Terahertz Frequency Generation Research Articles

Terahertz Frequency Generation Using Fiber Bragg Gratings: a Cost-Effective and Simplified Approach

Terahertz Frequency Generation Using Fiber Bragg Gratings: a Cost-Effective and Simplified Approach

Temperature-Dependent Optical Properties of Bismuth Triborate Crystal in the Terahertz Range: Simulation of Terahertz Generation by Collinear Three-Wave Mixing in the Main Crystal Planes

Terahertz (THz) frequency generation via nonlinear optical techniques is of particular interest due to the immense potential of this type of radiation in various scientific fields, ranging from medicine to telecommunications. Selecting suitable nonlinear media for laser frequency down-conversion presents a challenging task. Considering an approach that uses nonlinear crystals with high radiation resistance, pumped by intense laser pulses near their damage threshold, we suggest the crystal of bismuth triborate (BiB3O6, BIBO). Compared to other borate-class crystals, BIBO exhibits relatively high coefficients of quadratic susceptibility. In this paper, we have studied the optical properties of BIBO samples in a wide spectral range from 0.1 to 2.1 THz at temperatures of 473, 383, 295, and 77 K using Terahertz Time-Domain Spectroscopy (THz-TDS). Furthermore, we simulated collinear three-wave interactions with nonzero efficiency for difference frequency generation (DFG) in the THz range. For the pump wavelengths of about 800 nm, we determined phase-matching (PM) conditions and compared the generation efficiency for different crystal cuts. The potential of utilizing BIBO crystal for terahertz frequency generation is discussed.

Experimental observation of Berreman modes in an uniaxial anisotropic nanoporous alumina film on aluminum substrate.

In this Letter, we demonstrate experimentally and verify numerically the excitation of Berreman modes that propagate in a dielectric film of uniaxial anisotropic nanoporous alumina grown on an aluminum substrate. It is an air-dielectric-metal asymmetric polaritonic system with a real part of the effective permittivity having a value near zero. The modes are excited at a wavelength lower than the epsilon-near-zero wavelength region. Minimum reflection is observed for the mid-infrared p-polarized light, while maximum reflection is observed for the s-polarized light. The experimental results are numerically reproduced for both p- and s-polarized light and confirm the excitation of Berreman modes in the system. At the exciting wavelength, the field is confined in the dielectric region near the air-dielectric interface. The reported system is straightforward and can be easily fabricated over a large scale and is helpful in a variety of mid-infrared applications such as thermal management systems, sensors, passive radiative cooling devices, nonlinear applications, and terahertz frequency generation.

Topological insulator Bi2Se3 as a tunable crystal for terahertz frequency generation

Topological insulator Bi2Se3 as a tunable crystal for terahertz frequency generation

1.0–10.0 THz Radiation from Graphene Nanoribbon Based Avalanche Transit Time Sources

The possibilities of terahertz frequency generation by using graphene nanoribbon (GNR) based avalanche transit time (ATT) sources are investigated in this paper. The most promising candidate of ATT device family, i.e., the impact avalanche transit time (IMPATT) diode is chosen for the present study. Parallel connected GNR based IMPATT structures with inherent power combining capability are proposed and simulated by using self‐consistent quantum drift‐diffusion model based in‐house simulation codes in order to study the static, high frequency and noise performance of those at different millimeter‐wave and terahertz frequency bands. The detailed study reveals that the in‐build power combined GNR IMPATT sources are capable of performing more efficiently than the IMPATT sources based on some other popular semiconductor materials as well as some state‐of‐the‐art terahertz radiators within the terahertz frequency band from 1 to 10 THz.

Terahertz frequency generation with monolithically integrated dual wavelength distributed Bragg reflector semiconductor laser diode

Optoelectronic terahertz (THz) generation techniques have helped to narrow the THz gap and have opened up a wealth of new applications for THz technology. However, the development of THz systems into mass market is a major technical challenge, which is attributed to high cost of THz hardware components including sources and detectors. Here, the authors report THz generation from a distributed Bragg reflector (DBR) semiconductor laser diode together with fibre coupled photoconducting antennas. Two fibre coupled ion-implanted gallium arsenide photoconducting antennas were employed to generate and detect THz radiation. Two DBR lasers connected with a Y-shaped waveguide structure were monolithically integrated and used to simultaneously emit two wavelengths in the range of 785 nm. These lasers were employed as pumping source for the photomixers. An optical beat frequency of 286 GHz of the dual wavelengths was obtained from optical characterisation. A corresponding THz frequency was confirmed via photomixing in a homodyne set up. By variation of the operation parameters of the laser, the difference frequency was tuned in the range between 286 GHz to 320 GHz. In summary, they report the implementation of a compact and cost effective fiber coupled Terahertz source based on a monolithically integrated dual wavelength DBR semiconductor laser diode.

Potentiality of IMPATT Devices as Terahertz Source: An Avalanche Response Time-based Approach to Determine the Upper Cut-off Frequency Limits

Potentiality of Impact Avalanche Transit Time (IMPATT) devices based on different semiconductor materials such as InP, 4H-SiC, and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz (THz) frequencies. Drift-diffusion model is used to design double-drift region (DDR) IMPATTs based on above mentioned materials at different millimeter-wave (mm-wave) and THz frequencies and the upper cut-off frequency limits of those devices are obtained from the avalanche response times at those mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of both InP and 4H-SiC DDR IMPATTs are 1.0 THz; whereas, the same is 5.0 THz in Wz-GaN DDR IMPATTs. The Wz-GaN DDR IMPATTs emerge as the most suitable devices for generation of THz frequencies due to their small avalanche response time, high DC to RF conversion ratio, and sufficiently high RF power output at THz frequencies. But, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs due to their higher output power densities. Thus, the wide bandgap semiconductors such as Wz-GaN and 4H-SiC are highly suitable materials for DDR IMPATTs at both mm-wave and THz frequency ranges.

Circuit Implementations and Comparison betweenDifferent Multiplication Factors in Terahertz FrequencyGeneration in 90nm Process Using Linear Superposition

In this paper, the Linear Superposition technique for Terahertz frequency generation in CMOS circuits has been reviewed. The CMOS circuits are designed in 90nm process and oscillator parameters are designed to have a fundamental oscillation frequency of 91 GHz. Circuit designs for different values of multiplying factor N are demonstrated and their Pspice simulation results are presented and compared. In these simulations, oscillation of up to 910 GHz (for N=10) was observed. signal in simulation in 90nm process. The underlying mechanism and design techniques of the circuits are explained in detail, and the simulation results are presented and compared for different values of N. The paper organization is as follows: Section II gives a review of the Linear Superposition method. Section III presents the analysis of the circuit for N=2 for explanation of the underlying principle of the circuit. Section IV describes the circuits for N=4, 6, 8 and 10 and their design techniques. The Simulation results are presented and compared in Section V. Finally, Section VI concludes the paper.

Domain Suppression in the Negative Differential Conductivity Region of Carbon Nanotubes by Applied AC Electric Field

We study theoretically the electron transport properties in achiral carbon nanotubes under the influence of an external electric field E(t) using Boltzmann’s transport equation to derive the current-density. A negative differential conductivity (NDC) is predicted in quasi-static approximation i.e., ωτ 0 is equal to the amplitude of the AC electric field E1. The peak of the NDC intensity occurs at very weaker fields than that of superlattice under the same conditions. The peak intensity decreases and shifts to right with the increase in the amplitude of the ac field. This mechanism suppresses the domain formation and therefore could be used in terahertz frequency generation.