The development of optical frequency comb in optical frequency standard is presented. In order to put optical frequency comb into use, the carrier-envelope.offset frequency should be measured and the Octave-spanning laser should be developed. Five methods to broaden the ultra-broadband spectrum of an octave-spanning laser are presented, among which the method for making a laser which generates the ultra-broadband spectrum directly and a semiconductor saturable absorption mirror which plays an important role in the former are stated in detail. As far as now, the latter has not been reported in the world.