1

1Ming Wu

Optical MEMS for Optical MEMS for Telecommunication SystemsTelecommunication Systems

Ming C. Wu

University of California, BerkeleyDepartment of EECS &

Berkeley Sensor and Actuator Center (BSAC)wu@eecs.berkeley.edu

Lecture for EE 233

2Ming Wu

AcknowledgmentAcknowledgment

• Providing viewgraphs– Thomas Ducellier (Metconnex)– Dan Marom (Lucent)– Katsu Okamoto (Okamoto Lab)– Olav Solgaard (Stanford University)– Rod Tucker (Univ. Melborne)

• Graduate students and Postdocs at Berkeley and UCLA– Monolithic WSS: Josh C.H. Chi, Chenlu Hou, Chi-hung Lee– WSS: J.C. “Ted” Tsai, Dr. Li Fan, Dr. Dooyoung Hah, Sophia

Huang– PLC switch: Josh C.H. Chi, Ted Tsai, in collaboration with Dr.

Katsu Okamoto– PhC switch: M.C. “Mark” Lee– MEMS Microdisk: M.C. “Mark” Lee, Jin Yao, David Leuenberger– Si Photonics: Sagi Mathai, Joanna Lai, Xin Sun (Prof. Tsu-Jae

King)

2

3Ming Wu

OUTLINEOUTLINE

• Introduction

• Optical design considerations

• Space division switches– 2D MEMS optical switches– 3D MEMS optical switches

• Spectral domain processors– Wavelength-selective switches

• Planar lightwave circuits (PLC)-MEMS Integration

• Diffractive optical MEMS

• New directions

• Summary

4Ming Wu

Why Optical MEMS ?Why Optical MEMS ?

• Optical MEMS offers– Low optical insertion loss– Low crosstalk– Transparency (wavelength, polarization, bit rate, data format)– Low power consumption

• Why ?– The effect of moving optical elements is stronger than electro-

optic, thermal-optic effects– Very efficient beam steering devices

• What– Switches– Tunable devices (delay, dispersion, wavelength, bandwidth,

dynamic gain equalization, etc)

3

5Ming Wu

Optical MEMSOptical MEMS

6Ming Wu

25 Years of Optical MEMS25 Years of Optical MEMS

1980 1990 2000

Scanning Mirror (Petersen, IBM)

Digital Micromirror Device (DMD, TI)

TITI’’ss DMDDMD

Free-Space Optical Bench(UCLA/Berkeley)

3D MEMSSwitches

Micromotoers(Berkeley)

?

Grating Light Valve(GLV, Stanford)

2D MEMS Switches(Tokyo U)

TITI Silicon Light MachineSilicon Light Machine

4

7Ming Wu

Digital Micromirror Devices (DMD)Digital Micromirror Devices (DMD)

~ 1 million DMD’s on a chiphttp://www.dlp.com/dlp/resources/dmmd.asp

8Ming Wu

Digital Micromirror Device (DMD)Digital Micromirror Device (DMD)Texas InstrumentsTexas Instruments

Top View of DMD

L. Hornbeck, Electronic Imaging, 1997

5

9Ming Wu

Detailed Layer Structure of DMDDetailed Layer Structure of DMD

L. Hornbeck, Electronic Imaging, 1997

10Ming Wu

TITI’’ss Digital Micromirror Devices (DMD)Digital Micromirror Devices (DMD)

(Texas Instruments, Digital Micromirror DeviceTM)

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11Ming Wu

Transfer Characteristics of Torsion Transfer Characteristics of Torsion MirrorsMirrors

Voltage

Ang

leBistableRegime

AnalogRegime

Pull-inVoltage

CWLzVS 3

302

ε⋅

=

Pull-in voltage(or Stiffness Voltage)

12Ming Wu

Principle of Projection SystemPrinciple of Projection SystemUsing DMDUsing DMD

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13Ming Wu

Projection Display UsingProjection Display UsingDigital Micromirror Display (DMD)Digital Micromirror Display (DMD)

14Ming Wu

Bulk MicromachiningBulk Micromachining

• Anisotropic wet chemical etching (restricted to fixed crystalline orientations)<100>

<111>

<110>

<111>VerticalSidewall

• Deep reactive ion etching (DRIE or ICP-RIE)

• Combine with silicon-on-insulator (SOI) or III-V epi wafer

• Suspended structure in one-step etching + releasing

• Multi-layer structure by additional wafer bonding

• High aspect ratio (> 20:1)• Independent of crystal orientation• More efficient use of real estate of

substrate (e.g., can produce closely spaced structures)

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15Ming Wu

SurfaceSurface--Micromachining:Micromachining:2 2 ““StandardStandard”” Foundry ProcessFoundry Process

MUMPsMUMPs SUMMiTSUMMiT

Poly 1Poly 2

2 um

Poly 0

6.25 um

Poly 2Poly 1

Poly 4

Poly 3

0.5 um1 um

CMP1

CMP2

12.75 um

Poly 0

• MEMSCAP • Sandia National Lab

• Fairchild (SUMMiT-4)

Si Substrate Si Substrate

16Ming Wu

MEMS Technologies and Optical Element Size MEMS Technologies and Optical Element Size

ElectromagneticActuation Electrostatic Actuation

1 cm 1 mm 1 µm100 µm 10 µm

Scanning displayImaging

3D-MEMSOXC

DiffractiveMEMS

2DMEMSSwitch

2x2 SwitchesVOA

Projectiondisplay

OpticalElement

Size

Applications

MainActuation

Mechanisms

Micro-resonators

Photonic Crystals

Bulk-Micromachining(Single Crystalline Si, DRIE, Wafer Bonding)

Surface-Micromachining(Poly-Si, Al)

MainFabrication

Technologies

Mirror-basedVOA

OADMWSS

Gain equalizerDispersion

compensator

Nano-Fabrication

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17Ming Wu

Optical DesignsOptical Designs

18Ming Wu

Direct Coupling Without LensesDirect Coupling Without Lenses

0 200 400 600 800 1000-5

-4

-3

-2

-1

0

Inse

rtio

n Lo

ss (d

B)

Distance (um)

Single Mode Fiber (SMF)

Thermally Expanded Core(TEC) Fiber

SMF

TECAir Air

Index-Matching

Fluid

• Short propagation distance• May be used for small switches or VOAs

d

10

19Ming Wu

Example: 2x2 SwitchExample: 2x2 Switch

Marxer, et al., J-MEMS, vol.6, 1997. p.277-85.

CrossState

BarState

20Ming Wu

FreeFree--Space Optics: Gaussian BeamSpace Optics: Gaussian Beam

• Larger beam waist Long collimation length• System size ~ 2b• Mirror diameter ~ 2aw0, a ~ 1.5 to 2

λπ 2

0wb =

02w 022 w

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛+=

22

02 1)(

bzwzw (Confocal Parameter)

b

11

21Ming Wu

Space Division Switches:Space Division Switches:

(1) 2D MEMS Optical Switches

(2) 3D MEMS Optical Switches

22Ming Wu

Scaling of 2D MEMS Optical SwitchesScaling of 2D MEMS Optical Switches

Input Channels

OutputChannels

“ADD” Channels

“DROP”Channels

CollimatorArrays

2D MEMSSwitchChip

22

2

0

0

20

2

2

22

NaLwa

N

awRPR

wbNPL

PN

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛=≈⇒

=

=

=≈=

πηλ

λπη

η

λπ

2 to 1.5 ~ a Radius, Mirror :

rMicromirro of Factor Fill :

Length Chip :

Pitch Fiber : Count Port :

PL = 2b

02w 022 w

b2

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23Ming Wu

Port Count of 2D MEMS SwitchesPort Count of 2D MEMS Switches

0

20

40

60

80

0 50 100 150 200

1/e Beam Waist (μm)

Max

imum

Por

t Cou

nt

Fill Factor =

30%

50%

70%

0

1

2

3

4

5

0 50 100 150 200

1/e Beam Waist (μm)

Loss

due

to M

irror

Tilt

(dB

) Mirror Tilt =

0.05°

0.1°

0.2°

Port Count vs Beam Size Loss Due to Mirror Tilt

• Accuracy and uniformity of mirror angles impose a loss penalty, which limit the maximum port count2

2

2

0

2 NaL

wa

N

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛=

≈

πηλ

λπη

:Size Chip

:Count Port

24Ming Wu

SurfaceSurface--MicromachinedMicromachined2D MEMS Optical Switches (16x16)2D MEMS Optical Switches (16x16)

L. Fan, et al., OFC 200216x16 Switch

L. Fan, et al., OFC 2002

010203040506070

89.8

0

89.8

4

89.8

8

89.9

2

89.9

6

90.0

0

90.0

4

90.0

8

90.1

2

90.1

6

90.2

0

Mirror Angle (degree)

Num

ber

Absolute angular uniformity ~ ± 0.05°

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25Ming Wu

Scaling of 3D MEMS OXCScaling of 3D MEMS OXC

02 w

022 w( )

WaistBeam : 2 to 1.5 ~ a

Radius Mirror : AngleScan Mechanical :

:Length Path Optical

:Count Port

0

0

20

2

2

22

9

w

awR

wbL

aLN

=Δ

==

Δ=

θλ

πλθπ

3~ L

InputCollimators

InputCollimators

2D Array of 2-Axis Micromirrors

OutputCollimators

2D Array of 2-Axis Micromirrors

OutputCollimators2D Array of 2-Axis

Micromirrors

26Ming Wu

LucentLucent’’s Lambda Routers Lambda Router

(Lucent Lambda Router)

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27Ming Wu

2D Scanners with Staggered Vertical 2D Scanners with Staggered Vertical CombdrivesCombdrives

Fujitsu, 2002

Gold bumpElectrode substrate

Comb teethMirror surface

Mirror array substrate

28Ming Wu

Fujitsu Fujitsu MicromirrorMicromirror for 3for 3--D MEMS Optical SwitchD MEMS Optical Switch

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29Ming Wu

FujitsuFujitsu’’s 3s 3--D MEMS SwitchD MEMS Switch

Mitsuhiro Yano, Fumio Yamagishi, and Toshitaka Tsuda, IEEE J. SELECTED TOPICS QUANTUM ELECTRONICS, VOL. 11, p. 383, MARCH/APRIL 2005

30Ming Wu

FujitsuFujitsu’’s 3s 3--D MEMS SwitchD MEMS Switch

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31Ming Wu

FujitsuFujitsu’’s 3s 3--D MEMS SwitchD MEMS Switch

32Ming Wu

WavelengthWavelength--Selective Switches (WSS)Selective Switches (WSS)

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33Ming Wu

1xN Wavelength1xN Wavelength--Selective Switch & Selective Switch & NxN WavelengthNxN Wavelength--Selective Cross ConnectSelective Cross Connect

1×4 WSSλ1, λ2, …, λn

λ1, …λ3, λ4, …λ2, …λn, …

4×4 WSXC

λ1, λ2, …, λn λ1, …λ3, λ4, …λ2, …λn, …

λ1, λ2, …, λnλ1, λ2, …, λnλ1, λ2, …, λn

34Ming Wu

Optical Network Architecture Optical Network Architecture • OADM (Ring)

– Add-Drop with fixed λ’s• ROADM (Ring)

– Add-Drop with programmable λ’s• 1xN Wavelength-Selective Switch (Mesh)

– Multi-degree ROADM

• NxN Wavelength-Selective Cross Connect (Mesh)

Ring Network

DROP

ADD

DROP

ADD

DROP

ADD

OADMLack of

Connectivity

Mesh Network

WSSWSS

North

South

WSXC

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35Ming Wu

Fourier Transform Pulse ShaperFourier Transform Pulse Shaper

• Shaping femtosecond pulses by modulating the phases and amplitudes of their spectral components

A. M. Weiner, J. P. Heritage, and E. M. Kirschner, J. Opt. Soc. Am. 1988

36Ming Wu

Dynamic WDM FunctionsDynamic WDM Functions

f

f

Grating

Collimators

Femtosecond pulse shaperPiston Mirrors

Tunable dispersion compensator

Deformable mirrors

Wavelength-Selective Switch

(WSS)

1xN analog micromirrors

Optical add-drop multiplexer (OADM)

1x2 Digital micromirrors

Spectral (or gain) equalizer

Variable reflectivity

mirror

Wavelength blocker

ON-OFF reflectors

DynamicWDM

Functions

MEMS Spatial Light Modulator

Array

MEMS Spatia

l

Light Modula

tor

Array

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37Ming Wu

1x4 Wavelength1x4 Wavelength--Selective Switch (WSS)Selective Switch (WSS)

f

f

Grating

Y

X Collimators

Analog Micromirror

Array

38Ming Wu

1x4 WSS1x4 WSS

• D. Marom et al. (Lucent), OFC 2002– 1x4 WSS– Channel spacing: 50 or 100 GHz– MEMS performance: 12° ( > 55 V )

• T. Ducellier et al. (JDS-U), ECOC 2002

– 1x4 WSS– Channel spacing: 100 GHz– MEMS performance: ±2°

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39Ming Wu

WSS provides:• Port switching• Wide passbands• 10 dB DSE • Blocking• Low insert loss• Low PDL, DGD

64 Channel, Wavelength-Selective 4×1 Switch (D. Marom)Free-Space Implementation

40Ming Wu

Analog Micromirror Array (UCLA)Analog Micromirror Array (UCLA)

Fixed fingers

Movable fingers

Hidden springs

Mirror

Anchor

zy

x

+/- 6° (mechanical)Scan Angles

± 0.0035dBSystem (3hr)±0.00085°Stability (3hr)3.4 kHzRes. Freq.

98%Fill Factor6 VVoltage

0 5 10 15 20 250

2

4

6

8

Rot

atio

n A

ngle

(deg

)

Applied Voltage (V)

0.5μm 1μm2μm

3μm

DMD-Like

Comb Finger Spacing

• D. Hah, et al (UCLA) J. MEMS, 2004, p. 279• J.C. Tsai, et al (UCLA) IEEE PTL 2004, p. 1041

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41Ming Wu

Scaling of WSSScaling of WSS

Grating

spatial ⎟⎠⎞

⎜⎝⎛

∂∂

⋅=Δ λ

θλ

πλ #22 f

fNColl

MEMS wfw

⋅⋅

=π

λ

• System size ~ 2 f

• Total capacity (Nspatial x Nλ )is constant

– Proportional to f

Collimators

f f

AnalogMicromirror

Array

CollwMEMSw

Gratingspatial ⎟

⎠⎞

⎜⎝⎛

∂∂

⋅⋅

=⋅λθ

λπ λ

λ #22 ffBWNN

42Ming Wu

Approach for Increasing Port Count (1)Approach for Increasing Port Count (1)

• Use anamorphic prism pair to compress lateral beam size on MEMS micromirrors

• Elliptical beams on MEMS mirrors Rectangular micromirror

D. Marom(Lucent)

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43Ming Wu

Approach for Increasing Port Count (2)Approach for Increasing Port Count (2)

• 1xN2 WSS:– 2D collimator array – 1D array of 2-axis

micromirror array

• Port count is increased from N to N2

– N is the diffraction-limited linear port count

• High port count WSS– 1x32 WSS has been

demonstrated

f

f

Grating

Resolution lens

Y

X

• J.-C. Tsai, et al., (UCLA) ECOC 2004, Paper Tu1.5.2

44Ming Wu

HighHigh--Fill Factor 2Fill Factor 2--Axis Micromirror ArrayAxis Micromirror Array

2-DOF mirror joint

Mirror

Lever

Vertical combdrive actuators

• Gimbal-less– High Fill factor (> 98%)

• Large scan angle– 3x angle amplification by leverage

• Low voltage– Powerful vertical combdrive actuators

xy Original mirror position

J.C. Tsai, L. Fan, D. Hah, and M.C. Wu, IEEE LEOS International Conference on Optical MEMS 2004

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45Ming Wu

SEM of SEM of GimbalGimbal--less 2less 2--Axis Analog Micromirror Axis Analog Micromirror ArrayArray

• SUMMiT-V 5-layer surface micromachining process• Mirror pitch: 200 um• Large scan angles: ±6.7º (mechanically) @ 75 V• Fill factor: 98%• Resonant frequency = 5.9 kHz

J.C. Tsai, L. Fan, D. Hah, and M.C. Wu, IEEE LEOS International Conference on Optical MEMS 2004

46Ming Wu

Planar Lightwave Circuit (PLC) MEMS Planar Lightwave Circuit (PLC) MEMS

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47Ming Wu

(a) Configuration of 16ch-100GHz OADM (b) Photograph of OADM

K. Okamoto et al., Electron. Lett., vol. 31, pp.723-724, 1995

Drop Main outputport port

Main Addinput portport

Reconfigurable Optical Add/Drop Multiplexer Reconfigurable Optical Add/Drop Multiplexer (ROADM)(ROADM)

(VG courtesy of K. Okamoto)

48Ming Wu

PLC 1x9 WSSPLC 1x9 WSS

• 1x9 WSS

• Thermal optic switch– 450 mW / switch– Total power ~ 14W

• Loss ~ 5.4 dB

• Isolation > 46 dBInput

Output 1

Output 2

Output 3

Output 4

Output 5

1x2

C.R. Doerr, et al. (Lucent), OFC 2002 Postdeadline Paper, FA3

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49Ming Wu

2x2 MEMS Waveguide WSXC2x2 MEMS Waveguide WSXC

D.T. Fuchs, et al (Lucent) IEEE PTL, Jan. 2004

• 100 GHz channel spacing• 10.6 dB insertion loss• 20 dB extinction ratio

• 3 diffraction orders by AWG• Optical phases of (+1, 0, -1) orders

modulated by MEMS piston mirrors• Chip ~ 5 x 9 mm2

50Ming Wu

40 Channel, Wavelength-Selective 1×2 Switch (D. Marom)

Port 1

Input

Port 2Cylindricalcollimators

PLC 1 and PLC 2

Fourierlens

MEMSmicro-mirrorarray

Hybrid PLC and Free-Space Implementation

λ0

λ < λ0

λ > λ0

Switch to Port 1 Switch to Port 2

Hybrid WSS provides:• Same benefits as free space WSS• Compact implementation• Integration of additional functionality

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51Ming Wu

Compact Spectral Pulse Shaper (D. Marom)

Hybrid PLC and Free-Space Implementation

Pulse Shaper provides:• Spectral domain processing• Polarization independent• Gateway to optical arbitrary

waveform synthesis

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 20 40 60 80

Voltage

Phas

e [ π

]

MEMS piston motion micromirror array• >2π phase modulation• Polarization insensitive

Input Pulse Thru shaper Dispersion Compensated Shaped signal

52Ming Wu

2D arrangement of ports for scalable 1x9 2D arrangement of ports for scalable 1x9 WSSWSS

Array of Waveguide Dispersive Elements

Collimating/Focusing lenses MEMS mirror

linear array

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53Ming Wu

Interleaved spectrum switched to all Interleaved spectrum switched to all output portsoutput ports

54Ming Wu

FreeFree--Space and Hybrid Integrated 1xN Space and Hybrid Integrated 1xN WSSWSS

T. Ducellier et al. (Metconnex), ECOC, 2004D.M. Marom et al. (Lucent), OMEMS 2004D.M. Marom et al. (Lucent), ECOC 2005

Hybrid 1xN WSSFree-Space 1xN WSS

Resolution Lensf

f

GratingOptical Fibers

• Silica PLC has low insertion loss• Hybrid integration requires external

collimator and lens

Silica PLC

MEMS Chip

Bulk Lens

Microlens

• Large space• Complicated alignment

D. Marom, et al. (Lucent), OFC 2002.T. Ducellier, et al. (JDS-U), ECOC 2002.S. Huang, et al. (UCLA), O-MEMS 2002.

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55Ming Wu

SiliconSilicon--Based Monolithic 1x4 WavelengthBased Monolithic 1x4 Wavelength--Selective SwitchSelective Switch

• Silicon PLC is compatible with SOI-MEMS technologies• Excess Insertion loss can be reduced with AR coating and smoothed

sidewall (e.g. hydrogen annealing)C.H. Chi et al., CLEO 2005

56Ming Wu

Integrated Optical ComponentsIntegrated Optical ComponentsParabolic Collimator Parabolic Focusing Reflector

90° off-axis

Blazed Micro-grating

TIR

TIR TIR

Electrostatic Micromirror

C.H. Chi et al., OFC 2006

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57Ming Wu

4x4 Wavelength4x4 Wavelength--Selective Cross ConnectSelective Cross Connect

• Four passive 1x4 splitters (6.5 dB loss)• Four 4x1 WSS (4 dB loss)

D. M. Marom et al. (Lucent), ECOC 2003

Free-Space WSXC

WSSλ1 λ2 … λ8

λ1 …λ3 λ4 …λ2 …λ6 λ8 …

WSS1

WSS2

WSS3

WSS4

WSS5

WSS6

WSS7

WSS8

In1

In2

In3

In4

Out1

Out2

Out3

Out4

WSS1

WSS2

WSS3

WSS4

In1

In2

In3

In4

Out1

Out2

Out3

Out4

1x4 WSS

4x4 WSXC

C.H. Chi et al., OFC 2006

58Ming Wu

MonolithicMonolithic 4x4 WSXC 4x4 WSXC –– Planar IntegrationPlanar Integration

In1In2In3In4

Out1Out2

Out3Out4

46mm

32mm

1x4 MMI splitter

Waveguide Bending

Waveguide Crossing

Waveguide Shuffle Network

WSS1

WSS2

WSS3

WSS4

Support Broadcast and Multicast Functions

C.H. Chi et al., OFC 2006

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59Ming Wu

SimulationSimulation

Loss 0.05 dB

Crosstalk-66 dB

890 um

40 um

Waveguide Crossing (2D FDTD)

Waveguide Bend (2D FDTD)R = 100 μm

1 μm Offset

1 μm Offset

Loss = 1 dB

MMI (3D BPM)

Splitting Loss = 6.1 dBNonuniformity = 0.004 dB

C.H. Chi et al., OFC 2006

60Ming Wu

Fabricated DeviceFabricated Device

100μm

Micromirror

5μm

Micro-grating

50μm

Collimator 4x4 WSXC

1x4 WSSSolid Immersion Mirror

C.H. Chi et al., OFC 2006

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61Ming Wu

Spectral Response of 4x4 WSXCSpectral Response of 4x4 WSXC

• Six micromirrors tested with available tuning range: 1460-1580 nm• 3 dB passbands:

1477-1482 nm, 1488-1494 nm, 1507-1517 nm1527-1535 nm, 1539-1553 nm, 1561-1573 nm

• Additional passband from adjacent grating order

1460 1480 1500 1520 1540 1560 1580-70

-65

-60

-55

-50

-45

-40

-35

-35

-30

-25

-20

-15

-10

-5

0

Tran

smis

sivi

ty (d

B)

Wavelength (nm)

M3 M4 M5 M6 M7 M8

Grating Efficiency (Theoretical)

Gra

ting

Effic

ienc

y (d

B)

C.H. Chi et al., OFC 2006

62Ming Wu

Transfer Curve of 4x4 WSXCTransfer Curve of 4x4 WSXC

• Signals are selected from each input port and transported to the designated output port

• Extinction ratio from In1 is lower due to imperfect AR coating

0 20 40 60 80 100 120 140 160-70

-65

-60

-55

-50

-45

-40

-35

Tran

smis

sion

(dB

)

Voltage (v)

In 1 In 2 In 3 In 4In1In2In3In4

Out1Out2

Out3Out4

WSS4

WSS2

WSS1

WSS3

C.H. Chi et al., OFC 2006

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63Ming Wu

Diffractive Optical MEMSDiffractive Optical MEMS

64Ming Wu

Grating Light ValveGrating Light Valve

• Applications– Projection display– Variable optical attenuators (VOA)– Gain equalizers– Wavelength blockers

• Companies– Silicon light machine (Cypress),

Lightconnect, Polychromix, Kodak

Nitride withAl coating

Incident Light Reflected Incident Light Diffracted

O. Solgaard, F. S. A. Sandejas, D. M. Bloom, "A deformable grating optical modulator", Optics Letters, vol. 17, no. 9, pp. 688-690, 1 May 1992.

Polychromix

Silicon Light Machine

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65Ming Wu

Telecommunications ApplicationsTelecommunications Applications

Dynamic Spectral Equalizer (DSE)

Reconfigurable Channel Blocking Filter Dynamic Gain Equalizer

66Ming Wu

MEMS MEMS SwitchableSwitchable WDM WDM DeinterleaverDeinterleaver Based on Based on GiresGires--TournoisTournois InterferometerInterferometer

FocusingLens

OutputFiber Array

PowerDetectorPower

Detector

TunableLaser

TunableLaser

MEMSMirrorArray

BeamSplitter

Input fiber

Olav Solgaard, Stanford University

http://wdm.stanford.edu/snrc/kyoungsik12_10_01.ppt

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67Ming Wu

Nanophotonic MEMSNanophotonic MEMS

68Ming Wu

Whispering Gallery Mode (WGM)Whispering Gallery Mode (WGM)

St Paul’s Cathedral, London

• WGM first explained by Lord Rayleigh in 1910

• Used in– Acoustic waves– Microwaves– Optical waves

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69Ming Wu

WGM in Silica WGM in Silica MicrosphereMicrosphere

• Made by melting a fiber tip

• First demonstrated by Braginsky, et al, 1989

• Extremely high Q ~ 2x1010

– Maleki, et al, (JPL) 2004

70Ming Wu

Optical MicroresonatorsOptical Microresonators

• Filter proposed by Marcatili(Bell Labs), 1969

• Channel dropping filter

• Needs high Q > 105

Surface roughness < 1 nm

λ0

λ0

λ0

λ1

R C Lm:1 1:m’

Equivalent Circuit

36

71Ming Wu

Microring ResonatorMicroring Resonator--Based PICBased PIC

S. T. Chu, B. E. Little, V. Van, J. V. Hryniewicz, P. P. Absil, F. G. Johnson, D. Gill, O. King, F. Seiferth, M. Trakalo and J. Shanton (Little Optics) OFC 2004

Thermally Tuned with Vernier Architecture

42 μm

72Ming Wu

0.0 0.1 0.2 0.3 0.4 0.51e-4

1e-3

1e-2

1e-1

1e+0

Pow

er C

oupl

ing

(κ2 )

Variable Quality FactorVariable Quality Factor

Input

Output

Disk-Waveguide Spacing (μm)

Decoupled

Under-coupled

Critically Coupled

Over-coupled

λ1

Over-coupledCritically CoupledUnder-coupledDe-coupled

Tran

smis

sion

Frequency Frequency Frequency Frequency

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73Ming Wu

Scaling of Optical WiresScaling of Optical Wires

TE Like

TM Like

Waveguide Width, w (um)

Thic

knes

s, t

(um

)

SingleMode

Multimode

SiOX

Single Modew× t ≤ 0.18 μm2

w

t

Waveguide Width (um)

5 nm

3 nm

1 nm

Wav

egui

de L

oss

(cm

-1)

0.5um

0.25um

SurfaceRoughness

TM-like Mode

Surface Roughnessδrms ≤ 1 nm

• Higher density• Very sensitive to

surface roughness

• Insensitive to surface roughness

• Multi-mode • Lower density

74Ming Wu

< 0.25< 0.25--nm Surface Roughnessnm Surface Roughnessby Hby H22 AnnealingAnnealing

Microdisk

Substrate

Sidewall

Silicon Waveguide

Before Annealing

SiO2

Microdisk

Substrate

Sidewall

Silicon Waveguide

After Annealing

SiO2

Surface Roughness < 0.25 nm

38

75Ming Wu

Microdisk Resonator with MEMS Tunable Microdisk Resonator with MEMS Tunable Coupler (First Generation Device)Coupler (First Generation Device)

Microdisk

Waveguides

VV

VV

VV

VV

• Successfully demonstrated– Switchable notch filter (O-MEMS ’03)– Tunable dispersion, 0 ~ 400 ps/nm (CLEO ’04)

• Q ~ 10,000 due to vertical offset

Phase 2: Vertical Coupling

76Ming Wu

SecondSecond--Generation MEMS Microdisk ResonatorGeneration MEMS Microdisk Resonator

Microdisk Resonator

Waveguide Right Electrode

Waveguide

Left Electrode

Microdisk Resonator

Waveguide Right Electrode

Waveguide

Left Electrode• Microdisk

– Radius: 20 μm– Thickness : 0.25 μm

• Suspended deformable waveguides– Width: 800 nm– Thickness: 250 nm– Length: 100 μm

• Initial gap spacing– WG/Disk: 1 μm

39

77Ming Wu

UnderUnder-- to Overto Over--CouplingCoupling

Under Coupling (κ<α)

1548.5 1549 1549.5 1550-30

-25

-20

-15

-10

-5

0

Wavelength (nm)

Tran

smis

sion

(dB

)

1548.5 1549 1549.5 1550-30

-25

-20

-15

-10

-5

0

Wavelength (nm)

Critical Coupling (κ=α)

1548.5 1549 1549.5 1550-30

-25

-20

-15

-10

-5

0

Wavelength (nm)

Over Coupling (κ> α )

Microdisk Microdisk Microdisk

Slightly-bent Largely-bentStraight

Resonant Wavelength= 1549.37nm

23.5V0V 17V

78Ming Wu

Reconfigurable Optical AddReconfigurable Optical Add--Drop Multiplexer Drop Multiplexer (ROADM)(ROADM)

Input Through

AddDrop

Input ThroughAdd

Drop

Parallel ConfigurationParallel Configuration Cross ConfigurationCross Configuration

Tran

smis

sion

At R

eson

ance

Waveguide-Disk Spacing

ThroughDrop

40

79Ming Wu

Dynamic Wavelength AddDynamic Wavelength Add--DropDrop

Input

Through

DropInput

Through

Drop

• Cascadable, hitless operation• Almost 0 dB insertion loss is observed without bias

Applied Voltage: 30VApplied Voltage: 0V

1550 1555 1560-20

-10

0

1550 1555 1560-20

-10

0

Wavelength (nm)

Tran

smis

sion

(dB

)

Through Port

Drop Port

1550 1555 1560-20

-10

0

Wavelength (nm)

1550 1555 1560-20

-10

0

Tran

smis

sion

(dB

)

Through Port

Drop Port

80Ming Wu

Spoiling Q by MEMS Metal MembraneSpoiling Q by MEMS Metal Membrane

• Use a metal membrane to spoil the Q of microring resonator– Low loss resonant wavelength sent to “Drop” port– High loss all wavelengths transmitted to “Through” port

Enable resonance Disabled resonance

Gregory N. Nielson, et al., (MIT) “MEMS based wavelength selective optical switching for integrated photonic circuits”, CLEO 2004

41

81Ming Wu

SUMMARYSUMMARY

• Tremendous progresses have been made in– MEMS devices and manufacturing– Micro-optics– Packaging– Control

• New trends in Optical MEMS -- Integration– Higher level of integration, less free-space alignment– MEMS-PLC integration– MEMS-nanophotonics integration– Electronics integration– Single-chip optical MEMS system