Stability of HEB receivers at THz frequencies

Stability of a hot-electron bolometer (HEB) heterodyne receiver was investigated at frequencies from 0.6THz to 1.9THz. The Allan variance was measured as a function of the integration time and the Allan time was obtained for HEB mixers of different size, as well as with different types of the local oscillator: FIR laser, multiplier chain, and BWO. We have found that due to stronger dependence of the mixer gain and noise vs mixer bias voltage and current the Allan time is shorter for smaller mixers. At 1.6THz the Allan time is 3 sec for 4x0.4μm^2 bolometer, and 0.15-0.2 sec for 1x0.15μm^2 bolometer. Obtained stability apears to be the same for the FIR laser and the mulitplier chain. The Allan time for smaller bolometers increases to 0.4-0.5sec at 0.6-0.7THz LO frequencies. The influence of the IF chain on the obtained results is also analyzed

Design and Characterization of 1.8-3.2 THz Schottky-based Harmonic Mixers

A room-temperature Schottky diode-based WM-86 (WR-0.34) harmonic mixer was developed to build high-resolution spectrometers, and multi-pixel receivers in the THz region for applications such as radio astronomy, plasma diagnostics, and remote sensing. The mixer consists of a quartz-based Local Oscillator (LO), Intermediate-Frequency (IF) circuits, and a GaAs-based beam-lead THz circuit with an integrated diode. Measurements of the harmonic mixer were performed using a 2 THz solid-state source and 2.6906 THz QCL. A conversion loss of 27 dB for the 3rd harmonic mixing and a conversion loss of 30 dB for the 4th harmonic mixing was achieved. This is the first development of a wideband WM-86 (WR-0.34) harmonic mixer with planar Schottky diode integrated on a beam-lead THz circuit that uses a lower LO harmonic factor for 1.8-3.2 THz RF frequency. Furthermore, this result represents the best Schottky-based mixer in this frequency range

Phase Locking Of A 2.5 THz Quantum Cascade Laser To A Microwave Reference Using THz Schottky Mixer

The frequency of a 2.5 THz QCL are stabilized to sub-hertz accuracy by phase-locking to a stable 100 MHz microwave reference, using a 2.3–3.2 THz room temperature Schottky diode based harmonic mixer. The down-converted phase locked beat note is stable over a long term test

Stability of HEB receivers at THz frequencies

Stability of a hot-electron bolometer (HEB) heterodyne receiver was investigated at frequencies from 0.6THz to 1.9THz. The Allan variance was measured as a function of the integration time and the Allan time was obtained for HEB mixers of different size, as well as with different types of the local oscillator: FIR laser, multiplier chain, and BWO. We have found that due to stronger dependence of the mixer gain and noise vs mixer bias voltage and current the Allan time is shorter for smaller mixers. At 1.6THz the Allan time is 3 sec for 4x0.4μm^2 bolometer, and 0.15-0.2 sec for 1x0.15μm^2 bolometer. Obtained stability apears to be the same for the FIR laser and the mulitplier chain. The Allan time for smaller bolometers increases to 0.4-0.5sec at 0.6-0.7THz LO frequencies. The influence of the IF chain on the obtained results is also analyzed

Gain bandwidth of NbN hot-electron bolometer terahertz mixers on 1.5 mum Si3N4/SiO2 membranes

International audienceThe gain bandwidth of NbN hot-electron bolometer terahertz mixers on electrically thin Si3N4/SiO2 membranes was experimentally investigated and compared with that of HEB mixers on bulk substrates. A gain bandwidth of 3.5 GHz is achieved on bulk silicon, whereas the gain bandwidth is reduced down to 0.6-0.9 GHz for mixers on 1.5 mum Si3N4/SiO2 membranes. We show that application of a MgO buffer layer on the membrane extends the gain bandwidth to 3 GHz. The experimental data were analyzed using the film-substrate acoustic mismatch approach

Millimetre-wave phase shifter based on dielectric rod waveguide

In this work we propose a novel millimetre-wave phase shifter targeted on thin ferroelectric film technology. Architecture of the phase shifter is proposed to use a dielectric rod waveguide with a periodic printed array of electrically small dipoles loaded with a ferroelectric varactor (pin diode, Schottky diode, etc.) with the function of control the phase of the propagating wave. The proposed architecture of the phase shifter is verified by measuring two prototypes, where the tuneable elements (ferroelectric varactor) are replaced by non-tuneable capacitors with 10 fF and 15 fF respectively. The measurements revealed a considerable phase shift and small insertion losses. It is demonstrated that the proposed periodic structure using the dielectric rod waveguide allows to fully realize a potential of known tuneable elements at millimetre-wavelengths

1.8THz receiver development for the TELIS instrument

A new state-of-the-art balloon borne three channel (500GHz, 625GHz, 1.8 THz) cryogenic heterodyne spectrometer will allow enhanced limb sounding of the Earth's atmosphere within the submillimeter and far-infrared spectral range. The instrument, called TELIS (TErahertz and submm LImb Sounder), is being developed by a consortium of major European institutes that includes the Space Research Organisation of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) in the United Kingdom and the Deutschen Zentrum für Luft- und Raumfahrt (DLR) in Germany (lead institute). TELIS will utilise state-of-the-art superconducting heterodyne technology and is designed to be compact and lightweight, while providing broad spectral coverage, high spectral resolution and long flight duration. Target species are key atmospheric short-lived radicals such as OH, HO2, ClO, BrO together with stable constituents such as O3, HCl and HOCl. TELIS will consist of a common front end with a cassegrain based pointing telescope, common transfer optics and a digital autocorrelator spectrometer for each channel. One of the three receiver channels (developed by DLR) will focus on the measurement of the OH-triplett at 1.8 THz. Low noise NbN based Hot Electron Bolometers will be acting as heterodyne mixing elements. A Martin Puplett Interferometer designed for cryogenic operation in the cryostat is used to interfer signal- and LO radiation generated by a solid state based local oscillator unit. Recently athe laboratory DSB version of the TELIS heterodyne receiver (using a far infrad laser as preliminary LO source) has been set up and tested successfully. In this paper the current status of the THz-channel design and development in the framework of the TELIS project will be presented

2.5 THz multipixel heterodyne receiver based on NbN HEB mixers

A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5µm thick Si3N4/SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4/SiO2 membranes was found to be 0.7÷0.9 GHz, which is much smaller than for similar devices on silicon. Application of buffer layers and use of alternative types of membrandes (e.g. silicon-on-insulator) is under investigation

High-resolution absorption spectroscopy with a phase-locked quantum-cascade laser

We report on high-resolution spectroscopy using a quantum-cascade laser (QCL) with an emission of 3.3 THz, which is locked to a mm-wave reference signal using a harmonic Schottky diode mixer