Generation of cw-terahertz radiation using a two-longitudinal-mode laser diode

Coherent cw-terahertz (THz) radiation has been generated by photomixing with a photoconductive antenna fabricated on a low-temperature-grown (LTG) GaAs film using a two-longitudinal-mode distributed Bragg reflector (DBR) laser diode (LD). The frequency of the emitted radiation corresponds to the difference frequency between the two modes of the LD. The linewidth of the radiation is much narrower than that of each laser mode oscillating in the same cavity due to the common-mode rejection effect between the two modes oscillating in the same cavity. This property of the two-mode LD, as well as its compactness and ease of optical alignment, make the device promising as an excitation laser source for photomixing.