We present an optoelectronic mixer for the terahertz (THz) frequency-domain based on an iron-doped InGaAs layer integrated in a plasmonic microcavity. We show that this structure, under 1550-nm-wavelength illumination, allows for more than 70% absorption efficiency in a 220 nm-thin InGaAs absorber and very high Roff/Ron >1000. It leads to THz mixers driven by 1550-nm lasers showing conversion loss as low as ~30 dB at 300 GHz. Therefore, this design is very promising for application as receivers in high-data-rate wireless telecom, in cw-THz spectrometers, or in photonic-senabled THz spectrum analyzers.
We report the room-temperature frequency response, in the range 0-220GHz, of GaAs-based QWIP photodetectors operating at 10um. Detectors rely on 2D arrays of patch-antennas, connected to an integrated 50-Ohm coplanar line allowing on-wafer characterization. By difference frequency mixing of two QCLs, we obtain a RF 3dB bandwidth of ~90GHz. The frequency response of devices based on 4 antennas is compatible with a carrier capture-time of ~2.5ps. By replacing the coplanar line with a log-spiral antenna we also demonstrate devices radiating directly in free-space. The perspective of exploiting the latter as QCL-pumped photomixers for the generation of microwave/sub-mm radiation is discussed.
Recently we have improved the efficiency and the output power of our optically pumped continuous-wave THz sources.
These sources are based on the beating of two laser lines in a wide bandwidth photodetector. Its intrinsic nonlinear
behaviour is used to produce a beatnote at the frequency difference between the two laser lines (photomixing). These
photomixers are continuously tunable THz sources working at room temperature. We have developed two kinds of
photomixers: GaAs-based for 0.8 μm pumping and InP-based for 1.5 μm pumping. On GaAs the best results has been
obtained thanks to low-temperature-grown GaAs (LTG-GaAs) photoconductors (PC). Efficiency and power were
optimized by designing a new type of thin PC placed in a Fabry-Pérot resonator. The high impedance of the PC is a wellknown
limitation of this device but with our approach it was possible to reduce its impedance by a factor 100. Moreover
by designing an impedance matching network it was possible to obtain 1.8 mW at 252 GHz with a total efficiency of 0.5
%. On InP the best results are obtained with uni-travelling-carrier photodiodes (UTC-PD). The device was improved by
designing a new heterostructure and new semi-transparent contacts with sub-wavelength apertures. The active layer was
also bonded to a silicon substrate thanks to metal thermocompression. It is demonstrated that with this approach it is
possible to obtain a power of 0.7 mW at 300 GHz with a total efficiency of 0.7 %. More generally the efficiency of
optically pumped terahertz sources will be discussed.
KEYWORDS: Terahertz radiation, Signal to noise ratio, Signal detection, Signal attenuation, Photodiodes, Heterodyning, Tunable lasers, Physics, Spectroscopy, Metrology
THz has become a wide field of investigation opening new opportunities in a growing number of domains of physics,
chemistry, and biology. Among the different techniques existing today to generate THz fields, heterodyning two optical
frequencies is a useful approach when tunability is required. Moreover, to address high-resolution spectroscopy or
metrology applications, a key point is the achievement of a narrow linewidth source. To this aim, two-propagation-axis
dual-frequency lasers have been already shown to provide narrow linewidth tunable beat notes up to 2 THz. We report in
this paper the demonstration of a narrow linewidth THz radiation source based upon this laser. Indeed the beat note
provided by the laser is sent into a unitravelling carrier photodiode (UTC-PD), and radiated by a transverseelectromagnetic-
horn antenna (TEM-HA). All components operate at room temperature. The emitted THz signal is
detected by a subharmonic mixer coupled to an electrical spectrum analyzer. The THz signal is observed and analyzed
thanks to a heterodyne detection. The measured dynamic range is 75 dB at 282 GHz, 50 dB at 500 GHz, 35 dB at
700 GHz and decreases to 20 dB at 1 THz. The decrease is due to the UTC-PD efficiency and conversion losses in the
sub-harmonic mixer. The measured linewidth is better than 30 kHz at any frequency from DC to 1 THz.
We have developed a new generation of optoelectronic large bandwidth terahertz sources based on TEM horn antennas
monolithically integrated with several types of photodetectors: low-temperature grown GaAs (LTG-GaAs) planar
photoconductors, vertically integrated LTG-GaAs photoconductors on silicon substrate and uni-travelling-carrier
photodiodes. Results of pulsed (time-domain) and photomixing (CW, frequency domain) experiments are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.