1. Introduction
When GPS signals are weak or unavailable, gyroscopes take charge of navigation. Inertial sensors always face a balance between cost and accuracy: basic sensors are cheap but accumulate errors fast, while high-end sensors are accurate but costly. Fiber Optic Gyroscope (FOG) solves this problem with two simple and practical designs: open-loop FOG and closed-loop FOG. The two types serve different usage scenarios, covering daily industrial equipment and high-precision aerospace navigation.
2. How Does FOG Work?
The working principle of FOG is easy to understand. Simply put, it uses light to detect rotation. Inside the gyroscope, two beams of light travel in opposite directions around a coiled optical fiber. When the device stays static, the two beams return at the same time. When the device rotates, one light beam travels a slightly longer path than the other.
FOG captures this tiny light path difference and calculates the rotation speed accurately. Unlike traditional mechanical gyroscopes, FOG has no moving parts. This makes it durable, stable and almost maintenance-free for long-term use.
3. What Is Open-Loop FOG (O-FOG)
Open-loop FOG is the basic, cost-friendly version of fiber optic gyroscopes. It adopts a simple structure and circuit design, directly reading optical signals to measure rotation. It features small size, light weight and low power consumption.
It offers medium and stable accuracy, fully meeting the needs of most industrial and light tactical devices. It works well for short-term operation and scenarios with regular GPS calibration. It is the most cost-effective choice for civilian and commercial equipment.
Core Advantages of O-FOG
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Low cost, suitable for mass production and large-scale deployment
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Compact and lightweight, easy to install in small devices
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Low power consumption, perfect for battery-powered equipment
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Stable performance for daily industrial and drone applications
4. What Is Closed-Loop FOG (C-FOG)
Closed-loop FOG is the upgraded high-precision version. It adds a real-time feedback adjustment function. It automatically corrects signals during operation to keep measurement results accurate and stable at all times.
With ultra-high precision and extremely small error drift, C-FOG can work stably for a long time without GPS signal correction. It adapts to various harsh working environments and is specially designed for high-end precision navigation tasks that require zero error tolerance.
Core Advantages of C-FOG
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Ultra-high precision for professional and strategic navigation scenarios
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Super wide working range, stable for both slow and fast rotation
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Strong resistance to temperature change and vibration
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Almost no accumulated error, supporting long-term independent navigation
5. Simple Performance Comparison
5.1 Accuracy & Error Control
Open-loop FOG has medium accuracy with slight error accumulation after hours of operation, so it needs regular GPS correction. Closed-loop FOG has negligible errors. It can maintain high precision for days or weeks without external signal calibration, ideal for long-endurance missions.
5.2 Adaptability to Fast Movement
Open-loop FOG is suitable for low and medium-speed operation. Its accuracy will decrease under extreme fast rotation. Closed-loop FOG keeps stable and accurate output under all motion states, including high-speed and violent maneuvering, fitting for high-dynamic equipment like aircraft and missiles.
5.3 Environmental Stability
Open-loop FOG is suitable for conventional stable environments and is easily affected by extreme temperature and strong vibration. Closed-loop FOG has excellent environmental adaptability, working stably in the temperature range of -40°C to +85°C, and can resist severe vibration and harsh outdoor conditions.
5.4 Size, Power & Cost
Open-loop FOG has simple structure, small size, light weight and low power consumption with a competitive price, perfect for cost-sensitive projects. Closed-loop FOG has more precise and complex internal structures, so it is larger, consumes more power and costs more, but brings top-level stability and precision.
6. Application Scenarios
6.1 Open-Loop FOG Applications
Open-loop FOG is the preferred choice when cost, size and power saving are priorities. It is widely used in civilian drones, intelligent robots, automated handling equipment, industrial detection devices and ground vehicle attitude stabilization systems.
6.2 Closed-Loop FOG Applications
Closed-loop FOG is used for high-end precision scenarios that require high reliability and long-term stable navigation. Typical applications include submarine underwater navigation, aerospace equipment, missile guidance, fighter attitude control and high-precision surveying and mapping equipment.
7. Conclusion
Open-loop FOG and closed-loop FOG serve different market demands and do not replace each other. Open-loop FOG focuses on cost performance and miniaturization for civilian and industrial fields. Closed-loop FOG focuses on ultra-high precision and strong environmental adaptability for high-end defense and aerospace fields. Users can choose the right FOG type according to their actual working scenarios, task duration and budget needs.
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