Abstract-Fibonacci terahertz imaging by silicon diffractive optics

D. Jokubauskis, L. Minkevičius, M. Karaliūnas, S. Indrišiūnas, I. Kašalynas, G. Račiukaitis, and G. Valušis

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-12-2795

Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing a silicon diffractive zone plate in continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6 THz frequency with the spatial resolution of wavelength. Multifocus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 to 0.6 THz. Good agreement between experimental results and simulation data is revealed.

© 2018 Optical Society of America

Abstract-Terahertz multilevel phase Fresnel lenses fabricated by laser patterning of silicon

L. Minkevičius, S. Indrišiūnas, R. Šniaukas, B. Voisiat, V. Janonis, V. Tamošiūnas, I. Kašalynas, G. Račiukaitis, and G. Valušis

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-10-1875

Multilevel phase Fresnel lenses (MPFLs) with a high numerical aperture for 0.58 THz frequencies were developed. The components based on a monocrystalline silicon wafer are prepared by patterning by a high-speed industrial-scale laser direct writing (LDW) system. Two consistent series of the terahertz-MPFLs with phase quantization levels varying between 2 and the continuous kinoform shape for the focal lengths of 5 and 10 mm were produced employing inherent flexibility of the LDW fabrication process. The focusing performance was studied at the optimal 0.58 THz frequency using a Gaussian beam profile and scanning 2D intensity distribution with a terahertz detector along the optical axis. The efficiency of the terahertz-MPFL was found to be dependent of the number of subzones. The position and orientation angles of the patterned plane of the silicon wafer were considered to reduce the effect of standing waves formation in the experiment.

© 2017 Optical Society of America

Abstract-Focusing Performance of Terahertz Zone Plates with Integrated Cross-shape Apertures

• L. Minkevičius, 
• K. Madeikis, 
• B. Voisiat, 
• I. Kašalynas, 
• R. Venckevičius, 
• G. Račiukaitis, 
• V. Tamošiūnas, 
• G. Valušis

http://link.springer.com/article/10.1007/s10762-014-0086-8

Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems [1–3] remains as one of sensitive topics in THz photonics. As a rule, a particular attention is attributed to the development of compact THz sources and detectors, however, compact optic components – such as focusing lenses, mirrors, beam splitters, etc – as well plays important role in reducing size of the systems. Preferences here are usually given to inexpensive and relatively simple technology-based approaches, for instance, binary lenses [4], focusing elements of a combined design structures [5] or narrow-band laser-ablated filters [6]. These solutions can be found well-suited in THz heterodyne [7] and spectroscopic imaging [8] when only several specific spectral lines are used to record image, but still enabling to indentify an object under test. Very recently, terahertz zone plate with integrated resonant filters (TZP) was proposed and experimentally demonstrated for efficient radia.

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.