The Difference of Open-loop FOG and Closed-loop FOG

Fiber optic gyroscope is a kind of fiber optic sensor used in inertial navigation. Like ring laser gyro, fiber optic gyro has the advantages of no mechanical moving parts, no preheating time, insensitive acceleration, wide dynamic range, digital output, small size and so on. In addition, fiber optic gyro also overcomes the fatal shortcomings of ring laser gyro such as high cost and locking phenomenon.

Because it has no moving parts-high-speed rotor, called solid-state gyroscope. This new all-solid gyroscope will become the leading product in the future and has a wide range of development and application prospects.

The working principle of a fiber optic gyroscope is based on the Sagnac effect. Sagnac effect is a general correlation effect of the light propagated in the closed loop optical path rotating relative to the inertial space. That is, two beams of light with equal characteristics from the same light source in the same closed optical path propagate in opposite directions and finally converge to the same detection point.

Fiber optic gyroscopes can be classified in a variety of ways. According to the working principle can be divided into interference type, resonant type and excited Brillouin scattering fiber gyroscope three types. Among them, interferometric fiber gyroscope is the first generation of fiber gyroscope, which uses multi-turn fiber coil to enhance the Sagnak effect, and is widely used at present. According to the structure, it can be divided into single-axis fiber gyroscope and multi-axis ray gyroscope. The three-axis fiber gyroscope is an important development direction of fiber gyroscope because of its small size and can measure the space position. It can be divided into open-loop fiber gyroscope and closed-loop fiber gyroscope according to different electrical signal processing methods. Generally speaking, closed-loop fiber gyroscope has higher accuracy because it adopts closed-loop control.

Open-loop fiber optic gyro: Open-loop fiber optic gyro without feedback, it can direct detect the light output, with a simple structure, low price, high reliability, low power consumption and other advantages. The disadvantage is to increase the sensitivity of the gyro by increasing the single-mode fiber. The I/O has a poor linearity and a small dynamic range. It is mainly used as an angular velocity sensor.

Closed-loop fiber optic gyroscopes: Compared with open-loop circuits, closed loop fibers have a feedback loop that introduces feedback phase shifts. The effect of light drift is reduced, and the dynamic range of the fiber optic gyro is expanded. The effect on the change of light source intensity and the influence of component gain is insensitive, and the gyro drift is very small. The linearity of the output is related to the phase converter and plays an important role in the miniaturization and stability of the FOG.