光纤传感器的基本知识.ppt

Fiber Optic Sensors
Basic Components of FOS
Types of FOS
Application of FOS
1
Components of FOS
Optical Fibersquid-level sensor


The light returned in air
with total internal reflection
from a prism is 15 dB above
the value in water.
Air
Liquid
11
Intensity-Based and Fabry-Perot Interferometer Sensors(4)
Encoder-Based Position Sensors
Using an encoder plate to provide linear or rotary displacement measurement.
Wavelength
Light
Photodiodes
w1
w2
w3
w4
w1
w3
w4
1
2
3 4
Wavelength
Light
Combiner
Encoder plate
Wavelength divider
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Intensity-Based and Fabry-Perot Interferometer Sensors(5)
Variety of Sensor Construction
Gradient index lens
Mirrors
Refractive index
test liquid
Spacer
Temperature sensor
Pressure sensor
Pressure
Multimode fiber
Temperature
Temperature sensor
Liquid refractive index
13
Multimode Grating Sensors(1)
Theoretical Background


Where, N is the number of slits
m is the diffraction order
s
a
Slit
Incoming
Light
Screen
Diffraction from multiple slits
14
Multimode Grating Sensors(3)
Optical Encoding Techniques
The total amount of energy passed through a grating is proportional to the ratio a/s.
Used as wavelength encoding devices. The ratio a/s remains a constant, but s is modulated by some parameter of interest, the angular spectral distribution transmitted will be modulated.
Example: A wavelength-encoded temperature sensor.
15
Multimode Grating Sensors(4)
Based on Relative Movement of Opposed Gratings
Light in
Light out
Opposed Grating Structure
GRINrod Microlens
16
Multimode Polarization Sensors(1)
Retardation and Special Properties of the Half-Wave plate
Light Polarized
in X Direction
Retardation Plate with Fast
Axis at Angle to the x Axis
And Having Retardation
Polarizer with
Transmission
Axes along X
17
Multimode Polarization Sensors(2)
Photoelastic Effect
Where is the stress-optic