Low cost and long-focal-depth metallic axicon for terahertz frequencies based on parallel-plate-waveguides

 

A. I. Hernandez-Serrano,  Emma Pickwell-MacPherson

Photo of the triangular-shaped axicon and dimensions. (b) False color diagram representing the variation of the focal length as function of the frequency. (c) Experimental setup for the investigation of focal depth and cross-section properties of the metallic axicon. The blue regions denote THz light. The sample is represented by the orange line.

https://www.nature.com/articles/s41598-021-82503-x

In this work we demonstrate a triangular surface lens (axicon) operating at frequencies between 350 and 450 GHz using parallel-plate-waveguide technology. The proposed axicon offers longer focal depth characteristics compared to conventional plastic lenses, surpassing common TPX lenses by one order of magnitude. Additionally, due to the triangular surface of the axicon, this device is able to focus THz radiation onto smaller areas than TPX lenses, enhancing the resolution characteristics of THz imaging systems. The frequency range of operation of the proposed axicon can be easily tuned by changing the space between plates, making this approach a very attractive candidate for low-cost, robust and easy to assemble solutions for the next generation of active THz devices.

Abstract-Broadband amplitude, frequency, and polarization splitter for terahertz frequencies using parallel-plate waveguide technology

A. I. Hernandez-Serrano, Daniel M. Mittleman, and Emma Pickwell-MacPherson

 (a) Schematic diagram of the proposed demultiplexer. The incoming beam impinges on the back surface of the demultiplexer forming guided modes inside the structure. The exit beam is deflected by an angle 𝜃$\theta$ which depends on the frequency of the signal and on the dimensions of the structure. The inset shows a photograph of the device. (b)–(c) Finite-element simulation at 0.3 THz when the spacing between plates is 0.8 mm for the TE1${\mathrm{T}\mathrm{E}}_1$ and TEM guided-modes, respectively.

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-5-1208

In this Letter, we report a broadband frequency/polarization demultiplexer based on parallel-plate waveguides (PPWGs) for terahertz (THz) frequencies. The fabrication and experimental validation of this polarization sensitive demultiplexer is demonstrated for the range from 0.2 to 1 THz. Upgrading the demultiplexer by adding a second demultiplexer stage, a fifty-fifty amplitude splitter is also demonstrated in the same frequency range. The multiplexer is based on a stainless-steel traveling-wave antenna, exhibiting strong mechanical robustness. This unique device exhibits three splitting mechanisms in the same device: amplitude, polarization, and frequency splitting. This is a significant improvement for the next generation of THz passive components for communication purposes.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Guided-Mode Filters for Terahertz Frequencies Fabricated by 3D Printing

M. Ortiz-Martinez, E. Castro-Camus, A. I. Hernandez-Serrano,

https://link.springer.com/article/10.1007/s10762-019-00602-3

In this article, we present the design and characterization of the first 3D-printed guided-mode filter for terahertz frequencies. The device consist on a diffractive grating fabricated on top of a rectangular dielectric waveguide by 3D printing. Finite difference numerical modeling shows this device acts as a filter at a frequency that can be geometrically engineered and tuned around such frequency by varying the radiation incidence angle. Three devices were designed to operate at 200 GHz, 250 GHz, and 300 GHz; the devices were fabricated and successfully characterized using terahertz time-domain spectroscopy

Abstract-Design and fabrication of 3-D printed conductive polymer structures for THz polarization control

A. I. Hernandez-Serrano, Qiushuo Sun, Elizabeth G. Bishop, Elliott R. Griffiths, Christopher P. Purssell, Simon J. Leigh, J. Lloyd-Hughes, and Emma Pickwell-MacPherson

Fig. 1 (a) Diagram of the proposed polarizer; (b) Photograph of the printed devices; (c) and (d) show the refractive index and absorption coefficient of CPLA, respectively.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-8-11635

In this paper, we numerically and experimentally demonstrate the inverse polarization effect in three-dimensional (3-D) printed polarizers for the frequency range of 0.5 - 2.7 THz. The polarizers simply consist of 3-D printed strip lines of conductive polylactic acid (CPLA, Proto-Pasta) and do not require a substrate or any further metallic deposition. The experimental and numerical results show that the proposed structure acts as a broadband polarizer between the range of 0.3 THz to 2.7 THz, in which the inverse polarization effect is clearly seen for frequencies above 0.5 THz. In the inverse polarization effect, the transmission of the transverse electric (TE) component exceeds that of the TM component, in contrast to the behavior of a typical wire-grid polarizer. We show how the performance of the polarizers depends on the spacing and thickness of the CPLA structure; extinction ratios higher than 20 dB are achieved. This is the first report using CPLA to fabricate THz polarizers, demonstrating the potential of using conductive polymers to design THz components efficiently and robustly.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-q-plate for the Generation of Terahertz Cylindrical Vector Beams Fabricated by 3D Printing

• A. I. Hernandez-Serrano, 
• E. Castro-Camus, 
• D. Lopez-Mago

https://link.springer.com/article/10.1007%2Fs10762-017-0396-8

We present the design, fabrication, and characterization of a q-plate with continuous birefringence variation at terahertz frequencies. This q-plate was fabricated by three-dimensional printing and is a simple solution for the generation of cylindrical vector beams. This device can find a number of applications in future terahertz technologies such as telecommunications.

Abstract-Terahertz imaging for early screening of diabetic foot syndrome: A proof of concept

• G. G. Hernandez-Cardoso
• , S. C. Rojas-Landeros
• , M. Alfaro-Gomez
• , A. I. Hernandez-Serrano
• , I. Salas-Gutierrez
• , E. Lemus-Bedolla
• , A. R. Castillo-Guzman
• , H. L. Lopez-Lemus
•  & E. Castro-Camus

• http://www.nature.com/articles/srep42124 

Most people with diabetes suffer some deterioration of the feet. Diabetic foot syndrome causes ulceration in about 15% of cases and such deterioration leads to amputation in about 2.5% of diabetic patients, diminishing their quality of life and generating extraordinary costs for patients and public health systems. Currently, there is no objective method for the detection of diabetic foot syndrome in its early stages. We propose terahertz imaging as a method for the evaluation of such deterioration. This screening method could aid the prevention and medical treatment of this condition in the future.

Abstract-Quasi-Wollaston-Prism for Terahertz Frequencies Fabricated by 3D Printing

• A. I. Hernandez-Serrano, 
• E. Castro-Camus
• • 
    

http://link.springer.com/article/10.1007/s10762-016-0350-1

In this letter, we present the design, fabrication, and characterization of a quasi-Wollaston prism for terahertz frequencies based on form birefringence. The prism uses the birefringence induced in a sub-wavelength layered plastic-air structure that produces refraction in different directions for different polarizations. The component was simulated using the finite-difference-time-domain method, fabricated by 3D printing and subsequently tested by terahertz time-domain spectroscopy showing a polarization separation around of 23° for frequencies below 400 GHz, exhibiting cross polarization power extinction ratios better than 1.6 × 10−3 at 200 GHz.

Abstract-Low-cost 3D printed GRIN lens for terahertz applications

A. I. Hernandez-Serrano, M Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/abstract.cfm?uri=Sensors-2016-SeTu3E.4

We used 3D printing as a new technique to make gradient-refractive-index (GRIN) lenses for terahertz applications. This new low-cost lenses are demonstrated to work within the diffraction limit below 800 GHz.

© 2016 OSA

PDF Article

Abstract-Monte Carlo simulation of near-field terahertz emission from semiconductors

S. C. Corzo-Garcia, A. I. Hernandez-Serrano, E. Castro-Camus, and O. Mitrofanov

Phys. Rev. B 94, 045301 – Published 1 July 2016

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.045301

We simulated the carrier dynamics in InGaAs after ultrafast photoexcitation. By using a finite-difference time-domain approach we were able to analyze the near terahertz field emission caused by the motion of such carriers. We found that both the current parallel and normal to the interface take a relevant role in the terahertz emission. We also found that the ballistic motion of the carriers after photoexcitation dominates the emission rather than diffusion.

• 
• 
• 
• 
• 

Abstract-Fabrication of gradient-refractive-index lenses for terahertz applications by three-dimensional printing

A. I. Hernandez-Serrano, M. Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-928

In this article we present the design, fabrication, and characterization of gradient-refractive-index lenses for terahertz (THz) applications. The fabrication was performed by three-dimensional printing. These new low-cost lenses were tested using THz time-domain spectroscopy and imaging in order to measure their optical properties. The results show a focusing capacity within the diffraction limit for frequencies below 700 GHz.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Quality control of leather by terahertz time-domain spectroscopy

Quality control of leather by terahertz time-domain spectroscopy

A. I. Hernandez-Serrano, S. C. Corzo-Garcia, E. Garcia-Sanchez, M. Alfaro, and E. Castro-Camus  »View Author Affiliations

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-33-7872

We use terahertz time-domain spectroscopy, combined with effective-medium theory, to measure the moisture content and thickness of leather simultaneously. These results demonstrate that this method could become a standard quality control test for the industrial tanning process.

© 2014 Optical Society of America