The European project OPTHER - Optically Driven THz Amplifiers, is focused on the realization of a THz amplifier. This device aims to overcome the actual limitations of THz sources in terms of emitted power, opening the way to the use of THz in monitoring security systems. Two alternative schemes are under study for amplification. In the first one (THz drive signal amplifier) the continuous wave electron beam emitted by the CNT cathode is modulated by the electric field in the interaction structure driven by a THz signal (generated by QCL or laser mixing). In the second one (optically modulated beam THz amplifier), the CNT cathode emits bunches of electrons at the THz rate. Those bunches are transmitted to the interaction structure and generate the amplified output signal.