Fig. 1. Laser frequency noise PSD model

Fig. 2. Testing principle based on 3×3 unbalanced MZI

Fig. 3. Principle block diagram of phase demodulation

Fig. 4. PSD curve of frequency noise of semiconductor laser with linewidth of 3.1 kHz

Fig. 5. PSD curve of frequency noise of semiconductor laser with linewidth of 42 kHz

Fig. 6. PSD curve of frequency noise of NKT laser

Fig. 7. On-line measurement system of laser frequency noise before and after locking

Fig. 8. Noise PSD test results of a 3.1-kHz linewidth semiconductor laser before and after locking