Fig. 1. Setup of double Sagnac loop filter

Fig. 2. Setup of the multi-wavelength fiber laser based on the double Sagnac loop

Fig. 3. Output spectra of single wavelength

Fig. 4. Output spectra of dual-wavelength

Fig. 5. Stability measurements of dual-wavelength

Fig. 6. Measurements of (a) wavelength shift, (b) power fluctuation of double-wavelength in 27 min

Fig. 7. Output spectra of triple-wavelength

Fig. 8. Stability measurements of triple-wavelength

Fig. 9. Measurements of (a) wavelength shift, (b) power fluctuation of triple-wavelength in 27 min

Fig. 10. Output spectra of switchable (a) quadruple-wavelength, (b) five-wavelength, (c) six-wavelength

Fig. 11. Output spectra of switchable triple-wavelength

Fig. 12. Output spectra of switchable quadruple-wavelength