G. Ducournau

Highly coherent terahertz wave generation with a dual-frequency Brillouin fiber laser and a 1.55 μm photomixer

Thanks to a portable dual-frequency Brillouin fiber laser and a 1.55 μm photomixer, we report the generation of a highly coherent kilohertz level submillimeter wave emission. Low-cost telecommunications components are used to achieve very simple source architecture. The photomixer is composed of a unitravelling carrier photodiode integrated with an antenna. An emission at 316 GHz is observed and analyzed thanks to heterodyne detection with a signal-to-noise ratio >65 dB and a ~1 kHz linewidth. The phase noise of the proposed source has the same performance at 1.7 and 316 GHz. We show that this source has comparable or better phase noise compared to electrical oscillators and the tunability is much wider.

Optimized V-shape design of GaN nanodiodes for the generation of Gunn oscillations

In this work, recent advances in the design of GaN planar Gunn diodes with asymmetric shape, so-called self-switching diodes, are presented. A particular geometry for the nanodiode is proposed, referred as V-shape, where the width of the channel is intentionally increased as approaching the anode. This design, which reduces the effect of the surface-charges at the anode side, is the most favourable one for the onset of Gunn oscillations, which emerge at lower current levels and with lower threshold voltages as compared to the standard square geometry, thus enhancing the power efficiency of the self-switching diode as sub-millimeter wave emitters.

On the effect of δ-doping in self-switching diodes

Lowering the carrier concentration is presented as a way to considerably improve the performance of self-switching diode (SSD) detectors. A physics-based theoretical model was used to derive an expression for the responsivity of SSDs as a function of carrier concentration, mobility, and design parameters. Monte Carlo simulations confirmed the modeled effect of varying carrier concentration and channel width. SSDs were fabricated in InAs heterostructures with different δ-doping levels. Radio frequency (RF) characterization at 50u2009GHz reproduced the modeled trends. By reducing the carrier concentration in InAs SSDs with 40u2009nm wide channels from 2.7u2009×u20091012u2009cm−2 to 1.5u2009×u20091012u2009cm−2 (−44%), the noise equivalent power (NEP) improved from 130u2009pW/Hz½ to 87u2009pW/Hz½ (−33%).

Heterogeneously integrated III–V/silicon dual-mode distributed feedback laser array for terahertz generation

We demonstrate an integrated distributed feedback (DFB) laser array as a dual-wavelength source for narrowband terahertz (THz) generation. The laser array is composed of four heterogeneously integrated III-V-on-silicon DFB lasers with different lengths enabling dual-mode lasing tolerant to process variations, bias fluctuations, and ambient temperature variations. By optical heterodyning the two modes emitted by the dual-wavelength DFB laser in the laser array using a THz photomixer composed of an uni-traveling carrier photodiode (UTC-PD), a narrow and stable carrier signal with a frequency of 0.357xa0THz is generated. The central operating frequency and the emitted terahertz wave linewidth are analyzed, along with their dependency on the bias current applied to the laser diode and ambient temperature.

Room Temperature Direct and Heterodyne Detection of 0.28–0.69-THz Waves Based on GaN 2-DEG Unipolar Nanochannels

An experimental demonstration of GaN-based asymmetric nanodiodes as direct and heterodyne detectors up to 0.69 THz has been performed at room temperature. Responsivities of 2 and 0.3 V/W in a free-space configuration were obtained at 0.30 and 0.69 THz, respectively. An intermediate frequency (IF) signal has been measured up to 40 and 13 GHz in the same frequency ranges. The characterization of the nanodiodes as mixers did not show any deviation from linearity between the RF input power and the IF output. Monte Carlo simulations, used to estimate nanodevice intrinsic conversion losses of 27 dB at 0.69 THz, have confirmed these results.

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 22u2009dB at 100u2009GHz and ∼27u2009dB at 300u2009GHz were measured, which is an improvement by a factor of about 40u2009dB 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.

Monte Carlo analysis of thermal effects in self-switching diodes

An attempt of exploitation of very high frequency Gunn oscillations to generate a TeraHertz radiation is realized with an asymetric planar GaN self-switching diode. In this work we compare the measured static behavior of real devices with calculations performed by means of Monte Carlo simulations. We analyze the influence of the temperature on the I-V characteristic of the SSD and also on the high frequency oscillations.

Radiative Quality Factor in Thin Resonant Metamaterial Absorbers

Perfect electromagnetic absorption in an array of thin resonators is analyzed by means of the quality factor involving separately the contribution of losses and a coupling with free space. An equivalent electrical circuit based on an open-resonator model is introduced for an absorber made of dielectric cubes arranged in a square lattice deposited onto a metallic ground plane. From full-wave simulations, two regimes depending on the lattice period are pointed out. A quadratic dependence of the radiative quality factor is shown for largest periods, whereas the radiative <inline-formula> <tex-math notation=LaTeX>

Voltage controlled sub-THz detection with gated planar asymmetric nanochannels

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Woven metamaterials with an electromagnetic phase-advance for selective shielding

</tex-math></inline-formula>-factor is governed by a coupling between resonators at small periods. It results that an optimal period for obtaining a unitary absorption can be deduced from a single simulation and that a maximal absorption bandwidth emerges from a tradeoff between these two regimes. Finally, the radiative <inline-formula> <tex-math notation=LaTeX>