集成平面光波导器件 - 光调制器

《集成平面光波导器件》课程Chapter

13:

Optical

Modulators

Optical

Modulation

光调制就是将一个携带信息的信号叠加到载波光波上,完成这一过程的器件称为调制器。

直接调制(内调制)：把承载信息的电信号作为驱动电流直接施加在激光器上即以调制信号去改变激光器的振荡参数，从而改变激光输出特性以实现调制

2

Direct/External

Modulation•Direct

Modulation

of

Laser

DiodeBias

+

DATA驱动电流

LD或LED•

Laser

Carrier

induced

(chirp)Temperature

variation

due

to

carrier

modulationExternal

Modulation

of

Laser

Diode

BiasLaser

Bias

+

DATAModulator《集成平面光波导器件》课程Issues

--

Additional

ComponentC

直流偏置

Direct

Modulation半导体激光器调制原理以及输出光功率与调制信号的关系曲线。为了获得线性调制，使工作点处于输出特性曲线的直线部分，必须在加调制信号电流的同时加一适当的偏置电流Ib，这样就可以使输出的光信号不失真。

t输出光强信号LD输出功率

L~

调制信号(a)直流偏置

t调制信号

(b)半导体激光器调制

(a)

电原理图；(b)

调制特性曲线

4PoutDirect

Modulation

PouttIOIOIbID

t(b)t(a)(a)

LED数字调制特性(b)

加Ib后LD数字调制特性5

External

Modulation

外调制：通过光调制器，将携带信息的电信号与输入光调制器的连续光载波相作用。包括：幅度调制、频率调制、相位调制、偏振调制。

电信号激光器光载波调制光信号输出外调制器

外调制方式6Direct/External

Modulation

信息

电信号激光器

输出调制光

连续光信号外调制器激光器

输出调制光信息电信号LD

输出连续光信息电信号01

010信息电信号输出调制光波输出调制光波01

0

1

0（a）

直接调制（b）外调制直接调制：电路简单，容易实现，高速率时输出光光谱变宽，易受光纤色散影响；外调制：适合高速率光纤传输系统7Optical

Modulator

光调制器---外调制方式中采用，把激光的产生和调制分开，

可避免对光源直接调制产生线性调频的限制。调制器能使载波光波的参数随外加信号变化而变化，这些参数包括光波的振幅、位相、频率、偏振等。承载信息的调制光波在光纤中传输，再由光探测器系统解调，然后检测出所需要的信息。与光开关的区别：如果一个器件的主要作用是通过暂时改变光波的某一特性将信息加到光波上去，则为调制器；而光开关则是改变光线的空间线路或控制其通断。8

Optical

Modulator

1.

调制带宽f3dB:

光调制器的频域响应类似与低通滤波器，其

带宽对应与光调器的响应度减小到一半时的微波频率。

2.

消光比

3.

插入损耗:

表征光经过调制器时光功率的损失，包

括耦合损耗和传速损耗。

4.

能耗:

定义为单位比特所需消耗的能量。

半波电压光纤通信系统对调制器的要求高的调制速率

宽的调制带宽

低的半波电压

高的消光比低的插入损耗《集成平面光波导器件》课程

Optical

ModulatorElectro-Optic

Modulator

(LiNbO3)

Semiconductor

based

Modulator(EA,

Si

Modulator)

Others(Polymer,

Slot

Waveguide,

PhCs,

Graphene)《集成平面光波导器件》课程Electro-Optic

Modulation《集成平面光波导器件》课程Pockels

Effect/Kerr

Effect《集成平面光波导器件》课程EO

Phase

Modulator《集成平面光波导器件》课程EO

Phase

Modulator《集成平面光波导器件》课程EO

Phase

Modulator《集成平面光波导器件》课程EO

Intensity

Modulator《集成平面光波导器件》课程《集成平面光波导器件》课程Optical

Modulator-EOM-Z型LiNbO3调制器是目前光通信中实用的电光调制器输入光信号在C处被分为相等的两束，分别进入两波导传输。波导的折射率随外加电压大小而变化，导致两路光信号到达D时的相位延迟不同。若两束光光程差是半波长的偶数倍，两束光相干加强；若是半波长的奇数倍，则两束光相干抵消，输出很小。因此，控制外加电压，就能实现光调制。17用LN晶体制作的M-Z调制器n

E

n

2

2

n3

VL

0

0d

T

cos

(

Optical

Modulator-EO波导臂上产生的折射率变化1

3

1

3

V2

2

d

n

对于对称型M-Z干涉仪，L1=L2=L，两臂的相位差为

（2

n）L

令

＝

时的电压为半波电压

V

V

0d2n3

L)2

V

V2V

18Optical

Modulator-EO

电光调制的透过率(调制器被偏置在V

/2点上)

透射光强t

VV

/2V

调制电压半波电压V

是把调制器从最小光

强转换到最大光强所需的电压《集成平面光波导器件》课程注意：在调制的区域要求器件的线性度高。若调制器工作在非线性部分,则调制光将发生畸变。Optical

Modulator-EO《集成平面光波导器件》课程Optical

Modulator-EOData

From:

《集成平面光波导器件》课程Optical

Modulator-EO

Techniques

for

Down

Sizing-

reduction

the

driving

voltage

Ridge

Waveguideinstead

of

Diffused

Waveguide《集成平面光波导器件》课程Optical

Modulator-EO

Techniques

for

Down

Sizing-

reduction

the

driving

voltage《集成平面光波导器件》课程Optical

Modulator-EO《集成平面光波导器件》课程Optical

Modulator-EOFrequency

Response

of

an

Over-40

Gbps

Modulator

《集成平面光波导器件》课程Optical

Modulator-EO《集成平面光波导器件》课程Optical

Modulator-EO《集成平面光波导器件》课程Optical

Modulator-EO《集成平面光波导器件》课程Optical

intensityOptical

modulation-Semiconductor

ElectricaldriverModulated

opticalintensityt

OpticalmodulatorttElectroabsorption

Quantum

Confined

Stark

effect

Franz-Keldysh

effect

Electrorefraction

Free

carrier

concentration

variations

in

silicon

AccumulationInjectionDepletion《集成平面光波导器件》课程29Optical

modulation-Semiconductor

•

基于半导体材料的调制器的工作本质是通过

电信号改变介质的复折射率。

•介质的复折射率为:

~

n

jnn

r

i基于改变折射率nr的调

制器称为

折射率型光调制器基于改变折射率需不

虚部的调制器称为

电吸收型调制器

《集成平面光波导器件》课程Modulator-Electro-absorption《集成平面光波导器件》课程Franz-Keldysh

effect（弗兰茨－凯第希效应）Energy

band

diagram

of

a

semiconductor

exhibiting

the

Franz-Keldysh

effectin

the

presence

of

a

strong

electric

field.The

parameter

x

represents

the

distance

from

the

surface

of

thesemiconductor,

and

E

is

the

electron

energy.

Ec

and

Ev

are

the

conduction

andvalence

and

edges,

respectively.

《集成平面光波导器件》课程Franz-Keldysh

effectCurve

A

is

the

zero

field

absorption

curve

forGaAs.(Circular

dots

represent

experimentaldata

points

for

n-type

material

with

carrierconcentration

n=3x1016cm-3.

For

the

squaredot

n=5.3x1016cm-3)

Curve

B

shows

theshifted

absorption

edge

for

a

field

of1.3x105V/cm.A

very

effective

electro-absorption

modulatorcan

be

made

for

light

of

slightly

less

thanbandgap

wavelength.In

the

presence

of

a

strong

electric

field,

theabsorption

edge

of

a

semiconductor

is

shifted

tolonger

wavelengthvery

large

changes

in

absorption

of

wavelengthnear

the

band

edge

can

be

produced

byapplication

of

an

electric

field《集成平面光波导器件》课程Franz-Keldysh

shift

of

the

absorption

edge

of

GaAs.Franz-Keldysh

effectAluminum

concentration

b

in

the

waveguide

should

be

chosen

so

that

the

absorptionedge

wavelength

is

just

slightly

shorter

than

the

guided

wavelength,

i.e.,

the

guide

istransparent

with

V=0.

Carrier

concentrations

should

be

chosen

so

thatN3>>N2,

thus,

a

relatively

large

electric

field

is

produced

in

the

guide

when

V

isapplied.

《集成平面光波导器件》课程Franz-Keldysh

effectDevice

Structures

《集成平面光波导器件》课程Franz-Keldysh

effect《集成平面光波导器件》课程Quantum

Confined

Stark

effect（量子限制Stark效应）《集成平面光波导器件》课程Quantum

Confined

Stark

effect《集成平面光波导器件》课程Optical

Modulator-EA

Extinction

Ratio:

Insertion

Loss:

Modulation

Efficiency:《集成平面光波导器件》课程Optical

Modulator-EA

Reported

III-V

EAM

with

a

bandwdith

over

30GHz

after

2004《集成平面光波导器件》课程Optical

Modulator-III-V

EA集总电极行波电极UCSB.

Y.B

Tang,

40GbpsUCSB.

Y.B

Tang,

50Gbps在高频时，微波信号的波长和电极的长度可以比拟，因此需要将电极看成是传输线。利用行波电极，既能使器件的内部等效RC常数减小，也能使光波和微波信号的速度匹配从而提高调制器的带宽。

《集成平面光波导器件》课程Optical

Modulator-III-V

MZM

Reported

III-V

MZM

with

a

bandwdith

over

30GHz

after

2004

capacitively

loaded

TW

electrode(High

impedance,

low

RF

loss,

velocity

match)

《集成平面光波导器件》课程Klein

et

al.

(IPRM

2006)Modulator-III-V

QPSK

modulatorQPSK

constellation80Gb/s80Gb/s

QPSK

modulator

based

onnested

40GHz

III-V

MZMs(traditional

structure)《集成平面光波导器件》课程N.Kikuchi,

et.

al.,

PTL

21(12),

2009E1

2E

0,1

E2

E

(

1

j)E3

2

jE

0,1

Optical

Modulator-III-V

QPSK

modulator107Gb/s

1

2

(0,1)(0,0)

(1,1)(1,0)Compact

107Gb/s

QPSKmodulator

based

on

two

III-VEAMs

embedded

in

a

three-arminterferometer《集成平面光波导器件》课程C.Doerr,

et.

al.,

PTL

19(15),

2007Optical

Modulator-Si

PlatformPIPIN

diodeMetal

P‐doped

region

MetalN‐doped

region45Europe:

PSUD-IEF,

Surrey

Univ.

…Asia:

A*Star,

Petra,

AIST,

Chinese

Academy

ofSciences,

Samsung

Electronics,

Tokyo

Institute

ofTechnology

…North

America:Intel,

IBM,

Cornell,

Luxtera,

Ligthwire,

Kortura,

Oracle

…

《集成平面光波导器件》课程

Silicon

Modulators×

Kerr

Effect:

n=10-4@100V/

m×

Franz-Keldysh

effect:

~

1.1

m×

Thermal-Optic

effect:

1.86×10

-4/K√

Free

carrier

Plasma

dispersion

effect《集成平面光波导器件》课程

n

ne

nh=-

8.8

10-22

ne+8.5

10-18

nh

e

h=

8.5

10-18

ne

h

n

ne

nh=-

6.2

10-22

ne+6.0

10-18

nh

e

h=

6.0

10-18

ne

h

Free

carrier

Plasma

dispersion

effect

e

is

the

electron

charge,

c

is

the

light

velocity

in

vacuum,

ε0

is

the

vaccum

ermittivity,

λ

is

the

wavelength

in

vacuum,

n

is

the

refractive

index

of

intrinsic

silicon,

mce*

and

mch*

are

the

electron

and

hole

effective

masses,

μe

and

μhare

the

electron

and

hole

mobilities.当载流子浓度为5×10

17时，折射率变化达到10-3量级

《集成平面光波导器件》课程Drude–Lorenz

equation:

1550

nm：

0.8

+6.0

10-18

n

1310

nm：

0.8

+4.0

10-18

n

Silicon

Modulators

Free

carrier

Plasma

dispersion

effect

Carrier

accumulationThe

performance

of

the

freecarrier

plasma

dispersion

basedsilicon

modulator

is

essentiallydetermined

by

how

fast

and

howefficiently

the

free

carrier

densityis

modulated

in

the

area

whereoptical

mode

is

traveling.

Charging/discharging

over

a

capacitor.

Serious

RC

limit,

less

efficientCarrier

Injection

Forward

bias

Relative

efficient,

Slow

diffusion

processCarrier

Depletion

Reverse

bias

less

efficient,

fast

process《集成平面光波导器件》课程G.T.Reed,

et

.al.

Nat.

Photon

.

4,

518-526,2010Carrier

DepletionOptical

modulator-Si

Phase

shifters:

PN

diode

Figures

of

merit

Interleaved

PN

diode

PIN

diode

PIPIN

diodePIN

diodePIPIN

diode

V

L

ILfcERModulation

efficiencyInsertion

loss‐3dB

bandwidthExtinction

ratio

Interferometers

Ring

resonator

Voltage

swing

Power

consumption

Mach-Zehnder

Photonic

crystals《集成平面光波导器件》课程49Silicon

Modulators-Carrier

accumulationApply

VD

to

poly.

Charge

accumulation

on

both

sides

of

gate

oxide.

Ne

=

Nh

=

[

/etoxt]*(VD

–

VFB)

ne

=

-8.8

x

10-22

Ne

nh

=

-8.5

x

10-18(

Nh)0.8

=

(2

/

)

neffL

《集成平面光波导器件》课程Silicon

Modulators-Carrier

InjectionVD

is

applied

to

Anodevs.

Cathode.→

forward

biased

p-i-njunction.→

e

and

holes

injectedinto

guiding

region→

changes

refractiveindex《集成平面光波导器件》课程Silicon

Modulators-Carrier

Injection载流子浓度分布N+区深度影响

《集成平面光波导器件》课程Optical

Modulator-Si

Platform《集成平面光波导器件》课程Silicon

Modulators-Carrier

depletion3x1018cm-31.5x1017

cm-31x1020cm-3《集成平面光波导器件》课程Optical

Modulator-Si

PlatformMach-Zehnder

InterferenceHigh

Q

Structure

(Ring,

FP

etc)1,

wide

optical

bandwidth2,

high

speed

operation1,

large

footprint2,

pretty

large

power

consumption

Intel

2007,

OE.

15(2),

660;1,

very

compact2,

enhanced

ER/Voltage1,

environmental

sensitivity2,

small

optical

bandwidth/EObandwidth

limited.3,

high

resolution

lithographyrequired.

Cornell

2005,

Nat.

435,

325.

《集成平面光波导器件》课程Optical

Modulator-Si

PlatformMach-Zehnder

InterferenceHigh

Q

StructureIntel

2004,

Nat.

427,

616Intel

2009,

AOT,

ID

67894810Gb/s,

f3dB

:

10GHz,Vpp=1.1V,

ER=3.8dBVπL:

33

V

mmCornell

2005,

Nat.

435,

325Cornell

2007,

OE

15(2),

43012.5Gb/s,

Vpp=8V,

ER=9dBf3dB

:~1GHz,Pre-emphasis

to

16VIBM

2004,

OE.

15(25),

1710610Gb/s,

f3dB

:

~1GHz,Vpp=1.2V,

ER=?dBPre-emphasis

to

7V.VπL:

0.36V

mmIntel

2007,

OE.

15(2),

660Intel

2009,

AOT,

ID

678948Kotura

2009,

OE

17(25),

2248410Gb/s,

f3dB

=

11GHzVpp=2V,

ER=6.5dB《集成平面光波导器件》课程40Gb/s,

f3dB

:

33GHz,Vpp=6.2V,

ER=1.1dBPre-emphasis

to

7V.VπL:

40V

mmOptical

Modulator-Si

Platform《集成平面光波导器件》课程Optical

modulator

Space

charge

extension

due

to

carrier

depletion

is

limited

~100

nm

typically.n-Si

i-Sip-Si《集成平面光波导器件》课程58

The

optimization

of

“classical”

modulators

relies

on

the

optimization

of

the

overlap

between

the

optical

mode

and

the

depletedwaveguide

is

usually

much

smaller

than

the

modal

sizeFrom

the

idea

to

the

final

deviceOptimizationFigures

of

meriteSimulation

of

the

diode

CouplersOptimized

structure

10G

40G

Frequency

and

data

transmission《集成平面光波导器件》课程59TechnologyLayoutCharacterization(µm)

y

neffx

(µm)PIPIN

diode

principle

PIPIN

diodeActive

region8X10-42.0x10-4

Metal

Metal

P‐doped

region

N‐doped

region

Optimization

of

the

overlap

between

the

optical

mode

and

the

depleted

region.

Low

insertion

loss

2x101740,90,710,9

1.50,7-1V0

-5

-4

-3

-2Hole

concentration

variation3

1.00,50320,500.55410.0

20Refractive

Effective

variation

variationindex

index《集成平面光波导器件》课程

2,5x

(µm)2,5

3

Voltage

(V)60evel

(/cm3)

Doping

leSelf-aligned

fabrication

processDepth

(µm)《集成平面光波导器件》课程61RESISTInAll

silicon

carrier

depletionmodulator

OutModulator

lengths:

0.95

mm

and

4.7

mm《集成平面光波导器件》课程62RF

characteristics40Gbit/sL

=

4.7

mmExtinction

ratio:

6.6

dBInsertion

loss:

6

dB

《集成平面光波导器件》课程63Ring

resonator

modulators

PIPIN

diodeRing

radius:

50µmTETM10Gbit/sExtinction

ratio:

4-5

dBInsertion

loss:

~1dB《集成平面光波导器件》课程64DiodeV

L

Activeregionglength40Gbit/sEROn-chipIL(maximum(transmission)Opticallossat40Gbit/soperat.pointverticalpn[Intel]4V.cm1mm1dB4dB-lateralpn[Univ.Surrey]2.7V.cm3.5mm10dB15dB15dBMaincharalateralpn[Univ.Surrey]2.7V.cm

P1mmtobe3.5dB(improved:5dB35dBPowerlateralpn[Univ.Surrey]2.7V.cm

1mmti7dBJ/bit)5dB8dBVoltawrappedaroundpn14VV.cm[Univ.Surrey]geswing1.313mm(>5V)6.565dB15dB25dBpipin[Univ.ParisSud]3.5V.cm4.7mm6.6dB6dB6dBpipin[Univ.ParisSud]3.5V.cm0.95mm3.2dB4.5dB4.5dBState

of

the

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