New approaches to THz Bloch oscillator

The Bloch oscillator is a very promising suggestion for an inversionless terahertz semiconductor laser, which was not still realized in an experiment. The principle of operation of this tunable source of THz radiation is based on Bloch oscillations of miniband electrons in a biased semiconductor superlattice. The majority of researches attribute the difficulties in the realization of the Bloch oscillator to a distractive role of high-field domains inside a superlattice. In this report, we present a minireview of different new approaches to the generalized Bloch oscillator, for which it is possible to reach gain due to the Bloch oscillations and simultaneously to avoid the formation of domains in a superlattice.