The Glass Ceiling: Limits of Silica
Loss: amplifiers every 50–100km
…limited by Rayleigh scattering (molecular entropy)
…cannot use “exotic” wavelengths like 10.6µm
Breaking the Glass Ceiling:
Hollow-core Bandgap Fibers
Bragg fiber
[ Yeh et al., 1978 ]
[ figs courtesy
Y. Fink et al., MIT ]
Nonlinearities: after ~100km, cause dispersion, crosstalk, power limits
(limited by mode area ~ single-mode, bending loss)
also cannot be made (very) large for compact nonlinear devices
+ omnidirectional
white/grey
= chalco/polymer
= OmniGuide
fibers
silica
Radical modifications to dispersion, polarization effects?
…tunability is limited by low index contrast
High Bit-Rates
Long Distances
[ R. F. Cregan
et al.,
Science 285,
1537 (1999) ]
5µm
PCF
[ Knight et al., 1998 ]
Compact Devices
Dense Wavelength Multiplexing (DWDM)
PCF: Holey Silica Cladding
r = 0.45a
light cone
2r
n=1.46
State-of-the-art air-guiding losses
a
[Mangan, et al., OFC 2004 PDP24 ]
above air line:
guiding in air core
is possible
hollow (air) core (covers 19 holes)
" (2!c/a)
guided field profile:
(flux density)
air
h
lig
tl
in
e"
=
!c
[ figs: West et al,
Opt. Express 12 (8), 1485 (2004) ]
3.9µm
1.7dB/km
BlazePhotonics
over ~ 800m @1.57µm
! (2!/a)
below air line:
surface states of air core
Hollow Metal Waveguides, Reborn
State-of-the-art air-guiding losses
larger core = more surface states crossing guided mode
metal waveguide modes
… but surface states can be removed by proper crystal termination
OmniGuide fiber modes
100nm
frequency "
[ West, Opt. Express 12 (8), 1485 (2004) ]
20nm
13dB/km
1.7dB/km
Corning
BlazePhotonics
over ~ 100m @1.5µm
over ~ 800m @1.57µm
[ Smith, et al., Nature 424, 657 (2003) ]
[ Mangan, et al., OFC 2004 PDP24 ]
An Old Friend: the TE01 mode
lowest-loss mode,
just as in metal
(near) node at interface
= strong confinement
= low losses
r
E
1970’s microwave tubes
@ Bell Labs
wavenumber !
wavenumber !
modes are directly analogous to those in hollow metal waveguide
Suppressing Cladding Losses
Mode Losses
÷
Bulk Cladding Losses
1x10-2
EH11
1x10-3
Large differential loss
-4
non-degenerate mode
— cannot be split
TE01 strongly suppresses 1x10
cladding absorption
(like ohmic loss, for metal)
= no birefringence or PMD
[ Johnson, Opt. Express 9, 748 (2001) ]
1x10-51.2
TE01
1.6
2
# (µm)
2.4
2.8
Yes, but how do you make it?
A Drawn Bandgap Fiber
[ figs courtesy Y. Fink et al., MIT ]
[ figs courtesy Y. Fink et al., MIT ]
3
1
find compatible materials
• Photonic crystal structural
uniformity, adhesion,
physical durability through
large temperature excursions
(many new possibilities)
2
Make pre-form
(“scale model”)
chalcogenide glass, n ~ 2.8
white/grey
= chalco/polymer
+ polymer (or oxide), n ~ 1.5
fiber drawing
High-Power Transmission
at 10.6µm (no previous dielectric waveguide)
Log. of Trans. (arb. u.)
Polymer losses @10.6µm ~ 50,000dB/m…
-3.0
…waveguide losses < 1dB/m
Transmission (arb. u.)
8
6
4
-3.5
[ B. Temelkuran et al.,
Nature 420, 650 (2002) ]
-4.0
slope = -0.95 dB/m
Breaking the Glass Ceiling II:
Solid-core Holey Fibers
solid core
holey cladding forms
effective
low-index material
R2 = 0.99
Can have much higher contrast
than doped silica…
-4.5
2.5
3.0
3.5
Length (meters)
2
4.0
strong confinement = enhanced
nonlinearities, birefringence, …
0
5
5
6
6
7
7
8
8
9
9 10 10
10 11 11 12 12
12
Wavelength(µm)
(µm)
Wavelength
[ figs courtesy Y. Fink et al., MIT ]
[ J. C. Knight et al., Opt. Lett. 21, 1547 (1996) ]
Mode in a Solid Core
small computation: only lowest-" band!
(~ one minute, planewave)
2r
n=1.46
a
r = 0.3a
flux density
Endlessly Single-Mode
[ T. A. Birks et al., Opt. Lett. 22, 961 (1997) ]
at higher "
(smaller #),
the light is more
concentrated in silica
…so the effective
index contrast is less
…and the fiber can stay
single mode for all #!
fundamental
mode
(two polarizations)
http://www.bath.ac.uk/physics/groups/opto
Band Diagram in “Metallic” Limit
Band Gaps from “Metallic” Limit
Effective Area
Nonlinear Holey Fibers:
Supercontinuum Generation
(enhanced by strong confinement + unusual dispersion)
e.g. 400–1600nm “white” light:
from 850nm ~200 fs pulses (4 nJ)
[ W. J. Wadsworth et al., J. Opt. Soc. Am. B 19, 2148 (2002) ]
Holey Fiber PMF
Suppressing Cladding Nonlinearity
(Polarization-Maintaining Fiber)
[ Johnson, Opt. Express 9, 748 (2001) ]
Mode Nonlinearity*
÷
Cladding Nonlinearity
1x10-6
birefringence B = $!c/"
= 0.0014
(10 times B of silica PMF)
1x10-7
Loss = 1.3 dB/km @ 1.55µm
over 1.5km
TE01
Will be dominated by
nonlinearity of air
1x10-8
no longer degenerate with
~10,000 times weaker
than in silica fiber
Can operate in a single polarization, PMD = 0
(including factor of 10 in area)
1x10-9
1.2
* “nonlinearity” = $!(1) / P = %
(also, known polarization at output)
1.6
2
# (µm)
2.4
2.8
[ K. Suzuki, Opt. Express 9, 676 (2001) ]