Fabio Pavanello

Ultrawide-Bandwidth Single-Channel 0.4-THz Wireless Link Combining Broadband Quasi-Optic Photomixer and Coherent Detection

Free space communications with huge data capacity have become a key point for the development of mobile access, services, and network technologies convergence. Wireless links using emerging terahertz technologies, also referred to as T-ray communications, have become an intensive research field within last years since T-rays at the millimeter/submillimeter frontier remain more robust in terms of scintillation, dielectric obstacles, and fog compared with near-infrared signals. Using a passive THz hot-spot which can be fed by fiber optic networks, we investigate up bit rates up to 46 Gbps for a THz wireless transmission system at 400-GHz carrier frequency. Using a THz photomixer integrated with a specific broadband antenna and heterodyne electronic detection, we investigate the eye diagrams using 1-μW received power, highlighting the high sensitivity and ultra-wideband behavior of the whole THz system.

CW Source Based on Photomixing With Output Power Reaching 1.8 mW at 250 GHz

It is shown that a continuous wave output power reaching 1.8 mW at 252 GHz is generated by photomixing in a low-temperature-grown GaAs photoconductor using a metallic mirror-based Fabry-Pérot cavity. To the best of our knowledge, it is the highest power ever reported for a single photomixer in the J-band.

Broadband ultra-low-loss mesh filters on flexible cyclic olefin copolymer films for terahertz applications

The cyclic olefin copolymer (COC) has recently demonstrated promising properties for THz applications due to its extremely high transparency in the THz region. Here, we prove that COC can be efficiently used as substrate material for free-space THz devices through the design, fabrication, and characterization of high-pass metal mesh filters. Measurements are in good agreement with calculations, and a transmittance higher than 75% has been measured between 1.5 THz and 2.5 THz for a single-layer filter. In addition, we prove that stacked meshes can be easily embedded to improve their rejection ratio in the stop-band, while preserving a high transparency in the pass-band. The broadband behavior of these filters should extend up to their diffraction limit estimated at around 6.3 THz for the single-layer filter.

Narrow Linewidth Tunable Terahertz Radiation By Photomixing Without Servo-Locking

A beatnote, tunable from dc to 1 THz, provided by a dual-frequency laser is used to feed an unitravelling carrier photodiode in order to produce a highly coherent THz signal radiated by a transverse-electromagnetic-horn antenna. The THz signal is detected and analyzed by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this experiment operate at room temperature without phase locking the beatnote. So far, the dynamic range evolves from 58 dB at 282 GHz to 15 dB at 1.026 THz, and the measured linewidth is better than 30 kHz. Linewidth narrowing using a Brillouin fiber laser pumped by the dual-frequency laser leads to a beatnote of 500-Hz linewidth at 1 THz.

Highly efficient terahertz detection by optical mixing in a GaAs photoconductor

It is shown from accurate on-wafer measurement that a low-temperature-grown GaAs photoconductor using a metallic mirror Fabry-Perot cavity can serve as highly efficient optoelectronic heterodyne mixer in the terahertz frequency range. Conversion losses of 22 dB at 100 GHz and ∼27 dB at 300 GHz were measured, which is an improvement by a factor of about 40 dB as compared with the previous values obtained with photoconductors. Experimental results are interpreted satisfactorily by means of a simple electrical model of the optoelectronic mixing process.

High-Gain Yagi–Uda Antenna on Cyclic Olefin Copolymer Substrate for 300-GHz Applications

The cyclic olefin copolymer is a dielectric material with very attractive mechanical and electrical properties for millimeter- and submillimeter-based devices as recently demonstrated in a few applications. Here, we present the possibility of employing this material as a substrate for traveling-wave antennas through the design, fabrication, and characterization of a Yagi-Uda antenna working around 300 GHz. The developed fabrication process can be scaled to higher frequencies to take advantage of the extremely low absorption of such a dielectric at terahertz (THz) frequencies. The measurements agree well with the calculations, and a high gain of 15.4 dB has been achieved at 300 GHz. The measured bandwidth for a reflection coefficient of -10 dB is 10 GHz, and the radiation pattern presents a symmetrical main lobe with an angular width below 25 °.

Narrow linewidth tunable THz signal radiated by 1.55μm photomixing

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.