Frequency stability of absolute optical frequency references distributed over 200 km of fibre for use in large-scale HDWDM systems

The relative optical frequency stability of two optical references at 1547.825 nm were examined. The optical signal of one reference was split and one part was sent over 20 km of fibre to be heterodyned with a second reference laser. The second part was sent via more than 200 km of fibre over three Er-doped amplifiers, also heterodyned with the second reference in order to measure the influence of long haul transmission. No degradation of the stability of 8*10-11 (SQRT of Allanvariance at 500 s integration time) was found.