Graded-Index Polymer Optical Fiber (GI-POF)
Perfluorinated graded-index polymer optical fibers (GI-POFs) are characterized by high data transmission rates and low attenuation in the commercially desirable 850 – 1300 nm range. These features combined with their ease of use and affordability make them an excellent choice for the installation of high performance fiber networks. Moreover, GI-POFs provide a higher transmission bandwidth than any other type of plastic optical fiber, and they can be used as a direct replacement, low cost alternative to traditional glass.
Until recently, all commercially available POFs have been fabricated from non-fluorinated polymers such as polymethylmethacrylate (PMMA) and, as a result, have had a refractive index that changes in steps. Although inexpensive, these fibers exhibit large modal dispersion and typically operate at 530 nm or 650 nm, which is well outside of standard communication wavelengths (850 nm or 1300 nm) where high-speed transceivers are readily available. Due to the high attenuation in the near infrared, these fibers are restricted to low performance (<100 Mb/s), short range (<50 m) applications in the visible region.
With the advent of an amorphous perfluorinated polymer, polyperfluoro-butenylvinylether (commercially known as CYTOP®), the limitations presented by step-index POFs have been overcome. Perfluorinated fiber exhibits very low attenuation in the near infrared (~10dB/km) as shown in the figure above and to the right and can support transmission rates up to 10 Gb/s for distances up to 100 m. Moreover, since the perfluorinated optical fiber can be constructed with a graded refractive index, it is capable of supporting bandwidths that are 100 times larger than those provided by conventional POFs. This is due to the interplay between high mode coupling, low material dispersion, and differential mode attenuation.
Unlike conventional glass fibers, which suffer from high interconnection and receiver costs, perfluorinated GI-POFs are easy to install. To add a connector to a glass fiber, the fiber needs to be cleaved using an expensive, specialized tool. Then, epoxy is used to attach the fiber to the connector hardware. Finally, the assembled connector must be polished. In contrast, the GI-POF can be terminated using simple and inexpensive tools, connectors are crimped on, and polishing occurs in mere seconds, leading to a high quality optical link in a fraction of the time. Moreover, GI-POFs are compatible with standard multimode glass fiber transceivers.
Thorlabs is pleased to offer a line of graded-index polymer optical fibers from Chromis Fiberoptics, a pioneer in plastic optical fiber technology and a world leader in perfluorinated GI-POFs. Unlike conventional preform-based manufacturing processes for GI-POFs, Chromis' patented manufacturing process extrudes fibers directly from bulk materials, resulting in high production rates at unmatched prices.
Figure 1 Figure 2
In order to produce GI-POFs with the properties necessary to meet the demands of high performance applications, two major hurdles needed to be overcome. First, a technique needed to be developed to produce a high-quality, graded-index structure consistently. Second, the high purity of the perfluorinated material needed to bemaintained during the extrusion process so that attenuation levels below 30 dB/m could be achieved. Chromis' extrusion technology continuously converts high purity bulk materials into concentric layers of melt streams. As the melt streams are extruded into fiber, the concentric layers fuse to form the graded-index fiber. By controlling the temperature, residence times, and relative flow rates of the core and clad materials, fibers with a wide variety of dimensions and refractive index structures can be formed. By altering the polymer material used in the melt, specialty fibers, such as those used in high temperature or flameretardant applications, can be produced using the same process.
Chromis Fiberoptics has successfully realized Gigabit Performance from their Graded-Index Polymer Optical Fiber (GI-POF) as demonstrated by the open eye diagrams shown to the right. Since perfluorinated fiber can be made with a graded refractive index, it can support bandwidths that are more than 100 times larger than conventional POF. In addition, this fiber exhibits very low attenuation in the near infrared, making it a viable choice for data transmission over hundreds of meters. Using this POF technology and commercially available transceivers, Gigabit Ethernet transmission rates of 1.25 Gb/s have been demonstrated for distances up to 300 meters (see Fig. 1 above). Moreover, 10 Gb/s links for distances up to 100 meters have also achievable (see Fig. 2). While material and waveguide dispersion increase with core size, modal dispersion is the dominating factor in determining bandwidth of multimode fiber. Additionally, the graded index profile of our GIPOF fibers is optimized to provide high bandwidth, regardless of core size. All of our GIPOF fibers are thus able to achieve the high-speed transmission rates mentioned above.
Chromis’ GI-POF represents a real breakthrough in fiber optic technology since the bandwidth and loss performance rivals that of multimode silica fiber, yet it also possesses the speed and interconnection simplicity associated with conventional plastic optical fiber. With all of these advantages, GI-POFs are a strong candidate for high-speed premise networks as well as short-reach telecom and computer interconnections.
The figure to the right shows the spectral attenuation of extruded perfluorinated GI-POF as a function of wavelength. The attenuation is 10 times lower than that associated with polymethylmethacrylate (PMMA)-based POF for both the visible and infrared spectral regions. The relatively flat spectrum is a direct result of the low dispersion associated with the perfluorinated polymer material. Such fiber is useful for applications at numerous wavelengths including 650 nm, 850 nm, 1310 nm, and 1490 nm.