A broadly tunable single-mode quantum cascade laser source comprising: an array of individually addressed closely-spaced mid-infrared or THz distributed feedback grating quantum cascade semiconductor lasers fabricated on the same laser wafer, wherein each laser has a slightly different emission wavelength from the adjacent laser in the array, which wavelength is set by each distributed feedback grating having a slightly different period, and a difference in the emission wavelengths between two lasers in the array that are adjacent in frequency space is sufficiently small such that for any desired wavelength in a wavelength range supported by a broadband-gain, or multiple wavelengths, or any other quantum cascade laser material, a microelectronic controller is configured to set the temperature of a laser in the array in such a way that said laser emits at the desired wavelength and a difference in the target emission wavelengths between two lasers adjacent in frequency space in the array is smaller than a tuning range available with temperature tuning of each of said lasers, and each laser on a chip can be addressed independently by the microelectronic controller; and said microelectronic controller is configured to switch each semiconductor laser in the array on and off, to set current for each semiconductor laser in the array, and to control and set a temperature of each individual semiconductor laser in said array, as well as the temperature of the array as a whole to produce a broadly tunable single-mode quantum cascade laser source, and the microelectronic controller is configured to switch between the semiconductor lasers in the array and/or control an emission wavelength of each semiconductor laser in the array so as to provide continuous spectral coverage within the mid-infrared emission band or the Terahertz emission band. an array of individually addressed closely-spaced mid-infrared or THz distributed feedback grating quantum cascade semiconductor lasers fabricated on the same laser wafer, wherein each laser has a slightly different emission wavelength from the adjacent laser in the array, which wavelength is set by each distributed feedback grating having a slightly different period, and a difference in the emission wavelengths between two lasers in the array that are adjacent in frequency space is sufficiently small such that for any desired wavelength in a wavelength range supported by a broadband-gain, or multiple wavelengths, or any other quantum cascade laser material, a microelectronic controller is configured to set the temperature of a laser in the array in such a way that said laser emits at the desired wavelength and a difference in the target emission wavelengths between two lasers adjacent in frequency space in the array is smaller than a tuning range available with temperature tuning of each of said lasers, and each laser on a chip can be addressed independently by the microelectronic controller; and said microelectronic controller is configured to switch each semiconductor laser in the array on and off, to set current for each semiconductor laser in the array, and to control and set a temperature of each individual semiconductor laser in said array, as well as the temperature of the array as a whole to produce a broadly tunable single-mode quantum cascade laser source, and the microelectronic controller is configured to switch between the semiconductor lasers in the array and/or control an emission wavelength of each semiconductor laser in the array so as to provide continuous spectral coverage within the mid-infrared emission band or the Terahertz emission band.