|Fig. 1: Power consumption of various network access techniques as rates increase. All technologies are at their 2010 capabilities (after ).|
With network traffic demand continuously rising, the corresponding increase in power consumption will be of real concern for future technologies. While current optical networking techniques are already reducing power consumption, more power-reduction innovation are needed to fulfill future demand. The design of every modern optical data networks should now attempt to resolve challenging physical constraints associated with energy and capacity.
This report highlights research and findings about how optical communication networks function in more energy-efficient and sustainable manners. It will examine how energy constraints might shape the future directions of optical communication networks. For the purpose of this report, optical networking denotes any form of high data-capacity telecommunications networks based on optical components that provide capacity at the wavelength level. All-optical networking, a specific form of optical networking where data signals remain entirely optical from source to destination, will be considered because of its potential merits in power consumption.
The future of network design belongs to those who can leverage optical technologies to sustainably fulfill the ever-increasing demand for data services. Research agencies, companies, universities, governments, and telecommunications industry ought to include energy along with the traditional metrics of cost and operational complexity. There exist a variety of ways to access the Internet and manage other data networks. Moreover, optical systems have been proven to be the most energy-efficient communication platform available.  Consider the following comparison of power consumption per user of various networking techniques. The featured technologies include Passive Optical Networks (PON), Point-to-Point Optical Network (PtP), wireless access via the Universal Mobile Telecommunication System (UMTS) and Worldwide interoperability for Microwave Access (WiMAX), traditional digital subscriber lines (DSL), hybrid fiber coaxial network (HFC), and copper cables used in fiber-to-the-node technology (FTTN).
The study that acquired those power statistics modeled energy consumption of each access network by analyzing energy in three components: customer premises equipment (usually a modem), remote nodes or base stations, and the terminal units.  It can be irrefutably demonstrated that as data-access speeds increase, the wireless techniques UMTS and WiMAX, become the most power consuming; while optical communication techniques such as PON and PtP, remain the most power efficient. With these tradeoffs in mind, network designers, researchers, and the telecommunications industry in general must decide which architectures to invest in for the future. There is a clear divide in the advantages between the availability of wireless mobile access and the considerably higher-capacity and energy-efficient optical network access. As data demand continues, priorities must be assessed as larger and faster networks are designed.
A recent form of technology that was not considered in the referenced study is all-optical networking. The goal of having a network entirely in the optical domain is to remove the intermediate electronics, the so-called electronic bottleneck, which tend to be more costly, more power consuming, less scalable, but much simpler in electronic format.  Current techniques in long-distance systems with 100 Gb/s per wavelength require intensive electronic processing by the transmitter and receivers, which consume high power. Raising capacities and speeds in these systems will increase the power consumed correspondingly.  Signal regeneration and wavelength conversion, are currently accomplished with electronic circuits that consume much power; however, as bitrate per wavelength increases, performing these functions in the optical domain starts to be more attractive, but remain challenging because of the complex optical modulation and processing formats required. 
Two promising techniques essential to the prevalence of all-optical networking are optical burst switching (OBS) and optical packet switching (OPS). OBS involves the preparation and management of data bursts in networks. A control packet is transmitted shortly before a large data burst to schedule the required resources at the intermediate nodes. Scheduling bursts with OBS while maintaining high network utilization efficiency remains challenging.  This technique could immensely contribute to energy-efficiency because it allows dynamic functionality, which could reduce the network’s total equipment energy consumption during periods of low traffic levels by a factor of 2-100. 
OPS involves replacing the electronic switching process including and buffers of current switching with optical alternatives. Buffers are needed during current switches to reduce the noise spikes during circuit switching. The size and design of optical buffers pose significant difficulty in the advancement of OPS in all-optical networks. 
These techniques as well as other issues in all-optical networking are open topics for research. Movement toward networks’ virtual elimination of electronics is not just a fanciful quest, but has indicated possibilities of enormous savings in cost and energy consumption.  More investigation, implementation, and innovation are required before these potential savings can be widely realized.
Although not easily visible or quantified, large amounts of energy are being perpetually exhausted by operating the Internet and other electrical networks.  These networks provide services such as telephony, video streaming, e-mail, web browsing, and search that humans desire for and now expect. Research in energy-efficient networking techniques should become the focus as society becomes more ecologically mindful. Optical networking has an important role to play in modern communications as traditional copper wires are increasingly replaced by optical fibers in every network in the developed world.  A recent advancement is all-optical networking which could someday become the paragon of energy-efficiency. It remains an exciting and essential challenge to devise new techniques in optical networking that can offer energy-efficient improvements while sustaining the higher capacity rates required to satisfy the world’s escalation in service demand.
© Jomar Sevilla. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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