1

Photos and much of the content is courtesy of OmniGuide Communications

Cambridge, Massachusetts, USA(where M. Skorobogatiy served as a theory and simulation group leader)

and Prof. Yoel Fink fiber research group at MIT

Applications of omnidirectional reflectivity.

Communication and high power transmission through hollow

Bragg (OmniGuide) fibers.

Quasi - 1D systems, Bragg fibers

2 The problem: making the perfect mirror

Hollow core

Mirror Cladding

OmniGuide

CladdingCore

CladdingHollowCore

Conventional

Hollow Metallic

Conventional Dielectric Mirror

Angular dependent reflectivity with very

low optical loss

Metallic Mirror

Omnidirectional reflectivity with optical

loss

Omnidirectional Mirror

Reflects all angles with very low loss

3

High-Energy Laser High-Energy Laser Guidance in the IRGuidance in the IR

Laser Surgery, Laser Surgery, Materials ProcessingMaterials Processing

Fiber DevicesFiber Devices

Dispersion Compensating Dispersion Compensating fibers, Tunable Cavities, fibers, Tunable Cavities,

Lasers, Nonlinear DevicesLasers, Nonlinear Devices

Few applications of hollow Photonic Bandgap fibers

Low loss Low loss transmission of transmission of

IR signalsIR signals

IR ImagingIR ImagingCommunicationsCommunications

4 OmniGuide/MIT hollow core fiber

Output of a straight 25cm piece of fiber, =10.6m

B. Temelkuran et al.,Nature 420, 650 (2002) +

OmniGuide Communications

5 Spiral OmniGuide Preform Processing

Step 1: Stoichiometric Stoichiometric

thermal thermal evaporation of evaporation of AsAs22SeSe33 onto onto

free-standing free-standing PES filmPES film

Step 2: Rolling of Rolling of coated film into coated film into cladded hollow cladded hollow

multilayer cylinder multilayer cylinder on SiOon SiO22 tube tube

substratesubstrate

Step 3: Vacuum Vacuum thermal thermal

consolidationconsolidation

Step 4: Etching Etching and removal of and removal of

SiOSiO22

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6

Step 2

Evaporation

Step 1

Materials Synthesis

The OmniGuide Fabrication Sequence

Step 4

Fiber Drawing

Step 3

Structured Preform

Fabrication

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7 Preform-Based Fabrication Strategy

Partially Drawn Preform

1 in

Mirror(SEM Image)

Preform

5 µm

3-30 meter3-30 meterdraw towerdraw tower

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8 Bragg fiber by stacking technique

Silica-Air, Bragg Like fiber

G. Vienne, et al. “First demonstration of air-silica Bragg fiber,” OFC, PDP25, 2003

9 Reflection form the planar dielectric mirror, modes of hollow metallic waveguide and hollow Bragg fiber

"Analysis of mode structure in hollow dielectric waveguide fibers,“ M. Ibanescu, S.G. Johnson, M. Soljacic, J. D. Joannopoulos, Y. Fink, O. Weisberg, T.D. Engeness, S.A. Jacobs, and M. Skorobogatiy, Physical Review E, vol. 67, p. 46608, 2003

Modes of hollow metallic waveguide

Frequency regions (gray) of omnidirectional reflection form the multilayer reflector stack

Modes of hollow Bragg fiberAND =

10 Wavelength scalability. Different draw conditions shift the transmission spectrum

OmniGuide FTIR spectrum

Index contrast nh/nl~2.5/1.7; Rcore~200m; Fundamental bandgap at =3m

0.0

0.4

0.8

1.2

200040006000800010000

Wavenumber (cm-1)

Tra

nsm

issio

n (

arb

. u

.)W

avev

ecto

r

Courtecy ofY. Fink (MIT)

11 Colorful fibers

Fibers of different draw down ratio exhibiting continuously changing position of a higher order band gap

Fiber Outer Diameter decreases

Y. Fink et al., Advanced Materials 15, 2053 (2003)

12 Modes of OmniGuide hollow core fiber

Ultra low loss,hard to couple to Gaussian

laser source

Most compatible withGaussian laser source

and high power

•Leaky modes of a Bragg fiber are calculated using transfer matrix method

•Absorption losses and nonlinearities of the underlying imperfect materials are greatly suppressed as most of the field is concentrated in the hollow core

13 Modal radiation and absorption losses

Index contrast nh/nl~4.6/1.6, Rcore~15m,

bulk material loss 1dB/m, 12 mirror periods

"Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers,“ S.G. Johnson, M. Ibanescu, M. Skorobogatiy, O. Weisberg, T.D.Engeness, M. Soljacic, S. Jacobs, J. D. Joannopoulos and Y. Fink, Optics Express, vol. 9, pp. 748-779, 2001

14 High power guiding applications

HE11

Coupling to HE11, higher order and cladding modes

Region of increased heating

Beam degradation due to inter-modal scattering

Beam quality M2 degradation due to higher order mode

content

• Coupling efficiency at the fiber input

• Temperature rise due to imperfect coupling

Modeling tools• Design and optimization• Scattering/radiation due to

imperfections/bends• Excess heating due to bends

• Beam quality M2 estimation via free space propagation

HE11

Input Transmission

Region of increased heating

Rcore~100-500m

Radiation, absorption loss ~ 1/R3core Bending loss ~ R

core/Rbend

M. Skorobogatiy, S.A. Jacobs, S.G. Johnson, O. Weiseberg, T.D. Engeness, Y. Fink, “Power Capacity of Hollow Bragg Fibers, CW and Pulsed Sources,” TuA4.6, Digest of the LEOS Summer Topical Meetings, pp. 66-67 (2003)

Input

15 Components for high power guiding applications

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16 Imperfect coupling and heating (theory)

Metal tube coupler

OmniGuide fiber, =10.6m

Incoming

Gaussian,

m=1 mode

~80%-90% HE11 mode

Dry air cooling

Rc~300m

Amplitudes of excited modes are calculated by matching transverse electric and magnetic fields of the incoming Gaussian in free space and eigen fields of the fiber/coupler, for an unoptimized coupler power in the lowest loss m=1 mode HE11 is 80%-90%

17 Imperfect coupling and heating (theory)

•Temperature rise (red) along the fiber length due to imperfect coupling (80% in HE11 and 20% in parasitic modes) – full solution. In green, temperature distribution if 100% HE11 mode is excited. In blue, temperature distribution ignoring the interference effects between the modes.

•Heat flow equation is solved with heat sources defined by amplitudes of excited parasitic modes due to imperfect coupling

18 Imperfect coupling and heating (experiment)

Tem

pera

ture

MAX

MIN

Non-uniform temperature rise in a fiber under imperfect coupling

Fiber

Laser and coupler

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19 Bending loss in OmniGuide fiber (experiment)

Bend loss ~ 3 dB through full “knot” of 1 cm radius

B. Temelkuran et al.,Nature 420, 650 (2002)

0.0

1.0

2.0

3.0

4.0

200030004000500060007000

Wavenumber (cm -1)

Tra

nsm

issi

on

(ar

b.

u.)

Wavelength (m)1.67 2.0 2.5 3.33 5.0

0.0

1.0

2.0

3.0

4.0

200030004000500060007000

Wavenumber (cm -1)

Tra

nsm

issi

on

(ar

b.

u.)

Wavelength (m)1.67 2.0 2.5 3.33 5.0

20 Bends and beam degradation (experiment)

Straight – 25 cm long Bent – 360O, 10 cm radius

Courtecy ofY. Fink (MIT)

21 Bends and heating (theory)

Rbend=20cm

Rcooler

Rcore

•Temperature distribution in a fiber bend

•Amplitudes of excited modes in a bend are found by propagating HE11 incoming field through bend by Coupled Mode Theory

•Heat flow equation is solved with heat sources defined by amplitudes of excited modes

22 Transmission window and loss

10.6 10.6 mm

0

2

4

6

8

5 6 7 8 9 10 11 12Wavelength (m)

Tran

smis

sion

(arb

. u.)

slope = -0.9 dB/m

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

2.5 3.0 3.5 4.0 4.5 5.0Length (meters)

Lo

g o

f Tr

ans.

(ar

b. u

.)

0

2

4

6

8

5 6 7 8 9 10 11 12Wavelength (m)

Tran

smis

sion

(arb

. u.)

slope = -0.9 dB/m

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

2.5 3.0 3.5 4.0 4.5 5.0Length (meters)

Lo

g o

f Tr

ans.

(ar

b. u

.)

Ability to control location of transmission window for specific applications

Courtecy ofY. Fink (MIT)

23 Telecommunications applications

• Coupling of the laser source to the fiber HE11 or TE01 modes

• Mode converter design

Ultra low loss TE01 mode (~0.1dB/km), incompatible with Gaussian

Gaussian → TE01 mode converter

Gaussian → HE11direct launch

Moderate loss HE11 mode (~10dB/km)

HE11TE01

• Modal losses due to• absorption/radiation• micro and macro bends• fiber imperfections

• Dispersion management

• Signal degradation due to • nonlinearities• micro and macro bends• fiber imperfections

• Polarization Mode Dispersion

Modeling tools

Rcore~15m

HE11 radiation, absorption loss ~ 1/Rcore

Bending loss ~ 1/R2bend-1/Rbend

TE01 radiation, absorption loss ~ 1/R3core, non-linearities ~ 1/R7

core

Input

24 Highly designable group velocity dispersion of OmniGuide modes

Very high dispersion

Low dispersion

Zero dispersion

[2/a]

[2c

/a]

HE11

25 PMD of the TE01 and HE11 modes

E TE01 is a non-degenerate mode,

and thus cannot be split

PMD is zero

Polarization-mode dispersion (PMD) of a doubly degenerate HE11 mode:

differentgroup

velocities:stochastic stress,imperfections…

…pulse spreading!

samegroup

velocities:

“single-mode” fiber

HE11:

TE01:

26Challenges: coupling to Bragg fibers. HE11

→TE01 ”serpentine” mode converter (theory)

SMF-28 silica fiber at 630nm,

Rc=4.1m, n/nc=0.36%, 7 guided modes:

1) LP01 - HE11

2) LP11 - TE01,TM01,HE21

3) LP21 - EH11, HE31

4) LP02 - HE12

Amplitude of fiber wiggling =49nm, N=35 turns, Dw=512m

27HE11 → TE01 ”serpentine” mode converter (experiment)

33% LP01, 65% LP11, 2% LP21+LP0299.8% LP01

M. Skorobogatiy, C. Anastassiou, S.G. Johnson, O. Weiseberg, T.D. Engeness, S.A. Jacobs and Y. Fink, “Quantitativecharacterization of higher-order mode converters in weakly multimoded fibers,” Optics Express 11, 2838 (2003)

HE11TE01

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28 Bragg fiber components and systems

Device applications

and

functional fibers

29 Inter-Fiber Interaction

2) Bragg fiberIndividual fibers are drawn. Outer polymer cladding can be removed by dissolving the polymer.

2) Stacked fiberTwo closely spaced fiber cores are provisioned on the preform level. Directional coupler is then drawn from such a preform.

Core 1 Core 2Drawing

Claddingremoval

Fiber alignment

B.J. Mangan, J.C. Knight, T.A. Birks, P.S. Russell, A.H. Greenaway, Electron. Lett. 36, 1358 (2000).

30

1) Cabling of several photonic band gap fibersparasitic coupling between waveguides due to the radiation leakage outside of the fiber core

2) Fiber components (directional couplers)Coupling has to be strong enough so that power transfer from one waveguide to another happens on a length scale much smaller than modal decay length (radiation loss)

Coupling through radiation field resonance in the inter-fiber region

M. Skorobogatiy, "Hollow Bragg fiber bundles: when coupling helps and whenit hurts,” OPTICS LETTERS 29, 1479 (2004)

Two related problems of directional coupling

M. Skorobogatiy, K. Saitoh and M. Koshiba, "Resonant directional coupling of hollow Bragg fibers,” OPTICS LETTERS 29, 2112 (2004)

31 Functional Bragg fibers

By creating a “thick” layer in the reflector, fiber transmission can be suppressed in the middle of a band gap. Application of stress offers tuning by changing defect wavelength of a resonator.

Y. Fink et al., Advanced Materials 15, 2053 (2003)

32 Functional Bragg fibers

Optical fibers can be integrated during drawing with “non-trivial” components such as electric wires, semiconductor devices, etc.

Tin “wires”

Bragg reflector

Y. Fink et al., Nature 431, 826 (2004)

33 Functional Bragg fibers

Optical fibers can be integrated during drawing with “non-trivial” components such as electric wires, semiconductor devices, etc.

Tin “wire”

Bragg reflector

Semiconductor glass

Y. Fink et al., Nature 431, 826 (2004)