Glossary of Key Terms
Glossary of Key Terms
| Term | Definition |
| 3R-Regeneration | A signal regeneration process involving Reshaping, Retiming, and Regeneration, typically provided by means of optical-to-electrical conversion and vice versa. |
| Arrayed Waveguide Grating (AWG) | A device based on diffraction principles used in MUX/DEMUX units. It consists of an array of curved waveguides with fixed path length differences, which introduces phase delays that separate wavelengths to different output ports. |
| Bragg Grating | A passive component, created by modulating the refractive index of a fiber core, that acts as a wavelength-selective mirror. It reflects light at a specific Bragg wavelength and transmits all other wavelengths. |
| Circulator | A micro-optic, non-reciprocal device with multiple ports where light entering one port travels around and exits at the next sequential port (e.g., input on port 1 exits on port 2). |
| Client Signal Transparency | A principle of OTN where the network transports various client signals (e.g., IP, ATM, SDH) without needing detailed knowledge of their format between the network ingress and egress points. |
| Digital Wrapper | Technology that provides OAM functions (like performance monitoring and FEC) to an Optical Channel (OCh) by adding a digital TDM frame around the client payload, making the OCh management client-signal independent. |
| DWDM (Dense Wavelength-Division Multiplexing) | A technology that multiplexes a large number of optical signals (wavelengths or “colors”) onto a single optical fiber to increase its transmission capacity. |
| EDFA (Erbium Doped Fiber Amplifier) | An optical amplifier that uses erbium, a rare earth element, which when excited by a pump laser emits light around 1.54 micrometers, amplifying weak signals in that wavelength range. |
| Forward Error Correction (FEC) | A technique used to enhance the Bit Error Rate (BER) performance of a signal by adding redundant data that allows the receiver to detect and correct errors without retransmission. It is a key function of digital wrappers. |
| Four-Wave-Mixing | A non-linear effect in EDFA amplifiers where adjacent channels interact, leading to crosstalk and noise, which limits the ability to increase amplifier power to extend transmission distance. |
| Isolator | A non-reciprocal device that allows light to pass in one direction but provides very high attenuation in the opposite direction, used to prevent unwanted reflections from disrupting lasers. |
| OADM (Optical Add-Drop Multiplexer) | A network element that allows one or more wavelength channels to be “dropped” from or “added” to a WDM signal without having to demultiplex and regenerate all channels. |
| OCh (Optical Channel) | The fundamental unit of transport in an OTN, corresponding to a single wavelength carrying a client signal. |
| OSC (Optical Supervisory Channel) | A separate, dedicated wavelength (e.g., 1480 nm) used for transmission of management and control data (like EOW) to monitor and manage optical line devices, independent of the main traffic signals. |
| OTN (Optical Transport Network) | The underlying infrastructure “network of networks” designed to be a protocol-neutral transport layer capable of carrying a wide variety of client signals over an optical medium. |
| OXC (Optical Cross-Connect) | A network element that manages capacity at the optical layer by switching and rearranging a large number of wavelength channels among multiple input and output fibers. |
| Protection | A primary, very fast (<60ms) survivability mechanism that uses pre-planned, dedicated backup routes to switch traffic away from a failed primary route. |
| Raman Amplifier | An optical amplifier with a very wide bandwidth (approx. 300 nm) where a pump laser at the receiving end of the fiber stimulates amplification, resulting in greatly reduced crosstalk and noise compared to EDFAs. |
| Restoration | A secondary, slower survivability mechanism that computes new routes on the fly after a failure to provide more efficient routing or additional resilience. |
| ROADM (Reconfigurable Optical Add-drop Multiplexer) | An advanced type of OADM that allows the adding, dropping, or re-routing of wavelengths to be performed remotely via software, without physical intervention, enabling dynamic and flexible network management. |
| SDH (Synchronous Digital Hierarchy) | A standardized TDM technology for high-speed digital transport, widely deployed in legacy voice-optimized networks, which provides features like high capacity, self-healing rings, and multi-vendor interoperability. |
| Transponder (TP) | A device that serves as an interface between client equipment and the WDM system. It performs an Optical-to-Electrical-to-Optical (O-E-O) conversion to translate an incoming optical signal to the specific wavelength required by the WDM system. |
| WSS (Wavelength Selective Switch) | The core functional element of a ROADM. It uses components like diffraction gratings and MEMS to separate the incoming WDM signal into individual wavelengths and selectively switch or redirect them to different output ports. |