Terahertz multilevel phase Fresnel lenses fabricated by laser patterning of silicon

Minkevičius, Linas; Indrišiūnas, Simonas; Šniaukas, Ramūnas; Voisiat, Bogdan; Janonis, Vytautas; Tamošiūnas, V.; Kašalynas, Irmantas; Račiukaitis, Gediminas; Valušis, Gintaras

doi:10.1364/ol.42.001875

Cited by 57 publications

(37 citation statements)

References 27 publications

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“…Silicon is a highly suitable dielectric material for this purpose, as intrinsic silicon can have very low dissipation, and mature etching techniques are well-suited to produce a quasi-planar device with a finite number of levels. [98][99][100] These devices were significantly thinner than traditional lenses; the latter cited work had a device thickness of less than 500 µm. In another work, the negative shape of a stepped-lens structure was etched into silicon, and this was used in a stamp-like manner to imprint a stepped-phase focusing structure into a commonly used terahertz transparent polymer known as polypropylene.…”

Section: Wrapped Phasementioning

confidence: 99%

Tutorial: Terahertz beamforming, from concepts to realizations

et al. 2018

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The terahertz range possesses significant untapped potential for applications including high-volume wireless communications, noninvasive medical imaging, sensing, and safe security screening. However, due to the unique characteristics and constraints of terahertz waves, the vast majority of these applications are entirely dependent upon the availability of beam control techniques. Thus, the development of advanced terahertz-range beam control techniques yields a range of useful and unparalleled applications. This article provides an overview and tutorial on terahertz beam control. The underlying principles of wavefront engineering include array antenna theory and diffraction optics, which are drawn from the neighboring microwave and optical regimes, respectively. As both principles are applicable across the electromagnetic spectrum, they are reconciled in this overview. This provides a useful foundation for investigations into beam control in the terahertz range, which lies between microwaves and infrared light. Thereafter, noteworthy experimental demonstrations of beam control in the terahertz range are discussed, and these include geometric optics, phased array devices, leaky-wave antennas, reflectarrays, and transmitarrays. These techniques are compared and contrasted for their suitability in applications of terahertz waves.

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Section: Wrapped Phasementioning

confidence: 99%

Tutorial: Terahertz beamforming, from concepts to realizations

et al. 2018

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“…3. Peak signal of the THz detector dependence on the phase quantization number P. Theory is diffractive efficiency of the Si-lens depending on the number of phase quantization levels [5].…”

Section: Resultsmentioning

confidence: 99%

“…The group of the 17.5 mm diameter MPFL contained five samples with a different number of phase quantization levels for each focal distance allowing to figure out the optimal phase quantization level [5]. Radii and depths of the subzones were calculated according to the methodology presented in [7].…”

Section: Samples and Fabricationmentioning

confidence: 99%

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Compact diffractive optics for THz imaging

Minkevičius¹,

Indrišiūnas²,

Šniaukas³

et al. 2018

physics

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We present a compact diffractive silicon-based multilevel phase Fresnel lens (MPFL) with up to 50 mm in diameter and a numerical aperture up to 0.86 designed and fabricated for compact terahertz (THz) imaging systems. The laser direct writing technology based on a picosecond laser was used to fabricate diffractive optics on silicon with a different number of phase quantization levels P reaching an almost kinoform spherical surface needed for efficient THz beam focusing. Focusing performance was investigated by measuring Gaussian beam intensity distribution in the focal plane and along the optical axis of the lens. The beam waist and the focal depth for each MPFL were evaluated. The influence of the phase quantization number on the focused beam amplitude was estimated, and the power transmission efficiency reaching more than 90% was revealed. The THz imaging of less than 1 mm using a robust 50 mm diameter multilevel THz lens was achieved and demonstrated at 580 GHz frequency.

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“…The rate of removal of the laser‐induced excavated material also affects the feature profile. For example, the laser patterning technique has been employed in the fabrication of microfluidic channels, machining of optical waveguides in silica, and designing grating structure in fibers …”

Section: Lossless Dielectric Materialsmentioning

confidence: 99%

Dielectrics for Terahertz Metasurfaces: Material Selection and Fabrication Techniques

Ako

Upadhyay

Withayachumnankul

et al. 2019

Advanced Optical Materials

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on distinctive spectral signatures resulting from vibrational modes of covalent and hydrogen bonds. [8,[13][14][15][16] The focus on this spectrally rich region is attributed to the highly coherent and nonionizing nature of terahertz radiation, wide unallocated frequency bands, distinctive wavelengths, and their penetration through a significant depth of dielectric materials. Terahertz technology is geared toward realizing devices that can efficiently manipulate the phase, amplitude, and polarization of terahertz radiations for the above-mentioned myriad of applications.However, progress in this domain is held back by low terahertz power available from compact sources, high free-space path loss, and limited choice of materials that exhibit less absorption of terahertz waves. [17] Owing to the fact that natural materials demonstrate weak wave-matter interaction at terahertz frequencies, terahertz devices with engineered subwavelength resonant metallic inclusions on dielectric spacers have been realized, to interact strongly with an incident electromagnetic wave.In the past, metamaterials have been a promising route to building terahertz devices. These devices have in essence been engineered as 3D resonating elements that effectively manipulate both permittivity and permeability of an effective medium to couple to free space. The underlining disadvantage of these structures is the difficulty involved in the fabrication of 3D geometrical structures using standard semiconductor fabrication techniques. Standard fabrication techniques are generally amenable to 2D design with extrusion of these structures into thickness (the third, vertical dimension). Moreover, the choice and availability of dielectric materials and metals that provide sufficient interaction while retaining device efficiency has proved challenging. [13,[18][19][20] Recently, effective manipulation of electromagnetic wave has been widely demonstrated with 2D metasurfaces, which were originally employed as building blocks for 3D metamaterials. In these lower-dimension designs, effective manipulation of terahertz waves for various applications is achieved by carefully designing sub-wavelength resonant structures as is evident in published review articles. [21,22] Metasurfaces present high degree of compactness that enhances radiation efficiency. Additionally, the planar form factor of metasurfaces enables Manipulation of terahertz radiation opens new opportunities that underpin application areas in communication, security, material sensing, and characterization. Metasurfaces employed for terahertz manipulation of phase, amplitude, or polarization of terahertz waves have limitations in radiation efficiency which is attributed to losses in the materials constituting the devices. Metallic resonators-based terahertz devices suffer from high ohmic losses, while dielectric substrates and spacers with high relative permittivity and loss tangent also reduce bandwidth and efficiency. To overcome these issues, a proper choice of low loss and low relative permittivi...

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Terahertz multilevel phase Fresnel lenses fabricated by laser patterning of silicon

Cited by 57 publications

References 27 publications

Tutorial: Terahertz beamforming, from concepts to realizations

Tutorial: Terahertz beamforming, from concepts to realizations

Compact diffractive optics for THz imaging

Dielectrics for Terahertz Metasurfaces: Material Selection and Fabrication Techniques

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