Terahertz Technology – Continuous-Wave THz Generation
Principle of frequency domain terahertz generation. The photomixer translates the laser beat into the terahertz wave.
Continuous-wave (cw) terahertz radiation is obtained by so-called optical heterodyning: the terahertz emitter (“photomixer”) is irradiated with two near-infrared lasers of adjacent wavelengths. An antenna surrounding the photomixer emits an electromagnetic wave at the terahertz difference frequency. Benefits of this technique are a high resolution, spectral selectivity, and superior SNR values.
Most photomixers employ GaAs and, at room temperature operation, require laser wavelengths below 870 nm. Another option are InP-based emitters that operate at the telecom wavelength band of 1.5 µm. The TeraBeam operating at 1550 nm is the ideal laser for these emitters.
TOPTICA’s near-infrared distributed feedback (DFB) diode lasers are ideal sources for cw terahertz generation. DFB diodes comprise a grating structure within the active section of the semiconductor, restricting the laser emission to a single longitudinal mode. Thermal tuning of the grating pitch yields very wide continuous frequency scans (typ. > 1000 GHz / diode).
For the generation of tunable terahertz radiation, high output power, narrow linewidth and wide frequency tuning are the key benefits. By selecting two DFB diodes with appropriate wavelength offset, one can tune the terahertz difference frequency continuously, e.g. from 0 to 1.8 THz.