We experimentally demonstrated a high-order optical vortex pulsed laser based on a mode selective all-fiber fused coupler composed of a single-mode fiber (SMF) and a few-mode fiber (FMF). The fused SMF-FMF coupler inserted in the cavity acts as a mode converter from LP ₀₁ mode to LP ₁₁ (LP ₂₁ ) mode with a broadband width. Linearly polarized OAM modes can be obtained by combining different vector modes HE _2,m ^even (HE _2,m ^odd ) and TE _0,m (TM _0,m ) when l = 1 or combining HE ^even _{l+ 1,m} (HE _{l+ 1,m} ^odd ) and EH _l-1,m ^odd (EH _l-1,m ^even ) when l > 1 with a π/2 phase shift. To the best of our knowledge, this is the first report on the generation of high-order pulse vortex beams in a mode-locked fiber laser. The measured time duration of OVB pulses is 273 fs, 140 fs of OAM _±1 and OAM _±2 .

Generation of high-order modes with high quality is important for the application of cylindrical vector beams in fibers. We experimentally demonstrated high-order LP₁₁ mode generation and amplification with a broad bandwidth in an all few-mode fiber laser. A wavelength-division-multiplexing (WDM) mode selective coupler (MSC) is proposed to achieve efficient mode conversion from LP₀₁ mode to LP₁₁ mode, but also combine high-order LP₁₁ modes at the wavelengths of 980/1550 nm. To the best of our knowledge, this is the first report on the high-order mode oscillation in an all few-mode fiber laser. LP₁₁ mode and cylindrical vector beams including radially and azimuthally polarized beams are obtained with high modal purity. The purity of the generated high-order modes are all in excess of 95%.

We experimentally investigate high-order modes (HOMs) generating at the wavelength of 1.0 μm in all-fiber Yb-doped lasers based on mode-selective couplers (MSCs). Broadband MSCs for HOMs conversion are achieved by optimizing the phase-matching condition at 1.0 μm. Efficient generation of HOMs is demonstrated with the MSCs inserted both into continuous-wave and mode-locked fiber lasers. The slope efficiencies of HOMs (LP₁₁, LP₀₂ and LP₂₁) are presented and discussed. Additionally, cylindrical vector and orbital angular momentum beams are produced out of the MSCs by controlling the polarization states. The results show proof-of-concept implementation of the MSCs, which enables high efficiency of HOMs generation especially in pulsed fiber lasers and holds promising applications in laser material processing.

We experimentally demonstrate two kinds of all few-mode fiber (FMF) ring lasers with high-order mode (HOM) oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams (OVBs); the other is a $Q$-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams (CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve $Q$-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and $Q$-switched HOM beams in all-FMF laser cavities.

We experimentally obtain femtosecond cylindrical vector beams based on a mode-locked fiber laser (MLFL) by using a fused few-mode coupler. Pulses of 300 fs duration with radially and azimuthally polarized modes are directly delivered at the central wavelength of 1566 nm. The fused few-mode fiber coupler inserted inside the cavity acts as a mode converter from LP01 mode to LP11 mode with a wide bandwidth over 100 nm. The proof-of-concept generation of femtosecond cylindrical vector beams is efficient and useful in MLFLs.

We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams (OVBs) in an all-fiber laser. A polarization-dependent microknot resonator (MKR) functions as comb filter and accounts for the narrow linewidth (0.018 nm) of multiwavelength channels. The wavelength interval corresponds to the free spectral range of the MKR. We exploit a fused SMF–FMF (single mode fiber–few mode fiber) mode coupler to obtain broadband mode conversion and successfully achieve multiwavelength switchable OVBs. As far as we know, this is the first report about identical multiwavelength vortex beams with topological charges of $\pm 1$. It has been verified that each channel of the vortex beams preserves the same orbital angular momentum (OAM) properties through their clear spiral interferograms. Multiwavelength vortex beams with identical OAM properties are desirable for multiplexing, exchanging, and routing to further improve the capacity of optical fiber transmission.