Nanofiber Coupled Nanoplasmonics

Nanofiber Coupled Nanoplasmonics

Limin Tong State Key Laboratory of Modern Optical Instrumentation

College of Optical Science and EngineeringZhejiang University, Hangzhou, China

KITPC Program “Plasmonic Nanogaps and Circuits” , October 12-30, 2015, Beijing

Outline

1. Introduction

2. Nanofiber coupled nanowire plasmonics

3. Nanofiber coupled nanorod plasmonics

4. Conclusion

1. Introduction Nanoplasmonics in Metallic Nanostructures

Unique optical properties to enable routing and active manipulation of light at the nanoscale, and to bridge photonics and nanoelectronics.

M. L. Brongersma et al., Science 328, 440 (2010)

Special advantages

Size and Speed

http://nano.imra.com/

Size and Speed

Nano Lett. 9, 4515 (2009)

Nanosphere Nanorod Nanowire

Typical low-D metal nanostructures for nanoplasmonics

1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)


Size

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

Size Optical confinementDeep subwavelength /10 /50 @ 700 nm


Size

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

Y. P. Wang et al.,Opt. Express 20, 19006

(2012)

Size Optical confinementDeep subwavelength /10 /50

Au nanowireMode size diameter beam size possibly down to a single-molecule level

Optical confinement

Modal profiles of Au nanowires in water (a) 10 nm; (b) 20 nm @ 660 nm

In air

In water

Mode size 10 nm

Y. P. Wang et al., J. Lightwave Technol. 32, 3631 (2014)

Y. P. Wang et al., Opt. Express 20, 19006 (2012)

Au nanowireMode size diameter beam size possibly down to a single-molecule level

Optical confinement

In air

Y. P. Wang et al., Opt. Express 20, 19006 (2012)

Large momentum mismatchLow efficiency of photon-to-

plasmon conversion

High reflectivity at the nanowire endface

R. Kolesov et al., Nat. Phys. 5, 470 (2009)


Speed

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

0-D Nanoparticle (e.g., nanorod: 20nmX100nm): Plasmon life time (LSPR) 10 fs @ 700 nm

Speed


Speed

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

1-D Nanowire (e.g., 100-nm-diameter Ag Nanowire 0.4 dB/μm)

Plasmon life time (PSPP) 30 fs @ 700 nm

Speed


Speed

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

Speed highly desired for ultrafast optical response

e.g, Ultrafast optical modulation


Speed

Nano Lett. 9, 4515 (2009)



1. Introduction

0-D 1-D

Nano Lett. 12, 3145 (2012)

Speed but high loss and broad resonance bandwidth

e.g, Ultracompact waveguide and plasmonic sensing

Modal profiles of Au nanowires in water (a) 10 nm; (b) 20 nm @ 660 nm

Diameter (nm) Am (μm2) ƞ Lm (μm) α (dB/μm) 10 0.0001 29% 0.10 43.43 20 0.0004 30% 0.19 22.91 50 0.0023 38% 0.54 8.08

e.g., Au nanowire

Mode size 10 nm

Ultrahigh lossY. P. Wang et al., J. Lightwave Technol. 32, 3631 (2014)

Ultra tight confinement Ultrafast speed

Ultrahigh loss

Size and Speed

1. Introduction

Ultra tight confinement Ultrafast speed

Broad resonance bandwidth

Size and Speed

1. Introduction

e.g., Au nanorod

P. Wang et al., Nano Lett. 12, 3145 (2012)

Trade-off: “Confinement Loss Bandwidth” e.g., in subwavelength nanofiber/nanowire waveguides

X. Guo et al., Acc. Chem. Res. 47, 656 (2014)

Tight confinement High loss

Size and Speed

1. Introduction



M. L. Brongersma et al., Science 328, 440 (2010)

On the other side, dielectric and semiconductor nanostructures, with miniature size and low loss, may offer opportunities to nanoplasmonics…



On the other side, dielectric and semiconductor nanostructures, with miniature size and low loss, may offer opportunities to nanoplasmonics…

Nanofiber Coupled Nanoplasmonics

Optical micrograph of 650-nm light guiding through a silica (D=500 nm), a ZnO (D=300 nm) and a silver (D=100 nm) nanowires in cascade

X. Guo et al., Laser Photon. Rev. 7, 855 (2013)

20

http://image.baidu.com

125 μm

Hair

500 nm

Optical fiber with diameter close to or below

L. M. Tong et al., Nature 426, 816 (2003)

Optical Nanofiber

Also appeared as “microfiber, nanowire etc. ”

1. Introduction

Glass

Polymer

P. Wang et al., Light Sci. Appl. 2, e102 (2013)

Typical materials

L. M. Tong et al., Nature 426, 816 (2003)

1. Introduction Optical Nanofiber

X. Q. Wu et al., Nanophotonics 2, 407 (2013)

Glass: Taper drawing

Nanofiber drawing system

Fabrication


F. X. Gu et al., Nano Lett. 8, 2757 (2008)

Polymer: Solution drawing

Fabrication


Uniform diameter

Smooth sidewall

Surface roughness (RMS) 0.2 nm

Circular cross-section

L. Tong et al., Opt. Express 14, 82 (2006)

Fabrication


Elastic or plastic bending

L. Tong et al., Nano Lett. 5, 259 (2005)

Annealing-after-bending

Silica nanofibers

Silica nanofibers

Manipulation


26

Tensile strength @RT

Silica NF > 5 GPaSpider silk 2 GPa

300-nm-diameter silica nanofiber with a elastic bending to a 4-μm radius

High mechanical strength

Manipulation


Waveguiding Properties


.0)(

,0)(2222

2222

hkn

ekn

Helmholtz Equations

+Boundary conditions

Analytical solutions of guided modes [1]

[1] A. W. Snyder and J. D. Love, Optical waveguide theory, Chapman and Hall, New York, 1983.

Perfect cylindrical symmetry

rnrn

rn

,

0,)(

2

1

Propagation constants (β)

Air-clad silica microfiber @ 633 nm

L. M. Tong et al., Opt. Express 12,1025 (2004)



Air-clad silica microfiber @ 633 nm

X. Q. Wu et al., Nanophotonics 2, 407

(2013)



Evanescent fields & Energy distribution (HE11 modes)

D (nm)400 800 1200 1600

0.0

0.2

0.4

0.6

0.8

1.0

633 nm

1550 nm

Silica/air

Fractional power inside the core





D (nm)400 800 1200 1600

0.0

0.2

0.4

0.6

0.8

1.0

633 nm

1550 nm

Silica/air

D=200 nm

> 90% energy is guided in the air

Evanescent field

Near-field interactionFractional power inside the core





Effective mode size


λ =633 nm

Mode area for optical confinement of 86.5% in power

silica/air

Minimum effective mode size ～ 510 nm

Real diameter

Effective diameter

Possible to realize tightly confined large fractional

evanescent waves



Nanofiber coupled

1. Introduction Nanofiber Coupled Nanoplasmonics

Nanowire plasmonicsPSPP

Nanorod plasmonicsLSPR

High efficiency photon-to-plasmon conversion

Plasmon lasers and sensors

Extraordinary strong coupling effects in coupled nanorod

Outline

1. Introduction



4. Conclusion

dielectric plasmonic

1-D nanofiber/nanowire for optical waveguiding

Bound electrons Free electrons

Maxwell Equations + Boundary conditions

Supporting waveguide modes

Dispersion relation of SPP modes

The dashed line (ω=ck) denotes the dispersion line of light in free space.

To couple light into SPP modes in a nanowire

Momentum mismatch between the photons and plasmons must be compensated

PSPP excitation in a nanowire


2. Nanofiber Coupled Nanowire Plasmonics

Optical Launching

Prism coupling

Lens-focus coupling

Bulk components with relatively low efficiency e.g.,<1%

PSPP excitation in a nanowire Optical Launching

Conventional approaches




PSPP excitation in a nanowire Optical Launching Nanofiber coupling approach

photonic nanofiberplasmonic nanowire

Why it is possible?


X. Guo et al., Nano Lett. 9, 4515 (2009).


photonic nanowireplasmonic nanowire

the small end scatters evanescent waves for compensating momentum mismatch between the two waveguides

considerable overlap between the two modes

Why it is possible?

Light guided along a photonic nanowire leaves large fractional evanescent waves


Photon-to-plasmon coupling efficiency ~80%

Silica nanofiber: D=500 nmAg nanowire: D=240 nm, L=12µm

X. Guo et al., Nano Lett. 9, 4515 (2009)

large overlap between the photonic and plasmonic modes

Endface scattering for compensating momentum mismatch



Photon-to-plasmon coupling efficiency ~92%

Silica nanofiber Ag Nanowire

X. Y. Li et al., Opt. Express 21, 15698 (2013)

Nanofiber: 300-nm diameterAg nanowire: 120-nm diameterWavelength: 785 nm



Coupling length ~220 nm

270-nm-diameter ZnO nanowire

240-nm-diameter Ag nanowire


PSPP excitation in a nanowire Optical Launching Nanowire plasmonic branch couplers


Fractional output from the Ag nanowire: 488nm —— 4%

532nm —— 8%

650nm —— 64%

Coupling efficiency ~82%

Deducting the guiding loss:

Ag about 0.43 dB/µm

ZnO lower than 0.001dB/µm





PSPP excitation in a nanowire Optical Launching Nanowire plasmonic Mach-Zehnder Interferometer


(1) Mach-Zehnder Interferometer

3-2. Hybrid “Photon-Plasmon” circuits and devices

As-assembled MZI

ZnO Nanowire: D 330 nm, L 89 µm

Ag Nanowire: D 120 nm, L 6.5 µm


ZnO Nanowire: D 330 nm, L89 µm

Ag Nanowire: D 120 nm, L 6.5 µm

FSR = 2.75 nm @710 nm

Potential applications: sensors, modulators etc.X. Guo et al., Nano Lett. 9, 4515 (2009)

PSPP excitation in a nanowire Optical Launching Nanowire plasmonic Mach-Zehnder Interferometer


ZnO nanowire: 400-nm diameter

99.5-µm length

Ag nanowire: 265-nm diameter

16.5-µm length


PSPP excitation in a nanowire Optical Launching Nanowire plasmonic ring resonator


Reducing cavity loss without sacrificing confinement of the silver nanowire

Q = 520FSR = 3.8 nm


PSPP excitation in a nanowire Optical Launching Nanowire plasmonic ring resonator


Nanowire Plasmon Laser

X. Q. Wu et al., Nano Lett. 13, 5654 (2013)

Replacing the passive nanofiber with an active semiconductor nanowire



Hybrid photon-plasmon nanowire laser





(a, c) 390-nm-diameter CdSe NW 100-nm-diameter Ag NW

(b, d) The gain of the CdSe NW and the plasmonic resonance of the Ag NW are well matched in spectra.

(e) Assemble a hybrid cavity using the CdSe and Ag NWs.

(f) Coupling photoluminescene from the CdSe NW to the Ag nanowire.



(a) Lasing under a pump fluence of 97 μJ cm-2 (19.4 KW cm-2). (b) Lasing spectra collected from the Ag end-facet, under pump fluences of 27-97 μJ cm-2. (d) Emission intensity versus pump fluence collected from end-facets of the CdSe and the Ag NWs @ dominant lasing peak around 723 nm.

Photon-plasmon laser mode area of 0.008λ2



Provides spatially separated plasmonic cavity modes with mode size down to deep-subwavelength scale

Ultrafast modulate/switch the laser by plasmonic response

Optical sensing, imaging, quantum information




Outline

1. Introduction



4. Conclusion

Typical Au nanorods

3. Nanofiber Coupled Nanorod Plasmonics Plasmonic Nanorods

Size: 20 nm*100 nm; Lifetime: 10 fs Resonance wavelength: 700 nm; Resonance bandwidth: 50 nm

P. Wang et al., Nano Lett. 12, 3145 (2012) R. Ameling and H. Giessen, Laser Photon. Rev. 7, 141 (2013)

Typical Au nanorods

3. Nanofiber Coupled Nanorod Plasmonics Plasmonic Nanorods

Scattering from individual nanorods is clearly seen, but the excitation efficiency is low due to the small absorption cross-section of single nanorod compared with the size of the excitation beam.


Free-space excitation under an optical microscopy


3. Nanofiber Coupled Nanorod Plasmonics Optical launching single Au nanorods using nanofiber

Embed nanorods inside a polymer nanofiber

Photon-to-LSPR-conversion efficiency for single nanorod70% @ 785 nm (coincided with the LSPR peak)


Replacing the free-space excitation beam by tightly confined waveguiding mode of the nanofiber


Polymer nanofiber plasmonic sensors

3. Nanofiber Coupled Nanorod Plasmonics Nanofiber coupled Au nanorod sensor


500-nm-diameter nanofiber, 785-nm-wavelength probing light

Fast response ( 0.1 s) Very low operation power (0.5 nW) No photo-bleaching

Plasmonic nanorod humidity sensor


One possible approach coupling plasmonic nanorod to a photonic cavities similar to coupling an atom to a cavity

R. Ameling and H. Giessen, Laser Photon. Rev. 7, 141 (2013)

Resonance splitting

Anti- crossing

EIT …

Strong coupling Rabi splitting

3. Nanofiber Coupled Nanorod Plasmonics Plasmonic resonance band (life time) modification


Resonance splitting

R. Ameling and H. Giessen, Nano Lett. 10, 4394 (2010)

One example: a pair of nanorods in a microcavity


One example: a pair of nanorods in a microcavity

Fabry-Perot cavity (1 μm apart) formed by two parallel gold-mirrors

R. Ameling and H. Giessen, Nano Lett. 10, 4394 (2010)

Multi-band resonanceBandwidth > 5 nm

Resonance splitting

Typically, the modified plasmonic resonance band shows


coupling plasmonic nanorod to a photonic cavities

Multiple resonance peaks mode splitting is not large enough to keep only one mode but shift out

all others out of the plasmonic resonance range

Obviously large background photon-to-plasmon conversion is not highly efficient in a single cycles of

the resonance

Relatively large bandwidth relatively large loss of the coupled system

P. Wang et al., Nano Lett. (In press)


coupling plasmonic nanorod to a photonic cavities

Seeking a photonic microcavity with high Q, small size, and high photon-to-plasmon conversion efficiency


Typically, the modified plasmonic resonance band shows Multiple resonance peaks mode splitting is not large enough to keep only one mode but shift out

all others out of the plasmonic resonance range

Obviously large background photon-to-plasmon conversion is not highly efficient in a single cycles of

the resonance

Relatively large bandwidth relatively large loss of the coupled system

to single-band, narrow bandwidth, free background LSPR

3. Nanofiber Coupled Nanorod Plasmonics Plasmonic resonance band modification

Again, microfiber or nanofiber becomes an excellent choice.


Tightly confined large fractional evanescent field 0.2-nm-level roughness Optical microcavity with high Q

OMFC 1: using the fundamental (lowest-order) guiding mode

Optical Microfiber Cavity (OMFC)


typical cavity length > 50 μm

Bottle type

M. Sumetsky, Opt. Lett. 35, 2385 (2010)

Cylindrical microfiber

M. Pöllinger et al., Phy. Rev. Lett. 103, 053901 (2009)

possible to offer cavity length 5 μm

OMFC 2: using the whispering gallery (highest-order) mode


M. Sumetsky, Opt. Lett. 35, 2385 (2010)

Here, we choose cylindrical microfiber cavity

Easy fabrication No spatial requirement on nanorod

position Relatively high Q, despite of the

leakage “only 2.542 times less than that of a spheroidal microresonator”

Reasons

OMFC 2: using the whispering gallery (highest-order) mode


Most importantly, cavity length < 5 μm : 10-fs single-cycle flying time of a photon comparable to life time of plasmon in a Au nanorod

Critical to obtain strong-coupling-induced large mode splitting P. Wang et al., Nano Lett. (In

press)

Configuration & Structure

3. Coupled Microfiber-Nanoparticle System

Schematic: coupled microfiber-nanorod system

Coupled photonic WGMs of a microfiber and LSPR modes of a nanorod




Fabrication: coupled microfiber-nanorod system

Silica microfiberAu nanorods P. Wang et al., Nano Lett. (In press)



Characterization

Experimental setup

Broadband CW light




Characterization

WGM mode excited by a single nanorod

Experimental setup P. Wang et al., Nano Lett. (In press)

Weak Coupling


large microfiber diameter (D>10 μm) Splitting/Linewidth <1

D=25.4 μm


Weak Coupling



D=25.4 μm D=11.2 μm

Increase D Increase FSR P. Wang et al., Nano Lett. (In

press)

Weak Coupling



Diameter-dependent FSR

Experimental data are in good agreement with the calculation

Experimental

Calculation


3. Coupled Microfiber-Nanoparticle System Mode Splitting

When D is reduced below 10 μm single-cycle flying time <100 fs Mode splitting observed

e.g., D=5.6 μm

Splitting/Linewidth 1


3. Coupled Microfiber-Nanoparticle System Strong Coupling smaller microfiber diameter (D<5 μm)

Splitting/Linewidth >1

Strong coupling occurs large mode splitting




D=1.46 μm





Splitting 42.9 nmLinewidth 2 nm

Splitting/Linewidth 20Splitting energy 133 meV


D=1.46 μm

The narrowest LSPR linewidth reported in a nanorod

Almost free background

Single-band




Strong-coupling induced 2-nm-linewidth single-band plasmonic resonance in a Au nanorod !





Shining 2-nm-linewidth light to launch LSPR in an uncoupled Au nanorod

What’s the difference?

650-nm laser light P. Wang et al., Nano Lett. (In

press)




Shining 2-nm-linewidth light to launch LSPR in an uncoupled Au nanorod

What’s the difference?

650-nm laser light

Dotted line: excitated under same spectral density




Agrees very well with calculation

Normalized electric field distribution

Nanorod



Physical underlying Radiation to free space

Coherently pulled back into WGMs

D=1.46 μm P. Wang et al., Nano Lett. (In

press)


Physical underlying

Significantly increased life time > 200 fs

650-nm laser light 10 fs

Better coherence

Radiation to free space

Coherently pulled back into WGMs

D=1.46 μm P. Wang et al., Nano Lett. (In

press)


D=860 nm

Higher bending loss



Higher bending loss

D=860 nm P. Wang et al., Nano Lett. (In

press)


D=510 nm

No WGM availableBack to 50-nm


3. Nanofiber Coupled Nanorod Plasmonics

Narrow-linewidth single-band plasmonic resonance

Plasmonic sensing & detection Better spectral resolution Higher sensitivity Lower detection limit

Potential applications

Deep-sub- plasmon laser Narrower linewidth Lower threshold Higher efficiency

Many others …

Route and manipulate light at the nanoscale with longer lifetime, better coherence, higher field enhancement and lower loss.


Outline

1. Introduction



4. Conclusion

Nanofiber coupled

4. Conclusion Nanofiber Coupled Nanoplasmonics

Nanowire plasmonicsPSPP

Nanorod plasmonicsLSPR

High efficiency photon-to-plasmon conversion

Plasmon lasers and sensors

Extraordinary strong coupling effects in coupled nanorod

Single-band 2-nm-linewidth LSPR


Outlook

96


Outlook

97

Nanophotonics Group @ ZJU 2015 www.nanophotonics.zju.edu.cn

Current and former group members

Acknowledgement

Collaborators

Acknowledgement

Prof. Qihuang Gong,

Yunfeng Xiao, Guowei Lu

Peking Univ, China

Prof. Eric Mazur Harvard University (USA)

Prof. Min QiuZhejiang University (China)

Prof. C. Z. NingASU (USA)

Prof. Jimin BaoUniversity of Houston (USA)

Prof. Younan XiaGatech (USA)

National Science Foundation of China （ NSFC)

National Basic Research Program of China

Ministry of Education, China

etc.

Research Funds from

Acknowledgement

Thank you !

Nanofiber Coupled Nanoplasmonics

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