Optical Network Elements

1. Optical Network Elements

2. Optical Network Elements

3. Optical Add-Drop Multiplexer • 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 ,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. • 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.

4. Optical Add-Drop Multiplexer • 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. • Fixed OADM is not as flexible as a ROADM and may require a change of hardware components if a different set of wavelengths need to be dropped or added. • Most OADM are constructed using WDM elements like thin film filters, AWG, a series of Fiber bragg gratings with optical circulators etc. • The architecture selected depends on the implementation factors such as • number of wavelengths to be added or dropped • modularity of the OADM(how easy to upgrade the device) • designing a metro or a long-haul network

5. OADM-Configuration • All incoming wavelengths are separated into individual channels at the OADM input by means of a wavelength demultiplexer. • M wavelengths are dropped and remaining N-M wavelengths are passed. • This configuration is useful if a large fraction of the N wavelengths need to be added or dropped.

6. OADM-Configuration • N incoming channels are split into several bands of wavelengths which can be performed by using a thin film filter or and AWG. • The band to be dropped can be sent through a second demultiplexer followed by processing of individual wavelengths. • For eg:if N=12 and 3 wavelengths have to be dropped , the incoming wavelengths can be divided into 4 bands of 3 each. • An advantage here is that for future OADM upgrades, engineers can incorporate another 2nd demultiplexer to handle the next desired wavelength band.

7. OADM-Advantages • Reduce the equipment cost at the node. • Signal processing work is also reduced by dropping certain wavelengths that are not needed to express through.

8. Reconfigurable OADM • A reconfigurable optical add-drop multiplexer (ROADM) is a form of optical add-drop multiplexer that adds the ability to remotely switch traffic from a WDM system at the wavelength layer. • Advantages • The planning of entire bandwidth assignment need not be carried out during initial deployment of a system. • The configuration can be done as and when required without affecting traffic already passing the ROADM. • ROADM allows for remote configuration and reconfiguration. • In ROADM, as it is not clear beforehand where a signal can be potentially routed, there is a necessity of power balancing of these signals. • ROADMs allow for automatic power balancing.

9. WSS ROADM Architectures Optical bypass traffic • 2-Degree ROADM • Terminates wavelength services or passes them transparently through in the optical domain (no transponders / regenerators) • Connected to two fiber pairs (degree two) • Multi-degree ROADM • Connected to at least three fiber pairs • Can lead to cross connections restrictions or scalability issues • Directionally Independent OADM • Guarantees non-blocking wavelength switching between fiber pairs • Allows any wavelength to be re-routed to any path on the network without manual intervention Add/drop and regen traffic Optical bypass traffic Add/drop and regen traffic Optical bypass traffic Dir2 DirN Dir1 Directionally Independent Add/Drop

10. Optical Cross connects • The increasing demand for high bandwidth applications like HDTV and Video-on-demand created a need for extremely high capacity rings. • An optical cross-connect (OXC) is a device used by telecommunications carriers to switch high-speed optical signals in a fiber optic network, such as an optical mesh network. • OXC switches sits at the junctions in ring and mesh networks that are interconnected by many hundreds of optical fibers with different wavelengths. • At such a junction an OXC can dynamically route, setup and take down very high-capacity light paths. • Internally such a device can have either an electrical or optical switching fabric.

12. STS-N DS-1 DS-3 STS-1 DS-3 DS-1 ATM ATM STS-N STS-1 ATM DS-1 DS-1 STS-N STS-N DS-3 DS-3 ATM DS-1 STS-N Digital Cross-connects (OEO) SONET/SDH Digital Cross-connect (DXC) Also known as DigitalCross-connect Switch (DCS) Electrical Switch Matrix

13. l2 l4 l3 l1 l3 l2 l4 l1 All Optical Cross-connects (OOO) All Optical Cross-connect (OXC) Also known as PhotonicCross-connect (PXC) Optical Switch Fabric

14. Optical Cross connects Architecture

15. Optical Cross Connects (OXC) • Works on the optical domain • Can route high capacity wavelengths • Space switches are controlled electronically • Incoming wavelengths are routed either to desired output (ports 1-8) or dropped (9-12)