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Abstract
In this Letter, we propose a simple and high-precision differential modal group delay (DMGD) characterization method for few-mode fibers (FMF) by using the frequency-modulated continuous wave. Since the detected signals are located at the low-frequency range, our DMGD characterization method waives the use of expensive equipment, such as vector network or optical spectrum analyzers. Due to the high linearity of the used Mach–Zehnder modulator, our DMGD measurement is free from the complex auxiliary interferometer, leading to an improvement of characterization precision. Meanwhile, we propose a novel spectrum recovery algorithm to overcome the shortcoming that the traditional fast Fourier transform (FFT) method is incapable to deal with spectrum features arising in a periodic signal. Therefore, the characterization precision is no longer limited by the FFT length. When a commercial 23299.8 m two-mode fiber is used in the experiment, the DMGD measurement of ${{\rm LP}_{11}}$ mode relative to ${{\rm LP}_{01}}$ mode has a high precision of $\pm {0.007}\;{\rm ps/m}$ over the C-band. Our proposed method shows the potential for characterizing the wavelength-dependent DMGD of FMF with more than two LP modes.
© 2021 Optical Society of America
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