Dense Wavelength Division Multiplexing Channels Research Articles

Design of Ultra Dense WDM Optical Communication System to Reduce Signal Impairments Using DCF and Repeater Techniques

Linear and non-linear impairments are the major problems that affected the dense wavelength division multiplexing (DWDM) system performance. In this simulation designs, two different compensation techniques have been proposed to eliminate signal impairments. The repeater technique was proposed to reduce non-linear effects like four-wave mixing (FWM) which cause transfer power from DWDM channels to another new channels. The dispersion compensation fiber (DCF) technique was used to reduce dispersion effects which cause signal pulse broadening over long transmission distances. Also, three different modulation formats and four frequency separations were used to determine which modulation scheme is more compatible with the compensation techniques. The results is calculated in term of quality factor against power and noetic that the carrier suppressed return to zero (CSRZ) format offers the best performance with the DCF technique with 32.1804 Q-factor at 15dBm threshold power then, the differential phase shift keying (DPSK) format is compatible with the repeater technique with 27.7959 quality factor and 14dBm threshold power. Index Terms— Dense Wavelength Division Multiplexing (DWDM), Dispersion Compensation Fiber DCF, Repeater, and Non-linear Effects.

In-band full-duplex multiband mobile fronthaul network based on analog radio-over-fiber andtandem SSB modulation.

An in-band full-duplex multiband mobile fronthaul network is proposed based on analog radio-over-fiber and tandem single-sideband (TSSB) modulation. Two optical carriers with a wavelength spacing of 50GHz in accordance with international telecommunication union dense wavelength division multiplexing (DWDM) standards are employed in each distributed unit (DU): one is used to carry two different radio frequency (RF) vector signals at 3 and 10GHz, while the other is used to carry a vector signal at 15GHz and a single-tone signal at 15GHz. At the DU, a parallel TSSB modulation is applied, which eliminates the cross talk of TSSB modulation through two dual-polarization binary phase-shift keying (DP-BPSK) modulators. This allows the two vector signals carrying different data to be distributed on both sides of the optical carrier. At the active antenna unit (AAU), different RF vector signals centered at 3, 30, and 60GHz, each carrying distinct information, can be generated by selecting either one DWDM channel or two adjacent DWDM channels in a group. By utilizing the spacing between the two DWDM optical carriers, millimeter-wave signals can be generated without the need for additional electronic upconversion devices in the AAU. In the uplink, a DP-BPSK modulator is used to receive the signal of interest while canceling self-interference. Simulation results demonstrate the performance of the proposed system. After transmitting 25km through single-mode fiber and compensating for dispersion using corresponding dispersion-compensating fiber, the downlink and uplink achieve error vector magnitudes of less than 9% and 2%, respectively, when the receiving optical power is 6dBm.

Semiconductor Optical Amplifier (SOA)-Driven Reservoir Computing for Dense Wavelength-Division Multiplexing (DWDM) Signal Compensation

Optical signal processing (OSP) technology is a crucial part of the optical switching node in the modern optical-fiber communication system, especially when advanced modulation formats, e.g., quadrature amplitude modulation (QAM), are applied. However, the conventional on–off keying (OOK) signal is still widely used in access or metro transmission systems, which leads to the compatibility requirement of OSP for incoherent and coherent signals. In this paper, we propose a reservoir computing (RC)-OSP scheme based on nonlinear mapping behavior through a semiconductor optical amplifier (SOA) to deal with the non-return-to-zero (NRZ) signals and the differential quadrature phase-shift keying (DQPSK) signals in the nonlinear dense wavelength-division multiplexing (DWDM) channel. We optimized the key parameters of SOA-based RC to improve compensation performance. Based on the simulation investigation, we observed a significant improvement in signal quality over 10 dB compared to the distorted signals on each DWDM channel for both the NRZ and DQPSK transmission cases. The compatible OSP achieved by the proposed SOA-based RC could be a potential application of the optical switching node in the complex optical fiber communication system, where incoherent and coherent signals meet.

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.

Design of DWDM optical communication systems with different modulation formats using DCF and a repeater.

The dense wavelength division multiplexing (DWDM) technique has been used to provide a large capacity and low bandwidth loss for optical communication systems. In this paper, simulation designs by Optisystem15.0 of carrier-suppressed return to zero (CSRZ), differential phase shift keying (DPSK), and intensity modulation is proposed to determine which modulation format is more compatible with four and eight DWDM channels for transmitting an optical signal over 400km distance. For a long optical path, the dispersion compensation fiber (DCF) technique is proposed to eliminate dispersion effects and increase the possibility of transmitting multiple optical wavelengths over long single-mode fiber. Optical amplifiers are used to amplify the optical signal with a distorted signal and process the attenuation caused by the long transmission distance. In DCF network design, CSRZ offers the best performance because of the large quality factor (24.560) and high threshold power (15dBm), which make the system compatible with increased distance between the transmitter and receiver; next is intensity modulation with a 24.5604 quality factor and 13dBm threshold power value; DPSK comes in last with the worst performance, with a quality factor of 10 at 13dBm power due to non-linear effects, especially non-linear phase noise. In the repeater design, the DPSK modulation format has the best performance with a large quality factor of 20.7913 at a high threshold power of 14dBm for 150GHz spacing; this is because the repeater technique is compatible with reducing the non-linear effects of the DPSK format. CSRZ and intensity modulation have the same performance with a 12 quality factor at 4dBm power for intensity modulation and 3dBm power for CSRZ modulation.

Analysis of an active and passive optical fronthaul with dense wavelength division multiplexing for coexisting 4G/5G cloud radio access network architectures based on software defined radio

We experimentally investigate the performance of an active and passive optical fronthaul to be employed in a cloud/centralized radio access network (C-RAN) architecture based on software-defined radio (SDR) for 4G systems, and we discuss the viability to integrate these fronthaul configurations in coexisting 4G/5G systems based on SDR by considering the reconfigurable characteristics of SDRs and the capacity and latency characteristics of the optical fronthaul. The active optical fronthaul consists of two transponders employing dense wavelength division multiplexing (DWDM), whereas the passive optical fronthaul consists of a point-to-point scheme based on DWDM only. To perform a comparative study between the active and passive optical fronthaul in the C-RAN architecture, we have measured the throughput (bit rate) generated via iPerf® for uplink and downlink transmissions at different DWDM channels, and we analyze the losses and latency presented in both optical fronthaul schemes. We found that for different optical fronthaul lengths up to 21.76 km, the bit rate is practically the same for the passive and active fronthaul despite the higher optical losses present in the passive fronthaul in comparison to the active fronthaul. In addition, the latency among active and passive fronthaul are almost similar with an estimated increment of 20 μs in the active fronthaul. These results are independently of the number of remote radio heads (RRHs) and user equipment (UEs) considered in the C-RAN architecture. Our findings put forward the proposed DWDM passive fronthaul as a viable, less complex, and cost-sensitive solution for C-RAN systems with fronthaul lengths up to 21.76 km. These results and all the experiences reported on the C-RAN implementation provide valuable information to design and develop 4G and 5G C-RAN architectures based on SDR with the capability to operate in a DWDM optical fronthaul infrastructure.

Performance of subcarrier-wave quantum key distribution in the presence of spontaneous Raman scattering noise generated by classical DWDM channels

In this paper, we study the performance of the subcarrier-wave quantum key distribution system (SCW QKD) in the presence of spontaneous Raman scattering (SpRS) noise generated by classical channels of the dense wavelength division multiplexing (DWDM) network within a single-mode optical fiber. We present the mathematical model for evaluation of the quantum bit error rate and secure key generation rate with the SpRS noise taken into account. We consider two regimes of the SCW QKD system: the continuous wave regime, which uses a continuous wave laser, and the pulsed regime. For these regimes, performance of the system is analyzed depending on receiver sensitivity of classical DWDM. It is found that the pulsed regime outperforms the continuous wave regime in both the secure key generation rate and maximum achievable distance.

Focus on photonics, spectroscopy, and spectrometry

Focus on photonics, spectroscopy, and spectrometry

Intra-Datacenter Interconnects With a Serialized Silicon Optical Frequency Comb Modulator

Powerful warehouse-scale datacenters form the fabric of cloud computing. Efficient computing requires intra-datacenter interconnects with large capacity, low energy consumption, and high scalability. These unique goals present brand new scientific and technological challenges for short-reach optical communications. Silicon photonics (SiP) modulators are promising for intra-datacenter interconnects for its low energy consumption, with the superiority of low cost, small footprint, and complementary metal-oxide-semiconductor (CMOS) compatibility. While currently, the main research focus is to increase the modulation speed of a single SiP modulator for a large interconnect capacity, parallel schemes exhibit better scalability. In this article, we propose intra-datacenter interconnects using dense wavelength-division multiplexing (DWDM) techniques with a single SiP optical frequency comb modulator (OFCM) to achieve potential large capacity and high scalability. The SiP-OFCM consists of serially cascaded microring modulators (MRMs). The MRM based SiP-OFCM is intrinsically compatible with DWDM, performing simultaneously data modulation for multiple optical carriers, DWDM demultiplexing and multiplexing functionalities. We demonstrate an interconnect line rate of 400 Gbit/s with a PAM 4 modulation format using the SiP-OFCM. All four DWDM channels exhibit bit-error ratios below the 33% hard-decision forward-error correction threshold after 2-km single-mode fiber transmission.

MEMS tunable SOI waveguide Bragg grating filter with 1.3 THz tuning range for C-band 100 GHz DWDM optical network

A MEMS tunable integrated waveguide Bragg grating-based filter for C-band optical dense wavelength-division multiplexing (DWDM) network is presented and analyzed in this work. Waveguide Bragg grating being a notch filter in the transmission spectrum is used to realize a tunable filter by varying the applied voltages to the fixed–fixed beam loaded with this grating. The strain across the grating is enhanced by choosing MEMS beam configuration such that the metal electrode is the bottom-most layer of the composite fixed–fixed beam. Device dimensions are chosen to achieve a narrow full width half maximum of 0.77 nm, allowing filtering of adjacent channels of 100 GHz DWDM network. A large Bragg wavelength shift of 10.4 nm (1552.52–1562.92 nm) was achieved at 45.8 V actuation providing tuning for 14 DWDM channels with inter-channel cross talk below − 21 dB, with tuning range of 1.3 THz.

Electrostatically tunable MOEMS waveguide Bragg grating-based DWDM optical filter

An electrostatically actuated MEMS cantilever beam-based waveguide Bragg grating tunable optical filter has been designed and simulated. The tunable filter is obtained by shifting the reflected wavelength of the waveguide Bragg grating located on the electrostatically actuated cantilever beam. An approach to increasing the electrostatic actuation of the beam by having an electrode underneath the beam is used and a large wavelength tuning range for the optical filter is achieved. Dimensions of the device are chosen such that full-width-half-maximum is 0.75 nm, thus capable of filtering adjacent channels of the dense wavelength division multiplexing (DWDM) network. The filter has a tuning range of 10.65 nm (1552.52 to 1563.17 nm) providing add/drop functionality for 14 adjacent DWDM channels.

Investigation on Pointing Error in Multi-Beam Free Space Optical Communication System

Abstract Free space optical (FSO) communication has fascinated a lot of attention for a variety of applications in telecommunication area. It is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much favored because of its low maintenance cost and deployment time. Pointing error is one of the main challenges in FSO communication system which affects its performance especially at high data links that leads to significant performance degradation. In this paper, the impact of pointing error for multi-beam Hybrid Wavelength Division Multiplexing (HWDM) FSO system is investigated. Then the effect of link distance and Bit Error Rate (BER) are estimated by accounting the pointing error and atmospheric attenuation. The effect of change of link distance is examined while changing the number of beams between the transmitter and receiver as well. In this attempt, the HWDM system is considered by combining eight Dense Wavelength Division Multiplexing (DWDM) channels and four Coarse Wavelength Division Multiplexing (CWDM) channels. In addition, the influences of BER and receiver sensitivity are analyzed for the proposed system by incorporating Erbium Doped Fiber Amplifier (EDFA) at the receiver end. The data rate 2.5 Gbps is considered for both CWDM and DWDM channels for investigation.

Demonstration of 1.72 Tbit/s Optical Data Transmission Under Worst-Case Turbulence Conditions for Ground-to-Geostationary Satellite Communications

Optical dense wavelength division multiplexing (DWDM) can provide multiple Tbit/s throughput in the future geostationary satellite communications. In this letter, the proof-of-concept demonstration of this technology under worst case atmospheric channel conditions for satellite communications in geostationary orbit is presented. The highest-to-date throughput of 1.72 Tbit/s was transmitted over 10.45 km distance with passive transmitter pointing and active receiver tracking with active single-mode fiber coupling. This throughput was achieved by modulating 40 DWDM channels with uncoded 43.01824 Gbit/s rate per channel. Direct bit-error-rate and signal fluctuations measurements were carried out to assess the link performance. No forward error correction was used.

Single-photon frequency conversion via cascaded quadratic nonlinear processes

Frequency conversion of single photons is an important technology for quantum interface and quantum communication networks. Here, single-photon frequency conversion in the telecommunication band is experimentally demonstrated via cascaded quadratic nonlinear processes. Using cascaded quasi-phase-matched sum and difference frequency generation in a periodically poled lithium niobate waveguide, the signal photon of a photon pair from spontaneous down-conversion is precisely shifted to identically match its counterpart, i.e., the idler photon, in frequency to manifest a clear nonclassical dip in the Hong-Ou-Mandel interference. Moreover, quantum entanglement between the photon pair is maintained after the frequency conversion, as is proved in time-energy entanglement measurement. The scheme is used to switch single photons between dense wavelength-division multiplexing channels, which holds great promise in applications in realistic quantum networks.

Design of a Hybrid Optical amplifier for 64 DWDM Channels network by using EDFA and Raman Amplifier

In this paper a hybrid amplifier EDFA-RAMAN DWDM transmission system is proposed and demonstrated. A new hybrid two-stage optical fiber amplifier for dense wavelength division multiplexing (DWDM) network is observed. The hybrid amplifier is cascaded erbium- doped fiber amplifiers (EDFA) & Raman amplifier which provide a nearly flat gain over 80 nm. The hybrid amplifier has been modeled using an Optic-System version 14 on a DWDM transmission. In this paper we compare Q-factor at different input power i.e. at 0db and at 10 db. Here two different types of apodized function (Uniform & Gaussian) are selected as fiber Bragg grating parameters and system performance is analyzed. Performance of the system is analyzed by using BER analyzer.

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.

Performance Analysis of Hybrid WDM-FSO System under Various Weather Conditions

AbstractFree Space Optical (FSO) communication is being realized as an effective solution for future accessing networks, offering light passed through air. The performance of FSO system can be primarily degraded by various atmospheric attenuations such as rain, fog, haze and snow. At present, hybridization of Dense Wavelength Division Multiplexing (DWDM) with Coarse Wavelength Division Multiplexing (CWDM) becomes necessary to scale the speed and high bandwidth of the services. In this paper, primarily the attenuation values for different weather conditions are calculated. Then the hybrid WDM-FSO system is proposed, designed and the network parameters such as Bit Error Rate (BER), Quality factor (Q factor) and receiver sensitivity are analyzed with respect to link distance for various weather conditions. For investigation, four CWDM (1,510 nm, 1,530 nm, 1,570 nm and 1,570 nm) channel and eight DWDM channels (1,537.4 nm, 1,538.2 nm, 1,539 nm, 1,539.8 nm, 1,540.6 nm, 1,541.4 nm, 1,542.2 nm and 1,543 nm) are considered whose corresponding channel spacing is 20 nm and 0.8 nm, respectively. In addition, the Erbium Doped Fiber Amplifier (EDFA) is inserted at the receiver end in order to enhance the link distance. The proposed hybrid WDM-FSO system is designed to handle the quality of transmission for 12 users, each at a data rate of 2.5 Gbps along an FSO link distance of about 960 km.

Wavelength Resource Sharing in Bidirectional Optical Mobile Fronthaul

In this paper, we propose high-capacity spectrally-efficient optical mobile fronthaul (MFH) architectures featuring wavelength resource sharing, where multiple cell sites share one dense wavelength division multiplexing (DWDM) channel instead of occupying a number of separated DWDM channels. In the downlink (DL), subcarrier multiplexing (SCM) is integrated with DWDM passive optical network. The key technical innovation lies in the reception of uplink (UL) signals being optically aggregated with ultrasmall spacing. We introduce two novel schemes for spectrally-efficient and low-complexity upstream transmissions. The first method is based on SCM in remote radio heads (RRHs) and coherent detection in baseband units (BBUs), achieving channel spacing of as small as 100 MHz. For the first time, successful coherent reception of LTE signal, whose symbol rate (15 ksps) is much smaller than the laser linewidth, is achieved by pairing a radio frequency pilot tone from each RRH. Bidirectional transmission of four 20-MHz 16-QAM-OFDM LTE-like signals with 100-MHz spacing aggregated on one wavelength is demonstrated. For the second proposed UL scheme, we report a low-complexity ultradense WDM over DWDM allocation with 1-GHz wavelength spacing and novel phase-noise-insensitive heterodyne detection using MHz-linewidth lasers and an off-the-shelf envelope detector. We experimentally demonstrate the transmission and simple detection of multichannel 100/200 Mb/s OOK or 200 Mb/s 16-QAM-OFDM signals with 1-GHz spacing over 30-km standard single mode fiber using 5-MHz-linewidth lasers. By enabling ultrahigh spectral efficiency, high receiver sensitivity, and low-complexity, the proposed approach achieves a significant breakthrough for future high-capacity mobile fronthaul systems.

NG-PON2 Technology and Standards

This paper provides a tutorial overview of the latest generation of passive optical network (PON) technology standards nearing completion in ITU-T. The system is termed NG-PON2 and offers a fiber capacity of 40 Gbit/s by exploiting multiple wavelengths at dense wavelength division multiplexing channel spacing and tunable transceiver technology in the subscriber terminals (ONUs). Here, the focus is on the requirements from network operators that are driving the standards developments and the technology selection prior to standardization. A prestandard view of the main physical layer optical specifications is also given, ahead of final ITU-T approval.

Configuration of more than N DWDM channels with only one N × N cyclic-AWG-based wavelength routing device

A wavelength routing device based on only one N×N cyclic arrayed waveguide grating (AWG) having easy extended channels configuration is presented in this paper. It is easy to extend the dense wavelength division multiplexing (DWDM) channel configuration through this wavelength routing device. According to the cyclic wavelength of AWG, the wavelength routing devices are easy to configure more than N extended DWDM channels through cascading more proper tunable fiber Bragg gratings (FBGs). With only one 8×8 AWG, two different wavelength routing structures were built to evaluate static crosstalk and the bit-error-rate (BER). Three of the 16 inputted DWDM channels were demonstrated to verify that the proposed wavelength routing device, with only one 8×8 AWG, could configure extended DWDM channels without interfering with other channels. The results show that the wavelength routing device can produces a better performance and offers a cheaper way to extend the DWDM channel configuration for a dynamic network.