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Sensors and Actuators A 215 (2014) 89–95

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

j ourna l h o mepage: www.elsev ier .com/ locate /sna

EMS-based 3D confocal scanning microendoscope using MEMScanners for both lateral and axial scan

in Liua, Erkang Wanga, Xiaoyang Zhanga, Wenxuan Liangb, Xingde Lib, Huikai Xiea,∗

Department of Electrical & Computer Engineering, University of Florida, Gainesville, FL 32611, United StatesDepartment of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, United States

r t i c l e i n f o

rticle history:eceived 15 April 2013eceived in revised form1 September 2013ccepted 22 September 2013vailable online 23 October 2013

a b s t r a c t

A fiber-optic 3D confocal scanning microendoscope employing MEMS scanners for both lateral and axialscan was designed and constructed. The MEMS 3D scan engine achieved a lateral scan range of over±26◦ with a 2D MEMS scanning micromirror and a depth scan of over 400 �m with a 1D MEMS tun-able microlens. The lateral resolution and axial resolution of this system were experimentally measuredas 1.0 �m and 7.0 �m, respectively. 2D and 3D confocal reflectance images of micro-patterns, micro-particles, onion skins and acute rat brain tissue were obtained by this MEMS-based 3D confocal scanningmicroendoscope.

eywords:D confocal imagingD microendoscopeEMS mirrorEMS tunable lens

lectrothermal actuatorimorph

© 2013 Elsevier B.V. All rights reserved.

. Introduction

Confocal scanning microscopy has gained extensive applica-ions in biomedical imaging, industrial inspection and metrologyor its superior resolution, high contrast and powerful optical sec-ioning capacity [1–3]. It has revolutionized optical microscopyy introducing point-by-point illumination and pinhole filtering.owever conventional confocal scanning microscopes are bulkynd only suitable for lab use. Recently confocal scanning microen-oscopy has emerged as a new imaging technology that extends theuperior capability of confocal scanning microscopy to in vivo imag-ng of internal organs such as GI tracts, liver, and pancreatic duct,tc. [4]. It promises to enable in vivo optical biopsy and noninvasiveancer detection. The challenges for 3D confocal scanning microen-oscopy, however, include the miniaturization of laser beam scanngines especially for both lateral and axial scans, the requirementf large scan range under low drive voltage, and the miniaturizationf the optics without largely sacrificing optical performance.

In confocal scanning microendoscopy, the image pixel scanningan be obtained by scanning the laser beam across a fiber bundlet the proximal end [5–8]. Using a fiber bundle avoids the scan at

∗ Corresponding author at: 221 Larsen Hall, University of Florida, Gainesville, FL2611, United States. Tel.: +1 352 846 0441; fax: +1 352 392 8671.

E-mail address: hkx@ufl.edu (H. Xie).

924-4247/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.sna.2013.09.035

the distal end, thereby simplifying the miniaturization of the imageprobe. The limitations of fiber bundle scanning are the inherent pix-ilation artifact of the fiber bundle because of the spacing betweenfibers, the cross talk and reduced contrast [1,9].

More promisingly, many researchers demonstrated laser beamscanning at the distal end by utilizing MEMS mirrors [10–15].MEMS scanners can provide continuous beam scan with high sta-bility, uniform coupling and multidimensional scan capability atsmall footprint. For example, a 2D confocal microscope employ-ing a 2D electrostatic micromirror for lateral scan was reportedby Shin et al. [10], but depth scan was absent in this system. A2D confocal microscope previously reported by the authors in [11]was able to perform depth scan by a large-tunable-range MEMSlens-scanner, but lateral scan was accomplished by a bulky motor-ized stage which limited its application in endoscopic imaging. 3Dconfocal microscopes using MEMS mirrors for lateral scan werepresented by Arrasmith et al. [12] and Piyawattanametha et al. [13],but both of the reported systems relied on external motors andsliding stages for depth scan, which suffered from instability fromfrictions as well as size and speed limitations. An on-chip 3D con-focal microscope was reported by Gorecki et al. [14], in which twoelectrostatic scanning microlenses were stacked with the 1D z-axis

scanning microlens generating a 100 �m depth scan at 50 V and thex–y scanning microlens producing a 30 �m lateral scan at 200 V.The required high voltages may pose safety concerns if appliedinside human body. A 3D confocal microscope using an electrostatic

90 L. Liu et al. / Sensors and Actuators A 215 (2014) 89–95

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Fig. 3. (a) Optical design of the endoscopic probe. (b) Spot diagram at different

Fig. 1. Systematic design of 3D confocal scanning microendoscope.

icromirror for lateral scan and another electrostatic micromirroror depth scan was reported by Jeong et al. [15], but it had smalltatic axial displacement (10 �m) at high voltage (200 V) and theisplacement was still limited (±27.5 �m) even at resonance.

In this paper, a confocal scanning microendoscope is presented,hich incorporates a miniature MEMS 3D scan engine that can

enerate both large axial and lateral scan ranges under low driveoltage. The lateral scan is performed by a 2D scan micromirror andhe depth scan by a focal-tunable microlens. These two MEMS scan-ers together with high-quality micro-optics are packaged into aompact fiber-optic endoscopic probe. Polarization is also used toinimize the back-reflection and increase signal to noise ratio.This paper is arranged as follows. The confocal scanning

icroendoscope system including system design, endoscopicrobe design and optical simulations is described in Section 2. Then

n Section 3, the device design, fabrication process and characteri-ation of the MEMS scanners are presented. After that, the imagingxperimental results including system characterizations and 2Dnd 3D confocal reflectance images are reported in Section 4.

. MEMS-based 3D confocal laser scanning microendoscope

The schematic of the fiber-optic confocal microendoscopeystem is shown in Fig. 1. The system incorporates polarization-ensitive components to suppress unwanted back-reflections. Theaser beam (center wavelength: 638 nm) from the laser diodeCLAS2-638-100C, Blue Sky Research) first propagates through apatial filter (M-900, Newport), which uses a pinhole to filter outhe high spatial frequencies and produces a clean Gaussian beam toaunch into the system. After that, the laser beam is then collimatedo 1 mm in diameter by a lens. A polarizing beam splitter (PBS)hen reflects the s-polarized light at 90◦ while transmitting the-polarized light. The reflected s-polarized light is coupled into aingle-mode polarization maintaining (PM) fiber (P1-630PM, Thor-abs) by a fiber coupler (PAF-X-5, Thorlabs). The PM fiber maintainshe light polarization direction along the fiber cord and then deliv-

rs the linearly polarized light into the endoscopic probe.

The endoscopic probe as shown in Fig. 2 comprises a GRIN lens, quarter wave plate (QWP), a MEMS 2D scan mirror, a fixed mirror, pair of achromatic lenses and a MEMS tunable objective lens. The

Fig. 2. 3D model of the endoscopic probe design.

field angles: RMS spot size = 0.49 �m at 0◦; RMS spot size = 0.88 �m at 6◦; RMS spotsize = 2.8 �m at 12◦ .

quarter-pitch GRIN lens collimates the diverging light exiting fromthe fiber core. The diameter of the GRIN lens is 2 mm and the lengthis 5.17 mm. The linearly polarized beam, after passing through theGRIN lens, is incident on the QWP at 45◦ to the optic axis of the QWP.The linearly s-polarized light is divided into two equal orthogonalelectric field components with one component retarded by a quar-ter of the wavelength by the QWP, therefore producing a circularlypolarized light output. Then a MEMS 2D scan mirror perform thetwo-dimensional lateral scan of the collimated light beam, followedby a fixed mirror tilted at 45◦ to fold the light path by 90◦. A pairof achromatic lenses (Edmund Optics) is then employed for beamexpansion as well as aberration correction. After that, a 1D MEMStunable objective lens is used to focus the beam and also performthe depth scan.

The backreflected/backscattered light from the sample propa-gates back through the probe and passes consequentially throughthe MEMS tunable objective lens, the beam expander lens pair, thefixed mirror and the MEMS 2D mirror. Then the light passes throughthe QWP for the second time with another quarter wavelengthretardation introduced by the QWP, which changes the circularlypolarized light to linearly p-polarized light. The p-polarized sig-nal light is then focused by the GRIN lens, coupled back into thePM fiber, transmitted by the PBS, detected by an avalanche pho-todetector (APD) (C54601-01 Hamamatsu), and collected by a DAQto a PC. Meantime, the unwanted specular reflections at the fiberend and the GRIN lens end-face remain s-polarized and thereby arereflected by the PBS without entering the detector.

The optical path of the endoscopic probe in Fig. 2 is given inFig. 3(a). The single-mode PM fiber has a NA of 0.14. The GRINlens has a quarter pitch. The beam at the end of the GRIN lens is0.54 mm in diameter, which will under-fill the objective and leadto small effective NA. So a pair of beam expander lenses (EdmundOptics, f1 = 6 mm, f2 = 20 mm) is used to expand the beam by 3.33×to 1.8 mm in diameter. These two lenses form a telecentric sys-tem with a beam expansion factor of 3.33. The beam-expander pairis also used for aberration correction. The objective is an asphericlens with f = 1.45 mm and NA = 0.55. The collimated light beam afterthe beam-expander overfills the aperture of the aspheric objective;

therefore the NA of the system is equal to the NA of the asphericobjective. The objective is scanned in axial direction by the MEMSlens scanner to perform depth scan. The MEMS mirror is located

L. Liu et al. / Sensors and Actuators A 215 (2014) 89–95 91

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Fig. 6. (a) Z displacement vs. voltage of the MEMS tunable lens. (b) Frequency

ig. 4. (a) SEM of a lens-scanner. (b) Photograph of an assembled tunable lens.

t the conjugate plane of the back focal plane of the objective.ig. 3(b) shows the spot diagram calculated by ray tracing in CODE. The RMS spot sizes at optical scan angles of 0◦, 6◦, and 12◦ are.49 �m, 0.88 �m, and 2.8 �m, respectively. Scanning the MEMSirror at larger angle will introduce larger aberration and lead to

ower resolution.

. MEMS scanners

.1. MEMS tunable lens for depth scan

An electrothermal tunable microlens is used to perform theepth scan in the confocal scanning microendoscope. The tun-ble MEMS lens consists of a MEMS lens-scanner with a centralpening (Fig. 4(a)) and a 2.4 mm-diameter glass objective lensssembled onto the platform of the scanner (Fig. 4(b)). The centrallatform in the MEMS lens-scanner is symmetrically supported byour electrothermal lateral-shift-free large-vertical-displacementLSF-LVD) actuators [16] at two sides (Fig. 4(a)). The LSF-LVD actu-

tor is composed of three Al/SiO2 bimorphs with two rigid framesonnected in between. The actuation mechanism is electrothermalctuation, with a thin layer of Pt embedded along the bimorphs as

Fig. 5. Fabrication process of the MEMS lens scanner.

response of the MEMS tunable lens.

the heater. The large initial elevation due to residual stresses in thebimorph beams provides space for the platform to displace ver-tically in large range. Good stability and robustness are achievedusing wide actuator beams and connecting a large array of parallelactuator beams to each side of the platform. The platform is ele-vated upward at about 800 �m after the device release due to theresidual stresses in the bimorph beams.

The platform, together with the objective lens, will be actuateddownward when an electrical current passes through the Pt heaterin the bimorph beams, which introduces Joule heating and therebybending of the bimorph beams. A miniature glass lens with a diam-eter of 2.4 mm, a NA of 0.55 and a back focal length of 0.88 mm isselected as the objective lens for this system. The lens is fixed byUV glue to the platform with the clear aperture of the lens alignedto the central opening of the platform. The vertical elevation of

the platform after the lens being assembled is 510 �m. The devicefootprint of the lens scanner is 4.4 mm × 4.4 mm.

Fig. 7. (a) SEM of an ISC actuator. (b) SEM of the 2D MEMS mirror.

92 L. Liu et al. / Sensors and Actuators A 215 (2014) 89–95

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ig. 8. (a) Optical scan angle vs. driving voltage of the MEMS mirror. (b) Frequencyesponse of the MEMS mirror.

The MEMS lens scanner was fabricated on a SOI substrateith a 40 �m-thick device layer by a combined surface-and bulk-

icromachining process. As outlined in Fig. 5, the process startsith a PECVD deposition of 1.1 �m-thick SiO2 on the SOI wafer

a). This SiO2 layer serves as the bottom layer of bimorphs. Then

Fig. 9. Photograph of the assembled the endoscopic probe.

Fig. 10. (a) Reflectance image of group 7 elements in a USAF resolution target. Thesmallest elements are 2.2 �m wide. (b) Axial resolution measurement. (c) Lateralresolution measurement.

a Cr/Pt/Cr film of 20 nm/0.2 �m/20 nm is spluttered, and patternedby lift-off process on top of the 1.1 �m-thick SiO2 layer (b). Afterthat, a 0.15 �m-thick PECVD SiO2 layer is deposited and patternedwith RIE dry etch for electrical isolation (c). Next, a 1 �m-thick alu-minum layer is evaporated and lifted-off to form the top structurelayer of the bimorphs and the mirror plate surface as well (d). A sec-ond PECVD SiO2 layer is then deposited and dry etched to form ahard mask for the front-side silicon etch (e). Then, a back-side bulksilicon etch is performed until the etch stops at the buried oxide,followed by RIE etch of the buried oxide (f). Finally, an anisotropicsilicon etch is performed to etch through the device layer (g), fol-lowed by an isotropic silicon etch to undercut and release thebimorphs (h).

The vertical displacement and frequency response of this devicewere experimentally measured and shown in Fig. 6(a) and (b) [17].The vertical displacement was measure by an Olympus BX51 micro-

scope equipped with a QC200 micro-position recorder. To measurethe vertical displacement, the lens scanner was operated at thepiston mode by simultaneously driving all the actuators with asame dc voltage. After each step of the dc voltage change, the

L. Liu et al. / Sensors and Actuators A 215 (2014) 89–95 93

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Fig. 12. (a) Stack of 2D confocal reflectance images of the micro-particles at different

ig. 11. 3D volume-rendered image of micro-patterns under a 200-�m thick glasslide. The layers from up to down are the top surface of the glass slide, the bottomurface of the glass slide, and the micro-patterns.

icroscope was refocused onto the mirror plate and the coor-inates of multiple points on the mirror plate were recorded.

vertical actuation range of 400 �m was obtained at only 2 VFig. 6(a)). The frequency response was measured using a PolytecFV-511 laser Doppler vibrometer. The frequency response of thessembled lens scanner is shown in Fig. 6(b) with the first resonanceeak at about 24 Hz.

.2. MEMS scanning mirror for 2D lateral scan

.2.1. Device designThe 2D lateral scan in the confocal scanning microendoscope

s performed by an electrothermal MEMS mirror with a foot-rint of 2 mm × 2 mm (Fig. 7). A 1 mm × 1 mm mirror plate isupported by four identical and symmetrically located inverted-eries-connection (ISC) bimorph actuators at the four sides of theirror plate [18]. Each ISC bimorph actuator consists of inverted

imorphs, non-inverted bimorphs, and sandwiched overlaps con-ected in series to form an double S-shaped beam. Fig. 7(a) andb) show an SEM picture of one ISC actuator and an SEM of the

EMS mirror, respectively. This mirror was fabricated using theame process shown in Fig. 5.

.2.2. Device characterizationTip-tilt motion was generated by differentially driving two

pposite actuators of the mirror. The mirror scans optical angles

depths. The driving voltages of the MEMS lens scanner from up to bottom are at:1.6 V, 1.3 V, and 1 V. The image sizes are 180 �m × 180 �m. (b) 3D volume-renderedimage of the micro-particles embedded in PDMS.

of ±26◦ at 4.5 V as shown in Fig. 8(a). The frequency response wasmeasured also using a Polytec OFV-511 laser Doppler vibrometer.The frequency response of the mirror is given in Fig. 8(b) showingthe resonance at 460 Hz.

4. System integration and imaging experiments

4.1. System integration

As shown in Fig. 9, the assembled probe has a diameter of 7 mm.The probe mount consists of three separate precision-machinedmetal pieces. The first piece is designed to hold the fiber, GRIN andQWP. The fiber with the end cleaved is inserted into the trenchmachined in the first metal piece. The GRIN lens is then placednext to the fiber end with its end face adhesively attached to thefiber tip by optical UV glue. After that, the QWP is inserted andcarefully rotated to align its optical axis at 45◦ to the incident lightpolarization direction. The second metal piece is used to house the

MEMS mirror, fixed mirror and the first expander lens, while thethird piece is loaded with the second expander lens and the MEMStunable objective. Flexible printed circuit boards (FPCBs) are usedfor electrical connections. Two FPCBs are first glued on the metal

94 L. Liu et al. / Sensors and Actuators A 215 (2014) 89–95

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ig. 13. (a) 2D confocal reflectance image of onion skin. (b) 3D volume-renderedmage of onion skin.

ieces and then the MEMS mirror and MEMS lens are placed andlued on top of the FPCBs. Then silver epoxy is used to electricallyonnect the MEMS devices to the FPCBs. Finally, the three metalieces are adhesively assembled together to form a complete endo-copic probe. The diameter of the endoscopic probe is in the largeride for endoscopic applications and it may be reduced by mini-izing the MEMS devices and improving the optical design so high

ptical performance can be achieved at smaller sizes of the optics.he endoscopic probe is integrated with the polarization-sensitiveonfocal scanning microendoscope system.

.2. System characterization

Both lateral and axial resolutions of the confocal microen-oscopy system have been characterized. Fig. 10(a) shows an en

ace confocal reflectance image of the elements in Group 7 of aSAF resolution target by the confocal imaging system. There is

ome distortion in the image because the fast axis of the MEMSirror scans arc patterns near the resonance peak and the scan

peed of the mirror is not exactly uniform along the scan path.he distortion can be corrected by mapping the 2D scan pathsf the mirror under the same voltage and frequency settings andhen transforming the image data by a correction matrix. Theesolution would degrade as the beam scans toward the edgef the field of view, but the reflectance image of the resolutionarget shows that the smallest pattern with a width of 2.2 �m

s still resolvable. In order to find out the actual lateral resolu-ion, the reflective chrome surface of the USAF resolution targetas laterally translated on the focal plane and the 10–90% edgeidth was measured as 1.0 �m, as shown in Fig. 10(c). The axial

Fig. 14. (a) 2D confocal reflectance image of acute rat brain tissue. (b) 3D volume-rendered image of rat brain tissue.

resolution was measured by translating a mirror surface axiallyacross the focal plane and recording the change of the signalstrength detected by the APD; the FWHM axial resolution wasfound to be 7.0 �m, as shown in Fig. 10(b). The lateral and axialresolution can be further improved by increasing the numericalaperture of the objective lens, reducing the aberrations, or addinga lens immersion medium.

4.3. Confocal imaging results

Confocal imaging experiments have been performed usingthis MEMS-based confocal scanning microendoscope system. 2Dand 3D confocal reflectance images of micro-patterns (Fig. 11),micro-particles embedded in PDMS (Fig. 12) and onion skin (Fig. 13)have been obtained.

During the experiments, the four actuators of the 2D MEMSmirror were grouped into two pairs with each pair including twoactuators at the opposite sides of the mirror plate. The actuator paircontrolling the x-scan was differentially driven with a ramp wave-form of 0–2 V at 450 Hz. The scan in x-direction is driven near theresonance peak for large scan angle. The actuator pair driving they-direction scan was differentially driven with a ramp waveformof 0–4 V at 0.75 Hz. The 2D en face images have 300 × 300 pixels.Meanwhile, the z-direction scan was performed by simultaneouslydriving all the actuators of the MEMS lens scanner with a rampwaveform of 0–2 V at 1 mHz.

Fig. 11(a) shows a 2D reflectance confocal image of micro-patterns on the USAF resolution target. The micro-patterns shownin the figure include a number and a bar. Fig. 11(b) is a 3Dvolume-rendered image of the USAF resolution target covered by a

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Department of Electrical and Computer Engineering. His research interests include

L. Liu et al. / Sensors and

00-�m thick glass cover slide. The layers from up to down are theop surface of the glass slide, the bottom surface of the glass slide,nd the micro-patterns. The imaging volume shown in this figures 180 �m × 180 �m × 400 �m.

Fig. 12(a) shows a stack of 2D reflectance confocal images ofhe micro-particles acquired at different depths of the sample. The

icro-particles are alloy particles with the diameters in the rangef a few microns to tens of microns. The driving voltages on theEMS lens scanner from the top slice to the bottom slice were 1.6 V,

.3 V and 1.0 V, corresponding to the axial displacements of 281 �m,97 �m and 133 �m, respectively. Fig. 12(b) is a 3D image of theicro-particles reconstructed by stacking the 2D image slices. The

mage volume shown in this figure is 180 �m × 180 �m × 250 �m.Fig. 13(a) and (b) are the 2D and 3D confocal reflectance

mages of onion skin sample. The imaging volume shown inhis figure is 180 �m × 180 �m × 270 �m. Fig. 14(a) and (b) arehe 2D and 3D confocal reflectance images of an acute ratrain tissue sample. The imaging volume shown in this figure is80 �m × 180 �m × 380 �m.

. Summary

In conclusion, we have developed a confocal scanning microen-oscope using MEMS devices for both lateral and axial scans. Theull-MEMS 3D scan engine has been demonstrated as a viable wayo achieve large-scan-range 3D confocal imaging at low voltagend small size. 2D and 3D confocal reflectance images of micro-atterns, micro-particles embedded in PDMS, onion skin and ratrain tissue have been obtained by this system. The axial and

ateral resolutions are 7.0 �m and 1.0 �m, respectively. Due tots small size and 3D imaging capability, this miniature MEMS-ased confocal microendoscope may be used for early canceriagnosis.

cknowledgements

This work was funded in part by the National Science Founda-ion under award#1002209 and the National Institutes of Health01 CA153023. The MEMS devices were fabricated at the Nanoscaleesearch Facility at the University of Florida.

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Biographies

Lin Liu received her B.S. degree in optoelectronics from the Huazhong Univer-sity of Science and Technology, Wuhan, Hubei, China in 2008. She is currentlyworking toward a Ph.D. degree in electrical and computer engineering from theUniversity of Florida. Her graduate research involves the design and fabrication ofMEMS devices including micromirrors, microlenses and fiber scanners, and theirapplications in endoscopic imaging including endoscopic confocal imaging, opticalcoherence tomography and nonlinear optical imaging.

Erkang Wang is a graduate student in electrical engineering at the University ofFlorida, USA and will receive his master degree in May, 2013. He has been workingin the Interdisciplinary Microsystems Group in the University of Florida as a researchassistant specialized in MEMS based confocal microscopy under the supervision ofProf. Huikai Xie.

Xiaoyang Zhang was born in Nanyang, Henan Province, China, in 1989. He receivedthe B.S. degree in Microelectronics from Peking University in Beijing, China, in 2011.He is currently working toward Ph.D. degree in the Department of Electrical andComputer Engineering, University of Florida, Gainesville, USA. His research inter-ests include micro/nano fabrication, inertial sensors, optical MEMS and biomedicalimaging.

Wenxuan Liang received his B.S. degree and M.S. degree, both in Biomedical Engi-neering from Tsinghua University, Beijing, China, at 2008 and 2010, respectively. Heis currently working towards his PhD degree in Biomedical Engineering at the JohnsHopkins University, with research interest mainly in the development of transla-tional nonlinear optical endomicroscopy technologies for clinical applications.

Xingde Li received his Ph.D. degree in Physics and Astronomy from the Universityof Pennsylvania in 1998. He joined the Department of Bioengineering, Universityof Washington in 2001 and moved to the Department of Biomedical Engineering,Johns Hopkins University in 2009. He is currently a professor at the Departmentof Biomedical Engineering with a joint appointment at the Department of Electricaland Computer Engineering at Johns Hopkins. His general research interests researchinterest centers on development of novel and translational biophotonics technolo-gies that interface and bridge basic engineering research and medical diagnosis andintervention. Specifically, his research interests include optical coherence tomogra-phy (OCT), multiphoton endomicroscopy, optical molecular imaging, early detectionof cancer and inflammation, surgical guidance and brain functional imaging. He haspublished about 80 peer-reviewed journal papers with a total citation about 8400and an H-index of 39 (according to Google Scholar). He serves as an associate edi-tor or on the editorial board for the Journal of Biomedical Optics (SPIE), BiomedicalOptics Express (OAS), IEEE Transactions on Biomedical Engineering, and a few otherjournals in the area of biomedical optics. He is a Fellow of OSA, SPIE and AIMBE.

Huikai Xie received his MS and Ph.D. degrees in electrical and computer engineeringfrom Tufts University in 1998 and Carnegie Mellon University in 2002, respectively.He joined the University of Florida in 2002, where he is currently a professor at

MEMS/NEMS, integrated sensors, microactuators, integrated power passives, CNT-CMOS integration, optical MEMS, IR sensors, biophotonics, and biomedical imaging.He has published over 200 technical papers, and holds more than 30 patents. He isa senior member of IEEE and OSA and a member of SPIE.