Researchers at the U. of California, Los Angeles (UCLA) have used plasmonic photomixing to develop a room-temperature terahertz source with not only high spectral purity and broad tunability, but with nearly 1 mW of optical power at terahertz frequencies—significantly higher than previously demonstrated photomixing-based terahertz radiation sources.
The 1550 nm plasmonic photomixer operates under pumping duty cycles below 10%. By enhancing the device’s quantum efficiency through the use of plasmonic contact electrodes and by reducing thermal breakdown at high optical pump power levels using a 150 mW low-duty-cycle (2%) optical pump with a 1 MHz modulation frequency, 0.8 mW continuous-wave radiation at 1 THz has been demonstrated. The plasmonic photomixer is fabricated with a logarithmic spiral antenna integrated with plasmonic contact electrodes on an erbium arsenide: indium gallium arsenide (ErAs:InGaAs) substrate. The fine comb geometry of the plasmonic nanostructures better concentrates the laser light and enhances the generated photocarriers in close proximity to the contact electrodes, reducing transport path length of the photocarriers and increasing both output efficiency and power for the source. The pump’s repetition rate can also be specifically selected for a given duty cycle to control the terahertz radiation spectral linewidth. Reference: Chrisopher W. Berry et al. Opt. Lett. (2014); http://dx.doi.org/10.1364/OL.39.004522.