PLASMONICS: RECENT DEVELOPMENTS AND MAIN APPLICATIONS

Transcription

1 PLASMONICS: RECENT DEVELOPMENTS AND MAIN APPLICATIONS Alexandra Boltasseva Department of Photonics Engineering Technical University of Denmark Many thanks to Mark Brongersma (Stanford) Sergey Bozhevolnyi (Southern Denmark) Vlad Shalaev (Purdue) for lecture materials

2 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

3 HOT PLASMONICS Summer Nanophotonics conferences, 74 sessions 30 sessions on PLASMONICS and METAMATERIALS: > 40% + Plenary talks Summer 2006 First GORDON CONFERENCE on PLASMONICS Professor Neil E. Gordon chemistry faculty

4 GORDON CONFERENCES The Gordon Research Conferences provide an international forum for the presentation and discussion of frontier research in the biological, chemical, and physical sciences, and their related technologies. The GRCs were initiated by Dr. Neil E. Gordon, of the Johns Hopkins University, who recognized in the late 1920s the difficulty in establishing good, direct communication between scientists The GRCs promote discussions and the free exchange of ideas full week of intense discussion and examination of the most advanced aspects of their field. Johns Hopkins University, Baltimore, Maryland summer of 1931 Professor Neil E. Gordon, a member of the chemistry faculty.

5 GORDON CONFERENCES Johns Hopkins University Baltimore, Maryland 1931 Plasmonics Keene State College Keene, NH 2006

6 CENTURIES-OLD PLASMONICS E-field Surface plasmon = Collective electron motion Au nanoparticles red coloration Ag nanoparticles yellow coloration

7 CENTURIES-OLD PLASMONICS Czechoslovakian glass vase E-field Surface plasmon = Collective electron motion Au nanoparticles red coloration Ag nanoparticles yellow coloration

8 SP FOR SENSORS SPs are used as optical sensors in biology, medicine, chemistry The adsorption of fewer than hexadecanethiol molecules on single Ag nanoparticle results in a localized SP resonance shift of 40.7 nm Ag nano particles can be used as optical sensors with zeptomole sensitivity A. D. McFarland and R. P. Van Duyne, NanoLetters 3, 1057 (2003)

9 HOLEY MAGIC Ag film with a 440 nm hole metal d << λ Increased transmission through hole arrays in metal films Much more light than directly impingent on hole! Reason: excitation of surface plasmons H.F. Ghaemi, et al., Phys. Rev. B 58, 6779 (1998) T.Thio et al., Optics Letters 26, (2001)

10 PERFECT LENS Silver slab 40 nm 80 nm Object plane Image plane Thin metal film can act as near-field super lens Imaging of sub-wavelength features (tens of nm) Based on surface plasmon excitation J. Pendry and D. Smith, Physics Today (2003) J. Pendry, Contemporary Physics, 45, (2004)

11 NANOSCALE METAL OPTICS 40-nm-thick and 2.5-µm-wide silver strips on glass substrate Thin metal strips work as nano-scale optical waveguides W. L. Barnes, et. al., Nature 424, 824 (2003)

12 MAIN AREAS E-field Surface plasmon = Collective electron motion Propagating SP mode Surface Plasmon Polariton Localized SP mode Surface Plasmon SPs: Coupling light to nanoscale Interconnects Sensing

13 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

14 SURFACE PLASMON POLARITON R. H. Ritchie, Phys. Rev. 106, 874 (1957)

15 WHY PLASMONICS? λ SP is small Optical frequencies nm-scale wavelengths

16 SURFACE PLASMON POLARITON Confinement is wavelength-dependent For short wavelengths z << λ Strong localization of the EM field High local field intensity

17 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

18 ELECTRONIC-PHOTONIC INTEGRATION Modern communication systems Huge amount of data Ever increasing speed Electronic circuit + Very compact (<~ 100nm) - Operational speed is limited Diffraction limit Photonic circuit + Very fast - Component size is limited (>~ 1 µm) Optical mode in waveguide > λ 0 /2n CORE Electronic + Photonic circuit: Photonic functionality based on metals: Surface plasmon based circuits

19 DYNAMIC CONTROL Conventional IO devices Dielectric waveguides Control by externally applied electrical signals Plasmonic stripe guides Metal guides Light and electric signals along the same channel Dynamic components: Thermo-optic MZ modulator Directional coupler switch In-line extinction modulator T. Nikolajsen, et. al., APL (2004), OC (2005) P. Berini, et. al. (2005)

20 NORMAL SPP WAVEGUIDES Excitation Prism coupling Grating coupling Limited propagation length Silver-air interface

21 PLASMONIC WAVEGUIDES STRIP 2D FILM GAP WIRE GROOVE Weak confinement Low loss Integrated optics Efficient dynamic control Strong confinement Compactness Integrated optics

22 PLANAR SP WAVEGUIDES Propagation length: ~ tens of µm ~ mm Confinement: ~ hundreds of µm ~ several µm D. Sarid, Phys. Rev. Lett. 47, 1927 (1981) J. J. Burke, et. al., Phys. Rev. B 33, 5186 (1986)

23 LONG-RANGE SPP WAVEGUIDES 1.55 µm BCB-Gold-BCB

24 FINITE WIDTH METAL STRIP Dimensions Thickness 8 20 nm Width 2 10 µm P. Berini, Phys. Rev. B 61, (2000) R. Charbonneau, et. al, Opt. Lett. 25, 844 (2000)

25 SAMPLE FABRICATION MMP A/S by courtesy of MMP A/S MMP A/S

26 STRIP WAVEGUIDES FOR IO Easy fabrication (UV lithography) Low propagation loss ~ 2-7 db/cm (at 1.55 µm) Low coupling loss (SMF) ~ 1 db/facet and below (at 1.55 µm) R. Charbonneau, et. al., Optics Express 13, 977 (2005) A. Boltasseva, et. al., J. Lightwave Technol. 23, 413 (2005)

27 STRIP WAVEGUIDES FOR IO Interfacing with external world Passive components Active components MMP A/S VOA DCS

28 LR-SPP DIRECTIONAL COUPLERS Coupling length 0.8 mm Separation 4 µm A. Boltasseva and S. I. Bozhevolnyi, JSTQE 12, 1233 (2006)

29 METAL GRATINGS

30 SAMPLE FABRICATION E-beam resist Bottom cladding Substrate MMP A/S

31 SAMPLE FABRICATION Exposure Development Etching MMP A/S

32 SAMPLE FABRICATION Metal deposition MMP A/S

33 SAMPLE FABRICATION Lift-off Photoresist spin MMP A/S

34 SAMPLE FABRICATION Exposure Development MMP A/S

35 SAMPLE FABRICATION Metal deposition MMP A/S

36 SAMPLE FABRICATION Top cladding

37 LR-SPP GRATINGS (b) 28±1 nm Ridges on one side of the waveguide plane 40-µm-wide and 80-µm-long grating on 8-µm-wide strip waveguide

38 GRATING PERFORMANCE Ridge width 225 nm Grating period 500nm Grating length 40 µm

39 GRATING PERFORMANCE Reflection up to 60 % Reflection peak width from 5 to 40 nm Effective refractive index modulation Δn from ~ to ~

40 SIMPLE ADD-DROP FILTER Λ = 500 nm Input 200 µm 80 µm Direct arm 15-dB dip Drop arm peak with 13-nm-FWHM Device loss ~ 9 db Transmission/Reflection (db) Z-angle 10 Total ridge height 40 nm Ridge width 220 nm Grating period 500 nm Grating length 80 µm Direct arm 'Drop' arm Total power 15-dB dip Wavelength (nm) A. Boltasseva, et. al., Optics Express, 13, 4237 (2005)

41 2D GRATINGS FOR LR-SPP Period 570 nm Bump diameter 230 nm Total bump height 100 nm Structure length 6-50 µm courtesy of K. Leosson

42 FABRICATION CONCLUSIONS Plasmonic strip waveguide fabrication Simple Planar Reproducible Cheap Nanostructured strips Complicated Expensive Time-consuming Not suitable for real device fabrications Solution Nanoimprint-involving fabrication

43 NIL FOR POLYMER MOLDING Si, SiO 2 Stamp Resist Thermoplast T g o C PMMA T g ~ 100 o C Transfer-layer Substrate Si, SiO 2 Courtesy of A. Kristensen Hard stamp Substrate with a polymer layer

44 NIL FOR POLYMER MOLDING F Si, SiO 2 Courtesy of A. Kristensen Heat Pressure

45 NIL FOR POLYMER MOLDING F Si, SiO 2 Courtesy of A. Kristensen Cool down Pressure

46 NIL FOR POLYMER MOLDING Courtesy of A. Kristensen Resist hardened Separate

47 NIL FOR POLYMER MOLDING Advantages Unlimited resolution (given by the stamp fabrication) Paralel fabrication process: 1 sample processing at a time, containing several single chips Wafer-scale fabrication Simple and cheap process

48 NANOIMPRINT

49 NANOIMPRINTED GRATINGS by R. Pedersen Grating period 500 nm Protrusion depth 20 nm R. Pedersen, et.al, ME 84, 895 (2007)

50 NIL + PLASMONIC COMPONENT Metal stripe Fluidic channel Interaction zone Polymer cladding z y x Polymer buffer x Polymer

51 CONCLUSIONS Plasmonic strip waveguide components Simple design procedure Broad range of parameters Efficiency (gratings) Easy integration with other waveguide components Robust and reproducible fabrication procedure NIL-based process Integration with microfluidic channels Efficient active components Support only one polarization

52 MOTIVATION: NANOWIRES Eliminate polarization dependence Make plasmonic devices that are compatible with current standards in optical communications MMP A/S Utilize properties of metallic waveguides to realize new device concepts Reduce propagation loss

53 NANOWIRE SPP WAVEGUIDES P. Berini, Optical Waveguide Structures US patent number 6,741,782 ( 100 nm

54 NANOWIRE SPP WAVEGUIDES Long-Range SPP E E Both TE and TM guiding is demonstrated Propagation loss at 1.5 µm 4 db/cm (TE) 4.5 db/cm (TM) Coupling loss at 1.5 µm 3.5 db/facet (TE) 5 db/facet (TM) Propagation loss reduction materials and fabrication optimization K. Leosson, et. al.,optics Express, 14, (2006)

55 DOUBLE NANOWIRES 150 nm x 150 nm Separation nm with K. Leosson

56 DOUBLE NANOWIRES 75 nm 300 nm 450 nm with K. Leosson

57 APPLICATION EXAMPLE: VOA 1.5 mm Polymer has dn/dt < 0 Heating waveguide core reduces effective index Not possible to realize using dielectric waveguides by courtesy of MMP A/S Wavelength = 1550 nm TM-guiding devices Max drive voltage 4-5V Drive power can be reduced by using polymers with larger thermo-optic coefficient

58 NANOWIRES FOR LR-SPP Technology Simple EBL based NIL-compatible (in plans) Eliminated polarization dependence Compatible with current standards in optical communications Dynamic components Reduce propagation loss

59 FEATURES AND APPLICATIONS Metal strips/wires vs dielectric waveguides Technology Integrated Optical Circuits Simple High-quality Lasers Low cost Flexible Sensors Reproducible NIL-compatible: wafer-scale fabrication Easy design procedure Easy mode shaping (efficient coupling with fibers) Possible propagation loss reduction Only one dielectric material (no refractive index engineering) Efficient dynamic components

60 SURFACE PLASMONS IN SLITS/GAPS The coupling of SPPs E k SP Strong field confinement Larger propagation loss E Varying width Lateral confinement K. Tanaka & M. Tanaka, Appl. Phys. Lett. 82, 1158 (2003) I. P. Kaminow, et. al., Appl. Opt. 13, 396 (1974)

61 V-GROOVES Channel PP (CPP) θ= 16 / 25 0 h 1 μm 1.9-μm-thick gold layer on glass D.K. Gramotnev and D.F.P. Pile, Appl. Phys. Lett. 85, 6323 (2004) S. I. Bozhevolnyi, V. S. Volkov, E. Devaux,T. W. Ebbesen, Phys. Rev. Lett. 95, (2005)

62 V-GROOVES Subwavelength (in width) channel plasmon polariton guiding D.K. Gramotnev and D.F.P. Pile, Appl. Phys. Lett. 85, 6323 (2004) S. I. Bozhevolnyi, et. al, Phys. Rev. Lett. 95, (2005)

63 FABRICATION CHALLENGES Focused Ion Beam Milling Slow High roughness Complex S. I. Bozhevolnyi, V. S. Volkov, E. Devaux, T. W. Ebbesen, PRL 95 (2005) Si stamp by I. Fernandez-Cuesta V-Grooves by Nanoimprint Production-compatible Only standard processes High reproducibility Flexible process Wafer-scale

64 FABRICATION: GROOVES

65 FABRICATED V-GROOVES V-grooves by NIL-based process Parallel, wafer-scale fabrication Only standard processes Smooth sidewalls Shaping (angle change) by stamp oxidation or RIE/oxidation combination Adaptable to various designs and devices by I. Fernandez-Cuesta

66 SNOM CHARACTERIZATION Measurements: Valentyn Volkov Optics Letters, submitted (2008)

67 FEATURES AND APPLICATIONS Metal V-grooves Technology High quality Can be low cost Flexible Reproducible NIL-compatible: wafer-scale fabrication Sub-wavelength confinement Ultracompactness Bio-sensors Ultracompact plasmonic components

68 GROOVES AND WEDGES Transverse electric field for channel PP and wedge PP Modal sizes: WPP 0.46 µm, CPP 2.5 µm Propagation lenth ~ 35 µm E. Moreno, et. al., Phys. Rev. Lett. 100, (2008)

69 COUPLING WPP - SPP Adiabatic coupling to SPP: Adiabatic decrease in height E. Moreno, et. al., Phys. Rev. Lett. 100, (2008)

70 COUPLING WPP - SPP Adiabatic coupling to SPP: Adiabatic increase in wedge angle Incoupling using fibers E. Moreno, et. al., Phys. Rev. Lett. 100, (2008)

71 WPP: EXPERIMENT First experimental realization FIB fabrication D. F. P. Pile, et. al, APL 87, (2005)

72 WPP: LARGE SCALE FABRICATION

73 FABRICATED WEDGES

74 SNOM CHARACTERIZATION WPP propagates rightwards 32 x 10 μm 2 Optics Express, 16, 5252 (2008)

75 GROOVES AND WEDGES Technology High quality Flexible Reproducible NIL-compatible: wafer-scale fabrication Sub-wavelength confinement Ultracompactness Bio-sensors Ultracompact plasmonic components

76 METAL SURFACES 40-nm-thick and 2.5-µm-wide silver strips on glass substrate Thin metal strips work as nano-scale optical waveguides W. L. Barnes, et. al., Nature 424, 824 (2003)

77 2D MANIPULATION OF SPP 2D Surface nanostructures Elastic scattering of SPPs Waveguides, gratings, focusers,

78 2D MANIPULATION OF SPP H. Ditlbacher et al., APL 81, 1762 (2002)

79 PC WAVEGUIDES FOR SPP Topography l 740 nm l 795 nm l 825 nm Image size mm 2 min max S. I. Bozhevolnyi et.al., Phys. Rev. Lett. 86, 3008 (2001)

80 PC WAVEGUIDES FOR SPP Optical signal (arb. units) 2.5 A B C (c) Cross section coordinate (μm) Image size: 32 32μm 2, wavelength 740 nm min max S. I. Bozhevolnyi et.al., Phys. Rev. Lett. 86, 3008 (2001)

81 FABRICATION Surface plasmon waveguide Metal coating and lift-off Developing Resist spin and exposure Metal coating Glass substrate By K. Leosson

82 2D MANIPULATION OF SPP Quartz substrate I. P. Radko, et. al, OE 16, 3924 (2008)

83 2D MANIPULATION OF SPP I. P. Radko, et. al, OE 16, 3924 (2008) J. Beermann, et. al, OE 15, (2007)

84 2D MANIPULATION OF SPP I. P. Radko, et. al., Optics Express, 15, 6576 (2007)

85 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

86 LOCALIZED SURFACE PLASMONS 3D Concentration of EM energy on nanoscale By courtesy of V. Shalaev (Purdue)

87 LOCALIZED SURFACE PLASMONS Light-scattering spectra from a gold nanorod and a 60 nm gold nanosphere measured under identical conditions (light polarized along the long rod axis). The resonance energies E res and linewidths Γ are indicated. True color photograph of a sample of gold nanorods (red) and 60 nm nanospheres (green) in dark-field illumination (inset upper left). Bottom right: TEM images of a dense ensemble of nanorods and a single nanosphere. C. Sönnichsen et.al, PRL 88, (2002)

88 LOCALIZED SURFACE PLASMONS S. Lal, S. Link, N. J. Halas, Nature Photonics, 1 (2007)

89 NANOSHELS 120-nm silica core coated with gold S. Lal, S. Link, N. J. Halas, Nature Photonics, 1 (2007)

90 NANOSHELS FOR SERS S. Lal, S. Link, N. J. Halas, Nature photonics, 1 (2007)

91 LOCALIZED SURFACE PLASMONS S. Lal, S. Link, N. J. Halas, Nature Photonics, 1 (2007)

92 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

93 COUPLING LIGHT TO NANOSCALE E-field Surface plasmon = Collective oscillation of the conduction electrons Z. Liu et al, Metamaterials, (2008) Localized SP resonance = optical nano-antenna

94 COUPLING LIGHT TO NANOSCALE Antenna: - transducer to receive or transmit EM waves within a specific frequency band NanoAntenna: - simple metal resonator at optical frequencies (subwavelength in size) due to particle(s) plasmon resonance - function of: wavelength, polarization, particle geometry and host material Uses: - transducer for receiving or transmitting information on the sub-wavelength scale By courtesy of V. Shalaev (Purdue)

95 FIRST NANOANTENNAE SEM SHG / continuum generation resonance resonance no / weak resonance no / weak resonance 2D arrays of metallic ellipses NanoOptics group (Graz University) W. Rechberger, et al. Opt. Comm 220, 137 (2003) NanoOptics group (Basel / Wurzburg) P. Muhlschlegel, et al., Science, 308, 1607 (2005) By courtesy of V. Shalaev (Purdue)

96 DOUBLE ELLIPSE NANOANTENNAE 65 nm Top 65 nm 155 nm y 300 nm x 600 nm 25 nm Thick Quartz Substrate Side x y z y x Percentage nm wavelength (nm) Transmission (Across Gap) Reflection (Across Gap) Transmission (Orthogonal) Reflection (Orthogonal) Bakker et al, OE 15, (2007)

97 PLASMONIC NANOANTENNAE major axis: 110 nm minor axis: 55 nm gap: 17 nm height: 40 nm x period: 400 nm y period: 200 nm H1 H2 H1 H2; Averaged Liu, et al, Metamaterials (2008, in press)

98 NANOWIRES AS RESONATORS H. Ditlbacher et. al, PRL 95, (2005)

99 NANOWIRES AS RESONATORS

100 PLASMONIC RESONATORS Technology High quality Flexible High cost Small structures/gaps are hard to reproduce Quality of the surface should be good Chemical methods

101 OUTLINE Why plasmonics? Surface plasmons Plasmonic waveguides Localized SP Resonators and antennae Outlook MMP A/S MMP A/S

102 NANOSCALE PHOTONICS WITH SP E-field Surface plasmon = Collective electron motion Propagating SP mode Surface Plasmon Polariton Localized SP mode Surface Plasmon SPs: Coupling light to nanoscale Interconnects Sensing

103 PLASMONICS: OUTLOOK Advantages Optical processing of data Compactness Electrodes are already in place Any dielectric cladding can be used Many geometries/parameter space Large field enhancement State-of-the-art To do list Many promising configurations Basic components demonstrated Choice of optimal geometry Nanoscale functionality Large scale fabrication Material choice Surface quality

104 NANOSHELS S. Lal, S. Link, N. J. Halas, Nature Photonics, 1 (2007)

105 PLASMONIC NANOANTENNAE Gold Quartz substrate Gold y x Quartz substrate Bakker et al, OE 15, (2007), Bakker et al, APL 92, (2008) Liu, et al, Metamaterials (2008, in press)

106 SLOW SP Slow SP modes are far from the light line and keep field in metals: very good for storing the EM energy and field enhancement! By courtesy of S. I. Bozhevolnyi