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Optical Channel MonitorOptical Channel MonitorLiang-yu ChenLiang-yu Chen
Jian LiJian Li
Arvind NarayanaswamyArvind Narayanaswamy
Dilan SeneviratneDilan Seneviratne
Zhenhai ZhuZhenhai Zhu
Mentored byMentored by
Prof. George BarbastathisProf. George Barbastathis
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
Goals Goals
DeviceDevice• Monitor optical power in fiber carrying WDM Monitor optical power in fiber carrying WDM
signalssignals
ApplicationsApplications• Real-time optical performance monitoring of Real-time optical performance monitoring of
DWDM networks DWDM networks • Optical add/drop monitoring and diagnosticsOptical add/drop monitoring and diagnostics• EDFA gain balancing EDFA gain balancing
Design RequirementsDesign Requirements
• Scan 10 wavelengths (Scan 10 wavelengths (11 … … 1010) in 10ms) in 10ms
• 5% diffraction efficiency5% diffraction efficiency
• Central wavelength: 1.5Central wavelength: 1.5mm
• Operate under 50VOperate under 50V
• +/- 10% variation between +/- 10% variation between 11 and and 1010
Device conceptDevice concept
Grating operationGrating operation
actuatoractuator
gratinggrating
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
Grating designGrating design
• Type of grating - amplitude or Type of grating - amplitude or phasephase
• Pitch and spacing between Pitch and spacing between beams (nominal duty cycle)beams (nominal duty cycle)
xx
sspp
tt
xx
11
00sspp
Amplitude gratingAmplitude grating
Phase gratingPhase grating
Grating DesignGrating Design• Angle of incidence Angle of incidence • Thickness of beams Thickness of beams
00
+1+1
-1-1
00
+1+1
-1-1
--22
Normal incidenceNormal incidence Incidence at an angleIncidence at an angle
Design challengesDesign challenges
• Focusing on the detectorFocusing on the detector spot size
spot overlap
detectordetector
Design challengesDesign challenges
• Focusing on the detectorFocusing on the detector spot overlap
-40 -30 -20 -10 0 10 20 30 40-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
nnn-1n-1 n+1n+1
Overview of the Whole DeviceOverview of the Whole Device• Large number of grating beams neededLarge number of grating beams needed• Natural Frequency is too lowNatural Frequency is too low• Split into piecesSplit into pieces• Efficiency reduction caused by comb drive and space between two piecesEfficiency reduction caused by comb drive and space between two pieces
GratingCombDrive
AnchorFlexure
......
......
.........
....
......
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
Lumped model Resonant frequency >1khZ, for fabrication limitation
and operation limitation
Grating AnchorFlexure
FF ...
F
F
Grating DesignGrating Design
Grating Design (2)Grating Design (2) Resonant frequency
• Grating beam: 4khZ• Whole system: 1.5khZ
Number of gratings for each piece: N=500 Displacement of the gratings: N*22.5nm=11.3um Actuation force Needed: k*22.5nm=53uN
ActuatorActuator
• Requirements: Requirements: Displacement: 11.3um Force 53N Voltage 0-50V
• Options:Options: Electrostatic: Ease of fabrication, Low power, high stroke Piezoelectric: Low strain Thermal: High power, long response time
Electrostatic ActuatorsElectrostatic Actuators
t h
d
h0
t
L
d
g
t
• Comb DriveComb Drive • Capacitor PlateCapacitor Plate • Zipping ActuatorZipping Actuator
F1
2N 0
t
g U
2 F
1
2
0 L t U2
d2
F Constant
h
h 0
3
4
U
3
2 t
d
• Electrostatic actuators - ease of fabricationElectrostatic actuators - ease of fabrication• Different electrostatic actuatorsDifferent electrostatic actuators
Force-Displacement
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60
Displacement(um)
Fo
rce
(mN
) Zipper
Comb Drive
Capacitor Plate
Electrostatic Actuators (2)Electrostatic Actuators (2)
• Force Displacement curveForce Displacement curve
ResultsResults
• Displacement 20umDisplacement 20um• Force 255uN @ 50VForce 255uN @ 50V
• 4 times larger than needed4 times larger than needed• Can be used to calibrate Can be used to calibrate
the devicethe device• Air damping: quality factor Q Air damping: quality factor Q
~ 30~ 30
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
Two masks, SOI wafer, KOH back etchTwo masks, SOI wafer, KOH back etch
Fabrication: overviewFabrication: overview
FabricationFabrication
SOI
Silicon Silicon Oxide
Photo Resist
DRIE
strip PR
KOH etch
HF wet etch
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
DetectorDetector• Sensitivity – flat response at 1.5Sensitivity – flat response at 1.5mm
1.51.5mm
1.49625 1.49625 mmtoto
1.50375 1.50375 mm
LensesLenses• Collimating systemCollimating system
Lenses• Transmission - > 99.5%
Lenses (2)Lenses (2)
• Magnification systemMagnification system M = 22 = f1/f2 = 44mm / 2mm
Bi-convex• EFL - 44 mmBi-concave• EFL - 2 mm
f1
f2
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Drive signalDrive signal
• Assembly and alignmentAssembly and alignment
• SummarySummary
Assembly and AlignmentAssembly and Alignment• Requirements: Requirements:
Tolerances permissible by design• Perpendicular to optical axis – 0.2 – 0.4 m• Along optical axis - 0.8m
Precision achievable by assembly – +/- 10nm
• Assembly outsourcingAssembly outsourcing Axsys Technologies Zygo -
From Axsys TechnologiesFrom Axsys Technologies
CalibrationCalibration
Detector plane
Detector
Total swing possible
Total swing required
Total permissible error = (
Calibration (cont.)Calibration (cont.)
OutlineOutline
• IntroductionIntroduction
• Grating DesignGrating Design
• ActuatorActuator
• FabricationFabrication
• Sub-componentsSub-components
• Assembly and alignmentAssembly and alignment
• Drive signalDrive signal
• SummarySummary
Drive SignalDrive Signal
Drive Signal (Cont.)Drive Signal (Cont.)
AC/AC/DCDC
110/110/6060
OscillatorOscillator ++
--
50V50V
AC/AC/DCDC110/110/
6060
3.3V3.3V
++--
Drive Signal (Cont.)Drive Signal (Cont.)
AC/AC/DCDC
110/110/6060
++
--
50V50V
Conclusion(s)Conclusion(s)Central wavelength: 1.5Central wavelength: 1.5mm
Scan 10 wavelengths in 10msScan 10 wavelengths in 10ms
5% diffraction efficiency (+/- 10%)5% diffraction efficiency (+/- 10%)
Operate under 50VOperate under 50V
Device size - ~ 10cm X 10cmDevice size - ~ 10cm X 10cm
Easily calibratedEasily calibrated
Minimum alignmentMinimum alignment
In-expensive fabricationIn-expensive fabrication
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