Fiber Optic Gyroscope Applications

The gyroscope is an inertial system to the core component, which is used to measure the angular velocity of the moving carrier relative to the inertial space to the angular motion, and combines the displacement and the linear velocity generated by the linear velocity measured by the accelerometer to obtain an integral operation. The real-time posture, speed, position and other information of the carrier.

The basic principle of fiber optic gyroscopes is the Sagnac effect proposed by G. Sagnac in 1913, that is, the phase difference between two light waves propagating in opposite directions along a closed loop is proportional to the input angular velocity in the normal direction of the closed optical path. Since the concept of fiber optic gyroscope was first proposed in 1976 and experimentally realized for nearly 40 years, the development of fiber optic gyroscope has also made great progress, and its development has also benefited from fiber optic communication in recent years. The rapid development of the field has greatly improved the stability and reliability of optical components.

Compared with other types of gyroscopes, the main advantages of fiber optic gyroscopes are mainly in small size, light weight, low power consumption, long life, high reliability, and mass production, so they are in the gyroscope. The proportion of applications has increased year by year. The application of fiber optic gyroscope is mainly embodied in three aspects of positioning, attitude control and absolute measurement. It has a vital military role and has an irreplaceable advantage in the civilian field.

Fiber optic gyroscope working principle

At present, the application of the fiber optic gyroscope is basically interference type. Since the length of the sensing fiber can reach several kilometers by using a specific fiber winding method, the sensitivity of the fiber gyroscope can also meet the requirements of the medium and low precision gyroscope.

The fiber optic gyroscope includes an optical portion and a signal processing portion, and a common structural view of the optical fiber optic gyro optical portion using the integrated optical waveguide is as follows.

Figure 1: Block diagram of the optical path of an interferometric fiber optic gyroscope.

 a) Light source selection

The light source provides the required optical signal for the fiber optic gyroscope, and the factors affecting the accuracy of the fiber optic gyroscope mainly include: optical wavelength stability, power stability and polarization stability. At present, the commonly used fiber optic gyroscope light sources are Super-Luminescent Diode (SLD) and Amplified Spontaneous Emission (ASE) using erbium-doped fiber.

SLD sources have poor average wavelength stability and are suitable for use in low precision fiber optic gyroscopes. The ASE source has a much higher spectral width and spectral stability than the SLD source, and the output power is also high. The basic principle of the ASE light source is to amplify the spontaneous emission signal generated by the erbium-doped fiber under the action of pump light. The structure of the ASE light source using the double-pass backward structure is as follows: The specific structure is as follows:

Figure 2: Structure diagram of the ASE source.

• 980 nm pump: 980 nm pump laser;
• WDM (Wavelength Division Multiplexing): 980/1550 nm wavelength division multiplexer;
• EDF (Er-Doped Fiber): erbium-doped fiber;
• FRM (Fiber Rotation Mirror): Faraday rotator Mirror;
• ISO (Isolator): optical isolator;
• Filter: Optical filter.

b) Polarization control

Polarization fluctuation is one of the key factors affecting the performance of the gyro. In order to control the drift caused by polarization instability in the fiber optic gyroscope, usually the fiber coil adopts a polarization maintaining fiber, so the devices in the optical path part also need to adopt a polarization device, such as a polarization maintaining coupler, a polarization maintaining isolator, etc., in the integrated optical path. The polarization control part is a polarizer, which can ensure the gyro performance is greatly improved, but the cost is also high.

In addition, depolarization technology can also be used, so that the fiber coil only needs to use ordinary single-mode fiber, the device in the optical path part does not need to use the polarization maintaining device, and the polarization control device needs to use the fiber depolarizer.

DK Photonics offers a variety of passive components with compact package for building Fiber Optic Gyroscope systems. Contact DK Photonics regarding your requirements.

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