Fiber Optical Gyro, full name Fiber Optical Gyro, is a high-precision inertial sensor based on fiber optic technology, belonging to the gyroscope in a broad sense. A gyroscope, as the name means “rotation indicator”, is a sensor that can be sensitive to angular rate and angular deviation. A fiber optic gyroscope is made according to the principles of modern physics, has a gyro effect, and does not have a moving parts-high-speed rotor, it is also called a solid-state gyroscope. Its appearance has brought the development of modern gyroscopes into a new stage.
A fiber optic gyroscope is mainly used to measure the angular velocity or rotation angle of an object relative to inertial space. It has extremely critical applications in many fields such as aerospace, navigation, land navigation, oil exploration, and robots. It provides accurate direction and attitude information for equipment in these fields, just like giving them “directional eyes” to ensure the stable operation of the equipment.
Working Principle of Fiber Optical Gyro
The working principle of fiber optic gyroscope is based on the Sagnac effect, which was discovered and verified by French physicist Georges Sagnac in 1913. In principle, when a beam of light propagates in a closed fiber ring, assuming that the fiber ring is stationary, two beams of light with the same characteristics emitted from the same light source propagate in the fiber ring in opposite directions. They travel the same optical path and will not produce a phase difference when they finally converge.
But when the fiber ring rotates at a certain angular velocity relative to the inertial space, the situation is different. The propagation paths of the two counter-propagating beams of light in the fiber ring will be different, which leads to the appearance of an optical path difference. To put it more figuratively, it is like two people running clockwise and counterclockwise on a rotating circular track, and the distances they run will be different. According to the principle of optics, the optical path difference will further lead to the generation of phase difference, and this phase difference is proportional to the angular velocity of the fiber ring.
In practical applications, the fiber optic gyroscope precisely measures this phase difference to deduce the rotation speed and direction of the object. To improve the sensitivity and accuracy of the measurement, the fiber optic gyroscope usually uses multiple turns of fiber optic coils, and by increasing the length of the fiber and the total area of the loop, the Sagnac effect is enhanced, so that even a tiny rotation can generate a phase difference signal that can be accurately detected.
Rich and Diverse Types of Fiber Optical Gyro
Based on different working principles, fiber optic gyroscopes are mainly divided into three categories: interferometric fiber optic gyroscopes (I-FOG), resonant fiber optic gyroscopes (R-FOG) and stimulated Brillouin scattering fiber optic gyroscopes (B-FOG). They have their characteristics in structure, performance, and application scenarios.
Interferometric fiber optic gyroscope (I-FOG)
The interferometric fiber optic gyroscope is the most widely used type of fiber optic gyroscope and belongs to the first generation of fiber optic gyroscopes. It enhances the Sagnac effect through multiple turns of fiber coils. The double-beam annular interferometer composed of multiple turns of single-mode fiber coils can provide higher accuracy. In terms of detection technology, it uses interferometric measurement technology to convert phase-modulated light into amplitude-modulated light and converts the direct measurement of optical phase into light intensity measurement, to measure the Sagnac phase change more simply. The optical fiber components of the interferometric fiber gyroscope are generally made of single-mode fiber or polarization-maintaining fiber. At present, low- and medium-performance interferometric fiber gyroscopes have been put into practical use and are widely used in the navigation and attitude control of aerospace vehicles. For example, during the flight, an aircraft needs to know its flight attitude and direction accurately at all times. Interferometric fiber gyroscopes can accurately measure the angular velocity and angle changes of the aircraft, provide key data for the flight control system, and ensure the safety and stability of the flight. High-performance interferometric fiber gyroscopes are still in the development stage.
Resonant fiber optic gyroscope (R-FOG)
Resonant fiber optic gyroscopes belong to the second generation of fiber optic gyroscopes. They enhance the Sagnac effect through a ring resonant cavity and further improve the accuracy by using the circular propagation of light in the resonant cavity, so shorter optical fibers can be used. Its basic structure is that a resonant cavity is formed by optical fiber. When the gyroscope rotates, the resonant frequency of the resonant cavity will change with the size of the Sagnac effect. By detecting the frequency difference between the clockwise and counterclockwise waves caused by rotational non-reciprocity, the angular velocity can be measured. However, the resonant fiber gyroscope has very strict requirements for the light source. It needs to use a strong coherent light source to enhance the resonance effect of the resonant cavity. However, the strong coherent light source will also bring many parasitic effects. How to eliminate these parasitic effects has become the main technical obstacle at present. Although the technology is not yet mature, the resonant fiber gyroscope has shown potential application value and advantages in some special fields with extremely high precision requirements, such as high-end scientific research equipment and high-precision attitude control of satellites. Once the technical difficulties are overcome, it is expected to play an important role in these fields.
Stimulated Brillouin scattering fiber gyroscope (B-FOG)
The stimulated Brillouin scattering fiber gyroscope is the third generation of fiber gyroscope, also known as fiber ring laser gyroscope, or stimulated Brillouin scattering fiber ring laser gyroscope. It uses an active resonant cavity and uses high-power light to stimulate Brillouin scattered light in the optical fiber. When the light intensity transmitted in the fiber ring reaches a certain level, Brillouin scattering will occur. The frequency of the scattered light is affected by the Sagnac effect. The frequency difference between the two Brillouin scattered lights in the clockwise and counterclockwise directions is proportional to the rotational angular velocity. By detecting the frequency of the scattered light generated by the clockwise and counterclockwise light waves and performing beat frequency processing, the rotational angular velocity of the fiber ring can be obtained. This type of fiber gyroscope has the advantages of high detection accuracy, especially good linearity of the proportional factor, and the output signal processing method is simple, the required fiber length is short, and the noise factor is small.
However, the stimulated Brillouin scattering fiber gyroscope is still in the theoretical research stage. Researchers are working hard to break through technical bottlenecks, such as the need for high stability (including stable working wavelength and stable output power), narrow linewidth, high-power lasers, and solving locking problems. With the continuous advancement of fiber laser and fiber amplifier technology, the research on stimulated Brillouin scattering fiber gyroscopes has also ushered in new opportunities and may be used in fields with extremely high requirements for accuracy and stability in the future.
Advantages of Fiber Optical Gyro
No mechanical parts, high reliability
One of the biggest features of the fiber optic gyroscope is that there are no mechanical rotating parts, and it is a fully solid-state structure. Traditional electromechanical gyroscopes rely on high-speed rotating rotors to sense angular velocity. Mechanical parts are prone to wear and fatigue during long-term use, resulting in performance degradation or even failure. The fiber optic gyroscope does not have these mechanical parts, avoiding reliability problems caused by mechanical wear, greatly improving the stability and reliability of the system, and greatly extending its service life. Taking the aerospace field as an example, satellites need to operate stably for a long time in space. The high reliability of the fiber optic gyroscope has become a key factor in ensuring the stability and control of the satellite attitude, ensuring that the satellite can continue to work stably and complete various tasks in a complex space environment.
High precision and high stability
The fiber optic gyroscope can achieve extremely low zero bias instability and has excellent precision and stability. In some fields with extremely high precision requirements, such as high-end weapons and equipment, aerospace, etc., the high-precision characteristics of the fiber optic gyroscope are particularly important. In the process of missile precision guidance, the fiber optic gyroscope can accurately measure the angular velocity and attitude changes of the missile during flight, provide accurate data support for the flight trajectory of the missile, and ensure that the missile can accurately hit the target. Even in complex and changing environments, such as the dramatic changes in air pressure and temperature faced by aircraft at high altitudes, fiber optic gyroscopes can still maintain high-precision measurements, providing reliable guarantees for stable flight and precise control of aircraft.
Strong resistance to shock and acceleration
The structure of the fiber optic gyroscope gives it excellent resistance to shock and acceleration, making it very suitable for working in complex and harsh environments such as aircraft and missile launches. When an aircraft takes off, lands, or performs maneuvering flight, it will be subjected to huge impact forces and accelerations. At the moment of missile launch, it will experience extremely high accelerations and strong shocks. With its rugged all-solid-state structure, the fiber optic gyroscope can work normally in these extreme environments and accurately measure attitude and angular velocity information. For example, when a fighter jet performs a high-maneuverability flight, the fiber optic gyroscope can provide accurate attitude data to the flight control system in real-time and stably, helping pilots complete various complex flight actions and ensuring flight safety and mission execution.
Easy to integrate
The fiber optic gyroscope has great advantages in system integration. It can be directly connected to a computer interface, which facilitates data processing and system integration. In the autonomous driving system, the fiber optic gyroscope, as the core component of the inertial navigation system, can be seamlessly integrated with other sensors (such as cameras, radars, etc.) and the vehicle’s control system. Through the connection with the computer, the fiber optic gyroscope transmits the measured vehicle attitude and motion information to the computer in real-time. The computer accurately controls the vehicle’s driving state based on this information and other sensor data to realize various functions of autonomous driving, such as automatic parking and adaptive cruise control. In industrial automation control systems, fiber optic gyroscopes can also be easily integrated into robots, automated production lines, and other equipment to provide key attitude and position information for precise motion control of equipment.
Applications of Fiber Optical Gyro
With high precision, high reliability, and excellent anti-interference ability, fiber optic gyroscopes have been widely used in many fields and play an indispensable role.
Aerospace field
In the aerospace field, fiber optic gyroscopes are mainly used for navigation and attitude control of aircraft. During the flight, the aircraft needs to accurately grasp its flight attitude and direction at all times. The fiber optic gyroscope can measure the angular velocity and angle changes of the aircraft in real-time and accurately, providing key data for the flight control system to ensure the safety and stability of the aircraft flight. During satellite launch and operation, fiber optic gyroscopes are used for satellite attitude determination and orbit control to ensure that the satellite accurately enters the predetermined orbit and operates stably in space to complete various complex tasks, such as communication, remote sensing, and meteorological monitoring. For example, when the satellite performs high-precision earth observation tasks, the fiber optic gyroscope can help the satellite accurately adjust its attitude so that the observation equipment is always aimed at the target area to obtain high-quality images and data.
Navigation
In the navigation field, fiber optic gyroscopes play a key role in ship navigation and attitude measurement. Ships sail in the vast ocean and need accurate navigation information to ensure navigation safety and arrive at the destination on time. Fiber optic gyroscopes can accurately measure the ship’s heading, roll, pitch, and other attitude parameters, providing an important basis for the ship’s automatic driving system and improving the safety and accuracy of navigation. During ocean voyages, ships may encounter severe sea conditions and complex meteorological conditions. The high reliability and stability of fiber optic gyroscopes enable them to work normally in such harsh environments and provide reliable navigation information for crew members. In port operations, such as berthing, loading, and unloading of cargo, etc., fiber optic gyroscopes can help ships accurately control their attitude and ensure the smooth progress of operations.
Automobile field
In the automotive field, especially in autonomous driving systems, fiber optic gyroscopes also have important applications. With the continuous development of autonomous driving technology, the requirements for vehicle navigation and stability control are getting higher and higher. As the core component of the inertial navigation system, the fiber optic gyroscope can measure the attitude and motion state of the vehicle in real-time, and provide accurate position and direction information for the autonomous driving system. In autonomous driving test vehicles, fiber optic gyroscopes work together with other sensors (such as cameras, radars, etc.) to help vehicles accurately perceive the surrounding environment and realize functions such as automatic driving, obstacle avoidance, and parking. In some mass-produced high-end models, fiber optic gyroscope technology has also begun to be gradually applied to improve the vehicle’s handling stability and safety. For example, when a vehicle encounters an emergency and needs to avoid it during high-speed driving, the fiber optic gyroscope can quickly and accurately perceive the vehicle’s attitude changes, and assist the vehicle’s electronic stability control system to adjust the vehicle’s driving direction in time to avoid accidents.
Industrial automation field
In the field of industrial automation, fiber optic gyroscopes are often used for attitude control of robots and robotic arms. When industrial robots are performing operations such as handling and assembly, they need to precisely control their posture and position to ensure the accuracy and efficiency of the operation. Fiber optic gyroscopes can monitor the motion status of robots and robotic arms in real-time, provide feedback information to the control system, and enable robots to accurately adjust their posture according to task requirements and complete various complex operations. In automobile manufacturing plants, industrial robots use fiber optic gyroscopes to achieve high-precision assembly of parts and components, improving production efficiency and product quality. In the field of logistics and warehousing, automated handling robots use fiber optic gyroscopes to achieve autonomous navigation and precise positioning, and quickly and accurately complete the handling and storage tasks of goods.
Summary and Outlook
As a high-precision inertial sensor based on advanced optical fiber technology, fiber optic gyroscopes work with a unique Sagnac effect and occupy an important position in the field of modern science and technology. Its various types, such as interferometric, resonant, and stimulated Brillouin scattering, each show unique advantages and application potential, whether in the field of high-precision aerospace, the field of navigation with extremely high stability requirements, or the field of automotive autonomous driving and industrial automation full of innovative vitality, they all play an irreplaceable role.
Judging from the current development status, research on fiber optic gyroscopes at home and abroad has achieved remarkable results, with continuous technological breakthroughs and continued expansion of application areas. In the future, with the rapid development of science and technology, fiber optic gyroscopes are expected to be more widely used in more fields, such as in emerging intelligent transportation, virtual reality, augmented reality, and other fields. Fiber optic gyroscopes may be able to provide more accurate attitude and position information for equipment in these fields and promote further development in these fields. In terms of technology, it is also expected to achieve greater breakthroughs, further improve accuracy, reduce costs, improve reliability, and better meet the needs of different industries. I believe that in the future, fiber optic gyroscopes will play a more important role in the development of modern science and technology, and make greater contributions to promoting technological progress and innovative development in various industries.
