Optical Add-drop Multiplexer Research Articles

Elastic Optical Networking in the Microsoft Cloud [Invited

To keep pace with the tremendous bandwidth growth in cloud networking, web-scale providers, such as Microsoft, have been quick to adopt elastic features of modern optical networks. In particular, colorless flexible-grid reconfigurable optical add-drop multiplexers, bandwidth-variable transceivers, and the ability to choose a variety of optical source types are integral for cloud network operators to improve network efficiency while supporting a variety of service types. We take an in-depth look at Microsoft's deployed network infrastructure and discuss the impact of elasticity on network capacity and flexibility. As a proof-of-concept, a new elastic open line system (OLS), in which the line system components and the signal sources are disaggregated, was assembled in a laboratory environment, and 4000 km of propagation over primarily nonzero dispersion-shifted fiber using multiple source types is demonstrated. Finally, the long-term goal of unifying the control plane of the OLS, DWDM signal sources, routers, and Ethernet switches under a single software-defined network controller is briefly addressed.

Optical Label Switching Add-Drop Multiplexer for High-Performance Metro Networks

We demonstrate a novel fast optical add-drop multiplexer (OADM) for high-capacity and low-latency next-generation metro network by exploiting optical label switching technology. The parallel optical label processing technique allows nanoseconds OADM reconfiguration time for efficient statistical multiplexing of the data packets, and facilitates per channel power monitoring for implementing nanoseconds semiconductor optical amplifier-based per channel power equalization. Experimental results of a ring network with four OADM prototypes confirm nanoseconds dynamic add/drop operation, including multicasting and power equalization for 50-Gb/s data payload. The average delivery time is $ (40-km ring), and the packet loss is $ for a load of 0.4 and 16-packet buffer.

Infrastructure planning and topology optimization for reliable mobile big data transmission under cloud radio access networks

With the development of user-centered and environment sensing technology of 5G, large capacity and ubiquitous coverage and massive data collection and processing will bring new challenges in wireless networks. The cloud radio access network (C-RAN) has been envisioned to provide a new wireless architecture for reliable transmission of mobile big data. In this paper, we focus on network planning deployment issue based on the optical mixed diet (OMD) technology. Specifically, the ring and spur topology optimization (RSTO) problem under the C-RAN architecture is investigated. The RSTO problem is formulated as a generic integer linear program (ILP) which can optimally (i) minimize the network deploying cost; (ii) identify the locations of Remote Radio Units (RRUs) and optical add-drop multiplexers (OADMs); (iii) identify the association relations between RRUs and OADMs; and (iv) satisfy the mobile coverage requirements so as to allow the mobile big data to be transmitted through the RRUs. We propose a new heuristic algorithm based on C-RAN architecture. Numerical results validate the ILP formulation and show the performance benefits of the proposed algorithm in terms of efficiency and effectiveness against Gurobi, which is an ILP solver. In numerical studies, we also demonstrate the performance benefits of the incorporation of CoMP technology in terms of total deployment cost reduction.

Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators

We report on an eight-channel reconfigurable optical add-drop multiplexer (ROADM) based on micro-ring resonators (MRRs). The effective footprint of the device is about 1000×760μm2. The free spectral range (FSR) is about 18nm. The adjacent channel crosstalk ranges from −19.02dB to −8.29dB. With the help of the multi-wire structure heaters, compact footprint and high tuning efficiency are achieved simultaneously. Therefore, the minimum average tuning efficiency is 2.723mW/nm.

Analysis of SDWDM Ring Network and Enhancement Using Different Hybrid Optical Amplifiers and Modulation Formats

AbstractIn this paper, performance enhancement of super-dense wavelength division multiplexing (SDWDM) optical add–drop multiplexer optical ring network for six nodes, 50 wavelengths having channel spacing of 0.2 nm for 300 km unidirectional nonlinear fiber is successfully demonstrated. The performance of the designed system is enhanced by comparing different modulation formats (non-return to zero (NRZ), return to zero (RZ), soliton, chirped return to zero (CRZ), carrier-suppressed RZ (CSRZ)) and hybrid amplifiers (Erbium-doped fiber amplifier (EDFA)–EDFA, semiconductor optical amplifier (SOA)–SOA, SOA, EDFA, EDFA–SOA) on the basis of eye diagram and bit error rate (BER). It has been observed that CRZ modulation format and EDFA-SOA shows the best results. It has been reported that EDFA-SOA/CRZ modulation format can achieve BER as better as e-13, which gives best performance. The effect of channel spacing on SDWDM system and performance degradation due to crosstalk is also evaluated.

Design of an All-Optical Network Based on LCoS Technologies

AbstractIn this paper, an all-optical network composed of the ROADMs (reconfigurable optical add-drop multiplexer), L2/L3 optical packet switches, and the fiber optical cross-connection for fiber scheduling and measurement based on LCoS (liquid crystal on silicon) technologies is proposed. The L2/L3 optical packet switches are designed with optical output buffers. Only the header of optical packets is converted to electronic signals to control the wavelength of input ports and the packet payloads can be transparently destined to their output ports. An optical output buffer is designed to queue the packets when more than one incoming packet should reach to the same destination output port. For preserving service-packet sequencing and fairness of routing sequence, a priority scheme and a round-robin algorithm are adopted at the optical output buffer. The wavelength of input ports is designed for routing incoming packets using LCoS technologies. Finally, the proposed OFS (optical flow switch) with input buffers can quickly transfer the big data to the output ports and the main purpose of the OFS is to reduce the number of wavelength reflections. The all-optical content delivery network is comprised of the OFSs for a large amount of audio and video data transmissions in the future.

Software-Defined Optics in Last Mile for Research and Education in the Czech Republic

The Software Defined Networking (SDN) gained recognition due to its improvements at the packet switching and routing layers. The benefits of programmable, remotely controllable networking devices can be applied to the optical layer of contemporary networks as well. This work introduces CESNET's Czech Light~® family of devices and their role in enabling the SDN approach within the CESNET's production network. As a case study, an upgrade of the Cheb node in CESNET's network from a hard-spliced add-drop multiplexers to SDN-capable Reconfigurable Optical Add-Drop Multiplexers (ROADM) is presented. The upgrade improved operational capabilities of the network, including remote channel equalization, and the possibility to deploy new channels or lambdas without physical intervention. The deployment of ROADM also improved the optical properties of the network.

<inline-formula> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> Flexible Wavelength Cross-Connect for CDC ROADM Application

We propose and demonstrate an $8\times 8$ flexible wavelength cross-connect (FWXC) switch that supports flex-grid wavelength assignment switching with contentionless feature. The developed switch is characterized for insertion loss, passband, frequency-tuning granularity, and port crosstalk. Based on the FWXC, we experimentally demonstrate a novel ultracompact colorless/directionless/contentionless-reconfigurable optical add drop multiplexer supporting four directions. Mixed 10G/40G/100G signals on add, drop, and express paths are tested. The optical signal-to-noise ratio (OSNR) penalties are observed <0.25 dB for all the cases.

All-optical and digital non-linear compensation algorithms in flex-coherent grouped and un-grouped contiguous spectrum based networks

We have evaluated that in-line non-linear compensation schemes decrease the complexity of digital backward propagation and enhance the transmission performance of 40/112/224 Gbit/s mixed line rate network. Multiple bit rates, i.e. 40/112/224 Gbit/s and modulation formats (i.e. DP-QPSK and DP-16QAM) are transmitted over 1280 km of Large \(\hbox {A}_{eff}\) Pure-Silica core fiber. Both grouped and un-grouped spectral allocation schemes are investigated. Optical add-drop multiplexers are used to drop the required wavelength for signal processing in the transmission link. Moreover, hybrid mid-link spectral inversion and in-line non-linear compensation methods are also analyzed. This gives us enhanced system performance and DBP step-size of 400 km in WDM 224 Gbit/s DP-16QAM system, significantly reducing the complexity of digital backward propagation.

Passive ROADM Flexibility in Optical Access With Spectral and Spatial Reconfigurability

An energy-aware solution for physical-layer reconfigurability in metro-access networks is presented. The dynamicity of optical switching is introduced in nodes that are perceived as fully-passive by the network. Energy scavenging at low optical feed level of $- 10\;{\text{dBm}}$ supports field-deployment without local electrical power supply. Two types of network nodes are demonstrated experimentally. First, a resilience node is evaluated for fast protection switching in 10.7 ms at the feeder segment. Optical switching is further exploited for the purpose of dynamic allocation of spectral slices and routing in a new class of reconfigurable optical add-drop multiplexer. The spectral bandwidth of drop segments can be extended on demand while intranetwork communication among different segments of the access network is also enabled. Finally, we discuss the potential for realizing self-powering by means of tapping optical signals traversing the access network rather than utilizing a dedicated pump source.

Nyquist-Filtering (De)Multiplexer Using a Ring Resonator Assisted Interferometer Circuit

We present a Nyquist-filtering optical (de)multiplexer using a ring resonator-assisted interferometer circuit. It features a near-rectangular passband spectrum, scalable port count, and can be designed with sub-GHz spectral resolution. The circuit can be constructed using ordinary passive photonic-integrated circuit building blocks. In contrast to its counterparts using tapped-delay-line circuit topologies, this circuit has a chip area two-orders-of-magnitude smaller. The results of this study show the potential for realizing high-spectral-efficiency multicarrier transceivers and reconfigurable optical add-drop multiplexers in a fully integrated form.

Low crosstalk Bragg grating/Mach-Zehnder interferometer optical add-drop multiplexer in silicon photonics.

We characterize the interferometric crosstalk and system performance of two optical add-drop multiplexer (OADM) designs based on Bragg grating/Mach-Zehnder interferometers implemented in silicon-on-insulator. Both OADM designs exhibit low crosstalk and negligible crosstalk-induced power penalties over their 3 dB bandwidths. The devices are tolerant to wavelength drift and misalignment between the transmitter and OADM; moreover, their designs can be optimized further to enable high performance operation in WDM systems.

Elastic optical ring with flexible spectrum ROADMs: An optical switching architecture for future data center networks

Data center networks (DCN) are facing significant increase in both scale and bandwidth requirement, and various intra-DCN optical circuit switching architectures have been proposed to handle the inter-rack traffic. As the size of data centers are becoming larger, ring based architectures have received considerable interests, because a ring can provide connectivity to a large number of racks that are distributed far apart in a data center. However, due to the specific data center traffic pattern, fixed spectrum allocation scheme in existing ring based DCNs will lead to low spectrum utilization and hence low system throughput. In this paper, we propose to introduce flexible spectrum allocation into ring based intra-DCN optical switching, so that spectrum utilization can be improved. We design an elastic ring intra-DCN optical circuit switching architecture with flexible spectrum reconfigurable optical add-drop multiplexers (FS-ROADMs). Adopting flexible spectrum allocation in elastic ring, a spectrum allocation problem which is essentially a very complex yet interesting optimization problem arises. For a given set of inter-rack traffic requests, we develop an integer linear program formulation as well as a heuristic algorithm to solve the flexible spectrum allocation problem. We study how the inter-rack traffic pattern may affect the system performances in both fixed and elastic ring cases. For elastic ring, we also analyze and evaluate the computational complexity in solving the spectrum allocation problem. Our results demonstrate that, to handle uneven inter-rack traffic pattern in DCNs, elastic ring can remarkably improve system throughput, though its computational complexity of spectrum allocation problem is slightly higher than that of the fixed ring.

Energy efficiency in WDM fiber-optical links considering OADM/OXC nodes

In this paper, authors discuss the energy consumption for 1bit transmission as a function of spectral efficiency (SE, bps/Hz), aggregated traffic amount (C, bps), and overall transmission distance (LP2P, km) in wavelength division multiplexing (WDM) systems with optical add-drop multiplexer/ optical cross-connect (OADM/OXC) nodes. The choice of bitrate and modulation formats was limited to three options: 10G non-return-to-zero on-off keying (NRZ-OOK), 40G NRZ differential phase-shift keying (NRZ-DPSK) and 100 dual polarization quadrature phase-shift keying (DP-QPSK). The reasons for that is the legacy in transmission networks and high energy efficiency of 3R (re-amplification, re-timing, re-shaping) regenerators and transponders, respectively. In addition, these formats are commonly used for 10-40-100G mixed-line rate solutions in core networks. It is found out that 100G DP-QPSK is the best solutions among two other considered in terms of both energy consumption per bit and spectral efficiency. Finally and foremost, it is estimated that for the WDM channels added at the OADM/OXC node, energy consumption per 1 transmitted bit could growth more than two times as compared to wavelengths transmitted over point-to-point fiber-optical links and then dropped at the receiving node.

Multichannel OADM using cascaded Bragg grating/Mach–Zehnder interferometers in SOI

Multichannel optical add–drop multiplexers (OADMs) based on cascaded Bragg grating/Mach–Zehnder interferometers in silicon-on-insulator are reported. The OADMs are fabricated using electron beam lithography with a single etch. Three add–drop channels at wavelengths of 1542.5, 1557.0, and 1570.4 nm, each with a 3 dB bandwidth (BW) of 4 nm are obtained. All channels exhibit a transmission isolation of >20 dB, an interferometric crosstalk of 0.5.

A nonreciprocal add-drop multiplexer based on grating assisted couplers

We propose a nonreciprocal optical add-drop multiplexer with silicon waveguide, which is realized by grating assisted coupler employing magneto-optical nonceciprocal phase shift. This device can achieve different adding or dropping peak wavelengths when light is launched in the forward-directed and backward-directed propagation. The calculation results show that the shift of the different dropping peak wavelengths is up to 0.7nm. Also, we demonstrate its applications for narrowband optical isolators and circulators. This work demonstrates that on-chip nonreciprocal optical add-drop multiplexers and optical isolations can be implemented with the proposed device, which has promising applications for optical communication systems and photonic integrated devices.

Eight-Channel Optical Add-Drop Multiplexer With Cascaded Parent-Sub Microring Resonators

An eight-channel integrated optical add-drop multiplexer with cascaded parent-sub microring resonators is experimentally demonstrated on a silicon-on-insulator (SOI) substrate. Through thermal tuning, each channel can be independently switched between the adding and dropping states. The measured thermal tuning efficiency is 0.15 nm/mW. Typically, all eight channels can be multiplexed and demultiplexed with a 2.6-dB drop loss, a 0.36-nm bandwidth ( $>$ 40 GHz), and a $-$ 20-dB channel crosstalk. Moreover, the scheme to increase the number of operating channels is also discussed.

Performance Evaluation of Integrated OTN/WDM Metropolitan Networks in Static and Dynamic Traffic Scenarios

The introduction of optical transport network (OTN) switching technology in metropolitan networks enables efficient wavelength bandwidth utilization and reduces the number of wavelengths, leading to reduced network costs. It has been shown that the use of integrated OTN/WDM switch architecture is cost effective because it reduces the number of short-reach client interfaces and the rack space compared to an architecture that uses a reconfigurable optical add–drop multiplexer and a separate standalone OTN switch or one that uses back-to-back muxponder connections to perform manual grooming. We have proposed an integrated OTN/WDM switch that allows for significantly lower complexity and cost at the price of relaxing the nonblocking ideal performance requirements normally applied to this kind of switch. In this paper we investigate the impact that the switch blocking has on the network performance in static and dynamic scenarios. We formulate the routing problem in the integrated OTN/ WDM network as an integer linear problem and develop an efficient heuristic to evaluate the blocking performance in a static traffic scenario. We study the blocking degradation of the proposed switch in the case of some metropolitan networks, and we show how higher blocking occurs in networks having a larger average node degree. We also show that the degradation of two orders of magnitude in blocking probability occurring under a dynamic traffic scenario can be mitigated with the introduction of a spatial speedup equal to 1.5.

Four-channel optical add-drop multiplexer based on dual racetrack micro-ring resonators

In this paper we report on a four-channel optical add-drop multiplexer based on dual racetrack micro-ring resonators in submicron SOI rib waveguides. The free spectral range (FSR) is about 18.6nm. The device can add/drop four optical channels in half C-band. When the device acts as an optical drop multiplexer, the channel spacing is about 1.5nm, maximum extinction ratio is 23.75dB, the minimum insertion loss 9.94dB and the maximum adjacent channels crosstalk is −12.12dB. When the device acts as an optical add multiplexer, the maximum extinction ratio is 28.72dB and the minimum insertion loss 7.35dB. The fabricated device has effectively and perfectly realized the signals upload and download.

Optical signal-to-noise ratio monitoring based on four-wave mixing

The transmission rates of the next generation intelligent optical networks are high, and the use of dense wavelength division multiplexing and a reconfigurable optical add-drop multiplexer makes the traditional optical signal-to-noise ratio (OSNR) monitoring techniques unsuitable. Hence, we investigated the OSNR monitoring method based on the nonlinear effect of four-wave mixing (FWM), which applies to the next generation intelligent optical networks. Due to FWM in a highly nonlinear fiber, a converted wave is generated and its power is dependent on the OSNR of the input signal. Two scenarios are studied, single-pump and orthogonal-polarized dual-pump. Under the condition of the given fiber length and the appropriate pump power, the monitoring ranges of OSNR could be extended to 23 and 30 dB for single-pump and orthogonal-polarized dual-pump, respectively.