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What is Reconfigurable Optical Add-Drop Multiplexer

What is Reconfigurable Optical Add-Drop Multiplexer

In the fiber optic network which uses wavelength division multiplexing (WDM), reconfigurable optical add-drop multiplexer (ROADM) is used to remotely add, block, pass or redirect modulated light emissions-infrared and visible-within a range of wavelengths.

With ROADM devices, signal switching doesn’t need optical-to-electric and electric-to-optical conversions. Instead, outgoing light beams can be generated, incoming beams could be terminated or beams could be passed through the device unmodified. This is achieved through wavelength-selective switch (WSS) components within the device.

A ROADM allows remote configuration and reconfiguration of emissions; bandwidth could be assigned when needed and without interrupting concurrent traffic, and power balancing is automatic. Most ROADM devices use technologies according to first-generation, wavelength blocking (WB) or second generation, planar light-wave circuit (PLC) technology. Whenever a wavelength change is required inside a specific channel, these technologies filter light emissions, extract data and impress data onto another emission. This method is more streamlined using PLC technology.

The different switching technologies in ROADM devices include microelectronic mirrors, live view screen, thermo-optic and beam-steering switches in planar waveguide circuits, and tunable optical filters.

ROADM devices were initially used in long-haul DWDM equipment. By 2005, metropolitan networks began using ROADMs in reaction to increased interest in Ethernet, as well as high-speed data, audio and video services. Within the ensuing years, ROADM devices have brought bandwidth flexibility and operational efficiency to networks. ROADM-based networks are enabling an automated optical layer with dynamic multipoint connectivity, independent wavelength add-drop, remote bandwidth allocation that has been enhanced power management capabilities.

Combined with the benefits of ROADM comes the inevitable need for fiber optic testing that safeguards function and helps to make sure performance. Here are common testing-related challenges to consider in ROADM-based networks.

1. Increases both in insertion loss per node and insertion loss per channel

2. The need to measure optical loss per channel for multiple ROADM configurations

3. The necessity to measure optical signal-to-noise ratios utilizing a precise and repeatable method

4. The impact of possible bandwidth thinning, other changes to bandwidth, and dispersion, that is of particular concern in multiple cascaded devices and 40 Gbit/s systems

5. Compliance using the optical transport network (OTN) standard-ITU-T G.709 standard

Unlike the optical add-drop multiplexer, Capabilities of ROADM test equipment should encompass optical spectrum analysis (OSA), and OTN performance qualifiers for newly commissioned links, along with the transport layer and all ROADM-supported interfaces. Major manufacturers of OSA and related electronic test equipment include, FiberStore, Anritsu, Digital Lightwave, Exfo and JDSU Test.


Construct smarter fiber optic networks with ROADM technology

Construct smarter fiber optic networks with ROADM technology

As IPTV, triple play, VoIP and other new telecommunications services rise, people find that IP-bearing agreement business has rapidly spread in most regions of telecommunications and fiber optic networks.

IP-based packet-based carrier network transformation has been become an irreversible trend. In this trend, carriers are shifting the entire network infrastructure, business anticipates the integration of optical layer integration as a foundation bearing layer, making it even more right for carrying IP/MPLS and Carrier Ethernet services group transmission network. The brand new telecom services in contrast to traditional telecom services, with increased dynamic and unpredictable, therefore have to transfer the bearer network to provide greater flexibility.

Because the same time, long-distance dense WDM mature, making the network a real business of building from the bandwidth bottleneck within the transfer to the bandwidth management, within the core network nodes, often need to deal with dozens or perhaps hundreds of wavelengths, but long-distance transmission capability and much more nodes must have more capacity to the upper minimizing wavelength. Like a basis for carrying the network inside a more competitive market environment, it needs to provide faster service and various amounts of network protection and recovery capabilities. Therefore, as the traditional physical layer of optical layer network, we must adjust to a brand new generation of packet-based bearer networks, operational, bandwidth, large granular, and dynamic networking needs.

DWDM is the most common optical layer networking technology. Through multiplexing/demultiplexing, it can achieve tens or perhaps countless wave wave transmission capacity. However in the current WDM systems, its nature is still a point-line system, most of the optical layer network only through the terminal station (TM) to achieve the optical line system construction. Later, Optical add-drop multiplexer (OADM) gradually taken point to point network to the ring from the evolution. However, due to the limited OADM functions, usually merely a fixed number of levels and wavelengths of sunshine channel, and never really flexible optical layer networking. Thus, in this way, early WDM systems do not achieve true optical layer networking, IP-based networks can not meet the business requirements and packet-based until the emergence of the situation was able to enhance the ROADM. To meet up with the needs of IP networks, it provides a new idea that gradually adopt a reconfigurable optical add drop multiplexer plug (ROADM), represented by optical layer reconfiguration technology, and in line with the construction of the bearer network.

ROADM Technical Introduction is really a similar SDHADM optical layer network element, which can be completed in one node down and up road of sunshine channels (Add/Drop), and penetrating between your optical channel wavelength-level cross-scheduling. It can be remotely controlled by software, network aspect in achieving the lower and upper road wavelength ROADM sub-system configuration and adjustment. Currently, ROADM subsystem, there are three common techniques: planar lightwave circuit (PLC), wavelength blocker (WB), wavelength selection switch (WSS).

PLC is among low-cost ROADM solution. The advantage is that multiplexer and demultiplexer technology is mature and reliable, low insertion loss within the node, down way more when costs are lower wavelength, simple to upgrade to the OXC; drawback is poor modular structure, the initial configuration and high cost, large capacity the longevity of cross matrix must be improved.

Physical factors as transmission, all-optical transmission distance is susceptible to certain restrictions, within the backbone network applications, the company flow and also the flow can not be any change, still need to accurately design and planning, increasing the complexity of network planning. Deutsche Telekom is also clear the physical limitations affecting ROADM transport network of important reasons.

Based on existing ROADM these shortcomings, the proposed to increase the cross-field power. So had a ROADM OTN equipment form. Typical applications are now, in excess of 10G (with 10G) business, the node all-optical way through or up and down, for GE/2.5G business, its first node towards the electric field under the road crossing panels, according to further 2.5G particles and electric field-drop multiplexing. This drop multiplexing mode somewhat similar to the ADM, just the first-class all-optical processing. Equipment manufacturers have previously released products, and in certain applications inside the metropolitan area.

Optical WDM in Fiber Optic Network

Optical WDM in Fiber Optic Network

Optical WDM networks are networks that deploy optical wdm fiber links where each fiber link carries multiple wavelength channels.

An exciting Optical Network (AON) is definitely an optical wdm network which supplies end-to-end optical paths by using all optical nodes that allow optical signal in which to stay optical domain without conversion to electrical signal. AONs are often optical circuit-switched networks where circuits are switched by intermediate nodes in the granularity of the wavelength channel. Hence a circuit-switched AON can also be called a wavelength routing network where optical circuits are equal to wavelength channels.

A wavelength routing network includes optical cross-connect (OXC) and optical add-drop multiplexer (OADM) interconnected by WDM fibers. Transmission of information over this optical network is performed using optical circuit-switching connections, referred to as lightpaths. An OXC is definitely an N * N optical switch with N input fibers and N output fibers with every fiber carries wavelengths. The OXC can optically switch all the incoming wavelengths of its input fibers to the outgoing wavelengths of its output fibers. An OADM can terminate the signals on a quantity of wavelengths and inserts new signals in to these wavelengths. The rest of the wavelengths pass through the OADM transparently.

For a user to deliver data to some destination user, a circuit-switching connection is made by using a wavelength on each hop along the connection path. This unidirectional optical path is known as lightpath and also the node in between each hop is either an OXC or an OADM. These units are utilized within the 100G DWDM networks. A separate lightpath has to be established using different fibers to setup transmission within the opposite direction. To fulfill the wavelength continuity constraint, the same wavelength can be used on every hop along the lightpath. If a lightpath is blocked since the required wavelength is unavailable, a converter in an OXC can transform the optical signal transmitted in one wavelength to another wavelength.

Because the bandwidth of a wavelength is usually much larger than that requires by a single client, traffic glooming is used to allow the bandwidth of the lightpath to be shared by many people clients. The bandwidth of the lightpath is split into subrate units; clients can request one or more subrate units to carry traffic streams at lower rates. For instance, information is transmitted over an optical network using SONET (Synchronous Optical Network) framing with a transmission rate of OC-48 (2.488 Gbps). A lightpath is established from OXC1 to OXC3 through OXC2 using wavelength w, the subrate unit available on this lightpath is OC-3 (155 Mbps). A user on OXC1 can request any integer number of OC-3 subrate units up to a total of 16 to transmit data to another user on OXC3. A network operator can use traffic-groomed lightpaths to provide subrate transport services to the users with the addition of an online network towards the fiber optic network.

Information on a lightpath is typically transmitted using SONET framing. In the future, the data transmitted over optical network uses the brand new ITU-T G.709 standard, referred to as digital wrapper. In ITU-T, an optical network is referred to as the optical transport network (OTN). Listed here are some of the options that come with G.709 standard: 1) The conventional permits transmission of various kinds of traffic: IP packets and gigabit Ethernet frames using Generic Framing Procedure (GFP), ATM cells and SONET/SDH synchronous data. 2) It supports three bit rate granularities: 2.488 Gbps, 9.95 Gbps and 39.81 Gbps. 3) It offers capabilities to monitor an association on an end-to-end basis over several carriers, in addition to over a single carrier. 4) G.709 uses Forward Error Correction (FEC) to detect and correct bit errors brought on by physical impairments in the transmission links.

Lightpath may either be static or dynamic. Static lightpaths are in place using network management procedures and may remain up for a long time. Virtual Private Networks (VPN) could be set up using static lightpaths. Dynamic lightpaths are established instantly using signaling protocols, such as GMPLS (Generalized Multi-Protocol Label Switching) and UNI (User Network Interface) proposed by OIF (Optical Internetworking Forum). GMPLS is definitely an extension of MPLS and is built to apply MPLS label switching techniques to Time Division Multiplexing (TDM) networks and wavelength routing networks, in addition to packet switching networks. The OIF UNI specifies signaling procedures for clients to automatically create, delete and query an association over wavelength routing network. The UNI signaling is implemented by extending the label distribution protocols, LDP and RSVP-TE.

Optical add-drop multiplexer Wikipedia

Optical add-drop multiplexer Wikipedia

An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks. “Add” and “drop” here refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross-connect.

A traditional OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultipexer ports with those from the add ports, onto a single output fiber.

All the light paths that directly pass an OADM are termed cut-through lightpaths, while those that are added or dropped at the OADM node are termed added/dropped lightpaths. An OADM with remotely reconfigurable optical switches (for example 1×2) in the middle stage is called a reconfigurable OADM (ROADM). Ones without this feature are known as fixed OADMs. While the term OADM applies to both types, it is often used interchangeably with ROADM.

Physically, there are several ways to realize an OADM. There are a variety of multiplexer and demultiplexer technologies including thin film filters, fiber Bragg gratings with optical circulators, free space grating devices and integrated planar arrayed waveguide gratings. The switching or reconfiguration functions range from the manual fiber patch panel to a variety of switching technologies including microelectromechanical systems (MEMS), liquid crystal and thermo-optic switches in planar waveguide circuits.

Although both have add/drop functionality, OADMs are distinct from add-drop multiplexers. The former function in the photonic domain under wavelength-division multiplexing, while the latter are implicitly considered to function in the traditional SONET/SDH networks.

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