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Advances in Packet Optical Transport in Optical Networking and Broadband Transmission
Published in Shyamal Bhadra, Ajoy Ghatak, Guided Wave Optics and Photonic Devices, 2017
To summarize, data services will continue to grow in the next decade. New applications will emerge, which will demand faster connections, lower latency and service-level agreement (SLA) guarantees. It will change the way we communicate today and the way we build our telecom networks. While the amount of data traffic will increase exponentially, the revenues will not grow at the same pace. While all these pose challenges to telecom service providers, new technologies are coming to their rescue. Carrier Ethernet provides transport features in a packet-switched network, thereby providing the best of both worlds – TDM and data. The OTN provides large pipes for the wholesale transport of data over large networks. DWDM provides higher-speed connections and the ability to manage bandwidth at the optical layer and the POTP puts all these developments in one hardware platform to provide a single-box transport solution for the future.
Modulation for Short-Reach Access Optical Transmission
Published in Le Nguyen Binh, Optical Modulation, 2017
The capacity of an optical channel is based on its modulation type and baud rate. The modulation type defines how many bits are encoded per symbol, and the baud rate measures how fast the symbols are transmitted. Carriers can increase channel capacity by using more complex modulation formats, which encode more bits per symbol, by using faster baud rates or by combining both techniques. One limitation of more complex modulations is shorter optical reach, as described previously. An increased baud rate combined with the same modulation type enables longer reach and higher capacity. Baud rate flexibility is a powerful Super-channel Coherent Technology on next-generation DSPs. The maximum baud rate is limited by the speed of the electronics within the coherent DSP. For current-generation DSPs and 100G coherent transponders, the industry uses DSP baud rates of approximately 32 Gbaud. Total channel capacity is simply the baud rate (32 Gbaud) multiplied by the number of bits per symbol (2 bits/symbol) multiplied by the two polarization modes for PDM-QPSK modulation, resulting in a line rate of approximately 128 Gbps. The 128-Gbps rate is the actual line rate of a nominal 100G signal, including soft-decision forward error correction (SD-FEC) bits and Optical Transport Network (OTN) framing.
Optical Satellite Networking
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
The nature of the OTN, based on the use of wavelength multiplexed channels that cross several nonlinear optical elements (such as the Doped Fiber Amplifier DFAs) and many wavelength selective devices (filters, mux/demux, etc.), requires the examination of the potential appearance of crosstalk. The amplified spontaneous emission (ASE) produced at each DFA accumulates with the signal (the part that falls within the signal optical BW) along the optical path and it impairs the signal-to-noise ratio (SNR) by creating interferometric noise. In this way, it imposes an upper limit of the number of ISLs that a lightpath can propagate along before the SNR becomes prohibitively low and signal regeneration is required (estimating that at least a booster DFA and a preamplifier are involved at each ISL stage with a possible inline amplifier to compensate for the losses in the router) [Wilson, 1997]. Therefore, for the design of the OTN, careful estimation of the ASE must be performed to determine the lightpath feasibility. Given the maturity of optical components that now provide isolation better than 30 dB, no crosstalk from adjacent channels should be expected in a channel spacing of 1 nm to 3 nm. Also, due to the very high optical power levels involved in the DFAs, nonlinear phenomena such as four-wave mixing may appear despite the very short distance (of some meters) the light propagates in a single-mode fiber. The importance of these phenomena has to be evaluated for each particular layout of the onboard hardware (optical power levels and fiber lengths) and especially with the reference to the WDM transmission [Agrawal, 2012].
Bidirectional and wavelength unrestricted conversion for long–haul and data centre VCSEL optical fibre interconnects
Published in Journal of Modern Optics, 2019
D. Kiboi Boiyo, G. M. Isoe, E. K. Kipnoo, T. B. Gibbon
High capacity signal and data transmission have played a vital role in revolutionizing global industrialization and socio-economic lives. The demand for sustainable bandwidth, end-to-end connectivity that enables point to point and broadcast coverage for fixed and mobile devices has strained the optical transport infrastructure. Devices such as mobile phones, PCs, cell-phone towers, CCTVs, HD-TV, telepresence units, IoTs, cloud-computing and data centres have enabled end-to-end communication to drive e-commerce, e-agriculture, e-education, e-health and e-banking. As a result of the high demand for bandwidth by the devices, several techniques have been developed to improve capacity, spectral usage and management of the limited but available network resources. Techniques such as wavelength division multiplexing (WDM), Dense-WDM, flexible spectrum, advanced modulation and coherent detection are aimed at economically using the limited resources (1–3). The optical transport network (OTN) involves the long-haul transmissions within the O-, C- and L-bands which form the backbone transmission windows due to their low fibre loss and low-dispersion properties and compatibility with Erbium-doped fibre amplifier (EDFA) and Raman amplifiers (4,5). With un-interrupted long-haul transmission, incidences of denial of service, poor quality of the signal ensures and enhances access connectivity to the end-user. Among the end-users of an optical link are data centres which depend on long-haul fibre networks for both upstream and downstream data exchange between the centres and its users. Given that long-haul transmissions utilizes the 1310 and 1550 nm whereas data centres use 850 nm transmission windows (6), a technique of converting signals between the two wavelengths is very important. To ensure wavelength compatibility within the transmission windows, several techniques for wavelength conversion have been reported. Among the optical-based include; cross-phase modulation, cross gain modulation, all-optical injection, four-wave mixing and techniques involving optical–electrical–optical (OEO) conversion (7–9). Among the emerging technologies in the transmitters are the vertical cavity surface-emitting lasers (VCSELs) which due to their various attributes have been used in 1310/1550 and 850 nm transmission windows for long-haul and data centres, respectively (10, 6).