Fiber optic gyroscope, as a new type of inertial device, has the advantages of simple structure, no rotating parts, light weight, impact resistance, long service life, low power consumption, and large dynamic range compared with traditional mechanical gyroscopes. In the military field, fiber optic gyroscopes are widely used in control systems such as missile guidance, aircraft and ship navigation, military satellites and terrain tracking navigation. It also has broad prospects in the civil field: for example, in a variety of aerospace, aviation, navigation equipment, petroleum industry and underground pipeline measurement, among which the foreign civil field applications are more prominent.
Why does temperature affect fiber optic gyroscopes?
It consists of light source, photodetector, beam splitter and fiber optic coil. Temperature affects the accuracy of FOG by affecting the performance of its internal components. The refractive index of optical fiber is closely related to temperature. When the temperature changes, the refractive index of optical fiber will also change, resulting in a change in the transmission speed of optical signals in the optical fiber. This will affect the phase difference of the optical signal, which in turn affects the measurement results of the FOG. As a photoelectric sensor with relatively high detection sensitivity and reliability, the photodetector's performance directly determines the quality of the measured voltage signal. Changes in ambient temperature will cause the photodetector to generate a lot of noise. When there is no light, the photodetector will generate a special current that increases as the temperature increases.
There are two main aspects of the impact of ambient temperature on the performance of fiber optic gyroscopes. One is noise, and the other is drift. The former determines the minimum detectable phase shift of the FOG, which is the final accuracy. The latter is used to evaluate the long-term changes in the gyroscope output signal. For inertial guidance applications, drift is a more fundamental parameter.
Temperature effect mechanism
Shupe once pointed out in an article that the non-reciprocal phase shift (Shupe error) caused by time-related changes in ambient temperature will bring large drift to the fiber optic gyroscope and affect its measurement accuracy. As shown in Figure 1, when two beams of interference light propagate in clockwise and counterclockwise directions respectively, the Shupe error produced by a section of optical fiber element dz at a distance z from the end point A is:
It can be seen that if the thermal disturbances on the two sections of optical fiber that are symmetrical with respect to the midpoint of the optical fiber are the same, the phase difference caused by temperature will be offset. Normally, in optical path design, using methods such as bipolar symmetrical winding and quadrupole symmetrical winding to wind optical fiber coils can effectively suppress Shupe errors. However, due to the non-ideality of the fiber ring during the winding process, as well as the changes in components such as Y-waveguides and polarization-maintaining fiber couplers affected by temperature, residual temperature drift will be caused. Therefore, certain temperature compensation is required for the fiber optic gyroscope to ensure the accuracy of the gyroscope output.
Ericco has been committed to the research of inertial products for 18 years. For fiber optic gyroscopes, we not only have single-axis FOG but also multi-axis FOG. We also have our advantageous products: ER-FOG-50, ER-FOG-60 & ER-FOG-70, they have the characteristics of high precision, low power consumption, long life and small size. In short, Ericco strictly detects various indicators of fiber optic gyroscopes, not only in terms of temperature drift, but also in terms of earthquake resistance and stability, and continues to optimize them to create inertial products that are more suitable for the majority of customers. Interested friends can follow our website. In the next issue, we will share with you the technical analysis of FOG temperature compensation.
More Technical Questions
1.What causes the FOG measurement error?
2. Application of Fiber Optic Gyroscope in oil drilling field
3. Do You Know Fiber Optic Gyroscope and Its Typical Applications?
4. Fiber Optic Gyroscope: current status & development trends
6. The Working Principle of FOG
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