Flat Optics and Metasurfaces - Harvard...
Transcript of Flat Optics and Metasurfaces - Harvard...
Flat Optics and
Metasurfaces
Daniel Wintz
Patrice Genevet, Mikhail Kats, Antonio Ambrosio, Nanfang Yu, Francesco Aieta, Romain Blanchard, Alex
Woolf, Alan She, Zeno Gaburro, Federico Capasso
Andor Academy April 8th, 2015
School of Engineering and Applied Sciences, Harvard University
Overview
Introduction to flat optics
Examples of optical elements using phase discontinuities
Controlled steering of surface plasmon wakes
Active metalens for tunable focusing of surface waves
Conventional Optics
Transformation Optics
Ward, Pendry, J. Mod. Opt. 43 (1996)
Diffractive Optics
Can we replace bulky optical components with
nanoscale, flat ones?
• Goal: control amplitude, phase, and polarization of light
with a low footprint, nanoscale device
• 3 ideals and challenges: high efficiency, high bandwidth,
reconfigurability
• Metasurfaces: Optically thin, subwavelength arrays of
optical elements for engineering wavefronts
The Vision of Flat Optics
Smart Phones Stretchable
Materials Google glass
Wave optics (thin lens example)
Conventional optical elements rely on gradual phase accumulation through dielectric media—phase accumulates through propagation
Wave optics (thin lens example)
Conventional optical elements rely on gradual phase accumulation through dielectric media—phase accumulates through propagation
~𝝀 or thicker
Primary wavefront
Interface
z
Wave optics (Huygens principle)
Secondary wavelets
Primary wavefront
Interface
z
Wave optics (Huygens principle)
Secondary wavelets
Primary wavefront
Interface
z
Wave optics (Huygens principle)
A sin(ωt - kx x)
x
A sin(ωt - kx x + jump)
jump
Secondary wavelets
Primary wavefront
Interface
z
Interface
z
Huygens principle
Light propagation with phase discontinuities
A sin(ωt - kx x)
x
A sin(ωt - kx x + jump)
jump
What can we use to make these discontinuities?
Light propagation with phase discontinuities
Optical Antennas
++ --
L1
• The case of a single rod antenna—behaves as a driven, damped
harmonic oscillator
• Light scattered from an antenna does not always have the same phase
as the incident light!
More complicated antenna structures can be used to achieve full 2𝜋 coverage
Overview
Introduction to flat optics
Examples of optical elements using phase discontinuities
Controlled steering of surface plasmon wakes
Active metalens for tunable focusing of surface waves
Demonstrated optical capabilities of metasurfaces
• Refraction/beam deflection
• Complex beams—Bessel beams, vortex beams, Cosine-Gauss beams
• Full and half wave plates
• Flat lenses
• Dispersionless flat lenses
• Creation and control of surface plasmon wakes
• Metagratings for focusing of surface waves
Light propagation with phase discontinuities
Generalized reflection and refraction of light N. Yu, P. Genevet , M. A. Kats, F. Aieta, J. P. Tetienne, F. Capasso, Z. Gaburro, Science 334,333 (2011)
Refraction and beam deflection The antennas operate as secondary scatterers with a tailorable phase
response, re-directing a normally-incident beam away from the normal
Uniform scattering amplitude Controlled phase responses between 0 to 2π
Vortex beams
• Phase profile is an optical ‘vortex’ or helix that carries angular momentum ±𝑚ℏ
• Not just fancy: can be used for information transfer—2.5TB/sec already achieved: Nature Photonics 6, 488–496 (2012)
Applied Physics Letters 100, 13101 (2012)
Non-diffracting beams
• Diffraction is a consequence of the wave nature of light
• Can be turned off for small length scales
Flat Lenses
Nano Lett., 2012, 12 (9), pp 4932–4936
Multiwavelength dispersionless flat lens
Science 347, (2015)
Overview
Introduction to flat optics
Examples of optical elements using phase discontinuities
Controlled steering of surface plasmon wakes
Active metalens for tunable focusing of surface waves
Introduction to Surface Plasmon Polaritons
x
Surface Plasmon Polaritons (SPPs)—Light confined to a metal/dielectric interface Surface: confined to the interface Plasmon: free electrons (plasma) oscillate Polariton: light-like
Surface Plasmon Wakes?
Sonic booms Boat wakes
Cherenkov effect
What will be the disturbance for surface plasmons?
Wakes are a general wave phenomena where a disturbance propagating in the medium travels faster than the phase velocity of the waves it creates
The Disturbance: ‘Running Wave of Polarization’
sin 𝛾 =sin 𝜃
𝑛𝑒𝑓𝑓
𝑅𝑒 𝐸𝑧
Near-field scanning optical microscopy (NSOM)
• AFM tuning fork + Tapered optical fiber
• Probes near-field • Tip diameters ~50 − 100 𝑛𝑚
• Collection mode or scattering mode
• NOT diffraction limited
NSOM Details
Schematic of collection mode operation with metal coated tapered optical fiber.
𝑘𝑆𝑃𝑃
Experimental setup and sample data
Data for 𝜃 = 20°
Interferogram Peculiarity
𝛾 Δ𝑦
𝜆𝑅𝑊𝑃
Data for 𝜃 = 20°
Experimental Data on Slits for different 𝜃
Others have done nanoslit excitation of SPPs already: Lee, S.Y., et al. PRL (2012)
Phased array gives routing configurability
𝑠𝑖𝑛𝛾 =𝑠𝑖𝑛𝜃
𝑛𝑒𝑓𝑓+
1
𝑘𝑠𝑝𝑝
𝜕𝜙
𝜕𝑥
𝟏. 𝟓 𝝁𝒎
𝚫𝒙 𝛾 𝛾 𝚫𝒅
𝝓𝟏 𝝓𝟏 + 𝚫𝝓 𝚪
(a)
𝚫𝒅
𝑘𝑆𝑃𝑃 𝑘𝑆𝑃𝑃
Spin-Angular-Momentum dependent phasing
(a)
x
y
𝑬
Linear Polarization
(b)
x
y
𝑬
Spin-Angular-Momentum dependent phasing
𝜕𝜙
𝜕𝑥= 𝜎±
𝜋
Γ
(a)
x
y
𝑬
Linear Polarization Circular Polarization
𝑠𝑖𝑛𝛾 =𝑠𝑖𝑛𝜃
𝑛𝑒𝑓𝑓±
1
𝑘𝑠𝑝𝑝
𝜕𝜙
𝜕𝑥
Calculated results for the interferogram
3 𝜇𝑚
SPP Intensity
Calculated results for the interferogram
+ =
3 𝜇𝑚
SPP Intensity
Gaussian beam Intensity
Calculated results for the interferogram
+ =
3 𝜇𝑚
3 𝜇𝑚
SPP Intensity
Gaussian beam Intensity
Interferogram Intensity
Experimental Setup and Calculation vs. Experiment
Experimental Calculated
Comparison for different incident angles
• Varying angle of incidence changes angle of the wakes
• Changing from right circularly polarized to left circularly polarized light and completely reverse the direction of the wakes
𝑠𝑖𝑛𝛾 =𝑠𝑖𝑛𝜃
𝑛𝑒𝑓𝑓±
1
𝑘𝑠𝑝𝑝
𝜕𝜙
𝜕𝑥
Applications
• Polarization detection
• Angle of incidence detection
• Testbed for Cherenkov radiation without the need for particle accelerators
• Testbed for Reversed Cherenkov studies
Overview
Introduction to flat optics
Examples of optical elements using phase discontinuities
Controlled steering of surface plasmon wakes
Active metalens for tunable focusing of surface waves
Under review
Goals
• Can we overcome some of the coupling constraints for exciting surface plasmons?
• Can we focus the surface plasmons after coupling? • Can we achieve tunable unidirectionality after coupling?
• Optoelectronics applications
• On-chip spectroscopy
Motivations
Traditional Coupling Methods
Kretschmann-Raether Method
Traditional Coupling Methods
Kretschmann-Raether Method
Grating Coupling Method
• Polarization restraints
• Fixed directionality after coupling
New Age Coupling Methods
L. Yin, C.W. Kimball et al. Nano Letters (2005)
Z. Liu, X. Zhang, et al. Nano Letters (2005)
F. Lopez-Tejeira, A. Dereux, et al. Nature Physics (2007)
New Age Coupling Methods
L. Yin, C.W. Kimball et al. Nano Letters (2005) J. Lin, F. Capasso et al.
Science (2013)
T. Tanemura, D.A.B. Miller, et al. Nano Letters (2011)
Z. Liu, X. Zhang, et al. Nano Letters (2005)
F. Lopez-Tejeira, A. Dereux, et al. Nature Physics (2007)
Nanoslit excitation of SPPs
x
y
Nanoslit excitation of SPPs
±𝒌𝒔𝒑𝒑
Laser light
y
z
Δ𝑦
B x
y
Δ𝑦Δ𝑘~1
Metalens Design Principle a)
Metalens Design Principle a) b)
Metalens Design Principle a) b)
c)
Metalens Design Principle
Experiment and sample results
𝑬
𝑬
𝜆0 = 670 𝑛𝑚
Experimental
Calculated
to APD
Single Wavelength Excitation
d) 750 𝑛𝑚
a) 632 𝑛𝑚
b) 670 𝑛𝑚
c) 710 𝑛𝑚 Vertical Slits Horizontal Slits
Same experiment as before…
Experimental
Calculated
to spectrometer
Spectrally resolved wavelength demultiplexing
Full 580 − 700 nm band
𝜆0 [nm]
No
rmal
ized
Inte
nsi
ty
a) b)
632 𝑛𝑚 band 670 𝑛𝑚 band c) d)
Spectrally resolved wavelength demultiplexing
Full 580 − 700 nm band
𝜆0 [nm]
No
rmal
ized
Inte
nsi
ty
a) b)
632 𝑛𝑚 band 670 𝑛𝑚 band c) d)
Spectrally resolved wavelength demultiplexing
Full 580 − 700 nm band
𝜆0 [nm]
No
rmal
ized
Inte
nsi
ty
a) b)
632 𝑛𝑚 band 670 𝑛𝑚 band c) d)
640 𝑛𝑚
650 𝑛𝑚
660 𝑛𝑚
e)
Focusing Nature
Experiment Calculation
Polarization Selectivity
on off
For 710 nm
• Goal: control amplitude, phase, and polarization of light
with a low footprint, nanoscale device
• 3 ideals and challenges: high efficiency, high bandwidth,
tunability
• Metasurfaces: Optically thin, subwavelength arrays of
optical elements for engineering wavefronts
The Vision of Flat Optics
Smart Phones Stretchable
Materials Google glass
Funding: Support/Instrumentation:
Patrice Genevet, Mikhail Kats, Antonio Ambrosio, Nanfang Yu, Francesco Aieta, Romain Blanchard, Alex
Woolf, Alan She, Zeno Gaburro, Federico Capasso