sagnac interferometry

27
SagNAC Interferometry Matt Boggess and Devon Sherrow- Groves

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SagNAC Interferometry. Matt Boggess and Devon Sherrow -Groves. Overview. Intro Theory Improvements Problems Final Iteration Data Conclusions Future prospects. Introduction. Sagnac effect used in fiber optic gyroscopes Used for navigation in planes and boats - PowerPoint PPT Presentation

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Page 1: SagNAC Interferometry

SagNAC Interferometry

Matt Boggess and Devon Sherrow-Groves

Page 2: SagNAC Interferometry

Overview

• Intro• Theory• Improvements• Problems• Final Iteration• Data• Conclusions• Future prospects

Page 3: SagNAC Interferometry

Introduction

• Sagnac effect used in fiber optic gyroscopes• Used for navigation in planes and boats

– Lightweight alternative• Able to make measurements inside an inertial

frame

Page 4: SagNAC Interferometry

Basic Setup

Source

1550 nm

50/50

Detector

2 km loop

OI

Page 5: SagNAC Interferometry

Theory

• Counter propagating waves

• Difference in path length due to rotation

• Causes a phase shift, which causes interference

In/out at t=0

In/out at t=Δt

Page 6: SagNAC Interferometry

Second Iteration

• Confine inertial frame• Add polarization controller• Optimize detection scheme

Source1550 nm

50/50

Detector

2 km loop

Polarization Controller

Rotational Stage

OI

Page 7: SagNAC Interferometry

Second Iteration of Sagnac Interferometer

Page 8: SagNAC Interferometry

Improvements

• Qualitative vs. quantitative• Phase shift measurement

– Rotational rate measurement

Page 9: SagNAC Interferometry

Phase Modulator

• Wrapped PZT cylinder• Expansion causes the

fiber to stretch– Δr = d33 (V)

• Path length changes, causing a phase shift

• Characterize with a Mach-Zehnder

out

Radial Expansion

+-

in

Nonzero voltage

Zero voltage

Page 10: SagNAC Interferometry

Mach-Zehnder Interferometer

• Detects interference due to phase difference between two arms

Source

1550 nm

50/50

Detector

50/50

Phase ModulatorVoltage Driver

OI

Page 11: SagNAC Interferometry

PM Obstacles

• Epoxy (20 coil, hand-wrapped)– Weak bond– No phase shift visible

Page 12: SagNAC Interferometry

PM Obstacles Cont.

• Cyanoacrelate (122 coil, lathe-wrapped)– Bonding to the plastic coating– Still no phase shift

Page 13: SagNAC Interferometry

PM Obstacles Cont.

• Tensile test– Breaking fibers

• Free space phase shifter test

Page 14: SagNAC Interferometry

Third Iteration

• Improved design considering 50/50 couplers• Fiber Loop consolidation – Error minimization

Source1550 nm

50/50

Detector

Terminated ends

50/502 km loop

Polarization Controller

Rotational Stage

OI

Page 15: SagNAC Interferometry

Final Iteration of Sagnac Interferometer

Page 16: SagNAC Interferometry

Data● Measuring relative intensity change under

rotational influence● Rotational rate measurement, ΔV measurement

Page 17: SagNAC Interferometry

System Losses● Losses in optical power due to 50/50

coupling, backscattering, etc.

-12 -11.95 -11.9 -11.85 -11.8 -11.75 -11.7 -11.65 -11.6 -11.55 -11.50

500

1000

1500

2000

2500

3000

Laser Power vs. Optical Power

SourceDetectorCCW ArmCW Arm

Laser Operating Voltage (V)

Opti

cal P

ower

(μW

)

Page 18: SagNAC Interferometry

CW Rotation

●Slow rotational rate (0.10 rad/s)●ΔV = 0.800mV

●Regular rotational rate (0.15 rad/s)●ΔV = 1.20mV

●Fast rotational rate (0.22 rad/s)●ΔV = 1.52mV

Page 19: SagNAC Interferometry

CCW Rotation

●Slow rotational rate (0.079 rad/s)●ΔV = 0.720mV

●Regular rotational rate (0.11 rad/s)●ΔV = 1.28mV

●Fast rotational rate (0.20 rad/s)●ΔV = 2.48mV

Page 20: SagNAC Interferometry

Data Cont.

●Stable → CCW → stable → CW → stable

●Swinging motion ●Lower limit of detectable CCW rotation●0.0416 rad/s (~2 degrees per sec)

Page 21: SagNAC Interferometry

Rotational Rate and Intensity Shift

0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.260

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

CW Rotational Data

Rotational Rate (rad/s)

ΔV (m

V)

Page 22: SagNAC Interferometry

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.240

0.5

1

1.5

2

2.5

3

CCW Rotational Data

Rotational Rate (rad/s)

ΔV (m

V)

Page 23: SagNAC Interferometry

0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.260

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

CW Rotation and Theoretical Phase Shift

Rotational Rate (rad/sec)

Theo

retic

al P

hase

Shi

ft (r

ad)

Page 24: SagNAC Interferometry

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.240

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

CCW Rotation and Theoretical Phase Shift

Rotational Rate (rads/sec)

Theo

retic

al P

hase

Shi

ft (r

ads)

Page 25: SagNAC Interferometry

Conclusions

• Able to discern Sagnac effect in a fiber optic setup– Intensity change is linearly related to rotational

rate– Vibrational noise plays a large role– Without a phase modulator, limited range of

rotation rates• Phase modulator progress

Page 26: SagNAC Interferometry

Moving Forward

• Implementation of phase modulator• Examine intensity shift dependence on phase

difference• Phase shift nulling

– Integrated feedback circuit (PID loop) to control piezoelectric phase modulator

• Complete FOG setup

Page 27: SagNAC Interferometry

Questions?