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6Enhanced stability in WGM microresonator coupling using
reinforced tapered fiber
K.N. Min'kov12*, D.D. Ruzhitskaya1, K.E. Lakhmanskiy12, O.V. Borovkova13
1-Russian Quantum Center, 121205, Moscow, Skolkovo, Innovation Center territory
2- Moscow Institute of Physics and Technology, Dolgoprudny, Russia 3- Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia
This study introduces a method for reinforcing tapered fibers to ensure stable coupling with whispering gallery mode (WGM) microresonators. It has been found that a slight curvature in the tapered fiber enhances its fixation, thereby preventing adhesion between the fiber and the microresonator. Experimental evidence demonstrates the successful excitation of WGMs using a reinforced curved tapered fiber with a curvature radius of approximately 15 mm.
Optical microresonators have diverse applications in optoelectronics and quantum computing, including their use in optical comb generators, narrowband laser sources, and visible-range LIDAR systems [1]. Practical implementations require that both the microresonators and their associated coupling elements, which are essential for exciting the microresonator, maintain stable properties and fixed configurations.
Various coupling methods exist for optical microresonators [2]. The most effective techniques involve the tunneling of an evanescent field from either a prism coupler or a tapered fiber to the whispering gallery mode of an optical microresonator [3]. Tapered fibers are advantageous because they can operate in a single-mode regime, facilitating the achievement of critical coupling. However, there are challenges in adjusting and operating tapered fibers. Tightly stretched tapered fibers are prone to vibrations and can even adhere to the microresonator, disrupting the conditions necessary for the excitation of whispering gallery modes.
In this study, we present a method for securing tapered fibers that prevents undesirable vibrations and adhesion to the microresonator's lateral surface. The tapered fiber is produced using a fully automated version of the technique described in [4], allowing the creation of subwavelength tapered fibers with adiabatic properties along their length. This method enabled the fabrication of a quartz tapered fiber with a waist diameter of 400 nm and a length of up to 100 mm. The automated process ensures a transmission loss of 0.4 dB at a wavelength of 1550 nm.
Initially, the fabricated tapered fiber was fixed on a stand to form an arc, and then it was securely anchored. The curvature radius of the fabricated fiber is approximately 15 mm. Notably, this slightly bent waveguide does not exhibit vibrations or adhere to the microresonator. The quartz fiber's high stiffness helps maintain its curved shape. Experimental results demonstrate the excitation of WGMs at telecom wavelengths using the reinforced curved tapered fiber.
In summary, we propose a microresonator coupling element that utilizes a curved tapered fiber approaching the microresonator. We have developed a fabrication and fixation technique for this fiber on a stand. Our experimental results demonstrate the excitation of whispering gallery modes (WGMs) at telecom wavelengths using the reinforced curved tapered fiber, which has a curvature radius of approximately 15 mm.
[1] K.J. Vahala, Optical microcavities, Nature, Vol. 424, pp. 839-846, (2003).
[2] P. Solano, et al, Optical Nanofibers: A New Platform for Quantum Optics, Adv. At. Mol. Opt. Phys., 66, 439-505, (2017).
[3] M.L. Gorodetsky, Optical Microresonators with Giant Quality- Factor, Fizmatlit, (2011).
[4] A.D. Ivanov, K.N. Min'kov, A.A. Samoilenko, Method of producing tapered optical fiber, Journal of Optical Technology, Vol. 84, Issue 7, pp. 500-503, (2017).
