A Long and Winding Road Photonic-Crystal Fibers

1
A Long and Winding RoadPhotonic-Crystal Fibers
Photonic CrystalsPeriodic Surprises in
Electromagnetism
Steven G. Johnson MIT
Blochs theorem is more important than Maxwells
equations )
2
Optical Fibers Today(not to scale)
silica cladding n 1.45
R. Ramaswami K. N. Sivarajan, Optical
Networks A Practical Perspective
3
The Glass Ceiling Limits of Silica
Radical modifications to dispersion, polarization
effects? tunability is limited by low index
contrast
High Bit-Rates
Compact Devices
Long Distances
Dense Wavelength Multiplexing (DWDM)
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Breaking the Glass CeilingHollow-core Bandgap
Fibers
Photonic Crystal
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Breaking the Glass CeilingHollow-core Bandgap
Fibers
Bragg fiber
Yeh et al., 1978
figs courtesy Y. Fink et al., MIT
omnidirectional OmniGuides
white/grey chalco/polymer
silica
R. F. Cregan et al., Science 285, 1537
(1999)
5µm
PCF
Knight et al., 1998
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Breaking the Glass CeilingHollow-core Bandgap
Fibers
Guiding _at_ 10.6µm (high-power CO2 lasers) loss lt 1
dB/m (material loss 104 dB/m)
figs courtesy Y. Fink et al., MIT
white/grey chalco/polymer
Temelkuran et al., Nature 420, 650 (2002)
silica
Guiding _at_ 1.55µm loss 13dB/km
R. F. Cregan et al., Science 285, 1537
(1999)
5µm
Smith, et al., Nature 424, 657 (2003)
OFC 2004 1.7dB/km BlazePhotonics
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Breaking the Glass Ceiling IISolid-core Holey
Fibers
solid core
holey cladding forms effective low-index material
Can have much higher contrast than doped silica
strong confinement enhanced nonlinearities,
birefringence,
J. C. Knight et al., Opt. Lett. 21, 1547 (1996)

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Breaking the Glass Ceiling IISolid-core Holey
Fibers
nonlinear fibers
endlessly single-mode
Wadsworth et al., JOSA B 19, 2148 (2002)
T. A. Birks et al., Opt. Lett. 22, 961 (1997)
polarization -maintaining
low-contrast linear fiber (large area)
K. Suzuki, Opt. Express 9, 676 (2001)
J. C. Knight et al., Elec. Lett. 34, 1347
(1998)
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Omnidirectional Bragg Mirrors
a 1d crystal can reflect light from all angles
and polarizations
Winn, Fink et al. (1998)
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OmniGuide Fibers
omnidirectional mirrors
c.f. Photonic Bandgap Fibers Devices Group _at_ MIT
(also a Cambridge MA start-up www.omni-guide.com)
S. G. Johnson et al., Opt. Express 9, 748
(2001)
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Hollow Metal Waveguides, Reborn
metal waveguide modes
frequency w
1970s microwave tubes _at_ Bell Labs
wavenumber b
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Hollow Metal Waveguides, Reborn
metal waveguide modes
OmniGuide fiber modes
frequency w
1970s microwave tubes _at_ Bell Labs
wavenumber b
wavenumber b
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An Old Friend the TE01 mode
lowest-loss mode, just as in metal
Here, use R13µm for l1.55µm n4.6/1.6 (any
omnidirectional is similar)
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TE01 vs. PMD
non-degenerate mode, so cannot be split
i.e. immune to birefringence
i.e. PMD is zero
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Lets Get Quantitative
but what about the cladding?
Gas can have low loss nonlinearity
some field penetrates!
may need to use very bad material to get high
index contrast
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Lets Get Quantitative
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Perturbation Theory
Given solution for ideal system compute
approximate effect of small changes
solves hard problems starting with easy
problems provides (semi) analytical insight
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Perturbation Theoryfor Hermitian eigenproblems
given eigenvectors/values
find change for small
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Perturbation Theoryfor electromagnetism
e.g. absorption gives imaginary Dw decay!
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Suppressing Cladding Losses
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Suppressing Cladding Nonlinearity

(including factor of 10 in area)
nonlinearity Db(1) / P
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Absorption Nonlinearity Scaling
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Radiation Leakage Loss (17 layers)
leakage loss (dB/km)
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ther Losses
Acircularity Bending
main effect is coupling to lossier modes, but can
be 0.01 dB/km with enough (50) layers
Surface Roughness
suppressed like absorption
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Acircularity Perturbation Theory
(or any shifting-boundary problem)
e2
e1
just plug Des into perturbation formulas?
FAILS for high index contrast!
beware field discontinuity fortunately, a simple
correction exists
S. G. Johnson et al., PRE 65, 066611 (2002)
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Acircularity Perturbation Theory
(or any shifting-boundary problem)
e2
e1
(continuous field components)
Dh
S. G. Johnson et al., PRE 65, 066611 (2002)
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Yes, but how do you make it?
figs courtesy Y. Fink et al., MIT
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Fiber Draw Tower _at_ MITbuilding 13, constructed
20002001
6 meter (20 feet) research tower
figs courtesy Y. Fink et al., MIT
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A Drawn Bandgap Fiber
figs courtesy Y. Fink et al., MIT

• Photonic crystal structural uniformity, adhesion,
  physical durability through large temperature
  excursions

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Band Gap Guidance
Transmission window can be shifted by
scaling (different draw speed)
original (blue) shifted (red) transmission
figs courtesy Y. Fink et al., MIT
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High-Power Transmissionat 10.6µm (no previous
dielectric waveguide)
Polymer losses _at_10.6µm 50,000dB/m
waveguide losses 1dB/m
B. Temelkuran et al., Nature 420, 650 (2002)
cool movie
figs courtesy Y. Fink et al., MIT
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Enough about MIT already
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2d-periodic Photonic-Crystal Fibers
R. F. Cregan et al., Science 285, 1537 (1999)
air holes
a
silica
(usually)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.1a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.17717a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.22973a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.30912a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.34197a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.37193a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.4a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.42557a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.45a
light cone
w (2pc/a)
w bc
b (2p/a)
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PCF Holey Silica Cladding
n1.46
2r
a
r 0.45a
light cone
w (2pc/a)
air light line w bc
b (2p/a)
figs West et al, Opt. Express 12 (8), 1485
(2004)
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PCF Projected Bands
J. Broeng et al., Opt. Lett. 25, 96 (2000)
2.4
2.0
air light line
band gap fingers appear!
w (2pc/a)
1.6
bulk crystal continuum
1.2
0.8
1.11 1.27 1.43 1.59 1.75 1.91
2.07 2.23 2.39
b (2p/a)
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PCF Guided Mode(s)
J. Broeng et al., Opt. Lett. 25, 96 (2000)
2.4
fundamental 2nd order guided modes
2.0
air light line
w (2pc/a)
fundamental air-guided mode
1.6
bulk crystal continuum
1.2
0.8
1.11 1.27 1.43 1.59 1.75 1.91
2.07 2.23 2.39
b (2p/a)
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Experimental Air-guiding PCF
Fabrication (e.g.)
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Experimental Air-guiding PCF
R. F. Cregan et al., Science 285, 1537 (1999)
10µm
5µm
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Experimental Air-guiding PCF
R. F. Cregan et al., Science 285, 1537 (1999)
transmitted intensity after 3cm
w (c/a) (not 2pc/a)
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State-of-the-art air-guiding losses
Mangan, et al., OFC 2004 PDP24
hollow (air) core (covers 19 holes)
guided field profile (flux density)
1.7dB/km BlazePhotonics over 800m _at_1.57µm
3.9µm
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State-of-the-art air-guiding losses
larger core less field penetrates cladding
ergo, roughness etc. produce lower loss
13dB/km Corning over 100m _at_1.5µm Smith, et
al., Nature 424, 657 (2003)
1.7dB/km BlazePhotonics over 800m _at_1.57µm
Mangan, et al., OFC 2004 PDP24
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State-of-the-art air-guiding losses
larger core more surface states crossing guided
mode
100nm
20nm
13dB/km Corning over 100m _at_1.5µm Smith, et
al., Nature 424, 657 (2003)
1.7dB/km BlazePhotonics over 800m _at_1.57µm
Mangan, et al., OFC 2004 PDP24
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Index-Guiding PCF microstructured fiberHoley
Fibers
solid core
holey cladding forms effective low-index material
Can have much higher contrast than doped silica
strong confinement enhanced nonlinearities,
birefringence,
J. C. Knight et al., Opt. Lett. 21, 1547 (1996)

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Holey Projected Bands, Batman!
(Schematic)
band gaps are unused
bulk crystal continuum
w (c/a) (not 2pc/a)
guided band lies below crystal light line
b (a1)
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Guided Mode in a Solid Core
small computation only lowest-w band!
( one minute, planewave)
holey PCF light cone
flux density
1.46 bc/w 1.46 neff
fundamental mode (two polarizations)
n1.46
2r
endlessly single mode Dneff decreases with l
a
r 0.3a
l / a
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Holey Fiber PMF (Polarization-Maintaining Fiber)
birefringence B Dbc/w 0.0014 (10 times B of
silica PMF)
Loss 1.3 dB/km _at_ 1.55µm over 1.5km
no longer degenerate with
Can operate in a single polarization, PMD
0 (also, known polarization at output)
K. Suzuki, Opt. Express 9, 676 (2001)
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Nonlinear Holey Fibers
Supercontinuum Generation
(enhanced by strong confinement unusual
dispersion)
e.g. 4001600nm white light
from 850nm 200 fs pulses (4 nJ)
W. J. Wadsworth et al., J. Opt. Soc. Am. B 19,
2148 (2002)
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Endlessly Single-Mode
T. A. Birks et al., Opt. Lett. 22, 961 (1997)
at higher w (smaller l), the light is
more concentrated in silica
so the effective index contrast is less
and the fiber can stay single mode for all l!
http//www.bath.ac.uk/physics/groups/opto
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Low Contrast Holey Fibers
J. C. Knight et al., Elec. Lett. 34, 1347
(1998)
The holes can also form an effective low-contrast
medium
i.e. light is only affected slightly by small,
widely-spaced holes
This yields large-area, single-mode fibers (low
nonlinearities) but bending loss is worse
10 times standard fiber mode diameter
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Holey Fiber Losses
Best reported results 0.28 dB/km _at_1.55µm
Tajima, ECOC 2003
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The Upshot