Tunable, continuous-wave Terahertz photomixer sources and applications

Abstract

Realization of gigahertz-frequency impedance matching circuits for nano-scale devices Appl. Phys. Lett. 101, 053108 (2012) Synchronization of a renewable energy inverter with the grid J. Renewable Sustainable Energy 4, 043103 (2012) Monolithic high-temperature superconducting heterodyne Josephson frequency down-converter Appl. Phys. Lett. 100, 262604 (2012) Generation of pure phase and amplitude-modulated signals at microwave frequencies Rev. Sci. Instrum. 83, 064705 (2012) Additional information on J. Appl. Phys. This review is focused on the latest developments in continuous-wave (CW) photomixing for Terahertz (THz) generation. The first part of the paper explains the limiting factors for operation at high frequencies $ 1 THz, namely transit time or lifetime roll-off, antenna (R)-device (C) RC rolloff, current screening and blocking, and heat dissipation. We will present various realizations of both photoconductive and p-i-n diode-based photomixers to overcome these limitations, including perspectives on novel materials for high-power photomixers operating at telecom wavelengths (1550 nm). In addition to the classical approach of feeding current originating from a small semiconductor photomixer device to an antenna (antenna-based emitter, AE), an antennaless approach in which the active area itself radiates (large area emitter, LAE) is discussed in detail. Although we focus on CW photomixing, we briefly discuss recent results for LAEs under pulsed conditions. Record power levels of 1.5 mW average power and conversion efficiencies as high as 2 Â 10 À3 have been reached, about 2 orders of magnitude higher than those obtained with CW antenna-based emitters. The second part of the paper is devoted to applications for CW photomixers. We begin with a discussion of the development of novel THz optics. Special attention is paid to experiments exploiting the long coherence length of CW photomixers for coherent emission and detection of THz arrays. The long coherence length comes with an unprecedented narrow linewidth. This is of particular interest for spectroscopic applications, the field in which THz research has perhaps the highest impact. We point out that CW spectroscopy systems may potentially be more compact, cheaper, and more accurate than conventional pulsed systems. These features are attributed to telecom-wavelength compatibility, to excellent frequency resolution, and to their huge spectral density. The paper concludes with prototype experiments of THz wireless LAN applications. For future telecommunication systems, the limited bandwidth of photodiodes is inadequate for further upshifting carrier frequencies. This, however, will soon be required for increased data throughput. The implementation of telecom-wavelength compatible photomixing diodes for down-conversion of an optical carrier signal to a (sub-)THz RF signal will be required.

Terahertz Emitters, Detectors and Sensors: Current Status and Future Prospects

“…This effect provides a mechanism for the generation of tunable terahertz radiation using photomixing of infrared signals [Preu et al, 2011] .…”

Oscillations of electron–hole plasma in terahertz emitters

“…This assumption is justified by the fact that the kinetic energy of excited carriers exceeds the energy of electron confinement due to downward band bending. Then, the hydrodynamic model [20] gives the total photocurrent as (6) where…”

“…On the other hand, the frequency of electronhole plasma oscillations in semiconductors lies in the THz frequency range. Therefore, along with other methods of generation of THz radiation -selective thermal stimulation [4,5] and photomixing [6,7], the excitation of plasma oscillations is very attractive for THz technology.…”

Coherent synthesis of two continuous microwave signals generated by two optical beats

“…Power increase of THz continuous-wave generated by optical beat is an important issue to apply the THz continuous-wave to imaging, spectroscopic system, communications, etc [1,2,3,4]. Analysis and design of photomixer array is also studied as a way to increase the THz radiation power [5].…”