Wavelength Division Multiplexing Fiber Research Articles

Wavelength detection of serial WDM ultra-short fiber Bragg grating sensor networks based on a CCD interrogator using deep belief networks and sparrow search algorithm

In this paper, in order to make fiber Bragg grating spectra easier to overlap, it is proposed to use ultra-short fiber Bragg grating to build a sensor network, and for serial wavelength division multiplexing (WDM) fiber Bragg grating (FBG) sensor networks using charge-coupled device (CCD) interrogator as data acquisition devices, an efficient method for measuring strain sensor signals is presented, which combines a deep belief network (DBN) with the sparrow search algorithm (SSA). The FBG sensor network uses serial WDM connectivity, negating the need for optical switches and reducing latency of the whole sensor system. The application of a low-precision, low-resolution CCD interrogator as the data acquisition device enhances the model's generalizability and facilitates its implementation in real-world projects. DBN, a generative graphical model in machine learning, for learning features from overlapping spectra of FBGs and build the center wavelength detection model. SSA is a swarm intelligence algorithm, for optimizing the hyperparameters of the DBN model. Experimental results show that even using spectral data collected by a CCD interrogator, the DBN-SSA model can achieve good demodulation accuracy and speed, with an optimal root mean square error of 1.68pm and a single inference time of 1.4 ms. In summary, the demodulation system offers a dependable and effective solution for FBG sensor networks with limited data precision.

A new Ni/Bi Co-doping rare earth iron garnet crystal with high transmittance, low temperature and wavelength coefficients

Bi-doped rare earth iron garnet (Bi:RIG) crystal is an ideal magneto-optical material for optical isolators in the near-infrared band, which has been widely used in optical communication applications. In this paper, centimeter-sized and good-quality Ni2+-doped Bi:RIG crystals were successfully grown by top-seeded solution growth (TSSG). The transmittance reaches 72.6% at 1550 nm, which is higher than commercial Bi:TbIG crystal and close to the theoretical values of RIG crystals. Doping Ni can not only greatly improve the transmittance, magnetic, and magneto-optical properties, but also decrease the Faraday rotation temperature (FTC) and wavelength coefficients (FWC) of the Bi:RIG crystal. The FTC and FWC of (Bi0.37Ho1.18Eu0.83Gd0.62)(Fe4.20Ni0.25Ga0.55)O12 crystal reduced to − 6.3 × 10−4 K−1 and 8.0 × 10−4 nm−1, which are about 30% and 80% of commercial Bi:TbIG crystal, respectively. (Bi0.37Ho1.18Eu0.83Gd0.62)(Fe4.20Ni0.25Ga0.55)O12 exhibits potential for utilization in new high-performance, wideband magneto-optical isolators, and is expected to find application in the field of wavelength division multiplexing fiber communication.

Unidirectional Ring-Based WDM Fiber Network for Both Downlink and Uplink Signal Access

In the paper, a dual-bidirectional ring-type wavelength-division-multiplexing (WDM) access network with downlink and uplink signal access simultaneously using a single fiber backbone in clockwise and counterclockwise directions, respectively. The proposed network architecture is simple and easy to implement via the designed remote node (RN) and optical line termination (OLT) modules, but it also can double the downlink traffic using the original WDM downlink wavelengths. The presented ring-type WDM network can also avoid the Rayleigh backscattering (RB) beat noise when the same wavelengths are applied as downlink and uplink channels concurrently. In the measurement, 50 km long-reach and 15 km short-reach fiber transmission lengths are achieved for the symmetrical 10 and 28 Gbit/s on-off keying (OOK) data access, respectively. In addition, based on the obtained power budgets of eight downlink WDM signals and network design at the forward error correction (FEC) threshold, 16 optical network units (ONUs) can be supported simultaneously.

Theoretical investigations of weakly- and strongly-coupled multi-core fibers for the applications of optical submarine communications under power and fiber count limits.

The practical cable design for optical submarine communications has a limited fiber pair count due to the mechanical considerations of cable weight and size. Consequently, multi-core fibers (MCFs) could exhibit higher capacity than conventional single-mode fibers (SMFs) thanks to space division multiplexing (SDM). That is because the power supply to a submarine cable is fed by the voltage difference between shores. Under the power-limited condition, SDM improves the cable capacity by using more paths which outperforms the SMF link whose capacity approximately complies with a logarithmic relationship to optical power. At the same time, fiber nonlinearity can be alleviated by the reduced power density of transmitted light in MCFs, due to the increased spatial diversity and mode coupling among coupled cores. In this work, we theoretically investigate the potentials of MCFs including weakly-coupled multicore fiber (WC-MCF) and strongly-coupled multicore fiber (SC-MCF) as the propagation media for submarine communications across the Atlantic and the Pacific. To fairly compare the performances of SMFs- and MCFs-based submarine cables, the Gaussian noise (GN) model for SDM links is employed to optimize the systematic settings including spatial multiplicity and single span length. Then, we develop an SDM and wavelength division multiplexing (WDM) fiber transmission model based on coupled nonlinear Schrodinger equations (CNSE) to investigate the optical filed coupling effect in MCFs-based cables. The developed transmission model has been self-examined by measuring the inter-core crosstalk (IC-XT) and spatial mode dispersion (SMD), referring to the set values. As indicated by the theoretical analysis, the WC-MCFs cable exhibits a larger capacity than the SMFs cable, when the fiber pair count is limited below 32. Moreover, the SC-MCFs cable outperforms the WC-MCFs cable thanks to the reduced fiber nonlinearity due to the random mode coupling and the assistance of multiple-input and multiple-output digital signal processing (MIMO-DSP). At last, the marginal influences of IC-XT, SMD, and insertion loss of Fan-in and Fan-out couplers are also analyzed for the MCFs cable.

Fast and Accurate Waveform Modeling of Long-Haul Multi-Channel Optical Fiber Transmission Using a Hybrid Model-Data Driven Scheme

The modeling of optical wave propagation in optical fiber is a task of fast and accurate solving the nonlinear Schr\"odinger equation (NLSE), and can enable the optical system design, digital signal processing verification and fast waveform calculation. Traditional waveform modeling of full-time and full-frequency information is the split-step Fourier method (SSFM), which has long been regarded as challenging in long-haul wavelength division multiplexing (WDM) optical fiber communication systems because it is extremely time-consuming. Here we propose a linear-nonlinear feature decoupling distributed (FDD) waveform modeling scheme to model long-haul WDM fiber channel, where the channel linear effects are modelled by the NLSE-derived model-driven methods and the nonlinear effects are modelled by the data-driven deep learning methods. Meanwhile, the proposed scheme only focuses on one-span fiber distance fitting, and then recursively transmits the model to achieve the required transmission distance. The proposed modeling scheme is demonstrated to have high accuracy, high computing speeds, and robust generalization abilities for different optical launch powers, modulation formats, channel numbers and transmission distances. The total running time of FDD waveform modeling scheme for 41-channel 1040-km fiber transmission is only 3 minutes versus more than 2 hours using SSFM for each input condition, which achieves a 98% reduction in computing time. Considering the multi-round optimization by adjusting system parameters, the complexity reduction is significant. The results represent a remarkable improvement in nonlinear fiber modeling and open up novel perspectives for solution of NLSE-like partial differential equations and optical fiber physics problems.

Performance Evaluation of WDM Optical Fiber Communication System in the presence of PMD

This paper investigates for rising optical fiber transmission strength, increasing bandwidth, and decreasing communication system weakness by using wavelength division multiplexing (WDM). WDM gives today's distention speed and communication traffic. Systems using WDM faces nonlinearities, which the most intensive nonlinear attack is, four wave mixing (FWM). FWM creates and increases crosstalk between WDM channels as a result slows down and impairs the performance of the communication system. This investigation uses orthogonal frequency division multiplexing (OFDM) for evaluating execution of WDM fiber system by repairing Polarization Mode Dispersion (PMD). We took results in the case of trying PMD-Emulator and without trying PMD-Emulator in the system design. We compared the results got in both cases. Furthermore, we compared the performance of the system with the investigations done using different ways, methods, and techniques for compensating PMD and FWM appears in WDM systems. As PMD-Emulator, helps enhancing the system design performance, and OFDM gives the feature of robustness and useful execution to the system. OFDM examined by appointing interfered orthogonal signal sets, for 16 channels; with equally spaced OFDM channels. Oure results showed that the optical fiber communication system using OFDM technique gives perfect removing FWM signal crosstalk, and accurate data transmission, comparing to other techniques used in other researches. We got a decreased FWM power to -77dBm, and the BER of -0.317. Furthermore, the system quality increased with applying PMD-Emulator and OFDM. In addition, using PMD-Emulator in the system design raised the results effectiveness. The program used in the present work is optisystem-15, and the results obtained in this study coincide with the theoretical and actual results obtained by the previous studies.

Integrated role between VCSEL diodes and Gaussian pulse generators with ideal EDFA for self phase modulation instability management

Abstract This work outlined the integrated role between vertical cavity surface emitting laser diodes with Gaussian pulse generators and Ideal erbium doped fiber amplifier (EDFA) for the self-phase modulation instability management, as well as the signal/NP level (Power level [PL]) with the spectral frequency is simulated after wavelength division multiplexing (WDM) fiber at length of 10 km based third order Gaussian pulse generators. The light power variations against temperature after WDM fiber is also studied at length of 10 km based various order Gaussian pulse generators. Electrical received power (ERP) variations against temperature is clarified after avalanche photo diode (APD) photodetectors based various order Gaussian pulse generators. The study emphasis the bad effects of the increase of the temperature, and higher Gaussian pulse generators order on the signal power levels.

Trellis Shaping for Fiber Nonlinearity Mitigation in Coherent Optical OFDM Systems

In this article, trellis shaping technique is numerically and experimentally investigated to improve the performance of optical orthogonal frequency division multiplexing (OFDM) signal. Different from other constellation shaping techniques, trellis shaping can be designed to reduce the correlation value of OFDM data sequence and average power simultaneously in one OFDM symbol. It means that optical OFDM signals generated by trellis shaping can improve the performance under both linear and nonlinear channels. For comparison with trellis shaping technique, we also consider optimal Maxwell–Boltzmann (MB) shaping and uniform signaling techniques at spectral efficiency (SE) of 10 and 14 bits/4D-sym. Numerical simulations show that trellis shaping can provide certain shaping gain over uniform signaling under linear additive white Gaussian noise (AWGN) channel. The fiber transmission results indicate that OFDM signals with trellis shaping have higher effective signal-to-noise ratio (SNR) than those with MB shaping and uniform signaling. It means that trellis shaping technique has the ability to mitigate the fiber nonlinear noise. Considering both linear and nonlinear noise in the fiber link, trellis shaping can extend the transmission distance by $\sim$ 110 km and $\sim$ 200 km over MB shaping and uniform signaling at SE of 10 bits/4D-sym. At SE of 14 bits/4D-sym, trellis shaping provides similar performance as MB shaping but $\sim$ 120-km extension reach in comparison with uniform signaling. The performances of OFDM signals with trellis shaping, MB shaping and uniform signaling are also experimentally investigated in a four-channel wavelength division multiplexing (WDM) fiber transmission systems. The experimental results show that trellis shaping can also mitigate the nonlinear distortions induced by the clipping effects at the transmitter side. Compared with MB shaping, trellis shaping extends the transmission reach by $\sim$ 240 km and $\sim$ 90 km at SE of 10 and 14 bits/4D-sym, respectively.

The effect of the optical fiber design on reducing the nonlinear characteristics of the optical fiber

Fiber Bragg Grating FBG Works as a filter within a specific range to counteract the light whose wavelength is within the filter range and allows the light whose wavelength is outside the range of the filter to pass through the carrier light-medium. In communications (fiber-optic) the FBG is used to separate the optical signals. In this paper, the nonlinear optical properties study for optical transmission that consists of an optical transmitter that is transmitting the signal to two different fiber design first is single-mode fiber and second is Coarse Wavelength division multiplexing (CWDM) fiber. Then we enter the Bragg Grating on these two fiber and studies the effect of the Bragg on them. The nonlinear optical characteristic (Q factor and bit error rate BER) is calculated for different fiber length (Km) and input power (dBm) applied on these two fibers and found the best fiber type that has a high Q factor and zero BER. By using optiwave software and matlab (R2015) software program to measure the quality factor, eye diagram and BER of the received signal at the receiver, Results are obtained and installed with graphs and tables.

Research on Testing of Optical Fiber Wavelength Division Multiplexing System

In order to meet the requirement of long-distance high-speed data bus for information transmission in vehicles, optical fiber wavelength division multiplexing (FWDM) technology is used to realize the transmission of multiple optical signals by connector. Although wavelength division multiplexing technology has been widely used in the field of communication, the adaptability of the real-time control system needs to be further studied. In this paper, a prototype of the optical fiber wavelength division multiplexing system is tested and the test results are preliminarily studied, which provides a basis for evaluating transmission reliability margin and analyzing system failure.

High-Speed and Uninterrupted Communication for High-Speed Trains by Ultrafast WDM Fiber–Wireless Backhaul System

We developed a high-speed and handover-free communication network for high-speed trains (HSTs) using an ultrafast and switchable wavelength-division multiplexing fiber–wireless backhaul system in the W band. We successfully transmitted approximately 20-Gb/s and 10-Gb/s signals over the switched fiber–wireless links in the downlink and uplink directions, respectively. An ultrafast radio-cell switching of less than 10 μs was experimentally demonstrated in both downlink and uplink directions. Moreover, the possibility of connecting a central station to many remote radio cells was evaluated, confirming that an uninterrupted communication network up to several tens of kilometers can be achieved for HSTs. The proposed system can overcome the current challenges in mobile networks and can provide a potential solution for the provision of advanced services to users on HSTs in future 5G and beyond networks.

Tunable Multiwavelength Random Fiber Laser With Odd and Even Order Stokes Separated

A novel tunable multiwavelength random fiber laser (MRFL) based on stimulated Brillouin scattering (SBS) with odd and even order Stokes output separated is proposed and demonstrated experimentally. The laser resonator is a dual-branch structure, with each branch consisting of an erbium-doped fiber amplifier (EDFA) and a long-span single mode fiber (SMF). The output of two branches incites each other through a coupler to get a separated output. The gain is provided by an SBS and EDFA, while the SMFs provide random distributed feedback. As a result, we get six output lasing wavelengths with about 22-GHz frequency spacing for both odd and even order Stokes. The proposed MRFL is also wavelength tunable from 1549.75 to 1569.75 nm. The output of this MRFL is very stable, which is important for its further applications in dual parameter sensing systems and dense wavelength-division multiplexing fiber communication systems.

Non Regenerative Fiber backbone Power Loss Budget

The most important stage in the design of a Wavelength Division Multiplexing (WDM) fiber optic system is about the choice of the correct optical transmitter, and receiver combination. This depends on the signal to be transmitted over the channel. By adopting the WDM two (2) signals at two (2) different wavelengths of 1310nm and 1550nm, can conveniently be carried on the same fiber. The WDM fiber link can carry 32,256 channels and the throughput too is high (>=2.5Gbps). Many television channels can be accommodated. The amplification along the fiber backhaul remains a bottleneck due to the non-linearity effects that could be additive. In order to minimize the non-linearity effect of the amplifiers, non-regenerative solutions are nowadays used.This paper develops a power loss budget for an optical sparse WDM long haul without inserting any regenerator along the transmission line. The study gives details of establishing a 200 km fiber optic link, operating at 2.5Gbps and supporting a digital signal of Synchronous Transport signal-48/ Synchronous Transport Module 16 (STS-48/STM-16). The link is assumed to carry 8 (WDM). In the dimensioning, the optical interfaces were chosen in agreement with the ITU-T G 654 applicable values. The system power deficit was not satisfactory in the first attempt. Then, the Erbium Doped-Fiber Amplifiers (EDFA) were inserted at the light source, and a preamplifier at the optical detector side. The system power deficit was still negative but not much. The transmitting system should have a positive value of the system power deficit so that the link budget can be suggested for the required transmission. Finally the change of the detector sensitivity gave the best estimation in the design process for the required link budget.

Compact and portable 100-GHz microresonator-based optical frequency comb generation system for dense wavelength division multiplexing fiber optic communication

A compact and portable microresonator-based optical frequency comb generation system was developed to provide an array of multiwavelength laser sources for dense wavelength division multiplexing (DWDM) fiber optic communication. The reported comb generation system was capable of producing comb lines after 7 km of travel without environmental control, indicating the effectiveness of the packaging. The comb spacing is about 98.3 GHz (i.e., ∼0.79 nm around 1553 nm), thus the comb line frequencies coincide nicely with 100-GHz DWDM channel frequencies, assuming the suggested channel bandwidth is 0.3 nm. The quality of selected comb lines was evaluated individually based on error vector magnitude (EVM) measurements along with RF spectrum measurements. An average EVM value observed is as low as 3.8%, close to typical EVM values of less than 3% used for fiber optic communication.

Multi-objective design of an FBG sensor network using an improved Strength Pareto Evolutionary Algorithm

To improve the multiplexing capability is a key issue in designing a wavelength division multiplexing (WDM) fiber Bragg grating (FBG) sensor network. In this paper, we present a novel FBG sensor network design based on Pareto-based multi-objective optimization technology. In contrast to conventional WDM network, the proposed network model permits the spectral response to overlap each other. The multi-objective function is established by taking two objectives into account. One objective is to minimize the total source bandwidth occupation of the sensor system to improve the multiplexing capability, and the other is to minimize the overlap degree of spectra to reduce the wavelength measurement error. The improved Strength Pareto Evolutionary Algorithm (SPEA2) is applied to search for the so-called Pareto front. One appropriate solution is selected from the non-dominated solutions to determine the Bragg wavelength assignment. Numerical results show that the proposed approach is effective in saving the bandwidth occupation and maintaining the measurement accuracy simultaneously.

Wavelength detection in FBG sensor networks using least squares support vector regression

A wavelength detection method for a wavelength division multiplexing (WDM) fiber Bragg grating (FBG) sensor network is proposed based on least squares support vector regression (LS-SVR). As a kind of promising machine learning technique, LS-SVR is employed to approximate the inverse function of the reflection spectrum. The LS-SVR detection model is established from the training samples, and then the Bragg wavelength of each FBG can be directly identified by inputting the measured spectrum into the well-trained model. We also discuss the impact of the sample size and the preprocess of the input spectrum on the performance of the training effectiveness. The results demonstrate that our approach is effective in improving the accuracy for sensor networks with a large number of FBGs.

Ideal optical backpropagation of scalar NLSE using dispersion-decreasing fibers for WDM transmission

An ideal optical backpropagation (OBP) scheme to compensate for dispersion and nonlinear effects of the transmission fibers is proposed. The scheme consists of an optical phase conjugator (OPC), N spans of dispersion-decreasing fibers (DDFs) and amplifiers, placed at the end of the fiber optic link. In order to compensate for the nonlinear effects of the transmission fibers exactly, the nonlinear coefficient of the backpropagation fiber has to increase exponentially with distance or equivalently the power in the backpropagation fiber should increase exponentially with distance if the nonlinear coefficient is constant. In this paper, it is shown that a combination of DDFs and amplifiers can compensate for the nonlinear effects exactly. An analytical expression for the dispersion profile of the DDF is derived. Numerical simulation of a long haul wavelength division multiplexing (WDM) fiber optic system with the proposed OBP scheme shows that the system reach can be enhanced by 54% as compared to digital backpropagation (DBP).

High-birefringence fiber loop mirror sensor using a WDM fused fiber coupler

An intensity-based highly birefringent (Hi-Bi) fiber loop mirror (FLM) sensor is proposed which uses a wavelength-division multiplexing (WDM) fiber coupler. The effect of integrating the WDM coupler in a FLM configuration is first studied. A section of Hi-Bi (bow-tie) fiber of length 0.26 m is then placed in the fiber loop, making the spectral response of the device simultaneously dependent on the Hi-Bi fiber section and WDM coupler characteristics. When strain is applied to the sensing head, the spectral signal is modulated in amplitude, in contrast with the conventional Hi-Bi FLM sensors in which there are wavelength shifts. The sensor was characterized in strain and a sensitivity of (-2.2±0.4)×10(-3) με(-1) for a range of 300 με was attained. The self-referenced character of the sensor is noted.

Performance analysis of an optically amplified add/drop wavelength division multiplexing fiber communication link

The impact of power transients stemming from channel reconfiguration on erbium-doped fiber amplifier (EDFA) gain dynamics in wavelength division multiplexing (WDM) optical networks is investigated. The impact of power transients on EDFA gain dynamics leads to error bursts and impact on the network performance. First, we model an EDFA simulator with one-dimensional nonlinear differential equation that describes the time-dependent population density. For the model to show gain flattening multiplexed channels at different wavelengths, new function blocks are used. Next, to simulate the noise performance of EDFA, forward amplified spontaneous emission noise blocks are designed that add noise dynamically at signal wavelength. Finally, EDFA simulator is used as an in-line amplifier for amplitude shift keying-modulated WDM fiber communication link where the gain clamping facility is provided to protect power imbalance at the receiver. Next, we apply the mentioned model in the estimation on the link performance parameters, like signal-to-noise ratio and bit error rate, and variations in these values by channel add/drop results from variation in incremented signal output of EDFA. The variations are almost equal at different wavelengths in C- or L-band, which is due to flat gain and also the gain clamping facility of the present EDFA simulator.

A novel wavelength detection technique of overlapping spectra in the serial WDM FBG sensor network

Wavelength detection problem is addressed in a serial wavelength division multiplexing (WDM) fiber Bragg grating (FBG) sensor network, where the spectra of the FBGs are partially or fully overlapped. Specifically, an optimization model utilizing the transfer matrix method to analyze the reflection spectra is presented. The search space of this problem indicates that the optimal solution and the sub-optimal solution are completely symmetric. Considering the peculiarity of the problem, an improved differential evolution (DE) algorithm, named Swap-DE, is used to calculate the Bragg wavelengths. Experimental results show that the wavelength detection error is typically smaller than 0.2pm.