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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








• 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








• 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








• 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

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• 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

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• 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.)

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• 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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Documents

mmalong optical axis

high power

low power

ease of fabrication

high strokepiezoelectric

tolerances permissible

low strainthermal

angledesign challengesfocusing