Power Terahertz Wave Research Articles

THz Wave Power Enhancement Using a Microstrip Line-Based Combiner Integrated with Arrayed UTC-PDs

Advancements in semiconductor devices, such as Uni-travelling-carrier photodiodes (UTC-PDs), have played a significant role in the development of Terahertz communication technology. However, the persistent challenge is the limited output power from a single UTC-PD required for practical transmission distances. To enhance the output power, we propose and demonstrate a novel Terahertz wave power combining technique using a photomixer device comprising two arrayed UTC-PDs monolithically integrated with a microstrip line-based 2 × 1 Wilkinson power combiner and a patch antenna on a Silicon Carbide (SiC) substrate at 300 GHz. When the two UTC-PDs are activated at photocurrents of 8 mA and 10 mA, the device exhibits a 7.3 dB increase in power relative to the power obtained when only the 8 mA UTC-PD is activated, and a 4.4 dB increase in power relative to the power obtained with the 10 mA UTC-PD. This implies that power can be enhanced by a factor of N2 if the photocurrent is multiplied by N. Additionally, we demonstrate that the UTC-PD output saturation depends on the space charge effect, which modulates the electric field in the depletion region and results from critical charge density of about 80 kA/cm2 for the device in this work.

Expansion of measurement capabilities of the bolometric sensor of the terahertz wave power based on an inexpensive and stable measuring system

The paper discusses the results of a joint work of the Central Office of Measures in the Republic of Poland and the Military University of Technology in Warsaw within the framework of the project “Measurement Consistency in Electromagnetic Power Measurements in the Sub-THz Band”. The main problems in the study of electromagnetic radiation power in the terahertz range using a bolometric detector are considered. The design and parameters of the measuring system based on the use of a resistive bolometric detector, own signal amplifier, and measuring converter, which were designed and implemented at the Central Office of Measures in the Republic of Poland, are described. The results of metrological traceability to the SI units are presented. This paper is dedicated to expanding measurement capabilities of the bolometric detector based on a highly stable and inexpensive measuring system in the terahertz range. As a result of the joint work, a measuring system characterized by high parameter stability and a gain of more than 20 000 V/V was developed and tested.

Terahertz Wave Power Multiplication by Combining Photocurrents from Arrayed UTC-PDs

A terahertz (THz) wave generator for multiplying the output power from arrayed photomixers is developed. The generator is composed of two uni-traveling carrier photodiodes (UTC-PDs) as the photomixers, a [Formula: see text] T-junction power combiner and a microstrip rectangular patch antenna on a silicon carbide (SiC) substrate in which photocurrents of 300[Formula: see text]GHz from the UTC-PDs are combined to be fed to the antenna. Experimental results show that the output power is multiplied by 5.8[Formula: see text]dB (approximately fourfold) compared to that of a single UTC-PD. This advancement has the potential for further multiplication of THz power by cascaded combining of a larger number of UTC-PDs.

Terahertz power enhancement by combining photocurrent from arrayed UTC-PDs using Wilkinson power combiner

We designed a novel terahertz wave power combiner which combines HF currents from each photomixer in a micro strip line. The generator is composed of four uni-travelling carrier photodiodes (UTC-PDs) as the photomixers, a 4 × 1 Wilkinson power combiner and a microstrip rectangular patch antenna on a Silicon Carbide (SiC) substrate in which photocurrents of 300 GHz from the UTC-PDs are combined to be fed to the antenna. Experimental results show that the output power is multiplied by 11 dB (approximately 13 times) compared to that of a single UTC-PD. The combined power increases super-linearly with the number of the photomixers, confirms a great advantage of photomixing as a current source.

The laws and effects of terahertz wave interactions with neurons.

Introduction: Terahertz waves lie within the energy range of hydrogen bonding and van der Waals forces. They can couple directly with proteins to excite non-linear resonance effects in proteins, and thus affect the structure of neurons. However, it remains unclear which terahertz radiation protocols modulate the structure of neurons. Furthermore, guidelines and methods for selecting terahertz radiation parameters are lacking. Methods: In this study, the propagation and thermal effects of 0.3-3THz wave interactions with neurons were modelled, and the field strength and temperature variations were used as evaluation criteria. On this basis, we experimentally investigated the effects of cumulative radiation from terahertz waves on neuron structure. Results: The results show that the frequency and power of terahertz waves are the main factors influencing field strength and temperature in neurons, and that there is a positive correlation between them. Appropriate reductions in radiation power can mitigate the rise in temperature in the neurons, and can also be used in the form of pulsed waves, limiting the duration of a single radiation to the millisecond level. Short bursts of cumulative radiation can also be used. Broadband trace terahertz (0.1-2THz, maximum radiated power 100μW) with short duration cumulative radiation (3min/day, 3days) does not cause neuronal death. This radiation protocol can also promote the growth of neuronal cytosomes and protrusions. Discussion: This paper provides guidelines and methods for terahertz radiation parameter selection in the study of terahertz neurobiological effects. Additionally, it verifies that the short-duration cumulative radiation can modulate the structure of neurons.

Design and simulation of widely tunable picosecond synchronously pumped terahertz parametric oscillator based on silicon waveguide platform

AbstractA picosecond synchronously pumped terahertz optical parametric oscillator based on silicon membrane waveguide (Si‐based WTPO) is proposed and numerically simulated. Through designing the structure parameters of the silicon membrane waveguide, a broadband terahertz frequency range is obtained by satisfying the phase matching condition. The parametric oscillation process and output characteristics of Si‐based WTPO are numerically analyzed by solving the four‐wave mixing coupled‐wave equations, and the result has indicated that the parametric oscillation within the resonant cavity can apparently enhance the output terahertz wave power. Meanwhile, high bandwidth and efficiency output terahertz wave can be obtained, and too high pump power will lead to a reaction of reverse conversion. Finally, the threshold pump power is calculated. The Si‐based WTPO system we proposed is expected to make some contributions to the study of compact and efficient terahertz wave sources.

Analysis of the Effect of Antenna Pointing Error Caused by Satellite Perturbation on Space Terahertz Communication

The terahertz frequency band has the advantages of having a large bandwidth, narrow beam, strong penetration, and high security, and is an important direction for the frequency expansion of next-generation satellite communications. Due to the narrow terahertz beam, the pointing error caused by satellite perturbation will affect the attenuation of the terahertz wave power, resulting in a decrease in the received power of the system and affecting the communication performance of the system. In order to accurately analyze the influence of pointing error caused by satellite perturbation on the performance of space terahertz communication system, based on satellite perturbation model and Gaussian channel model, this paper deduces the accurate analysis of signal power attenuation model without pointing error and with pointing error untie. The antenna pointing error in the real environment is simulated by using the TLE data of the actual satellite, and the influence of the pointing error on the space terahertz communication is analyzed. The results show that the antenna pointing error caused by satellite perturbation changes periodically with the operation of the satellite, which will cause great signal power attenuation, reduce the signal-to-noise ratio of the space terahertz communication system, and seriously affect the communication quality. In addition, the higher the frequency, the greater the impact on space terahertz communication, which needs to be solved through attitude control and antenna compensation.

Optical thin film coated organic nonlinear crystal for efficient terahertz wave generation

In the process of terahertz (THz) wave generation via optical rectification of infrared femtosecond pulses in a non-linear optical crystal, the power of terahertz wave is directly proportional to the square of the optical pump power. Therefore, high power terahertz wave can be generated using a high power femtosecond laser provided that the crystal has both high laser induced damage threshold and optical non-linear coefficient. However, a significant amount of pump power is lost in this process due to the Fresnel’s reflection at the air-crystal boundary. In this paper, we numerically and experimentally demonstrate that the coat of optical thin film called Cytop on the 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium tosylate (DAST) crystal effectively reduces the reflection loss of pump power, thereby increasing the THz wave emission efficiency of the DAST crystal. We found that the average power of THz wave emitted by the thin film coated crystal is about 28% higher than the THz power emitted by the uncoated crystal when an equal amount of laser power is used. The thin film coated DAST crystals can be used not only in terahertz measurement systems but also in optical devices such as modulators and waveguides.

Transmission terahertz power beam splitter based on a single-layer metal metasurface.

A periodic metasurface composed of a single layer of copper structure is proposed. The general transmission power beam splitter is composed of a multilayer structure, which is difficult to fabricate. The proposed single-layer terahertz wave power beam splitter contains only a single-layer circular hole cell structure, and it can control the transmission angle by controlling the arrangement mode of the coding cells. At the same time, we can control the transmission angle and the transmitted energy distribution of each beam based on different incident angles. A simple monolayer round-hole metasurface was prepared and its transmission characteristics were analyzed based on a terahertz time domain spectrometer. Compared with traditional splitter devices, our coding metasurface beam splitters with a single layer have the potential to promote the development of integrated optical systems.

A Full Investigation of Terahertz Wave Power Transmission in Plasma from Theoretical, Numerical, and Experimental Perspectives

Radio communication is a vital challenge during vehicle reentry into the Earth’s atmosphere in practice, because the plasma covering the aerospace vehicle can block the communication as the spacecraft reenters the atmosphere. To investigate the potential of the terahertz wave, the transfer function method is first applied to study the wave propagation behavior in plasma, validated by the numerical and the experimental results. The comparison of all three results shows a decent agreement, with the average absolute difference around 1.1 dB for the power loss between the theoretical and numerical results for 100 GHz and 220 GHz and around 0.8 dB for the power loss between the simulation and measurement for 100 GHz and 220 GHz, which shows the validity of the transfer function method and the great potential of the numerical model for future study. Moreover, the results shows the possibility of the application of the THz wave to deal with the blackout problem.

Terahertz wave amplification by a laser-modulated relativistic electron beam

Generation of tunable terahertz radiation based on the interaction of a frequency-chirped low power terahertz wave with a relativistic electron beam is proposed. The electron beam is first modulated temporally due to the ponderomotive force induced by the beat wave of two copropagating intense laser beams of slightly different frequencies. Then the electron beam interacts with a low-amplitude driver wave at terahertz frequency with a linear frequency chirping. A nonlinear transverse current density is driven that emits terahertz radiation at an up-shifted frequency with a relatively enhanced amplitude. The modulation process is analyzed theoretically by a complete set of fluid equations and considering the effects of both the electrons space-charge potential and the beat wave ponderomotive force. The initial density and energy of the electron beam are both optimized in order to improve the terahertz amplification process. The effect of the driver's frequency chirping, as well as the effects of the initial electron beam density and energy on the emitted terahertz radiation are investigated numerically. It is shown that the frequency chirping of the driver wave plays a key role in terahertz amplification. It is shown that there is an optimum chirp value for which the terahertz radiation is amplified significantly compared with the case without chirping. Moreover, transverse effects of the laser beams and the driver wave on the emitted terahertz radiation are also investigated.

Theoretical and experimental study on the enhancement of seed injection in terahertz-wave generation

We have studied the seed enhancement of an injection-seeded terahertz (THz)-wave parametric generator (is-TPG) with the help of a theoretical model. During simulation, the power of the seed beam varied from 1 W to 1 MW as the initial condition, while the pump power is set to 18.5 MW. When the peak power of the seed beam reaches megawatt level, the output power of THz wave increases rapidly and the peak position for the THz output dramatically moves towards the front of the crystal. The calculated output power of the injection-pulse-seeded TPG (ips-TPG) with 0.3 MW pulsed seed is 3.4 kW in the case of a surface-emitting configuration and 14 kW in the case of a Si-prism coupled output configuration. The enhancement ratios are 3.5 and 1.4 times, respectively, compared with the watt level CW-seeded is-TPG. Guided by the simulation, we experimentally demonstrated an 11 kW peak power Si-prism output coupled ips-TPG. The enhancement ratio is 1.6 times. The energy of the pulsed seed is 30 µJ (0.3 MW). The pump energy is 7.2 mJ, which is about half that of the typical is-TPG with the same output power. Compared with a typical is-TPG, most of the THz power in ips-TPG accumulates in the front of the crystal and thus is easier to collect. One obvious advantage of ips-TPG is that the output THz energy can be increased while keeping the pump power at a safe level.

Excellent Terahertz shielding performance of ultrathin flexible Cu/graphene nanolayered composites with high stability

Electromagnetic interference (EMI) shielding at Terahertz (THz) frequency range attracts increasing attention due to the rapid development of THz science and technologies. EMI shielding materials with small thickness, high shielding effectiveness (SE), good flexibility and stability are highly desirable. Herein, an ultrathin flexible copper/graphene (Cu/Gr) nanolayered composite are prepared, which can reach the average EMI SE of 60.95 dB at 0.1–1.0 THz with a thickness of only 160 nm, indicating that more than 99.9999% of the THz wave power can be shielded. Furthermore, the Cu/Gr nanolayered composite also exhibits excellent oxidation resistance, with a 93.09% maintenance rate for EMI SE value after heating at 120 °C for 3 h in air, far higher than that of the bare Cu film (62.15%). Besides, the Cu/Gr nanolayered composite exhibits good mechanical flexibility and flexural fatigue resistance. The EMI SE value of the Cu/Gr nanolayered composite shows a maintenance rate of 98.87% even after 1500 times bending cycles, obviously higher than that of multilayer Cu film (93.07%). These results demonstrate that the ultrathin flexible Cu/Gr nanolayered composites with excellent shielding performance and good stability have a broad application prospect in THz shielding for wearable devices and next generation mobile communication equipment.

Influence of laser-preformed plasma on THz wave generation in air by bichromatic laser pulses

Influence of laser-preformed plasma on the energy and spatial properties of terahertz (THz) emission generated in air by focused femtosecond bichromatic laser pulses has been investigated. It was found that the power of THz waves decreases in the presence of the prepulse-created plasma even when the crossing point of the two laser beams is well before or after the pump beam focus. Analysis of the experimentally obtained data revealed that at least two different mechanisms—namely, phase modification of the pump waves and screening of THz radiation by preformed plasma filaments—are responsible for this effect.

Ultra-compact 1 × 8 Channel terahertz Wave Power Splitter

Relying on 1 × 2 photonic crystal waveguide and photonic crystal resonator, a compact eight-channel terahertz wave power splitter is proposed. The mechanism of such a device is further theoretically analyzed and numerically investigated with the aid of the plane wave expansion method and the finite-difference time-domain method. With an appropriate design, the proposed power splitter can split the input terahertz wave energy equally into eight output ports at the frequency of 0.667 THz. Furthermore, the total size of the present device is of 4.33 mm × 3.74 mm. Due to its small size, the multi-channel terahertz wave power splitter has practical applications in the terahertz wave integrated circuit fields.

Investigation of 0.38 THz backward-wave oscillator based on slotted sine waveguide and pencil electron beam

A novel backward wave oscillator (BWO) is presented by utilizing a slotted sine waveguide with a pencil electron beam to produce the high power terahertz wave. The high frequency characteristics including dispersion properties, interaction impedances, and transmission characteristics of the slotted sine waveguide are analyzed in detail. The high frequency system including the output coupler, slow wave structure (SWS), and reflector are designed properly. A 3-D particle-in-cell mode is applied to predict the device performance of the BWO based on the novel SWS. The investigation results demonstrate that this device can generate over 8.05 W output power in the frequency range of 363.4–383.8 GHz by using a 30 mA pencil electron beam and adjusting the beam voltage from 20 kV to 32 kV.

Improving a Terahertz Time-Domain Spectroscopy Apparatus Using Neodymium Magnets

The signal-to-noise ratio obtained from terahertz time-domain spectroscopy is significantly affected by the low available power of terahertz waves. We constructed a terahertz-wave source with emission power enhanced by a magnetic field. The emitter is composed of an InAs wafer and two neodymium magnets. The emitter was irradiated by femtosecond laser pulses. The data quality of terahertz spectroscopic measurements was evaluated, and reduction of error in the data obtained due to the terahertz power enhancement was observed.

Improving a Terahertz Time-Domain Spectroscopy Apparatus Using Neodymium Magnets

The signal-to-noise ratio obtained from terahertz time-domain spectroscopy is significantly affected by the low available power of terahertz waves. We constructed a terahertz-wave source with emission power enhanced by a magnetic field. The emitter is composed of an InAs wafer and two neodymium magnets. The emitter was irradiated by femtosecond laser pulses. The data quality of terahertz spectroscopic measurements was evaluated, and reduction of error in the data obtained due to the terahertz power enhancement was observed.

A 0.14 THz relativistic coaxial overmoded surface wave oscillator with metamaterial slow wave structure

This paper presents a new kind of device for generating the high power terahertz wave by using a coaxial overmoded surface wave oscillator with metamaterial slow wave structure (SWS). A metallic metamaterial SWS is used to avoid the damage of the device driven by a high-voltage electron beam pulse. The overmoded structure is adopted to make it much easy to fabricate and assemble the whole device. The coaxial structure is used to suppress the mode competition in the overmoded device. Parameters of an electron beam and geometric structure are provided. Particle-in-cell simulation results show that the high power terahertz wave at the frequency of 0.14 THz is generated with the output power 255 MW and conversion efficiency about 21.3%.

Tunable dual-wavelength terahertz wave power splitter

We demonstrate, for the first time, a tunable dual-wavelength terahertz wave power splitter based on the multimode interference effect and self-imaging principle in 1×2×2 photonic crystal waveguides. Both plane wave expansion method and finite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The simulation results demonstrate that the power splitter not only split the input power into output1 and output2 branches with equal power at frequency of 1.09THz, but also split the power into output3 and output4 branches symmetrically at frequency of 1.20THz. Furthermore, for the frequency of 1.09THz, the input terahertz wave power can be split into output1 and output2 branches with an arbitrary ratio by tuning the refractive index of the tuning rods.