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EE 539A
Integrated Optics and Optical MEMS 7 ― Optical MEMS: Applications in Optical Fiber Communications, Part II
Optical Crossconnect (Optical Switch)
Lih Y. Lin EE 539A
7b-2
Purpose: Optical Network Provisioning In the current core network, provisioning of 2.5Gb/s or 10 Gb/s connections is a paper-mediated process that takes weeks This process should be automated in response to service-layer request and achieve seconds to minutes provisioning time.
IP router
IP router
Lih Y. Lin EE 539A
7b-3
Purpose: Optical Network Restoration Current core network: Basic restoration equipment: Digital electronic crossconnects or SONET ADMs Basic units of restoration: 45 Mb/s or 155 Mb/s
There is an emerging need to move to larger units of restoration, at or approaching the wavelength level
X
IP router
IP router
Lih Y. Lin EE 539A
7b-4
Optical Crossconnects for Provisioning and Restoration
Wavelength -interchange crossconnect
... ...
Wavelength -selective crossconnect
...
... ...
...
...
...
...
Standard interfaces
Transparent network
...
Opaque network
SONET ATM
IP
Require high-port-count optical switches
...
...
OXC
SONET ATM
IP
Require medium-port-count optical switches
Lih Y. Lin EE 539A
7b-5
2-D MEMS Digital Crossbar Switches
Virtues:
Simple binary mirror-control. Precise angular alignment can be achieved easily. Challenges: Scalability. 32 x 32 is probably a reasonable limit for single stage → Good for wavelengthselective crossconnects. Lih Y. Lin EE 539A
7b-6
Example of Micro-actuated Switch Mirror Compact translation-to-freerotation conversion 22 µm translation → 90° rotation
Switch mirror
Pushrod
Hinge joint
Hinge Actuated translation stage Lih Y. Lin EE 539A
7b-7
Scratch-drive Actuation Fabrication
Si
Working principle
Poly-2 PSG-2 PSG-1 Si3N4
∆X ~ 10’s of nm
Si
Akiyama et al., IEEE J. of Microelectromechanical Systems, 1993.
Lih Y. Lin EE 539A
7b-8
2-D MEMS Optical Switching Video
Uni-directional
actuation. Micromirror pulled back by springs. Bi-directional
actuation. Actuators with opposite moving directions are connected by insulating material. Lih Y. Lin EE 539A
7b-9
8 x 8 MEMS Optical Switch • Low loss (1.7 dB for 8x8) • Negligible crosstalk (< -60 dB) • Negligible polarizationdependent loss • Negligible wavelengthdependence • Bit-rate transparent • Sub-millisecond switching time • Compact (1 cm x 1 cm) • Standard IC fabrication → Optical prealignment, low cost • Enhanced functionality in integrated form Characteristics of most 2-D digital crossbar switches Lih Y. Lin EE 539A 7b-10
Electro-static Torsion-mirror Switch
H. Toshiyoshi and H. Fujita, J. Microelectromechanical Systems, 1996.
Lih Y. Lin EE 539A 7b-11
Stress-induced Bending Switch
Au-coating on polysilicon plate to create stress Single-point contact Switching times: < 12ms Insertion loss for 16x16: < 6dB Angular uniformity: < ±0.1° PDL < 0.4 dB 100 million cycles demonstrated
R. T. Chen, H. Nguyen, and M. C. Wu, “A low voltage micromachined optical switch by stress-induced bending,” IEEE MEMS Conference, 1999. Lih Y. Lin Fan, et al., “Digital MEMS switch for planar photonic crossconnects,” OFC 2002 EE 539A 7b-12
Magnetic-actuated Crossbar Switch
B. Behin, K. Y. Lau, and R. S. Muller, Solid-State Sensor and Actuators Workshop, 1998.
Lih Y. Lin EE 539A 7b-13
Integrated Networking Functionality
― Signal Monitoring Signal-monitoring required for performance monitoring and restoration trigger 45o beam splitter
Photodetector
Lih Y. Lin EE 539A 7b-14
Signal-monitoring Module Microwave coplanar Microwave coplanar transmission line transmission line
45oo beam-splitter 45 beam-splitter
Wire-bonding Wire-bonding Vertical Vertical support support Photodiode Photodiode
Side support Side support
Lih Y. Lin EE 539A 7b-15
Design Consideration for the High-speed Hybrid-integrated Photodetector Impedance of coplanar transmission line G S G
2.5 Gb/s
t
s
h
Substrate, εr K (k e ) 30 π ⋅ ε eff ( f ) K ' ( k e )
Z0 ( f ) = ke =
w
se se + 2 we
5 Gb/s
se = s + ∆
Effective width
we = w − ∆
Effective gap
∆=
1.25t π
K (ke ) = ∫
Impedance
4 πw 1 ln + t π dφ 2
0
1 − k e2 sin 2 φ
K ' ( k e ) = K ( 1 − k e2 ) Lih Y. Lin EE 539A 7b-16
Integrated Networking Functionality
― Connection Verification Connection-verification required for network-surveillance
... ... ...
...
... ...
...
... ...
...
SONET
ATM
IP
Optical crossconnect is a black box
...
...
OXC
SONET
ATM
IP
But the network needs to know if the connection configuration is right
Lih Y. Lin EE 539A 7b-17
MEMS Optical Switch with Integrated Connection-Verification Micro-mirror Electrode plate
45o beam splitter
Output Photodetector
Bias on the electrode Frequency = f Input
Mirror-dithering encodes pilot-tone into measured photocurrent intensity
Photocurrent intensity Frequency = 2f
Lih Y. Lin EE 539A 7b-18
3D-MEMS Analog Beam-steering Switches Lens array
Fiber array
MEMS mirror array Optical path
Use both gimbal mirrors to adjust the propagation direction of the optical beam Lih Y. Lin EE 539A 7b-19
Pros and Cons of 3D MEMS Optical Switches Virtues: Scales beyond 1000 x 1000 in single stage Challenges: Arrays of ~ 1000 elements with mrad, µm tolerances Require exquisite engineering of: • • • • •
Fiber array MEMS mirror array Optical path Lens array
MEMS chip and electrical I/O Mirror-control algorithm Fiber arrays Lens arrays Mechanical packaging Lih Y. Lin EE 539A 7b-20
3-D MEMS Optical Switching Video Fiber array Lens array
Optical path
MEMS mirror array
Video shows steering the optical beam to different angles at various speed
Lih Y. Lin EE 539A 7b-21
Self-assembled Polysilicon Beam-steering Mirror (Lucent Lambda Router)
Lih Y. Lin EE 539A 7b-22
Beam-steering Mirror with Piezo-resistive Torsion Sensing • Piezo-resistive torsion sensors – Resistivity changes with torsion strength – Provide closed-loop feedback control capability of mirror angle
Torsional flexures with sensors
Developed by Xros/Nortel
Lih Y. Lin EE 539A 7b-23
Beam-steering Mirror with Terraced Electrode
Sawada et al., “Improved single crystalline mirror actuated electrostatically by terraced electrodes with high-aspect ratio torsion spring,” Optical MEMS 2003.
Lih Y. Lin EE 539A 7b-24
Optical Coupling Loss from Beam Divergence The shorter focal length collimating lens produces a narrower beam which diverges faster Launch = waist
Coupling efficiency D
Γ=
* ∫ E ( x , y , z = D ) ⋅ E ( x , y , z = 0)
2
∫ E E ( x , y , z = D ) ⋅ ∫ E E ( x , y , z = 0) *
*
Launch = waist
Larger beam produces lower losses or longer propagation distance
Lih Y. Lin EE 539A 7b-25
Mode-Matching for Reduced Optical Loss Backing fiber away from the lens focal point slightly allows us to place the beam waist exactly between the two collimating lenses. Launch is NOT waist Waist is here
w
w0
Identical mode-filling of both lenses D 2
Dλ Dλ Dλ = ~ w0 Diffraction limit: w = w0 1 + 2 2 2πw0 2πw0 2πw0 Still, long propagation distance requires large beam width, and large mirrors are not desirable Lih Y. Lin EE 539A 7b-26
Coupling Loss vs. Propagation Distance (Use 2-D digital crossbar switch as an example)
15
Experiment Theory
a = 1.5
R = 100 µm
Loss (dB)
10 32 x 32
R: Mirror radius Gaussian beam half-width = R/1.5 Estimated pitch = 800+3R (µ µm)
R = 150 µm
5 R = 200 µm
16 x 16
0
R = 300 µm R = 400 µm R = 500 µm
0
20
40 # of mirrors traveled
60
80
Optical-path length = 7.04 cm (R = 100 µm) 8.00 cm (R = 150 µm) 8.96 cm (R = 200 µm) 10.9 cm (R = 300 µm) 12.8 cm (R = 400 µm) 14.7 cm (R = 500 µm)
Lih Y. Lin EE 539A 7b-27
Angular-Misalignment in Free-Space Optics After angular-misaligned micro-mirror
Lowest-order Gaussian beam w0 r 2 E ( x, y , z ) = E 0 exp − 2 w ( z) w( z ) z × exp − j kz − tan −1 z 0 kr 2 × exp − j 2 R( z )
amplitude factor longitudinal factor
(
radial phase
Amplitude of the field
w0 x '2 + y 2 E ( x ', y , z ' ) = E0 exp − 2 w( d1 + z ' ) w ( d1 + z ' ) d + z ' × exp − j k ( d1 + z ') − tan −1 1 z 0 k x '2 + y 2 × exp − j 2 R( d1 + z ' )
Coordinate transformation x ' = x ⋅ cos(θ ) − z ⋅ sin(θ ) z ' = x ⋅ sin( θ ) + z ⋅ cos(θ )
X’ Z’
Micro-mirror
(0,0)
x
θ
Coupling efficiency
z Receiving plane
)
Γ=
∫E
*
( x ' , y , z ' ) ⋅ E ( x , y , z = 0)
2
∫ E E ( x ' , y , z ' ) ⋅ ∫ E E ( x , y , z = 0) *
*
Input optical beam Lih Y. Lin EE 539A 7b-28
Coupling Loss Due to Angular Misalignment Theoretical results
(Use 2-D digital crossbar switch as an example)
10 R = 400 µm
Experimental verification
R = 300 µm
8
30
20
6 R = 200 µm
4
20
10 10
R = 150 µm
2 R = 100 µm
0
0
0.05
0.10 0.15 θ (Degrees) θ: Twice the mirror-angle variation
d = 5 cm z = 5 cm w0 = 160 µm 0
-0.2
-0.1
Normalized Loss (dB)
Experiment Theory
Loss (dB)
Additional loss (dB)
i = 63 32 x 32 switch
0 0
0.1
0.2
Angular Misalignment of Mirror (Degrees)
0.20
The digital nature of the 2-D crossbar switch makes this a less serious problem → A serious challenge for 3-D analog beam-steering switch Lih Y. Lin EE 539A 7b-29
Torsion Mirrors are Generally High-Q Resonators Frequency and step function responses for a high-Q MEMS mirror. 400 x 400 micron mirror, 75% covered with 10 microns of nickel (ρ=8.9 g/cc) f=711 Hz Q=142
w02 Lorentzian response: P ( w) = (iw)2 + 2iζww0 + w02
w0 : Resonant frequency Q= 1
2ζ
, ζ : Damping coefficient
S. Pannu, C. Chang, R. S. Muller, A. P. Pisano., Optical MEMS Conference 2000.
Lih Y. Lin EE 539A 7b-30
Open-loop vs. Closed-loop + V -
Tilt angle (deg)
Snap down
Open-Loop
Closed-Loop
8
8
6
6
4
4
2
2
0
0
-2
-2
-4
-4
-6
-6
-8
-8 400
550 Time (msec)
600
650
400
550 Time (msec)
600
650 Lih Y. Lin EE 539A 7b-31
Switching Time and Angular Noise
→ Corresponds to angular variation well under 0.01º
Lih Y. Lin EE 539A 7b-32
Optical Add/Drop Multiplexers (OADM)
Lih Y. Lin EE 539A 7b-33
Motivation for Wavelength Add/Drop •
Increase in WDM channel counts Lengthening of unregenerated systems Increasing need to drop and add a small fraction of fiber capacity
Tb/s
λ
λ
...
...
•
-Optical wavelength add/drop multiplexer
Lih Y. Lin EE 539A 7b-34
2x2 Add/Drop Switch Configuration Optical circulators create 4 distinct ports from two I/O fibers
IN
PASS
In
In Back Pass
Out Drop Pass Add
V1
V2
ADD OUT
DROP
ADD
DROP IN
IN
PASS
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
Lih Y. Lin EE 539A 7b-35
OADM using MEMS Tilting Mirror Array In Pass Drop Grating ADD V1
C2
V2
DROP
Switch Array
L o s s o n 1 0 d B g r id
IN
W a v e le n g th o n 2 0 0 G H z g rid
C1
PASS
Low loss: deMUX / switch / reMUX - 5 dB (pass), 8 dB (drop) Polarization independent - 0.2 dB PDL Low chromatic and polarization mode dispersion Fast (0.02 ms) and low power dissipation switching > 30 dB isolation for all 16 channels, all paths
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
Lih Y. Lin EE 539A 7b-36
MEMS Tilting-Mirror OADM Performance Pass: 5 dB loss, 30 dB contrast
-5
Add/Drop: 7 dB loss, 30 dB contrast
-5
Pass Mix
-15
-15
-25
-25
-35
-35
-45
-45
1531
Wavelength (200 GHz grid)
1557
1531
Pass Mix
Wavelength (200 GHz grid)
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
1557 Lih Y. Lin EE 539A 7b-37
MEMS OADM with Full Client Configurability Any wavelength can be dropped to any drop-port. Any wavelength can be added to any output. 1 3 5 7 2 4 6 add add add add add add add
...
M add Tunable lasers 1 out
2 in
2 out
3 in
3 out
4 in
4 out
5 in
5 out
6 in
6 out
7 in
7 out
...
...
1 in
N in
N out
Wavelengthmultiplexer
... 1 3 5 7 2 4 6 drop drop drop drop drop drop drop
M drop
2D MEMS matrix switch can be used for this purpose.
NxM four-port optical matrix switch Lih Y. Lin EE 539A 7b-38
Wavelength-selective Optical Switch
N λ’s
Wavelength-selective optical switch
M add/drop ports
N >> M Limited client configurability
D. M. Marom, et al., "Wavelength-selective 1 × 4 switch for 128 WDM channels at 50 GHz spacing," OFC 2002 (postdeadline paper). J.-C Tsai, S. Huang, D. Hah, H. Toshiyoshi, and M. C. Wu, “Open-loop operation of MEMS-based 1 × N wavelengthselective switch with long-term stability and repeatability," IEEE Photonics Technol. Lett., v. 16, p. 1041-1043, 2004. Lih Y. Lin 7b-39 EE 539A
Integrated Optics and Optical MEMS 7 ― Optical MEMS: Applications in Optical Fiber Communications, Part II
Optical Crossconnect (Optical Switch)
Lih Y. Lin EE 539A
7b-2
Purpose: Optical Network Provisioning In the current core network, provisioning of 2.5Gb/s or 10 Gb/s connections is a paper-mediated process that takes weeks This process should be automated in response to service-layer request and achieve seconds to minutes provisioning time.
IP router
IP router
Lih Y. Lin EE 539A
7b-3
Purpose: Optical Network Restoration Current core network: Basic restoration equipment: Digital electronic crossconnects or SONET ADMs Basic units of restoration: 45 Mb/s or 155 Mb/s
There is an emerging need to move to larger units of restoration, at or approaching the wavelength level
X
IP router
IP router
Lih Y. Lin EE 539A
7b-4
Optical Crossconnects for Provisioning and Restoration
Wavelength -interchange crossconnect
... ...
Wavelength -selective crossconnect
...
... ...
...
...
...
...
Standard interfaces
Transparent network
...
Opaque network
SONET ATM
IP
Require high-port-count optical switches
...
...
OXC
SONET ATM
IP
Require medium-port-count optical switches
Lih Y. Lin EE 539A
7b-5
2-D MEMS Digital Crossbar Switches
Virtues:
Simple binary mirror-control. Precise angular alignment can be achieved easily. Challenges: Scalability. 32 x 32 is probably a reasonable limit for single stage → Good for wavelengthselective crossconnects. Lih Y. Lin EE 539A
7b-6
Example of Micro-actuated Switch Mirror Compact translation-to-freerotation conversion 22 µm translation → 90° rotation
Switch mirror
Pushrod
Hinge joint
Hinge Actuated translation stage Lih Y. Lin EE 539A
7b-7
Scratch-drive Actuation Fabrication
Si
Working principle
Poly-2 PSG-2 PSG-1 Si3N4
∆X ~ 10’s of nm
Si
Akiyama et al., IEEE J. of Microelectromechanical Systems, 1993.
Lih Y. Lin EE 539A
7b-8
2-D MEMS Optical Switching Video
Uni-directional
actuation. Micromirror pulled back by springs. Bi-directional
actuation. Actuators with opposite moving directions are connected by insulating material. Lih Y. Lin EE 539A
7b-9
8 x 8 MEMS Optical Switch • Low loss (1.7 dB for 8x8) • Negligible crosstalk (< -60 dB) • Negligible polarizationdependent loss • Negligible wavelengthdependence • Bit-rate transparent • Sub-millisecond switching time • Compact (1 cm x 1 cm) • Standard IC fabrication → Optical prealignment, low cost • Enhanced functionality in integrated form Characteristics of most 2-D digital crossbar switches Lih Y. Lin EE 539A 7b-10
Electro-static Torsion-mirror Switch
H. Toshiyoshi and H. Fujita, J. Microelectromechanical Systems, 1996.
Lih Y. Lin EE 539A 7b-11
Stress-induced Bending Switch
Au-coating on polysilicon plate to create stress Single-point contact Switching times: < 12ms Insertion loss for 16x16: < 6dB Angular uniformity: < ±0.1° PDL < 0.4 dB 100 million cycles demonstrated
R. T. Chen, H. Nguyen, and M. C. Wu, “A low voltage micromachined optical switch by stress-induced bending,” IEEE MEMS Conference, 1999. Lih Y. Lin Fan, et al., “Digital MEMS switch for planar photonic crossconnects,” OFC 2002 EE 539A 7b-12
Magnetic-actuated Crossbar Switch
B. Behin, K. Y. Lau, and R. S. Muller, Solid-State Sensor and Actuators Workshop, 1998.
Lih Y. Lin EE 539A 7b-13
Integrated Networking Functionality
― Signal Monitoring Signal-monitoring required for performance monitoring and restoration trigger 45o beam splitter
Photodetector
Lih Y. Lin EE 539A 7b-14
Signal-monitoring Module Microwave coplanar Microwave coplanar transmission line transmission line
45oo beam-splitter 45 beam-splitter
Wire-bonding Wire-bonding Vertical Vertical support support Photodiode Photodiode
Side support Side support
Lih Y. Lin EE 539A 7b-15
Design Consideration for the High-speed Hybrid-integrated Photodetector Impedance of coplanar transmission line G S G
2.5 Gb/s
t
s
h
Substrate, εr K (k e ) 30 π ⋅ ε eff ( f ) K ' ( k e )
Z0 ( f ) = ke =
w
se se + 2 we
5 Gb/s
se = s + ∆
Effective width
we = w − ∆
Effective gap
∆=
1.25t π
K (ke ) = ∫
Impedance
4 πw 1 ln + t π dφ 2
0
1 − k e2 sin 2 φ
K ' ( k e ) = K ( 1 − k e2 ) Lih Y. Lin EE 539A 7b-16
Integrated Networking Functionality
― Connection Verification Connection-verification required for network-surveillance
... ... ...
...
... ...
...
... ...
...
SONET
ATM
IP
Optical crossconnect is a black box
...
...
OXC
SONET
ATM
IP
But the network needs to know if the connection configuration is right
Lih Y. Lin EE 539A 7b-17
MEMS Optical Switch with Integrated Connection-Verification Micro-mirror Electrode plate
45o beam splitter
Output Photodetector
Bias on the electrode Frequency = f Input
Mirror-dithering encodes pilot-tone into measured photocurrent intensity
Photocurrent intensity Frequency = 2f
Lih Y. Lin EE 539A 7b-18
3D-MEMS Analog Beam-steering Switches Lens array
Fiber array
MEMS mirror array Optical path
Use both gimbal mirrors to adjust the propagation direction of the optical beam Lih Y. Lin EE 539A 7b-19
Pros and Cons of 3D MEMS Optical Switches Virtues: Scales beyond 1000 x 1000 in single stage Challenges: Arrays of ~ 1000 elements with mrad, µm tolerances Require exquisite engineering of: • • • • •
Fiber array MEMS mirror array Optical path Lens array
MEMS chip and electrical I/O Mirror-control algorithm Fiber arrays Lens arrays Mechanical packaging Lih Y. Lin EE 539A 7b-20
3-D MEMS Optical Switching Video Fiber array Lens array
Optical path
MEMS mirror array
Video shows steering the optical beam to different angles at various speed
Lih Y. Lin EE 539A 7b-21
Self-assembled Polysilicon Beam-steering Mirror (Lucent Lambda Router)
Lih Y. Lin EE 539A 7b-22
Beam-steering Mirror with Piezo-resistive Torsion Sensing • Piezo-resistive torsion sensors – Resistivity changes with torsion strength – Provide closed-loop feedback control capability of mirror angle
Torsional flexures with sensors
Developed by Xros/Nortel
Lih Y. Lin EE 539A 7b-23
Beam-steering Mirror with Terraced Electrode
Sawada et al., “Improved single crystalline mirror actuated electrostatically by terraced electrodes with high-aspect ratio torsion spring,” Optical MEMS 2003.
Lih Y. Lin EE 539A 7b-24
Optical Coupling Loss from Beam Divergence The shorter focal length collimating lens produces a narrower beam which diverges faster Launch = waist
Coupling efficiency D
Γ=
* ∫ E ( x , y , z = D ) ⋅ E ( x , y , z = 0)
2
∫ E E ( x , y , z = D ) ⋅ ∫ E E ( x , y , z = 0) *
*
Launch = waist
Larger beam produces lower losses or longer propagation distance
Lih Y. Lin EE 539A 7b-25
Mode-Matching for Reduced Optical Loss Backing fiber away from the lens focal point slightly allows us to place the beam waist exactly between the two collimating lenses. Launch is NOT waist Waist is here
w
w0
Identical mode-filling of both lenses D 2
Dλ Dλ Dλ = ~ w0 Diffraction limit: w = w0 1 + 2 2 2πw0 2πw0 2πw0 Still, long propagation distance requires large beam width, and large mirrors are not desirable Lih Y. Lin EE 539A 7b-26
Coupling Loss vs. Propagation Distance (Use 2-D digital crossbar switch as an example)
15
Experiment Theory
a = 1.5
R = 100 µm
Loss (dB)
10 32 x 32
R: Mirror radius Gaussian beam half-width = R/1.5 Estimated pitch = 800+3R (µ µm)
R = 150 µm
5 R = 200 µm
16 x 16
0
R = 300 µm R = 400 µm R = 500 µm
0
20
40 # of mirrors traveled
60
80
Optical-path length = 7.04 cm (R = 100 µm) 8.00 cm (R = 150 µm) 8.96 cm (R = 200 µm) 10.9 cm (R = 300 µm) 12.8 cm (R = 400 µm) 14.7 cm (R = 500 µm)
Lih Y. Lin EE 539A 7b-27
Angular-Misalignment in Free-Space Optics After angular-misaligned micro-mirror
Lowest-order Gaussian beam w0 r 2 E ( x, y , z ) = E 0 exp − 2 w ( z) w( z ) z × exp − j kz − tan −1 z 0 kr 2 × exp − j 2 R( z )
amplitude factor longitudinal factor
(
radial phase
Amplitude of the field
w0 x '2 + y 2 E ( x ', y , z ' ) = E0 exp − 2 w( d1 + z ' ) w ( d1 + z ' ) d + z ' × exp − j k ( d1 + z ') − tan −1 1 z 0 k x '2 + y 2 × exp − j 2 R( d1 + z ' )
Coordinate transformation x ' = x ⋅ cos(θ ) − z ⋅ sin(θ ) z ' = x ⋅ sin( θ ) + z ⋅ cos(θ )
X’ Z’
Micro-mirror
(0,0)
x
θ
Coupling efficiency
z Receiving plane
)
Γ=
∫E
*
( x ' , y , z ' ) ⋅ E ( x , y , z = 0)
2
∫ E E ( x ' , y , z ' ) ⋅ ∫ E E ( x , y , z = 0) *
*
Input optical beam Lih Y. Lin EE 539A 7b-28
Coupling Loss Due to Angular Misalignment Theoretical results
(Use 2-D digital crossbar switch as an example)
10 R = 400 µm
Experimental verification
R = 300 µm
8
30
20
6 R = 200 µm
4
20
10 10
R = 150 µm
2 R = 100 µm
0
0
0.05
0.10 0.15 θ (Degrees) θ: Twice the mirror-angle variation
d = 5 cm z = 5 cm w0 = 160 µm 0
-0.2
-0.1
Normalized Loss (dB)
Experiment Theory
Loss (dB)
Additional loss (dB)
i = 63 32 x 32 switch
0 0
0.1
0.2
Angular Misalignment of Mirror (Degrees)
0.20
The digital nature of the 2-D crossbar switch makes this a less serious problem → A serious challenge for 3-D analog beam-steering switch Lih Y. Lin EE 539A 7b-29
Torsion Mirrors are Generally High-Q Resonators Frequency and step function responses for a high-Q MEMS mirror. 400 x 400 micron mirror, 75% covered with 10 microns of nickel (ρ=8.9 g/cc) f=711 Hz Q=142
w02 Lorentzian response: P ( w) = (iw)2 + 2iζww0 + w02
w0 : Resonant frequency Q= 1
2ζ
, ζ : Damping coefficient
S. Pannu, C. Chang, R. S. Muller, A. P. Pisano., Optical MEMS Conference 2000.
Lih Y. Lin EE 539A 7b-30
Open-loop vs. Closed-loop + V -
Tilt angle (deg)
Snap down
Open-Loop
Closed-Loop
8
8
6
6
4
4
2
2
0
0
-2
-2
-4
-4
-6
-6
-8
-8 400
550 Time (msec)
600
650
400
550 Time (msec)
600
650 Lih Y. Lin EE 539A 7b-31
Switching Time and Angular Noise
→ Corresponds to angular variation well under 0.01º
Lih Y. Lin EE 539A 7b-32
Optical Add/Drop Multiplexers (OADM)
Lih Y. Lin EE 539A 7b-33
Motivation for Wavelength Add/Drop •
Increase in WDM channel counts Lengthening of unregenerated systems Increasing need to drop and add a small fraction of fiber capacity
Tb/s
λ
λ
...
...
•
-Optical wavelength add/drop multiplexer
Lih Y. Lin EE 539A 7b-34
2x2 Add/Drop Switch Configuration Optical circulators create 4 distinct ports from two I/O fibers
IN
PASS
In
In Back Pass
Out Drop Pass Add
V1
V2
ADD OUT
DROP
ADD
DROP IN
IN
PASS
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
Lih Y. Lin EE 539A 7b-35
OADM using MEMS Tilting Mirror Array In Pass Drop Grating ADD V1
C2
V2
DROP
Switch Array
L o s s o n 1 0 d B g r id
IN
W a v e le n g th o n 2 0 0 G H z g rid
C1
PASS
Low loss: deMUX / switch / reMUX - 5 dB (pass), 8 dB (drop) Polarization independent - 0.2 dB PDL Low chromatic and polarization mode dispersion Fast (0.02 ms) and low power dissipation switching > 30 dB isolation for all 16 channels, all paths
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
Lih Y. Lin EE 539A 7b-36
MEMS Tilting-Mirror OADM Performance Pass: 5 dB loss, 30 dB contrast
-5
Add/Drop: 7 dB loss, 30 dB contrast
-5
Pass Mix
-15
-15
-25
-25
-35
-35
-45
-45
1531
Wavelength (200 GHz grid)
1557
1531
Pass Mix
Wavelength (200 GHz grid)
J. Ford, V. Aksyuk, D. Bishop and J. Walker, “Wavelength add/drop switching using tilting micromirrors,” J. of Lightwave Technology 17(5) p.904-911, 1999
1557 Lih Y. Lin EE 539A 7b-37
MEMS OADM with Full Client Configurability Any wavelength can be dropped to any drop-port. Any wavelength can be added to any output. 1 3 5 7 2 4 6 add add add add add add add
...
M add Tunable lasers 1 out
2 in
2 out
3 in
3 out
4 in
4 out
5 in
5 out
6 in
6 out
7 in
7 out
...
...
1 in
N in
N out
Wavelengthmultiplexer
... 1 3 5 7 2 4 6 drop drop drop drop drop drop drop
M drop
2D MEMS matrix switch can be used for this purpose.
NxM four-port optical matrix switch Lih Y. Lin EE 539A 7b-38
Wavelength-selective Optical Switch
N λ’s
Wavelength-selective optical switch
M add/drop ports
N >> M Limited client configurability
D. M. Marom, et al., "Wavelength-selective 1 × 4 switch for 128 WDM channels at 50 GHz spacing," OFC 2002 (postdeadline paper). J.-C Tsai, S. Huang, D. Hah, H. Toshiyoshi, and M. C. Wu, “Open-loop operation of MEMS-based 1 × N wavelengthselective switch with long-term stability and repeatability," IEEE Photonics Technol. Lett., v. 16, p. 1041-1043, 2004. Lih Y. Lin 7b-39 EE 539A
