Fig. 1. (a) Schematic of the dispersion-managed mode-locked all-fiber laser with OAM mode output. LD, semiconductor laser; SESAM, semiconductor saturable absorber mirror; WDM, wavelength division multiplexer; EDF, erbium-doped fiber; PC, polarization controller; MSC, mode selective coupler; OC, optical coupler; DCF, dispersion compensating fiber; Obj, microscope objective; BS, beam splitter; CCD, charge-coupled device. (b) Schematic structure of the MSC.

Fig. 2. Relative refractive index difference versus radius. Inset: the actual transverse profile of the ring-core fiber.

Fig. 3. Pulse generated at −495 × 10⁻³ ps² net-cavity-dispersion. (a) Mode-locked optical spectra. (b) Pulse train in a 1500 ns time window range. (c) RF spectrum in 15 MHz with 3 kHz resolution frequency and 100 MHz with 10 kHz resolution frequency. (d) AC trace (blue line) with the sech² fitting (black line).

Fig. 4. (a) Mapping of dispersion-managed mode-locked regimes for various net-cavity-dispersions and pump powers. CW, continuous wave; QML, Q-switched mode-locked regime; NLP, noise-like pulse; CS, conventional soliton. The numbers denote the order of the harmonic mode-locked regime. (b) The first- and second-harmonic mode-locked pulse trains at −159 × 10⁻³ ps² net-cavity-dispersion.

Fig. 5. Pulse generated at -159 × 10^-3 ps² net-cavity-dispersion. (a) Mode-locked optical spectra. (b) RF spectrum in 100 MHz with 10 kHz resolution frequency. (c) AC trace in 200 ps time windows.

Fig. 6. Experimental results. (a) Pulse optical spectra under different net-cavity-dispersions. (b) Pulse energies under different net-cavity-dispersions.

Fig. 7. Experimental results. Mode patterns: (a1), (b1) LP11 even mode and LP11 odd mode; (a2), (b2) LP21 even mode and LP21 odd mode; (a3), (b3) LP31 even mode and LP31 odd mode; (c1) OAM+1 mode; (c2) OAM+2 mode; (c3) OAM+3 mode. (d1)–(d3) Interference patterns between fundamental and OAM modes with corresponding topological charges.

Fig. 8. Experimental results. (a) OAM+1 mode intensity pattern. (b) Azimuthal gray value profile of the r ring. (c) Amplitude profile of the r ring. (d) Phase profile of the r ring.