We compared two methods for measuring large optical frequency differences: an optical frequency comb generator, which creates a large number of sidebands from a single-mode laser through electro-optic modulation, and an optical frequency interval divider chain, which divides a frequency gap successively by two until it becomes accessible to a radio-frequency counter. By locking two diode lasers to two modulation sidebands of a comb generator, ∼1 THz apart, and measuring this interval with a chain of four phase-locked interval dividers, we demonstrate for the first time to our knowledge the accuracy of both techniques within an experimental limit of 6.8 × 10<sup>-15</sup>.
© 1998 Optical Society of America
Th. Udem, J. Reichert, T. W. Hänsch, and M. Kourogi, "Accuracy of optical frequency comb generators and optical frequency interval divider chains," Opt. Lett. 23, 1387-1389 (1998)