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Plastic optical fiber enables cost sensitive high-end networking

  • 01-Mar-2019
  • Articles|Technical Articles


New plastic optical fiber (POF) cables exhibit lower attenuation allowing longer distance transmission with higher throughput. Mark Patrick says POF is significantly easier to work with, meaning that installation costs are significantly lower than with glass fiber.
 
High capacity data applications such as telecoms installations and data centers have generally relied on traditional optical networking to provide the necessary carrier-class performance to fulfill their bandwidth needs. Other than the throughput, this technology has also delivered other benefits including galvanic isolation, immunity from noise and reduction of issues associated with electromagnetic effects. These additional attributes have made the technology useful in industrial environments and invaluable in safety-critical or hazardous areas.
 
However, the installation process for glass fiber and the associated optical connectors is a costly process – and it is the time and skills that drive this cost more than the cost of the components (cables and transceivers). If the fiber is not cut correctly, then reflections will cause a reduction in data integrity, so specialist cutting equipment is necessary to avoid this problem. The ultra-fine cables (10µm for single-mode and around 50-62.5µm for multi-mode) need perfect alignment with the transceiver to attain the performance for which fiber is known. This challenging task can only be performed correctly by highly trained people with the correct tools – which drives the cost higher. 
 
Plastic optical fiber (POF) expands availability
 
Some Ethernet installations have used POF and, until recently, bit rates of 150Mbit/s have been possible over links up to 50m in length, with proprietary transmission protocols extending this figure up to approximately 250Mbit/s. As with all things, the technologies have advanced, and modern polymers have significantly improved the transparency of POF. These newer cables exhibit lower attenuation allowing longer distance transmission with higher throughput. In fact, speeds up to 1Gbit/s have been achieved and it is expected that these could be increased to 10Gbit/s in future, especially in POF-backbone installations. While these figures are less than could be attained using glass fiber, in lower-end applications, such as home networking, they would be more than adequate.
 
POF is significantly easier to work with, meaning that installation costs are significantly lower than with glass fiber. An ordinary sharp knife can be used to cut POF, eliminating the specialist cutter. The cut end can be polished with readily available abrasives and then polished and, with the larger diameter (around 960-980µm for a 1mm-gauge cable) alignment is simpler and faster. All of these advantages significantly reduce installation costs, which is the most substantial cost of using optical technology.
 
Home usage of fiber technology
 
In the world of infrastructure, fiber is becoming highly popular as Internet service providers (ISPs) look to deliver more data faster to more customers, requiring ever more bandwidth. Consumers and small / home office (SOHO) users can now access speeds ranging from 50Mbit/s up to 1Gbit/s.
 
Once indoors, speeds can be restricted as modern home networks typically have many simultaneously connected devices ranging from mobile devices to Internet-connected TV’s, gaming consoles and other IoT devices such as thermostats. This can create bottlenecks that impinge upon the bandwidth available for data-hungry services such as gaming or IPTV.
 
One solution would be to revert to wired connections for some of these services although as, unlike some parts of the US, home-wide cabling is not common in Europe there is the challenge of running the cabling. This is either difficult (i.e., expensive) or unsightly. 
 
Alternatives such as powerline networking attempt to use the home’s mains wiring to transmit data but are rarely successful as circuit breakers and electrical noise can significantly reduce the data transmission.
 
As many home networks are based on a single router located centrally in the house, POF can offer a viable alternative to WiFi. As it is not galvanic, it can be safely passed through the same conduit as mains cables, allowing for a discreet and relatively easy way of running a home backbone. As it is an optical system, any spikes on the co-located mains cable do not affect data throughput, giving consistent and reliable data rates.
 
A typical POF based home network could consist of smaller, lower power, WiFi access points in each room, linked by a POF backbone that ensured the full network bandwidth is available to each router. There would be no congestion, and each room would have the full WiFi signal available, and each router would require less RF power than a single router that was intended to cover the whole house. DIY installation of the POF backbone becomes a realistic possibility given the relative ease of cutting, polishing and aligning the POF media.
 
POF moves to vehicles
 
Vehicles are complex communication centers in their own right, incorporating many diverse and data-hungry systems as they become more intelligent. Many cars already have advanced driver assistance systems (ADAS) that incorporate cameras, LiDAR, integrated navigation systems and more. As cars continue to become more autonomous, these systems (and the need to provide high bandwidth connectivity) will increase.
 
There is little spare space in the modern vehicle, so the ability to accommodate tight bends and the low weight of POF make it an ideal choice for in-vehicle networking. The fact that POF is relatively easy to install means that modules are lower cost and vehicle assembly is easy – and service technicians can offer maintenance and repair without special tooling or skills. 
 
As POF has bandwidth capability in the Gigabit range, it can provide the backbone for current (and many future) in-vehicles including media oriented systems transport (MOST), digital video cameras or general Ethernet. The galvanic isolation provided by POF contributes to safety, allowing modules that operate at different voltages such as electronic control units (ECUs), actuators, sensors, and battery management systems (BMS) to be safely and rapidly connected.
 
The IoT benefits from optical sensing
 
The low-cost nature and ability to be handled easily make POF attractive for industrial and IoT sensing applications. This includes sensors that use the POF as the sensing element as well as applications that send and receive data via an optical connection. 
 
Sensors for parameters such as strain or temperature that would have previously been complex to create using a fiber Bragg grating (FBG) inside multimode glass fiber can now be made using POF. Using optical phase interrogation (OPI), Broadcom recently developed POF-based sensors with accuracy that is similar to classic FBG sensors. OPI techniques are based on measuring the phase shift in a light source in a POF sensing coil when compared to a reference coil that is not subject to any strain.
 
The elasticity of POF has allowed these sensors to be used to monitor stress within wind turbine blades that are subject to high levels of flexing during windy conditions.
 
Another application is to use POF for gas sensing to monitor indoor environments. To achieve this, a thin layer of reactive material is deposited on the POF which changes the light transmission characteristics in the presence of the pollutant. For example, 40nm of silver is used to detect hydrogen disulfide or 200nm of silicon dioxide can be used to detect fluoride ions.
 
POF also allows simple and low-cost production of reflective or transmissive presence detectors where the sensor output is sent directly to the host system some distance away. As the whole sensor is light-based, there is no need for any electronics, meaning that no energy is used – a very desirable characteristic in IoT applications.
 
POF is also making an appearance in projects conducted by makers and/or hobbyists. Using typical ingenuity, light guides have been fabricated by inserting POF into the adapted case of a small plastic LED which, when held together with heat shrinkable sleeving, creates a light guide that is both effective and low-cost.
 
Summary
 
POF is known to be easy to use and low cost and as polymers have improved, so has the data performance of POF. This has allowed applications that cannot be developed with copper cable, wireless technology or glass fiber (either for technical or economic reasons) to be developed. POF is allowing a whole generation of cost-sensitive applications to 
benefit from the many benefits of optical technology. 
 
About the Author:
 
Mark Patrick is the Supplier & Technical Marketing Manager EMEA of Mouser Electronics. Mark joined Mouser Electronics in July 2014 having previously held senior marketing roles at RS Components. Prior to RS, Mark spent 8 years at Texas Instruments in Applications Support and Technical Sales roles and holds a first class Honours Degree in Electronic Engineering from Coventry University. For details, contact Helen Chung, Asia PR Specialist of Publitek, on email: helen.chung@publitek.com



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