A Concept: Transmitting and Receiving Fiber Optic Signals with Petabit per Second Capacity

1. A Concept: Transmitting and Receiving Fiber Optic Signals with Petabit per Second Capacity Tom Juliano ECE-641 February 20, 2003

2. Three Main System Components • Signal Generation: Carbon Nanotubes Tunable Laser Bioluminescent Materials • Signal Transmission: Erbium-Doped Silica Fibers or Other • Signal Detection Silicon and Other Semiconductor Multilayer Photodetector Array

3. Carbon Nanotubes for Signal Generation • These nanotubes can be selectively doped to change the value of their electronic band gap. • Nanotubes are known for their ability to act as fast switches in the MHz-GHz range.

4. Carbon Nanotubes for Signal Generation • They can be grown on an array in discrete locations • One or more of these squares could couple into a fiber, because each square’s area can be made on a small scale Bundle of Nanotubes that are selectively doped

5. Nanotube Oriented Growth • It has been shown that nanotubes can be selectively and reliably grown on SiO2 in predetermined orientations. B. Wei et al.Nature,416, 495-6 (04 Apr 2002)

6. Nanotubes can be used as field emitters in flat panel displays (<8 mm thick) [Samsung] Nanotubes as Emitters

7. Transmission of the Signal • Wavelengths of 850, 1310, or 1550 nm should be used to minimize signal attenuation losses • Silica fibers doped with erbium should be used at 1550 nm

8. Transmission of the Signal • If indices of refraction (1.4 and 1.395) and  (1550 nm) are chosen as reasonable values, then fiber diameter is about 5 m. • Main problem is the generation of power from source. About 15% of the power is lost to the cladding. • Chromatic signal distortion is not significant compared to signal attenuation. For a 5 nm wavelength difference in generated signal, a 50 km fiber length is permissible.

9. Detection of the Signal • Technology (X3) is currently patented by Foveon for use in digital cameras to increase pixel resolution • Production of many different elements (millions) on the array is possible with one chip

10. Absorption of Silicon at Different Wavelengths

11. Transmission of the Signal • Multiple layers may be made, instead of just three. The shortest wavelength will penetrate to the shallowest depth, and the longest will penetrate to the deepest. In this example, one signal may have 6 permissible values instead of 2.

12. Transmission of the Signal • Lithography may be used to fabricate such device arrays • Silicon is the substrate, but germanium or another semiconductor may be heteroepitaxially grown on the surface by chemical vapor deposition, followed by another layer of silicon, etc. Interconnects must be employed.

13. Conclusions • Sufficient power generation and losses are the main issue over long distances, so this may be the most feasible over short distances, such as between computer components or LANs. • The bitrate for a single step index fiber for normal conditions is about 30 Gbit/s (only in theory). However, by comparison, a system using 100,000 of these fibers with base 6 logic can produce a theoretical bitrate of 7.68 Pbit/s! • It is not likely that these speeds could actually be realized, but the idea of multiple fibers transmitting signals with simplified generation and detection is the same.