© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

7.2.5.2 Infrared and Optical Cables

Photon energy equals thermal noise (hn_equal / kT ln(2) = 1) in the far infrared, specifically, at n_equal = 6 x 10¹² Hz for T = 310 K. At still higher frequencies, the cost per bit becomes the energy per photon, or hn_optical, hence the maximum transmission frequency becomes

{Eqn. 7.17}

Silica optical fibers are damaged by near-UV photons at frequencies exceeding ~10¹⁵ Hz (l ~ 300 nm), giving an upper limit on optical information transfer rates. Transmitting 10¹⁵ UV photons per second requires a power budget of P_comm = 1 milliwatt; holding intensity to <10⁵ watts/m² for safety reasons (Section 6.4.3.2) mandates a fiber >100 microns in diameter. Cables this large are suitable primarily for relatively short internodal trunk lines (Section 7.3.1). At ~10⁵ watts/m² a 1 micron² fiber can safely continuously transmit ~10⁵ pW, enough to generate 10¹³ photons/sec at 10 THz (~10¹³ bits/sec), or ~10 zJ/bit. Note that below n_equal, the energy cost per bit is constant; above n_equal, the energy cost per bit rises linearly with frequency. Regenerative systems could in theory recover and reuse some of this energy.

Last updated on 19 February 2003