Broadband THz quantum cascade lasers and arrays

Abstract

Terahertz Quantum Cascade lasers are very versatile sources of terahertz radiation. Frequency comb operation, surface emitting arrays, external cavity tuning have been demonstrated. For all these implementations broadband gain is strongly demanded. The intersubband gain mechanism allows to the design of different wavelength active region and their integration in the same waveguide. We have developed active regions consisting of up to four different intersubband designs. To enable a common operation not only the gain curve needs to be aligned over all sections but also the alignment electric field and subsequently the operating current. Fabry-Perot devices fabricated from the four-section active region show lasing over more than one octave. Ring resonators show also broadband laser operation and comb formation. Broadband operation is a large advantage of random lasers which we turn into useful devices by an optical machine learning approach. This allows the control of the emission wavelength beyond discrete cavity modes.