High Bandwidth Multimode Fiber Optic Cabling

The need for high-speed data interconnects within modern fighter aircraft is clear, and development of optical components for speeds up to 100Gbps has been ongoing. However, one area that has not been adequately addressed is the optical fiber used to transport the signals. Today, links have employed 100mm, 62.5mm or 50mm core optical fiber. These fibers have limited optical bandwidth (ranging from 160 to 4700MHz/km at 850nm, and generally 500MHz/km at 1310nm) and add impairments to the overall link budget which is already constrained by the passive optical loss requirements. To address the need for 100Gbps optical links, wavelength division multiplexing solutions in the 850 to 985nm band (SWDM) and 1270 to 1390nm (CWDM) bands are being developed. The commercial optical fiber is not suitably rated for operation over both of these bands, and would benefit from optimization. The optical bandwidth is limited by the combination of modal and chromatic dispersion of the optical fiber. In phase 1, commercial 50mm OM5 optical fiber Effective Modal Bandwidth (EMB) will be characterized over both the SWDM and CWDM bands to develop a baseline for improvement. The Differential Mode Delay (DMD) technique measures the arrival time of pulses of light launched using single mode fiber into the multimode fiber core as a function of the launch position. The difference in arrival time and pulse shape distortion are aggregated to calculate the total fiber bandwidth. In the SWDM band, a Ti:Sapphire laser will be used, and in the CWDM band a combination of DFB lasers and electro-optic pulse slicers will be used to generate the optical pulses. Also in phase 1, a modal and chromatic dispersion model will be developed that can be used to predict the current performance and will be used in phase I option to design a higher bandwidth capable optical fiber. To validate the extensibility of the models, an OM5 fiber core will be extruded to 30mm and the EMB will be characterized during the option period. It is anticipated that the optimized core diameter will be approximately 30mm diameter. The final diameter will be a trade-off between the enhancement of the total bandwidth, optical coupling efficiency of the lasers and photodiodes, and the required alignment tolerances.  In phase II, a fully optimized multimode fiber will be designed for the SWDM and CWDM bands and fabricated at a commercial fiber manufacturer. The new fiber will again be characterized for DMD profiles and extracted bandwidth over the SWDM and CWDM bands. Finally, the fiber will be demonstrated with 100Gbps optical links in the SWDM and CWDM bands, and performance under passive and misalignment losses will be characterized.