instrument

1. G. Giuliani - OEINSTR - Intro 1
ELECTRO-OPTICAL
INSTRUMENTATION
Guido Giuliani
Università di Pavia
e-mail: guido.giuliani@unipv.it
Recommended textbook:
S. Donati, “'Electro-Optical
Instrumentation”, Prentice Hall, 2004

2. G. Giuliani - OEINSTR - Intro 2
Introduction
 Opto-electronic sensing techniques are curently applied to many sectors:
 Aerospace
 Automotive
 Mechanics
 Bio-medical
 Precision Industries
 Industrial manufacturing
 …
 Measurement Techniques
 Telemetry
 Triangulation
 Interferometry
 Velocimetry
 Giroscopy
 Fiber optic based…

3. G. Giuliani - OEINSTR - Intro 3
Optical sensor
 One single device
 Photodiode
 …
 A “small” optoelectronic instrument
 CONTENT:
 Optoelectronic devices (SC lasers, photodetectors, …)
 Electronic devices and circuit
 Optics (lenses, filters, beamsplitters, mirrors, …)
 Mechanics / Opto-mechanics
 I/O
 User’s point of view:
 It is a transducer
 Distance  Voltage (or digital information)
 ? Laser safety ?

4. G. Giuliani - OEINSTR - Intro 4
Optical Sensors / Instruments
 ADVANTAGES
 Non-contact operation
 Remote measurements (fiber optic sensors)
 Optical transducers do not suffer from electronic noise & interferences
 Price ?
 Integration ?
 High precision / accuracy / resolution
 Spatial resolution
 DISADVANTAGES
 Price ?
 Integration ?
 Not multi-purpose

5. G. Giuliani - OEINSTR - Intro 5
Telemetry vs. Triangulation
 TELEMETRY: measurement of the “time of flight” (TOF) of a light pulse
 TRIANGULATION: measurement of the position of a laser spot onto a focal plane
L = 2c

6. G. Giuliani - OEINSTR - Intro 6
TELEMETRY
 LURE (LUnar Ranging Experiment)
 carried out in 1970 when the astronauts of Apollo 11 brought on the moon an array
of corner-cubes (100 x 1” dia.) . Five telescopes on earth aimed the array with their
Qswitched ruby laser, launching a 0.5-J, 10-ns pulse. Three telescopes got the return,
a ≈10-photon pulse. The time-of-flight measurement translated into a distance
measured with an accuracy ≈30cm of the 384000 km baseline.

7. G. Giuliani - OEINSTR - Intro 7
TELEMETRY
 MOLA (Mars-Orbiter -Altimeter)
 In 1999, the MOLA of the Pathfinder mission has completed a 2-year survey of the
topography with 5-m height resolution on 100x100-m individual areas covering Mars

8. G. Giuliani - OEINSTR - Intro 8
TELEMETRY / LIDAR (Laser IDentification And
Ranging)
 Car anti-collision radar

9. G. Giuliani - OEINSTR - Intro 9
TELEMETRY / LIDAR (Laser IDentification And
Ranging)
 Self-driving car
Google car

10. G. Giuliani - OEINSTR - Intro 10
TRIANGULATION
Valve motion measurement for engine R&D

11. G. Giuliani - OEINSTR - Intro 11
TRIANGULATION
Valve motion measurement for engine R&D

12. G. Giuliani - OEINSTR - Intro 12
INTERFEROMETRY
 Interferometric techniques exploit the high temporal and spatial coherence of laser
light, to perform high-accuracy and high-resolution measurements
LASER
experiment
PHOTO-
DETECTOR
REFERENCE
ARM
MEASUREMENT
ARM
frequency
shifter
(optional)
E0
Em
Er
Iph
 
m r
/2 
/2
 
I
ph
I
r
 Light travels along two paths:
 Reference path (Er)
 Measurement path (E0  Em)
 The two beams produce an interference on
the photodetector: the output signal is a
periodic function of the difference between
the two pathlengths
 Iph =  Em+Er 2
=  Em exp im +Er exp ir 2
Iph = Em
2+Er
2+2EmEr Re{exp i(m-rIm +r+2(√ImIrcos(m-r
 It is possible to measure the relative phase difference that arises along the measuring
arm

13. G. Giuliani - OEINSTR - Intro 13
Interferometric Configurations
FD
LASER
Fixed mirror
50/50 BS
Moveable
mirror
FD 1
LASER
FD 2
measurand
LASER
FD
measurand
Michelson
Mach-Zehnder
Sagnac

14. G. Giuliani - OEINSTR - Intro 14
APPLICATIONS
VIBRA
TION
Analyzers
LASER
INTER
FER
O
METR
Y
scientific
uses
technical
uses
s1km
s
1OOm
s1m
s<1cm
INTERFEROM
ETERS for
MECHANICAL
METROLO
GY
DOPPLER
VELOCIMETERS
forANEMOMETR
Y
ESPI(SPECKLEPA
TTERN)
RLG andFOG
GYROSCOPES
avionics
industrial
uses
SPACETELEMETR
Yof
GEODETICSA
TELLITES
EARTHTIDES
SENSING
LARGESTRUCT
VIBROMETR
Y
METROLOGYof
LENGTH (andderived
quantities)
BIOLOGICAL
MOTILITY
SENSING
ACOUSTICEMISSION
and SA
WSENSING
GEODETIC
GRA
VIMETRY
GRA
VITA
TIONAL
ANTENNAS
OPTICALFIBER
SENSORS
OPTICS ELECTRO
NICS
W
AVEandFIELDS
TECHNOLOGY
MEASUR.SCIENCE