Fig. 1. Experimental setup of the RFL. RBGA, random Bragg grating array; OSA, optical spectrum analyzer; PM, power meter; CIR, circulator; OC, optical coupler; ISO, isolator.

Fig. 2. Detailed random spacing along the fiber during the RDFF fabrication process.

Fig. 3. Reflection and transmission spectra of the RDFF.

Fig. 4. Output power of the RFL versus pump power. The upper inset shows an enlargement of the output-input curve near the threshold.

Fig. 5. Changes in the output spectrum of the RFL with in the pump power.

Fig. 6. Time-stability test results of emission spectra of the proposed RFL (a) without a π–FBG and (b) with a π–FBG.

Fig. 7. Stability of emission wavelength and output power with time at 40, 80, and 153 mW pump power.

Fig. 8. Detection signal of the laser beat linewidth based on an optical heterodyne.