Abstract
Abstract Terahertz (0.1–10 THz corresponding to vacuum wavelengths between 30 μm and 3 mm) research has experienced impressive progress in the last few decades. The importance of this frequency range stems from unique applications in several fields, including spectroscopy, communications, and imaging. THz emitters have experienced great development recently with the advent of the quantum cascade laser, the improvement in the frequency range covered by electronic-based sources, and the increased performance and versatility of time domain spectroscopic systems based on full-spectrum lasers. However, the lack of suitable active optoelectronic devices has hindered the ability of THz technologies to fulfill their potential. The high demand for fast, efficient integrated optical components, such as amplitude, frequency, and polarization modulators, is driving one of the most challenging research areas in photonics. This is partly due to the inherent difficulties in using conventional integrated modulation techniques. This article aims to provide an overview of the different approaches and techniques recently employed in order to overcome this bottleneck.
Highlights
The terahertz (THz) frequency range, broadly defined between 0.1 and 10 THz, lies in the mm and sub-mm wavelength range of the spectral region
An example of an emitter above 1.5 THz from the electronic side is the uni-travelling carrier photodiode (UTC-PD) source based on III–V semiconductor technology [3, 4], which is directly linked to lasers emitting in the optical communication window
When dealing with physically moving parts, there is a limit to the modulation speeds which can be performed, with Microelectromechanical systems (MEMS) limited to modulation speeds between tens of kilohertz and MHz, compared to the gigahertz (GHz) speeds required in typical communication environments
Summary
The terahertz (THz) frequency range, broadly defined between 0.1 and 10 THz, lies in the mm and sub-mm wavelength range of the spectral region. The lack of active THz optoelectronic components, such as amplitude, phase, frequency, and polarization modulators, as well as beam condenser and beam steering devices has hindered this frequency range from achieving its full exploitation. We aim to provide an overview of the basic principles and the main approaches which have recently been developed to overcome these hurdles with a specific focus on integrated devices capable of implementation in practical applications. In order to overcome the typical poor material response in the THz, artificial resonances are commonly implemented in the device architecture in a large variety of approaches to boost the efficiency and increase the device miniaturization. The main avenues for achieving active amplitude, frequency, and polarization modulation in the THz frequency range are reported. The implementation of this new class of optoelectronic devices in potential future applications in the scientific areas of spectroscopy, communication, and imaging is presented
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