Expansion of span-width of an optical frequency comb using a higher harmonic wave modulation

We propose a novel method for expanding the spanwidth of an optical frequency comb that utilizes modulation by a superposition of higher harmonic waves. Based on the calculations, it was found that in the terms up to third-order harmonic wave, the optimum superposition is the one whose power ratio between the fundamental and the third-order harmonic waves is 1:1. The validity of this method was experimentally confirmed at 1.5-μm wavelength region. By this optimum modulation with a wave power of 1.0 W, the span-width of OFC was increased to 72 mn (=9.1 THz).