Analysis of Methods to Break Through the Free Spectral Range Limitation

Abstract

The Free Spectral Range (FSR) is a key intrinsic parameter of interferometric and resonant photonic devices, and it has a trade-off relationship with the device sensitivity and dynamic range of measurement. This trade-off has become a critical bottleneck that limit to improve the performance of fiber optic sensing, integrated photonic filtering, and microcavity optoelectronic devices. Therefore, it has becomean an important research direction in photonic sensing and integrated photonics to break through the FSR limitation while maintaining both high sensitivity and large measurement range. This paper systematically reviews four major technical routes: demodulation algorithms, deep learning approaches, structural design, and material selection and properties. For each route, the implementation principles, research progress, and performance advantages of representative schemes are discussed. Finally, the current challenges are summarized, and the development trend toward multi-technology integration is envisioned.