Real-time active alignment
using mechanical dynamics
of optical interconnection systems
Makoto Naruse (1)(2), Alvaro Cassinelli(3), Masatoshi Ishikawa(3)
1: Communications Research Laboratory,
4-2-1 Nukui-Kita, Koganei, Tokyo 184-8795, Japan
Phone: +81-42-327-6209
Fax: +81-42-327-7035
Email: naruse@crl.go.jp
2: Japan Science and Technology Cooperation, PRESTO
3: University of Tokyo
Dept. Information Physics and Computing
7-3-1 Hogo, Bunkyo, Tokyo 113-8656, Japan
Abstract
Real-time active alignment for short-distance optical
interconnections is demonstrated by taking into account
most mechanical properties of the optical hardware.
Alignment performances has been successfully
controlled by considering internal and external
mechanical properties of the interconnection system
(such as micro-actuator dynamics or disturbance), with
the aid of H-infinity control theory.
Contents
•High density parallel optical interconnection fabric
•Dynamic alignment / switching technology
Control Theory for optical interconnection systems
(H-infinity theory)
Simulation ／ Experimental system／Experimental results
Parallel high-density interconnection
• High-bandwidth, low-latency optical
interconnections inter-computers, boards, or VLSI
chips
• Interconnection fabric, switching fabric
High-parallelism demanded
by two-dimensional (2D) parallelism
Alignment issues
High-density parallel interconnect fabric / switching fabric
Alignment is one of the critically important issues
Methods
Passive alignment
Redundant alignment
Real-time Active alignment
Mechanical dynamics and Optical interconnects
Active alignment or optical switching:
Using mechanical dynamics
Real-time control
HISTORY
Static：Alignment tolerance analysis
Dynamic：
•Insertion control (NTT) (JLT, Vol. 15, pp. 874–882, 1997)
•MEMS optical switch
•Active alignment using PID control methods (University of Tokyo) (PTL Vol.
13, pp. 1257-1259, 2001)
Dynamics in optical interconnection systems
Parallel optical channels (input) = VCSELs, Fibers, Free-space, etc
Disturbance（s）
Parallel interconnection /
Switching block
(Free-space / 2D Guided wave)
Actuator（s）
Sensor（s）
Parallel optical channels (output)
Desired specification
Dynamic
properties
Two-dimensional
High-density
Channels
Performance we want for active systems
Disturbance
compensation
Mechanical-based
Optical switching
Active alignment
Fast transition between status
Modeling of the system
GOAL
Design the controller that
doesn’t transfer disturbance w to the misalignment y
Disturbance
Control input
u
w
Active alignment
actuator
Controller
＋
＋
Misalignment
y
Using H-infinity control theory
Disturbance
w(s)
Generalized Plant
Control variable
z (s )
G (s)
Control input
u (s )
Output variable
y (s )
Controller
K (s)
GOAL
z ( s)  ( s) w( s)
Influence from Disturbance to Control variable
Make this as small as possible
Using H-infinity control theory (cont.)
F

F

 sup

H infinity control theory derives a controller K(s)
so that  is small.
Fu
u
L2
L2
A framework of active alignment system
(Virtual) Disturbance dynamics
Disturbance
w
W
Control variable
z
Actuator
Control input
u
P
＋
－
 z ( s) 
 w( s) 
 y ( s)  G ( s)  u( s) 




Output variable
W
G
1
y
 WP 

G 
Experimental system
Vibration
generator
Disturbance Dynamics
W (s )
～
VCSEL
VCSEL
Vibration
generator
Interconnection
optics
Interconnection
optics
Quadrant
photodetector
Misalignment error
Piezo actuator
H∞ controller
K (s)
Quadrant detector
Controller
(PC)
Piezo microstage
Control signal
Active alignment actuator dynamics
P (s )
Specifications
VCSEL
: Roithner TMC-4A (Wavelength: 850nm)
Quadrant Detector
: Hamamatsu S2544 (1mmφ, 20mm gap)
AD/DA Converter
: National Instrument PCI-MIO-16E-4
Personal Computer : DELL OptiPlex GX200
Sampling Rate
: 200ms
Vibration Generator : Wilcoxon Research F5B/Z11
Interconnection Optics: 4f lens system (Spindler&Hoyer f 100 plano-convex)
Disturbance dynamics
1.2
4.532e4
W ( s)  2
s  95.2 s  2.266e5
1
Gain[a.u.]
0.8
0.6
0.4
Experimental
0.2
0
30
40
50
60
70
Frequency[Hz]
80
90
100
110
Actuator dynamics
P ( s) 
4.532e4
s 2  95.2 s  2.266e5
Performance evaluations（simulation）
Compensate the disturbance with respect to its dynamical property.
Gain from disturbance d to misalignment y
Bode Diagram
Magnitude (dB)
-80
-85
-90
-95
180
Phase (deg)
Disturbance
concerned
Cf
Disturbance dynamics
not concerned
135
90
45
0
20
30
40
50
60
Frequency (Hz)
70
80
90
100
Experiment
Virtually giving several sets of disturbance dynamics
Observe corresponding active alignment performance
disturbance dynamics
W1 ( s)
0
Magnitude (dB)
Low frequency enhanced
W2 ( s)
W1 ( s ) 
-1
-2
s
1
2  100
-3
-4
High frequency enhanced
-5
30
Phase (deg)
1
s
1
2


50
W2 ( s ) 
s
1
2  100
0
-30
-60
10
20
30
40
50
60
Frequency (Hz)
70
80
90
100
Experimental Results
Reduction ratio =
Amplitude of the misalignment: Active alignment operated
Amplitude of the misalignment: Active alignment not operated
1.4
Reduction ratio
1.2
1
W2 ( s)
0.8
W1 ( s)
0.6
0.4
0.2
0
0
20
40
60
80
100
Frequency [Hz]
120
Dynamical property appeared in the active alignment performance
140
160
Summary
• Theory for dynamic optical interconnection system
shown.
• It concerns most of mechanical dynamics such as
disturbance or actuator dynamics with the aid of Hinfinity control theory.
• Experimental results shown
Future prospect
 Adapt to real application systems such as interconnection fabric,
optical crossconnect (OXC) among others