optimization of modulation properties of terahertz metamaterial by tuning fabry–pérot resonances

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IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY 1

Optimization of Modulation Properties of TerahertzMetamaterial by Tuning Fabry–Pérot ResonancesDalius Seliuta, Member, IEEE, Dovilė Zimkaitė, Gediminas Šlekas, Andžej Urbanovič, Jan Devenson, and

Žilvinas Kancleris, Member, IEEE

Abstract—In this work, we investigate the transmission proper-ties of planar arrays of split-ring resonators formed on the surfaceof a dielectric plate. The modulation concept is demonstrated byusing several metamaterial structures with a different effective ca-pacitance of the split gap, thus imitating a metamaterial of tunablefrequency. The proposed modulation scheme can be employed inthe fabrication of a fast narrow-band terahertz modulator. The in-fluence of Fabry–Pérot resonances in the dielectric substrate on theparameters of the possible metamaterial-based modulator is ana-lyzed in the terahertz region. Our results demonstrate that tuningthe dielectric plate parameters allows for the optimization of themodulator performance. The presented modulation scheme basedon frequency-tunablemetamaterial offers a highmodulation depth(95% at 425 GHz) with the resonant frequency tuning as small as

%. Measurement results are found in agreement with calcu-lations.

Index Terms—Metamaterial (MM), split ring resonator (SRR),Terahertz (THz), modulation, Fabry–Pérot resonance (FPR).

I. INTRODUCTION

M ETAMATERIALS (MM) exhibit numerous phenomenathat cannot be observed in natural materials. MM are

geometrically scalable, which translates their operability overmany decades of frequency including also the “THz gap” andmakes them useful for potential applications of THz radiation.However, to achieve full potential of the unique propertiesof MM, the ability to control them in real time is required[1]. Intensity modulator is a key component for a variety ofapplications such as optical communication, high resolutionspectroscopy, sensing, and other schemes where time-gating isneeded. For instance, the short-range wireless THz communica-tion systems or ultrafast THz interconnects [2] require switchesand modulators. Modulation of THz radiation with appliedvoltage was demonstrated by using a hybrid structure con-sisting of a planar MM array with integrated Schottky diodes[3]. An optical approach has also been demonstrated where the

Manuscript received August 03, 2014; revised September 16, 2014, October22, 2014; accepted October 24, 2014. This work was supported by the ResearchCouncil of Lithuania under Grant MIP-059/2014.D. Seliuta is with the Center for Physical Sciences and Technology, LT-01108

Vilnius, Lithuania, and also with Vilnius Gediminas Technical University,LT-03227 Vilnius, Lithuania (e-mail: [email protected]).D. Zimkaitė, G. Šlekas, A. Urbanovič, J. Devenson, and Ž. Kancleris are with

the Center for Physical Sciences and Technology, LT-01108 Vilnius, LithuaniaColor versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TTHZ.2014.2367240

photoexcitation of free charge carriers in the semiconductingsubstrate shunts the MM resonance [4]. The advantage of theoptical approach is the possibility of extremely fast switchingby using femtosecond optical pulses.Alternatively, THz waves can be controlled with frequency-

agile MM. To achieve frequency tunability, a semiconductor isincorporated into MM resonators, allowing frequency tuning oftheMM resonance by photoexcitation [5]. At lower frequencies,effective MM frequency sweeping was demonstrated by addingthe capacitance of the varicap diode to the distributed capaci-tance of the split ring resonators (SRRs) [6]. Frequency-agiledevices can serve as amplitude modulators in the case of thenarrow-band THz source [7]. This would allow, for example, forthe amplitude modulation of narrow-band devices, such as THzquantum cascade lasers, often used as effective THz sources inspectroscopy and imaging.Typically, planar MM resonators are deposited on a par-

allel dielectric slabs with finite thickness. Various methodsare applied to eliminate the effects of the multiple reflections[Fabry–Pérot resonances (FPR)] within the substrate. In THztime-domain spectroscopy, the time-domain data are normallytemporally windowed. Furthermore, a thin conducting layeron the surface of a dielectric plate can suppress FPR in THzrange [8]; however, this method is related to the excess energydissipation and increased insertion loss. In the case whenFourier-transform infrared spectroscopy is used, FPR fringescan be eliminated by passing the transmission spectra througha digital notch filter [9]. The effect of FPR fringes can be min-imized by using thin semiconductor substrates. This approachallows for shifting FPR away from the designed frequenciesof MM [10]; however, fabrication and handling of a very thinsubstrate is impractical.On the other hand, FPR have demonstrated the ability to

enhance plasmon resonances in plasmonic band-gap structures[11] in THz region. Multiple reflections in semiconductorplate between two metasurfaces serving as a high-qualityFabry–Pérot cavity [12] or in a cavity of the photonic crystal[13] result in remarkably increased efficiency of the opticallycontrolled THz modulator.If the frequency-tunable MM structure is designed for the dy-

namic modulation of a narrow-band source, FPR influence themodulator performance considerably. In this work we performa detailed investigation of the transmission properties of MMstructures with different resonant frequencies to imitate MM oftunable frequency. In particular, the multiple reflections insidethe parallel dielectric substrate are taken into account. Our re-sults indicate that FPR can remarkably improve the performance

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2 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY

Fig. 1. Geometry of SRRs of the investigated structures. m,m, m. The capacitive gap width: (a) m. (b) m;

(c) m.

of frequency-tunable MM applied for narrow-band THz modu-lation. We demonstrate that the parameters of such a modulatorcan be optimized by the proper adjustment of MM propertiesand parameters of the dielectric substrate.

II. EXPERIMENTAL DETAILS

MM devices used in this work are based on a planar arrayof squared SRRs. The geometry and dimensions of SRRs areshown in Fig. 1: the side length of the square is 40 m, the pe-riodicity along x and y directions is 54 m, and the width of theconducting stripes is 4 m. To imitate the frequency tuning ofthe intended frequency-agile MM we fabricated structures S1,S2, and S3. S1 is characterized with maximum effective capaci-tance ( m, m), S2—has intermediate effectivecapacitance ( m) and S3—has minimal effective capac-itance ( m). Each sample was realized in 37 37 arraywith dimensions approximately 2 mm 2 mm.500 m thick plate of semi-insulating GaAs was used as

a dielectric substrate. The planar array of SRRs is fabricatedusing conventional photolithography and thermal deposition ofa 10-nm-thick adhesion layer of titanium on the GaAs substrate,followed by 190 nm of gold. A terahertz time-domain spec-trometer was used to characterize the performance of the MMstructures. In the experiment, a polyethylene lens focused thelinearly polarized THz beam onto the MM sample to a diameterof about 2 mm, and another polyethylene lens recollimatedthe transmitted THz beam. The experiments were performedat room temperature. In all experiments the THz beam wasnormally incident on a surface of SRRs with the THz magneticfield lying completely in plane of SRRs. Therefore, oscillatingcurrents are driven only by the electric field of THz radiation.Polarization of THz electric field was perpendicular to the splitgaps as indicated in Fig. 1. All spectra were normalized to thebeam intensity collected without a sample in place.Different effective capacitances of the split gaps result in dif-

ferent resonant frequencies of the investigated structures. In thisresearch, three different structures are used to imitate the per-formance of a dynamically tunable MM filter based on a planararray of SRRs capacitance of which is modulated optically [5]or electrically [6]. Thus, each structure represents a particularstate of a filter with dynamically modulated central frequency.

III. MODELING

The transmission characteristics of planar SRR arrays werecalculated using finite-difference time-domain (FDTD)method.Planar arrays have translational symmetry which allows the unitcell approach reducing the modelling space to a single SRR el-ement. Modeling of a single cell with periodic boundary condi-

tions corresponds to the infinite array of SRRs. A differentiatedGaussian pulse is applied as a current source to excite a planewave with a wide spectrum (up to 3 THz). Uniaxial perfectlymatched layers were used to truncate the computational domainand introduce absorption of the propagating pulse without re-flections [14]. The polarization of the electromagnetic wave ischosen so that the electric field is perpendicular to the capaci-tive gap of SRRs (Fig. 1). For modelling of the metal stripes weused the Maloney–Smith sub-cell technique [15] usually usedfor modeling of a thin conductive sheet. In this way, the in-fluence of the thin conductive layer on the propagation of theelectromagnetic wave was calculated using a discretization stepsize much larger than the thickness of the SRR stripes leadingto considerable savings of computer resources.The following parameters were used for the calculations:

thickness of the stripes 0.2 m, dielectric constant of GaAs. Specific conductivity of the metal stripes 3 10

S/cm—was measured experimentally in DC field using Hall-bargeometry and four-probe method. Obtained from FDTD simu-lation the incident and transmitted through the MM structure,pulses were transformed into the frequency domain usingFourier transform. The incident and transmitted signal spectrawere compared to determine the transmission properties of theSRR arrays.

IV. RESULTS AND DISCUSSION

Inductive–capacitive (LC) resonance [3], [16] correspondingto the circular current mode occurring in S1, S2 and S3 lies in theregion 360–460 GHz, whereas the higher-frequency quadrupoleresonance [17] is located within 1100–1300 GHz range. In thisresearch, we concentrate on LC resonance which is mostly suit-able for filter or modulator applications because of the lowerdamping and higher -factor [17], [18]. Measured transmit-tance spectra for MM structures at LC resonance are shownin Fig. 2. In Fig. 2(a), FPR were eliminated by temporal win-dowing of the transmission signal prior to Fourier transforma-tion. The interferogram is truncated just before the arrival ofthe first reflected pulse (see insets in Fig. 2). Such a technique isoften used in THz spectroscopy to highlight spectral propertiesof a MM structure and to determine its resonant frequency [5],[19]. Transmittance minimum for a particular structure in Fig. 2can be attributed to the corresponding LC resonance of SRRs.It is seen that the increase of the split gap capacitance leads todecrease of the resonance frequency.For further analysis of a MM THz modulator we consider

monochromatic radiation normally incident on MM surfacesupposing that SRR effective capacitance can be dynamicaltuned so that MM transmittance spectrum is gradually changedstarting with the spectrum of structure S1 and ending at thespectrum of structure S3 with the intermediate state corre-sponding to the spectrum of structure S2. The described abovemodification further is referred to as transition .To characterize the modulator performance, vertical spacingbetween the transmission curves at frequency of interest isanalyzed. Obviously, frequencies of LC resonances 360,425, and 460 GHz—corresponding to structures S1, S2, andS3 [see Fig. 2(a)] are preferred. The shift of the resonancefrequency between structures S1 and S3 is roughly 20%. Asimilar dynamic frequency change was recently demonstrated


SELIUTA et al.: OPTIMIZATION OF MODULATION PROPERTIES OF THz METAMATERIAL 3

Fig. 2. Experimentally measured transmittance of MM structures obtainedfrom (a) the truncated interferogram and from (b) the interferogram accountingmultiple reflections inside of GaAs substrate of thickness 500 m. Theinterferograms are shown in the insets.

by photodoping of the capacitor plates [5]. A similar frequencytuning with nearly constant transmittance at transmissionminimum was achieved by using mode switching in SRRsof complex geometry [20]. The following considerations arebased on optically controlled planar MM with tunable resonantfrequency used for narrow band modulation in THz range.We shall characterize the modulator performance with the

modulation depth parameter which is commonly defined as rel-ative intensity deviation from average intensity level [21]:

(1)

where and are the modulator transmittances corre-sponding to “on” and “off” states.One can obtain from Fig. 2(a) that in the case when varia-

tion of the split gap capacitance results in transitionthe modulation depth at 360 GHz equals to 0.42. At 425 GHztransition results in modulation depth 0.85 and at 460GHz transition yields the modulation depth 0.82.The truncation of the transmitted interferogram cannot be

applied when monochromatic or narrow-band radiation hasto be modulated with a MM structure. Therefore, for prac-tical modulator design transmission including FPR must beconsidered. The multiple reflections inside the semiconductorsubstrate modulate sample transmission spectra with periodic

Fig. 3. Transmittance of structure S1. Symbols correspond to measurement re-sults, line demonstrates the modelling results. Substrate thickness 500 m.

high-transmission peaks (Fig. 2(b)). By comparing spectrain Figs. 2(a) and (b) one can see that FPR practically do notinfluence frequency of the transmission minima correspondingto LC resonances in MM structures. Also, transmittance inthe transmission minima is only moderately changed, whereastransmission away from LC resonances is strongly affected bythe reflections inside the substrate.The presence of FPR results in reduction of the modulation

depth corresponding to transition to 0.77 at frequency460 GHz. On the other hand, transition , characterizedby the smaller change of capacitance, gives modulation depth0.95 at frequency 425 GHz and modulation depth at 360 GHzfor transition is practically unchanged . Con-sequently, the location of FPR with respect to MM resonancesis essential for the optimization of MM structures used for themodulation of narrow-band THz signal. On the other hand, themodulator presented in this paper offers the particular advantageof high modulation depth (95% at 425 GHz) with the resonantfrequency tuning as small as 15% (transition ).Modelling and experimental results for structure S1 deposited

on 500 m thick GaAs substrate are shown in Fig. 3. The agree-ment between the theory and experimental results is fairly good.The calculations result in a higher Q-factor of MM LC reso-nance corresponding to smaller bandwidth and deeper transmis-sion minimum [22], practically reaching zero at a resonant fre-quency. It might be related to imperfections of the fabricatedSRRs. A similar agreement between the theory and experimentwas found for the other MM structures.For the practical tuning of FPR transmission pattern we an-

alyze the MM structures deposited on GaAs substrates with adifferent thickness. Modelling was performed using the FDTDmethod described above. Transmittance spectra were calculatedfor structures S1 and S3. Calculated spectra show that thinningof GaAs plate results in a shift of FPR to higher frequenciesand an increased separation between adjacent maxima/minima,whereas location of MM LC resonance in frequency axis is in-dependent of the substrate thickness within the thickness range200–520 m.To elucidate the influence of FPR on the MM modulator per-

formance transmission data at frequencies 360 and 460 GHzfor structures S1 and S3 were retrieved and plotted in Fig. 4as functions of the substrate thickness. All curves in Fig. 4 areperiodic with period ( is the radiation wavelength in



Fig. 4. Calculated dependence of S1 and S3 transmittance (symbols) at 360GHz (a) and at 460 GHz (b) on GaAs substrate thickness. Lines are fits to (2)and (4).

free space) which is characteristic for FPR in GaAs plate of thesame thickness at a given frequency. Furthermore, one shouldnote that a characteristic phase shift is observed between the os-cillating curves corresponding to structures S1 and S3 [Fig. 4(a)and (b)].To describe the transmission oscillations related with FPR

we apply the formula which includes different reflectances andphase shifts at both sides of a dielectric slab [23]. For normallyincident radiation transmittance of a MM sample can be given

(2)

where is the transmittance at FPR maximum, the coefficientof finesse can be expressed as

(3)

and the phase difference

(4)

Here and are the reflection coefficients from the frontand rear interfaces, is the substrate thickness, is the radiationwavelength in free space, and is the phase shift on reflectionfrom the front interface covered with SRRs. We assume thatlosses in SI-GaAs are negligible; therefore, the phase shift atthe rear interface GaAs-air equals to zero.

Fig. 5. Dependence of the (a) reflection amplitude and (b) phase at MM inter-face on frequency for structures S1 and S3. Horizontal line in (a) shows reflec-tion amplitude at interface GaAs-air.

Fig. 6. Modulation depth of a MM modulator corresponding to transitionat frequencies 360 and 460 GHz.

We apply (2), (3), and (4) for fitting the calculated depen-dences of the transmittance on thickness as shown in Fig. 4with solid lines. Similar dependencies were plotted for variousfrequencies in the range 100–700 GHz. Assuming that the re-flection amplitude at the rear interface GaAs-air is constant,the reflection amplitude and phase shift at the front in-terface covered with SRRs were determined at every frequencyvalue. Results are shown in Fig. 5. It can be seen that reflectionamplitudes are maximal at resonance frequencies. At lower fre-quencies as well as at higher frequencies, the influence of SRRson reflection amplitude is negligible and approaches to .Also, in some frequency range the reflection amplitude islower than that at the interface GaAs-air. At resonant frequen-cies the phase shifts for both structures are equal to 180 . Thedifference between the phase shifts in structures S1 and S3 isaround 80 at 360 GHz and nearly 180 at 460 GHz as it is seenin Fig. 5. Alternatively, the complex reflectivity including am-plitude and phase at substrate-MM interface can be calculateddirectly by numerical simulations [24].Considering the difference between the transmittance curves

in Fig. 4 we can find the optimal substrate thickness for a MMmodulator corresponding to transition . The relationbetween the modulation depth and the substrate thickness atfrequencies 360 and 460 GHz (Fig. 6) demonstrate oscillations



Fig. 7. Measured transmittance of MM structures at 360 GHz versus substratethickness.

with a period correspondingly equal to that of curves presentedin Fig. 4(a) and (b).The variation of the sample transmission with substrate

thickness was measured experimentally by thinning the GaAssubstrates. GaAs plates were thinned chemically in a polishingHNO :H O (3:2) solution at etching rate 8.5 m/min. Trans-mission measurements were performed at a substrate thickness500, 470, 440, 410, and 380 m. Transmission data at 360 GHzwere retrieved and plotted versus substrate thickness (Fig. 7).In agreement with the modelling (Fig. 4) transmission maximafor all three structures are observed corresponding roughly toone half of the oscillation period.The measured modulation depth corresponding to transition

at 360 and 460 GHz is presented in Fig. 8. It is seenthat modulation depth at maximum is significantly higher thanthat in the case when FPR are eliminated (indicated with dashedline). The measured modulation depth (Fig. 8) is in qualitativeagreement with the calculation results presented in Fig. 6. Themanufactured MM structures had a lower -factor of LC reso-nance resulting in lower radiation extinction at the transmissionminimum. For this reason the experimentally observed modula-tion depth is smaller. Nevertheless, our results demonstrate thatthe modulation depth of the MMmodulator can be optimized bytuning the FPR. It can be easily done by a wet etching of semi-conductor substrate by several tens of micrometers. Polishingetchant solutions allow for keeping the rear side of a substraterelatively flat; therefore, scattering losses in THz region are neg-ligible. On the other hand, control of substrate thickness is morepractical than other procedures required to eliminate FPR suchas excessive thinning of the substrate, polishing a wedged plate,or the deposition of antireflection coatings.As discussed above, SRRs on a surface of a dielectric plate

introduce the phase shift for the reflected beam; moreover, thereflectance phase is frequency dependent [Fig. 5(b)]. The phaseshift on reflection is of particular importance for MMmodulatoroptimization. In the case when the transmittance oscillationswith respect to the substrate thickness are characterized withthe same peak to valley ratio [Fig. 4(a)], a zero phase shift be-tween the oscillating curves would lead to the modulation depthindependent of the substrate thickness. Only the phase differ-ence between the oscillating curves caused by different phaseshifts on reflection would make optimization of the modulationdepth possible. Obviously, the variation of the modulation depth

Fig. 8. Modulation depth of MM modulator corresponding to transition be-tween structures S1 and S3 versus GaAs substrate thickness at frequencies 360and 460 GHz. Horizontal lines—modulation depth in the absence of FPR.

Fig. 9. Modulation depth of MM modulator corresponding to transition be-tween structures S1 and S3 at substrate thickness 440 m versus frequency.Dashed lines mark resonant frequencies of structures S1 and S3.

with the substrate thickness is largest when the transmission os-cillations between the two relevant structures are in oppositephases [Fig. 4(b)]. This happens when the phase shifts forthe two relevant structures differ by 180 . As one can see fromFig. 5(b), the phase difference between S1 and S3 is close to180 at 460 GHz.The position of FPR transmission peaks is essential for the

practical design of MM modulators. The optimal substratethickness for the modulation of THz waves at 360 GHz iswithin the range 410–440 m and near 440 m for modulationat 460 GHz. For more precise optimization additional thicknesspoints (decrease of the thinning step) are required. One shouldnote that calculations yield a low transmission in the “off”state ( and, consequently, high extinction ratio atMM resonance practically at any value of substrate thickness.Therefore, modulation depth according to (1) is always close tounity and optimization of the modulation depth by tuning thesubstrate thickness is limited (see Fig. 6). However, in practicethe extinction ratio is lower resulting in lower modulationdepth. On the other hand, this allows one to optimize themodulator performance in a wider range as it is seen in Fig. 8.The modulation depth versus frequency is shown in Fig. 9 atsubstrate thickness 440 m corresponding to maximum mod-ulation depth. Two modulation bands correspond to resonant



frequencies of structures S1 and S3. The modulation bandwidthis 30–50 GHz.Transmittance oscillations shown in (a) and (b) parts of Fig. 4

for two relevant states of the modulator demonstrate a similaroscillation amplitude in the logarithmic scale indicating thatthe relative variation of the transmittance with plate thicknessweakly depends on whether the frequency under considerationis resonant for a particular MM structure or not. The optimiza-tion of the modulation depth is determined mainly by the phaseshift between the oscillating curves presented in Fig. 4. There-fore, by tuning FPR peak to MM resonance one can achieve themaximum modulation depth. In absolute scale, transmittanceoscillations caused by FPR are strongly dependent on MM res-onant conditions. By changing , the transmittance variation atMM resonance (“off” state) is much smaller than that away fromthe resonance (“on” state). This gives an additional high-trans-mission in the “on” state and, consequently low insertion loss ofa MMmodulator. Moreover, as it can be seen in Fig. 9, the mod-ulation mechanism is fairly broadband which means that thesedevices can still operate even if the resonant frequency is notperfectly matched to the source emission spectrum.

V. CONCLUSION

The effect of FPR on transmission of a planar array of thesplit-ring resonators is analyzed experimentally and numeri-cally. The application of a tunable MM filter for the modulationof narrow-band terahertz waves is simulated. It was found thatthe phase shift on reflection at the surface covered with SRRsallows for the optimization of the modulation depth parameterby tuning the thickness of a dielectric plate. The tuning of anFPR high-transmission peak at resonant frequency of a MMstructure allows one to achieve maximum modulation depthand minimal insertion loss of a MM modulator.

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Dalius Seliuta (M’13) was born in Vilnius,Lithuania. He received the physics diploma degreefrom Vilnius University in 1991, and the Ph.D.degree from the Semiconductor Physics Institute,Vilnius, in 1998.He was a visiting researcher in the Royal Institute

of Technology, Stockholm, Sweden, in 1996, and inWeizmann Institute of Science, Rehovot, Israel, in2000. He is currently a Senior Research Associatewith the Optoelectronics Department, Center forPhysical Sciences and Technology, Vilnius. His

research activities are mainly dedicated to the tunable metamaterials in tera-hertz range. His fields of research also concern the development of advancedterahertz detectors and detector arrays. Since 2004, he is an Associate Professorwith the Electronics Department, Vilnius Gediminas’ Technical University. Heis the coauthor of more than 100 scientific publications.

Dovilė Zimkaitė received the B.S. degree in physicsfrom Vilnius University, Lithuania, in 2013. Since2013, she is working toward the master’s degreeunder the Materials and Technology of Optoelec-tronics master programme in Vilnius University, andis currently an exchange student at Universita deglistudi di Padova, Italy.From 2012 to 2014, she was an engineer with the

Terahertz Photonics Laboratory, Center for PhysicalSciences and Technology, Vilnius, Lithuania.



Gediminas Šlekas received the B.S. degree in com-putational physics and M.S. degree in theoreticalphysics and astrophysics from Vilnius University,Vilnius, Lithuania, in 2007 and 2009, respectively,and the Ph.D. degree in semiconductor physics fromthe Center for Physical Sciences and Technology,Vilnius, in 2014.Since 2003, he is a researcher with the Center for

Physical Sciences and Technology, Vilnius. His re-search interests include modeling of small scale ob-jects, specifically, microwave sensors, antennas, split

ring resonator arrays, using finite-difference time-domain (FDTD) method. Heis also involved with the application of FDTD techniques for modeling thin con-ductive sheets, FDTD algorithm parallelization and implementation on multi-processor systems-computer cluster and Graphics Processing Unit (GPU).

Andžej Urbanovič received the B.S. and M.S. de-grees in physics from Vilnius University, Lithuaniain 2001 and 2003, respectively, and Ph.D. degreein semiconductor physics from the SemiconductorPhysics Institute in 2008.From 2009 to 2010, he has been a Postdoctoral

Researcher with the University of Savoy, Chambery,France. He is currently a researcher with the Centerfor Physical Sciences and Technology, Vilnius, andan engineer with the Teravil Ltd, Vilnius. His pastand present research interests include ultrafast phe-

nomena in semiconductors, terahertz radiation generation and detection tech-niques, terahertz spectroscopy and engineering of terahertz systems.Dr. Urbanovič received the Young Scientist Award from the Lithuanian

Academy of Science in 2009.

Jan Devenson received the B.S. degree in appliedphysics and the M.S. degree in semiconductorphysics from Vilnius University, Lithuania, in 2002and 2004, respectively, and the Ph.D. degree inphysics from Vilnius University in 2010.From 2005 to 2009, he was a visiting researcher

with the University of Montpellier 2, France, underthe Marie Curie Actions Research Fellowship Pro-gram. From 2010 to 2012, he was a Research Asso-ciate with the Centre for Physical Sciences and Tech-nology, Vilnius. Since 2012, he is a Senior Research

Associate with the Centre for Physical Sciences and Technology. His currentresearch interests include epitaxial growth and fabrication of MIR and FIR op-toelectronic devices.

Žilvinas Kancleris (M’04) received the physicsdiploma (with hons) in 1969, and the Ph.D. degree(candidate of physical and mathematical science)and Doctor of Science (Doctor of Physical andMathematical Science) in 1976 and 1990, respec-tively, all from Vilnius University, Lithuania. In1993, Lithuanian Scientific Council recognized hima degree of Doctor Habilitatus in physics.In 1969, he joined the Semiconductor Physics

Institute, Vilnius, as a Junior Research Associate.He was involved in the investigation of the weakly

heated electron gas in semiconductors using microwave methods. Later on,he started theoretical investigation of the electron heating phenomenon. Hedeveloped the Monte Carlo method for calculation of the properties of semicon-ductors subjected to weakly heating microwave electric field. In the nineties,he switched to the applied research and actively participated in developmentof the resistive sensor, performance of which is based on the electron heatingeffect in semiconductors. Since 2010, he is a Principal Researcher with theCentre for Physical Sciences and Technology. He is a head of the Departmentof Physical Technologies. He is also giving lectures as a Professor at VilniusUniversity. He was an invited lecturer giving lectures on the pulsed highpower microwave measurement methods in USA, Sweden, and France. Hewas a head of several national and international projects. He is the coauthor ofmore than 150 scientific publications and 3 monographs. His research interestsinclude experimental and theoretical study of the interaction of electromagneticwaves with the solid state structures, high-power microwave technologies, hotelectrons effects, computational methods and modeling.Dr. Kancleris is a member of the Lithuanian and European Physical Soci-

eties. He was corecipient of the Lithuania State Scientific Award in 2003, foroutstanding contribution to Lithuanian Science. In 2014, he was elected to thegrade of HPEM (high-power electromagnetics) Fellow for the contributionto development of the resistive sensors for the pulsed high power microwavemeasurements.

optimization of modulation properties of terahertz metamaterial by tuning fabry–pérot resonances

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