WDM Optical Systems Research Articles

Review of FBG and DCF as dispersion management unit for long haul optical links and WDM systems

Review of FBG and DCF as dispersion management unit for long haul optical links and WDM systems

Suppression of Four Wave Mixing Effects Under Different Spectrally Efficient Modulation Techniques in Hybrid DWDM-OTDM Systems

Next generation optical networks require high spectral efficiency to meet the demand of high bandwidth for ultra-long haul communication. Spectrally efficient modulations using hybrid DWDM-OTDM systems can be used to achieve this. However, fiber nonlinearities such as four-wave mixing (FWM) will increase simultaneously and this will degrade the performance of WDM optical system. This paper explores the FWM reduction in 32 channels, 40 Gb/s hybrid DWDM-OTDM network using RZ-OOK, 16-QAM and PDM-QPSK modulation format at 200 GHz and 100 GHz channel spacing. Optical received power, BER, Q- factor, eye diagram and FWM side band power are analyzed at -15dBm to +15dBm channel power. All these modulations have shown a significant reduction in FWM. In addition, the 16-QAM gives highest reduction in FWM along with least BER of 7.9×10−158 and maximum Q-value of 27.74.

On‐Chip Metamaterial Enabled Wavelength (De)Multiplexer

AbstractWavelength‐division multiplexing (WDM) technology can offer considerable parallelism for large‐capacity data communications. While several configurations have been demonstrated to realize on‐chip WDM systems, their practical applications might be hindered by large footprints or compromised performances. Recently, metamaterial‐assisted silicon photonics is emerging for on‐chip light manipulation by subwavelength‐scale control of optical wavefronts. They can reach more compact footprints and broadband functionalities beyond the classical waveguide‐based architectures. Herein, wavelength (de)multiplexers are experimentally demonstrated in the subwavelength‐structured metamaterials regime with highly compact footprints. Two‐dimensional metamaterials composed of quasi‐periodic dielectric perturbation arrays patterned on a multimode waveguide are proposed to stimulate multiple high‐order waveguide modes at different wavelengths, which are then coupled to different WDM channels by cascading mode (de)multiplexers. The four‐channel wavelength (de)multiplexer is demonstrated in a box‐like spectrum with a compact footprint of 2.5 × 250 µm2, with the measured losses less than 2 dB and channel crosstalk less than –14.3 dB. By varying the patterned metamaterial structures, the proposed devices also have the merits of flexible operating wavelengths and bandwidths. The concept features large scalability, compactness, and competitive performance, which can offer versatile on‐chip light manipulation and significantly improve the integration density for various on‐chip WDM optical systems.

Optimization strategy of power control for C+L+S band transmission using a simulated annealing algorithm.

To increase the transmission capacity, ultra-wideband wavelength-division multiplexing (UWB WDM) has been exploited to enlarge the spectral range. However, inter-channel stimulated Raman scattering (ISRS) results in power transition from high-frequency channels to low-frequency channels in wideband scenarios, which degrades the Q-factor of signals. Hence, we modify the optimization method of power control by applying the simulated annealing (SA) algorithm to search for the optimal power slopes and offsets of three bands to construct an optimum distribution of launch powers over channels. High transmission capacity can be reached by carrying 384 channels (96+96+192) in the C+L+S band with the consideration of dynamic Raman gain and channel-dependent parameters. We show that compared to using brute-force searching (BFS), a comparable and even higher transmission capacity can be achieved by the SA algorithm. Meanwhile, the searching speed of the SA algorithm is much faster. Also, different optimizing strategies can be selected to balance the trade-off between capacity and spectral flatness. This method can be used for designing arbitrary optical fiber UWB WDM systems before practical testing.

Design and evaluation of 2.3 Tb/s (23 ch. × 100 Gb/s) multi-carrier WDM optical transmission systems

Multilevel phase modulation formats with coherent detection enable a new generation of high speed optical transport platform. We demonstrate 23 × 100 Gbps (2.3 Tb/s) WDM Optical systems employing multicarrier generation concept. Three lasers are used to generate 23 sub-carriers using multicarrier generator at transmitter section. Each sub-carrier transmits at a transmission rate of 100 Gbps using polarization division multiplexed quadrature phase shift keying (PDM-QPSK) modulation format with spacing of 25 GHz between sub carriers. The analysis is carried out for 23 × 100 Gb/s (2.3 Tb/s) PDM-QPSK WDM optical systems with ultra large area fiber (ULAF), standard single mode fiber (SSMF) and large effective area fiber (LEAF) at transmission reach from 600 to 5000 km. Coherent detection with DSP is used for all the systems at receiving end. Systems are verified with parameters like symbol error rate, error vector magnitude (EVM) and Q-factor using analytical and simulation results. Improvement of 1.66 dB to 3.21 dB and 2.08 dB to 4.63 dB is noted in Q-factor for system with ULAF in comparison with system using SSMF and LEAF respectively over 600 km to 5000 km transmission reach. EVM values are found 2.24% to 2.68% and 2.68% to 12.43% lower in system with ULAF than system with SSMF and LEAF respectively. Log of estimated symbol error is observed less for system with ULAF than systems with SSMF and LEAF fibers, respectively, at transmission distance of 5000 km. The results clearly show that WDM optical system with ULAF fiber gives better performance.

Accurate Closed-Form Real-Time EGN Model Formula Leveraging Machine-Learning Over 8500 Thoroughly Randomized Full C-Band Systems

We derived an approximate non-linear interference (NLI) closed-form model (CFM), capable of handling a very broad range of optical WDM system scenarios. We tested the CFM over 8500 randomized C-band WDM systems, of which 6250 were fully-loaded and 2250 were partially loaded. The systems had highly diversified channel formats, symbol rates, fibers, as well as other parameters. We improved the CFM accuracy by augmenting the formula with simple machine-learning factors, optimized by leveraging the system test-set. We further improved the CFM by adding a term which models special situations where NLI has high self-coherence. In the end, we obtained a very good match with the results found using the numerically-integrated Enhanced GN-model (or EGN-model). We also checked the CFM accuracy by comparing its predictions with full-C-Band split-step simulations of 300 randomized systems. The combined high accuracy and very fast computation time (milliseconds) of the CFM potentially make it an effective tool for real-time physical-layer-aware optical network management and control.

Embedded tunable laser control for WDM optical communications systems

In this work we present the design, implementation and evaluation of an embedded control solution for a WDM tunable laser. A brief description of the tunable laser components and operation is given and the required hardware is proposed. The required temperature, power and wavelength controllers are designed placing great emphasis on response time. Additionally, we present the characteristics and configurations of the microcontroller, along with the control algorithms implementation. Finally, the time response and wavelength accuracy of the solution is evaluated.

An efficient DFG induced wavelength exchanged-OPC using only two Ti:PPLN waveguides with single pump configuration

An unconventional single pump configuration of Wavelength Exchanged Optical Phase Conjugation (WE-OPC) through Difference Frequency Generation (DFG) employing two identical Ti:PPLN waveguides having same grating period and a single pump source is theoretically analyzed and simulated resulting in higher conversion efficiency of OPC.WE-OPC has been found very effective in extenuating nonlinearity and inflating spectral efficiency in optical transmission systems. The proposed WE-OPC enabled WDM optical transmission system modeled as a wavelength converter has been simulated with 10 channels offering much higher conversion efficiencies of about 3.3 dB and 3.49 dB for higher frequency band to lower frequency band and vice versa respectively.

Design of feedforward master–slave carrier phase recovery in frequency comb-based superchannel coherent transmission systems with nonlinear phase noise

Master–slave common carrier phase recovery (MS-CCPR) is a method for reducing computational complexity of the phase recovery in multi-channel systems where the channels have correlated phase noise. However, these systems will suffer performance penalties if there are phase-noise differences between the channels. Since MS-CCPR schemes rely on phases of the subchannels being same, the intra-channel phase-drift will inevitably influence the design and performance of such schemes. In addition, fiber nonlinearities may introduce further different phase perturbations on the subchannels of a superchannel. This paper presents a master–slave carrier recovery method with compensation of the phase-noise differences based on the blind phase search method for optical frequency comb-based WDM systems. Specifically, we investigated in details using simulations, for the first time, the impact of this phase-noise differences on the performance of master–slave scheme in long-haul transmission systems with laser and nonlinear phase noise effects. In the MS-CCPR strategy used, the slave subchannels are preprocessed with the master–slave scheme, then a low-complexity slave phase-tracker is used to correct the phase-noise differences remaining on them. The concept has been numerically verified in simulations for square 16-QAM format, where the BER limit for soft-decision FEC could still be achieved in a link of 3000 km.

Embedded tunable laser control for WDM optical communications systems

In this work we present the design, implementation and evaluation of an embedded control solution for a WDM tunable laser. A brief description of the tunable laser components and operation is given and the required hardware is proposed. The required temperature, power and wavelength controllers are designed placing great emphasis on response time. Additionally, we present the characteristics and configurations of the microcontroller, along with the control algorithms implementation. Finally, the time response and wavelength accuracy of the solution is evaluated.

Efficient hetero amplifier for DWDM system

Theoretical studies on gain characteristics of fluoride based hetero amplifier is thoroughly exhibited in the current research, which can be effectively used for S-band amplification in dynamic WDM optical network system, where the proposed hetero amplifier deals with both Raman amplifier and thulium doped fiber amplifier (TDFA) to achieve different characteristics such as flatten gain and low noise figure with respect to wavelength 1455 nm–1480 nm (S- band) for different channel spacing. Aside this, numerous parameters of hetero amplifier such as pump power, pump frequency, length of the fiber, doping concentration etc. are suitably manipulated to realize maximum gain, minimum gain variation ratio (GVR)and lower noise figure for aforementioned wavelength band. Further, simulation outcomes explored that a very low gain variation ratio of 0.14 dB, 0.4 dB, and 0.73 dB is obtained for channel spacing of 0.4 nm, 0.8 nm and 1 nm respectively. Moreover it has been revealed that the proposed hetero amplifier bestows a maximum gain of 23.44 dB at wavelength 1470.4 nm for 25 nm band (1455 nm–1480 nm) and lowest noise figure of -9.3 dB at wavelength 1470 nm for 1 nm channel spacing. Owing to the aforesaid remarkable upshots, the proposed hetero amplifier can be more conducive candidate for amplification in DWDM optical network systems.

A Performance Analysis of Proposed Hybrid Dispersion Compensation Techniques for WDM Optical Systems

A Performance Analysis of Proposed Hybrid Dispersion Compensation Techniques for WDM Optical Systems

Analysis of proposed hybrid amplifier model for single to multi-channel WDM optical system at 10 Gbp/s with 100 GHz of channel spacing

In this paper, we have investigated a possible single to multi-channel upgrade employing different amplification (Booster, EDFA amplifier and Raman amplifier). A 10 GB/s single channel signal is launched onto a fiber (D = 3 ps/nm/km) link of 140 km. The system works at the sensitivity limit. To upgrade the system, the power-budget at the receiver must increase employing an optical preamplifier. Two alternatives are explored: an EDFA or a RA. Two 10-channels WDM systems are shown employing respectively an EDFA and a Raman amplifier. EDFA gain and Rama amplifier counter propagating pump are determined to obtain the same optical gain for both the system configurations. A multiple run has been carried on to search the optimum RA configuration.

EDFA Design and Analysis for WDM Optical Systems Based on Modal Multiplexing

Modal multiplexing (MDM) is a core technology to allow a capacity increase in modern optical systems. However, in MDM links, the amplified WDM signal suffers not only from lack of spectral gain equalization but also from unequal modal gain. The proper design of the MDM-EDFA is crucial to provide modal gain equalization and to overcome those impairments, thereby ensuring long haul transmission. In this paper, our methodology of project EDFA design for MDM-WDM systems is presented. The technique is based on a figure of merit arising from the rate and propagation equations which describe the EDFA behavior. This figure of merit is then used for the definition of the objective functions employed in the optimization step, which is based on the non-dominated sorting genetic algorithm NSGA-II. Finally, the method is applied to demonstrate gain equalization through the simulation of a WDM optical system composed of two group modes (LP 01,s and LP 11,s ) with up to 16 channels in each mode. It is demonstrated that, for a MDM-WDM system with optimized EDFAs, the differential spectral gain is the main cause of non-equalization of the amplified signal.

Information Rates of Next-Generation Long-Haul Optical Fiber Systems Using Coded Modulation

A comprehensive study of the coded performance of long-haul spectrally-efficient WDM optical fiber transmission systems with different coded modulation decoding structures is presented. Achievable information rates are derived for three different square QAM formats and the optimal format is identified as a function of distance and specific decoder implementation. The four cases analyzed combine hard-decision (HD) or soft-decision (SD) decoding together with either a bit-wise or a symbol-wise demapper, the last two suitable for binary and nonbinary codes, respectively. The information rates achievable for each scheme are calculated based on the mismatched decoder principle. These quantities represent true indicators of the coded performance of the system for specific decoder implementations and when the modulation format and its input distribution are fixed. In combination with the structure of the decoder, two different receiver-side equalization strategies are also analyzed: electronic dispersion compensation and digital backpropagation. We show that, somewhat unexpectedly, schemes based on nonbinary HD codes can achieve information rates comparable to SD decoders and that, when SD is used, switching from a symbol-wise to a bit-wise decoder results in a negligible penalty. Conversely, from an information-theoretic standpoint, HD binary decoders are shown to be unsuitable for spectrally-efficient, long-haul systems.

Probabilistic 16-QAM Shaping in WDM Systems

This work proposes a probabilistic shaping scheme for optical WDM systems, where nonlinear interference noise depends on the input optical signal power distribution. With $16$ -QAM, a white Gaussian channel analysis shows that the shaped constellation is able to achieve a reach improvement of up to $7\%$ , while split-step Fourier method simulations suggest that even higher gains are possible in practice. An example system is developed for a transmission distance around $3280$ km. A constellation mapping and a low-density parity-check code are developed for this regime to show a reach improvement of $7.1\%$ . These shaping schemes can also be extended to $64$ -QAM, where a reach improvement of over $10\%$ is expected.

Injection Locked Wavelength De-Multiplexer for Optical Comb-Based Nyquist WDM System

We report a standalone four-output wavelength de-multiplexer (de-mux) using optical injection locking for simultaneous comb tone separation, amplification and power equalization. Optical amplification from −30 to 5 dBm per output wavelength is achieved. We illustrate the flexibility of the de-mux by separating two input combs with tone spacing of 12.5 and 6.25 GHz into 12.5-GHz spaced outputs. The system performance of the de-mux is demonstrated in a 100-km Nyquist ultra-dense wavelength division multiplexed network where the de-multiplexed comb tones are each encoded with 12-GBd Nyquist polarization division multiplexed quadrature phase shift keying. Experimental results indicate a worst case 1.5-dB receiver sensitivity penalty at 1.5e-2 bit error ratio for the transmitted comb tone channels when compared with the 400-kHz linewidth comb source seeding laser.

Effect of Fiber Length on Four Wave Mixing in WDM Optical Fiber Systems

Effect of Fiber Length on Four Wave Mixing in WDM Optical Fiber Systems

Design Performance of High Speed Optical Fiber WDM System with Optimally Placed DCF for Dispersion Compensation

factors like chromatic dispersion, polarization mode dispersion, attenuation, non-linear effects, second order and third order dispersion impress limit on the performance of all the optical fiber networks. Dispersion compensation fiber are being used in this paper , we projected three techniques (pre, post, and mix-compensation of dispersion compensation) of dispersion compensation methods for non-return to zero links using standard for high date rate optical transmission system. The performances have been compared on the basis of parameters such as Q factor, bit error rate (BER), eye height and threshold level at the receiving end. The simulation model of the WDM system using the software Optisystem 12.0 is presented according to the above principle. It is observed that the post-compensation technique performs better than pre-, mix-compensation technique for 40 Gb/s in the WDM system.

Raman Amplifier Performance under New Wavelength Ranges

AbstractDue to the benefits of Raman amplifier (RA) for long-haul Ultra Wideband (UW)-WDM optical communications systems, we are studying and investigating how to widen the bandwidth and flatten the gain of RA by testing it in a new wider range of wavelengths (1.4 μm≤1. 1.4 μm≤2. 1.45 μm≤3. 1.65 μm≤4. 1.43 μm≤Different model sizes are used and analyzed to get wider bandwidth and more flat gain.