ocw 5 optical and optoelectronic sensors and...
Post on 13-Oct-2020
2 Views
Preview:
TRANSCRIPT
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Electronic InstrumentationElectronic Instrumentation
Chapter 5
Optical and Optoelectronic Sensors
and Measurements
1Jose A. García Souto / Pablo Acedo
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Module 5. Optical and Optoelectronic Sensors and Measurements
• Introduction
• Basic components and signal conditioning• Basic components and signal conditioning
• Position, Displacement and Rangefinders
• Laser interferometry
• Fiber Optic sensors
• Gyroscopes
2Jose A. García Souto / Pablo Acedo
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Introduction
• In this chapter we will focus on the principles of measurement used in optical and optoelectronic sensors .
• A survey of input sensor mechanisms will be addressed but only some applications will be described in more detail.
• In this case the classification of the sensors is due to the
3Jose A. García Souto / Pablo Acedo
• In this case the classification of the sensors is due to the characteristics of the light (electromagnetic wave) that are changed by the measured physical phenomena:– Amplitude (Intensity)
– Polarization (Polarimetry)
– Optical phase (Interferometry)
– Frequency of emission / wavelength (Spectroscopy / Gratings)
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Introduction
• Some advantages of optical and optoelectronic
measurements:
– Non-contact and non-invasive approaches
4Jose A. García Souto / Pablo Acedo
– Non-contact and non-invasive approaches
– EMI inmunity
– High precission measurements (e.g. interferometry)
– Withstanding harsh environments and preserving
electro-magnetic isolation (e.g. optical fiber)
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Optical Conditioning
Basic Architecture for an Opto-Electronic Instrumentation Measurement System
mp1
p2
Light InputLight Output
DetectionAnalog Signal Conditioning
q Vop2
p3
Detection
• Light Input from a light source (LASER, LED), but sometimes is not necessary.
• Output from the detector can be either a current (photodiode) an impedance change (photoconductor) or a voltage (photovoltaic sensor).
• Optical conditioning and lead-in/ lead-out of the light sometimes present (e.g. optical fiber) .
• The optical conditioning frequently converts the information from an optical magnitude to another (eg. Interferometer: optical phase to intensity) .
Conditioning
5Jose A. García Souto / Pablo Acedo
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Analog signal conditioning of optoelectronic sensors
• Primarily light is detected by photodiodes, APDs,
photoconductors.
• Current output with high impedance or variable high impedance
is mainly obtained.
6Jose A. García Souto / Pablo Acedo
is mainly obtained.
• Current to voltage circuits are basically used.
• Light may be externally injected into optoelectronic
measurement systems by means of Lamps, LEDs and LASERs
biased by a current source or voltage to current conversion
circuit.
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Equivalent of photo-detectorsPhoto-diode and APD
Jose A. García Souto / Pablo Acedo 7
Photoconductor/Photo-resistor
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Current to voltage circuit
Jose A. García Souto / Pablo Acedo 8
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Biasing light detectors
Jose A. García Souto / Pablo Acedo 9
PHOTOVOLTAIC PHOTOCONDUCTIVE
Zero Bias Reverse Bias
No “Dark” Current Has “Dark” Current
Low Noise (Johnson) Higher Noise (Johnson + Shot)
Precision Applications High Speed Applications
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Example of electronic signal conditioning
Div
10Jose A. García Souto / Pablo Acedo
Current to voltage converter
Normalization to the intensity mean
Adjustment of sensitivity
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Basic Components for optical conditioning
• Emitters: LASER, LED and other light sources (lamps, SLED, etc.)
• Detectors: Photodiodes, APD, photo-conductors and others (Photo-transistors, LDR, etc.)
• Optical components: – Lenses, mirrors, beam-splitters, …
– Polarizer, optical retarder, Wollaston prism, crystals, …
11Jose A. García Souto / Pablo Acedo
– Polarizer, optical retarder, Wollaston prism, crystals, …
– Diffraction gratings
• Optical fiber:– Transmission fibers
– Intrinsic sensing
– In fiber components (e.g. in fiber Bragg gratings)
• Optical modulators– Acousto-optic modulators and other actuators (e.g. PZT onto a fiber)
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
• On/off intensity sensors, grating sensors and encoders:
• An optical displacement transducer can be fabricated with two overlapping gratings which serve as light-intensity modulator. They can be used as proximity sensors or position encoders.
Position, Displacement and Rangefinders
12Jose A. García Souto / Pablo Acedo
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Position, Displacement and Rangefinders
• Intensity sensor (attenuation):
Projected area
• Intensity attenuates with distance. Sometimes mirrored reflection on the target is present, but in general diffused reflection must be considered.
Jose A. García Souto / Pablo Acedo 13
d
x
θ
y Detected area
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
d/2 x
θ
r
d/2
OF1 OF2
Example: Vibrations
Measurement Reference
Jose A. García Souto / Pablo Acedo 14
Differential Synchronous detection
Carrier
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Position, Displacement and Rangefinders
• Optical Range Finders (time of flight):
• Range is obtained measuring the time difference between the sent pulse and
the received signal. Pulsed and amplitude modulation systems are used.
Transmitter Pulsed Range Finder
15Jose A. García Souto / Pablo Acedo
Target
TransmitterLaser diode
Reception lens
d
APD
r tflight
φshift
Pulsed Range Finder
CW Range Finder
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Position, Displacement and Rangefinders
• Laser Doppler:TransmitterLaser diode
r
θ
Jose A. García Souto / Pablo Acedo 16
]/21[]/)(2··[
cvwdt
ctdwtwdw xo
oor +=+=
Target
Reception lens
d
APD
θ
v
xv
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
• Triangulation
• The position of light spot on a position sensitive photo-detector is related to the
distance by triangulation. As an example, a PSD is a differential current device that
gives an output related to the position of a collimated beam on the device surface. It
provides one and two-dimensional position. Others are photo-detector arrays.
Position, Displacement and Rangefinders
17Jose A. García Souto / Pablo Acedo
Target
Laser/LEDDiode
Receptor Lens
D
a
x
f
PSD
x = 0
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Intensity
Laser Emitter
Beam-splitter
Reference path
Measurement path
MirrorLens
Position, Displacement and Rangefinders
• Laser interferometry
Jose A. García Souto / Pablo Acedo 18
0 2π 4π 6π 8π ϕ (rad)0 λ 2λ 3λ 4λ β1-β2 (µm)
( )[ ])(cos12
0 tVI
I φα+=
rmrm LtLtt −= − = )(2
)()(λπφφφ
mínmáx
mínmáx
II
IIV
+−
=
( )[ ])(cos1 tφ+( )[ ])(cos1 tφ−
DetectorBS
rm LLt
t −=)(
2)(
λπφ
Measurement of displacement Measurement of wavelength
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Laser MmL
Mr
Mr
BS1
reference
measurement
L
BS2 D1
Laser interferometers
Laser
reference
BS
D
measurement
D2
BS2
Mm
D1
DM2
L M1
(b)
(a)
(c)
Jose A. García Souto / Pablo Acedo 19
Laser
measurement
l∆=λπφ 4 l∆=
λπφ 2
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Optical Fiber Interferometers
Laser
BS
Lens
Reference
DetectorModulator BS
Jose A. García Souto / Pablo Acedo 20
nLλπφ 2=
Laser
Optical Fiber
Measurement
Sensor
Magnitude
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Optical fiber intrinsic sensing
∆φFiberφoφ
∆xX
Reference Fiber
Measurement Fiber
X
Jose A. García Souto / Pablo Acedo 21
βλπφ ⋅== knL
2
( )nLLnkk ∂⋅+∂⋅=∂⋅=∂ βφ
εξφ ⋅=∂kn
L
∂∂+
∂∂=
∂∂
T
n
nT
L
Lkn
TL
111 φ
x ∆xExposed sensing length
Strain
Temperature
Optical path
Gage factor (includes strain-optic)
Thermo-optic
coefficient
Thermo-elastic
coefficient
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Example: Closed-loop
Intensity (Ι)
Laser
PZT
FO sensor
φ1: Measurement
φ2: Reference
+
_G
I2
I1
∫
Vo: Output
Feedback
Jose A. García Souto / Pablo Acedo 22
[ ])cos(12 210
1 φφ −+= II
[ ])cos(12 210
2 φφ −−=I
I
Optical phase (φ)
φ’ 0(2)
φ’ 0(1)
∆φ’ 0
Ι1(φ) Ι2(φ)
FO sensor
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
PolarimetryIntensity
Ι1(φ)
Ι2(φ)
Lens
Current Cable
Detector
FO Coil
Jose A. García Souto / Pablo Acedo 23
Rotation of polarization angle (2φ)
φ’ 0Ligth emitter PolarizerLens
Optical Fiber
Detector
Wollamston Prism
[ ])2cos(120 φ−= I
I
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Gyroscopes• Optical gyroscope is based on the Sagnac effect and are
implemented both using fiber optics and free-space optics.
CCW
Detector
CCWCW
24Jose A. García Souto / Pablo Acedo
Ω=∆oc
AL
4 Ω=∆oo c
A42
λπφ
P
cqf o= Ω−=∆
nP
Af
qλ4
Light source
Detector
CW
Ω
Polarizer
Active medium (laser)Mirror Mirror
Ω
CCWCW
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
Optical fiber Bragg gratings• Wavelength based sensor.
ελλ ⋅=∂
KB
B
Strain
Light source
Detector
Optical Fiber In-Fiber GratingPower Input
Power Back-reflected Power Transmitted
n
Jose A. García Souto / Pablo Acedo 25
Taa TnTlB
B ∂+=∂)(
λλ
Strain
Temperature
Detector
Λn1
n2
n3 > n2
PInput
λ
PBack-R
λλB
PTrans
λλB
δλB
Electronic InstrumentationOptical and Optoelectronic Sensors and Measurements
• In this chapter we have focused on the principles of measurement used in
optical and optoelectronic sensors and their optical and electronic basic
signal conditioning. Examples of sensors based on intensity, polarization,
optical phase and wavelength have been presented.
Summary
optical phase and wavelength have been presented.
• A survey of input sensor mechanisms have been addressed through the
case of position, displacement and rangefinders: grating sensors and
encoders, attenuation, time of flight, laser Doppler, triangulation and laser
interferometers.
• Some applications have been described in more detail through
representative examples of fiber-optic sensing: optical fiber
interferometry, polarimetry, gyroscopes and in-fiber Bragg gratings.
Jose A. García Souto / Pablo Acedo 26
top related