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Several metasurface-based terahertz (THz) devices, including lens, computer generated holograms, spin selected focusing lens, as well as wavelength selected diffractive elements, have been designed and fabricated. The thickness of these device is only 1/4000 of the working wavelength. A THz focal plane imaging system is employed to characterize the function of the devices. Theoretical expectations...
In a first part, we are reporting on high-7c superconducting (YBCO) hot electron bolometers for high sensitivity and ultra-wide bandwidth terahertz heterodyne mixing and passive imaging. Here applications are sought in space programs as well as in civil security. In a second part, we are reporting on pyroelectric detectors using amorphous semiconducting (i.e., oxygen depleted) YBCO films; various...
In this paper, multiple techniques for generating and radiating picosecond pulses from a single silicon chip are reported. These techniques do not require a laser. They are based on direct conversion of a digital trigger to a THz impulse. The first technique is based on storing magnetic energy on an on-chip slot-bow-tie antenna and then releasing it with an external trigger through a fast switching...
In the THz spectral region quantum detectors are intrinsically limited by the small energy of the electronic transition involved in photon absorption. To overcome this problem and improve detector performances, we propose novel approaches in which concepts borrowed from high frequency electronics and metamaterials are exploited to realize THz detectors. In particular, we have investigated sub-wavelength...
We explore the nonlinear optical properties of plasmonic semiconductor antennas resonant in the mid infrared. The nanostructures are fabricated on silicon substrates from heavily doped germanium films with a plasma frequency of 30 THz, equivalent to a wavelength of 10 μm. Illumination with ultrashort pulses at 10.8 μm produces coherent emission at 3.6 μm via third-harmonic generation.
This paper describes metal-oxide-semiconductor field effect transistors working as detectors of THz radiation integrated monolithically with a source follower (the common-drain amplifier). This solution makes lock-in measurements independent of the length of the connecting cable.
Maximising the power extracted from UTC photodiodes is central to the successful realisation of photonic terahertz emitters. For antenna integrated UTCs this requires the optimisation of the impedance match between UTCs and antennas. We present a comprehensive investigation of the UTC output impedance up to 400 GHz, by means of a semi-analytical approach and using 3D full-wave modelling. We introduce...
We present non-contact characterization of GaAs Schottky contacts in the 140–220 GHz band. The non-contact probing technique utilizes planar on-chip antennas that are monolithically integrated with the coplanar waveguide environment housing the Schottky diode under test. The diode contact is fabricated through a 6 mask lithographic process with a 5 μm deep-trench under the contact to minimize parasitics...
We discuss the numerical simulation of high current density InGaAs/AlAs/InP resonant tunneling diodes with a view to their optimisation as THz emitters. We introduce a figure of merit based upon the ratio of maximum extractable THz power and the electrical power developed in the chip. The aim being to develop high efficiency emitters as output power is presently limited by catastrophic failure. A...
In this paper three different field-effect transistor (FET) configurations are analyzed so as to improve responsivity and noise performance when used as terahertz detectors. FET configurations such as extended source and trapezoidal gate are realized: measurements on a fabricated prototype demonstrate relevant increase of the photoresponse, in the order of 40%, and an improvement of approximately...
Compact and coherent source is a key component for various applications of the THz waves. We report on our recent results of THz oscillators using resonant tunneling diodes (RTDs). To achieve high-frequency oscillation, the electron delay time in RTD and conduction loss around the antenna integrated with RTD were reduced. By these methods, a fundamental oscillation up to 1.92 THz was obtained at room...
VOx microbolometer, which is coupled with thin-film spiral antenna, was fabricated on a Si3N4/SiO2 membrane by metal-organic decomposition (MOD). The DC sensitivity of the device was 3120 W−1 and this value is about two orders of magnitude higher than that of the Bi bolometer fabricated on a dielectric substrate. The responsivity of the device was 370 V/W at 190 GHz for Ib = 50 μA.
The aim of this research is to investigate the behaviour of neural systems in an electromagnetic environment in millimetre-wave (MMW) region of the spectrum. A small-size phantom mimicking the nerve fibre has been manufactured for modelling the effects of MMW on pulse transmission in this neural system.
This paper presents the analysis of Fe doped InGaAs grown by molecular beam epitaxy (MBE) utilized in photoconductive antennas (PCAs) for the optical generation and detection of pulsed THz radiation at 1.55 μm wavelength. InGaAs: Fe shows very favorable characteristics for the application as THz antennas due to its large resistivity of ∼2000 Ω·cm and mobility of almost 1000 cm2/V·s, while still exhibiting...
We investigate various metals for their robustness against damage caused by strong THz field. Even though the damage process is not of a thermal nature we observe a correlation between robustness and the melting temperature. Influence of the substrate material on the damage pattern is also studied.
We present a THz quasi time-domain spectroscopy (QTDS) system based on fiber coupled antennas operating at 1550 nm excitation wavelength. Frequency components up to 950 GHz can be generated with this setup. The signal to noise ratio of a single shot measurement is around 60 dB between 40 GHz and 240 GHz.
Continuous-wave (CW) terahertz (THz) photomixers are fabricated using 1-D nanocontacts on low-temperature-grown (LTG) GaAs and InGaAs, for operation wavelengths of 850 nm and 1550 nm, respectively. Silver (Ag) nanowire (NW) used as the nanocontact is aligned between the antennas patterned onto these photoconductive material by dielectrophoresis (DEP) technique. Reliable photocurrent measurements for...
The emission mechanism of continuous wave (CW) terahertz (THz) photomixers that make use of nanostructured gratings (NSGs) is studied. Two different photomixer designs, based on a single-sided NSG and a double-sided NSG, embedded in the same antenna design and fabricated on an Fe doped InGaAsP substrate, are characterized with ∼1550 nm excitation. They are shown to exhibit similar performance in terms...
A test structure comprehending an antenna-coupled FET-based THz detector integrated with readout electronics is designed and fabricated in a 0.15-μm standard CMOS technology. A low-noise preamplification technique has been employed, based on parametric chopper amplifier, substituting the lock-in apparatus and performing direct analog-to-digital conversion by means of an incremental ΣΔ converter. The...
This paper presents a high responsivity THz detector formed of two depletion mode pseudomorphic high electron mobility transistors (D-pHEMT) coupled to an on-chip bowtie antenna in GaAs 130 nm technology. The measured absolute responsivity of the integrated detector is 10 V/W at 250 GHz at a gate bias voltage of −0.3 V. A silicon lens attached to the GaAs substrate improves the responsivity of the...
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