Chap5 Passive Components

8/2/2019 Chap5 Passive Components

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Outline

Optical couplers Optical splitter

Optical combiner

Star coupler

Wavelength Selective and Routing Devices

Optical filters

Wavelength Mux/Demux

Optical add/drop (OADM)

Wavelength router

Other Passive Devices

Optical isolators

Optical circulators

Optical Switches


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Key Parameters

Insertion loss

Excess loss

Back Reflection

Polarization dependent loss (PDL)

Splitting Ratio

Splitting uniformity

Channel Isolation or Crosstalk

Optical bandwidth (-1, -3, -20dB)

Isolation ratio (isolators or circulators)


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Optical Couplers

Fabrication: can be made out of fiber fusing, bulk optics, andintegrated optics

Excess loss = the ratio of power input to power output

Insertion loss = the loss from a given input (1) to an output (4)

Through loss : insertion loss for through path

Tap loss: insertion loss for cross path

(1) 2x2 Directional coupler 1

2

3

4

)(log10 43

1

dBPP

P

+

=

)(log104

1

dBP

P= Input (1) to output (4)


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Optical splitter and Combiner

For an ideal 1xN splitter (N > 1),

For an ideal Nx1 beam combiner, the output is the

sum of all inputs, but in fact

NPP inout = at each output port

=i

iinout PN

P ,1


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Star Coupler

The power of each input isdistributed evenly to all

outputs

Device types: fused fibers,

cascade of directional

couplers, planar waveguides

)(log10lossSplitting dBN=

=N

joutiin PP1

,,log10lossExcess

Slab Waveguide Region

Input Waveguides Output Waveguides

Fused Portion

Splitting uniformity is critical


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Optical Filters

For channel selection, require

Flat passband

Low adjacent-channel crosstalk

Good alignment to wavelength grid

Wavelength tunable filter is useful for dynamicchannel selection or switching

Fixed- filter


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Filter Characteristics

3 dB 1 dB1-dB

bandwidth

3-dBbandwidth

20-dB

bandwidth

Passband

skirtsCrosstalk

energy

Adjacent

channel

1 1.002 1.0040.9980.996-40

-30

-20

-10

0

0/

Filtertr

ansmission(dB)

Fixed- filter


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Filter Types

Thin-Film Filters

Mach-Zehnder type

Fabry-Perot Interferometer

Diffraction gratings

Reflective (fiber) gratings

Acousto-optic tunable filter


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Thin-Film Filters

Input

T( )R( )

GRINCommon

ReflectionWDM filter

Lenses

Pass


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Fiber Gratings

CladdingIncident Light

ReflectedLightGrating planes

2

4

1

3

2

4

1

3

Incident light

Reflected light

Transmittedlight

Grating responseFiber Bragg

grating


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Coupler vs. Multiplexer

1

2

N

M

P1

P2

P3

M =iout

PP

1

2

N

M

P1

P2

P3

M

1

2 L N

1

2

N

M

=iout

PN

P1

= iout PN

P 211

2L

N

12L

N

12L

N

12L

N

ioutPP =

Optical coupler is wavelength insensitive, while Mux is

wavelength selective


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Wavelength Router

Input/Output

Waveguide

Slice-

Substrate

Array-Waveguide

WaveplateSlab

Wave uide

1,

2, ...,

N

1

2

N

0

0

0

0

0

1

1

1

1N

1N

1N

1N

2

2

2

3

3

2N

2N

2N

3N

3N

1

4N

4

wavelengthw

Outputv

Inputu

w=(N-u+v) mod N

Route signals according to

their wavelengths


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OADM

OADM

k

k k

k

Selectively extract and Insert optical channels atintermediate sites

Manage the WDM traffic in the fiber

Optical circulator + fiber grating = Fixed OADM Flexible and reconfigurable OADMs will be needed in

future DWDM networks


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OADM Characteristics

-50

-40

-30

-20

-10

0

1530 1532 1534 1536 1538 1540 1542

Transmission(dB)

In -> Drop

&

Add -> ThruCrosstalk

-50

-40

-30

-20

-10

0

1530 1532 1534 1536 1538 1540 1542

Transm

ission(dB)

In -> ThruCrosstalk


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OADM with Thin-Film Filters

In

OutAdd

Drop

Add-1

Add-2

Drop-2

Drop-1

Express

In


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OADM with Fiber Gratings

1

,2

....,n

1,

2....,

n

1

1Drop

Add

Fiber Gragg grating

Circulator Circulator

Fiber Gragg grating

Drop Add

WDM

Drop

1

3

21

3

21

3

21

Fiber Bragg

grating 2

Fiber Bragg

grating n

M

Circ nCirc2Circ1 Fiber Bragg

grating 1

Drop

2

Drop

n

i

1

2

3

n


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Optical Isolators

Fiber in

SOPSWP SWP

SWPSWP

Fiber in

Fiber out

Faraday

rotator

Faraday

rotator /2 plate

/2 plate

(b)

(a)

Forward

Backward

For reduce or eliminate back reflection


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Optical Circulator

1

2

3

1

4

3

2

To de-couple transmitted and received signals

traveling along the same fiber (bi-directional)

Use Faraday rotators, similar to isolators


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Optical Switches

To dynamically control the physical connections between

input ports and output ports

Design criteria:

Low power loss Low crosstalk

Polarization independence

Simple interconnection

Low switching energy

Types of switches

Mechanical switch

Waveguide switch Self-electro-optic effect Devices (SEED)

SOA Gated switch


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Mechanical SwitchesFiber Fiber

ON/OFF gate

FiberFiber

2XN switch

FiberFiber

1XN switch


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Hot Switches

Applications:

Circuit switch:

Packet switch: require fast switching speed (ns)

Protection switch

Large-scale switch (>1000 ports) MEMS

Liquid crystal

Agilents champange switch

Control signal Microlens

Switch

Mirror

Silica Substrate


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SOA Gate Switches

Passive

Splitters

Amplifier

Gates

Passive

Combiners

Documents

Chap5 Passive Components