286. Development and experimental analysis of piezoelectric optical scanner with implemented periodical microstructure

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1 286. Development nd experimentl nlysis of piezoelectric opticl scnner with implemented periodicl microstructure G. Jnušs 1,, A. Plevičius 1,, V. Ostsevičius 1,c, R. Bnsevičius 2,d, A. Busils 3,e 1 Interntionl Studies Centre of Kuns University of Technology, A.Mickevičius 37, LT Kuns, Lithuni 2 Kuns University of Technology, K.Doneličio 73, LT Kuns, Lithuni 3 Kuns University of Technology, A.Mickevičius 37, LT-44244, Kuns, Lithuni E-mil: giedrius.jnuss@ktu.lt, rvyds.plevicius@ktu.lt, c vytuts.ostsevicius@ktu.lt, d rmutis.nsevicius@ktu.lt, e lfreds.usils@ktu.lt (Received 15 My 2007, ccepted 03 July 2007) Astrct. Piezoelectric opticl scnner is developed for multi-coordinte control of opticl lser em y excittion of microstructures. The mnufctured microstructure is the periodicl structure which ws implemented in piezoelectric opticl scnner design. Such type of opto-micro-mechnicl systems cn e used for ccurte ngulr or liner deflection of opticl elements in vrious optomechnicl nd optoelectronic systems. The operting principle of these devices is sed on piezoelectric effect nd on conversion of high-frequency multi-dimensionl mechnicl oscilltions of piezoelectric virtion trnsducers into directionl multi-coordinte motion of the opticl elements in the mesurement chin. The min distinctive feture of such opticl piezoelectric scnners is the comintion of high micrometer rnge resolution with wide rnge of ngulr deflections of the scnning elements. The mnufcturing process nd visuliztion of the microstructure were presented. The device consists of piezoelectric cylinder nd scnning element with three degrees of freedom. The control model of this device ws derived using simultion results of opticl scnner y COMSOL Multiphysics softwre. ESPI digitl hologrphic PRISMA system ws used to vlidte the result of simultion of piezoelectric opticl scnner nd to test the functionlity of piezoelectric opticl scnner with implemented microstructures. Keywords: Piezoelectric opticl scnner, hologrphy, periodicl microstructure. Introduction Opticl scnning equipment is exploited in numerous res of engineering nd science pplictions rnging from defense to communictions [1-3]. The oject of this pper is to investigte possiilities for development of fst operting two-coordinte enhnced ngulr rnge scnner of opticl lser em. The tendency of development of high frequency onecoordinte scnners sed on ngulr oscilltions t fixed pre-designed frequencies is descried in [4]. Tht confirms lso our experience ccumulted t Kuns University of Technology in the re of design of precision scnning mechnisms [5-8]. Angulr oscilltion systems with piezoelectric virtion concentrtors seem to e optiml solution for high frequency scnning t predefined frequencies constnt in time. Different types of opticl scnners developed t Kuns University of Technology [5] re presented in Fig. 1. We will concentrte on investigtion of development nd experimentl nlysis of one of the working regimes of piezoelectric opticl scnner comprising piezoelectric exciter, wveguide, virtion concentrtor nd microstructure, s periodicl structure which is used for lser em control. The periodicl structure is ttched to the end of the concentrtor Fig. 1. Different types of piezoelectric opticl scnners developed t Kuns University of Technology: twisted plte (1), with implemented diffrction element (2); concentrtor of virtions (1), with implemented diffrction element (2) t the end 10

2 Mnufcturing nd nlysis of periodicl structure The diffrctive opticl element produced in the min technologicl steps such s origintion (sed on microlithogrphy nd dry etching), repliction either y UV hrdening or y emossing of Ni replic in polymer. Periodic trpezoidl profile structures were produced in crystlline silicon using stndrd contct-opticl lithogrphy processes nd rective ion etching (RIE). 2D structures in Si sustrte were formed y RIE in the SF 6 /N 2 gs mixture plsm, using plsm-etching equipment PK- 2420RIE [9]. Replics of these periodicl structures were formed y UV light hrdening repliction using commercil photopolymer (crylic trimethylolpropne ethoxylte) (lyer thickness 2µm, re 3cm 2 ), PET sustrte nd home mde technologicl device (T=20 C, irrdition distnce 10cm, UV light source DRT-230: λ=360nm, I=10000lx) [10]. Then photopolymer replic ws metllized with nickel or Al film (thickness of 20 nm). Then nickel stmp ws fricted y using the electroplting process (electroplting sed on nickel sulfmte ( Ni(SO3 NH2 ) ) electrolyte nd dditives) following conditions: ph , temperture 50 o C, current density 4 ma/cm 2. During the process of repliction surfce relief of ptterned mster - the nickel stmp ws trnsferred to the thin polymer film coted onto hrd sustrte using het nd pressure [11, 12]. Emossing experiments were performed using roll therml pressure device of originl construction controlling pressure force, temperture nd durtion of exposure (p= MP, T= C, t=1 5s) [13, 14]. Anlysis methods. The following nlyticl methods were used to nlyze geometricl nd opticl prmeters of the mster mtrix nd different replics: lser diffrctometer (He-Ne, λ=632.8nm, the reflection diffrction spectr were registered y photodiode), nd tomic force microscope NANOTOP-206 (AFM) operting in contct mode (cntilever force constnt 0.35 N/m). Diffrction efficiencies could e mesured y photodiode of diffrcted light in ll mxim (0, ±1, ±2, nd etc.) for different ngles of incidence light with respect to the norml. This method could e used for nondestructive nlysis of opticl prmeters (Fig. 2) of the sensor shown in AFM photogrph (Fig. 2). The sme method could e used for evlution of geometricl prmeters nondestructively nd directly in the system. 0,35 0,3 Diffrction efficiency, r.u. 0,25 0,2 0,15 0,1 0, Mximum order Fig. 2. Reltive diffrction efficiencies () nd AFM photogrph () of the metlized photopolymer diffrction grting (trpezoidl profile, period d=3µm) Simultion of the dynmicl excittion In order to determine working regimes two types of piezoelectric opticl scnners (Fig. 1) were nlyzed numericlly using finite element method (FEM) y COMSOL Multiphysics. There re presented surfce plots for oth scnners: the displcement, nd deformed shpe plots corresponding to the six different eigenfrequencies re presented in Fig f=1729 Hz f=2008 Hz 11

3 f=3899 Hz f=6154 Hz f=6898 Hz f=8142 Hz Fig. 3. Surfce plot of displcement, nd deformed shpe plot corresponding to the six different eigenfrequencies Experimentl investigtion A numer of experimentl studies re needed in order to ensure high dynmic ccurcy of opertion of the opticl scnners. In most cses the exciting frequencies re quite high, nd the mplitudes corresponding to them re mesured in micrometers. Therefore the hologrphic method cn e effectively pplied for the visul representtion of wve processes tking plce in the wveguide of the opticl scnner. The most effective method for studying the stnding wve processes is the method of digitl hologrphic interferometry. The tests used the PRISMA system [9] lyout shown in Fig 5. The PRISMA system shown in Fig. 5 is two em speckle pttern interferometer. The lser em directed t the oject is the oject em, the other em, which goes directly to the cmer, is the reference em. Lser light is scttered from the oject nd collected y the cmer lens, which lso imges the oject onto the CCD cmer sensors. The reference em goes directly to the cmer, usully in n opticl fier, where it overlps the imge of the oject. Shpe chnges tht occur etween reference nd stressed stte of the oject produce fringes on top of the imge of the oject, which is displyed on the TV monitor. f=8450 Hz f=8757 Hz 12

4 f=12233 Hz f=22888 Hz f=23547 Hz f=43902 Hz Fig. 4. Surfce plot of displcement, nd deformed shpe plot corresponding to the six different eigenfrequencies Phse shifting is required for TV hologrphy. Phse shifting is usully ccomplished y pplying voltge to piezoelectric (PZT) crystl ehind one of the mirrors in the reference em. This chnges the opticl pth length of the reference em y qurter wve length of light etween ech frme. A common test procedure is to collect eight TV frmes of phse shifted dt. The first four frmes re collected nd stored in computer memory s the reference stte of the oject. The oject is then stressed for the test, nd nother four frmes of dt re collected nd stored. The eight frmes of dt, four frmes from the oject reference stte nd four frmes from the oject stressed stte, re then processed in the PC. The result is displyed s fringes on top of the imge of the oject on the TV monitor. The fringes show contour mp of the shpe chnge etween the oject reference nd the stressed stte. Becuse the TVH system is n opticl interferometer, frction of wve length of light pth length chnge etween the reference em nd the oject em shifts the fringe pttern, nd rndom pth length chnges cused y unwnted virtion completely wipe out the fringes nd destroy the dt. TVH lso imposes specil conditions on the lser light source. If the lser hs mny longitudinl modes, then the reference nd the oject em pth lengths must e crefully mtched. This is of course possile on lrge opticl tle, ut inconvenient for uilding smll TVH system. Single frequency lsers re convenient for TVH. They hve long enough coherence length tht oject nd reference em pth lengths do not need to e the sme; consequently, with single frequency lsers it is possile to configure convenient TVH interferometer pckge. The disdvntge, of course, is tht high power, single frequency lsers re expensive. PRISM comines ll the necessry equipment for deformtion nd virtion mesurement of most mterils in smll lightweight system. A stndrd system includes hologrphy nd computer systems integrted with proprietry stte of the rt softwre. The min prts of the PRISMA system setup re presented in Fig. 5. Fig. 5. PRISMA system: opticl setup; PRISMA system setup: 1 videohed; 2 control lock; 3 illumintion hed of the oject; 4 circulr piezocermic plte 13

5 Fig. 6 shows pttern of hologrphic interference fringes on the surfce of the wveguide when the piezoelectric exciter performs resonnce virtions t 20.5 khz. A well developed mode of ending virtions cn e noted. Fig. 6 presents time verge hologrm of the wveguide t the frequency of excittion of 25 khz. As this frequency is out of resonnce, one cn note lrge white res in the hologrm which correspond to very smll field of dynmic mplitudes. The rections of the wveguide to piezoelectric excittion re poor nd the functionlity of the scnner is uncceptle. Fig. 6. Time verge lser hologrphic interferogrms of the piezoelectric rectngulr plte () nd cylinder () exciters Fig. 6 shows time verge lser hologrphic interferogrms of the piezoelectric cylinder exciter. It is seen tht pttern of fringes in hologrphic interferogrms (Fig. 6) confirms the simultion results of working regimes presented Figure 3 nd Figure 4. Concluding Remrks New type of piezoelectric opticl scnner with periodicl microstructure is designed nd nlyzed. The methodology of identifiction of virtion modes enled experimentl optimiztion nd numericl simultion of the working regimes of the system. Such type of nlysis could e successfully pplied in the design stge of different precise virtory systems. REFERENCES [1] Ankur Jin, nd Huiki Xie A single-crystl silicon micromirror for lrge i-directionl 2D scnning pplictions, Sensors nd Actutors A: Physicl Vol (2006), pp [2] Ho Nm Kwon, Jong-Hyun Lee, Kzuhiro Tkhshi nd Hiroshi Toshiyoshi MicroXY stges with spider-leg ctutors for two-dimensionl opticl scnning, Sensors nd Actutors A: Physicl, Vol (2006), p [3] Nnying He, Weipu Ji, Mli Gong nd Lei Hung Design nd mechnism nlysis of novel type compct single mirror lser scnner, Sensors nd Actutors A: Physicl, Vol. 125(2) (2006), p [4] Plevičius A. nd Rgulskis M. Hologrphic interference method for investigtion of wve trnsport systems, SPIE Proc. of the 2-nd Intl. Conf. on Virtion Mesurements y Lser Techniques, Ancon, Itly (1996). [5] R. Bnsevičius, A. Busils, M. Rgulskis, A. Plevičius, V. Ostsevičius Development nd Experimentl Anlysis of Opticl Scnner Bsed on FEM nd Lser Hologrphy, IMAC-XXV Conference Proceedings, Orlndo, Florid USA, Ferury 19-22, [6] S. Tmulevičius, A. Guoienė, G. Jnušs, A. Plevičius, V. Ostsevičius, M. Andrulevičius Opticl Chrcteriztion of Diffrctive Opticl Elements Replicted in Polymers, Journl of Microlithogrphy Microfriction nd Microsystems 5 (1), Jn-Mr (2006), p [7] T. Tmulevičius, S. Tmulevičius, M. Andrulevičius, G. Jnušs, A. Guoienė Opticl evlution of geometricl prmeters of micro-relief structures, Mterils science (Medžigotyr), Kuns University of Technology, Acdemy of Sciences of Lithuni, Kuns, Vol. 12, no. 4 (2006), p [8] Jnušs G., Dučnskienė K., Tmulevičius S., PlevičiusA., Tmulevičius T. Anlysis of microstructures sed on coherent optics methods Viroengineering 2006 : proceedings of the 6th Interntionl Conference, Octoer 12-14, 2006, Kuns, Lithuni (2006), p [9] Plevičius A., Hymn G., Steinzig M. Hologrphic PRISMA system for investigtion of mechtronic systems // Viroengineering 2006 : proceedings of the 6th Interntionl Conference, Octoer 12-14, 2006, Kuns, Lithuni / Lithunin Acdemy of Sciences, IFToMM Ntionl Committee, Kuns University of Technology. - ISSN Kuns , p