Industrial Applications of Terahertz Sensing: State of Play

This paper presents a frequency-modulated optical signal generator in the THz band. The proposed method is based on a fast optical frequency sweep of a single narrowband laser diode used together with an optical fiber interferometer. The optical frequency sweep using a single laser diode is achieved by generating short current pulses with a high amplitude, which are driving the laser diode. Theoretical analysis showed that the modulation frequency could be changed by the optical path difference of the interferometer or optical frequency sweep rate of a laser diode. The efficiency of the optical signal generator with Michelson and Fabry–Perot interferometers is theoretically analyzed and experimentally evaluated for three different scenarios. Interferometers with different optical path differences and a fixed optical frequency sweep rate were used in the first scenario. Different optical frequency sweep rates and fixed optical path differences of the interferometers were used in the second scenario. This paper presents a method for optical chirp generation using a programmable current pulse waveform, which drives a laser diode to achieve nonlinear optical sweep with a fixed optical path difference of the interferometer. The experimental results showed that the proposed signals could be generated within a microwave (1–30 GHz) and THz band (0.1–0.3 THz).

Section: Introductionmentioning

confidence: 99%

THz Signal Generator Using a Single DFB Laser Diode and the Unbalanced Optical Fiber Interferometer

Pongrac

Đonlagić

Njegovec

et al. 2020

“…Coatings on metallic and dielectric substrates were shown to be in good agreement with the results obtained from the analysis of micrographic images. The thickness range was also impressive; a dielectric substrate of 3 mm with a thin coating of 10 µm was successfully measured; this area of application is described in more detail in [6].…”

Section: Automotive Paintmentioning

confidence: 99%

“…The average price of a basic THz system is around US$75k [6], it is still high compared to other established NDT techniques such as X-rays and ultrasound, which are a fraction of the cost [66]. The bulk of the system cost is for the ultrafast lasers used for THz generation.…”

Section: Multimode Laser Diodesmentioning

confidence: 99%

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Non-Contact, Non-Destructive Testing in Various Industrial Sectors with Terahertz Technology

Tao

Fitzgerald

Wallace

2020

178

In this article, we survey various non-contact, non-destructive testing methods by way of terahertz (THz) spectroscopy and imaging designed for use in various industrial sectors. A brief overview of the working principles of THz spectroscopy and imaging is provided, followed by a survey of selected applications from three industries—the building and construction industry, the energy and power industry, and the manufacturing industry. Material characterization, thickness measurement, and defect/corrosion assessment are demonstrated through the examples presented. The article concludes with a discussion of novel spectroscopy and imaging devices and techniques that are expected to accelerate industry adoption of THz systems.

“…On the other hand, they have the capability to see through dielectric materials that are opaque to infrared and visible light. These properties make them attractive for a variety of applications, including material identification [ 1 , 2 ], material characterization [ 3 , 4 ], and imaging [ 5 , 6 ]. However, while electronic terahertz systems already exhibit a high degree of integration [ 7 , 8 ], their instantaneous bandwidths have yet failed to exceed a few tens of GHz.…”

Section: Introductionmentioning

confidence: 99%

Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations

Kolpatzeck

Haring

et al. 2020

Photonic true time delay beam steering on the transmitter side of terahertz time-domain spectroscopy (THz TDS) systems requires many wideband variable optical delay elements and an array of coherently driven emitters operating over a huge bandwidth. We propose driving the THz TDS system with a monolithic mode-locked laser diode (MLLD). This allows us to use integrated optical ring resonators (ORRs) whose periodic group delay spectra are aligned with the spectrum of the MLLD as variable optical delay elements. We show by simulation that a tuning range equal to one round-trip time of the MLLD is sufficient for beam steering to any elevation angle and that the loss introduced by the ORR is less than 0.1 dB. We find that the free spectral ranges (FSRs) of the ORR and the MLLD need to be matched to 0.01 % so that the pulse is not significantly broadened by third-order dispersion. Furthermore, the MLLD needs to be frequency-stabilized to about 100 MHz to prevent significant phase errors in the terahertz signal. We compare different element distributions for the array and show that a distribution according to a Golomb ruler offers both reasonable directivity and no grating lobes from 50 GHz to 1 THz.