J. Eur. Opt. Society-Rapid Publ. 22, 26( 2026) 273
Fig. 4.( a) Evolution of the cladding( blue triangles) and core diameters( red dots) versus the z position in the taper drawn from fiber 1. Error bars on U core are ± 0.1 lm( smaller than the size of the cladding marks).( b) Evolution of the ratio of the core and cladding diameter R = U core / U clad versus the z position in the taper in the area where the core diameter is measurable. Error bars are smaller than the size of the marks(± 0.1 %).
Fig
. 5.( a) Evolution of the cladding( blue triangles) and core diameters( red dots) versus the z position in the taper drawn from fiber 2. Error bars on U core are ± 0.5 lm( smaller than the size of the cladding marks).( b) Evolution of the ratio of the core and cladding diameter U core / U clad versus the z position in the taper in the area where the core diameter is measurable. Error bars are smaller than the size of the marks(± 0.1 %).
based on measurement of the chemical composition of the taper( synchrotron or X-rays for instance) would be necessary to confirm this assumption. Moreover, fewer data points were acquired, which prevents a definitive comparison. Similar measurements were performed on 3 identical microfibers drawn from fiber 1 and 2 from fiber 2, showing the same results.
4 Conclusion and perspectives
To our knowledge, we report for the first time measurements of the evolution of the cladding and core diameters along the tapered section of a microfiber fabricated using the classical pull-and-brush technique, obtained by LC- OCT. This imaging technique is particularly attractive, as it does not require complex preparation of the samples and enables fast high-sensitivity measurements with micrometer-scale resolution of semi-transparent objects such as silica tapers.
The results show that, contrary to assumptions commonly used in numerical models, the ratio of the core to cladding diameters is not constant along the taper. We attribute this behavior to both the fiber origin and the fabrication process. Moreover, the step-index is found to decrease, at least down to a value of 10 �4, corresponding to the detection limit of LC-OCT. At last, for both fibers, we measured that the critical diameter is not obtained for a diameter of 40 lm as currently used but depends on the single mode fiber: for fiber 1, this diameter is 67 lm whereas for fiber 2, it is 91 lm. These results can be used to optimize the shape of the tapers and to calculate more precisely the effective index of the propagation mode in the taper.
Future work will focus on collecting additional data to obtain reliable statistics and on investigating other types of optical fibers( e. g., polarization-maintaining fiber, visible single-mode fibers, fibers with other silica dopings,...). These results will enable the refinement of numerical models of mode propagation in tapers, particularly for the design and optimization of adiabatic taper profiles.
Funding The work was supported by internal fundings.
Conflicts of interest
The authorsdeclare that there areno conflicts of interest related to this article.
Data availability statement This article has no associated data generated.