What Is Fiber Optic Gyroscope (FOG)? How Does It Work? | STABLE INERTIAL SYSTEMS LTD.

The Fiber Optic Gyroscope (FOG) is a high-end solid-state inertial sensor that completely abandons traditional mechanical rotor structures and conventional vibrating MEMS gyro architectures. Independently engineered and optimized by our technical team, this core precision optical inertial device adopts pure optical fiber transmission sensing technology to accurately capture and measure the angular velocity of moving carriers, delivering unparalleled performance for high-reliability inertial navigation scenarios.

Different from mainstream MEMS gyroscopes and mechanical gyroscopes on the market, our self-developed FOG features zero mechanical moving parts, ultra-low long-term drift, instantaneous cold start, and extreme environmental stability. It effectively fills the precision gap of commercial-grade inertial sensors and meets the stringent technical requirements of aerospace, deep-sea exploration, marine navigation, and high-precision industrial measurement that ordinary inertial devices cannot support.

Our FOG boasts an ultra-wide dynamic measurement range with outstanding sensing flexibility. It can precisely capture ultra-slow rotation equivalent to the Earth’s rotation and rapidly respond to high-speed dynamic rotation of aircraft, unmanned vehicles, and marine equipment. Supporting zero-delay startup with no warm-up time required, our fiber optic gyroscopes deliver stable output instantly after power-on, which is critical for fast-response, high-precision mission scenarios.

Based on structural design and application positioning, our FOG series are divided into single-axis and three-axis configurations. The single-axis FOG adopts a compact lightweight structure with low cost and simple calibration procedures, perfectly matching single-direction attitude stabilization and basic navigation systems for medium-end industrial and unmanned equipment. The three-axis FOG integrates full-dimensional optical sensing design, realizing complete 3D attitude tracking and ultra-high comprehensive navigation accuracy, serving high-end full-position navigation equipment such as manned aircraft, long-endurance UUVs, offshore vessels, and deep-sea detection platforms. With superior comprehensive performance, our FOG products are widely deployed in global high-precision inertial measurement and navigation fields.

All our fiber optic gyroscopes operate based on the classic Sagnac effect, the fundamental physical principle of optical inertial sensing, ensuring non-contact, high-stability, and drift-suppressed rotation measurement without mechanical interference.

The working mechanism can be intuitively illustrated with a standardized physical analogy: two light beams act as precise "high-speed runners", and the tightly wound high-precision optical fiber coil serves as a closed circular optical transmission track. When the gyroscope is in a static state, two identical low-coherence light beams emitted by the internal stable light source are split and propagate clockwise and counterclockwise along the fiber loop respectively, returning simultaneously with zero phase difference.

Once the carrier rotates, the effective optical transmission path of the two reverse-propagating light beams changes synchronously. One beam travels an extended optical path while the other travels a shortened path, generating a tiny but detectable time difference and phase shift. Strictly proportional to the carrier’s real-time angular velocity, this phase difference is captured, analyzed, and calculated by our self-developed signal demodulation algorithm system.

It is worth emphasizing that the Sagnac phase shift generated by our FOG originates purely from the change of effective optical path under rotational motion, rather than light speed variation. This core physical advantage eliminates fundamental measurement errors, endowing our FOG series with ultra-high long-term measurement stability and repeatability, far exceeding the accuracy limit of conventional inertial sensors.

Our FOG is a highly integrated optoelectronic system composed of five core in-house developed and calibrated components. Every structural design and technological process is independently optimized by our R&D team to realize precise coordination from optical signal transmission to electrical signal output, converting tiny optical phase changes into high-precision, high-stability angular velocity data.

• Professional Stable Light Source Equipped with customized SLD/ASE low-coherence light sources independently screened and calibrated in-house, delivering ultra-stable and low-noise optical output. It suppresses optical stray interference from the source, ensuring long-term consistent measurement accuracy and anti-attenuation performance for long-duration navigation missions.
• High-Precision Optical Coupler & Y-junction Waveguide Adopting self-calibrated 2*2 X-type coupler and high-stability Y-waveguide components, achieving equal-beam light splitting and efficient light combining. It integrates precise polarization control and linear phase modulation functions, providing a reliable optical foundation for high-sensitivity Sagnac effect detection.
• High-Grade Wound Fiber Coil (Core Sensing Unit) The core sensing component adopts ultra-low-loss special optical fiber with multi-layer dense winding technology independently optimized by our team. Reasonable fiber length and coil turns amplify subtle Sagnac phase differences significantly, greatly improving sensor resolution and detection sensitivity. Our exclusive winding process and fixed structural design effectively resist external vibration and temperature deformation, avoiding sensing performance attenuation.
• High-Sensitivity Photodetector Customized photoelectric sensing components capture tiny interference light intensity changes, converting subtle optical phase differences into weak electrical original signals with ultra-high signal-to-noise ratio, providing pure and effective raw data for subsequent algorithm solving.
• Self-Developed Signal Processing Circuit System Our exclusive adaptive demodulation, noise filtering, and temperature compensation circuits realize amplification, calibration, and error compensation of original electrical signals. It eliminates environmental noise interference in real time and finally outputs stable, high-precision, and available angular velocity and attitude data.

Compared with traditional mechanical gyroscopes and commercial MEMS gyroscopes, our independently developed FOG series have irreplaceable core strengths in high-end inertial navigation fields:

1. Full Solid-State & Zero Wear: No mechanical rotating parts or vibration structures, zero mechanical wear and fatigue loss, greatly extending service life and reducing post-maintenance costs.
2. Ultra-Low Long-Term Drift: With full-temperature range calibration and self-adaptive error compensation algorithms, it maintains extremely low drift during long-duration continuous operation, solving the core pain point of cumulative errors of conventional inertial sensors.
3. Instant Startup & Fast Response: No preheating required, achieving real-time navigation output after power-on, fully adapting to rapid-response mission scenarios.
4. Extreme Environmental Adaptability: Excellent vibration resistance, shock resistance, and wide-temperature stability, supporting long-term stable operation in harsh environments such as high altitude, deep sea, high humidity, and strong vibration.

Restricted by high-precision optical devices and ultra-long fiber coil processes, our FOG features higher precision and reliability but has relatively larger volume, higher manufacturing cost, and slightly higher power consumption compared with miniature consumer-grade MEMS sensors. Therefore, it is not applicable to ultra-miniature, ultra-low-power portable civilian devices, forming a differentiated product positioning with MEMS inertial sensors.

In the global inertial navigation market, our FOG and SI-MIMU MEMS series form a complete product matrix with differentiated positioning and complementary performance. Our self-developed SI-MIMU MEMS IMUs focus on miniaturization, low cost, and mass civilian scenarios such as commercial UAVs, industrial robots, and low-speed autonomous vehicles. In contrast, our fiber optic gyroscopes target high-end precision scenarios, covering aerospace equipment, marine ships, deep-sea detection systems, and high-precision surveying and mapping inertial navigation systems.

As a core high-end inertial sensor independently developed by our team, our FOG series breaks overseas technical monopoly, realizes full domestic independent controllability of core optical inertial technology, and provides reliable, high-precision, cost-effective inertial navigation solutions for global high-end intelligent equipment and marine aerospace industries.