Fig. 1. DBR single-longitudinal-mode fiber laser. (a) Schematic diagram; (b) photo of the fiber laser prototype

Fig. 2. Characteristics of longitudinal mode and frequency tuning of DBR fiber lasers. (a) Single-longitudinal-mode oscillation characteristics of the laser measured by F-P scanning interferometer; (b) measured the relationship between the amount of change in output laser frequency and the modulation frequency of the tuning voltage when the PZT is applied at different voltage values

Fig. 3. Characteristics of optical spectrum and linewidth of DBR fiber lasers. (a) Output optical spectrum of the laser prototype measured by an optical spectrum analyser; (b) measured results of beat frequency spectrum of the laser using a self-heterodyne system with a 50 km single mode fiber delay line

Fig. 4. Schematic diagram of the experimental setup of fiber laser frequency stabilization using PDH technology based on ultrastable optical cavity

Fig. 5. Error signal before and after laser frequency stabilization. (a) Error signal recorded by the oscilloscope when a triangular-wave sweep voltage of 7 V, 20 Hz is applied to PZT, in which the inset is a partial enlarged view of the error signal at the laser carrier; (b) error signal after the laser frequency is locked to the reference cavity

Fig. 6. Beat frequency signal drift and frequency instability of frequency-stabilized lasers. (a) Relationship of the beat frequency signal with time measured by the frequency counter, in which the inset is the change of the ambient temperature over time at the location of the frequency stabilization system; (b) modified Allan deviation of the frequency instability of each fiber laser calculated using the data of beat frequency signal in the Fig.6 (a)

Fig. 7. Frequency noise and linewidth of frequency stabilized laser. (a) Measured frequency noise power spectrum of the frequency-stabilized fiber laser in the range of 1 mHz~100 kHz, and the frequency noise power spectrum of the free-running fiber laser shown in the figure; (b) beat frequency linewidth of frequency-stabilized laser measured by FFT spectrum analyzer