13 GHz direct modulation of terahertz quantum cascade lasers

By directly modulating the bias voltage of a double-metal waveguide, 2.8 THz quantum cascade laser, we observe the appearance of multiple gigahertz sidebands in the emission spectrum, with a spacing that can be continuously tuned up to 13 GHz. By using an upconversion technique, the terahertz spectrum is shifted at 1.57 mu m, and displayed on an optical spectrum analyzer. A marked increase in the number of sidebands is observed when the modulation frequency approaches the round-trip frequency (similar to 12.3 GHz). The laser packaging high frequency response has been measured using a microwave rectification technique, and is limited by the bond-wire parasitic inductance. (c) 2007 American Institute of Physics.