High-Precision and Synchronous Measurement of Fiber Length and Dispersion Using Optical Frequency Comb-Based Time-Delay Dispersion Interferometry

Optical fiber is the cornerstone of the contemporary inter-network and has produced profound and far-reaching effect on modern information society ever since it was invented. The detection of key parameters of optical fiber such as length, refractive index, and chromatic dispersion is of great significance to ensure the quality and security of communication network. Here, a synchronous, fast, and high-precision measurement method for the length and dispersion of optical fibers is proposed, where the time-of-flight measurement and spectral interference are organically combined using an optical frequency comb (OFC) with the assistance of a modulated narrow linewidth single-frequency laser. The length and the dispersion coefficient distribution can be preciously obtained directly and simultaneously by measuring only single-frame interference spectrum. The excellent time–frequency characteristics of the OFC and our unique algorithm enable the realization of extremely high measurement accuracy and resolution: a resolution of $10~\mu \text{m}$ @ 500 m and an accuracy of 1.5 cm ( $1.364\times 10^{-6}$ relatively) @ 11 000 m, as well as a dispersion measurement accuracy of 0.5%. The method boasts rapid measurement, ample bandwidth, elimination of scanning, and exceptional precision, making it highly applicable in both optical communication and optical fiber sensing systems.

I. Introduction

Optical fibers play a vital role in modern society, building high-speed information networks that tightly connect the world [1], [2]. In optical fiber system, the measurement of fiber key parameters is the guarantee of system performance, and the dispersion is one of the key parameters that determine the transmission distance, maximum modulation rate, multiplexing amount of channel, bit error rate (BER), and so on [3]. Therefore, the dispersion of fiber must be measured accurately. In general, the accumulated dispersion is determined by the product of two parameters, namely, the length of the fiber and the chromatic dispersion coefficient of the fiber. Hence, in order to calibrate the dispersion, the two parameters must be accurately measured [4], [5], [6], [7]. At the same time, the length of the fiber itself is also an important parameter, which is indispensable in the application scenarios, such as line fault diagnosis and distributed sensing [8], [9].