revealed that such a system's average spectral efficiency depends also on a combined system's configuration in the case of channel separation with equal frequency intervals.

With rapidly increasing demand for communication channels, wavelength division multiplexing (WDM) system are being deployed to expand the capacity. WDM systems require devices for the manipulation of multi-wavelength channels. Among these devices, the integrated acousto-optic tunable filter (AOTF) is rapidly gaining importance in the field of WDM communication systems because it has the combined features of rapid switching time, broad tuning range and parallel processing capability. The technology of hybrid unidirectional and focused transducer was adopted for the design of the AOTF. The AOTF consisted of a single-mode optical waveguide placed along the SAW propagation direction. Extensive researches areas, which were in optical add-drop multiplexers (OADM), gain equalization and optical switches, have been done.

We experimentally and theoretically investigate GeSi-based photonics for future on-chip optical interconnect on bulk Silicon substrates with dense wavelength division multiplexing (WDM) system. We experimentally show that Ge-rich Si_1-xGe_x can be used as both a passive low loss waveguide and a substrate to facilitate low-temperature epitaxial growth of Ge-based active devices working at low optical loss wavelength of Ge-rich Si_1-xGe_x waveguides. We also theoretically discussed the possibilities to realize a compact passive component based on Ge-rich Si_1-xGe_x material system on bulk Si wafer. From simulation the system based on Ge-rich Si_1-xGe_x waveguide and the Si_1-yGe_y (y < x) lower cladding layer is good enough to ensure compactness of important on-chip photonic components including passive waveguide and GeSi-based array waveguide grating (AWG). The small refractive index contrast between Ge-rich Si_1-xGe_x waveguide and the Si_1-yGe_y lower cladding layer potentially avoid the polarization dependent loss and detrimental fabrication tolerance of WDM system. Our studies show that GeSi-based photonics could uniquely provide both passive and active functionalities for dense WDM system.

For wavelength division multiplexing (WDM) systems, excessive linear and nonlinear noise will seriously decrease the quality of optical signals, and the effective joint monitoring scheme can prevent the degradation of system performance due to noise accumulation. In this paper, we propose a probability information assisted knowledge distillation (PIAKD) scheme that achieves intelligent joint monitoring for linear signal-to-noise ratio (SNRL) and nonlinear signal-to-noise ratio (SNRNL) in WDM systems. Under the condition of multi-task regression, outputs are independent and continuous, PIAKD addresses the longstanding challenge that the student model fails to effectively learn knowledge from the teacher model by introducing probability information into the loss function. The effectiveness of the scheme is verified by WDM simulation and experiment system which has a symbol rate of 28 GBaud per channel. The simulation results demonstrate that the overall mean absolute error (MAE) for jointing SNRL and SNRNL monitoring of the student model after PIAKD is reduced by 0.08 dB and 0.09 dB, corresponding to 32% and 34% error reductions respectively. Furthermore, when compared with the KD scheme without probability information, our scheme also reduces the overall MAE of SNRL and SNRNL by 16% and 11%, respectively. The results of the experiment reveal that the estimated MAE could be reduced by 0.13 dB and 0.16 dB, respectively, corresponding to error reductions of 17% and 18%. Moreover, the floating-point operations (FLOPs) and parameters (Params) of the student model is only 3.30 M and 0.0015 M, respectively, which is both significantly lower than the complexity of existing joint monitoring schemes for SNRL and SNRNL.

Crosstalk due to four-wave mixing (FWM) is increasing sharply when lightwave channel is upgrading in wavelength division multiplexing (WDM) fiber-optical communication systems. A technique, designed the channel wavelength allocation to reduce the crosstalks due to FWM, is submitted, when multi-channel is extended easily from 3-channel to 22-channel in WDM system. The result of simulation is presented. It is shown that suitable unequally channel separations can be found for which no FWM product term is superimposed on any of the transmitted channels, and the bandwidth expansion factor is not always increasing, and the span between the FWM crosstalks and channel wavelengths are not always decreasing, when increasing WDM system channels.

Performance of Wavelength Division Multiplexing (WDM) System is analyzed using Dispersion Compensating Fiber. In this work, Optimized link of 8-channel WDM (Wavelength Division Multiplexing) system using OptiSystem is designed. Comparison of the link performance is investigated at different wavelength i.e. 980nm, 1300nm and 1550nm. The better Performance of the WDM link can be achieved at wavelength of 1550nm as compared to 1300 and 980nm using dispersion compensating fiber along with single mode fiber for link length of 105 km operating at data rate of 3Gb\s with 8-channel of WDM System. The BER, Q-factor and eye diagram have been used for evaluating the performance of the system.

In this paper, we propose a concept of wavelength division multiplexing (WDM) system using microring resonator radius variation method. The free spectral range is used to analyze the characteristics of the microring resonator where an increase in ring radius will decrease the FSR value. Consequently, the design concept of this WDM system is justified using the simulation results. The number of channels that can be incorporated is approximately 52 channels with 0.8nm spacing for a reference ring resonator of 1.05µm radius.

Different distortions that affect gridless wavelength division multiplexing (WDM) systems due to nonlinear impairments of the optical fiber and linear interchannel interference (ICI) errors cause signal degradation and a decrease in the transmission system quality. Overcoming these effects is a challenge if there is no information about the source of the distortion. In this work, we propose two asymmetric demodulation methods based on decision tree (DT) algorithms to mitigate distortions associated with linear ICI in gridless WDM systems, even when optical channels are spectrally overlapped. The first method uses the conventional DT and random forest (RDF) algorithms adapted to create asymmetrical thresholds in m-QAM digital demodulation. The second method uses the density-based spatial clustering of applications with a noise (DBSCAN) algorithm, including the K-Dimensional tree (K-D tree) algorithm to treat symbols in boundary conditions. Both methods were experimentally validated in a 3×16GBd gridless Nyquist WDM system modulated in 16-QAM with different channel spacing. DT-based demodulation, including RDF, achieved gains up to ∼1.6dB in the FEC limit 3.8×10−3, while demodulation based on DBSCAN plus the K-D tree achieved gains up to ∼1.2dB compared to conventional demodulation. Additionally, we performed a brief latency analysis in comparison to other previous machine learning-based demodulation methods, where DT and RDF presented latency up to ∼0.3% and ∼32% of the DBSCAN + K-D tree latency, respectively. Finally, the proposed asymmetric demodulation methods can improve the performance of future elastic optical networks by offering easy interpretation of the digital demodulation process and the possibility of adapting them to any m-QAM modulation format being agnostic to signal distortion.

In this paper, we presented the wavelength division multiplexing (WDM) system based on optical add-drop multiplexer (OADM). We analysed the effect of loss on Q factor and BER for different fiber lengths. The NRZ modulation format is used for transmitting the signal for 9.953-Gb/s 16-channel WDM system based on OADM.

Fiber suppliers now manufacture nonzero dispersion-shifted fiber (NZDSF), which is dispersion shifted but has a finite dispersion in the erbium-doped fiber amplifier (EDFA) transmission window, to minimize four-wave mixing (FWM). The choice of which sign of dispersion offers the best performance depends on several factors, such as self-phase modulation/dispersion pulse shaping and modulation instability (MI), which occurs on anomalous dispersion fiber. We show, for the first time to our knowledge, that amplitude cross talk due to cross-phase modulation (XPM) can also act as a seed for the MI process, giving an increased penalty for wavelength-division multiplexing (WDM) systems using anomalous dispersion fiber.

Wavelength division multiplexing (WDM) optical interconnect technology offers an effective solution for addressing the ever-increasing data traffic. Microring modulators (MRMs), owing to their high bandwidth, compact footprint, and inherent wavelength selectivity, have become key building blocks in WDM systems. However, the limited free spectral range (FSR) of MRMs restricts the number of available wavelength channels and the corresponding overall data rate capacity in WDM systems. In this study, we propose an optimized Bezier-bent MRM, in which the device radius is reduced to 3 μm to significantly enhance the FSR. The proposed MRM operates without the need for a DC bias voltage and an RF amplifier, exhibiting a low insertion loss of 0.4 dB, an ultrawide FSR exceeding 4 THz, and a high electro-optic bandwidth of over 110 GHz. Back-to-back (BtB) transmission experiments demonstrate that the modulator supports 400 Gbps PAM-8 data transmission under a driving voltage of only 1 V, satisfying the 7% hard-decision forward error correction (HD-FEC) bit-error-rate (BER) threshold of 3.8 × 10–3. Owing to the compact-radius design, the junction capacitance is substantially reduced, enabling an exceptionally low modulation power consumption of 0.2 fJ/bit. The proposed MRM presents significant potential for dense integration in future optical communication systems.

In this work, a maintenance issues resolved suppression method of four-wave mixing (FWM) is proposed using optical phase conjugation (OPC) modules and different placements of OPCs are investigated in ultradense wavelength division multiplexing (WDM) system with coherent orthogonal frequency division multiplexing (OFDM) incorporation. Moreover, comparison of the placements of OPC in six different cases has been done and compared with conventional WDM (no-OPC) system in terms of Q-factor, BER and induced FWM. Analysis has been done at different launched power levels. It is observed that placement of OPC after each laser source performs exceptionally well and suppresses FWM with ease of maintenance.