Fiber optic cable: the future of faster and farther high-speed data links
By constantly looking for ways to reduce signal attenuation, distortion, and susceptibility to external interference, copper PCB traces and cables have dominated the world of high-speed data transmission. For a long time, these are expected to be replaced by optical fibers. Advanced signal conditioning, multi-level modulation, and error correction technologies have enabled engineers to design twin-axis copper cables running at 112 Gb/s, far exceeding expectations a few years ago.
Each technology has its limitations, and high-speed copper channels may be approaching those required by the laws of physics. As the demand for increased bandwidth continues to grow, attenuation reduces the effective length of the channel, also known as reachable distance. In addition to extremely low attenuation, fiber optic links also provide higher bandwidth capacity, making fiber an attractive alternative.
Switching from copper cable to optical fiber can achieve a huge leap in system coverage
For many years, long-distance telecommunication lines have taken advantage of the arrival of optical cables. The cost and power consumption of the required electro-optical conversion process has become a major obstacle to the industry-wide adoption of external, especially internal, optical fiber interconnection. Advances in silicon photonics and the performance characteristics of optical fibers are changing this equation.
The basic structure of an optical fiber cable is composed of a thin glass wire surrounded by a thin layer of cladding material, which can make light reflect inside. Additional sheath layers and internal buffers can be added to protect the core and cladding.
Fiber optic cables are further defined as multi-mode and single-mode. Multimode fiber can use low-cost LED light source to transmit multiple modes of light. Single-mode cables usually require the use of modulated lasers, but they are characterized by greatly increased range and bandwidth. Low-cost plastic optical fiber is used for relatively short distance, low data rate applications.
In the International Organization for Standardization (ISO), a series of OM 1-5 specifies the performance of standardized optical fiber cables.
Optical fiber has undergone a continuous improvement process in terms of bandwidth, robustness, reduced attenuation, ease of termination, reduction of fiber diameter and cost. Early fiber optic cables were extremely vulnerable to signal degradation and damage due to rough handling or sharp bends. The new "bend-insensitive" single-mode and multi-mode cables allow for reduced bend radius limits without failure.
Axon' Cable provides hybrid cables and multi-core solutions, and its insulation materials can withstand high-demand environments such as industry, military and space.
The glass used to form the optical conductor is continuously optimized to reduce scattering loss, chromatic dispersion, polarization mode dispersion, and microbending attenuation. The attenuation of the current generation of optical cables at 1550 m is only 0.15 dB/km.
The proliferation of campuses and metropolitan area data centers is an emerging trend. The ultra-high-capacity optical communication link up to 100 kilometers is essential for the network to function as a large-scale system. Increasing the capacity of cost-effective optical links has become a requirement to support the exponential growth of network traffic.
One solution is to use multi-core fibers. Multi-core optical fiber allows different signals to be transmitted simultaneously along different cores within the same cladding diameter, thereby increasing the data transmission density on a single optical fiber.
Advanced, extremely high fiber density cables are also entering the market to support increasing traffic. Furukawa recently installed 6,912 fiber optic cables in a 1.25-inch diameter conduit between two North American data center campuses. The outer diameter of the optical cable is only 35mm.
Hollow fiber is another interesting variant. Instead of passing through glass or plastic, light is transmitted in the central core of the air. Improvements in manufacturing have reduced loss and delay characteristics, making hollow-core fibers attractive in applications that require the transmission of light or data with extremely short pulses or minimal delay.
AirBorn's RAOC active optical cable is reinforced and is suitable for harsh military and commercial aerospace environments.
Active Optical Cable (AOC) has become extremely popular because of its ability to extend the coverage of traditional copper cable assemblies. Using a standard copper interface, the signal is converted into an optical pulse in the connector strain relief and coupled to the optical fiber. The opposite process occurs at the receiving end. From the perspective of the installer, the cable coverage is increased and the cable volume is reduced.
The rugged fiber optic cable has internal strength members and a strong outer sheath, and can be used in harsh military, avionics, and industrial applications.
Optical fiber packaging options continue to expand, including flat ribbon configurations that simplify wiring and reduce cooling airflow resistance. High-density, multi-fiber MPO and MXC connectors can terminate up to 72 fibers.
Optical fiber can be used for standard and customized planar components. Multiple optical fibers are bonded to a flexible substrate to form a shuffle or optical backplane.
Engineers can meet the growing demand for network capacity by laying more fiber (high cost) or finding ways to make the existing fiber infrastructure more efficient.
Parallel optics provides an alternative to traditional single fiber or dual fiber.
The transmitter at one end communicates with the receiver at the other end, propagating a single data stream through multiple optical fibers. With this configuration, the parallel optical link can use four 2.5 Gb/s transmitters to send a 10 Gb/s signal.
Instead of using a single color of light, you can use slightly different colors of light to send multiple data streams through the same fiber at the same time.
The multiplexer at the transmitting end uses light of different frequencies to encode multiple data streams, which are embedded in a light beam and coupled to a single optical fiber. The opposite process occurs at the receiving end of the channel. Two-way optical signals can be transmitted through an optical fiber. With dense wavelength division multiplexing, up to 80 data channels can be multiplexed into a single optical fiber.
Advanced modulation technology enables designers to further improve the optical transmission link. Quadrature amplitude modulation (QAM) combines multi-level amplitude and phase changes to increase the capacity of optical data communication links.
Using a combination of amplitude, phase, and polarization, coherent technology is the most powerful and effective modulation for optimizing optical data transmission. Coherent transmission combines four levels of amplitude modulation and phase modulation with the vertical and horizontal polarization of light to maximize the data capacity of a single fiber. The next-generation 800 Gb link using this technology has entered the market.
Each of these technologies pushes the capacity of optical fiber to a higher level. The industry is now facing the prospect of approaching the theoretical limit of a single communication channel. The Shannon limit can be traced back to 1948. It is the calculated maximum rate of error-free data. These data can be transmitted through any type of communication channel that can cause transmission errors due to noise. Until a few years ago, considering the capacity of the existing optical channels, this was not a particular concern. However, a new generation of hardware and modulation technology has put Shannon's limit within sight.
The demand for high-speed data links is driven by a variety of trends, including the growth of hyperscale data centers, the shift of computing resources to the edge, the continued adoption of 5G, and the expansion of fiber to the home. Advances in fiber performance and advanced modulation technology, coupled with improved high-density multi-fiber connectors, provide a roadmap for the future of high-speed computing and communications.
