Types of fiber optic sensors | Fiber Optic Sensor working principle

This article describes types of Fiber Optic Sensors including their working principle and applications. It describes working operation of different types of Fiber Optic Sensors viz. Intrinsic, Extrinsic and Hybrid.

Introduction: The sensor is a device which measures physical quantity and converts it into signal which can be measured by instrument or read by the user or observer. In other words, the device which senses or reacts to any physical, chemical or biological condition is known as sensor. For example, thermocouple is a sensor which detects the temperature and converts it into current or voltage. It displays the information in analog or digital form.

What is Fiber Optic Sensor?

• A sensor which measures physical quantity based on its modulation on intensity, spectrum, phase or polarization of light traveling through the optical fiber system is known as fiber optic sensor.
• Optical sensor is a device which converts light rays into electronic signals.
• This is similar to photoresistor >> which changes its resistance based on quantity of light falling on it and the same is read by the instrument.

fiber optic sensor system

Figure-1 above depicts basic elements of an optical fiber sensing system. It is found in everything from computers, printers to motion detectors. For example, when printer or copier door is machine, light falls on the sensor and as a result machine is stopped for safety reason. Usually sensor is in completely dark condition when door is closed.

Fiber Optic Sensor Working principle

Let us understand fiber optic sensor working principle of different types of fiber optic sensors.
• As shown, it consists of light source, optical fiber, sensing element or transducer and a detector.
• The working operation of fiber optic sensor is that transducer modulates some parameter of optical fiber system (e.g. intensity, wavelength, polarization, phase etc.).
• This gives rise to change in characteristics of the optical signal at the detector.

Applications of fiber optic sensors

Optical fiber sensors are used in various areas as mentioned below.
• Mechanical measurements (Includes rotation, acceleration, electric/magnetic fields, temperature, acoustic, pressure, vibration, linear & angular position, strain, humidity, viscosity etc. )
• Chemical and biological sensing
• Electrical and magnetic measurements
• To monitor physical health of the structures in real time
• Building and Bridges: Inspection and monitoring of deformation (of creep and shrinkage), displacement, damage evaluation, neutral axis evolution, concrete-steel interaction etc.
• Dams: Joint expansion monitoring, Foundation monitoring, spatial displacement measurement, leakage monitoring, distributed temperature monitoring etc.
• Tunnels: Monitoring optical extensometers, convergence monitoring etc.
• Heritage structures: Displacement monitoring, post-seismic damage evaluation, crack opening analysis etc.
• Detection of leakage

Fiber Optic Sensor Types | Types of Fiber Optic Sensors

Types of fiber optic sensors

Following are the types of Fiber Optic Sensors based on their construction and principles of operation.
• Intrinsic: In this type, sensors are embedded in or are part of the fiber optic system. This results in slight modifications to optical fiber itself. This sensor is known as intrinsic sensor. In this sensor type, fiber itself ia sensing element as fiber is directly affected by measurand. The effect of measurand on light to be transmitted takes place in fiber itself. In this type, light beam does not leave the optical fiber but it is changed whilst still contained within it.
• Extrinsic: In this type, transducers are external to the fiber optic system. Hence fiber merely registers and transmits the sensed quantity. This sensor is known as extrinsic sensor. In this type, fiber simply transports light to/from the sensing element. Here fiber carries the light from the source and to the detector end, but the modulation occurs outside the optical fiber.
• Hybrid: This fiber optic sensor type is combination of intrinsic and extrinsic sensors. Here fiber carries light in and out of the device.
Refer difference between Extrinsic optical sensor vs Intrinsic optical sensor >> for more information.

Other types of fiber optic sensors

Following are the other fiber optic sensor types.
• Point sensor, Distributed sensor
• Extrinsic sensor, Intrinsic sensor
• Through Beam Sensor, Diffuse reflective Sensor, Retro-reflective sensor
Refer optical sensor types >> for more detailed information.

Basics and Types of Sensors

Proximity Sensor   Occupancy Sensor vs Motion Sensor   LVDT and RVDT sensor   Position, displacement and level sensor   force sensor and strain sensor   temperature sensor   pressure sensor   Humidity sensor   MEMS sensor   Touch sensor   Haptic sensor   Wireless sensor

Advantages and Disadvantages of other Sensor Types

Capacitive    Inductive    Photoelectric    Ultrasonic    Infrared    Motion    Biometric    Force    Humidity    Temperature    Light    Barometer    Sound    pH    Soil Moisture   

Different Types of sensors and Transducers

RF and Wireless Terminologies

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