As continuous wave (cw) THz spectroscopy advances rapidly, its high potential for sensing and non-destructive testing is becoming increasingly apparent. This is demonstrated in two recent developments: First, I will present our novel terahertz receivers for frequency-domain spectroscopy based on rhodium-doped InGaAs grown by molecular beam epitaxy. These new devices provide a peak dynamic range of 130 dB, an 18 dB improvement over the state of the art. Secondly, I will present a compact terahertz spectroscopy system with a measurement rate of 1 kHz, made possible by a single photonic integrated circuit that acts as the optical driver engine.
These new results demonstrate the excellent performance and flexibility of frequency-domain spectroscopy, paving the way for compact and task-specific terahertz systems for science and industry.
Sources for high frequencies in the THz range are of interest in both precision measurements in spectroscopy as well as high carrier frequencies and bandwidth in next-generation communication. Optically generated THz frequencies allow for broad tunability based on telecom technologies. Optical frequency division via an optical frequency comb has the potential to generate ultralow phase-noise THz sources. We present a system that is capable of generating tunable THz frequencies of up to 10 THz at 0.5 THz/s scan rates, phase-locked to a common comb spectrum providing absolute frequency calibration. We show results of combining the photonic source with an electronic receiving system in the waveguide band WR 2.2 (330-500 GHz).
In THz homodyne systems, optical delay lines are the key to time-resolved measurements but they come with a high cost and complexity. They also limit the application of the system in industrial environment, due to their sensitivity to vibrations. Another important point is the scanning speed, for which the mechanical delay line sets severe limitations. Frequency scanning-based systems need a change in THz frequency to recover phase information. Furthermore, there is a tradeoff between phase sensitivity and necessary tuning range. This tradeoff is based on the difference in the length of transmitter and receiver arm in the setup. With our approach, we can introduce a controllable phase shift at 280 GHz by frequency tuning of both lasers. For that purpose, chirped mirrors were designed and introduced into a standard continuous wave Terahertz homodyne system, in order to induce a variable phase shift. In our chirped mirror-based configuration, the phase shift between both optical modes depends on the center frequency of the lasers. Thus, moving the delay stage can be replaced by variation of the center frequency in order to record a THz trace. This means that the measurements are no longer limited by the speed of the delay line. This phase shift is independent of the path length difference in the setup and does not need phase modulators. Simulations show, that these mirrors may achieve a phase shift up to π inside the C-Band for a difference frequency of 280 GHz. To confirm the calculated behavior of the chirped mirrors, initial characterization measurements were performed. We modified an existing delay stage-based THz system to include the chirped mirrors in front of the receiver. This enables the direct comparison while keeping all other parameters constant.
We report on novel continuous wave (cw) photoconductive terahertz (THz) receivers based on rhodium (Rh) doped indium gallium arsenide grown by molecular beam epitaxy. The Rh-doped material exhibits outstanding charge carrier mobility up to 1800 cm2/Vs while maintaining ultrashort carrier lifetimes between 0.26 and 1.5 ps. The photoconductive antennas (PCAs) made from this material exhibit a THz responsivity significantly improved by a factor of 20 to 100, which overcompensates their slightly higher noise levels. In a homodyne coherent THz spectroscopy setup, these novel receivers enable us to measure THz spectra with a record peak dynamic range up to 125 dB and a spectral bandwidth of 4.5 THz. This is an improvement of 13 dB over the previous record with InGaAs:Fe-based PCAs and leads to improved accuracy and measurement speed in cw-THz spectroscopy.
Photonic integrated circuits (PICs) are one of the key enablers for beyond 5G networks. A novel generation of fully integrated photonic-enabled transceivers operating seamlessly in W- D- and THz-bands is developed within the EU funded project TERAWAY. Photonic integration technology enables key photonic functionalities on a single PIC including photonic up/down conversion. For efficient down-conversion at the photonic integrated receiver, we develop the first waveguide-fed photoconductive antenna for THz communications. Finally, we report on the experimental implementation of a fully photonic-enabled link operating across W- D- and THz-bands.
We demonstrate a fully photonic sub-THz communication link using a PIN photodiode (PD) emitter and an optimized photoconductive antenna (PCA) as a heterodyne receiver. The novel receiver comprises an iron-doped indium gallium (InGaAs) PCA on a silicon lens and passive radio frequency (RF) circuitry, all packaged into a fiber-coupled module. A 3-dB-bandwidth of 11 GHz for the intermediate frequency was measured. We analyzed the capabilities of the receiver in a wireless communication link over a distance of 1 m with a PIN photodiode as the emitter. At a carrier frequency of 120 GHz, we demonstrate error free transmission for net data rates up to 10 Gbit/s with quaternary quadrature amplitude modulation (4-QAM) modulation.
We describe the assembly of a 5G transceiver leveraging photonics for the generation, emission and detection of THz wireless signals. The transceiver and all associated control electronics and power supplies are designed for mounting in a mobile aerial unit. A photonics motherboard concept that brings together polymer, III-V and SiNbased photonic platforms and provides optical fiber connectivity is used for the assembly. In addition, scalable integration of 3D components, in this case an antenna rod or rod array, is demonstrated. Thermal considerations arising from the dense integration of photonic and electronic components and the resulting concentrated heat load are also discussed.
We present novel photoconductive antennas (PCAs) compatible with 1550 nm excitation for terahertz (THz) time-domain spectroscopy (TDS). Rhodium (Rh) doped InGaAs grown by molecular beam epitaxy is used as the underlying photoconductor. Due to the advantageous combination of sub-picosecond carrier lifetime and excellent electronic properties, InGaAs:Rh based emitters feature an unprecedented emitted THz power of 637 µW. A record peak dynamic range of 110 dB is demonstrated with a THz TDS system using InGaAs:Rh based PCAs only. This sets a new benchmark for THz TDS systems operating at 1550 nm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.