Research On Construction And Optical Capture Characteristics Of All-fiber Bessel-like Beams

Durnin firstly proposed the concept of non-diffracted beams in 1987,deduced the mathematical form of Bessel beam.The transverse field distribution of Bessel beams is determined by Bessel function.The zero-order Bessel beams manifests as a central bright spot and several concentric rings in space.Moreover,the Bessel beams has been widely used in optical tweezers because of its unique light field distribution,non-diffracting and self-healing properties.The production of the optical trap depends on the balance of the optical gradient force and scattering force generated by the strong laser convergence.Most of the methods to realize the traditional optical tweezers and Bessel beams are based on the spatial optical path,which inevitably causes the system to be bulky and complicated.Through the combination of various optical fibers,mode transmission and phase modulation in optical fiber can be used to generate new Bessel-like beams.The research work in this article aims to combine Bessel beams with optical fiber tweezers technology.Through the unique light field distribution of Bessel beams,particles can be transmitted along self-accelerating beams and large-size particles can be captured.In this paper,the origin and development of Bessel beams and optical tweezers are briefly introduced,and the generation methods and applications of Bessel beams are listed.The characteristics and differences of traditional optical tweezers and optical fiber optical tweezers are discussed.This paper expounds the characteristics and mathematical mechanism of Bessel beams,and demonstrates in detail the basic principle of Bessel-like beams produced by optical fiber combination.The single-beam gradient force optical trap is briefly described,and the calculation method of the optical trap force based on the law of conservation of electromagnetic field momentum is introduced and deduced.The simulation method based on the finite difference time domain method is briefly described,which provides theoretical support for the research work of this article.In this paper,a solution based on the all-fiber self-accelerating Bessel-like beams to achieve 2×2 channel particles curve trajectory transport is proposed.A fiber probe composed of a dual-core fiber,a hollow capillary fiber and a coreless fiber is prepared and an experimental system is built.The multi-frustum cascade shape of the coreless fiber realizes the modulation of the beams,and produces two Bessel-like beams with transverse self-acceleration properties and crosses at the front end of the fiber.By adjusting the optical power ratio of the two beams,the yeast cell parabolic trajectory transportation and controllable steering is realized.Since the solution we proposed is based on an all-fiber probe completed by optical fiber assembly,it has a higher degree of integration than a multi-fiber array and spatial optical path system,and the dual-channel self-accelerating beams is easier to control the transport direction of yeast cells.In this paper,a method for trapping large-size particles based on all-fiber hollow Bessel-like beams is designed,which breaks through the particle size limitation of existing optical fiber tweezers.Through a step multimode fiber with a special refractive index profile,a hollow Bessel-like beams without a central bright spot is constructed,which is more conducive to achieving a coaxial multi-point strong convergence of concentric rings at the front end of the fiber,extending the trapping area,and the superposition of the optical trapping force realizes the stable three-dimensional capture of particles with a diameter of 32 μm.At present,most optical fiber tweezers can only capture small-sized particles with a diameter of about 5μm,while the gravity of large-sized particles with a diameter greater than 30 μm is about 200 times that of the former.The stable three-dimensional trap of particles with a diameter of 32μm shows that compared with the traditional optical fiber tweezers,optical fiber tweezers probe proposed in this paper has a larger trapping force and effective trapping range.