Fig. 1. Structure of the WDM-MSC.

Fig. 2. (a) Converted LP11 mode, (b) LP11 mode at the FM-EDF input port, and (c) LP11 mode at the FM-EDF output port.

Fig. 3. ASE spectra under different pump powers.

Fig. 4. Amplified spectra of the FM-EDF amplifier (a) with different pump powers of LP11 mode and (b) at different signal wavelengths.

Fig. 5. Schematic setup of our proposed all-FMF ring laser. FM-EDF: few-mode erbium-doped fiber; ISO: isolator; CNT-SA: carbon nanotube saturable absorber; OSA: optical spectrum analyzer; OSC: oscilloscope; CCD: charge coupled device; Col: collimator; PC: polarization controller.

Fig. 6. Output mode-locked (a) pulse trains, (b) spectrum at a pump power of 340 mW.

Fig. 7. (a) Mode-locked optical spectrum evolution with different pump powers; (b) average output power and 3 dB bandwidth versus pump power.

Fig. 8. (a) RF spectrum of the all-FMF laser with a span of 1 GHz, (b) the fundamental peak located at the cavity repetition rate of 30.58 MHz with a resolution bandwidth of 1 Hz.

Fig. 9. Intensity distributions of (a) APB and (b) RPB without a polarizer before and after passing a linear polarizer.