Optical references for telecom wavelengths and measurement of their absolute frequency

Our group is developing a femtosecond laser based frequency comb that is to be linked with the Sr⁺ single ion frequency standard and other frequencies of interest. The comb is of a design similar to systems reported by previous workers. A mode-locked Ti:sapphire ring laser produces 30-50 fs pulses at a repetition rate of approximately 700 MHz. The output is focused into a 15-cm-long piece of microstructure fibre (OFS Fitel) where the 40-nm bandwidth of the laser is broadened into a comb of optical frequencies extending over an octave.