Connecting Plastic Optical Fibers
Remember when Mr. McGuire pulled Ben aside in the movie “The Graduate”1 and said just one word to him? “Plastics!”
Look at all the products that we buy today made of plastic or contained in plastic packaging. Even our cars and homes have more and more plastic in them. “There’s a great future in plastics,” Mr. McGuire told Ben. He wasn’t wrong. That’s especially true for plastic optical fibers. In fact, fibers made of plastic can conduct light and communication signals using the same principal of total internal reflection as glass optical fibers. They are also easier, safer, more resilient and less expensive to terminate and deploy than glass optical fibers.
For many years, plastic optical fiber (POF) has been used by audiophiles to connect digital audio/video (AV) equipment using inexpensive visible LEDs operating at 650 nanometers. POF has also been employed extensively in the process control industry for short distance/low-cost digital links, as well as for illumination, sensors and many other applications such as children’s toys and decorations.
However, the intrinsically higher transmission losses and lower bandwidth of POF have limited its widespread use for longer distance/higher bandwidth communication links, such as data centers and local area networks.
Market research supporting POF’s impact
Information Gatekeepers (IGI) stated in a recent marketing report on plastic optical fibers:2
“The market for POF could never be brighter with the trend to “all optical networks”, need for higher bandwidth, EMI protection, lower cost, lighter weight, ease of use and other factors. POF’s main competitor, copper, is fast running out of steam. New applications are starting to appear in data centers, commercial aircraft, unmanned aerial vehicles (UAVs), Internet of Things (IoT), machine vision, sensors for structural health monitoring, and home networking for Ultra High Definition TVs (UHD TV/4K and 8K), to only name a few. Over the past three years, there has been a dramatic increase in the GI-POF technology and its availability in the market. This has resulted in increased interest by component suppliers and end users. The market for short, high-speed optical links is experiencing extraordinary growth. These links are less than 100 meters, with speeds up to 40Gbps.”
IGI estimated the current global market for POF to be over $5B with an expected growth to be over $7B in 2020:2
With advancements being made in the materials and manufacturing technologies of POF, as well as developments in new laser technologies, POF communication links could also be poised for significant breakthroughs for other applications, such as data centers and building networks, down the road.3, 4
So, what’s different about POF?
We’re all familiar with the glass optical fibers used today in data centers and local area networks for high speed optical communications. So what about plastic fibers? How come they haven’t used these fibers for other applications?
POF negatives – Currently higher losses and lower bandwidths:
It turns out that, operating with the infrared spectrum provided by today’s communication lasers, the ultra pure glass (silica) in today’s low loss communication fibers provide much lower optical signal loss for longer distance links than polymer-based optical fibers. Standard communication grade silica optical fibers operate in the infrared spectrum from about 850 nanometers to just past the 1550 nanometer wavelength, with a peak in attenuation at roughly around 1400 nanometers. On the other hand, Standard POF made from polymethyl methacrylate (PMMA) resin material typically operates with its lowest transmission losses in the visible light spectrum from about 500 nanometers (green) to 650 nanometers (red). In other words, standard PMMA plastic optical fiber, used with visible LEDs and lasers, does not maintain the data signal integrity as well over longer distances as the glass optical fibers operating with the VCSEL and edge-emitting lasers found in today’s data center fiber networks.
In addition, the larger (980 micron step-index) core of standard POF fibers provides a much lower bandwidth than the 9 micron step-index single mode core and 50 micron graded-index multimode core of conventional silica communication fibers.
POF Positives – Durability and ease of use:
One of the key benefits of POF is its toughness when subjected to bending and pulling forces making it an excellent choice for short distance low-speed data transmission applications in rugged environments.
Step Index POF (SIPOF) is a great choice for digital audio and video applications in the home since cost effective connectors can be applied safely and easily without the need for special tools or materials. The large core of SIPOF allows a significant amount of light to be coupled into the fiber from low cost LED light sources and also drastically reduces the sensitivity to mechanical misalignment in the connectors used to terminate these fibers. The result is a very low cost connection that’s easy to terminate in the field without the need to epoxy, polish or fusion splice.
Typical SIPOF applications: 5
- Automotive data, sensor and illumination networks
- Lighting for pools, signs and other applications such as solar lighting and luminous textiles
- Industrial process control data connectivity and sensor systems
- Chemical, biological and environmental sensors
Typical SIPOF Cable Specifications:
- Core Material: PMMA
- Core Diameter: 0.98mm
- Cladding Material: Fluorinated Polymer
- Core Refractive Index: 1.49
- Clad Reflective Index: 1.41
- Refractive Index Type: Step Index
How do POF connectors work?
As mentioned previously, one of the significant advantages of using POF is the ability to use inexpensive connectors and apply them in the field without the need to epoxy and polish. Many of the connectors require no special tools or simply a razor blade to trim the end of the plastic fiber to a flat perpendicular surface. The connectors can also be applied by simply crimping a metal sleeve. Many of these connectors and adapters are readily available from local sources such as Radio Shack and Walmart. POF connectors and cable assemblies are also readily available in familiar fiber connector footprints such as ST, FC, SC and SMA.
Did you know?
Researchers are also developing new types of POF core materials doped with fluorine (perfluorinated POF) to provide lower transmission losses than PMMA POF in the 850, 1300 and 1550 nanometer infrared wavelengths. In addition, graded index plastic optical fibers (GIPOF) have been produced to increase the bandwidths of POF for higher speed data transmission, and hollow core POF fibers are also being developed for single mode operation.
Where is POF headed?
Recently, perfluorinated graded-index multimode plastic optical fibers (PF GIPOF) have been shown to provide higher bandwidth and less optical signal noise than graded index silica fibers for applications such as 4K/8K ultra high definition (UHD) video transmission. In addition, new low cost expanded beam (lensed) “ball point pen” interconnects have been developed for POF fiber.6
Data transmission rates of 40 gigabits per second have been demonstrated over 100 meters using PF GIPOF.7
To sum it all up:
Plastic optical fibers show great potential to offer new possibilities for high speed communications over longer distances as the technology progresses in the materials and manufacturing processes for these types of fibers. With developments like the new PF GIPOF, along with reduced costs of 1300 nanometer VCSEL lasers, we may not be too far away from seeing POF take hold in the data center. Some say it could be a “disruptive technology”.2 Stay tuned for further developments in POF technology.
1 “The Graduate”, Written by Charles Webb, New American Library (Publisher, 1963), Movie, Mike Nichols/Lawrence Turman Producers
References and further reading:
2 Information Gatekeepers Inc. (IGI) Market Report on Plastic Optical fibers
3 “Connecting the Quantum Dots” Legrand Connecting the Dots series, June 6, 2016
4 “VCSEL Based 100m 25 Gb/s Plastic Optical Fiber Links”, C. Patrick Caputo, Patrick J. Decker, and Stephen E. Ralph, OSA/OFC NFOEC, 2011
5 Bones Electronics Co., Ltd (Website information)
6 “High-Speed Graded-Index Plastic Optical Fibers and their Simple Interconnects for 4K/8K Video Transmission”, Yasuhiro Kioke and Azusa Inoue, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. 34, No. 6, March 15, 2016
7 “The future of plastic optical fiber “NPG Asia Materials 1(1):22-28 · September 2009