Fangjing Hu

Ultra-low cost THz short-range wireless link

This paper demonstrates an ultra-low cost THz system for implementing a short-range wireless communications link in the far/mid-infrared parts of the electromagnetic spectrum. The basic prototype front-end hardware is deliberately kept very simple; based around miniature incandescent light bulbs, THz filters and pyroelectric infrared sensors. While only a low data rate has been experimentally demonstrated so far, this does not represent a fundamental limitation, as a number of technological enhancements are possible. It is believed that this “THz torch” technology has its niche in ubiquitous security applications that do not require high data rates or large distance operation (e.g. secure RFID, smart key fobs and remote controls).

Emerging Thermal Infrared ‘THz Torch’ Technology for Low-Cost Security and Defence Applications

Terahertz (THz) systems are notoriously large and very expensive, from complete systems down to individual front-end active devices and passive components. This is a major reason why there are currently no ubiquitous applications in the terahertz frequency spectrum (from 0.3 to 10 THz). However, by moving into the high-THz part of the frequency spectrum (thermal infrared region, from 10 to 100 THz), for specific niche applications, it is possible to create affordable systems for commercial exploitation.

Predicting Atmospheric Attenuation under Pristine Conditions between 0.1 and 100 THz

This multidisciplinary paper reports on a research application-led study for predicting atmospheric attenuation, and tries to bridge the knowledge gap between applied engineering and atmospheric sciences. As a useful comparative baseline, this paper focuses specifically on atmospheric attenuation under pristine conditions, over the extended terahertz spectrum. Three well-known simulation software packages (‘HITRAN on the Web’, MODTRAN®4, and LBLRTM) are compared and contrasted. Techniques used for modeling atmospheric attenuation have been applied to investigate the resilience of (ultra-)wide fractional bandwidth applications to the effects of molecular absorption. Two extreme modeling scenarios are investigated: horizontal path links at sea level and Earth-space path links. It is shown by example that a basic software package (‘HITRAN on the Web’) can give good predictions with the former, whereas sophisticated simulation software (LBLRTM) is required for the latter. Finally, with molecular emission included, carrier-to-noise ratio fade margins can be calculated for the effects of line broadening due to changes in macroscopic atmospheric conditions with sub-1-THz ultra-narrow fractional bandwidth applications. Outdoors can be far from pristine, with additional atmospheric contributions only briefly introduced here; further discussion is beyond the scope of this paper, but relevant references have been cited.

Link budget analysis for secure thermal infrared communications using engineered blackbody radiation

The ‘THz Torch’ concept was recently introduced as an ultra-low cost means of providing secure short-range wireless communications in the thermal infrared spectral range (10–100 THz). This technology exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels; the energy in each channel is then independently pulsed modulated and transmitted. This technology can be further enhanced by multiplexing schemes, e.g. frequency division multiplexing (FDM) and frequency-hopping spread-spectrum (FHSS). In this paper, the end-to-end link budget analysis for a 4-channel ‘THz Torch’ working demonstrator, operating over a short transmission range of 1 cm, is given for the first time. Mathematical modelling of the end-to-end wireless link is presented. In the analysis, different bias points for the source are considered and the corresponding RMS output voltages at the receivers are calculated. The predicted results show the capability for each channel, and will serve as a guide for further improving the overall performance of this multi-channel ‘THz Torch’ system.

Technology demonstrators for low-cost terahertz engineering

There is no doubt that terahertz (THz) technology is rapidly growing in interest. Its frequency range lies in a commercially unexploited part of the electromagnetic spectrum. Front-end systems operating in the THz gap, i.e. frequency range between where the performance of conventional electronics falls off and that of photonics increases, have generally existed for expensive scientific applications and have relied on precision free-space (quasi-) optics and often cryogenic cooling. However, in order to move away from less profitable high-end applications, engineering solutions are needed to create a positive spiral of technological growth with more profitable ubiquitous applications. This review paper introduces recent examples of THz technologies that may have the potential for future commercial exploitation.

Multi-channel thermal infrared communications using engineered blackbody radiation for security applications

The thermal (emitted) infrared frequency bands, typically from 20-40 THz and 60-100 THz, are best known for applications in thermography, such as target acquisition, surveillance, night vision, and remote sensing. This unregulated part of the spectral range offers opportunities for the development of short-range secure communications. The ‘THz Torch’ concept was recently demonstrated by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels. The energy in each channel is then independently pulse-modulated, transmitted and detected, creating a robust form of short-range secure communications in the far/mid infrared. In this paper, recent progress for the ‘THz Torch’ technology will be presented; the physical level integrity for multichannel proof-of-concept working demonstrators will be evaluated. By exploring a diverse range of methods, significant enhancements to both data rate and distance can be expected. Our thermodynamics-based approach represents a new paradigm in the sense that 19th century physics can be exploited with 20th century multiplexing concepts for low-cost 21st century ubiquitous security and defence applications in the thermal infrared range.