Advanced Navigation is a leading manufacturer of fiber optic gyroscopes (FOG) for commercial and defense applications. Our latest FOG INS, Boreas D90, features revolutionary Digital Fiber Optic Gyroscope technology, to achieve the highest performance for the lowest SWaP-C (Size, Weight, Power, and Cost).
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A fiber-optic gyroscope (FOG) is a device used to measure angular velocity and orientation. It provides extremely accurate rotational rate information while being low maintenance and offering a long lifespan. Fiber optic gyroscopes have become more affordable and the technology has proved to be beneficial for an expanding array of different high-performance inertial navigation systems (INS). As a result, FOGs have become the default choice for strategic and tactical grade applications that demand long-term navigation in environments where the use of GNSS (global navigation satellite system) is denied.
A fiber optic gyroscope uses the properties of light in a closed circuit to estimate changes in orientation. Two beams of light are sent in opposite directions in a fiber optic coil. As the vehicle rotates, the beam traveling against the rotation experiences a slightly shorter path delay than the other beam, a phenomenon called the Sagnac effect. The difference in phase shift between the two beams is then used to estimate the rate of rotation.
For an INS, typically three gyroscopes on axes orientated orthogonal to one another, combined with accelerometers provide the sensed acceleration and rotation across six degrees of freedom (6DOF). Combined with an estimate of gravity, a velocity is established, which integrated over time allows a position to be maintained for the purpose of dead reckoning.
FOG-based navigation systems are often used with other types of sensors to provide robust estimates of position and heading. Traditional systems have used magnetometers to estimate true north, although these are very vulnerable to interference from numerous sources, and lack sufficient accuracy for precision or high-speed applications.
Dual-antenna GNSS-based systems are increasingly preferred to magnetometer-based compasses to provide the best available heading accuracy for vehicles and systems with a clear view of the sky. High-performance FOGs can provide an advantage to these systems, allowing very small changes in heading to be measured that would not be detectable using dual-antenna heading methods alone.
FOGs and similar high-grade gyroscope technologies also offer another means of determining heading that is not available to MEMS-based systems: the ability to establish a heading via north-seeking based on the rotation of the earth (gyro compassing). This purely passive method allows a system to measure the slight changes of orientation that occur as the vehicle or system rotates around the earth’s axis. In addition to operating effectively where GNSS is unreliable or denied, these are relatively immune to magnetic interference. They do however lose accuracy at very high latitudes.
- Extremely precise rotation measurement
- Reliability and a long lifetime due to lack of moving parts
- High-performance long-term navigation when no absolute source of position is available
A MEMS (micro-electromechanical systems) gyroscope is a smaller, lightweight gyroscope made from microscopic devices. MEMS gyroscopes have a significantly lower SWaP-C, meaning they’re preferred in applications where a small payload is necessary. FOGs have higher inertial performance and lower bias, making them the preferred solution for GNSS-denied environments or high accuracy applications such as antenna pointing.
Like a FOG, a ring laser gyroscope (RLG) is an optical gyroscope that utilises the Sagnac effect. The key difference between the two is in how they are constructed, as ring laser gyroscopes use lasers that travel through a system of mirrors to determine a vehicle’s rotation, rather than a simple fiber coil. As well as requiring extremely high manufacturing accuracy and special mirrors, RLGs are gas-filled and require the laser to be “dithered”, or mechanically vibrated in order to prevent laser lock-in from erasing small rotations.
While both gyroscopes operate on similar principles and are exceptionally accurate, the older ring laser gyroscope technology is more delicate given its construction, requires more maintenance, and is typically more expensive. In contrast, a fiber optic gyroscope is a solid-state piece that doesn’t utilise a dithering mechanism, meaning it won’t produce any acoustic vibrations, making it more durable and reliable than an RLG. Furthermore, the applications of fiber optic gyroscopes can be scaled by altering the length and diameter of the fiber optic coil.
The fiber optic gyroscope technology is conducive to a growing variety of applications where accurate headings and navigation are crucial. This includes manned vehicles and unmanned vehicles.
- Surface marine vehicles: Marine surveying vessels use FOGs to determine pitch, roll, and heading in real-time as well as establishing accurate position data for Unmanned Underwater Vehicles (UUVs). They are particularly useful for side-scan sonar and similar applications.
- Subsea vessels: Manned vehicles (such as submarines) and UUVs (unmanned underwater vehicles), including autonomous underwater vehicles (AUV) and remotely operated vehicles (ROV), rely on fiber optic gyroscopes for accurate navigation in an incredibly challenging and hazardous environment with minimal or unreliable sources of absolute position. ROVs and AUVs used for hydrography benefit greatly from the precision of FOGs in particular.
- Aviation: Helicopters can be subjected to electromagnetic interference and benefit greatly from FOG-based INS. Unmanned Aerial Vehicles (UAVs) and commercial aircraft often require FOG-grade performance to mitigate the risks of losing GNSS position while in flight. The accuracy of roll, pitch and yaw data is essential to safely operate the aircraft.
- Defense: Land-based defense vehicles must not be reliant on GPS/GNSS due to the risk of local jamming or spoofing of these signals, or simply terrain blocking or altering positioning data from satellites. FOG-based INS can allow these vehicles to operate seamlessly, preventing adversaries from gaining an advantage from these tactics.
- Space exploration: Fiber Optic Gyroscopes are well suited to space applications due to their long lifespan, little need for maintenance, minimal power consumption, and precise navigational data.
- Robotics: Orientation data from a fiber optic gyroscope is used for robotic navigation, ensuring safe operation as adjustments are made for any changes in velocity, position, or acceleration.