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Integrated optics
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Nikolaus Boos, Christian Lerminiaux
Add–drop multiplexers are wavelength selective switches allowing dropping of one or more signals from an incoming data stream and adding signals to the outgoing data stream. Different monolithic arrangements based on AWGs (Chapter 17.2.4) and switches are shown in Figure 17.40 (top) [17], and configurations (a) and (b) use the same AWG for demultiplexing and multiplexing the incoming traffic into individual wavelength channels. The loop back configuration (a) has been chosen for the monolithic InP component in Figure 17.40 (bottom) [180], which is designed for four channels on a 200 GHz grid. The component is extremely compact (3 × 6 mm2) and uses electro-optic MZI 2 × 2 switches for passing through or adding/dropping traffic on each of the four channels.
Optical multiplexers and amplifiers
Published in Matthew N. O. Sadiku, Optical and Wireless Communications, 2018
The realization of WDM systems requires specific building blocks. WDM devices include transmitters, receivers, multiplexers, demultiplexers, tunable optical filters, star couplers, routers, and cross-connects. A powerful source (LED or laser) with sufficient tenability to allow rapid selection of the desired wavelength is also required. As stated earlier, a multiplexer combines the output of several transmitters and launches it into an optical fiber. The demultiplexer splits the received signal into individual channels for different receivers. The same device can serve as a multiplexer or a demultiplexer, depending on the direction of propagation. An add/drop multiplexer is necessary when one or more channels are to be dropped or inserted. A star coupler combines the output of several transmitters and broadcasts the signal to different receivers. Star couplers do not contain wavelength-selective elements but do attempt to separate channels. The optical filter constitutes the basic building block of WDM systems because it provides the required wavelength selection to isolate individual channels. An optical filter selects or separates one channel at a specific wavelength at the receiver. It has a passband characteristic that can be changed by proper tuning. A wavelength router combines the functions of a star coupler with multiplexing and demultiplexing — the signal entering into an N × N router from each input port is split into N parts, one for each of the N output ports of the router. An optical cross-connect performs the same function as the digital switches in telephone networks.
Introduction to Optical Networks
Published in Bijoy Chand Chatterjee, Eiji Oki, Elastic Optical Networks: Fundamentals, Design, Control, and Management, 2020
Bijoy Chand Chatterjee, Eiji Oki
SONET/SDH[6, 7] is a standardized protocol that transfers multiple digital bit streams over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). It provides support for the operations, administration, and maintenance (OAM) functions that are required to operate digital transmission facilities. SONET has defined a hierarchy of signals called synchronous transport signals (STSs). These levels are known as synchronous transport modules (STMs). The physical links that transmit each level of STS are called optical carriers (OCs). The optical carrier equivalent to STS-1 is OC-1, which supports a data rate of 51.84 Mb/s. Table 1.1 provides the hierarchy of the most common SONET/SDH data rates. A typical SONET transmission system consists of a transmission path and devices as depicted in Fig. 1.3. In this figure, STS multiplexers and demultiplexers perform the task of multiplexing several incoming signals onto single trunk and vice versa. Add-drop multiplexers are used in SONET technology to add signals and remove a required signal from the data stream without demultiplexing the entire signal. SONET consists of four functional layers, namely, (i) photonic layer, (ii) section layer, (iii) line layer and (iv) path layer. Photonic layer communicates to the physical layer of Open System Interconnection (OSI) model which is concerned with transmission of optical pulses. The section layer deals with signals in their electrical form. It also handles framing, scrambling, and error control. The line layer is concerned with the multiplexing and demultiplexing of signals. The path layer handles the transmission of a signal from source to destination.
Multiple-period planning of Internet Protocol-over-Elastic Optical Networks
Published in Journal of Information and Telecommunication, 2019
Sridhar Iyer, Shree Prakash Singh
In the current study, we adopt the EON architecture from our previous study (Iyer & Singh, 2017b) in which the EON is assumed to consist of (i) fibre links comprising single-mode fibre spans, and Erbium Doped Fiber Amplifiers (EDFAs) and (ii) optical switches which operate as Reconfigurable Optical Add Drop Multiplexers (ROADMs) that employ flexi-grid technology, and also support lightpaths of individual or multiple contiguous 12.5 GHz slots of spectrum. The IP/MPLS routers comprise optical domain edges, and it may occur that no, single or multiple such routers are connected to an optical switch. The IP/MPLS router and ROADM connection occur via a short TR grey transceiver, and to achieve long-haul transmission, BVTs are plugged into ROADMs so that the client signal can be transformed. It must be noted that in our current study, we do not consider deployment of flexible coloured transceivers (coloured transceivers can generate signals that can directly enter optical domain) to be plugged into IP router ports since, in terms of cost and functionality, such transceivers perform similarly to transponders (BVTs) (IDEALIST Project, 2014). Furthermore, we assume that the transponders perform as transmitters and receivers simultaneously. As a transmitter, transponder’s main function is to convert arriving electrical packets from the IP/MPLS source router into the optical domain and then to route traffic which enters the ROADM over the optical network in the form of lightpath connections. The lightpath can pass intermediate ROADM either as a transparent or as a translucent (in our study we assume that multiple transmission parameters of BVTs and regenerators are under our control, and, they are ‘flexible’ and affect TR and bit-rate at which they can transmit) lightpath, and reach its destination ROADM where it is dropped which, in this domain, may correspond to final destination or an intermediate hop. As a receiver, the transponder converts optical signal back into the electrical type at the destination of lightpath. Then, the packets are forwarded and handled by IP/MPLS router which, for some packets, can be either a destination or an intermediate hop. If router is the destination for a packet(s), then such packet(s) are forwarded towards their corresponding final destination via the lower hierarchy level networks which are connected to the router, else, if the router is an intermediate hop for a packet, then the packet re-enters optical network, and eventually, is forwarded to its destination.