The work of the winners of the 2005 Nobel prize in physics is briefly reviewed. They measured the frequency of light with mode-locked laser comb. Femtosecond laser-frequency comb techniques are vastly simplifying the measurement. A single mode-locked femtosecond laser,its spectrum broadened by self-phase modulation in a photonic crystal fiber,can produce millions of sharp laser lines in a precise evenly spaced grid spanning much of the visible and near-infrared spectrum,the spacing of the frequency equal to the repetition of the modelocked pulse. They measured the radio frequency instead of optical frequency measurement with optical frequency comb and technology of octave-spanning. This is a significant step toward precision of optical frequency measurement and precision of atomic clock and a new brilliancy in physics and metrology.