Recently, a research team from Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS), proposed a new method of using surface mode coupling to adjust the thermal coefficient of delay (TCD) of photonic-bandgap hollow-core fiber (PBG-HCF) in an extended range. The relevant results have been published on Optics Express on Jan. 3, 2022.

The temperature dependence of group delay in the conventional optical fiber comes from the intrinsic properties of the material which is hardly eliminated. As a result, the fluctuation of ambient temperature inevitably results in thermal-related phase noise on light transmitted through the fiber, which is hazardous for propagation time sensitive applications.

After a series of numerical simulations, researchers found that the redshift of the avoided crossing of surface mode coupling can significantly tune the TCD of PBG-HCF from -400 ps/km/K to 400 ps/km/K, approximately -120 ppm/K to 120 ppm/K. The local loss introduced by SM coupling is predicted to be moderately low showing the promising potential of long length fiber application in practical use.

Researchers point it out that the application of their method for PBG-HCF design for the practical TCD control over a long fiber length will depend on the suppression of increase of local loss by surface mode coupling, which will take more efforts to explore in both theory and experiment in future.

The research was supported by the International Science and Technology Cooperation Program, the National Natural Science Foundation of China, and the Key Research Program of Frontier Sciences CAS.