Alexandre Beck

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.

Analysis of a narrowband terahertz signal generated by a unitravelling carrier photodiode coupled with a dual-mode semiconductor Fabry-Pérot laser

A narrowband terahertz signal generated by a unitravelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry–Perot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. A terahertz signal at a frequency of 372 GHz, featuring a linewidth of 17 MHz is recorded by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this experiment operate at room temperature. The linewidth and the frequency of the emitted terahertz wave are analyzed, along with their dependency on dc-bias conditions applied to laser diode.

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.

All-fiber continuous wave coherent homodyne terahertz spectrometer operating at 1.55 µm wavelengths

Room temperature homodyne and heterodyne THz detections are reported using an 1.55 µm-based THz source. The first experimental demonstration is a continuous wave terahertz homodyne detection, where THz emission is performed with an InGaAs/InP uni-travelling carrier photodiode monolithically integrated with a horn antenna. The coherent homodyne detection is achieved with an ion-irradiated InGaAs photoconductor integrated with a spiral antenna. Experimental results has been obtained up to 700 GHz with a good signal to noise ratio. The second experimental setup is a room temperature heterodyne detection with a schottky mixer.

High spectral purity microwave and terahertz oscillator

We report on the design of an ultra stable microwave/THz oscillator and on the realization and the characterization of its laser source. The tunable oscillator is expected to show below -150 dB rad2/Hz phase instability at an offset frequency of 10 kHz for a 30 GHz carrier frequency, as well as 18 GHz, 100 GHz, 400 GHz and 1 THz carrier frequencies.

Generation of mW Level in the 300-GHz Band Using Resonant-Cavity-Enhanced Unitraveling Carrier Photodiodes

We present a resonant-cavity-enhanced broadband unitraveling carrier photodiode optimized for terahertz (THz) generation. It uses a novel semitransparent top-contact utilizing subwavelength apertures for enhanced optical transmission. The contact allows front-side illumination of the photodiode using 1.55-μm-wavelength light, while still retaining a small contact resistance suitable for photomixing at THz frequencies. The responsivity of the device is improved by introducing a metallic mirror below the diode mesa through wafer bonding, producing an optical resonant cavity. A record continuous-wave output power of 750xa0μW is measured for a single photodiode at 300 GHz. Record values of efficiency are also demonstrated.

Narrow linewidth terahertz signal generation using a dual-mode semiconductor Fabry-Pérot laser and a uni-travelling carrier photodiode

A narrowband terahertz signal generated by a uni-travelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry-Pérot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. All components involved in this experiment operate at room temperature. The terahertz signal at a frequency of 372 GHz is recorded, and the linewidth is 17 MHz. The linewidth and the tunability of the emitted terahertz wave are analyzed, as a function of the laser bias.

Radiation pattern measurements of an integrated TEM horn antenna

A TEM horn antenna is integrated with a uni-travelling-carrier photodiode. Its radiation pattern is measured from 280 to 540 GHz thanks to a 1.55 µm photomixing set-up and a sub-harmonic mixer. The direction the main lobe shifts to a lower incidence when the frequency is increased.

Investigation on fabrication of GaAsSb/InP UTC-PD based photomixer operating at 1.55 µm wavelengths

We report our investigation on realization of 1.55 µm wavelengths sensitive photomixer based on GaAsSb/InP uni-travelling-carrier photodiode. The epitaxial structure and technological steps are described.

Silicon substrate low-temperature-grown GaAs terahertz photomixers

We have developed an epitaxial layer transfer technique for THz devices. Here we report the fabrication and the characterization of a THz photomixer on a silicon substrate. The active part of the photomixer is a low-temperature-grown GaAs mesa which has been transferred and layer bonded onto a Si substrate. The preliminary measurement of the THz signal generated in a photomixing configuration at 0.78 µm shows that the overall performance is comparable to standard GaAs substrate photomixers at frequencies up to 2 THz.