SPP waveguides. Introduction Size Mismatch between Scaled CMOS Electronics and Planar Photonics. dielectric waveguide ~ 10.

Transcription

1 SPP waveguides Introduction Size Mismatch between Scaled CMOS Electronics and Planar Photonics CMOS transistor: Medium-sized molecule dielectric waveguide ~ 10

2 Silicon Photonics?

3 Could such an Architecture be Realized with Metal rather than Dielectric Waveguide Technology?

4 Metal Optics: An introduction Photonic functionality based on metals?!

5 Harry Atwater, California Institute of Technology A World of Nanophotonic Devices On-chip light source Long-range(~ cm) waveguides ~ cm Short-range(~ nm) waveguides Photonic integrated circuit Nano-photonics Nano-electronics Could such an Architecture be Realized with Metal rather than Dielectric Waveguide Technology?

6 Plasmons at Planar Metal-Dielectric Interfaces surface plasmons are longitudinal charge density fluctuations on the surface of a conductor surface plasmon dispersion relation: k x : dielectric : metal c x (10 15 s -1 ) Surface Plasmon dispersion relation for Ag in air Harry Atwater, California Institute of Technology = 337 nm =c k x (Light line) =337 nm; 1 = -1 Plasmon Dispersion Relation k x ( m -1 ) << 337 nm Plasmons are highly localized at metal-dielectric interfaces, so potential for: Ultrasmall Optical Devices 2D-Optics on metal surfaces

7 Nano Focusing & Wave Guiding 8 =c k x ' 1 At large kx ( 1 2), z i. kx E ie ( air : i, metal :- i) z x 6 =337 nm; 1 = -1 Strong confinement at the interface (10 15 s -1 ) 4 2 Broad dispersion Nano focusing k x ( m -1 ) At low k ( 1), E E z x x i ' 1 ' 1 in air : E E z x i 1 ' 1 in metal : Low loss at the interface Wave guiding

8 Several 1 cm long, 15 nm thin and 8 micron wide gold stripes guiding LRSPPs 3-6 mm long control electrodes low driving powers (approx. 100 mw) and high extinction ratios (approx. 30 db) response times (approx. 0.5 ms) total (fiber-to-fiber) insertion loss of approx. 8 db when using single-mode fibers

9

10

11 Fundamental symmetric mode of a metal stripe : thickness (T) W=10um T LR-SP WG 14nm 16nm 18nm 20nm

12 P. Berini, PhotonicWest 2005.

13 (Spectalis Co.)

14 Fundamental asymmetric mode of a metal stripe : n n T=16 nm, W=10um n = n = n = 0.003

15 Symmetric mode guided by a metallic channel waveguide fiber Polymer 1.55 m silicon Au (-96+i11) 9 m 20nm 15mm ~10 m Propagation loss : 21dB/ cm

16 Y-branch Channel-1 Channel-2 1 2

17

18

19

20

21 Wavelength shifts by direct heating a metal wire Polymer 2 INPUT OUTPUT + - Polymer 1 Substrate Transmittance (db) Wavelength (nm)

22 Tunable Wavelength Filter

23 Vertical directional couplers H. Won, APL vol.88, (2006)

24 Vertical directional couplers d=4um 254 um d=6um 558 um m i t= 20nm d d R /k metal = i (gold) dielectric = =1550nm t=20nm symmetric even mode symmetric odd mode distance(d : distance between two slabs)

25 Even mode and odd mode : directional couplers based on LRSPP Vertical D Lateral D m, even mode m, odd mode m, even mode m, odd mode m, even mode m, odd mode m, even mode m, odd mode m, even mode m, odd mode m, even mode m, odd mode

26 Vertical directional couplers odd odd even mode odd mode Lateral DC

27 Vertical directional couplers Channel 1 Channel 2 Extinction ration at 400um : 27dB

28 Variable optical attenuator based on LR-SPP Submitted to EL, S. Park & S. Song

29 Extremely long-range SPP? Symmetrically coupled LRSP frequency Anti-symmetrically coupled LRSP in-plane wavevector

30 Extension of SPP propagation length LR SPP Thin metal film Finite-width metal strip D. Sarid (PRL, 1981) J. J. Burke (APL, 1986) P. Berini (PRB, 2000) Double metal films n2 > n1 Metal-dielectric films n1 > n0~n4 Metal n1 n2 n1 G. I. Stegman et al (APL, 1983) n4 metal n3 n2 n1 n0 F. Y. Kou et al (OL, 1987)

31 Extended Long-Range SPPs n1 Metal n2 n D n5 ~n1> n0~n2~n4 n5 n4 metal n3 n2 n1 n0 propagation length(mm) separation distance(d : m)

32 Range extension with finite-width metal stripes t n 1 n 2 D No good w Two fundamental modes Even mode only D<D cutoff n 2 < n 1

33 propagation length (mm) Propagation length and effective index separation distance (D: m) n w 5 m t 20nm m i, nm r /k separation distance (D: m) n Cutoff (D: m ) P-length (mm) Propagation length of a single stripe is only about 11mm. Propagation length of double stripes can be extended more than 10 times!

34 Mode profile & Mode size n 1.47, n 1.45, w 5 m 1 2 Double metal stripe Single metal stripe D=100nm, t= 20nm D=300nm, t= 20nm t= 20nm 10 m D=500nm, t= 20nm D=780nm, t= 20nm t= 16 nm Both of two modes have mode size of ~ 10 m Propagation length = 230 mm Propagation length = 46 mm

35 Fraction of field energy in metal and area n D = 780nm 0.8 Abs(Ey) metal stripe vertical distance( m) In metal stripes In n2 dielectric fraction of the field confined metal area (%) 4.0x x x separation distance ( D : nm ) fraction of the field confined n 2 area (%) separation distance ( D : nm )

36 Butt-coupling efficiency with a SM fiber 0.70 Abs(E y ) Vertical profile double stripe single stripe coupling loss wtih fiber ( db ) Single metal strip vertical distance ( m ) thickness of metal ( t : nm) Abs(E y ) Lateral profile lateral distance ( m ) single stripe double stripe 1 double stripe 2 coupling loss wtih fiber ( db ) Double metal strips separation distance ( D : nm ) Mode profile Coupling loss with fiber

37 Plasmonic Flexible-wires for 40 GHz interconnections Jung (ETRI), 40 Gbit/s light signal transmission on a long-range SPP waveguide, APL, PTL, Tx Drive IC TIA & Pre amp IC LR-SPP waveguide SMA VCSEL array PD array SMA Rx 14 nm-thick, 2.5 m-wide gold stripes Gb/s World best Loss (db) = 1310 nm Waveguide length (cm) 0.6 db/cm : World best record in propagation loss. (Previous world record : 3.2 db/cm by Berini, 2006)

38 Double-electrode metal waveguides : Lines, S-band, Y-branch Joo, Long-range surface -plasmon--polaritons on asymmetric double-electrode structures, APL, D metal strip SPP mode d3 w 2 d1 D core metal slab d3 cladding S-band metal strip metal slab Y-branch

39 Localized Surface Plasmons : Nanofocusing and Nanolithography 8 =c k x ' 1 At large kx ( 1 2), z i. kx E ie ( air : i, metal :- i) z x 6 =337 nm; 1 = -1 Strong confinement at the interface (10 15 s -1 ) 4 2 Broad dispersion Nano focusing k x ( m -1 )

40

41 Propose metal nanowires. Propagation Loss (asymmetric mode) High Beam radius -> zero!

42 Asymmetric mode : field enhancement at a metallic tip E r E r E z E z M. I. Stockman, Nanofocusing of Optical Energy in Tapered Plasmonic Waveguides, Phys. Rev. Lett. 93, (2004)] 50nm * See MOVIES : SPP propagation through a metallic tip

43 Plasmonic Crystal Demultiplexer and Multiports the realization of two-dimensional optical wavelength demultiplexers and multiports for surface plasmons polaritons (SPPs) based on plasmonic crystals, i.e., photonic crystals for SPPs.

44

45 2007/5/1 ~ an optical range resonator based on single mode metal-insulator-metal plasmonic gap waveguides. A small bridge between the resonator and the input waveguide can be used to tune the resonance frequency. FDTD with the perfectly matched layer boundary conditions

46 Slow Propagation, Anomalous Absorption, and Total External Reflection of Surface Plasmon Polaritons in Nanolayer Systems n=2 n=1 n=0

47

48 we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.

49 * Short-range (asymmetric modes) : Nano localization is achievable! * Long-range (symmetric modes) : Low loss is achievable! -> Trade-off between Localization and Loss