Optical networking and the use of optical fiber have been omnipresent for decades. From the usage of fiber optics in communications in the 1970s for transmitting telephone traffic to the implosion of the telecommunications industry around 2001, fiber optics has lived a rather storied existence. Optical fibers are now used in a wide range of applications, from experimental use to long-haul networks. As the need for larger bandwidth availability grows, so does the favor toward using optical networks over electronic networks.
Electronic vs Optical Networking
As it happens, the primary differences between electronic and optical networks are straightforward. Electronic networks send information encoded through electrical signals through wire. Optical networks send information modulated in light pulses through fiber. In comparing the network formats, there are some tradeoffs between them.
Since optical networks are light based, they will always win on the side of speed. The electronic signals beings sent will not surpass those moving at the speed of light—even if said light is bouncing down the fibers. (Here the descriptor ‘bouncing’ is being used very loosely of course.) However, electronic interconnects and components tend to be cheaper and of lower complexity with a higher integration in the supply chain. While this is true, the amount of network traffic growth surpasses the speed of growth in electronic circuit capacity. This shifts the focus to optical networking rather rapidly.
The fibers used in optical networking can support a much larger bandwidth than electronic networks can. Fibers require less repeaters than copper wires and will not experience interference, though dispersion can occur. Even fiber, though, can come at a cost depending on the rate of the transmitted data. We will look into the cost-side of the optical networking a bit later in this post.
With the already high usage of bandwidth intensive data applications, solutions need to be found to accommodate the still growing demand. This causes the scalability of the network to be one of the primary points of interest. Optical communication and the breadth of optical networking help meet this need. Part of this is due to the number of modes that multimode fibers can support, as well as the ease of wavelength division multiplexing and demultiplexing. Fiber is used in many Metropolitan Area Networks (MAN), and combinations of fiber and copper are used in Wide Area Networks (WAN). However, fiber and copper are not the only methods of transmission for WANs. Other popular transmission mediums are through space using satellites and using antennas/wireless signals.
QAM Optical Networking Model
As could be expected, it is useful to be able to mathematically show in what instances optical networking is advantageous to electronic networking. The quantification of the viability of using optical networks/links over electronic methods was presented in a paper on quadrature amplitude modulated (QAM) optical transmission channels. Here, they compared the energy efficiency of QAM optical transmission channels using optical grooming to electronic grooming, existing networking schemes, and projected future networks.
The idea of using optical signal grooming has been explored by multiple researchers. Optical grooming is a way of coherently mixing signals and performing grooming functions without employing the use of optoelectronic or optical-electrical-optical conversion. This is achieved through taking advantage of nonlinear optical phenomena. The team evaluated optical grooming techniques at different baud rates and modulation schemes and compared the energy efficiency against electronic grooming setups and existing transmission techniques. This was accomplished through power consumption models.
Through their work, it was found that although using nonlinear optics increases cost and complexity, as information rate increases, the cost and energy consumption scales down on a per bit basis. This means that the efficiency per bit was improved at higher speeds. Optical grooming became preferential to electronic grooming at symbol-rates above 30 GBaud, which is where it became more energy efficient. Their projections also had optical grooming scenarios predicted to perform at an energy consumption a full order of magnitude less than that of current technology at high baud rates. This suggested that at lower symbol rates it may not be worth the cost to use optical grooming but to remain with electronic grooming or methods of coherent or direct detection.
Optical vs Electrical Interconnects
Not only have optical and electrical networks been compared, but the optical and electronic components themselves have been too. Yet another paper analyzed the energy consumption and energy density between optical and electronic signal processing, but from the view point of optical versus electrical interconnects. It argues that electronic components in signal processing are preferable to those for optical signal processing. CMOS transistors have features on the order of 22 nm whereas the optical communication band operates in the 1550 nm range. The team considered the energy density with respect to the chip area to evaluate the energy consumption. Consideration was also given if energy would be needed to perform optical-electrical-optical conversion.
They found the energy consumption of optical signal processing to be competitive with electronic signal processing only when few digital operations were performed on the data. They also favored optical signal processing when high speed is the primary concern. Their final determination was that further exploration needed to be done to provide a more thorough and correct model and understanding of the energy consumption of optical devices. This was noted as the biggest hurdle to surmount before digital optical technologies can really take over the majority of the signal processing or switching applications.
Optical networking and signal processing is already widely used with projections to only gain even more prominence. Fiber-based networks outperform electronic networks at high data rates and can provide a wide bandwidth. For them to become more dominant, however, optical components must become more cost-effective and energy efficient.