The difference between ring laser gyro and fiber optic gyro

Both FOG and RLG are optical gyros, all based on the Sagnac effect. The difference is that one propagates in the fiber and one propagates in the cavity, and the ring laser gyro has high precision. The principle of fiber optic gyro is similar to ring laser gyro, but the various optical effects that actually occur make this method difficult to achieve.

Fiber optic gyroscope measures the phase difference of the light in two directions. The gyroscope used will lock the phase difference of light in two directions through the Y waveguide device. In order to increase the phase difference/rotational speed coefficient, a larger enclosing area is required, that is, a longer optical fiber is required. The fiber optical has a low cost but is susceptible to non-uniform thermal expansion and contraction due to temperature change and tension variation during winding.

Ring laser gyro measures light frequency difference in two directions. The smaller surrounding area can have a relatively obvious frequency difference. Ring laser gyro expresses the rotational speed through fringe count and does not require closed-loop control. Ring laser gyro light travels in a resonant cavity and is affected little by the outside, so its precision is high, but the resonant cavity is expensive.

Compared with mechanical gyro(dynamically tuned gyro) or ring laser gyro, FOG (fiber optic gyro) is the best choice to replace mechanical gyro or ring laser gyro, with the following characteristics:
(1) There are few parts, the instrument is firm and stable, and it has a strong resistance to shock and anti-acceleration;
(2) The length of wound fiber is longer so that the detection sensitivity and resolution are several orders of magnitude higher than those of the ring laser gyro;
(3) no mechanical transmission parts, there is no wear problem, and thus have a longer service life;
(4) It is easy to adopt integrated optical circuit technology, the signal is stable, and can be directly used for digital output, and is connected with computer interface;
(5) Different accuracy can be achieved by changing the length of fiber or the number of times or the light propagates in the coil, and has a wider dynamic range;
(6) The propagation time of coherent beam is short, so the principle can be instantaneously started without preheating;
(7) It can be used together with a ring laser gyro to form a variety of sensors for inertial navigation systems, especially used as Strapdown Inertial Navigation Systems sensors;
(8) Simple structure, low price, small size, and lightweight.

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