Fiber Optic Gyro, also known as Fiber Optic Gyro, or FOG for short, is a new type of optical gyroscope that uses laser and optical fiber technology to measure the angular velocity or rotation angle of an object relative to inertial space. It belongs to the gyroscope in a broad sense and is a sensor with gyro effect made according to the principles of modern physics. Because it does not have the moving parts of traditional gyroscopes, namely high-speed rotors, it is also called a solid-state gyroscope. It occupies a pivotal position in the field of inertial navigation and is the core component of the inertial navigation system. It is like the “heart” of the navigation system, which can accurately sense the rotation information of the object and provide key data support for the navigation, positioning and attitude control of the carrier.
Working Principle of Fiber Optic Gyroscope
Sagnac Effect
The working principle of fiber optic gyroscope is based on the Sagnac Effect, which was discovered by French physicist Georges Sagnac in 1913. In essence, the Sagnac effect describes a universal and relevant phenomenon presented by propagating light in a closed-loop optical path rotating relative to inertial space. Specifically, when two beams of light with equal characteristics emitted by the same light source propagate in opposite directions in the same closed optical path and finally converge at the same detection point, if the plane where the optical path is located rotates around an axis perpendicular to itself, relative to the inertial space, the optical paths of the light beams propagating in the positive and reverse directions will be different, resulting in an optical path difference, and the optical path difference is proportional to the angular velocity of rotation. Simply put, it is like two people running clockwise and counterclockwise on a rotating circular track. When the track is stationary, the distance they run in one lap is the same; but when the track rotates, the distance they run in one lap will be different, and this difference corresponds to the optical path difference, and the rotation speed of the track corresponds to the angular velocity in practical applications.
In fiber optic gyroscopes, the Sagnac effect is used to achieve angular velocity measurement. By accurately measuring the optical path difference between the two beams of light due to the rotation of the optical path, the corresponding phase difference can be calculated, and finally the angular velocity of rotation can be obtained. This effect is the theoretical cornerstone for the fiber optic gyroscope to achieve precise measurement, and it makes it possible for the fiber optic gyroscope to be used in many fields.
Specific Working Process
To understand the working process of the fiber optic gyroscope more clearly, we will explain it in detail in combination with the optical path diagram (assuming that the reader can see a typical fiber optic gyroscope optical path diagram, including the main components such as light source, beam splitter, fiber ring, detector, etc.).
- Light source light emission and beam splitting: A beam of light is emitted by the light source. This light source usually uses a superluminescent diode (SLD) or a laser diode (LD), which can provide optical signals with high coherence and stability. The light first reaches the beam splitter, which splits the light into two beams of equal intensity, which enter the fiber ring for transmission in the clockwise direction (CW) and the counterclockwise direction (CCW). This is like dividing a river into two tributaries through a water diversion port, flowing in different directions.
- Propagation in the fiber ring: The fiber ring is the core component of the fiber optic gyroscope, usually wound with hundreds to thousands of meters of single-mode optical fiber, and wound on a cylindrical skeleton to reduce the temperature effect. After the two beams of light enter the fiber ring, they propagate in opposite directions. When the fiber ring does not rotate relative to the inertial space, the two beams of light have the same path length in the fiber ring and their propagation time is also the same. However, once the fiber ring rotates with the carrier, according to the Sagnac effect, the propagation path lengths of the two beams of light will differ. For example, when the fiber ring rotates clockwise, the light propagating clockwise needs to catch up with the rotating fiber ring, and its propagation path becomes relatively longer; while the light propagating counterclockwise faces the direction of rotation, and its propagation path becomes relatively shorter.
- Producing phase difference: Due to the difference in the propagation path lengths of the two beams of light in the fiber ring, a phase difference is generated when they converge again. This phase difference is proportional to the angular velocity of the fiber ring, that is, the greater the angular velocity of rotation, the greater the phase difference. The phase of light can be imagined as the position of the hands of a clock. When the propagation paths of the two beams of light are different, the “time” (phase) when they arrive at the confluence point will be different, resulting in a phase difference.
- Detecting phase difference: After the two beams of light with phase difference converge, they enter the detector. The detector usually uses a photodiode (PD) or an avalanche photodiode (APD), which can convert optical signals into electrical signals. By detecting the change of this electrical signal, the phase difference between the two beams of light can be measured. In practical applications, to improve the measurement accuracy, some signal processing technologies, such as phase modulation and demodulation technology, are also used to more accurately extract the phase difference information. For example, commonly used methods such as square wave modulation and sine modulation can modulate the phase difference information into the optical signal, and then restore it through demodulation technology for subsequent calculation and processing. Finally, based on the measured phase difference and the formula of the Sagnac effect, the rotational angular velocity of the optical fiber ring can be accurately calculated, and then the rotation information of the carrier can be obtained.
Advantages of Fiber Optic Gyroscopes
Compared with traditional electromechanical gyroscopes
Traditional electromechanical gyroscopes maintain angular momentum through high-speed rotating rotors to sense the rotation of objects. This mechanical structure determines that it has many inherent deficiencies. Mechanical rotating parts will wear out due to friction during long-term operation, which not only reduces the accuracy of the gyroscope, but also shortens its service life, just like the parts of a car engine will wear out after long-term use, affecting the performance of the car. Moreover, mechanical structures are very sensitive to vibration and shock, and their measurement accuracy will drop significantly when they are disturbed by external factors. For example, when a vehicle is driving on a bumpy road, a traditional electromechanical gyroscope may not be able to accurately measure the vehicle’s attitude changes due to vibration.
In contrast, a fiber optic gyroscope has no mechanical rotating parts, which fundamentally avoids the problems caused by mechanical wear, which greatly improves its reliability. In terms of sensitivity, a fiber optic gyroscope is far superior to a traditional electromechanical gyroscope. Because it works based on the Sagnac effect, it can detect extremely small phase difference changes, thereby achieving high-precision measurement of angular velocity. For example, in the field of aerospace, a fiber optic gyroscope can accurately sense the tiny attitude changes of an aircraft, provide more accurate data for flight control, and ensure the safe and stable flight of the aircraft, while a traditional electromechanical gyroscope is difficult to achieve such accuracy requirements.
Compared with Ring Laser Gyroscope
Ring laser gyroscope uses the frequency difference generated by the propagation of laser in the ring optical path to measure angular velocity. It performs well in terms of accuracy and stability, but it also has some limitations. Ring laser gyroscope requires a precision-machined optical cavity, and has extremely high requirements for the accuracy of the optical mirror and the sealing of the optical cavity. The manufacturing process is complex and the cost is high. To overcome the lock area problem, a mechanical frequency deviation mechanism is also required, which further increases the complexity and cost of the system. In addition, the ring laser gyroscope usually requires a high-voltage power supply of several thousand volts to drive, which not only increases the difficulty of power management, but also poses certain safety hazards.
Fiber optic gyroscope is relatively simple in manufacturing process. It does not require a precision-machined optical cavity and a complex mechanical frequency deviation mechanism, which reduces the difficulty and cost of manufacturing. In terms of service life, fiber optic gyroscope has higher reliability and longer service life because it does not have complex mechanical parts and high-voltage power supply. For example, in satellite navigation systems, fiber optic gyroscopes can work stably for a long time, provide accurate attitude measurement data for satellites, and ensure the normal operation of satellites, while ring laser gyroscopes may fail during long-term use due to complex structures and high-voltage power supply problems.
Compared with MEMS Gyroscopes
MEMS gyroscopes are miniaturized gyroscopes manufactured based on micro-electromechanical system technology. They have the advantages of small size, low cost, and low power consumption. They have been widely used in some consumer electronics fields that do not require high precision, such as gyroscopes in smartphones, which are used to realize functions such as automatic screen rotation and game control. However, there is a large gap between MEMS gyroscopes and fiber optic gyroscopes in terms of technical indicators and environmental adaptability. MEMS gyroscopes have relatively low precision, poor zero bias stability and scale factor stability. Under long-term operation or complex environments, their measurement errors will gradually accumulate, resulting in reduced measurement accuracy. For example, during the flight of a drone, if a MEMS gyroscope is used for attitude measurement, as the flight time increases, its measurement error may cause the flight attitude of the drone to deviate, affecting flight safety.
Fiber optic gyroscopes can maintain stable performance in various complex environments, and can accurately measure angular velocity regardless of high temperature, low temperature, strong vibration or strong electromagnetic interference environment. In the military field, fiber optic gyroscopes are widely used in key systems such as missile guidance and ship navigation. They can provide reliable navigation and attitude control information for weapons and equipment in harsh battlefield environments to ensure the combat effectiveness of weapons and equipment, while MEMS gyroscopes are difficult to meet these high-demand application scenarios.
Application of Fiber Optic Gyroscopes
Due to its significant advantages such as high precision, high reliability, long life and strong anti-interference ability, fiber optic gyroscopes have been widely used in many fields and have become key core components to promote technological development in various fields and improve system performance.
Aerospace field
In the field of aerospace, fiber optic gyroscopes are an indispensable and important part of key systems such as aircraft flight control and satellite attitude adjustment. Taking an aircraft as an example, during flight, the fiber optic gyroscope can accurately measure the angular velocity and attitude changes of the aircraft in real time, provide key data for the flight control system, enable the pilot to accurately control the aircraft, and ensure the safety and stability of the flight. For example, during takeoff and landing of an aircraft and flight under complex weather conditions, the high-precision measurement of the fiber optic gyroscope can help the pilot adjust the aircraft attitude in time to avoid flight accidents.
In terms of satellites, fiber optic gyroscopes play a vital role in the attitude control and orbit maintenance of satellites. When a satellite is operating in space, it needs to precisely control its attitude to ensure that the solar panels are aimed at the sun to obtain energy, and at the same time ensure that the communication antenna and various detection instruments are accurately pointed at the target. Fiber optic gyroscopes can provide satellites with high-precision attitude measurement information. The satellite control system adjusts the satellite’s attitude based on this information to keep it running normally on the predetermined orbit. For example, my country’s Beidou satellite navigation system is equipped with high-precision fiber optic gyroscopes on satellites to ensure that the satellites can operate stably in a complex space environment and provide accurate navigation and positioning services to global users.
Military field
In the military field, the application of fiber optic gyroscopes has greatly improved the accuracy and performance of weapons and equipment, and provided a strong guarantee for the victory of modern warfare. In the missile guidance system, the fiber optic gyroscope can accurately measure the flight attitude and angular velocity of the missile, and correct the flight trajectory of the missile in real time, so that the missile can hit the target more accurately. For example, the US “Tomahawk” cruise missile uses a high-precision fiber optic gyroscope inertial navigation system, which can achieve high-precision long-range strikes in a complex battlefield environment, causing great deterrence to enemy targets.
In terms of ship navigation, fiber optic gyroscopes can provide ships with accurate heading and attitude information, helping ships to navigate accurately in complex marine environments. Whether in ocean voyages or offshore operations, fiber optic gyroscopes can ensure that the ship’s navigation system is stable and reliable, and improve the ship’s combat capability and survivability. In addition, fiber optic gyroscopes are also widely used in the navigation and fire control systems of ground combat equipment such as tanks and armored vehicles, improving the maneuverability and shooting accuracy of these equipment.
Civilian field
In the civilian field, fiber optic gyroscopes also play an important role, promoting the development and progress of many industries. In oil exploration, fiber optic gyroscopes are used in drilling guidance systems, which can measure the attitude and orientation of the drill bit in real time, help workers accurately control the drilling direction, improve drilling efficiency and success rate, and reduce energy waste and environmental pollution.
In the field of industrial robots, fiber optic gyroscopes can provide robots with accurate attitude and position information, enabling robots to more accurately complete various complex tasks, such as welding, assembly, handling, etc., to improve production efficiency and product quality. For example, in automobile manufacturing plants, industrial robots use fiber optic gyroscopes to achieve high-precision motion control to ensure the welding and assembly quality of automobile parts.
In high-speed rail operation, fiber optic gyroscopes are used in the positioning and navigation systems of trains, which can monitor the running status and position information of trains in real time, and improve the safety and stability of train operation. Even in the case of weak signals or interference, fiber optic gyroscopes can provide reliable navigation data for trains to ensure the normal operation of trains.
With the rapid development of autonomous driving technology, fiber optic gyroscopes are increasingly used in driverless cars. It can provide accurate attitude and angular velocity information for driverless cars, help cars accurately perceive their motion state, and achieve precise control of autonomous driving. For example, in operations such as vehicle turning, changing lanes, and avoiding obstacles, fiber optic gyroscopes can provide real-time data on vehicle attitude changes, enabling the autonomous driving system to make correct decisions promptly to ensure driving safety.
Future Development Trends
- Miniaturization and integration: With the pursuit of miniaturization and lightweight of equipment by modern science and technology, fiber optic gyroscopes are also developing in the direction of miniaturization and integration. In the future, the development of multifunctional integrated optical chips and the use of three-axis measurement instead of single-axis measurement will become a trend, which can not only reduce the size and weight of fiber optic gyroscopes, but also reduce costs and improve the reliability and stability of the system. For example, integrating fiber optic gyroscopes with other sensors on the same chip to form a multifunctional inertial measurement unit can provide more comprehensive and accurate motion information for various devices, and has broad application prospects in small electronic devices such as smartphones and wearable devices.
- Low cost: At present, the cost of fiber optic gyroscopes has limited its wider application to a certain extent, especially in the cost-sensitive civilian market. In the future, through technological innovation and process improvement, such as the use of new optical fiber materials, optimization of production processes, and improvement of production automation, the manufacturing cost of fiber optic gyroscopes can be effectively reduced. At the same time, with the increase in market demand and the realization of large-scale production, the cost will be further reduced. Low-cost fiber optic gyroscopes will be able to be used in more civilian fields, such as intelligent transportation, logistics warehousing, consumer electronics, etc., to promote the technological upgrading and development of these fields.
- High precision: In the fields of aerospace, military and other fields with extremely high precision requirements, continuously improving the precision of fiber optic gyroscopes has always been the focus of research. In the future, by studying new physical effects, optimizing optical path design, and improving signal processing algorithms, it is expected that the measurement accuracy of fiber optic gyroscopes will be further improved and errors will be reduced. For example, new fiber optic materials and structures can be studied to reduce noise and interference in optical fibers; more advanced signal demodulation technology and error compensation algorithms can be developed to improve the detection and processing capabilities of weak signals, thereby achieving higher-precision angular velocity measurement.
- Application expansion in emerging fields: In addition to its application in traditional fields such as aerospace, military, and civil, fiber optic gyroscopes have also shown great application potential in emerging fields. In the field of intelligent robots, fiber optic gyroscopes can provide robots with accurate posture and motion information, enabling them to complete various tasks more flexibly and accurately. With the continuous development of robot technology, the demand for fiber optic gyroscopes will continue to increase. In the fields of virtual reality (VR) and augmented reality (AR), fiber optic gyroscopes can be used to achieve more accurate head tracking and motion capture, enhance users’ immersion and interactive experience, and provide strong support for the development of VR and AR technologies. With the popularization of Internet of Things technology, fiber optic gyroscopes can also be applied to smart homes, environmental monitoring and other fields to achieve intelligent control and data collection of equipment.
Summary and Outlook
As an advanced angular velocity sensor based on the Sagnac effect, fiber optic gyroscopes, with their unique working principle, have demonstrated many advantages that traditional gyroscopes cannot match, such as high precision, high reliability, long life, strong anti-interference ability, small size, and light weight. These advantages have enabled them to be widely and deeply used in many fields such as aerospace, military, and civil use, becoming a key force in promoting technological progress and development in various fields.
From the current development status, although both domestic and foreign countries have achieved remarkable results in the research and application of fiber optic gyroscope technology, the advancement of technology is endless, and fiber optic gyroscopes still have broad development space and huge development potential in the future. In terms of miniaturization and integration, the continuous pursuit of smaller size and higher integration will create conditions for its application in more small devices and complex systems; the realization of low cost will further expand its market application scope, especially in the civilian market that is more sensitive to cost, and is expected to achieve large-scale popularization and application; the continuous improvement of high precision will enable it to play a more important role in key fields such as aerospace and military that require extremely high precision, and provide more reliable guarantees for the precise navigation of aircraft and the precise strike of weapons and equipment; and the expansion of applications in emerging fields, such as intelligent robots, virtual reality, and the Internet of Things, will open up new market areas for fiber optic gyroscopes and bring more development opportunities.
As an important part of the field of modern science and technology, fiber optic gyroscopes will play a more important role in the future process of scientific and technological development. We have reason to believe that with the continuous innovation and breakthroughs in technology, fiber optic gyroscopes will be widely used in more fields and make greater contributions to promoting the development and progress of various industries. At the same time, we also hope that readers can continue to pay attention to the development of fiber optic gyroscope technology and witness this advanced technology create more miracles in the future.
