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An optimization of terahertz local oscillators based on LT-GaAs technology.

We report on photonic technologies developed at the MPI fur Radioastronomy and the Research Center Julich to generate Terahertz Local Oscillator reference signals for use on e.g. ALMA/APEX and SOFIA. The principle is to mix two (NIR) laser colours in a biased LTG-GaAs layer, thus creating a high-frequency beat (difference) frequency signal. This output signal is coupled to free space through an antenna. In this work a systematic study of the photomixer design, in order to optimize the RF power, is presented. Part of the experiments were done with photomixers integrated to with a broadband spiral antenna designed for frequencies up to 1 THz. The LT GaAs photomixers are prepared on materials with various growth temperatures as well as using resonant cavity material structures and various finger contact geometries. An improvement in the output power up to around 3 μW of submillimeter radiation (0.5 THz) is demonstrated.