@conference{202091,
  author = {Paul Williams and Nathan Newbury and William Swann},
  title = {Optical frequency transmission over 251 km of fiber at 6x10<sup>-19</sup> residual frequency instability in 100 s},
  year = {2007},
  month = {2007-10-15},
  publisher = {Tech. Dig., OFMC, Optical Fibre Measurement Conf., Teddington, UK},
  url = {https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32720},
  language = {en},
}