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1Microlenses at the ends of optical fibers that preserve radiation
polarization
A.S. Pankov1*, R.S. Ponomarev1
1-Perm State University, integrated photonics laboratory, Perm 614990, Russia
Abstract: The paper describes a method for creating microlenses based on Panda fibers, while maintaining the radiation polarization. It also presents methods for measuring the key characteristics of these lenses: focal length, mode field diameter (MFD), polarization attenuation coefficient. Funding: This study was funded by "The development of the element base for photonic systems in telecommunications and sensing applications" (grant number [FSNF-2024-0001]).
Introduction
One of the main challenges in integrated optics is the issue of the inextricable connection between optical fibers (OF) and waveguides in a photonic integrated circuit (PIC), which has a characteristic diameter comparable to the wavelength of the guided light [1]. The use of OF with a core diameter of approximately 9 micrometers to dock with PIC with waveguide dimensions of approximately 1.5-2 micrometers results in an increase in optical signal loss. An effective solution to minimizing optical losses when connecting these optical elements is the use of lensed tapered fiber (LTF) with a focal spot size of approximately 2 micrometers. LTF - optical components, which are a fiber-optic guide, on the end of which a microlens is formed [2].
Materials and Methods
For the manufacture of microlenses at the ends of the OF, fiber was used while maintaining the polarization of radiation. The Fujikura FSM-100 welding machine was used to create microlenses. Microlensing occurs in several stages. At the first stage, by continuously exposing the OF to an electric arc, it is softened and stretched until the desired tightness with the required parameters is achieved. Then, in the absence of an electrical arc, the OF breaks in the narrowest area of the constriction. As a result of the breakage, two segments of OF with conical tips are obtained. Additionally, the resulting cones are melted using an electrical arc. The fused section of the optical fiber, under the influence of surface tension forces, forms a symmetrical, convex surface. As a result, a conical lens is created at the end of the fiber.
Polarization-preserving microlenses have the following characteristics: focal length, MFD and polarization attenuation coefficient. The focal length and MFD were measured using the Fabry-Perot method and far-field infrared camera methods, respectively. The polarization attenuation coefficient of a microlens is the numerical difference between the value of this coefficient at the entrance of the lensed fiber and its value at the exit of the lens [3].
Results and Discussion
This paper presents a method for manufacturing and measuring the key parameters of microlenses, with a focal spot size of 2 micrometers. The proposed method makes it possible to obtain lenses with radiation polarization at the output up to 40 dB and a polarization drop in the lens of no more than 3 dB.
[1] Y. Jung, G. Brambilla, D.J. Richardson, Polarization-maintaining optical microfiber, Opt. Lett., vol. 35(12), pp. 2034-2036, (2010).
[2] C.-H. Lin, S.-C. Lei, et al, Micro-hyperboloid lensed fibers for efficient coupling from laser chips, Optics Express, vol. 25(20) pp. 2448024485, (2017).
[3] A.S. Pankov, L.O. Zhukov, R.S. Ponomarev, Measurement of key characteristics of a lensed optical fiber, A special issue of Photon Express Science, vol. 6, pp. 494-495, (2023).
