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Terahertz Communications for Terabit Wireless Imaging
Published in Laurent A. Francis, Krzysztof Iniewski, Novel Advances in Microsystems Technologies and Their Applications, 2017
Kao-Cheng Huang, Zhaocheng Wang
Photomixing process is commonly used to generate THz CWs from two CW laser beams. We define that these lasers have angular frequencies ω1 and ω2, respectively. Both beams with the same polarization are mixed and then focused onto an ultrafast semiconductor material such as GaAs. Due to the photonic absorption and the short charge carrier lifetime in the material, we obtain the modulation of the conductivity at the expected THz frequency ωTHz = ω1 − ω2. Figure 8.2a schematically shows the two beams photomixing with a photomixer coupled to a hemispherical substrate lens. Figure 8.2b shows a schematic diagram of the photoconductive emitter and an identical detector.
THz Photonics
Published in Chi H. Lee, Microwave Photonics, 2017
Albert Redo-Sanchez, X.-C. Zhang
The most common technique for generating low power (from 100 μW to 20 mW) CW THz radiation up to 0.6 THz is through up-conversion of lower frequency microwave oscillators such as voltage controlled oscillators and dielectric resonator oscillators. Up-conversion is typically achieved using a chain of planar GaAs Schottky diode multipliers after a Gunn or Impact Ionization Avalanche Transit Time (IMPATT) diode. Other technologies available to generate CW THz radiation are BWO, gas laser, free electron lasers, quantum cascade lasers (QCLs), and photomixing (Table 10.5).
Biological Effects of Millimeter and Submillimeter Waves
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
Stanislav I. Alekseev, Marvin C. Ziskin
Millimeter wave generators use different sources of oscillators. Vacuum tube based sources include backward wave oscillators (BWO), orotrons (high-power BWO), magnetrons, gyrotrons, gyro-klystrons, and gyro-traveling wave tubes (gyro-TWT). Solid-state sources include widely used Gunn diodes and impact ionization avalanche transit-time (IMPATT) diodes. Magnetrons, gyrotrons, gyro-klystrons, and gyro-TWT are used in high output power generators. Pulse magnetrons operate in the frequency range up to 220 GHz with peak power of 30 kW. Gyrotrons depending on cooling conditions can generate power at fixed frequencies up to 20 kW. Gyro-klystrons operate at fixed frequencies with output power up to 340 kW. Gyro-TWT can generate peak power up to 180 kW. The low output generators commonly used in biological experiments have oscillators such as BWO, Gunn diodes, and IMPATT diodes. These sources of mm waves cover the frequency range of 30–178 GHz at maximum output power up to 400 mW. Generators based on BWO operate at frequencies from 36 to 178 GHz with output powers up to 80 mW. BWO are the most wide-banded sources with electronic control of frequency. Cavity stabilized Gunn oscillators generate from 40 to 140 GHz with maximum CW power at lower frequencies up to 200 mW, which drops at higher frequencies to 30 mW. CW IMPATT diodes are used for oscillators and amplifiers. They operate in the frequency range of 30–140 GHz with output power up to 400 mW. IMPATT diodes are used in noise generators. Some generators use frequency synthesizers. A frequency synthesizer is an electronic circuit for generating any of a range of frequencies from a single fixed oscillator. A frequency synthesizer uses the techniques of frequency multiplication, frequency division, direct digital synthesis, and frequency mixing (photomixing) to generate new frequencies, which have the same stability and accuracy as the master oscillator. Commercially available synthesizers cover the frequency ranges from 36 to 1250 GHz and 0.45 to 2.85 THz.
Analytical Modelling of Terahertz Photomixing Antennas
Published in IETE Journal of Research, 2022
Mrinmoy Bharadwaj, Jitendra Prajapati, Ratnajit Bhattacharjee
Terahertz (THz) Photomixing Antennas (PMA) are amongst the promising devices that can generate continuous-wave (CW) radiation in the THz frequency range. These antennas radiate on the principle of radiation from accelerated charge carriers in a photoconductive material, under the application of a DC bias voltage across an optically illuminated region of the material. These charge carriers are generated due to focused optical irradiation of the photoconductive material by two CW and above-bandgap laser sources with a small difference in wavelengths in the order of THz. For application of a DC bias voltage, metallic patterns are printed on the photoconductive substrate material. Different ways of cooling the device from the heat generated due to laser irradiation have been discussed in [1].