Design and fabrication of collimating ball lensed fiber for the system of optical radiation output from radiophotonic components

The output of optical radiation from the source into a fiber optic cable is an important problem in photonic integrated circuits packaging and implementation of hybrid integration technology. Optical radiation output losses are caused by the mismatch of the mode spot of radiation in the optical fiber and in the waveguide as well as by the deviations of optical elements from the optimal mounting position that occur during the assembly of photonic integrated circuits. This work demonstrates the design, fabrication, and investigation of a lensed optical fiber to solve the problem of coordinated output of optical radiation from radiophotonic components into the fiber. A scheme for outputting optical radiation from a semiconductor laser diode included a discrete ball microlens and a collimating lensed optical fiber. The lensed optical fiber with a lens diameter of 250 μm was formed by arc-fusing a segment of FG125LA fiber which was welded to the SMF-28 fiber to form a coreless insert. A model with coreless inserts of different lengths was proposed to determine the optimal geometrical parameters of the lensed optical fiber that provide a collimated beam of radiation at the exit of the lensed optical fiber. The modeling was performed using the Comsol Multiphysics software package. The optical radiation beam type at the output of the formed ball lensed fiber was verified experimentally. The optimal design of the collimating ball lensed fiber was determined. The fabricated experimental sample of collimating ball lensed fiber allowed to realize the optical scheme for optical radiation output and to investigate the efficiency of the scheme. The implemented optical scheme allows to increase the efficiency of optical power transmission from the source to the fiber by a factor of two compared to the butt coupling. In addition, the developed optical radiation output scheme provides the range of acceptable deviation of its elements from the optimal position by at least 12.8 μm. This value is twice as much as the range of permissible deviation of the elements for the butt connection of the radiation source with the optical fiber. The presented scheme of optical radiation output is recommended to be used with an integral beam expander to increase the efficiency of optical power transmission.