A Concept: Transmitting and

Receiving Fiber Optic Signals with Petabit per Second Capacity

Tom JulianoECE-641

February 20, 2003

Three Main System Three Main System ComponentsComponents

Signal Generation:Signal Generation:Carbon NanotubesCarbon NanotubesTunable LaserTunable LaserBioluminescent Materials Bioluminescent Materials Signal Transmission:Signal Transmission:Erbium-Doped Silica Fibers or OtherErbium-Doped Silica Fibers or Other Signal DetectionSignal Detection Silicon and Other Semiconductor Multilayer Silicon and Other Semiconductor Multilayer

Photodetector ArrayPhotodetector Array

Carbon Nanotubes for Signal Carbon Nanotubes for Signal GenerationGeneration

These nanotubes These nanotubes can be selectively can be selectively doped to change doped to change the value of their the value of their electronic band electronic band gap.gap.

Nanotubes are Nanotubes are known for their known for their ability to act as fast ability to act as fast switches in the switches in the MHz-GHz range.MHz-GHz range.

Carbon Nanotubes for Signal Carbon Nanotubes for Signal GenerationGeneration

They can be grown on an array in discrete locationsThey can be grown on an array in discrete locations One or more of these squares could couple into a One or more of these squares could couple into a

fiber, because each square’s area can be made on a fiber, because each square’s area can be made on a small scalesmall scale

Bundle of Nanotubes that are selectively doped

Nanotube Oriented GrowthNanotube Oriented Growth It has been shown It has been shown

that nanotubes can that nanotubes can be selectively and be selectively and reliably grown on reliably grown on SiOSiO22 in in predetermined predetermined orientations.orientations.

B. Wei et al. Nature, 416, 495-6 (04 Apr 2002)

Nanotubes as EmittersNanotubes as Emitters Nanotubes can be Nanotubes can be

used as field used as field emitters in flat emitters in flat panel displays (<8 panel displays (<8 mm thick) mm thick) [Samsung][Samsung]

Transmission of the SignalTransmission of the Signal Wavelengths of 850, 1310, or 1550 Wavelengths of 850, 1310, or 1550

nm should be used to minimize nm should be used to minimize signal attenuation lossessignal attenuation losses

Silica fibers doped with erbium Silica fibers doped with erbium should be used at 1550 nmshould be used at 1550 nm

Transmission of the SignalTransmission of the Signal If indices of refraction (1.4 If indices of refraction (1.4

and 1.395) and and 1.395) and (1550 nm) (1550 nm) are chosen as reasonable are chosen as reasonable values, then fiber diameter values, then fiber diameter is about 5 is about 5 m. m.

Main problem is the Main problem is the generation of power from generation of power from source. About 15% of the source. About 15% of the power is lost to the cladding.power is lost to the cladding.

Chromatic signal distortion is Chromatic signal distortion is not significant compared to not significant compared to signal attenuation. For a 5 signal attenuation. For a 5 nm wavelength difference in nm wavelength difference in generated signal, a 50 km generated signal, a 50 km fiber length is permissible. fiber length is permissible.

Detection of the SignalDetection of the Signal Technology (X3) is Technology (X3) is

currently patented currently patented by Foveon for use by Foveon for use in digital cameras in digital cameras to increase pixel to increase pixel resolutionresolution

Production of many Production of many different elements different elements (millions) on the (millions) on the array is possible array is possible with one chip with one chip

Absorption of Silicon at Absorption of Silicon at Different WavelengthsDifferent Wavelengths

200 250 300 350 400 450 500 550 600 650 700 750 800 850

0

2

4

6

8

10

12

14

(m

)

Pen

etra

tion

dept

hSi-I (cd)

Excitation wavelength (nm)

0.00.20.40.60.81.01.21.41.61.82.0

(m)

468101214

(nm

)

Ar-ionlaser

Diodelaser

(near-IR)

He-Cdlaser(UV)

200 250 300 350 400 450 500 550 600 650 700 750 800 850

0

2

4

6

8

10

12

14

(m

)

Pen

etra

tion

dept

hSi-I (cd)

Excitation wavelength (nm)

0.00.20.40.60.81.01.21.41.61.82.0

(m)

468101214

(nm

)

Ar-ionlaser

Diodelaser

(near-IR)

He-Cdlaser(UV)

Transmission of the SignalTransmission of the Signal Multiple layers Multiple layers

may be made, may be made, instead of just instead of just three. The three. The shortest shortest wavelength will wavelength will penetrate to the penetrate to the shallowest depth, shallowest depth, and the longest and the longest will penetrate to will penetrate to the deepest. In the deepest. In this example, one this example, one signal may have signal may have 66 permissible values permissible values instead of 2.instead of 2.

Transmission of the SignalTransmission of the Signal Lithography may be used to fabricate such Lithography may be used to fabricate such

device arraysdevice arrays Silicon is the substrate, but germanium or Silicon is the substrate, but germanium or

another semiconductor may be another semiconductor may be heteroepitaxially grown on the surface by heteroepitaxially grown on the surface by chemical vapor deposition, followed by another chemical vapor deposition, followed by another layer of silicon, etc. Interconnects must be layer of silicon, etc. Interconnects must be employed.employed.

ConclusionsConclusions Sufficient power generation and losses are the Sufficient power generation and losses are the

main issue over long distances, so this may be main issue over long distances, so this may be the most feasible over short distances, such as the most feasible over short distances, such as between computer components or LANs.between computer components or LANs.

The bitrate for a single step index fiber for normal The bitrate for a single step index fiber for normal conditions is about 30 Gbit/s (only in theory). conditions is about 30 Gbit/s (only in theory). However, by comparison, a system using 100,000 However, by comparison, a system using 100,000 of these fibers with base 6 logic can produce a of these fibers with base 6 logic can produce a theoretical bitrate of 7.68 Pbit/stheoretical bitrate of 7.68 Pbit/s!!

It is not likely that these speeds could actually be It is not likely that these speeds could actually be realized, but the idea of multiple fibers realized, but the idea of multiple fibers transmitting signals with simplified generation transmitting signals with simplified generation and detection is the same.and detection is the same.