Abstract-Compact solutions for spectroscopic solid-state-based terahertz imaging systems

Rimvydas Venckevičius,  Linas Minkevičius,  Antanas Reklaitis, Vincas Tamošiūnas,  Irmantas Kašalyns,  Domas Jokubauskis,  Dalius Seliuta,  Bogdan Voisiat,  Gediminas Račiukaitis,  Gintaras Valušis,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10383/103830S/Compact-solutions-for-spectroscopic-solid-state-based-terahertz-imaging-systems/10.1117/12.2273353.short

Convenience in use of room-temperature terahertz (THz) imaging systems, reduction of their dimensions and presence of on-chip solutions remains one of prime interests for direct implementation aims. Solid-state-based solutions in miniaturization of spectroscopic THz imaging systems including novel semiconductor nanostructures bias-free emitters, diffractive THz optics components and their on-chip integration with THz detectors are discussed. In particular, pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1−xAs heterostructure was studied and it is demonstrated that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Diffractive optics elements – Fresnel zone plates –with integrated band-pass filters were simulated employing Finite-difference time domain method. Structures were fabricated using the laser direct writing and investigated using electronic THz sources and an optically pumped terahertz laser. Advantages of on-chip integration of diffractive optics and bow-tie-shaped InGaAs-based terahertz detectors are revealed via detection enhancement. Bow-tie diodes properties in frequency scale and detection sensitivity are considered and compared for different materials. Homodyne detection and imaging of low-absorbing objects at 0.6 THz are demonstrated and discussed.

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Abstract-Spectroscopic Terahertz Imaging at Room Temperature Employing Microbolometer Terahertz Sensors and Its Application to the Study of Carcinoma Tissues

Irmantas Kašalynas 1,* , Rimvydas Venckevičius 1

, Linas Minkevičius 1

, Aleksander Sešek 2

,Faustino Wahaia 3

, Vincas Tamošiūnas 1

, Bogdan Voisiat 1

, Dalius Seliuta 1

, Gintaras Valušis 1

,Andrej Švigelj 2

 and Janez Trontelj 2

1 Department of Optoelectronics, Center for Physical Sciences and Technology, Savanoriu Ave. 231, Vilnius 02300, Lithuania2 Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, Ljubljana 1000, Slovenia3 Instituto de Investigacao e Inovacao em Saudeand, Instituto de Engenharia Biomedica, University of Porto, Rua do Campo Alegre, 823, Porto 4150-180, Portugal

* Author to whom correspondence should be addressed.

Academic Editors: Dragan Indjin and Vincenzo Spagnolo

Received: 6 February 2016 / Revised: 4 March 2016 / Accepted: 18 March 2016 / Published: 25 March 2016

http://www.mdpi.com/1424-8220/16/4/432

A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to be a very sensitive frequency selective sensor which was used to develop a compact all-electronic system for multispectral THz measurements. This system was successfully applied for principal components analysis of optically opaque packed samples. A thin diffractive lens with a numerical aperture of 0.62 was proposed for the reduction of system dimensions. The THz imaging system enhanced with novel optics was used to image for the first time non-neoplastic and neoplastic human colon tissues with close to wavelength-limited spatial resolution at 584 GHz frequency. The results demonstrated the new potential of compact RT THz imaging systems in the fields of spectroscopic analysis of materials and medical diagnostics.

Abstract-On-chip integration solutions of compact optics and detectors in room-temperature terahertz imaging systems

 Linas Minkevičius; Vincas Tamošiūnas; Irmantas Kašalynas; Rimvydas Venckevičius; Karolis Madeikis; Bogdan Voisiat; Dalius Seliuta; Gediminas Račiukaitis; Gintaras Valušis

http://spie.org/Publications/Proceedings/Paper/10.1117/12.2187921

On-chip integrated solutions employing properties of Fresnel zone plates with integrated band-pass filters for the room temperature terahertz imaging systems are discussed. Finite-difference time-domain simulations were used to predict properties of conventional zone plates and ones with resonant filter areas as flat optics components. They are produced employing the laser direct writing and characterized by electronic THz sources and an optically pumped terahertz laser. It was shown that more than one order of magnitude detection enhancement can be observed of bow-tie-shaped InGaAs-based terahertz detectors by on-chip incorporation of the secondary diffractive optics.

Abstract-Exploration of Terahertz Imaging with Silicon MOSFETs

• Alvydas Lisauskas, 
• Maris Bauer, 
• Sebastian Boppel, 
• Martin Mundt, 
• Bassam Khamaisi, 
• Eran Socher,
• Rimvydas Venckevičius, 
• Linas Minkevičius, 
• Irmantas Kašalynas, 
• Dalius Seliuta, 
• Gintaras Valušis, 
• Viktor Krozer, 
• Hartmut G. Roskos, 

• http://link.springer.com/article/10.1007%2Fs10762-013-0047-7

We summarize three lines of development and investigation of foundry-processed patch-antenna-coupled Si MOSFETs as detectors of THz radiation: (i) Exploiting the pinciple of plasma-waved-based mixing in the two-dimensional electron gas of the transistors’ channels, we demonstrate efficient detection at frequencies as high as 9 THz, much above the transit-time-limited cut-off frequencies of the devices (tens of GHz). Real-time imaging at 600 GHz with a 12 × 12 detector array is explored. (ii) Given the limited THz power usually available for applications, we explore imaging with enhanced sensitivity in heterodyne mode. We show that real-time operation of a 100 × 100-pixel heterodyne camera should be possible at 600 GHz with a better dynamic range (30 dB) than for direct power detection (20 dB), even if only a quarter-milliwatt of local-oscillator power, distributed radiatively over all detector pixels, is available. (iii) Finally, we present an all-electronic raster-scan imaging system for 220 GHz entirely based on CMOS devices, combining the CMOS detectors with an emitter circuit implemented in a 90-nm CMOS process and delivering radiation with a power on the 100- μW scale. Considering progress in the field, we anticipate that the emitter concept of oscillator-based power generation with on-chip frequency multiplication will carry well into the sub-millimeter-wave regime.