1. Z. Lu and D. W. Prather, “Dispersion-Engineered Photonic Crystals,” ISBN: 3639063767, VDM Verlag Dr. Mueller e.K., 2008.
2. K Shi and Z Lu “Ultracompact Field Effect Electro-Absorption Plasmonic Modulator” arXiv:1509.08828 (2015).
Abstract: One of the technical barriers impeding the wide applications of integrated photonic circuits is the lack of ultracompact, high speed, broadband electro-optical (EO) modulators, which up-convert electronic signals into high bit-rate photonic data. In addition to direct modulation of lasers, EO modulators can be classified into (i) phase modulation based on EO effect or free-carrier injection [ , ], or (ii) absorption modulation based on Franz-Keldysh effect or quantum-confined Stark effect [ - ]. Due to the poor EO properties of regular materials, a conventional EO modulator has a very large footprint. Based on high-Q resonators, recent efforts have advanced EO modulators [ , , ] into microscale footprints, which have nearly reached their physical limits restricted by the materials. On-chip optical interconnects require ultrafast EO modulators at the nanoscale. The technical barrier may not be well overcome based on conventional approaches and well-known materials. Herein, we report an EO modulator, more specifically electro-absorption (EA) modulator, based on the integration of a novel yet inexpensive active material, indium tin oxide (ITO), in a metal-insulator-metal (MIM) plasmonic waveguide platform, where the field effect is then greatly enhanced by high-k insulator and double capacitor gating scheme. The modulator waveguide length is only 800 nm, which is the smallest recorded dimension according to our knowledge. Preliminary results show that it has extinction ratio of 1.75 (2.43 dB) at 10 MHz, works up to 500 MHz (limited by testing setup for now), and can potentially operate at high speed.
3. Z Lu and K Shi, "Photonic MOS Based on" Optical Property Inversion", arXiv:1504.07546 (2015).
4. K. Shi, R. R. Haque, L.-F. Mao, and Z. Lu, "Graphene-sandwiched silicon structures for greatly enhanced unpolarized light absorption," Opt. Commun. 339, 47–52 (2015).
5. K. Shi and Z. Lu, "Optical modulators and beam steering based on electrically tunable plasmonic material," J. Nanophotonics 9, 93793 (2015).
6. K. Shi, R. R. Haque, B. Zhao, R. Zhao, and Z. Lu, “Broadband electro-optical modulator based on transparent conducting oxide,” Opt. Lett. 39, 4978-4981 (2014).
7. W Zhao, K. Shi, and Z Lu, “Greatly enhanced ultrabroadband light absorption by monolayer graphene,” Optics letters, vol. 38, 4342-4345 (2013).
8. R. Yang and Z. Lu, “Subwavelength Plasmonic Waveguides and Plasmonic Materials,” International Journal of Optics, vol. 2012, 258013 (12) (2012).
9. Z. Lu and W. Zhao, “Nanoscale electro-optic modulators based on graphene-slot waveguides,” J. Opt. Soc. Am. B vol. 29, 1490-1496 (2012) (Top Downloaded paper).
Abstract: Research on graphene has revealed its remarkable electro-optic properties, which promise to satisfy the needs of future electro-optic modulators. However, its ultrasmall thickness, compared with operating light wavelength, downplays its role in an optoelectronic device. The key to achieve efficient electro-optic modulation based on graphene is to enhance its interaction with light. To this end, some novel waveguides and platforms will be employed to enhance the interaction. Herein, we present our recent exploration of graphene electro-optic modulators based on graphene sandwiched in dielectric or plasmonic waveguides. With a suitable gate voltage, the dielectric constant of graphene can be tuned to be very small due to the effect of intraband electronic transition, resulting in “graphene-slot waveguides” and greatly enhanced absorption modes. Up to 3 dB modulation depth can be achieved within 800 nm long silicon waveguides, or 120 nm long plasmonic waveguides based on three-dimensional numerical simulations. They have the advantages of nanoscale footprints, small insertion loss, low power consumption, and potentially ultrahigh speed, as well as being CMOS-compatible.
10. Z. Lu, W. Zhao, and K. Shi, “Ultracompact electro-absorption modulators based on tunable epsilon-near-zero-slot waveguides,” IEEE Photonics Journal, vol. 4, 735-740(2012).
Abstract: We present a promising application of epsilon-near-zero (ENZ) materials in optical modulators. When a thin ENZ film is sandwiched in a single-mode waveguide, an ENZ-slot waveguide is formed, where the absorption can be greatly enhanced. We propose electroabsorption modulators based on tunable ENZ materials and slot waveguides. Transparent conducting oxides (TCOs) may be employed as the active slot, which can be tuned between ENZ (high absorption) and epsilon-far-from-zero (low absorption) by accumulation carriers. Numerical simulation shows that over 3-dB modulation depth can be achieved in a 250-nm-long TCO-slot waveguide. The modulators have the advantages of nanoscale footprints, small insertion loss, potentially ultrahigh speed, and easy fabrication.
11. A. Kaur, S. Banerjee, W. Zhao, J. Venkataraman, and Z. Lu, “Deep Subwavelength Power Concentration Based Hyperbolic Metamaterials,” International journal of optics, vol. 2012, 879392 (6) (2012).
Abstract: Hyperbolic metamaterials can manipulate electromagnetic waves by converting evanescent waves into propagating waves and thus support light propagation without diffraction limit. In this paper, deep subwavelength focusing (or power concentration) is demonstrated both numerically and experimentally using hyperbolic metamaterials. The results verify that hyperbolic metamaterials can focus a broad collimated beam to spot size of ~λ0/6 using wired medium design for both normal and oblique incidence. The nonmagnetic design, no-cut-off operation, and preferred direction of propagation in these materials significantly reduce the attenuation in electromagnetic waves.
12. R. Yang, X. Huang, and Z. Lu, “Arbitrary Super Surface Modes Bounded by Multilayered Metametal,” Micromachines 3(1), Special Issue on Nano-photonic Devices, 45-54 (2012).
Abstract: The dispersion of the fundamental super mode confined along the boundary between a multilayer metal-insulator (MMI) stack and a dielectric coating is theoretically analyzed and compared to the dispersion of surface waves on a single metal-insulator (MI) boundary. Based on the classical Kretschmann setup, the MMI system is experimentally tested as an anisotropic material to exhibit plasmonic behavior and a candidate of “metametal” to engineer the preset surface plasmon frequency of conventional metals for optical sensing applications. The conditions to obtain artificial surface plasmon frequency are thoroughly studied, and the tuning of surface plasmon frequency is verified by electromagnetic modeling and experiments. The design rules drawn in this paper would bring important insights into applications such as optical lithography, nano-sensing and imaging.
13. R. Yang and Z. Lu, “Silicon-on-Insulator Platform for Integration of 3D Nanoplasmonic Devices,” IEEE Photon. Tech. Lett. 23, 1652(2011).
Abstract: We experimentally demonstrate a compact platform to convert near-infrared signals between nanoplasmonic and nanophotonic domains. In particular, we utilize a pair of adiabatic nanoplasmonic tapers to assist direct-coupling and shrink the plasmonic guiding area to deep-subwavelength scale as small as 50-nm-by-80-nm with a propagation loss of 2.28 dB/µm. The integrated plasmonic devices developed on a silicon-on-insulator (SOI) substrate could build up a solid platform for plasmonic gauges of ultra-fast communications and optical sensing.
14. W. Zhao and Z. Lu, “Nanoplasmonic optical switch based on Ga-Si3N4-Ga waveguide,” Opt. Eng. 50, 074002(2011).
Abstract: In this paper, we propose an optical switch based on a metal-insulator-metal plasmonic waveguide with Si3N4 core sandwiched between two gallium (Ga) metal layers. Combining the unique structural phase transition property of gallium, within a total length of only 400 nm, an extinction ratio as high as 7.68 dB can be achieved in the proposed nanoplasmonic structure. The phase transition may be achieved by changing the temperature of the waveguide or by external light excitation.
15. W. Zhao, X. Huang, and Z. Lu, "Super Talbot effect in indefinite metamaterial," Opt. Express 19, 15297-15303 (2011).
Abstract: The Talbot effect (or the self-imaging effect) can be observed for a periodic object with a pitch larger than the diffraction limit of an imaging system, where the paraxial approximation is applied. In this paper, we show that the super Talbot effect can be achieved in an indefinite metamaterial even when the period is much smaller than the diffraction limit in both two-dimensional and three-dimensional numerical simulations, where the paraxial approximation is not applied. This is attributed to the evanescent waves, which carry the information about subwavelength features of the object, can be converted into propagating waves and then conveyed to far field by the metamaterial, where the permittivity in the propagation direction is negative while the transverse ones are positive. The indefinite metamaterial can be approximated by a system of thin, alternating multilayer metal and insulator (MMI) stack. As long as the loss of the metamaterial is small enough, deep subwavelength image size can be obtained in the super Talbot effect.
16. W. Zhao, O. M. Eldaiki, R. Yang, and Z. Lu, "Deep subwavelength waveguiding and focusing based on designer surface plasmons,"Optics Express, vol. 18, 21498-21503 (2010).
Abstract: We experimentally demonstrate focusing and guiding electromagnetic (EM) waves in a designer surface plasmonic waveguide with deep subwavelength mode cross section. Our experiments show that a metal grating with suitable parameters, functioning as a designer surface plasmonic waveguide, can support deep subwavelength surface modes and the width of the modes can be squeezed also into deep subwavelength by tapering the width of the waveguide. The results provide a new insight into deep subwavelength waveguiding and focusing.
17. W. Zhao and Z. Lu, “Negative refraction imaging by three-dimensional metamaterial at microwave frequencies,” Microwave and Optical Technology Letters, vol. 52, 2253-2256 (2010).
Abstract: We experimentally demonstrate negative refraction imaging at microwave frequencies by a three-dimensional (3D) metamaterial with simple cubic unit structure, which is fabricated based on the electronic textile technology.A four-layer metamaterial sample was tested in a series of experiments. The experimental result of the characteristic plasma frequency of the metamaterial was in good agreement with the theoretical result. The fabrication approach for 3D metamaterial may find many novel applications at microwave frequencies.
18. R. Yang, R. A. Wahsheh, Z. Lu, and M. A. Abushagur, “Efficient light coupling between dielectric slot waveguide and plasmonic slot waveguide,” Optics Letters, vol. 35, 649-651 (2010)
Abstract: An efficient coupler between a dielectric waveguide and a plasmonic metal–insulator–metal (MIM) waveguide is proposed, modeled, fabricated, and characterized. Based on the platform of a silicon slot waveguide, a quasi-MIM plasmonic junction is formed via e-beam lithography and lift-off process. Coupling efﬁciency between the silicon slot waveguide and plasmonic waveguide up to 43% is obtained after normalizing to reference waveguides at 1550 nm. This coupling scheme can be potentially used for fast optical switching and small-footprint optical modulation.
19. R. A. Wahsheh, Z. Lu, and M. A. Abushagur, “Cross Talk Reduction in Square Cavities,” IEEE Photonics Journal, vol. 1, 191-196 (2009).
Abstract: Theoretically and experimentally, we demonstrate that low crosstalk between two crossed line-defect waveguides formed in a square lattice photonic crystal (PC) structure can be achieved using a resonant cavity at the intersection area. The PC resonator consists of cubic air-holes in silicon air-holes. The Q-factor of the cavity can be changed by increasing the number of holes that form the cavity. The theoretical and experimental crosstalk results are about -40 dB and -20 dB, respectively.
20. R. A. Wahsheh, Z. Lu, and M. A. Abushagur, “Nanoplasmonic Directional Couplers and Mach-Zehnder Inerferometers,” Optics Communications, vol. 282, 4622-4626 (2009).
Abstract: We present a novel design and analysis of two nano-scale plasmonic devices: a directional coupler and a Mach–Zehnder interferometer. The designs of the two devices are based on our recent work on the air-gap coupler that resulted in high coupling efﬁciency between a dielectric waveguide and a plasmonic waveguide. The two devices are embedded between two dielectric waveguides and operate at optical telecom wavelengths. The overall efﬁciency was 37% for a 22 directional coupler switch and above 50% for the proposed designs for a Mach–Zehnder Interferometer. The efﬁciency in the proposed devices can be increased using broader plasmonic waveguides.
21. R. A. Wahsheh, Z. Lu, and M. A. Abushagur, “Nanoplasmonic Couplers and Splitters,” Optics Express, vol. 17, 19033-19040 (2009)
Abstract: In this paper, we present novel designs and analysis of ultracompact couplers and 1 × 2 splitters based on plasmonic waveguides. Numerical simulation shows coupling efficiency up to 88% for the former one and 45% for each branch for the latter one. The proposed coupler design has the advantages of improving the alignment tolerance of the plasmonic waveguide with respect to the dielectric waveguide and broadening the spectrum response of the splitter.
22. R. Yang, M. A. Abushagur, and Z. Lu, “Efficiently squeezing near infrared light into a 21nm-by-24nm nanospot,” Optics Express, vol. 16, 20142- 20148 (2008).
Abstract: Recent work demonstrated light transmission through deep subwavelength slits or coupling light into waveguides with deep subwavelength dimension only in one direction. In this paper, we propose an approach to squeeze light (λ = 1550 nm) from a dielectric waveguide into a deep subwavelength spot. Vertical confinement is achieved by efficiently coupling light from a dielectric waveguide into a 20-nm metal-dielectricmetal plasmonic waveguide. The horizontal dimension of the plasmonic waveguide is then tapered into 20 nm. Numerical simulation shows that light fed from a dielectric waveguide can be squeezed into a 21nm-by-24nm spot with efficiency 62%.
23. Z. Lu, “Efficient fiber-to-waveguide coupling through the vertical leakage from a microring,” Optics Letters, vol. 32, 2861-2863 (2007).
Abstract: A ﬁber-to-waveguide coupler is proposed to efﬁciently couple light from a single-mode ﬁber into a submicrometer semiconductor waveguide for integration with optoelectronic circuits. A microring with a speciﬁc refractive index is designed on the top of the semiconductor waveguide. The gradual vertical leakage from the microring forms steady coupling into the semiconductor waveguide. Coupling efﬁciency up to 93% is demonstrated using the three-dimensional ﬁnite-difference time-domain method. A tapered-waveguide or microring structure can be used to convert the lateral-mode size for coupling light into a single-mode semiconductor waveguide
24. Z. Lu, B. Miao, T. R. Hodson, C. Lin, J. A. Murakowski, and D. W. Prather, “ Negative refraction imaging in a hybrid photonic crystal device at near-infrared frequencies,” Optics Express, vol. 15, 1286-1291 (2007).
Abstract: We present the experimental demonstration of imaging of a point source by negative refraction at near-infrared frequencies using a hybrid photonic crystal device. The photonic crystal device, fabricated by patterning holes in 260nm silicon-on-insulator, integrates a triangular-lattice photonic crystal with a large photonic bandgap and square-lattice photonic crystal with negative refraction. Experimental results show that the output of a line-defect photonic bandgap waveguide provides a nearly ideal point source and then is imaged through the photonic crystal by negative refraction.
25. Z. Lu and D. W. Prather, “Calculation of effective permittivity, permeability, and surface impedance of negative-refraction photonic crystals,” Optics Express, vol. 15, 8340-8345 (2007).
Abstract: We consider the eigen-fields of a two-dimensional negativerefraction photonic crystal and obtain negative effective permittivity and negative effective permeability. Effective permittivity, permeability, and surface impedance are calculated by averaging the eigen-fields. The value of the surface impedance is shown to be location-dependent and is validated by finite-difference time-domain simulations. The unique power propagation mechanism in the photonic crystal is demonstrated through time-evolution of eigen-fields.
26. Z. Lu, S. Shi, J. A. Murakowski, G. J. Schneider, C. A. Schuetz, and D. W. Prather, “Experimental demonstration of self-collimation inside a three-dimensional photonic crystal,” Physical Review Letters,vol.96, No.17, 173902(4) (2006).
Abstract: We present our experimental demonstration of self-collimation inside a three-dimensional (3D) simple cubic photonic crystal at microwave frequencies. The photonic crystal was designed with unique dispersion property and fabricated by a high precision computer-controlled machine. The self-collimation modes were excited by a grounded waveguide feeding and detected by a scanning monopole. Selfcollimation of electromagnetic waves in the 3D photonic crystal was demonstrated by measuring the 3D ﬁeld distribution, which was shown as a narrow collimated beam inside the 3D photonic crystal but a diverged beam in the absence of the photonic crystal.
27. Z. Lu, J. A. Murakowski, C. A. Schuetz, S. Shi, G. J. Schneider, J. P. Samluk, and D.W. Prather “Perfect lens makes a perfect trap,” Optics Express, vol.14, No.6, 2228-2235 (2006).
Abstract: In this work, we present for the first time a new and realistic application of the “perfect lens”, namely, electromagnetic traps (or tweezers). We combined two recently developed techniques, 3D negative refraction flat lenses (3DNRFLs) and optical tweezers, and experimentally demonstrated the very unique advantages of using 3DNRFLs for electromagnetic traps. Super-resolution and short focal distance of the flat lens result in a highly focused and strongly convergent beam, which is a key requirement for a stable and accurate electromagnetic trap. The translation symmetry of 3DNRFL provides translation-invariance for imaging, which allows an electromagnetic trap to be translated without moving the lens, and permits a trap array by using multiple sources with a single lens. Electromagnetic trapping was demonstrated using polystyrene particles in suspension, and subsequent to being trapped to a single point, they were then accurately manipulated over a large distance by simple movement of a 3DNRFL-imaged microwave monopole source.
28. I. O. Mirza, S. Shi, Z. Lu, and D. W. Prather, “Calculation of the negative refractive index of a LHM slab by the free-space mapping of the laterally shifted refracted beam,” Microwave and Optical Technology Letters, vol. 48, No. 3, 593 – 596 (2006).
Abstract: In this paper, we present a novel method to calculate the effective negative refractive index of a left-handed material (LHM) - a composite of split-ring resonators (SRRs) and thin wire structures. A LHM slab was first fabricated and then the measured transmission and reflection results were used to determine the LHM passband. To obtain the effective negative-refractive index, a microwave beam was obliquely launched to illuminate the slab for which a 2D spatial-field profile of the refracted beam outside the slab was obtained by scanning the lateral shifting of the field with respect to normal for a band of frequencies. A lateral shift of the refracted beam towards the same side of the incident beam for the LHM passband confirmed negative refraction in the LHM slab and the refractive index calculated for that frequency region was conclusively negative according to Snells law. The presented method provides an alternate and efficient way to measure the effective refractive index of a LHM.
29. S. K. Lohokare, Z. Lu, C. A. Schuetz, and D. W. Prather, “Electrical Characterization of Flip-Chip Interconnects Formed Using A Novel Conductive-Adhesive-Based Process,” IEEE Transactions On Advanced Packaging, vol. 29, No. 3, 542-547 (2006).
Abstract: Using conventional microfabrication techniques, we have developed a new, low-cost wafer bumping process that enables a high degree of control over patterning of conductive adhesive interconnects. This approach obviates the need for development of dispensing and scraping head equipment that may otherwise be required for mass fabrication of lithographically patterned adhesive bumps. Flip-chip interconnects formed using this new process offer better electrical performance as compared to those formed by squeegee-based deﬁnition techniques. This is inferred in this paper by experimentally demonstrating lower contact resistance with the polished bumps as compared to the squeegeed bumps. Furthermore, in order to study the high-speed electrical performance characteristics of these conductive adhesive bumps, a 10-GHz 1.55- m p-i-n photodetector fabricated in the antimonide material system was used as case study. The results from the bandwidth characterization of the polymer ﬂip-chip-integrated detector showed minimum degradation in the high-speed performance characteristics of the detector.
30. Z. Lu, J. A. Murakowski, C. A. Schuetz, S. Shi, G. J. Schneider, and D. W. Prather, “Three-dimensional subwavelength imaging by a photonic-crystal flat lens using negative refraction at microwave frequencies,” Physical Review Letters, vol.95, No.15, 153901(4) (2005).
Abstract: We experimentally demonstrate subwavelength resolution imaging at microwave frequencies by a three-dimensional (3D) photonic-crystal ﬂat lens using full 3D negative refraction. The photonic crystal was fabricated in a layer-by-layer process. A subwavelength pinhole source and a dipole detector were employed for the measurement. By point-by-point scanning, we obtained the image of the pinhole source shown in both amplitude and phase, which demonstrated the imaging mechanism and subwavelength feature size in all three dimensions. An image of two pinhole sources with subwavelength spacing showed two resolved spots, which further veriﬁed subwavelength resolution.
31. Z. Lu, C. Chen, C. A. Schuetz, S. Shi, J. A. Murakowski, G. J. Schneider, and D. W. Prather, “Sub-wavelength imaging by a flat cylindrical lens using optimized negative refraction,” Applied Physics Letters, vol. 87, No.9, 091907(3) (2005).
32. Z. Lu, C. A. Schuetz, S. Shi, C. Chen, G. P. Behrmann, and D. W. Prather, “Experimental demonstration of self-collimation in low index contrast photonic crystals in the millimeter wave regime,” IEEE Transactions on Microwave Theory and Techniques, vol.53, No. 4, 1362-1368(2005).
Abstract: In this paper, we present the theoretical and experimental results for self-collimation in low-index-contrast photonic crystals (PhCs) in the millimeter-wave (MMW) region of the electromagnetic spectrum. The design of the PhCs is based on their equifrequency contours and the two-dimensional ﬁnite-difference time-domain simulation results. In the experiments, the MMW PhCs are fabricated in Rexolite slabs by a CNC micro-milling system. A MMW imaging system is built based on a vector network analyzer. The input source is launched either through a waveguide or a monopole, while the ﬁeld distribution is acquired by scanning a monopole antenna over the surface of the photonic crystal to detect the proﬁle of the evanescent waves. In both cases, we have observed and characterized the self-collimation effect for both the amplitude and phase of the propagating electromagnetic wave in low-index-contrast photonic crystals.
33. Z. Lu, S. Shi, C. A. Schuetz, J. A. Murakowski, and D. W. Prather, “Three-dimensional photonic crystal flat lens by full 3D negative refraction,” Optics Express, vol.13, No.15, 5592-5599 (2005).
Abstract: We present the experimental demonstration of imaging by allangle negative refraction in a 3D photonic crystal flat lens at microwave frequencies. The flat lens is made of a body-centered cubic photonic crystal (PhC) whose dispersion at the third band results in group velocity opposite to phase velocity for electromagnetic waves. We fabricated the photonic crystal following a layer-by-layer process. A microwave imaging system was established based on a vector network analyzer, where two dipoles work as the source and the detector separately. By scanning the volume around the lens with the detector dipole, we captured the image of the dipole source in both amplitude and phase. The image of two incoherent sources separated by 0.44λ showed two resolvable spots, which served to verify subwavelength resolution.
34. Z. Lu, S. Shi, C. A. Schuetz, and D. W. Prather, “Experimental demonstration of negative refraction imaging in both amplitude and phase,” Optics Express, vol.13, No.6, 2007-2012(2005).
Abstract: We studied a two-dimensional square-lattice photonic crystal with all-angle negative refraction at its first band. Using this photonic crystal, we designed and fabricated a flat lens functioning as a cylindrical lens by increasing the vertical dimension of the photonic crystal. Twodimensional finite-difference time-domain simulation validated negative refraction imaging. To perform the experiment, a microwave imaging system was built based on a vector network analyzer. Field distributions were acquired by scanning the imaging plane and object plane. The experiment demonstrated negative refraction imaging in both amplitude and phase, and obtained an image with feature size, 0.77λ.
35. C. Lin, Z. Lu, S. Shi, G. Jin, and D. W. Prather, “Experimentally demonstrated filters based on guided resonance of photonic crystal films,” Applied Physics Letters, vol. 87, 091102(3) (2005).
Abstract: We demonstrate a guided resonance ﬁlter based on photonic crystals PhCs, which are fabricated in a high-permittivity material. The resulting spectra from a three-dimensional analysis of the structure and experimental measurement results show sharp dips and ﬂattop transmissions. These provide promising properties in constructing sensitive and compact wavelength-selective devices, such as wavelength-division multiplexers.
36. C. Lin, Z. Lu, G. J. Schneider, and D. W. Prather, “Experimental demonstration of prism coupling of infrared wave into planar photonic crystal waveguide devices,” Optical Engineering, vol. 44, 114601 (2005).
37. C. Lin, C. Chen, S. Shi, Z. Lu, and D. W. Prather, “CO2 laser light characterization of low loss planar-photonic crystals self-collimated waveguides,” Optical Engineering, vol. 44, 114602 (2005).
Abstract: We demonstrate nondefect mid-infrared waveguides based on the self-collimation effect in photonic crystals (PhCs). Due to the spatial dispersion properties serving to confine and route light, propagation loss as low as 2.56 dB/mm is obtained in a silicon-on-insulator (SOI)-based waveguide. The efficiency, together with their ability of arbitrary and structureless routing of electromagnetic beams, of these self-collimation devices provide a potential candidate for miniaturizing devices.
38. Z. Lu and D. W. Prather, “Total internal reflection-evanescent coupler for fiber-to-waveguide integration of planar optoelectronic devices,” Optics Letters, vol. 29, No.15, 1748-1750(2004).
Abstract: We present a method for parallel coupling from a single-mode fiber, or fiber ribbon, into a silicon-on-insulator waveguide for integration with silicon optoelectronic circuits. The coupler incorporates the advantages of the vertically tapered waveguides and prism couplers, yet offers the flexibility of planar integration. The coupler can be fabricated by use of either wafer polishing technology or gray-scale photolithography. When optimal coupling is achieved in our experimental setup, the coupler can be packaged by epoxy bonding to form a fiber-waveguide parallel coupler or connector. Two-dimensional electromagnetic calculation predicts a coupling efficiency of 77% 1.14-dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling efficiency is experimentally achieved to be 46% (-3.4-dB insertion loss), excluding the loss in silicon and the reflections from the input surface and the output facet.
39. S. K. Lohokare, C. A. Schuetz, Z. Lu, T. Dillon, A. Sure, and D. W. Prather, “10GBps, 3-D, chip-level, parallel micro-optical interconnects using a novel conductive polymer flip-chip process,” Optical Engineering, vol. 43, No. 11, 2511-2517(2004).
1. R. Yang and Z. Lu, “Integration of 3D plasmonic devices with silicon-on-insulator-based optical,” SPIE Photonics West 2012, San Francisco, CA.
2. W. Zhao, X. Huang, and Z. Lu, “Demonstration of self-imaging effect without paraxial approximation,” SPIE Photonics West 2012, San Francisco, CA.
3. R. Yang, X. Huang, and Z. Lu, “Dispersion engineering for surface waves on multilayer metal-insulator stacks,” SPIE Photonics West 2012, San Francisco, CA.
4. S. Banerjee, W. Zhao, X. Huang, and Z. Lu “Subwavelength imaging achieved by indeﬁnite metamaterial,” SPIE Photonics West 2012, San Francisco, CA.
5. Z. Wang, X. Huang, and Z. Lu, “Super Talbot effect in anisotropic metamaterial,” SPIE NanoScience+Engineering, San Diego, CA, 21-25 August, 2011.
6. R. Yang, W. Zhao, R. A. Soref, and Z. Lu, "Semiconductor-coated deep subwavelength spoof surface plasmonic waveguide for THz and MIR applications", Proc. SPIE 7938, 79380A (2011).
7. W. Zhao, O. M. Eldaiki, R. Yang, X. Huang and Z. Lu, "Experimental demonstration of linear deep subwavelength spoof surface plasmonic waveguides", Proc. SPIE 7946, 794620 (2011).
8. Z. Lu, R. Yang, R. A. Wahsheh, and M. A. G. Abushagur, “Nanoplasmonic couplers and modulators based on metal-insulator-metal structures,” SPIE Photonics West 2010, in press.
Abstract: We propose a “slot-to-slot” coupler to convert power between optical and metal-insulator-metal (MIM) plasmonic modes. Coupling efficiency of larger than 60% is obtained from 2D FDTD simulation. Based on this prototype, a quasiMIM plasmonic junction is demonstrated using e-beam lithography onto an SOI substrate. The junction is formed by depositing a thin layer of gold (~20 nm) on part of a dielectric slot. When probed by 1520-nm laser, coupling efficiency of 36% is achieved for a 500-nm long quasi-MIM junction. Optical modulation is under investigation by pumping the device using visible light to change the optical property of gold.
9. R. A. Wahsheh, Z. Lu, J. Yang, and M. A. G. Abushagur, “Silicon microring vertical coupler,” International Symposium on High Capacity Optical Networks and Enabling Technologies, HONET 2009, in press.
Abstract: Silicon microring vertical couplers a r e proposed and fabricated to efficiently couple light into silicon-on-insulator waveguides for silicon photonic integration. A specific mode is excited to match the effective index of the silicon-on-insulator guided mode by oblique incidence. The vertical leakage from the microring forms gradual coupling into the silicon-on-insulator slab. Coupling efficiency up to 91% is demonstrated using the three-dimensional finite-difference time-domain method. A semi-disk and lateral t ape r can be used to convert the lateral mode size for coupling light into a single mode silicon-oninsulator waveguide.
10. R. A. Wahsheh, Z. Lu, and M. A. G. Abushagur, “Compact nanoplasmonic Mach-Zehnder interferometers,” International Symposium on High Capacity Optical Networks and Enabling Technologies, HONET 2009,in press.
Abstract: We present a novel design of two nano-scale plasmonic devices: a 2×2 directional coupler switch and a MachZehnder interferometer. The overall efficiency was 37% for the former one and 70% for the latter one.
11. R. A. Wahsheh, Z. Lu, and M. A. G. Abushagur, “Ultra-compact nanophotonic splitter,” International Symposium on High Capacity Optical Networks and Enabling Technologies, HONET 2009, in press.
12. R. Yang and Z. Lu, “Efficient 3D Nanofocusing Based on Surface Plasmon Polaritons,” Frontiers in Optics (FiO) 2008/Laser Science XXIV (LS), Rochester, New York, Oct. 2008.
Abstract: We present a nanotaper for coupling light from a dielectric waveguide into a nanoscale plasmonic waveguide. Numerical simulation shows that light can be focused into a 21nm-by- 24nm spot with efficiency over 60%.
13. K. Narayanan, F. Preble, Z. Lu, and M. A. G. Abushagur, “Optical Multi-Level Logic on a Silicon Chip,” Frontiers in Optics (FiO) 2008/Laser Science XXIV (LS), Rochester, New York, Oct. 2008.
Abstract: We demonstrate all-optical multi-level logic using a system of symmetric ring resonators in parallel. The device can form the basis of an on-chip optical digital to analog converter (ODAC).
14. R. A. Wahsheh, Z. Lu, S. F. Preble, M. A. G. Abushagur, “Cross Talk Reduction by Photonic Crystal Cavities,” Frontiers in Optics (FiO) 2008/Laser Science XXIV (LS), Rochester, New York, Oct. 2008.
Abstract: Using a square lattice to reduce the cross talk between two photonic crystal structures composed of silicon pillars in air and air holes in silicon shows a reduction of -90.60 dB and -30 dB, respectively.
15. R. A. Wahsheh, Z. Lu, and M. A. G. Abushagur, “Efficient Couplers and Splitters from Dielectric Waveguides to Plasmonic Waveguides,” Frontiers in Optics (FiO) 2008/Laser Science XXIV (LS), Rochester, New York, Oct. 2008.
Abstract: We introduce a novel design and analysis of an ultra-compact coupler and a 12 splitter from silicon waveguides into plasmonic waveguides with high coupling efficiency and flexible splitting ratios.
16. R. A. Wahsheh, M. A. G. Abushagur, Z. Lu, and S. F. Preble, “Ultralow cross talk in crossed strip waveguides with the assistance of a photonic crystal cavity,” SPIE Optics and Photonics, San Diego, CA, Aug. 2008.
17. D. W. Prather, Z. Lu, S. Shi, J. Murakowski, Y. Peng, and G. Schneider, “Simulation, Fabrication, and Application of Three-Dimensional Dispersion-Engineered Photonic Crystals,” 3D Photonic Crystals: Simulation Coupled with Experiment, 2007 MRS Spring Meeting, San Francisco, CA, USA, Apr. 2007.
18. R. A. Wahsheh, M. A. G. Abushagur, and Z. Lu, “A Method for Cross Talk Reduction in Crossed Strip Waveguides,” 4th International Symposium High Capacity Optical Networks and Enabling Technologies, Dubai, UAE, November 2007.
Abstract: In this paper, cross talk reduction is achieved by using a resonant cavity at the intersection area between two crossed strip waveguides formed in a square photonic crystal structure. Simulation results show that reducing the separation distance between the waveguide and the cavity resulted in cross talk reduction.
19. Z. Lu, S. Shi, J. A. Murakowski, C. A. Schuetz, G. J. Schneider, and D. W. Prather, “Experimental demonstration of self-collimation in 3D photonic crystal at microwave frequencies,” Proc. of SPIE, vol. 6128, 61281T (Mar. 2006) (Photonics West, San Jose, CA, Jan., 2006).
Abstract: We present our experimental demonstration of self-collimation inside a three-dimensional (3D) simple cubic photonic crystal at microwave frequencies. The photonic crystal was designed with tailored dispersion property and fabricated by a high precision computer-controlled machine. The self-collimation modes were excited by a grounded waveguide feeding and detected by a scanning monopole. Self-collimation of electromagnetic waves in the 3D photonic crystal was demonstrated by measuring the 3D field distribution, which was shown as a narrow collimated beam inside the 3D photonic crystal whereas a diverged beam in the absence of the photonic crystal.
20. D. W. Prather, Z. Lu, S. Shi, and C. A. Schuetz, “Dispersion engineering for 3D subwavelength imaging using photonic crystals,”Proc. SPIE vol. 6128, 61280U (Mar. 1, 2006) (Photonics West, San Jose, CA, Jan., 2006).
Abstract: We experimentally demonstrate subwavelength resolution imaging at microwave frequencies by a three-dimensional (3D) photonic crystal flat lens using full 3D negative refraction. The flat lens is made of a body-centered cubic photonic crystal (PhC) whose dispersion at the third band results in group velocity opposite to phase velocity for electromagnetic waves. The photonic crystal was fabricated in a layer-by-layer process. Two different sources (monopole and pinhole) were used as imaged objects and a monopole detector was employed for detection in the image region. By scanning the detector, we obtained the images of the pinhole and monopole sources, seperately. The image of the pinhole sources had subwavelength feature size in all three dimensions, which predicts a 3D imaging capability of the flat lenses. An image of two pinhole sources with subwavelength spacing showed two resolved spots, which further verified subwavelength resolution.
21. D. W. Prather, Z. Lu, J. A. Murakowski, S. Shi, G. J. Schneider, C. A. Schuetz, P. Yao, and B. Citla “Design, fabrication, and application of three dimensional dispersion engineered photonic crystal devices,” Integrated Photonics Research and Applications and the Nanophotonics Topical Meetings (IPRA/NANO), Uncasville, CT, Apr., 2006.
Abstract: The development of photonic crystals (PhCs) has enabled groundbreaking approaches to mold the flow of electromagnetic waves with frequency spanning optical regime to RF regime. Periodic electromagnetic materials (RF PhCs) are presently one of the most rapidly advancing sectors in the electromagnetic arena. Herein, we demonstrated the applications of RF PhCs in improving the performance of naval communication system and decreasing scattering crosssection of naval vessels. To this end, we designed, fabricated, and characterized dielectric devices based on the unique dispersion properties of PhCs to achieve confinement, waveguiding, radiation, and filtering in the microwave to millimeter-wave portion of the electromagnetic spectrum.
22. D.W. Prather, Z. Lu, J. A. Murakowski, C. A. Schuetz, S. Shi, and G. J. Schneider, “A perfect lens makes a perfect trap,”CLEO/QELS '06, Long Beach, CA, May, 2006.
23. D. W. Prather, Z. Lu, J. A. Murakowski, S. Shi, C. Chen C. A. Schuetz, and G. J. Schneider, “Subwavelength imaging by full 3D negative refraction using a 3D photonic crystal,” Photonic Metamaterials: From Random to Periodic Topical Meeting, The Bahamas, Jun., 2006.
24. D. W. Prather, Z. Lu, C. Lin, J. A. Murakowski, S. Shi, and G. J. Schneider, “Design, Fabrication, and Applications of Dispersion-Engineered Photonic Crystals,” XV International Materials Research Congress 2006 and the V National Engineers Nace International Section Mexico Congress, Optical Characterization of Materials (Session 20-22), Cancún, México, Aug. 2006.
25. D. W. Prather, C. Lin, and Z. Lu, “Demonstration of Compact Microwave and Terahertz Photonic "Crystal Devices,” XV International Materials Research Congress 2006 and the V National Engineers Nace International Section Mexico Congress, Optical Characterization of Materials (Session 20-24), Cancún, México, Aug. 2006.
26. C. Lin, Z. Lu, and D.W. Prather, “Demonstration of Compact Microwave Photonic Crystal Channelizers and Displacement Tunable Filters,” Wireless and Microwave Technology Conference, 2006. WAMICON '06. IEEE Annual.
Abstract: We demonstrate a new way to design ultra-compact microwave channelizers by the combination of different types of lattices and properties of photonic crystals (PhCs). We also present and experimentally validate sensitive displacement tunable filters based on the guideded resonance of PhCs. PhCs offer the opportunity to construct ultra-small integrated circuits to overcome the limitations of integrated electric circuits. In this talk, we experimentally demonstrate hybrid lattice PhC channelizers that display these unique properties by allowing the control of the wavelength selective dropping characteristics by engineering both the dispersion surface and the bandgap of the PhC. In addition, we present experimental results of a series of simple yet efficient spectral filters. In particular, if two PhC slabs are combined, they form a sensitive displacement-tunable structure that can be utilized in designing functional tunable devices, such as switches, filters, modulators, and sensors.
27. D. W. Prather, S. Shi, S. Venkataraman, Z. Lu, J. Murakowski, and G. Schneider, “Self-collimation in 3D photonic crystals,” Proc. of SPIE, vol. 5733, Photonic Crystal Materials and Devices III, pp. 84-93 (2005).
Abstract: In this paper we present self-collimation in three-dimensional (3D) photonic crystals (PhCs) consisting of a simple cubic structure. By exploiting the dispersive properties of photonic crystals, a cubic-like shape equi-frequency surface (EFS) is obtained. Such surfaces allow for structureless confinement of light. Due to the degeneracy of propagation modes in a 3D structure, self-collimation modes can be distinguished from other modes by launching a source with a particular polarization. To this end, we found that polarization dependence is a key issue in 3D self-collimation. The results hold promise for high-density PhCs devices due to the lack of structural interaction. Finally, a novel method for the fabrication of three-dimensional (3D) simple cubic photonic crystal structures using conventional planar silicon micromachining technology is presented. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivation and deep anisotropic reactive ion etching in combination with isotropic etch processes to create three-dimensional photonic crystal devices. Initial experimental results are presented.
28. Z. Lu, S. Shi, C. A. Schuetz, C. Lin, C. Chen, A. S. Sharkawy, and D. W. Prather, “Photonic crystal planar lens working at low frequencies,” Proc. of SPIE, vol. 5733, Photonic Crystal Materials and Devices III, pp.444-449 (2005).
Abstract: In this paper, we demonstrate the design and fabrication of a planar lens based on the dispersion property of a photonic crystal. When a photonic crystal is illuminated with a low frequency within its dispersion diagram it behaves very similar to an isotropic material, whose resultant index is kept a constant, and is determined by the ratio of high index material and low index material. To validate our design, we performed the experiment in millimeter regime, where the photonic crystal lens was fabricated using a CNC micro-milling machine, and a millimeter wave imaging system was built based on a vector network analyzer. For the lens, we have observed its ability to collimate an incident point source both in the amplitude and phase.
29. Z. Lu, S. Shi, and C. A. Schuetz, and D. W. Prather, “Design, fabrication, and characterization of engineered materials in the microwave and millimeter wave regime,” IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, Washington, DC, July 3-8, 2005.
30. D.W. Prather, S. Shi, T. Hwang, R. Shireen, Z. Lu, and C. A. Schuetz, “Design and fabrication of millimeter wave photonic modulators,” IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, Washington, DC, July 3-8, 2005.
Abstract: In this paper we presented the modeling, design and fabrication of a millimeter wave (MMW) photonic modulator operating at 94GHz. Our approach combines high quality factor (Q) photonic cavities with the nonlinear property of an electro-optic material that interacts with the applied millimeter wave to achieve optical modulation. The high Q values and strong field densities associated with WGMs in microdisk resonators result in the enhancement of the nonlinear interaction of optical fields with a material that exhibits coherent attributes, even with weak millimeter waves. To achieve efficient modulation, careful designs are implemented and initial experimental results are presented.
31. C. Lin, C. Chen, G. J. Schneider, Z. Lu, and D. W. Prather “Fabrication of terahertz two-dimensional photonic crystal lens on silicon-on-insulator,” Proc. of SPIE, vol. 5411, Terahertz for Military and Security Applications II, pp. 116-120 (2004).
Abstract: Using the special dispersion properties of photonic crystals (PhCs), we present a promising novel coupling device, the terahertz (THz) planar photonic crystal (PhC) lens. Three-dimensional finite-difference time-domain (3DFDTD) calculations show a 90% power transfer from a 100 µm waveguide to a 10 µm waveguide, and experimental results confirm its high efficiency. Furthermore, the PhC lens couples the wave into a PhC line-defect waveguide is also reported. These achievements manifest the usefulness of the PhC lens as an effective approach to couple the wave into future THz circuits.
32. S.K. Lohokare, C.A. Schuetz, Z. Lu, D.W. Prather, O.V. Sulima, J.A. Cox, V.A. Solovev, S.V. Ivanov, and J.V. Li, “Polymer flip-chip integrated, AlGaAsSb/AlGaSb p-i-n photodetectors for 1550 nm high-speed optical interconnects,” Proc. of SPIE, vol. 5353,Semiconductor Photodetectors, pp. 36-47 (2004).
Abstract: AlGaAsSb/AlGaSb heterostructures offer the ability to realize high-performance devices for 1550 nm high-speed optical interconnect applications. In this context, we present the design, fabrication, integration and characterization of 10 GHz p-i-n photodetectors in this material system. This effort has involved an investigation into inductively coupled plasma (ICP) etching of these materials and the development of a novel process for their conductive polymer based flip chip die attach.
33. C. Chen, Z. Lu, S. Shi, and D. W. Prather, “Self-guiding in low-index-contrast planar photonic crystals,” International Journal of High Speed Electronics and Systems, Proceedings of the 2004 IEEE Lester Eastman Conference, vol. 14, No. 3, 720-725 (2004).
34. Z. Lu, P. Yao, S. Venkataraman, D. Pustai, C. Lin, G. Schneider, J. Murakowski, S. Shi, and D. W. Prather, “Fiber-to-waveguide evanescent coupler for planar integration of silicon optoelectronic devices,” Proc. of SPIE, vol. 5358, Photonics Packaging and Integration IV, pp. 102-110 (2003).
Abstract: We present a method for parallel coupling from a single-mode f iber, or f iber ribbon, into a silicon-on-insulator waveguide for integration with silicon optoelectronic circuits. The coupler incorporates the advantages of the vertically tapered waveguides and prism couplers, yet offers the f lexibility of planar integration. The coupler can be fabricated by use of either wafer polishing technology or gray-scale photolithography. When optimal coupling is achieved in our experimental setup, the coupler can be packaged by epoxy bonding to form a f iber-waveguide parallel coupler or connector. Two-dimensional electromagnetic calculation predicts a coupling eff iciency of 77% (21.14-dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling eff iciency is experimentally achieved to be 46% (23.4-dB insertion loss), excluding the loss in silicon and the ref lections from the input surface and the output facet.
1. Z. Lu and D. W. Prather, “Optical Coupler for Coupling an Optical Fiber into a Waveguide,” US Patent and Trademark Office, Document Number 20070031088, International publication number WO2005120187, January (2004).
2. D. W. Prather, Z. Lu, J.M. Murakowski, S. Shi, and G. J. Schneider, “Electromagnetic/optical tweezers trap using a full 3D negative-refraction flat lens,” US Patent and Trademark Office, Document Number 20070285803, April (2006).
3. Z. Lu and R. Yang, “Methods for Three-Dimensional Nanofocusing of Light and Systems Thereof,” patent pending.
4. Z. Lu and W. Zhao, “Tunable Graphene-Slot Waveguides and Methods Thereof,” patent pending.
SPIE Newsroom: “Modulating light on the nanometer scale using polyvalent metal,” 2011.
Laser Focus World: feature story (“BEAM SHAPING: Plasmonics squeeze IR light into nanospot”), 2009.
Science: ScienceNOW story on web (“A perfect lens makes perfect traps”), 2006.
Optics & Laser Europe: news article (“Negative refraction lenses trap particles”)
Photonics Spectra: feature story (“Research and development of left-handed materials continues,” pp.96-100, October 2005).
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