Switchable dual-wavelength cylindrical vector beam generation from a passively mode-locked fiber laser based on carbon nanotubes

Cylindrical vector beams (CVBs) with axial symmetry in both polarization and field intensity have attracted much attention because of their unique optical properties. Conventional methods to obtain CVBs including direct modulation of light beams in free space and high-order mode excitation by offset splicing single-mode fiber (SMF) with few-mode fiber (FMF) usually works at single wavelength with rather narrow bandwidth. Here, for the first time to the best of our knowledge, we demonstrate switchable dual-wavelength CVB generation from a passively mode-locked fiber laser using carbon nanotubes (CNTs) as saturable absorber for mode-locking and a home-made mode-selective coupler (MSC) as both mode converter and birefringence filter. In experiments, the mode-locked fiber laser delivers CVB pulses of dual-wavelength (1532.5 nm, 1555.5 nm) and corresponding single wavelength with duration of hundreds of femtosecond, respectively. Moreover, the output polarization status is switchable between radially and azimuthally polarized states. The mode-locked CVBs with wavelength and polarization flexibility may have potential applications in mode-division multiplexing optical fiber communication, nanoparticle manipulation, material processing, nonlinear optics, and so on

Mode and wavelength-switchable pulsed fiber laser with few-mode fiber grating

We propose and demonstrate a mode and wavelength-switchable pulsed fiber laser using two-mode fiber Bragg grating (TM-FBG) as both transverse mode converter and wavelength selector. The mode-locking mechanism is based on saturable absorption of semiconductor saturable absorption mirror (SESAM). Due to the use of low polarization-dependent mode-locking method, polarization disturbation between mode-locking and transverse-mode selection has been effectively eliminated, thus enabling flexible transverse-mode selection with simultaneous mode-locking operation. Moreover, through the optimized offset launching technique, this laser can operate at the wavelengths of the fundamental mode (LP01) and second-order mode (LP11), and thus export cylindrical vector beams (CVBs) and fundamental mode beams at the TM-FBG output port, respectively. This all-fiber laser is a simple, low-cost and flexible source for mode-division multiplexing system and other applications

Passively mode-locked ytterbium-doped fiber laser with cylindrical vector beam generation based on mode selective coupler

We propose and demonstrate, for the first time to the best of our knowledge, a passively mode-locked ytterbium-doped fiber laser generating cylindrical vector beams (CVBs) using a mode selective coupler (MSC) as the transverse mode converter and splitter, and a semiconductor saturable absorber mirror (SESAM) for mode-locking. According to the coupling mode theory and the phase matching principle, the MSC was fabricated by weakly fused technology, having a low loss of about 0.5 dB and achieving LP11 mode with a high purity of > 96%. The CVB fiber laser operates at a center wavelength of 1042.3 nm, with a 3 dB spectral width of 1.5 nm. The repetition rate of the mode-locked laser pulses is 18.58 MHz. The radially and azimuthally polarized vector beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be > 95%. The mode-locked CVB ytterbium-doped fiber laser has potential applications in optical tweezers, optical imaging, and so on

Dissipative soliton resonance Ytterbium-doped fiber laser with cylindrical vector beam generation

We experimentally demonstrate a dissipative soliton resonance (DSR) Ytterbium-doped fiber laser with high-purity cylindrical vector beam (CVB) generation, using a mode-selective coupler (MSC) as transverse mode converter and splitter. The all-normal-dispersion mode-locked Ytterbium-doped fiber laser operating at DSR regime without spectral filter can deliver CVB pulses with a pulse duration of ∼733 ps and a pulse energy as high as ∼0.439 nJ. The radially and azimuthally polarized beams can be switched by adjusting the polarization controller, with a high mode purity measured to be >94.5%. This compact DSR fiber laser could find potential applications in the field of material processing, nonlinear optics and so on

All-fiber fused-type mode selective coupler with high performance and free of pre-tapering

In this paper we propose and demonstrate a novel all-fiber fused-type mode selective coupler (MSC) that capable of converting LP01 mode to LP11 mode with high efficiency and purity. Unlike other coupler fabrication techniques for which single mode fiber (or few mode fiber) must be pre-tapered, the advantage of our proposed coupler is that pre-tapering is not required. Two different fibers of the MSC have the same diameter. We achieve LP11 mode with a high modal purity of > 90% and a coupling efficiency of >20%, with a low insertion loss of about 0.3 dB at the wavelength of 1064 nm

A mode-locked fiber laser generating high purity cylindrical vector beams based on a mode selective coupler in a figure-8 cavity

We propose and demonstrate an all-fiber passively mode-locked laser with pulsed cylindrical vector beam output based on a mode selective coupler (MSC) in a figure-8 cavity, The MSC made of a two mode fiber and a standard single mode fiber is used as both the intracavity transverse mode converter and mode splitter. Through adjusting the polarization state in the laser cavity, both radially and azimuthally polarized beams have been obtained with high mode purity which are measured to be > 94%. The mode-locked laser pulses have duration of 17 ns and a repetition rate of 0.66 MHz, operating near a wavelength of 1556.3 nm with a spectral bandwidth of 3.2 nm

Single-longitudinal-mode Fiber Ring Lasers With Taper-coupled Double-microsphere-cavities

This letter proposes and demonstrates a fiber ring laser using taper-coupled double-microsphere-cavities (DMC) to achieve single-longitudinal-mode operation. Whispering-gallery-mode (WGM) intensity distributions and transmission spectra of the DMC with different microsphere diameters are investigated both theoretically and experimentally. Due to the Vernier effect, the DMC can produce WGM spectra with a higher extinction ratio, a higher side-mode-suppression ratio (SMSR), a larger FSR and a narrower bandwidth, as compared to a single-microsphere cavity. A single-longitudinal-mode fiber ring laser operating near 1.5 μm with a bandwidth of < 0.01 nm and a signal-to-background ratio of about 60 dB is demonstrated using the taper-coupled DMC as an all-fiber mode selector

An injection-locked single-longitudinal-mode fiber ring laser with cylindrical vector beam emission

We demonstrate a fiber ring laser with narrow bandwidth single-longitudinal-mode cylindrical vector beam (CVB) output at C-band wavelength range for the first time to the best of our knowledge. A step index two-mode fiber Bragg grating is used as a transverse mode selector for CVB generation, while both the injection-locking technique and narrow bandwidth of the fiber Bragg grating lead to single-longitudinal-mode operation. The 3-dB bandwidth of the laser output is measured to be 60 dB. Mode distribution and optical spectra of few-mode fibers with periodic modulated refractive index profile, namely the few-mode fiber Bragg gratings with bent radius, are investigated theoretically and experimentally, which provide a comprehensive exploration of CVB's generation

A 1.0 μm Cylindrical Vector Beam Fiber Ring Laser Based on A Mode Selective Coupler

We propose and demonstrate a continuous-wave all-fiber ring laser generating cylindrical vector beams (CVBs) using a MSC as transverse mode converter and mode splitter. The MSC is fabricated by a novel method free of pre-tapering, achieving LP11 mode with a high purity of > 96% near the wavelength of 1064 nm. The CVB fiber laser operates at a center wavelength of 1053.9 nm, with a 3 dB linewidth of less than 0.04 nm and a signal-to-background ratio of > 60 dB. The laser slope efficiency is > 9%. The radially and azimuthally polarized beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be > 96%

Solid optical fiber with tunable bandgaps based on curable polymer infiltrated photonic crystal fiber

We demonstrated the realization and characterization of a solid photonic bandgap fiber (SPBF) with a compact size of about 10 mm and a high wavelength sensitivity of up to -4.034 nm/°C by means of fully infiltrating an ultraviolet curable polymer with a high refractive index of 1.515 into air holes of a photonic crystal fiber (PCF). To the best of our knowledge, it was the first time that the SPBF with tunable bandgaps was fabricated in the conventional index-guiding PCF. Compared with conventional fluid filled PBFs, the proposed SPBF can be stable to temperature and other environmental effects and maintain a large extinction ratio of more than 30 dB within a broad wavelength. The splicing between the SPBF and single mode fibers has been solved. Moreover, it is observed that the bandwidth of bandgap (G2) gradually broadens with the increase in temperature