In this paper, dual-mode semiconductor laser is presented and demonstrated experimentally based on multimode Fabry-Perot laser diode with a built-in cavity. The spacing of both emission modes can be tuned by adjusting the bias current and operating temperature of active region. The generated dual-mode resonance can give rise to terahertz (THz) photonic signal with more than 300 GHz frequency. Under an external injection mode launched into the two-color semiconductor laser condition, it is possible to simultaneously generate photonic signals with various frequencies, ranging from less than 10 GHz to several THz, by selecting a proper resonance mode as the reference mode of injection beam. In this study, photonic signal including microwave (MW), millimeter-wave (mm-wave), and THz wave whose frequency range is from a few gigahertz to more than 0.5 THz are given, and the corresponding optical spectrum and electrical spectrum for low-frequency MW signal as well as simulated electrical spectrum for high-frequency mm-wave and THz wave signal are presented and discussed in detail.