Fig. 1. Experimental setup used to excite OVB pulse. WDM, wavelength division multiplexing coupler; EDF, erbium-doped fiber; PC, polarization controller; OSA, optical spectrum analyzer; CCD, charge-coupled infrared camera; PMF, polarization-maintaining fiber.

Fig. 2. Microscopy image of (a) the fabricated MKR and (b) the overlapping region.

Fig. 3. Spectral response of MKR: (a) Transmission spectrum with different incident states of polarization (SOP); (b) transmission spectra from 1553 nm to 1557 nm; and (c) polarization-dependent loss of the MKR.

Fig. 4. Simulation results: (a) Coupling efficiency as a function of the wavelengths; and (b) power exchange in the coupling region when LP01 mode in SMF converts to LP11 mode in FMF.

Fig. 5. Output near-field intensity distribution from a mode selective coupler by inputting a femtosecond pulse. (a), (e) Intensity profiles of the LP11 and LP21 modes; (b), (f) donut-shaped OAM mode patterns when pressing the output FMF; (c) and (d), and (g) and (h) corresponding clockwise and anticlockwise spiral interferograms of OAM±1 and OAM±2, respectively.

Fig. 6. Output spectra of successively tunable (a) single-, (b) dual-, (c) triple-, and (d) quadruple-wavelength lasing operations.

Fig. 7. Stability of triple-wavelength output spectrum. (a) Repeat scans of triple-wavelength output spectrum every minute. (b) Power fluctuation (black) and central wavelength (blue) of each channel in the triple-wavelength output every minute.

Fig. 8. Near-field distribution of LP11 intensities, OAM patterns, spiral interferograms, and the out spectra of wavelength-switchable laser. Four columns present (a)–(e) single-, (f)–(j) dual-, (k)–(o) triple-, and (p)–(t) quadruple-wavelength lasing operations. First row, LP11 intensity profiles; second row, donut-shaped mode patterns of vortex beams; third and fourth rows, corresponding clockwise and anticlockwise spiral interferograms; and fifth row, the output spectra.