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What Is Y-Waveguide? Core Component of FOG

2026-07-21

1. Overview of Y-Waveguide

The Y-waveguide is a key integrated optical component made of lithium niobate crystal. It is an essential core part for closed-loop fiber optic gyroscopes (FOG). Unlike ordinary optical parts, a single Y-waveguide integrates three important functions: light splitting and combining, polarization control, and phase modulation. It greatly improves the FOG’s accuracy, stability and working range, and directly decides the overall performance of fiber optic gyroscopes.

2. Three Core Functions of Y-Waveguide

2.1 Light Splitting and Combining

The Y-waveguide has a special Y-shaped structure to manage the optical path of FOG. The light from the gyroscope’s light source enters the Y-waveguide and is evenly split into two beams. These two beams travel clockwise and counterclockwise around the fiber coil separately. After passing through the fiber coil, the two beams return to the Y-waveguide. It combines them back into one single beam and sends it to the photodetector. This steady light splitting and combining enables the FOG to generate standard optical interference signals for rotation measurement.

2.2 Polarization Control

Steady light polarization is very important for accurate gyroscope measurement. The Y-waveguide can adjust the input light into a stable and unified polarization state. During light transmission, it filters out abnormal light signals and blocks interference caused by unstable polarization. This simple but effective control greatly reduces measurement errors and improves the long-term working stability of FOG.

2.3 Phase Modulation and Closed-Loop Control

Made of professional lithium niobate material, the Y-waveguide has stable electro-optical properties. When voltage is applied to its electrodes, the internal optical properties change slightly. This creates a controllable phase difference for the transmitted light beams.

This function supports the core closed-loop working mode of high-precision FOG. When the gyroscope detects rotation and generates a Sagnac phase shift, the system feeds back voltage to the Y-waveguide. The Y-waveguide produces an opposite phase difference to offset the rotation-caused signal deviation. This keeps the gyroscope working in a stable and accurate state at all times. With this closed-loop adjustment, FOG achieves high linearity, wide measuring range and reliable output in various working environments.

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