Photonic Terahertz sources and receivers (WP1):
We tailored the photonic sources and receivers to the requirements of the project. In terms of sources, a continuous-wave (CW) photoconductor mixes a pair of lasers with a difference frequency of, say, 1 THz to a THz current by absorbing the beat note. An attached antenna converts the current into THz light. The detection process works inversely, i.e. a THz signal is mixed with a beat note of two lasers, resulting in a down-conversion to DC. The following work has been performed:
• The absorption within the source n-i-pn-i-p superlattice photomixer was increased by a factor of 2.7 by integrating them with an on-chip passive optical waveguide.
• We have employed in-house developed ErAs:In(Al)GaAs photoconductors in both continuous-wave and pulsed (time domain spectroscopy) systems.
• For the pulsed PVNA, we have also realized a transceiver, where source and detector are realized on the same chip.
• For CW receivers, we have developed Vivaldi endfire-coupled photoconductors that receive the signal right from a dielectric waveguide.
• For a free space version, we have developed fiber-pigtailed packages with an integrated silicon lens.
Photonic spectrum analyzer (WP2+WP6):
We have developed a concept based on a photoconductor where a laser beat note acts as local oscillator:
• We have demonstrated a free space system that covers <50 GHz to 1.15 THz with potential extension to several THz.
• A noise floor of -90 dBm/Hz has been achieved at 1 THz.
• We have developed systems with two different resolutions: a system with ~2 MHz resolution based on a standard THz photomixing system and a Hz-level resolution based on an electro-optic continuous-wave comb.
• Several demonstration examples have been carried out, e.g. analyzing the stability of several lines of a mode-locked THz pulse on the few Hz level, characterization of the emitted spectrum of several sources (backward wave oscillator, photomixer, WR-coupled electronic VNA head)
• On-chip transition via a WR hollow metal waveguide enables characterization of integrated circuits.
Pulsed Photonic Vector Network Analyzer (WP3):
• Demonstration of pulsed 1.5 port and two port photonic VNAs.
• The dynamic range of 35-47 dB at 10 Hz equivalent noise bandwidth in the 1.1-1.5 THz band exceeds that of state of the art two port electronic VNAs.
• Calibration techniques developed.
• Data analysis techniques developed for synchronous evaluation of transmission and reflection in order to improve the data quality of extracted material and device parameters.
• Several application examples demonstrated and published: a THz isolator, low loss and lossy dielectric plates, a Bragg mirror.
On-Chip PVNA and planar dielectric waveguide circuitry (WP4+WP5):
• On-chip dielectric waveguides with a frequency coverage from 0.45-1.5 THz developed
• Various components developed: splitters/combiners, bends, and coupling structures
• Transition to hollow metal WR waveguides demonstrated in order to enable on-chip measurements
On-Chip PVNA calibration and applications (WP7):
• Calibration techniques developed
• Data analysis and noise rejection techniques developed.
• Several waveguide-integrated devices were characterized: Whispering gallery mode resonator, on-chip Fabry-Pérot resonator, THz fiber Bragg grating
