Fiber Optic Sensors 

 
Properties, which can be sensed: 

 

Displacement 
Force 
Liquid Level 
Magnetic Fields 
Motion 
Temperature 
Vibration 

Position (linear, angular) 
Pressure (fluid, gas, etc.) 
Sound 
Radiation 
Speed 
Weight 
Pressure

 

 

How does a Fiber Optic Sensor work? 

 

In a fiber optic sensor, one of the following characteristics of a propagating 
lightwave is altered under an externally induced physical parameter:  

 

Intensity 
of light 

Frequency  
of light  

Phase 
of light 

Polarization state 
of light 

 
 

Why are fiber optic sensors becoming so popular? 
 
Small/lightweight 
Allow access into normally inaccessible areas (often embedded) 
Passive (non-electrical) 
Highly sensitive 
Easy to install 
 
 

 

 

 

The Fabry-Perot fiber optic sensor. 
 

Fabry-Perot Filter (interferometer) 

 

 

 

 
 
 
 
 

The Fabry-Perot fiber optic sensor: 
 

 

 
Principal applications: 
Pressure, Strain, Temperature sensing etc. 
 
 
Design of Fabry-Perot strain sensor: 
  

 

 

Fiso, Inc. sensor: see www.fiso.com 

 
 
 

 

 
 

 

 
 
 

Fiber optic Bragg grating temperature and strain sensors 

 

Schematic diagram of fiber Bragg grating 

 

Principle of operation of fiber Bragg grating: 

 

 

 
 
 

Schematic of instrumentation for fiber optic Bragg 

                                                                          sensor. 

 

 

 

 
 
 

Fiber optic Bragg sensors advantages: 

 

High sensitivity  
Low –cost sensors 
Small/lightweight 
Linear response 

 

Drawbacks 

Sensitive to more than one parameter 
Require relatively expensive processing equipment 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Fiber Optic Sensing by  
Optical Time Domain Reflectometry (OTDR) 

 

The Optical Time-Domain Reflectometer enables us to look at a fiber link 
from inside the fiber. In reality it is just a radar system for looking at fiber. 
High intensity pulses are sent into the fiber from a specialised laser and 
when the pulse returns its strength is displayed on an oscilloscope screen in 
the form of a trace. A schematic of such a display is shown in Figure 

 

In the trace you see reflections coming from all along the fiber itself. This 
is the result of Rayleigh scattering. Rayleigh scattering was mentioned in 
the chapter on optical fiber as the major limiting factor in fiber attenuation. 
This scattering occurs backwards towards the transmitter and we can 
receive it and display the result. 
 
 
 
 
 
 
 
 
 

Fiber optic sensing by OTDR. 
 

 

 
 

Optical Time-Domain Reflectometer- Based  
Strain Monitoring System 

 
 

Fiber optics is emerging as a mainstream sensor technology capable of 
measuring numerous physical parameters; 
 
 
 
New low-cost sources, detectors, and processing hardware and industry 
maturity are making FO sensors more cost effective.