Plastic Optical Fiber Overview

This overview talks about the history and current development in plastic optical fiber (POF) technology for data networking applications. You can find the plastic optical fiber products here or clicking on the following picture.

Do we really need plastic optical fiber for computer networking?

For a very long time, single mode and graded-index multimode glass optical fibers based on silica material have been the only media for optical communication networking. They offer high bandwidth, very low attenuator, and extremely high reliability.

But this benefit comes at a cost. Glass optical fibers require highly trained technician for installation and very expensive tools and equipment for termination. This limits silica glass optical fibers’ applications for long distance telecommunications and enterprise data networking.

However, homes and small offices are increasingly require more bandwidth as the world becomes even more connected. For these situations, the network has to be low cost and can be installed by untrained personnel. Consequently, plastic optical fibers which offers high bandwidth and ease of installation begin to supplant copper cabling.

With ongoing progress in plastic optical fiber design and manufacturing, it indeed offers a promising future for these applications.

The history of plastic optical fibers (POF)

Plastic optical fibers were introduced into optical links in the 1960s and they have been offering simple and cost effective advantages compared to other media.

POF can have very large core yet still remain very flexible. Furthermore, the termination of plastic fiber can be a simple cutting without any expensive and time consuming fiber cleaving and fiber polishing as in glass optical fibers. That is why installations of POF is very easy and has large tolerances for mechanical couplings.

Since plastic optical fibers do provide advantages, step-index PMMA fibers are still widely used for short distance and low data rate applications.

However, traditional step-index PMMA fiber does have its intrinsic limitations. Because of strong optical absorption at visible and near-infrared wavelengths, PMMA fiber is limited to a single transmission wavelength near 650nm. But even at this wavelength, step-index PMMA still has large attenuation which limits its practical link length to be 50 meters or less.

New Development in Plastic Optical Fibers

Graded-Index PMMA Fibers

Graded-index refractive index profile has long been used in glass optical fiber to increase its bandwidth and remove other limitations. This is also introduced to plastic fibers. By grading the refractive index of the core, POFs have achieved much higher bandwidth.

How are graded-index PMMA fibers made?

In the method to produce grade-index plastic fiber, a mixture of MMA monomer and a index-raising dopant are placed in a PMMA tube and heated. The MMA penetrates the inner tube wall, producing a swollen “gel” phase in which polymerization begins. The larger dopant molecules is partially excluded from the gel phase, and as polymerization progresses inward, the dopant becomes increasingly concentrated in the central portion of the preform. When the preform becomes fully polymerized, the dopant forms a graded-index core, bounded by the PMMA tube that serves are the cladding.

This graded-index PMMA fiber offers bigger bandwidth. However, they are limited to the visible wavelength too as traditional step-index PMMAs.

The development of PFBVE (Perfluoro-butenylvinylether) fibers

A new type of graded-index plastic fibers were invented in 1996 to overcome the wavelength limitations presenting in step-index and graded-index PMMA fibers. The fiber is based on a new material – perfluoro-butenylvinylether, which is also called CYTOP by Asahi Glass Co.

The PFBVE fibers have very low absorption attenuation at most wavelengths and excellent transparency at near-infrared wavelengths.

Although PFVBE fibers have low absorption losses, they still present big attenuation due to scattering loss. But this is expected to be largely reduced with the progress of PFBVE fibers.

If you would like to know more about PFBVE fibers, you can take a look at the CYTOP page at Asahi Glass Co.

Here is paper regarding emitters for plastic optical fibers.

Here are two demos of how plastic optical fiber is used and terminated.