Terahertz free space communication based on acoustic optical modulation and heterodyne detection

Abstract

A terahertz free space communication system based on acoustic optical modulation and heterodyne detection is demonstrated. A high resistivity silicon acoustic optical modulator was used to modulate a continuous terahertz wave at 2.52 THz. A pyroelectric detector was used to detect the modulated terahertz signal via heterodyne detection mode. A modulation frequency of 937 kHz and sampling rate of 1 kbit/s was achieved.Introduction: In the last twenty years, research in terahertz technologies (0.1 -10 THz) has grown significantly owing to its promising applications such as nondestructive imaging, spectroscopy and wireless communication. Although terahertz imaging and spectroscopy have been intensively investigated, only a few studies have been reported regarding terahertz wireless communications. This is due to the technical barriers that have to be overcome for developing suitable sources, modulators and receivers. Yet the advantages of terahertz communication over conventional microwave wireless are obvious [1]. Terahertz systems have the potential to provide a much broader bandwidth, more directional transmission (useful to reduce the size of the antenna) and more secure information communication due to the short transmission distance.Considerable work has been carried out into components and systems for terahertz communications [2 -7]. One of the key components is the modulator. Liu et al. and Möller et al. have demonstrated direct modulation of terahertz sources by applying a modulation signal onto the photoconductive antennas in a terahertz time domain spectroscopy system [2,3]. A modulation rate of 1 Mbit/s and bandwidth of 23 kHz was achieved. External modulation based on semiconductor devices with a quantum-well structure has also been demonstrated [4,5]. However, the operating temperature must be extremely low, which is not suitable for practical applications. For room-temperature operation, Kleine-Ostmann reported a terahertz semiconductor modulator with a modulation frequency of 23 kHz and demonstrated audio transmission based on this modulator in THz TDS [6]. Chen et al. reported a terahertz modulator based on all electrically driven active metamaterial. A modulation frequency up to 2 MHz was achieved [7].In this Letter, we demonstrate a potential signal communication system at room temperature using an acoustic optical modulator (AOM) and a pyroelectric heterodyne detector. The AOM provides a simple method for modulation over a broadband frequency range. In an AOM, a travelling acoustic wave at frequency v A causes the incident terahertz wave at frequency of v T to diffract, as shown in Fig. 1a. The diffracted beam is frequency modulated by the acoustic wave at v A . The diffracted beam together with the undiffracted beam are focused onto the pyroelectric detector that works in a heterodyne mode. Pyroelectric detectors have broad detection bandwidth at room temperature, from visible to terahertz frequencies. In addition, they are capable of responding to modulation frequencies of the order of several ...

Terahertz wireless communications

“…Several approaches for external THz modulators have been discussed 77 including acousto-optic, 78 ferroelectric materials, liquid crystals, 79 , 80 and optically or electronically free carriers in semiconductor structures. 81 , 82 Optically or electrically driven external intensity and phase modulators based on active metamaterials have been demonstrated.…”

Optical Controlled Terahertz Modulator Based on Tungsten Disulfide Nanosheet

“…Basic devices for THz wireless communication, such as THz wave sources, THz wave detectors and THz wave modulators, have been investigated by many research groups. Different mechanisms and devices for THz modulators have also been reported 1 – 5 . THz modulators are based on traditional materials, such as silicon and gallium arsenide (GaAs), and they always have a small modulation depth because of the recombination of carriers in materials 2 .…”

Free electron terahertz wave radiation source with two-section periodical waveguide structures

“…Yet till now, it is still an urgent problem to develop the compact, room temperature, and relatively high power terahertz radiation source, even though great efforts have been made. [1][2][3][4][5][6][7][8][9][10] Traditional vacuum electronic devices, such as backward wave oscillator (BWO) and extended interaction oscillator (EIO), 11,12 can generate radiation with milliwatt to watt power level in the low frequency terahertz regime, and they are also the most commonly used radiation sources in real applications. But it is hard for this kind of devices to reach the high frequency terahertz region (higher than 0.5 THz) due to the requirement of extremely high starting beam current density.…”