Terahertz Wireless Communication Systems Research Articles

Live Streaming of Uncompressed HD and 4K Videos Using Terahertz Wireless Links

Taming the Terahertz waves (100 GHz–10 THz) is considered the next frontier in wireless communications. While components for the ultra-high bandwidth Terahertz wireless communications were in rapid development over the past several years, however, their commercial availability is still lacking. Nevertheless, as we demonstrate in this paper, due to recent advances in the microwave and infrared photonics hardware, it is now possible to assemble a high-performance hybrid THz communication system for real-life applications. As an example, in this paper, we present the design and performance evaluation of the photonics-based Terahertz wireless communication system for the transmission of uncompressed 4K video feed that is built using all commercially available system components. In particular, two independent tunable lasers operating in the infrared C-band are used as a source for generating the Terahertz carrier wave using frequency difference generation in a photomixer. One of the IR laser beams carries the data which is intensity modulated using the LiNbO3 electro-optic modulator. A zero bias Schottky diode is used as the detector and demodulator of the data stream followed by the high-gain and low-noise pre-amplifier. The Terahertz carrier frequency is fixed at 138 GHz and the system is characterized by measuring the bit error rate for the pseudo random bit sequences at 5.5 Gbps. By optimizing the link geometry and decision parameters, an error-free ( $\text {BER} ) transmission at a link distance of 1 m is achieved. Finally, we detail the integration of a professional 4K camera into the THz communication link and demonstrate live streaming of the uncompressed HD and 4K video followed by the analysis of link quality.

100 Gbit/s THz Photonic Wireless Transmission in the 350-GHz Band With Extended Reach

In this letter, we experimentally demonstrate terahertz (THz) photonic wireless transmission of high-speed quadrature-phase-shift-keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) signals in the 350-GHz band, with an effort to extend the wireless reach of ultrafast 100 Gbit/s. In the experiment, a narrowband unitraveling-carrier photodiode (UTC-PD) is used for heterodyne generation of THz communication signals, which is transparent to optical modulation formats. Experimental results show that 30 GBd/s QPSK (60 Gbit/s) and 25 GBd/s 16-QAM signals (100 Gbit/s) are successfully transmitted over a 350-GHz wireless link with an extended distance of 2 m. This enhancement is enabled by combining the techniques of employing cutting-edge narrowband UTC-PD as the photomixing THz emitter, spectrally efficient modulation format and advanced digital signal processing algorithms. The achievement makes 100 Gbit/s THz wireless communication systems promising for future smart wireless services.

Design and tests of 21 km, 5 Gbps, 0.14 THz wireless communication system

A terahertz wireless communication system is designed. The 16QAM modulation scheme is used in baseband processing, and mixers are used for cascading frequency up and down-converting. Cascading power amplification technique is adopted with a solid-state power amplifier and a vacuum electronic device. Several watts power is emitted at 0.14 THz. An all solid-state receiver running in room temperature is used, whose equivalent noise temperature is 1100 K and receiving sensitivity is -57 dBm. A 21 km wireless communication testing is carried out between the Shuangliu district and the Xinjin county of Chengdu, by means of two Cassegrain antennas with 50 dBi gain each. A 5 Gbps single-channel transmission speed is measured with bit error rate below 10-6. For testing, two standard HD-SDI uncompressed video streams are successfully transmitted in real time simultaneously, with an effective speed of 1.485 Gbps for each one.

THz Wireless Transmission Systems Based on Photonic Generation of Highly Pure Beat-Notes

In this paper, a terahertz (THz) wireless communication system at 400 GHz with various modulation formats [on–off keying (OOK), quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM), and 32-quadrature amplitude modulation (32-QAM)] is experimentally demonstrated based on photonic generation of highly pure THz carriers. The experimental THz wireless photonic transmission system is enabled by the ultrawideband behavior of an antenna-integrated unitraveling-carrier-photodiode-based transmitter and a Schottky mixer-based THz receiver. In the experiment, a phase-correlated optical frequency comb (OFC) is created for photomixing generation of the desired THz carrier frequencies with low phase noise. The OFC allows for the generation of flexibly tunable THz carrier frequencies. The performance of the generated THz carriers is experimentally characterized in terms of phase noise, spectrum purity, tunability, and long-term stability. In the case of generating 400 GHz carrier, the measured timing jitter, linewidth, and long-term stability in the experiment are 51.5 fs, less than 2 Hz, and less than ±1 Hz with 3 hours, respectively. We also theoretically analyze the phase noise of photonically generated THz beat-notes when phase correlation of two optical comb tones is damaged due to their path-length difference. In addition, we demonstrate THz wireless transmission of various modulation formats, including OOK, QPSK, 16-QAM, and 32-QAM at beyond 10 Gb/s in such a system, and the measured bit error rate (BER) performance for all the signals after 0.5 m free-space delivery is below the hard decision forward error correction threshold of 3.8 × 10–3. Furthermore, the influence of THz carrier purity on the system performance is experimentally analyzed with respect to the BER of the THz communication signals.

Far-field characteristics of the square grooved-dielectric lens antenna for the terahertz band.

In order to improve the gain and directionality of a terahertz antenna, a square grooved-dielectric lens antenna based on a Fresnel zone plate is proposed. First, a diagonal horn, which is adopted as the primary feed antenna, is designed. Then, the far-field characteristics of the lens antenna are studied by using Fresnel-Kirchhoff diffraction theory and the paraxial approximation. The effects of the full-wave period, the focus diameter ratio, the subregion, and the dielectric substrate thickness on radiation characteristics are studied. The experimental results show that the proposed lens antenna has axisymmetric radiation patterns. The gain is over 26.1 dB, and the 3 dB main lobe beam width is lower than 5.6° across the operation band. The proposed lens antenna is qualified for applications in terahertz wireless communication systems.

Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

Capture of a terahertz wave in a photonic-crystal slab

Trapping of a terahertz wave in a photonic-crystal slab and subsequent ‘capture’ through absorption are demonstrated. Over 90% of the wave lying within 17% of the centre frequency is absorbed. Application to the stabilization of terahertz wireless communication systems is shown.

Design of a wideband continuous-wave photomixer antenna for terahertz wireless communication systems

We propose a bandwidth-enhanced four-leaf-clover-shaped photomixer antenna for use in terahertz wireless communication systems. The antenna was designed with a highly resonant radiation element, a stable DC feed element with photonic bandgap structure, and two symmetrical parasitic elements electromagnetically coupled with the main radiator for bandwidth enhancement. The antenna was optimized to have a maximum antenna-efficiency bandwidth and maximum directivity on an extended hemispherical lens. The half-maximum antenna-efficiency bandwidth of this structure was approximately 16%, and it completely covered the 275–320 GHz band. The antenna produced a maximum antenna-efficiency of 18% and a maximum directivity of 25 dBi, with a 2.4 dBi variation within the frequency band of interest, thus promising for efficient and stable operation.

A Geometric-Statistic Channel Model for THz Indoor Communications

The eventual practical deployment of a terahertz (THz) wireless communication system requires a proper channel model. By considering the unique characteristics of THz propagation, this paper proposes a geometric-statistic channel model for system-level simulation. This work also provides an evaluation methodology for investigating the system performance. Numerical results reveal that the proposed channel model is not only suitable to describe the physical characteristics of the THz channel, but also to investigate system-level performance.

Plasma-Wave Detectors for Terahertz Wireless Communication

We report on terahertz wireless communication experiments at 0.3 THz using 250-nm gate-length GaAs/AlGaAs field-effect transistor (FET) as a detector and unitraveling-carrier photodiode as a source. The physical mechanism of the detection process is terahertz wave rectification on nonlinearities related to overdamped plasma oscillations in the transistor channel. We present an experimental study of rectification bandwidth and show for the first time that room-temperature direct detection with modulation bandwidth of up to 8 GHz can be achieved, thus showing that nanometer-sized FETs can be used as valuable detectors in all-solid-state terahertz wireless communication systems.

Research on reflectors in terahertz wireless communication systems

Terahertz （THz） wireless communication system, which exhibits great potential in the future short-range wireless communications, is known to be a kind of ultra-broadband system with high data rates. THz sources, modulators and detectors are key elements in these systems, while in order to maintain high-quality connection, the THz reflectors are also very important. Here, a reflector which is a kind of one-dimensional photonic crystal made of polyvinylidene fluoride （PVDF）/polycarbonate （PC） is studied carefully. According to the refractive indices of materials in the THz range, the reflection coefficients for THz waves are obtained through transfer-matrix method and Fresnel formula calculation. We demonstrate that, in sub-THz waveband, this device shows high performance and wide reflection band. Furthermore, based on the calculation, the research and the design of THz reflectors are also discussed in this article.