A method of absolute optical frequency measurement is realized by using mode-locked laser frequency combs to measure the optical frequency of an unknown laser. By varying the repetition frequency, the relative frequency location of the unknown laser to the beating comb line is determined according to the corresponding variation of the beat frequency. Also, by varying the offset frequency of the mode-locked laser, the real offset frequency detected by a self-referencing technique can be determined according to the corresponding variation of the beat frequency between the unknown laser and the mode-locked laser frequency combs. The mode number of the frequency comb is uniquely and adequately determined through measuring the beat frequencies between the unknown laser and the mode-locked laser frequency combs at various repetition frequencies and through measuring the corresponding mode number change, and hence the optical frequency of the unknown laser is determined.
