Post on 13-Apr-2018
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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)
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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)
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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
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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
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Detailed Layer Structure of DMDDetailed Layer Structure of DMD
L. Hornbeck, Electronic Imaging, 1997
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TITI’’ss Digital Micromirror Devices (DMD)Digital Micromirror Devices (DMD)
(Texas Instruments, Digital Micromirror DeviceTM)
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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)
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Principle of Projection SystemPrinciple of Projection SystemUsing DMDUsing DMD
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Projection Display UsingProjection Display UsingDigital Micromirror Display (DMD)Digital Micromirror Display (DMD)
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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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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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Optical DesignsOptical Designs
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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
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Example: 2x2 SwitchExample: 2x2 Switch
Marxer, et al., J-MEMS, vol.6, 1997. p.277-85.
CrossState
BarState
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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
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Space Division Switches:Space Division Switches:
(1) 2D MEMS Optical Switches
(2) 3D MEMS Optical Switches
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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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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
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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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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
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LucentLucent’’s Lambda Routers Lambda Router
(Lucent Lambda Router)
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2D Scanners with Staggered Vertical 2D Scanners with Staggered Vertical CombdrivesCombdrives
Fujitsu, 2002
Gold bumpElectrode substrate
Comb teethMirror surface
Mirror array substrate
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Fujitsu Fujitsu MicromirrorMicromirror for 3for 3--D MEMS Optical SwitchD MEMS Optical Switch
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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
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FujitsuFujitsu’’s 3s 3--D MEMS SwitchD MEMS Switch
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FujitsuFujitsu’’s 3s 3--D MEMS SwitchD MEMS Switch
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WavelengthWavelength--Selective Switches (WSS)Selective Switches (WSS)
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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
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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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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
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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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1x4 Wavelength1x4 Wavelength--Selective Switch (WSS)Selective Switch (WSS)
f
f
Grating
Y
X Collimators
Analog Micromirror
Array
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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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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
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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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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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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
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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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(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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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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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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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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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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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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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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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
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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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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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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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Nanophotonic MEMSNanophotonic MEMS
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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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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
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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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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