Crosstalk in Two Intersecting Optical Microfibers

Structural hybridization and size miniaturization of integrated photonic devices are among the hotspots of photonics research field. The crosstalk between densely arranged subwavelength-width optical waveguides such as optical microfibers has become an important issue. Here we investigate a common case of crosstalk in two intersecting subwavelength-diameter optical microfibers at 1550-nm wavelength by numerical simulations and experiments, and obtain the dependence of coupling efficiency and crosstalk on modal polarizations, intersection angle, fiber diameter and separation of the two fibers, respectively. The simulation results show that, the crosstalk decreases with increasing intersection angle and separation between the two microfibers. Especially, for single-mode microfibers, the crosstalk is lower than 1% (i.e., better than -20 dB) when the intersection angle is larger than 60°, and can be minimized to less than 0.05% (i.e., better than -33 dB) for perpendicular intersection (i.e., intersection angle of 90°). However, the dependence of crosstalk on fiber diameter is not monotonous, typically, from the single-mode cutoff diameter, the crosstalk increases with decreasing diameter until reaching a maximum, and decreasing afterward. To verify the simulation, we have experimentally measured the angle-dependent crosstalk between contacting microfibers with typical diameters. With increasing intersection angle, the crosstalk drastically decreases to a negligible value (less than -41 dB for vertically intersecting microfibers), which is consistent with the simulation results. Our results offer a valuable reference or guideline for designing compact optical interconnection and integration with optical microfibers or other subwavelength-width waveguides alike.