Measurement of the 'single-photon' velocity and classical group velocity in standard optical fibre

J. D. Ingham, J. E. Carroll, I. H. White, R. M. Thompson

Research output: Contribution to journalArticlepeer-review

2 Citations (SciVal)


When engineering secure optical communication networks, it may be important to know if the photon velocity may be altered in a dispersive fibre by selecting photonic states with different ranges of Schrödinger frequencies, (N + 1/2)f where f is the modal frequency. This paper reports on a comparison between the velocity of approximate single-photon states (N ≈ 1) and the classical optical group velocity (N ≫ 1 with a range of N). The experiments use the same source and the same novel technique with a single temporal standard to measure the time of flight of both 'single photons' and classical optical energy over standard optical fibre. Within the experimental accuracy (approximately 0.2 ns in 30 000 ns, or 6.3 km of fibre) there is no evidence for changes of velocity as the composition of the number states varies. This suggests that photons travel in a dispersive fibre with a velocity that is independent of the Schrödinger frequencies. It is believed that this is the first such test on kilometre lengths of standard fibre.

Original languageEnglish
Article number045
Pages (from-to)1538-1546
Number of pages9
JournalMeasurement Science and Technology
Issue number5
Publication statusPublished - 1 May 2007


  • Group velocity
  • Optical fibre propagation
  • Quantum optics
  • Single photons
  • Time-of-flight measurement

ASJC Scopus subject areas

  • Instrumentation
  • Applied Mathematics


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