The calculation and analysis of terahertz communication system and modules
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Abstract:
The terahertz high rate wireless communication system plays an important role in terahertz technology. There are two typical occasions for terahertz communication to be applied, the satellite communication and short-range communication on the ground. In this paper, the link budget calculations of terahertz communication in different scenes have been finished, which prove the terahertz wave source is the key of terahertz system. Among the terahertz source devices, mixer and resonant tunneling oscillator are more appropriate for terahertz communication in space and indoors. The simulation and analysis of sub-harmonic mixer and resonant tunneling oscillator characteristics is discussed according to different application scenes. At last, the prospect of terahertz communication is given.Keywords:
Terahertz gap
Photomixing
Communications satellite
Terahertz time-domain spectroscopy
We report a terahertz spectroscopy technique based on a stable terahertz frequency comb from a photoconductive terahertz emitter driven by a stabilized femtosecond laser. To this end, a photocurrent frequency comb is induced in a photoconductive terahertz detector by instantaneous photogating with another detuned femtosecond laser and is applied to read out the terahertz frequency comb. The detailed structure of the terahertz frequency comb was clearly observed with frequency accuracy of 2.5×10−7 and resolution of 81.8MHz using multifrequency-heterodyning photoconductive detection, which in turn is caused by the slightly mismatched frequency spacing between terahertz and photocurrent frequency combs.
Photomixing
Photoconductivity
Photocurrent
Terahertz gap
Terahertz time-domain spectroscopy
Comb generator
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Citations (207)
In a continuous-wave terahertz spectrometer, we employ photomixing of three lasers, allowing us to measure at three terahertz frequencies simultaneously. Whilst two of the terahertz frequencies can be tuned to obtain terahertz spectra, one terahertz frequency remains fixed. The data recorded at the fixed frequency is used to normalize the spectra of the two other frequencies. As a result, the accuracy of the terahertz phase measurement can be greatly enhanced.
Photomixing
Terahertz gap
Terahertz time-domain spectroscopy
Continuous wave
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Terahertz region is the electromagnetic gap between the infrared optoelectronics and the high frequency electronics, which is of broad prospects in applications. The application requirements drive the rapid development in Terahertz technologies including sources, detectors and systems. In the last two decades, quantum cascade laser has made great progress as one of the most promising terahertz sources. In this paper, we present the development of terahertz quantum cascade lasers in our group.
Terahertz gap
Photomixing
Quantum cascade laser
Electromagnetic spectrum
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Manipulation of Terahertz Waves with a Right- or Left-handed Metasurface for Directivity Enhancement
The manipulation of terahertz waves based on flat optics with metasurfaces is being employed in terahertz continuous-wave (CW) sources, such as resonant tunneling diodes (RTD) and quantum cascade lasers (QCL) for 6G wireless communications and terahertz imaging. However, two-dimensional optical components in terahertz flat optics are strongly subject to the distance from CW sources because metaatoms with different dimensions optimize the gradient distribution of the refractive indices, such as in gradient-refractive-index (GRIN) metalenses. Here we demonstrate that an original terahertz metasurface with identical double-sided meta-atoms on a dielectric substrate enhances the directivity of terahertz waves. Terahertz time-domain spectroscopy (THz-TDS) measures that the metasurface has right- or left-handed dispersion characteristics, resulting in transmittance enhancement with 177% at 0.47 THz. The metasurface could be mounted on terahertz CW sources without considering the design of the distance between the metasurafce and sources to enhance the directivity. Our findings suggest that the manipulation of terahertz waves has the potential to significantly accelerate the growth of terahertz industrial applications.
Photomixing
Terahertz gap
Directivity
Terahertz time-domain spectroscopy
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Abstract Terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation are currently the only electrically pumped monolithic semiconductor light sources operating at room temperature in the 1–6-THz spectral range. Relying on the active regions with the giant second-order nonlinear susceptibility and the Cherenkov phase-matching scheme, these devices demonstrated drastic improvements in performance in the past several years and can now produce narrow-linewidth single-mode terahertz emission that is tunable from 1 to 6 THz with power output sufficient for imaging and spectroscopic applications. This paper reviews the progress of this technology. Recent efforts in wave function engineering using a new active region design based on a dual-upper-state concept led to a significant enhancement of the optical nonlinearity of the active region for efficient terahertz generation. The transfer of Cherenkov devices from their native semi-insulating InP substrates to high-resistivity silicon substrates resulted in a dramatic improvement in the outcoupling efficiency of terahertz radiation. Cherenkov terahertz QCL sources based on the dual-upper-state design have also been shown to exhibit ultra-broadband comb-like terahertz emission spectra with more than one octave of terahertz frequency span. The broadband terahertz QCL sources operating in continuous-wave mode produces the narrow inter-mode beat-note linewidth of 287 Hz, which indicates frequency comb operation of mid-infrared pumps and thus supports potential terahertz comb operation. Finally, we report the high-quality terahertz imaging obtained by a THz imaging system using terahertz QCL sources based on intra-cavity difference frequency generation.
Photomixing
Terahertz gap
Quantum cascade laser
Laser linewidth
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Citations (82)
A 650-nm chaotically oscillating multi-mode semiconductor laser was used to generate and detect a stable continuous terahertz signal from a photoconductive antenna. The intensity of the generated terahertz was ~10 times stronger compared to the excitation without chaotic oscillations. The frequency comb-type spectrum is obtained in the sub-terahertz region, which makes terahertz time-domain spectroscopy systems with this kind of economically superior laser very promising for the evaluation of 5G and 6G components.
Photomixing
Terahertz gap
Terahertz time-domain spectroscopy
Continuous wave
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Citations (1)
High-power pulsed terahertz radiation sources are highly in demand for time-domain terahertz imaging and spectroscopy systems. A common way to generate pulsed terahertz radiation is exciting a biased ultrafast photoconductor with a femtosecond optical pulse. The photo-generated carriers drift to a terahertz radiating element under the induced bias electric field and a pulsed terahertz radiation is generated. Developing photoconductive terahertz sources operating at telecommunication wavelengths (~1550 nm) is very attractive because of the availability of high-power, narrow-pulse-width, and compact fiber lasers at these wavelengths. However, photoconductors responsive to telecommunication wavelengths often have low resistivity due to their small bandgap energy, resulting in excessive dark current levels under an applied bias voltage. As a result, telecommunication-compatible photoconductive sources experience a premature thermal breakdown under high bias voltages and cannot offer high terahertz radiation powers. To address this limitation, we introduce a new type of telecommunication-compatible photoconductive terahertz source that does not require an externally applied bias voltage and relies on a built-in electric field formed at the interface between the photoconductor and terahertz antenna contact electrodes. By eliminating the bias voltage, the device operates at a zero dark current, enabling a highly reliable operation. We use an array of plasmonic nanoantennas as the terahertz radiating elements to achieve a broad terahertz radiation bandwidth and high optical-to-terahertz conversion efficiency. We demonstrate pulsed terahertz radiation with powers exceeding 100 μW, enabling time-domain terahertz spectroscopy with a 100 dB dynamic range over a 0.1-3 THz bandwidth.
Photomixing
Terahertz gap
Terahertz time-domain spectroscopy
Biasing
Photoconductivity
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Citations (1)
An innovative external cavity dual-mode laser has been developed for continuous-wave terahertz generation via photomixing. Photomixing is a method of generating terahertz radiation at the beat frequency developed by two input optical light modes. Dual-mode lasers are an intriguing option for photomixing sources because the differential frequency produced is stabilized by the common mode rejection ratio effect. The laser presented here utilizes an acousto-optic tunable filter for frequency selection, which creates an ultra-wideband tunable range and provides the potential for tuning speed on the order of microseconds. The unique design of this laser enables 100% solid state operation resulting in a robust and compact system for applications in terahertz imaging or spectroscopy. Operating at around 1550 nm, this laser is capable of producing differential frequencies between 300 GHz and 18 THz with a side-mode-suppression-ratio of 50 dB and peak amplitudes of over 0 dBm. The device presented here represents a significant achievement in the advancement of dual mode lasing technology for tunable terahertz generation with high phase and amplitude stability.
Photomixing
Terahertz gap
Wideband
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Abstract Terahertz quantum cascade laser sources with intra-cavity non-linear frequency mixing are the first room-temperature electrically pumped monolithic semiconductor sources that operate in the 1.2–5.9 THz spectral range. However, high performance in low-frequency range is difficult because converted terahertz waves suffer from significantly high absorption in waveguides. Here, we report a sub-terahertz electrically pumped monolithic semiconductor laser. This sub-terahertz source is based on a high-performance, long-wavelength (λ ≈ 13.7 μm) quantum cascade laser in which high-efficiency terahertz generation occurs. The device produces peak output power of 11 μW within the 615–788 GHz frequency range at room temperature. Additionally, a source emitting at 1.5 THz provides peak output power of 287 μW at 110 K. The generated terahertz radiation of <2 THz is mostly attributable to the optical rectification process in long-wavelength infrared quantum cascade lasers.
Photomixing
Quantum cascade laser
Terahertz gap
Terahertz time-domain spectroscopy
Optical rectification
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Citations (57)
Using gases as the emitter and detector media in a THz system allows for good phase matching over the full terahertz range (0.3 to 10 THz), without interruptions from crystal phonon modes or other instrument artifacts. A heterodyne technique facilitates coherent measurement of the electric field waveform, enabling this technique to be used for time-resolved spectroscopy in which a single measurement can continuously cover the entire terahertz region of the electromagnetic spectrum.
Terahertz time-domain spectroscopy
Terahertz gap
Photomixing
Heterodyne detection
Heterodyne (poetry)
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