Abstract : Continuous high-purity THz generation through photomixing is a very promising technique for future THz local oscillators. Consequently, we have proposed an innovative photomixing architecture based on a dual frequency laser emitting around 1 µm associated with a matched band gap photoconductor. Working with this wavelength allows the use of compact and low cost diode pumped solid state laser and also the use of photoconductive materials with the required electrical properties for a CW generation over a large frequency bandwidth.
Therefore, we have developed 2 dual-frequency lasers using Yb doped active mediums (KGW and CaF2) emitting around 1 µm. They permit the generation of narrow line-width (<30 kHz) electrical beat-notes. With the use of Yb doped fiber amplifiers, we have been able to amplify the total optical output power up to 1W.
We then have studied and characterised 2 photoconductive materials compatible with an illumination around 1 µm: InGaAsN and LTG-In.23Ga.77As grown on metamorphic layer and Beryllium doped. Optical and electrical properties of those two materials have been tested and compared to the LTG-GaAs properties.
After a theoretical study of photomixers (including the hole participation), we have performed CW THz generation experiments using the LTG-InGaAs devices coupled to the dual-frequency laser: we have detected signals of few tens of nW, tunable up to 2 THz.
Finally, we have proposed a new travelling wave vertical photomixer architecture. Modelisation have shown that the expected generated power (0,2 mW at 1 THz), the tunability (0-3 THz) and spectral purity (< 30 KHz) of such a device would provide one of the best device in this frequency range.