ACCURACY OF OPTICAL FREQUENCY COMB GENERATORS AND OPTICAL FREQUENCY INTERVAL DIVIDER CHAINS

We compared two methods for measuring large optical frequency differen ces: an optical frequency comb generator, which creates a large number of sidebands from a single-mode laser through electro-optic modulatio n, and an optical frequency interval divider chain, which divides a fr equency gap successively by two until it becomes accessible to a radio -frequency counter. By locking two diode lasers to two modulation side bands of a comb generator, similar to 1 THz apart, and measuring this interval with a chain of four phase-locked interval dividers, we demon strate for the first time to our knowledge the accuracy of both techni ques within an experimental limit of 6.8 x 10(-15). (C) 1998 Optical S ociety of America.