Wdm standards and components
- 2. 2 Contents • System Features. • WDM Standards. • Optical Network. • Optical/WDM Components. - Multiplexer. - Demultiplexer. - Switches. - OADM and ROADM. - OXC and MG-OXC.
- 3. 3 WDM System Features • Capacity Upgradation: - Each wavelength supports independent network channel of a few Gb/s. - Capacity enhancement with each additional channel. • Transparency: - Information can be sent simultaneously and independently over the same fiber. - No need for a common signal structure.
- 4. 4 WDM System Features • Wavelength Routing: - Pure optical end to end connection between users. - Light paths routed and switched at intermediate network nodes. - Wavelength conversion along the route permitted.
- 5. 5 WDM Standards* • Analogous to FDM. • Standards developed by ITU**. • Channel spacings specified in terms of frequency. • Fixed frequency spacing since frequency of laser is fixed when locked to a particular operating mode.
- 6. 6 WDM Standards* • G692 – Optical Interfaces for Multichannel Systems with Optical Amplifiers specifies channel selection from a grid of frequencies referenced to 193.100 THz (1552.524 nm) and spacing them 100 GHz apart (0.8 nm at 1550 nm). • G692 suggests alternate spacings of 50 and 200 GHz (spectral widths of 0.4 and 1.6 nm at 1550 nm).
- 7. 7 WDM Standards* • G694.1 – DWDM wavelength ranges and spacings, WDM operation in S-, C- and L- Bands for high quality, high rate MAN and WAN services. • G694.2 - CWDM wavelength ranges and spacings – 18 wavelengths, range 1270-1610 nm spaced by 20 nm with wavelength drift tolerances of +/- 2 nm. • G652, G653 & G655 - targeted transmission distances on single mode fibers for CWDM.
- 9. 9 Optical Network • Optical nodes interconnected with optical fiber links. • Optical node as a multifunctional element - transceiver unit capable of receiving, transmitting and processing the optical signal. • Optical fibers provide point-to-point physical connections between network nodes.
- 10. 10 Optical Network • Point-to-point fiber links used to establish logical links. • Destination node reached by travelling through one or more intermediate nodes in single or multiple hops. • Each channel assigned a specific signal wavelength from source to destination. • A signal carried on a dedicated wavelength from source to destination node called ‘lightpath’.
- 11. 11 Optical Network • Controlling mechanism required to provide for data flow during its transmission. • Need to authenticate data transportation between each transmitting and receiving node. • Unidirectional or bidirectional transmission over the same single optical fiber.
- 12. 12 Network Topologies Bus Ring Star Mesh
- 13. 13 Node Elements • Node as a router to direct an input signal wavelength to a specified output port. • Wavelength router comprises of optical couplers. • Four different router functions: - Demultiplexing. - Multiplexing. - Optical Add/Drop Multiplexer – OADM. - Optical Switch. • Reconfigurable OADM (ROADM) – OADM + Optical Switch.
- 14. 14 Wavelength Demultiplexer • Analogous to DEMUX in electronics. • Splits an optical signal at input port 1 containing two signal wavelengths (i.e. λ1 and λ2). • Routes them to ports 2 and 3. 1x2 wavelength demultiplexer
- 15. 15 Wavelength Multiplexer • Analogous to MUX in electronics. • Combines two wavelength signals λ1 and λ2 at ports 1 and 2. • Multiplexed optical signal available at port 3. 3 port wavelength multiplexer
- 16. 16 OADM • Optical Add-Drop Multiplexer (OADM) comprises of a wavelength add/drop device (WADD). • Adds or Drops wavelengths while multiplexing different wavelengths. • Fixed OADM drops a particular wavelength, adds another specific wavelength.
- 17. 17 Optical Switch • Wavelengths switched and multiplexed at the output ports. • Possible to produce optical switch with greater number of ports (say N x N). 2 x 2 optical switch
- 18. 18 ROADM • Combines an OADM and an optical switch. • Can drop one or more wavelength channels after demultiplexing a wavelength multiplexed signal. • Can also add a new single or more wavelength channels through an optical switch. • Brings together all desired wavelength channels at the output.
- 19. 19 ROADM • Passive ROADM can be constructed using a fiber Bragg grating and an optical circulator. • Useful in providing for simple optical network topologies. • Cannot facilitate complex mesh topologies with large number of nodes - cross connects required.
- 20. 20 Optical Circulators An optical signal can leave the device at an end terminal or it can continue to flow towards the next connected isolator. Optical signal follows a closed loop.
- 22. 22 Optical Cross Connect (OXC)Block Diagram Fiber-Cross Connections Logical Cross Connections
- 23. 23 OXC • Capable of switching connection between two interfaced points. • Large number of wavelength signals can be demultiplexed at the input ports. • Internally connected to the desired output ports. • Different wavelength signals multiplexed for onward transmission.
- 24. 24 OXC • Provides an interface between different transmission methodologies. • Comprises an N x N optical switching fabric to provide interconnections between network nodes. • OXC with wavelength conversion features can switch (or interchange) different wavelength signals - wavelength interchangeable cross-connect (WIXC).
- 25. 25 OXC • OXC with optoelectronic conversions known as an opaque OXC. • OXC with all-optical/optical wavelength converters known as a transparent OXC. • N x N optical switching fabric in an OXC facilitates either physical (fiber) or logical interconnections. • Logical wavelength interconnection for multiple wavelength signals.
- 26. 26 Multigranular Optical Cross- Connect ((MG-OXC) • Multilayered OXC - each layer apart from providing specific switching capability can be connected to another layer. • Logical interconnection (i.e. single wavelength, multiple wavelengths, wavebands*) & physical interconnections (i.e. fiber cross-connect) combined together in a multilayer structure. • Can be routed individually/as wavebands*.
- 27. 27 Thank You