Development of an ultrastable fiber optic frequency distribution system using an optical delay control module [for frequency standard and VLBI]

An ultrastable fiber optic frequency distribution system is described. The ultrastable phase stability is achieved by configuring a closed phase-locked loop with a single-mode optical fiber transmission line in which two optical carrier signals with different wavelengths are transmitted as a forward and a backward signal, and installing an optical delay control module which has no differential dispersion effect between the two optical carrier waves and induces no electrical noise. A phase stabilized optical fiber (PSOF) is used for the signal transmission line. The stabilities of this system are 7.5/spl times/10/sup -17/ and 1.1/spl times/10/sup -17/ in Allan standard deviation at 1000 and 10000 s averaging time, respectively, while the environmental temperature of the PSOF cable varies as much as the range of 10/spl deg/C and the rate of 10/spl deg/C/12 h.