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Advantages of Fiber Optic Gyroscope | disadvantages of Fiber Optic Gyroscope

This page covers structure,working,advantages and disadvantages of Fiber Optic Gyroscope (FOG). It mentions Fiber Optic Gyroscope advantages or benefits and Fiber Optic Gyroscope disadvantages or drawbacks.

Introduction:
The measurement of angular velocity is used in various applications ranging from missile navigation to motion control. Three sensors are mainly used to measure angular velocity viz. fiber optic gyroscope (FOG), ring laser gyroscope (RLG) and MEMS gyroscope.

What is Fiber Optic Gyroscope (FOG)?

• It uses Sagnac effect to measure angular velocity.
• The figure-1 depicts basic configuration of fiber optic gyroscope.
• It consists of a passive interferometer where a coupler is used to split the radiation from the light source into two counter propagating waves viz. clockwise and counter clockwise, in the fiber coil and to recombine the waves, after propagation, on a photodetector (PD).
• Due to Sagnac effect, the light beam travelling against the rotation experiences a slightly shorter path delay compare to the other light beam. The resultant differential phase shift is measured using interferometry in FOG. The Sagnac effect depends on effective area of the closed optical path.
• It is also known as fiber optic rotation sensor. It is very essential tool for navigation, guidance and control of missiles, aircrafts, robots, automobiles, spacecrafts etc.

Fiber Optic Gyroscope

• The figure-2 depicts circular loop of fiber. The phase shift of fiber optic gyroscope is expressed as follows.
➨ ΔΦs = (8*π*Ω*A*N) / (c * λ)
Where,
N = Number of Turns
A = π *(R)2, R is radius of fiber loop
Ω = Earth's rotation in rad/sec
λ = Operating wavelength
c = 3 x 108

Fiber Optic Gyroscope working

• When used along with accelerometer, it provides accurate path of flight or movement of vehicle or the object.

Benefits or advantages of Fiber Optic Gyroscope

Following are the benefits or advantages of Fiber Optic Gyroscope:
➨It offers higher sensitivity. Hence it helps in determining direction of the Earth's poles based on measurements of angular velocity only. Its rotational sensitivity is superior (~ 0.1o/Hr) and faster compare to conventional gyroscope.
➨FOG does not have any dither mechanism. Hence it is perfectly silent device. It is used for submarine navigation.
➨Since it is a solid state device with no moving part nor sealed cavity. It is highly raliable and offers longer life time. Moreover it does not need any preventive maintenance.
➨It offers high performance due to its inherent low random noise.
➨It offers same compactness and cost like ring laser gyroscope (RLG) and MEMS gyroscope.

Drawbacks or disadvantages of Fiber Optic Gyroscope

Following are the drawbacks or disadvantages of Fiber Optic Gyroscope:
➨Some designs of FOG are sensitive to vibrations. The impact can be mitigated when multiple-axis FOG is coupled witn accelerometers.
➨The FOGs are required to be calibrated.
➨Detectable angular velocity is limited to +/- π/2 rad with respect to the phase difference due to the Sagnac effect.
➨Linearity and scale factor stability of gyroscope are easily deteriorated due to fluctuations in the intensity of incident light on the photodetector.



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