Wavelength Division Multiplexing Technology Research Articles

Advanced optical access technologies for next-generation (5G) mobile networks [Invited

Fixed optical transport is the predominant fronthaul technology for 4G mobile access networks, carrying the traffic between the central office and subtended antenna sites. With the new functional splits and related standards introduced in 5G, new capacity and quality-of-service requirements are imposed on optical transport. In this paper, we discuss low-cost high-capacity optical fronthaul solutions enabled by advanced modulation formats and wavelength-agnostic passive wavelength division multiplexing (WDM) technology. As the key component, a low-cost remotely tunable WDM transceiver is introduced, specifically designed on a hybrid InP-polymer platform. We also explain why an Ethernet-based 5G fronthaul solution requires additional means to improve the latency and timing performance of the conventional packet forwarding and multiplexing. We review the recent standardization effort on time-sensitive networking in support of 5G fronthaul and present an FPGA-based implementation providing low latency and low packet delay variation following the latest IEEE 802.1CM specification. These advanced technologies can facilitate an effective packet-optical transport for 5G.

Mechanophotonics: Flexible Single-Crystal Organic Waveguides and Circuits.

We present the one-dimensional optical-waveguiding crystal dithieno[3,2-a:2',3'-c]phenazine with a high aspect ratio, high mechanical flexibility, and selective self-absorbance of the blue part of its fluorescence (FL). While macrocrystals exhibit elasticity, microcrystals deposited at a glass surface behave more like plastic crystals due to significant surface adherence, making them suitable for constructing photonic circuits via micromechanical operation with an atomic-force-microscopy cantilever tip. The flexible crystalline waveguides display optical-path-dependent FL signals at the output termini in both straight and bent configurations, making them appropriate for wavelength-division multiplexing technologies. A reconfigurable 2×2-directional coupler fabricated via micromanipulation by combining two arc-shaped crystals splits the optical signal via evanescent coupling and delivers the signals at two output terminals with different splitting ratios. The presented mechanical micromanipulation technique could also be effectively extended to other flexible crystals.

Flexible coherent UDWDM-PON with dynamic user allocation based on limited-tunability lasers

Coherent wavelength division multiplexing (WDM) technologies have leveraged the optical communication systems in core networks, increasing the fiber capacity by transmission with advanced modulation formats and mitigation of impairments with digital signal processing. However, these solutions are too expensive for access networks, where cost, power budget, and footprint are limited. Hence, the key technology will be developing low-cost coherent transceivers providing an excellent selectivity and giving high sensitivity, which allows high splitting ratios. This paper reports an experimental design of a low-cost coherent ultra-dense WDM passive optical network (UDWDM-PON) with 6.25 GHz channel spacing. The users’ optical network unit (ONU) is built employing coherent transceivers with two paired low-cost distributed feedback (DFB) lasers, one as the local oscillator and another as the transmitter, offering simplicity and low-cost hardware; likewise, the optical line terminal (OLT) at the central office can profit from the same design. The ONU DFB lasers have wavelengths with limited thermal tunability, controlled by a thermo-electric cooler, which is used to allocate the wavelengths. A medium access control (MAC) at the OLT manages the spectrum channel allocation for ONUs, demanding connection when activation is requested: the OLT furnishes an optical carrier wavelength for the ONU to obtain connection by a control algorithm, assigning a down-channel and another paired up-channel assigned to the ONU DFB transmitter. The MAC can reassign the channels because of interference or collision in a dynamic wavelength allocation. Measures in an activation process and in channel reassignment have been performed in environmental conditions, including control signals and the physical parameters of DFB lasers, demonstrating the practical viability of the PON scaling from 32 up to 256 wavelength channels.

Design of Four-Channel Wavelength-Selectable In-Series DFB Laser Array With 100-GHz Spacing

A four-channel wavelength-selectable in-series DFB laser array with good single-longitudinal-mode (SLM) property is proposed and theoretically analyzed. To realize good SLM property, a linearly chirped Bragg grating with multiple π phase shifts are implemented in the laser cavity. In addition, two reflector sections with chirped Bragg grating are specially designed for reflection compensation at both ends. In our simulation, the split-step time-domain model with coupled-wave equations and carrier rate equations are used. Based on the simulation results, all the channels work with low threshold currents and the SLM properties are considerably enhanced compared with the conventional in-series laser array. Notably a high precision control of grating phase is required in the practical fabrication due to the ultra-small variation of grating period. Therefore, the reconstruction-equivalent-chirp technique is discussed to provide the fabrication of high-precision grating. In addition, the complex heterogeneous integration or butt-joint technique is not required during the whole fabrication process, which simplifies the fabrication and reduces the cost. The proposed wavelength-selectable in-series laser array is deemed to be applied in the dense wavelength division multiplexing technology, especially when fast wavelength switching is needed, such as in the application of NG-PON2.

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.

Research on the X-ray wavelength division multiplexing technology for blackout region communication

After the concept of X-ray communication was proposed, its application in complex electromagnetic environment has received more attention, such as data transmission in re-enter special electromagnetic condition. In this article, a new type of X-ray source was introduced firstly, which was expected to generate multiple characteristic lines and achieve wavelength division multiplexing technology in X-ray band. Then an experimental platform was built for analyzing transmission characteristics of X-ray photon in various plasma media. Finally, the calculation model for a link power equation was given. Experiment results show that transmittance of 8–18 keV X-ray signal is relatively stable, atomic numbers from 29 to 42 are the most suitable materials for wavelength division multiplexing, the X-ray communication system is expected to realize about 200 kbps data transmission rate in adjacent space.

Design of Novel Fiber Optical Flexible Routing System

In this paper, we propose a new versatile routing device that utilizes arrayed waveguide gratings (AWGs), optical switches, and optical circulators to implement reconfigurable optical add/drop multiplexers (ROADMs), optical interleavers, and optical cross-connect (OXC). With the development of dense wavelength division multiplexing (DWDM) technology, ROADM and OXC technologies have also been put into practical use. Thus, the optical signal can be routed directly in the optical network according to its wavelength without the need for optical-electrical-optical (OEO) conversion. Although different optical network units (ONUs) have different bandwidth requirements, the use of optical interleavers has successfully solved the connection problem between old and new systems. According to the numerical experiments of static characteristics, the proposed routing device can effectively implement three different functionalities, thereby providing greater flexibility for fiber optic network applications.

Effect of different temporal light fields on compressive temporal ghost imaging reconstruction

In this paper, we study the effect of different temporal light field patterns on compressive temporal ghost imaging. Wavelength division multiplexing technology is used for temporal ghost imaging to improve imaging efficiency. The applicability, robustness, and reconstruction performance of different temporal light fields are verified on the basis of research on the temporal ghost imaging mechanism. Simulation shows that Hadamard temporal light field pattern has better reconstruction effect and anti-noise ability than other light field patterns, and applies to different kinds of signals.

SD‐MAC: Design and evaluation of a software‐defined passive optical intrarack network in data centers

AbstractWith rapid development of cloud computing services, traffic in data centers (DCs) increases dramatically. Top‐of‐rack Ethernet switches dominate network cost and energy consumptions in DCs. Optical switching technologies have been introduced into DC networks to increase switching capacity and to reduce energy consumption. However, how to design high‐performance optical intrarack networks is still a great challenge. This paper presents a software‐defined passive optical intrarack network (SD‐POIRN) based on optical coupler fabrics. The data plane of SD‐POIRN is a broadcast‐and‐select optical network combining wavelength division multiplexing and time division multiplexing technologies. The control plane of SD‐POIRN has a centralized rack controller for scheduling intrarack data transmissions. This paper proposes a software‐defined media access control (SD‐MAC) protocol for SD‐POIRN. The SD‐MAC utilizes dynamic transmission and receiving server grouping methods and max‐min fair share bandwidth allocation algorithms to dynamically allocate bandwidth among servers in an efficient and fair manner. Network performance evaluation results show that, when the offered load is high, the proposed SD‐MAC protocol effectively increases network throughput and reduces average packet delay compared with previous works.

Vapour-Phase Epitaxial Growth of Dual-Colour-Emitting DCM-Perylene Micro-Heterostructure Optical Waveguides.

Organic micro-heterostructures (MHS) with dual optical emissions are essential to produce miniaturized optical waveguides for wavelength division multiplexing technologies. The bimolecular MHS produced by solution-based bottom-up self-assembly technique often leads to poor surface smoothness, edge imperfection, defects, and unwanted thin films deposits. Conversely, sequential sublimation technique at ambient pressure facilitates effective integration of α-perylene micro-square with dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) microrods in an epitaxial manner to produce MHS. The obtained DCM/perylene MHS act as optical waveguides to produce red (λmax ≈670 nm) or/and yellow (λmax ≈607 nm) dual optical outputs via an energy transfer mechanism depending upon the heterostructures geometry and optical excitation positions. The presented dual-color emitting MHS optical waveguides are essential for the integrated nano-photonic and optoelectronic device structures.

Key building blocks of a silicon photonic integrated transmitter for future detector instrumentation

The data throughput of future detector readout systems is ever increasing. We propose a high-performance optical link, based on silicon photonics and wavelength-division multiplexing (WDM) technology, to cope with ultra-broad bandwidth requirements. The key components of the proposed optical link are monolithically integrated transmitter units, each one integrating multi-channel on-chip Echelle grating (de-)multiplexers and Mach-Zehnder modulators (MZMs). In our current design, each transmitter unit consists of four MZMs, which corresponds to four transmission channels with distinct optical carrier wavelengths, a common optical demultiplexer and a common optical multiplexer. In this paper, we present the design and experimental results of all these building blocks as well as a first transmission experiment. Additionally, experimental results of a thermal modulator to be used in a future design for working point control are presented.

Wavelength assignment method based on ACO to reduce crosstalk for ring-based optical Network-on-Chip

Silicon photonic interconnect is a promising way for Network-on-Chip (NoC) to meet the high-performance computing requirement. Thanks to Wavelength Division Multiplexing (WDM) technology, the bandwidth is greatly improved compared to the tradition electrical interconnect. However, due to the inherent characteristics of silicon photonic devices, the existence of crosstalk deteriorates the optical signal-to-noise ratio (OSNR) at the network level. In order to mitigate the effects of crosstalk in the WDM-based Optical NoC, a wavelength assignment method is proposed in this paper. The simulation results indicate that our wavelength assignment based on ant colony optimization algorithm (WA-ACO) improves the worst-case OSNR by at least 21.2% and 19.84% for two applications (pip and mwd), compared to several fixed wavelength assignment methods.

Improved offline multi-objective routing and wavelength assignment in optical networks

Optical networks act as a backbone for coming generation high speed applications. These applications demand a very high bandwidth which can be exploited with the use of wavelength division multiplexing (WDM) technology. The issue of setting light paths for the traffic demands is routing and wavelength assignment (RWA) problem. Based on the type of traffic patterns, it can be categorized as offline or online RWA. In this paper, an effective solution to offline (static) routing and wavelength assignment is presented considering multiple objectives simultaneously. Initially, the flower pollination (FP) technique is utilized. Then the problem is extended with the parallel hybrid technique with flower pollination and intelligent water drop algorithm (FPIWDA). Further, FPIWD is hybrid in parallel with simulated annealing (SA) algorithm to propose a parallel hybrid algorithm FPIWDSA. The results obtained through extensive simulation show the superiority of FPIWD as compared to FP. Moreover, the results in terms of blocking probability with respect to wavelengths and load of FPIWDSA are more propitious than FP and FPIWD.

60 Gbit/s coherent wavelength-division multiplexing free-space optical modulating retro-reflector in a turbulence-tunable atmospheric cell

A novel high-speed coherent modulating retro-reflector (MRR) is presented and experimentally demonstrated for free-space optical (FSO) communications by using an in-phase quadrature (IQ) modulator with quadrature phase-shift keying (QPSK) signals to break the conventional speed limitation. The transmission performance is tested in a turbulence-tunable atmospheric cell. The received sensitivity is measured to be <14.7 dB PPB, and the power penalty is <2.0 dB for 20 Gbit/s single-channel QPSK signal at the BER of 0.01 when the temperature difference is <250 °C. Moreover, this MRR scheme is compatible to wavelength-division multiplexing (WDM) technology, and a 60 Gbit/s WDM MRR is demonstrated using three channels with only about 0.6 dB degradation.

Co-existence of OFDM and FBMC for resilient photonic millimeter-wave 5G mobile fronthaul

This paper presents a novel co-existence of multiple Fifth-Generation (5G) services employing Orthogonal Frequency Division Multiplexing (OFDM) and Filter Bank Multicarrier (FBMC) waveforms in a resilient photonic Millimeter-wave (mmWave) mobile fronthaul architecture. The 5G services are delivered to the remote antenna using shared optical infrastructure and simultaneously upconverted to mmWave frequencies using only one optical local oscillator (LO) for heterodyne upconversion. Radio-over-fiber technology is employed for cloud-radio access network, in which the optical LO used for mmWave upconversion can be placed either at the remote radio head shared by both downlink and uplink signals or remotely delivered from the central office. In addition, the proposed architecture supports the integration of wavelength division multiplexing technology, which enables seamless scalability and management of the photonic infrastructure. As multiple lasers beat to generate the mmWave signals, laser phase noise becomes the dominant system impairment, degrading the detection performance. In order to mitigate the effect, frequency averaging technique is applied to enhance the channel estimation. The comprehensive analysis of different transmission scenarios using industry standard VPI Transmission Maker® simulation platform has demonstrated successful co-existence and transmission of OFDM and FBMC 5G services simultaneously upconverted to 28 GHz, 38 GHz and 60 GHz mmWave signals after 40 km fiber and 2 m wireless. Compared with FBMC, OFDM exhibits better resilience to phase noise with better Error Vector Magnitude (EVM) values at low received powers, but with the application of intra-symbol frequency-domain averaging, the EVM performance of FBMC is comparable to OFDM.

Multiwavelength Q-switched erbium-doped fibre laser-based aluminum nanoparticles saturable absorber and sagnac loop filter

In this paper, we experimentally demonstrate a stable multiwavelength Q-switched erbium-doped fiber laser generation based on aluminum nanoparticles (AlNPs) as the saturable absorber (SA), with the aid of a Sagnac loop filter for the first time, to the best of author’s knowledge. The fabricated AlNPs-SA has a modulation depth, a non-saturable loss and saturable intensity of 7%, 10% and 0.0015 MW cm−2, respectively. By carefully adjusting the polarization controller and progressively increasing the pump power, up to 11 lasing lines in the Q-switching regime are obtained with a channel spacing and an optical signal-to-noise ratio of 0.48 nm and 30 dB, respectively. Meanwhile, the Q-switched performance has a minimum pulse width of 2.36 µs and a maximum pulse repetition rate of 33.45 kHz by varying the pump power to 300 mW. The proposed laser may become valuable for numerous applications such as dense wavelength division multiplexing technology.

Integrated silicon multifunctional mode-division multiplexing system.

Chip-scale optical interconnects have been widely investigated using the wavelength-division multiplexing (WDM) technology, while it has been rarely reported using the mode-division multiplexing (MDM) technology that further improves communication capacity by using multiple spatial mode channels. On the other hand, to achieve large-bandwidth multi-core computing, a flexible and reconfigurable network is highly desired. Here, we proposed and demonstrated a 4 × 4 chip-scale multifunctional MDM system to realize the interconnects among 4 dual-core computing processors. The proposed system integrates fundamental components such as high-speed modulator arrays, multimode switches, and large-bandwidth photodetector arrays, in addition to various multimode devices. The thermal heaters are utilized to achieve multifunctional routing, including inter-mode and inter-path cases. The transmission of 10 Gb/s On-Off Keying (OOK) signal is verified, which demonstrates the reconfigurable inter-core and inter-processor interconnects.

Fat‐tree‐based optical networks‐on‐chip with WDM: crosstalk noise exploiting

Wavelength division multiplexing (WDM) technology as an extension of optical networks-on-chip (ONoCs) performance, can be applied to further overcome shortages of low bandwidth and high-power consumption in multiprocessor systems-on-chip. Nevertheless, WDM-based ONoCs (ONoCs_W) can encounter performance degradation and network scalability constraints because of its power loss and intrinsic crosstalk noise, especially the non-linear four-wave mixing crosstalk noise. Here, a formal systematical exploiting for worst-case crosstalk noise and optical signal-to-noise ratio (OSNR) in arbitrary fat-tree-based ONoCs with WDM (FONoCs_W) is proposed. Meanwhile, the worst-case OSNR optical link candidates are identified. To verify the proposed analysis method, FONoCs_W employing an optical turnaround router with WDM (WOTAR) is used for case study. The study results demonstrate that crosstalk noise significantly diminishes OSNR and restricts scalability of FONoCs_W. For instance, when input optical signal power equals 0 dBm in worst case, the average OSNR is -9.47 dB, the mean power of crosstalk noise for eight wavelengths is slightly greater than that of signal when the number of processor cores is 64; when it equals to 128, the average OSNR is -34.37 dB, decreased by 24.90 dB compared with the network with 64 processor cores.

Semi‐passive optical front‐haul supporting channel monitoring and link protection for the cloud radio access network

To accommodate the extremely large traffic load on the front-haul of a cloud radio access network, optical fibres along with wavelength division multiplexing (WDM) technology have become the de facto solution. In this study, the authors propose the model of a semi-passive front-haul device that can overcome the vulnerability of the optical fibre by using duplicated optical fibres and optical power monitoring for each WDM channel. Experiments conducted on the implemented prototype demonstrate that the link protection mechanism satisfies the regulation imposed by the international standard and that the optical power monitoring results are accurate. Thus, the proposed semi-passive front-haul device provides a high link reliability, fault reporting capability, and low operating cost.

Review and analysis of elastic optical network and sliceable bandwidth variable transponder architecture

Traditional dense wavelength division multiplexing (DWDM) technology is no longer enough to meet the extensive growth in the demand of bandwidth in an efficient and effective manner under the fixed grid environment. Thus, a technology is needed to overcome the challenges raised by the ever-increasing demand of bandwidth in an effective manner with efficient utilization of spectral resources. To solve this problem, an elastic optical network (EON) paradigm comes into existence. It uses a flexible grid technology that removes the limitations of fixed grid DWDM technology and increases the channel capacity to meet current bandwidth demand with proper utilization of optical spectrum. We present the evolution of EON from the DWDM network. We have discussed the main components and characteristics of EON that includes superchannel and sliceable bandwidth variable transponder (SBVT). Thereafter, we discuss the different modulation and transmission techniques used in EON. Next, we present the recently proposed architectures of SBVT followed by its applications. Lastly, we have discussed various subcarrier generation techniques in brief.