A novel scheme of optical frequency up-conversion is proposed by using the high order sideband of the directly modulated low-speed baseband signal for injection locking of a distributed feedback semiconductor laser (DFB-LD). The operational principle of the proposed optical frequency up-conversion scheme is theoretically analyzed. Based on this scheme, optical frequency up-conversion of a 2.5 Gb/s is directly modulated baseband signal to 30, 35 and 40 GHz subcarrier modulation signal respectively. Higher carrier frequency (up to 60 GHz) can also be achieved in potential. The proposed scheme does not need expensive components like high-speed external modulator or high frequency radio frequency (RF) local oscillator, and it has the benefit of simple structure. It provides a viable solution for the optical-wireless hybrid access.