Fibre optic sensors

Fibre Optic Sensors

Basic principle

         A fiber optic sensor in general, consists of a light source. The light source is coupled to an optical fiber. A light detector which receives the signal-carrying light beam as it emerges from the fiber. The signal from detector is processed electrically for getting the desired output.

Advantages

          A fiber optic sensor has the following advantages compared to other conventional sensor:

1. It has very safe in explosive environment.
2. It is of low volume and weight.
3. It is resist the nuclear or ionizing radiations’
4. It is easy to interface with low loss optical telemetry and hence used for remote sensing.
5. It is chemically inert and hence, it can readily used in chemical and biochemical instrumentation due to their small size and flexibility.
6. The sensed signal is immune to electromagnetic interference and radiofrequency  interference, and
7. It gives high accuracy and sensitivity.

Classification

     The fiber optic sensors are generally classified into two types, namely,

1.      Active sensors, and

2.      Passive sensors.

 

1. Active or Intrinsic sensor

          

              In the case of intrinsic or active sensor, it senses physical properties such as temperature, pressure etc. and hence the change in transmission characteristic. Different types of active sensors are,

        

        

      *    Intensity modulated sensors

      *    Phase modulated sensors

      *    Polarization modulated sensors, and

      *    Wavelength modulated sensors.

Example: Phase modulation sensors.                                                                                                                                                                                          

                                                                                                                                                                2.  Passive or extrinsic sensors

              These types of sensors have separate sensing element and the fiber only                    as a wave guiding media. In this type of sensor, the fiber is used largely as         transmission medium.

Example:  Displacement sensor.