Thermal noise suppression in large fiber-optic gyroscopes

Large fiber-optic gyroscopes (FOGs) are used in gravitational wave detectors to dampen the effects of small ground vibrations, in measuring the earth’s velocity for universal time, and as a direct sensor for seismic waves. With such broad applications in high precision fields, it is important to reduce noise as much as possible.

Temperature is the most significant environmental factor causing the degradation of large FOGs, so Chen et al. propose using high-order frequency modulation to suppress FOG noise caused by temperature variation.

Under varying temperature conditions, the optical fibers that constitute the gyroscope extend and contract, altering its refractive index. This creates a phase shift and causes the output to drift.

In long fiber-optic coils, like those used in high precision fields, temperature variation has more impact on the FOG outputs. In FOGs longer than 5.7 kilometers, the thermal phase noise replaces the light source’s relative intensity noise as the dominant noise.

“The method of high-order frequency modulation is proposed in our work. We up-convert the operating frequency of FOGs to a frequency with lower thermal phase noise. In our experiments, this method reduced the temperature sensitivity of large FOGs by 32 times compared with the conventional eigenfrequency modulation,” said author Yanjun Chen.

Not only is this method effective, it does not require any additional equipment to operate, making it an easily implemented and low-cost solution.

This study also found that the conventionally studied mechanism for temperature degradation in FOGs does not account for all the thermal noise.

“Digging deeper into other mechanisms will not only help to understand the complex temperature-caused degradation phenomenon but also help to propose more targeted methods to suppress the temperature effects,” said Chen.

Source: “Suppression of effects of temperature variation by high-order frequency modulation in large fiber-optic gyroscopes,” by Yanjun Chen, Yuwen Cao, Lanxin Zhu, Yan He, Wenbo Wang, Huimin Huang, Xiangdong Ma, and Zhengbin Li, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0135848 .