Optical frequency link between an acetylene stabilized laser at 1542 nm and an Rb stabilized laser at 778 nm using a two-color mode-locked fiber laser

We have demonstrated optical frequency link of two frequency-stabilized las er diodes operating at 1542 nm (a rotational-vibrational line of isotope ac etylene molecule) and 778 nm (an Ph two photon transition) using a two-colo r mode-locked fiber laser. The laser produces a frequency comb (300 fs puls e) in the 1560 nm region and, through the second harmonic generation (SHG) process, another frequency comb (100 fs pulse) in the 780 nm region. Beat n ote signals have been observed between each of the stabilized laser radiati on and a mode of the mode-locked fiber laser in the vicinity of the stabili zed laser frequency. The S/N ratios were 25 dB and 30 dB with 100 kHz resol ution bandwidth for brat notes at lambda = 1542 nm and lambda = 778 nm, res pectively. Preliminary result has shown the potential of the system for fre quency measurements with the accuracy of below 100 kHz. This limitation wil l be overcome by improving the frequency counting system using a phase-lock ed tracking oscillator and installing a PZT element in the fiber laser cavi ty, Supposing the accuracy of the mode spacing is similar to the case of a mode-locked Ti:sapphire laser, the accuracy of kHz level is very presumable . (C) 2000 Elsevier Science B.V. All rights reserved.