An all-fiber laser oscillating directly at a single TE₀₁ mode with ring-core fibers

Abstract

Cylindrical vector beams (CVBs) have a wide range of applications owing to their particular polarization characteristics and optical field distributions. For the first time, an azimuthally polarized fiber laser without any polarization controller is proposed and demonstrated experimentally.The scheme is based on a self-designed ring-core fiber and transverse mode filter (TMF). The ring-core fiber can break the degeneracy of LP11 modes and make the TE01 mode propagate stably in the fiber laser.The TMF, which made from the ring-core fiber by depositing a layer of Aluminum on the cladding surface, can effectively suppress the modes other than TE01 mode. The fiber laser can stably operate at TE01 mode with a narrow 30dB linewidth of 0.18nm, which indicates the laser is polarization-maintained.This study opens a new avenue toward the true application of CVBs fiber lasers.Recently, researchers have shown an increased interest in cylindrical vector beams (CVBs) because of their unique axisymmetric polarization and doughnut-shaped optical field distributions [1]. These particular characteristics are highly desirable in a wide range of applications, including material processing [2], surface plasmon excitation [3,4], optical trapping and manipulation [5], electron acceleration [6], high-resolution metrology [7,8], optical storage [9] and mode division multiplexing systems [10][11][12]. The systems of generating CVBs in free space is rather complicated and expensive, which made researchers try to find other simpler and more flexible ways. Compared with free space devices, fiber lasers show the advantages of low cost, compactness, high efficiency, flexibility and excellent heat management. The second order mode (LP11 mode) in few-mode fibers is a linear superposition of four degenerate vector modes, including TM01 (radially polarized), TE01 (azimuthally polarized), HE21 (even) and HE21 (odd) modes. In 2002, Grosjean et al. [13] first generated CVBs in fiber lasers by introducing an offset between a single-mode fiber (SMF) and a few-mode fiber (FMF). Since then, several kinds of methods for generating CVBs in fiber lasers have been proposed and demonstrated,

Stable generation of orbital angular momentum mode with an all-fiber laser

“…To achieve this, we designed and fabricated a ring-core fiber that breaks the degeneracy of LP 11 mode to support stable propagation of OAM mode (HE 21 ). 33) A long-period fiber grating (LPFG), which is fabricated on the ring-core fiber, is used to realize mutual mode coupling between the fundamental mode and desired HE 21 mode. By incorporating two fiber Bragg gratings (FBGs) as the coupler and reflector, the fiber laser could oscillate at HE 21 mode and output OAM beam by adjusting the relative phase between HE 21 even and HE 21 odd modes.…”