No abstract

OSA grants to the Author(s) (or their employers, in the case of works made for hire) the following rights:(a) The right, after publication by OSA, to use all or part of the Work without revision or modification, including the OSAformatted version, in personal compilations or other publications consisting solely of the Author(s') own works, including the Author(s') personal web home page, and to make copies of all or part of the Work for the Author(s') use for lecture or classroom purposes; (b) The right to post and update his or her Work on any internet site (other than the Author(s') personal web home page) provided that the following conditions are met: (i) access to the server does not depend on payment for access, subscription or membership fees; and (ii) any such posting made or updated after acceptance of the Work for publication includes and prominently displays the correct bibliographic data and an OSA copyright notice (e.g. "© 2009 The Optical Society").. Abstract: We demonstrate long-distance (100-km) synchronization of the phase of a radio-frequency reference over an optical-fiber network without needing to actively stabilize the optical path length. Frequency mixing is used to achieve passive phase-conjugate cancellation of fiber-length fluctuations, ensuring that the phase difference between the reference and synchronized oscillators is independent of the link length. The fractional radio-frequency-transfer stability through a 100-km "real-world" urban optical-fiber network is 6 × 10 17 with an averaging time of 10 4 s. Our compensation technique is robust, providing long-term stability superior to that of a hydrogen maser. By combining our technique with the short-term stability provided by a remote, high-quality quartz oscillator, this system is potentially applicable to transcontinental optical-fiber time and frequency dissemination where the optical round-trip propagation time is significant. 723-727 (2010). 14. G. Marra, H. S. Margolis, S. N. Lea, and P. Gill, "High-stability microwave frequency transfer by propagation of an optical frequency comb over 50 km of optical fiber," Opt. Lett. 35(7), 1025-1027 (2010). 15. G. Marra, R. Slavík, H. S. Margolis, S. N. Lea, P. Petropoulos, D. J. Richardson, and P. Gill, "High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser," Opt. Lett. ©2013 Optical Society of America 36(4),

No abstract

Very-long-baseline interferometry (VLBI) for high-resolution astronomical imaging requires phase-stable frequency references at widely separated radio-telescope antennas. For the first time to our knowledge, we have disseminated a suitable radio-frequency (RF) reference for VLBI over a "real-world" telecom optical-fiber link between radio telescopes that are >100 km apart, by means of an innovative phase-conjugation technique. Bidirectional optical amplification is used in parallel with live traffic, and phase perturbations in the effective optical-fiber path length are compensated. This RF-over-fiber approach obviates the need for separate hydrogen masers at each antenna, offering significant advantages for radio-astronomy facilities such as the Square Kilometer Array.

Motivated by the potential use of electromagnetically induced transparency (EIT) to measure atomic parity nonconservation (PNC), we have studied EIT and associated optical rotation for a three-level system in thallium vapor. EIT allows sub-Doppler resolution of the 6P 1͞2 ! 6P 3͞2 mixed magnetic dipole, electric quadrupole transition at 1.28 mm when 0.535-mm radiation acts on the 6P 3͞2 ! 7S 1͞2 transition. Our measurements include rotation due to electromagnetically induced birefringence and Faraday rotation perturbed by EIT. We also identify a new method for determining the amplitude ratio E 2͞M 1 for the 1.28-mm transition. The possible advantages of an EIT technique for measuring atomic PNC are discussed in the context of our results. [S0031-9007(98)