Optical Frequency Transfer

Optical frequency enables highly stable dissemination of frequency signals to remote sites. Aiming frequency transfer based on stable and accurate clocks developed by NICT without any degradation of its stability, we study on the transfer techniques via an optical fiber or free space *1, *2.

A remote comparison of 87Sr lattice clock developed by NICT and University of Tokyo was performed by a fiber-based optical carrier transfer in 2011 *3. We detected the frequency difference in the 10-15 level caused by the differential gravitational redshift, by measuring for a few seconds.

*1; M. Kumagai et al., Optics Letters, 34, 19, 2949-2951, 2009.
*2; M. Fujieda et al., Optics Express, 19, 17, 16498, 2011.
*3; A. Yamaguchi et al., Applied Physics Express, 4, 082203, 2011.