IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 21, NO. 4, JULY/AUGUST 2015 4600206

Tunability and Optimization of CouplingEfficiency in Tamm Plasmon Modes

Che-Yuan Chang, Yi-Hsun Chen, Yu-Lin Tsai, Hao-Chung Kuo, Senior Member, IEEE,and Kuo-Ping Chen, Member, IEEE

Abstract—A Tamm plasmon polariton is a plasmonic resonanceexcited at the boundary between a photonic crystal and a metal. Inthis paper, a novel approach based on admittance loci is proposed todemonstrate the relation between thin-film structures and the cor-responding Tamm plasmon modes. The tunability of the resonancewavelength and optimization of coupling efficiency are demon-strated. In addition, by using different metals to couple Tammplasmon modes in the visible spectrum, silver has 4.7 times largerQ-factor than gold and 84 times larger than aluminum at 700 nm.The near-field enhancement of silver Tamm plasmon modes couldbe up to eight times larger than incident EM waves.

Index Terms—Nanophotonics, nanostructures, plasmons.

I. INTRODUCTION

P LASMONIC resonance has received enormous attentionfor the past few decades due to its extraordinary behavior

and nanoscale localization of immense electromagnetic fields.Having the above-mentioned properties, the well-known plas-mon state surface plasmon (SP) has been intensively studied formany possible applications, such as surface-enhanced Ramanscattering [1], sensors [2], optical tweezers [3], and solar cellenhancement [4]. In addition, a plasmon state which behaveslike an electron surface state, also known as a Tamm state,has recently been theoretically modeled [5] and experimentallytested [6]. Due to its similarity to a Tamm state, this plasmonstate is called a Tamm plasmon (TP). A TP structure is generallycomposed of a 1-D photonic crystal (PC) with a metallic struc-ture on top of it. While a Tamm state describes how electrons arelocalized at the edge of a crystal, TP describes how an electro-magnetic (EM) field localizes at the boundary of a PC and metal,as shown in Fig. 1. Numerous studies have focused on couplingTP modes with other resonance modes [7]–[11] and applica-tions such as the Tamm Laser [12], [13], solar cell enhancement[14], sensors [15], and plasmonic waveguide [16]. Unlike SPs,the propagation constant dispersion of TPs lies within the lightcone and thus does not require a coupling system to excite the

Manuscript received October 1, 2014; revised November 14, 2014; acceptedNovember 16, 2014. This work was supported by the National Science Council,Taiwan, (No. 102-2218-E-009-004-MY2 and NSC 103-2221-E-009-067).

C.-Y. Chang and K.-P. Chen are with the Institute of Imaging and Biomed-ical Photonic, National Chiao-Tung University, Tainan 711, Taiwan (e-mail:pipichang3@hotmail.com; kpchen@nctu.edu.tw).

Y.-H. Chen is with the Institute of Lighting and Energy Photonics, NationalChiao-Tung University, Tainan 711, Taiwan (e-mail: yhchen28@gmail.com).

Y.-L. Tsai and H.-C. Kuo are with the Department of Photonics and Instituteof Electro-Optical Engineering, National Chiao-Tung University, Hsinchu 300,Taiwan (e-mail: eclipse947346@hotmail.com; hckuo@faculty.nctu.edu.tw).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSTQE.2014.2375151

Fig. 1. (a) Potential of a crystal. Electrons are localized at the edge of thecrystal, creating Tamm states. (b) Dielectric constant of PC and metal. EM fieldis localized at the edge between the PC and metal.

plasmonic polaritons. Instead, it can only be excited within theoptical stop band of the utilized PC.

For a quarter-wavelength PC with central wavelength λ0 , theTP resonance wavelength λTP is within the optical band gapand can be approximated by (1) [17],

λTP = λ0 + αλPlasma (1)

and α is described by (2),

α = 2|nH − nL |

π√

εB(2)

where nH and nL are the refractive indices of the high and lowrefractive layers which compose the PC, and εB and λPlasmaare the background dielectric constant and plasma wavelengthof the utilized metal, respectively. However, the equations de-scribe λTP only for TP structures using quarter-wavelength PCs.Many recent studies have shown that λTP can be changed byvarying the thickness of the metal film [18] or PC [5], [19], [20].Although this behavior of a TP resonance has been demon-strated by simulation and experiment, the mechanism behindλTP shifting and variation of resonance coupling efficiency hasbeen less studied, which coupling efficiency from the incidentplane wave to the resonance mode can be determined by theheight of the dip in reflectance [21]. Furthermore, a system-atic approach to design TP resonances at specific wavelengthsand optimize the coupling efficiency remains unstudied. In this

1077-260X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See http://www.ieee.org/publications standards/publications/rights/index.html for more information.

4600206 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 21, NO. 4, JULY/AUGUST 2015

Fig. 2. (a) Three admittance loci calculated at λ1 , λTP , λ2 where λ1 >λTP > λ2 , are represented by red, blue, and green lines, respectively. Thesolid lines represent admittance loci of an infinitely long Ag thickness placedon PC, circles represent the start points of the metallic film admittance loci, andthe ellipse represents the isoreflectance curve for 10%. (b) The enlarged plot ofthe black square in (a). The asterisks represent negative YM .

work, a novel approach based on admittance loci is proposedto analyze the TP resonance modes and further design the layerstructure for shifting λTP and tuning resonance coupling effi-ciency. An admittance loci plot depicts the effective admittanceof the structure as the number of layers between the substrateand interface of the incident medium increases [22]. If the over-all effective admittance is close to that of the incident medium,then a reflectance drop can be observed in the spectrum.

In order to better understand how a TP resonance can be ob-served from an admittance loci plot, it is helpful to first under-stand how SP resonance can be explained by admittance loci.For a Kretschmann-coupling–excited SP resonance, the startpoint of the metal film is on the imaginary axis and stronglydepends on the incident angle, while the shape of loci is signif-icantly determined by both the start point and the YM , whereYM is the admittance of metal under calculation wavelength.Only under a proper relation between the positions of the startpoint of metallic film and negative YM are the shapes of ad-mittance loci able to intersect at points close to the admittanceof the incident medium. Then, the well-known SP resonancephenomenon can be excited [23]–[25]. The TP resonance ex-cited from the metal side can be understood in a similar way.The only difference between the two phenomena is that the startpoint of the metal film in the TP resonance case is determinedby the effective admittance of the PC, while in the SP resonancecase it is determined by the effective admittance of the couplingprism. If the material used is not strongly dispersive, then theTP structures will generally have narrower resonances dip thanSP structures will, because the effective admittance of PC willbe drastically altered by the shift in the calculated wavelength.Fig. 2 demonstrates how TP resonances respond to wavelength

shifting. The three different colored lines in Fig. 2 represent allpossible admittances of TP structures with a silver film, as cal-culated under different wavelengths of incident light. The bluecurve passes through the 10% isoreflectance curve (purple el-lipse) and converge at the YM for λTP , where λ1 > λTP > λ2 .This implies that with a proper choice of silver film thickness, tomake the overall effective admittance of the TP structure close toincident medium, a maximize reflectance drop can be reached,appearing as a sharp resonance dip in the spectra. In addition,with just a slight adjustment of the wavelength, the shape ofthe admittance locus changes and will no longer intersect theisoreflectance curve, like the red and green lines. It is also ap-parent that the initial slopes of the metallic film admittance lociis determined by the virtual lines which connect the start pointsof metallic film admittance loci and negative YM , as shown withthe dotted lines in Fig. 2(b). If the imaginary part of the negativeYM is higher than the start points of metallic film admittanceloci, then the admittance loci tend to intersect the real axis closerto the origin. This fact is important when designing a sharp TPresonance with a different incident medium.

II. SIMULATION AND MEASUREMENT RESULTS

A transfer matrix method shown in (3) is applied to calculatethe reflectance spectrum and admittance loci of TP resonance[

Ea

Ha

]=

[cos δ i sin δ/η

iη sin δ cos δ

] [Eb

Hb

](3)

where Ea and Eb are the tangential components of the electricfield at the top and bottom boundaries of a layer, Ha and Hb arethe components of the magnetic field, η is the admittance of thelayer, and δ is the optical path length in the layer.

To begin our study, a TP structure is applied, using a standardquarter-wavelength PC composed of eight pairs of TiO2 andSiO2 with λ0 designed to be 500 nm. The TiO2 and SiO2 layerswere deposited onto B270 glass substrate at room temperatureby a multi-target magnetron co-sputtering system. The thick-nesses of TiO2 and SiO2 are 50.4 and 86.7 nm, respectively.Then a 30 nm-thick silver thin film is coated on top of the PCusing E-gun evaporator as shown in Fig. 3 [26]. The averageroughness of the sample is 1.46 nm by atomic force microscopymeasurement.

A. Layer Design for Enhancing TP Resonance

Fig. 3 shows the schematic diagram, of the employed TPstructures, the normalized electric fields excited by incidentlight at resonance wavelength, and the cross-section SEM im-age of the sample. For the sample with metal and dielectricheterostructures, a resonance dip is located at λTP when lightis incident from the metal side, as shown with the blue dottedline in Fig. 4(b). The admittance loci calculated at such a wave-length explain the phenomenon, which is shown as a solid linein Fig. 4(a). Although the overall effective admittance of the PCis away from the incident medium, which is air in this model, theadmittance loci of the metal layer make the total effective admit-tance close to one, leading to a dip in the reflectance spectrum.

CHANG et al.: TUNABILITY AND OPTIMIZATION OF COUPLING EFFICIENCY IN TAMM PLASMON MODES 4600206

Fig. 3. (a) Schematic of TiO2 /SiO2 PC with Ag film on top placed on a glasssubstrate. The thicknesses of the TiO2 and SiO2 layers are 50.4 and 80.7 nmrespectively; the thickness of the silver film is 30 nm. (b) The normalized electricfield when excited by incident light at resonance wavelength. (c) The SEM crosssection image of PC.

However, by observation of the admittance loci of 30 nm silverTP structure, the reflectance dip in this case can be tuned to nearzero by slightly modifying the layer thickness. It is clear thatthe imaginary part of the silver-film-admittance-loci start pointat the resonance wavelength is slightly too small compared tothe negative YM . Therefore, the metal film admittance loci startwith a large slope, causing the intersection of the admittance andthe real axis to be smaller than one. Although tuning the effec-tive admittance of the PC by calculating at a shorter wavelengthwill theoretically move the intersection close to one, in that casethe silver film is not thick enough to allow the admittance locito reach the real axis. Therefore increasing the thickness of thesilver layer from 30 to 46 nm will make the effective admittanceclose to the incident medium at a shorter resonance wavelength.Consequently, a reflectance drop near zero is observed in therevised structure, leading to a higher absorbance, narrower dip,and better coupling efficiency, as shown with the dashed linein Fig. 4(a). The spectra of TP for 30 and 46 nm silver filmsalong with SP for a 58 nm silver film are plotted in Fig. 4(b) forcomparison. Evidently TP resonances are narrower than the SPresonance, especially when the silver film thickness is chosento reach the maximum reflectance drop. Quality factor enhance-ment, as determined by Q46Ag divided by Q30Ag is 2.5 times,where Q factor is Δλ/λTP in Table I. Fig. 4(c) shows the electricfield for two TP structures with 30 nm and 46 nm silver filmsunder respective resonance wavelengths. It is clear that the TPstructure using 46 nm silver also has a 20% stronger maximumelectric field than the 30 nm silver structure near the boundarybetween the PC and the silver.

B. Tuning TP Wavelength (λT P )

The same approach can be applied to design the wavelengthof λTP . The TP structures designed in Section IIA both have

Fig. 4. (a) and (b) show the admittance loci and reflectance of the TP casesbefore and after reflectance-drop maximization, along with SP case. The closedcircles in (a) indicate the interface for the top PC layer and metal layer, while theasterisks indicate the gold/air interface, and the purple ellipses are isoreflectancecurves for every 5%. The subplot in (b) shows how incident light excites thestructure. (c) Electric field for TP structures using 30 and 46 nm silver, respec-tively. Maximum electric field can be observed near the boundary between thePC and the silver.

λTP larger than λ0 , because when the PCs used in TP struc-tures are of strictly quarter-wavelength thickness and have thehigh refractive index layer (H) on top, the effective admittanceof PC calculated under λ0 will always be a large number onthe real axis (neglecting the imaginary part of using dielectric).With a calculated wavelength longer than λ0 , the effective ad-mittance of PC will shift counterclockwise, so the start point ofthe metallic film admittance loci and YM will be able to formthe proper relation, as discussed regarding Fig. 2. Therefore, todesign a TP resonance close to λ0 , the effective admittance ofPC can be adjusted to cause it to stop at certain region underthe calculated wavelength λ0 , so just a slight wavelength shiftcan create the proper position relation between the metallic filmadmittance loci start point and YM . Several different approachescan achieve this goal. We chose to extend the top H layer of PCfrom 50.4 nm to 125.4 nm, a new λTP is found at nearly 500 nmwhich is the λ0 of PC. Figs. 5(a) and 5(b) show both simulationand measurement results in reflectance and transmittance spec-tra obtained from a spectrometer (Ocean optics USB 2000+).From Fig. 5, one can observe that extending the top H layer

4600206 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 21, NO. 4, JULY/AUGUST 2015

TABLE IQ FACTORS FOR THREE DIFFERENT RESONANCE CASES

58 Ag 42.9° SP 30 Ag_PC 0° TP 46Ag_PC 0° TP

λr e s o n a n c e (nm) 591.8 584.3 579.0Δλ (nm) 33.06 9.16 3.59Q factor 17.9 63.79 161

Fig. 5. (a) and (b) show reflectance and transmittance spectra for both simula-tion and measurement results. Blue lines represent the original structure shownin Fig. 3, while brown lines represent the structure with extended top H layer.The solid lines represent measurement results, and the dash lines representsimulation results.

in simulations shifts the λTP from 584 to 504 nm. Measuredresults agree well with these simulation results.

C. Different Metals for TP in Visible Wavelengths

In the introduction, the relation between the start point of themetallic film admittance loci and YM was discussed. Effectsof dispersion of the employed materials on the resonance werementioned as well. In this section, three commonly used metalsare discussed in regard to generation of narrow TP resonances invisible wavelengths. The admittance dispersions of gold, silver,and aluminum, are plotted in Fig. 6. When one chooses a metalfor TP structures with narrow resonance, a lossless metal ashaving less real part of admittance is recommended. Thus, whenthe wavelength shifts, the admittance of the metal will changein the imaginary part more than in the real part, significantlychanging the position relation between the start point and YM , asdiscussed in the introduction. As a result, only for a very narrowwavelength region can a TP resonance be excited. Althougha lossless metal is unobtainable in practice, if the metal hasan imaginary admittance term significantly larger than the realterm, it can be considered a lossless metal. For instance, if

Fig. 6. Dispersion in the visible spectrum of the admittances of gold, silver,and aluminum, respectively.

Fig. 7. (a) and (b) present TP structures designed to have resonances near 500and 700 nm, respectively, using gold, silver, and aluminum as the metal layer.

one wishes to design a narrow TP resonance near 500 nm,silver has larger ratio of imaginary part to real part than gold oraluminum do, based on the analysis in Fig. 6. Therefore, silveris recommended for such a design, while aluminum is a betterchoice than gold. On the other hand, if the desired λTP is chosenas 700 nm, then gold will become a better choice than aluminum,while silver is still the best choice. Fig. 7(a) and (b) present TPstructures using gold, silver, and aluminum designed to haveresonance wavelengths at 500 and 700 nm, respectively. Thecorresponding Q factors for the different cases are tabulatedin Table II. The Q factor of the TP structure is 15.7 timeslarger when silver is used than when aluminum is used, forTP resonance wavelengths close to 500 nm, and 4.7 times largerthan when gold is used, for TP resonances wavelengths near700 nm. Table II also shows the electric field enhancementfactor (EF) at the metal-dielectric boundary, which enhancementis compared with air reference. At 700 nm, silver can provide

CHANG et al.: TUNABILITY AND OPTIMIZATION OF COUPLING EFFICIENCY IN TAMM PLASMON MODES 4600206

TABLE IIQ FACTORS FOR TP STRUCTURES USING THREE DIFFERENT

METALS DESIGNED TO HAVE RESONANCE

NEAR 500 AND 700 nm, RESPECTIVELY

Au Ag Al

λT P (nm) 500 700 500 700 500 700

Δλ (nm) 57.04 7.09 2.25 1.51 35.64 127.67Q factor 8.8 98.7 221.5 463.9 14.1 5.5electric field EF 0.96 3.84 5.51 8.04 1.53 1.13

eight times field enhancement, while gold can provide 3.8 times,and aluminum 1.13 times.

III. CONCLUSION

We have demonstrated the use of admittance loci for TPstructure design. The reflectance drop for TP resonances couldbe adjusted to near zero, leading to a 2.5 times Q factor enhance-ment. Also, a shift of λTP from 584 to 504 nm in both simulationand experiment is achieved. Noting that these cases are only ademonstration of how our proposed tool can be used, one candesign the drop of reflectance and the resonance wavelengthsbased on the requirements of the application, such as VCSEL ornarrow band optical filters. Furthermore, how a metal should bechosen for TP structures has also been discussed. If one wishesto have narrow TP resonances, then metals with high ratios ofimaginary part to real part in the target wavelength region arerecommended. It should be noted that all analyses and discus-sions in this article are only applicable for incident light fromthe metal side. Although TP resonances can be excited whenlight is incident from the substrate side, the admittance loci willdiffer from the behavior discussed in this article, and thereforewill require other design approaches. Nevertheless, this designtool will be helpful for those who wish to study the TP reso-nance mode and its possible applications such as sensors andnotch filter, etc.

ACKNOWLEDGMENT

The authors would like to thank Prof. C.-H. Kuo from Na-tional Chiao Tung University; Dr. Bo-Huei, Liao, and Chu,Nancy from Instrument Technology Research Center for re-source supply.

REFERENCES

[1] W.-C. Lin et al., “Size dependence of nanoparticle-SERS enhancementfrom silver film over nanosphere (AgFON) substrate,” Plasmonics, vol. 6,pp. 201–206, Jun. 2011.

[2] K. M. Mayer and J. H. Hafner, “Localized surface plasmon resonancesensors,” Chem. Rev., vol. 111, pp. 3828–3857, 2011.

[3] M. L. Juan, M. Righini, and R. Quidant, “Plasmon nano-optical tweezers,”Nat. Photon., vol. 5, pp. 349–356, 2011.

[4] S. Pillai, K. Catchpole, T. Trupke, and M. Green, “Surface plasmon en-hanced silicon solar cells,” J. Appl. Phys., vol. 101, art. no. 093105, 2007.

[5] M. Kaliteevski et al., “Tamm plasmon-polaritons: Possible electromag-netic states at the interface of a metal and a dielectric Bragg mirror,” Phys.Rev. B, vol. 76, art. no. 165415, 2007.

[6] M. Sasin et al., “Tamm plasmon polaritons: Slow and spatially compactlight,” Appl. Phys. Lett., vol. 92, pp. 251112-1–251112-3, 2008.

[7] H. Liu et al., “Optical magnetic field enhancement through coupling mag-netic plasmons to Tamm plasmons,” Opt. Exp., vol. 20, pp. 19160–19167,2012.

[8] B. Afinogenov, V. Bessonov, A. Nikulin, and A. Fedyanin, “Observation ofhybrid state of Tamm and surface plasmon-polaritons in one-dimensionalphotonic crystals,” Appl. Phys. Lett., vol. 103, art. no. 061112, 2013.

[9] H. Liu et al., “Controllable coupling of localized and propagating surfaceplasmons to Tamm plasmons,” Plasmonics, vol. 7, pp. 749–754, 2012.

[10] R. Bruckner et al., “Hybrid optical Tamm states in a planar dielectricmicrocavity,” Phys. Rev. B, vol. 83, art. no. 033405, 2011.

[11] M. Kaliteevski et al., “Hybrid states of Tamm plasmons and ex-citon polaritons,” Appl. Phys. Lett., vol. 95, pp. 251108-1–251108-3,2009.

[12] C. Symonds et al., “Lasing in a hybrid GaAs/silver Tamm structure,” Appl.Phys. Lett., vol. 100, pp. 121122-1–121122-3, 2012.

[13] C. Symonds et al., “Confined Tamm plasmon lasers,” Nano Lett., vol. 13,pp. 3179–3184, 2013.

[14] X.-L. Zhang, J.-F. Song, X.-B. Li, J. Feng, and H.-B. Sun, “Optical Tammstates enhanced broad-band absorption of organic solar cells,” Appl. Phys.Lett., vol. 101, art. no. 243901, 2012.

[15] W. L. Zhang, F. Wang, Y. J. Rao, and Y. Jiang, “Novel sensing conceptbased on optical Tamm plasmon,” Opt. Exp., vol. 22, pp. 14524–14529,2014.

[16] Y. Gong, X. Liu, H. Lu, L. Wang, and G. Wang, “Perfect absorbersupported by optical Tamm states in plasmonic waveguide,” Opt. Exp.,vol. 19, pp. 18393–18398, 2011.

[17] O. Gazzano et al., “Evidence for confined Tamm plasmon modes undermetallic microdisks and application to the control of spontaneous opticalemission,” Phys. Rev. Lett., vol. 107, art. no. 247402, 2011.

[18] R. Bruckner et al., “Parabolic polarization splitting of Tamm states in ametal-organic microcavity,” Appl. Phys. Lett., vol. 100, pp. 062101-1–062101-4, 2012.

[19] K. Leosson et al., “Comparing resonant photon tunneling via cavity modesand Tamm plasmon polariton modes in metal-coated Bragg mirrors,” Opt.Lett., vol. 37, pp. 4026–4028, 2012.

[20] K. J. Lee, J. Wu, and K. Kim, “Enhanced nonlinear optical effects due tothe excitation of optical Tamm plasmon polaritons in one-dimensionalphotonic crystal structures,” Opt. Exp., vol. 21, pp. 28817–28823,2013.

[21] P. R. Villeneuve, S. Fan, and J. Joannopoulos, “Microcavities in photoniccrystals: Mode symmetry, tunability, and coupling efficiency,” Phys. Rev.B, vol. 54, p. 7837, 1996.

[22] H. A. Macleod, Thin-Film Optical Filters. Boca Raton, FL, USA: CRCPress, 2001.

[23] H. A. Macleod, “Surface plasmon resonance effects and the admittancediagram,” in Proc. Tech. Symp. Southeast, 1987, pp. 300–309.

[24] C.-W. Lin et al., “Admittance loci design method for multilayer surfaceplasmon resonance devices,” Sens. Actuators B, Chem., vol. 117, pp. 219–229, 2006.

[25] Y.-J. Jen, A. Lakhtakia, C.-W. Yu, and T.-Y. Chan, “Multilayered structuresfor p-and s-polarized long-range surface-plasmon-polariton propagation,”J. Opt. Soc. Amer. A, vol. 26, pp. 2600–2606, 2009.

[26] P. B. Johnson and R.-W. Christy, “Optical constants of the noble metals,”Phys. Rev. B, vol. 6, art. no. 4370, 1972.

Che-Yuan Chang received the B.S. degree in electri-cal engineering from National Chiao Tung University,Hsinchu, Taiwan, in 2013. He is currently workingtoward the M.S. degree at the Institute of Imag-ing and Biomedical Photonic, National Chiao TungUniversity.

4600206 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 21, NO. 4, JULY/AUGUST 2015

Yi-Hsun Chen received the B.S. degree in Under-graduate Honors Program of Electrical Engineeringand Computer Science, National Taipei University ofTechnology, Taipei, Taiwan, in 2012, and the M.S.degree from the Institute of Lighting and EnergyPhotonics, National Chiao Tung University, Hsinchu,Taiwan.

Yu-Lin Tsai received the M.S. degree from the Insti-tute of Electro-Optical Engineering, National ChiaoTung University, Hsinchu, Taiwan, in 2011. He is cur-rently working toward the Ph.D. degree with the Insti-tute of Electro-Optical Engineering, National ChiaoTung University. His main research interests includenanostructured GaN-based light-emitting diodes andsolar cells, and nanostructure fabrication.

Hao-Chung Kuo (S’98–M’99–SM’06) received theB.S. degree from Taipei, Taiwan, in 1990, the M.S.degree in electrical and computer engineering fromRutgers University, Camden, NJ, USA, in 1995, andthe Ph.D. degree in electrical and computer engi-neering from the University of Illinois at Urbana-Champaign, Urbana, IL, USA, in 1999. He has anextensive professional career both in research and in-dustrial research institutions. From 1995 to 1997, hewas a Research Consultant with Lucent Technolo-gies, Bell Lab, Holmdel, NJ, USA. From 1999 to

2001, he was an R&D Engineer with the Fiber-Optics Division, Agilent Tech-nologies. From 2001 to 2002, he was the R&D Manager with LuxNet Cor-poration. Since September 2002, he has been a Member of the faculty withthe Institute of Electro-Optical Engineering, National Chiao Tung University,Hsinchu, Taiwan. He has authored or coauthored more than 60 publications. Hiscurrent research interests include the epitaxy, design, fabrication, and measure-ment of high-speed InPand GaAs-based vertical-cavity surface-emitting lasers,as well as GaN-based light-emitting devices and nanostructures.

Kuo-Ping Chen received the Ph.D. degree in elec-trical and computer engineering from Purdue Uni-versity, West Lafayette, IN, USA, in 2011. Afterreceiving the graduate degree from school, he waswith Intel Corp. for one year (2011–2012) as a pro-cess technology and development Engineer at Port-land, OR, USA. Since September 2012, he has beena Member of the faculty with the Institute of Imagingand Biomedical Photonics, National Chiao Tung Uni-versity, Hsinchu, Taiwan. His current research inter-ests include metamaterials, plasmonics, biosensors,

nanofabrication, and nonlinear optics.