Fig. 1. Experimental setup of the tunable MWFL. LD, laser diode; YDF, Yb-doped fiber; AOTF, acoustic optical tunable filter; CIR, optical circulator; ISO, optical isolator; MFA, mode field adaptor; CLS, cladding light stripper; QBH, quartz block head; PM, power meter; OSA, optical spectrum analyzer.

Fig. 2. AOTF-based spectrum manipulation techniques. (a) Illustration of the AOTF’s operational mechanism. (b) AOTF’s transmission spectra under varying applied RF powers. (c) AOTF’s transmission spectra with adjustable RF frequencies, highlighting the shift in the central wavelength. (d) Demonstration of wavelength spacing adjustability in AOTF’s transmission spectra. (e) AOTF’s transmission spectra for a dual-channel configuration with varied RF power to illustrate channel-specific control.

Fig. 3. Power and spectrum characteristics of the multi-wavelength operating seed laser. (a) Output power and backward power at varied wavelengths and 3.5 W LD pump power. (b) Normalized spectrum and output power of varied single wavelength. (c) Spectra of multi-wavelength operation with channel numbers 2–5. (d) Power stability of one, three and five channels. (e) Spectral stability of tri-wavelength mode measured over 30 minutes. (f) Spectral stability of penta-wavelength mode measured over 30 minutes.

Fig. 4. Spectra and power conversion efficiency of varied wavelengths at the kilowatt level. (a) Spectra of wavelengths from 1065 to 1095 nm at the kilowatt level. (b) Conversion efficiency from the pump to output power. (c) ASE of the 1055 nm laser. (d) Spectrum evolution of 1060 nm. (e) Spectrum evolution of 1080 nm. (f) Spectrum evolution of 1095 nm.

Fig. 5. Interval and intensity tunability under dual-wavelength operation. (a) Interval tunability ranges from 6 to 32 nm. (b) Relative intensity can be flexibly adjusted within 0–10 dB.

Fig. 6. Tunability of the MWFL envelope. (a) Uphill and downhill shape. (b) Peak and basin shape.

Fig. 7. MWFL operation with wavelength quantities of four and five. (a) Spectrum of flattened four-wavelength output. (b) Spectrum of flattened five-wavelength output.

Fig. 8. Spectral evolution of varied wavelength sets. (a), (b) 1060 + 1070 nm. (c), (d) 1070 + 1080 nm. (e), (f) 1080 + 1090 nm. (g), (h) 1070 + 1080 + 1090 nm.