Fiber Sensor Application
Gyroscope is the core component of the inertial system, which is used to measure the relative inertial space of the moving carrier to the angular velocity caused by the angular movement. Combined with the displacement and linear velocity generated by the linear velocity measured by the accelerometer, the real-time attitude, velocity, position and other information of the carrier can be obtained through integration and other operations.
The basic principle of Fiber Optic Gyroscope (FOG) is the Sagnac effect proposed by G. Sagnac, that is, the phase difference between two light waves propagating along the closed loop is directly proportional to the normal input angular velocity of the closed optical path.
Compared with other types of Gyroscopes, the main advantages of Fiber Optic Gyroscopes (FOG) are Small Size, Light Weight, Low Power Consumption, Long Life Service, High Reliability, Suitable of Mass Production and so on. Therefore, its proportion in the application of Gyroscopes is increasing year by year. The application of Fiber Optic Gyroscope is mainly used in three application fields: Positioning, Attitude Control and Inertial Measurement. It plays an important military role and has irreplaceable advantages in many industrial fields.
According to the working principle, Fiber Optic Gyroscopes can be divided into three types: Interference Type (IFOG), Resonator Type (RFOG) and Brillouin Type (BFOG). At present, the Interference Fiber Optic Gyroscopes(I-FOG) are widely used. Because the length of sensing fiber can reach several thousand meters by using specific fiber coil winding method, the sensitivity of Fiber Optic Gyroscopes can also meet the needs of low and medium accuracy Gyroscopes. However, there are still many difficulties to further improve the accuracy, mainly due to the constraints of temperature stability, etc, to reach high accuracy.
Fiber Optic Gyroscope includes optical part and signal processing part.
a) Light Source
The light source provides the optical signal needed by FOG, and its influence factors on FOG accuracy mainly include: optical wavelength stability, power stability and polarization stability. At present, the commonly used light sources of FOG are Super Luminescent Diode (SLD) and Amplified Spontaneous Emission (ASE) using erbium-doped fiber.
SLD light source has poor stability of average wavelength, so it is suitable for low accuracy FOG. The ASE light source has a lot of improvement in spectral width and spectral stability compared with SLD light source, and the output power is also very high. The basic principle of ASE light source is to amplify the spontaneous emission signal generated by Erbium-Doped fiber under the action of pump light.
b) Polarization control
Polarization fluctuation is one of the key factors that affect the performance of Gyro. In order to control the bias caused by polarization instability in FOG, Polarization Maintaining fiber is usually used in the Fiber Coil, so the components in the optical path also need to use Polarization Maintaining Components, such as Polarization Maintaining Coupler, Polarization Maintaining Isolator, etc. the polarization controlling part in the integrated optical path is the polarizer, which can ensure the performance of FOG to be greatly improved, but the cost is also high.
In addition, depolarization technology can also be used. In this way, only ordinary Single-Mode optical fiber is needed for Fiber Coil, and no polarization maintaining device is needed for components in optical path, while fiber depolarizer is needed for polarization controller.