Ring Laser Gyroscopes and Fiber Optic Gyroscopes: Principles, Types, and Performance Comparison

Modern inertial navigation systems rely heavily on high-precision rotation sensors. Among them, the Ring Laser Gyroscope (RLG) and Fiber Optic Gyroscope (FOG) are the most widely used due to their stability, accuracy, and reliability.

This article provides a clear overview of how these gyroscopes work, the different classifications of fiber-optic gyros, and how their performance compares internationally.

1. What Is a Ring Laser Gyroscope (RLG)?

The academic name of a laser gyroscope is the Ring Laser.
Its internationally recognized term is Ring Laser Gyroscope (RLG).

An RLG is essentially a He-Ne (Helium–Neon) laser with a closed ring cavity.
Inside the cavity, two laser beams propagate in opposite directions. When the system rotates, the optical path lengths change asymmetrically, resulting in a measurable frequency difference.

This physical mechanism is known as the Sagnac Effect — the same principle used in all optical gyroscopes.

Why RLGs Are Important

Large dynamic range

Very high accuracy

Exceptional long-term stability

Mature and proven in aerospace and defense applications

2. Fiber Optic Gyroscopes (FOG): Types and Measurement Principles

Fiber Optic Gyroscopes also rely on the Sagnac Effect, but instead of a laser cavity, light travels through a long coil of optical fiber.

FOGs can be categorized into three main types:

2.1 Resonant Fiber Optic Gyroscope (RFOG)

Measures frequency difference between counter-propagating beams

Uses a resonant optical cavity

Potential for extremely high accuracy

Favored for next-generation navigation systems

2.2 Interferometric Fiber Optic Gyroscope (IFOG)

Measures phase difference

Currently the most mature and widely used type

High reliability and good cost-performance ratio

2.3 Brillouin Scattering Fiber Optic Gyroscope (BFOG)

Measures phase difference

Utilizes Brillouin scattering effects in optical fiber

Suitable for high-precision applications

3. Open-Loop vs. Closed-Loop FOG Architecture

Open-Loop Fiber Optic Gyro

Relatively simple design

Small dynamic range

Poor scale-factor linearity

Lower accuracy

Best for cost-sensitive or mid-performance applications.

Closed-Loop Fiber Optic Gyro

More complex design

Large dynamic range

Excellent scale-factor linearity

High accuracy

Widely adopted in aerospace, robotics, marine, and unmanned systems.

4. RLG vs. FOG: Performance Comparison

5. Accuracy Levels: Domestic vs. International

China (Domestic):

RLG accuracy: >5 ppm

Bias stability: 0.01–0.001°/h

International (Top Tier):

RLG accuracy: <1 ppm

Bias stability: 0.0001°/h

These specifications place foreign high-end RLGs among the most accurate inertial sensors available in the world.

6. Summary

Both Ring Laser Gyroscopes and Fiber Optic Gyroscopes are indispensable components of high-performance inertial navigation. Their differences can be summarized as:

RLGs provide superior precision and long-term stability, making them ideal for aerospace and strategic systems.

FOGs offer a flexible, scalable approach with multiple architectures (IFOG, RFOG, BFOG) suited for various performance levels.

Closed-loop FOGs bridge the gap between cost and performance, dominating mainstream industrial and UAV applications.

With continuous innovation in resonant and Brillouin FOG technologies, and steady advancement of RLG manufacturing processes, optical gyroscopes will continue to set new standards in inertial navigation accuracy.