Frequency and Intensity Noise of Single Frequency Fiber Bragg Grating Lasers

The relative intensity (RIN) and optical frequency (νrms) noise of Er-doped fiber Bragg grating lasers are investigated theoretically and experimentally. For a 1480-nm pumped fiber distributed feedback (DFB) laser with 170-μW output power we observe a typical RIN floor of −118 dBHz/Hz for frequencies above 10 Hz, with a strong relaxation oscillation resonance peak at 222 kHz reaching −77dBHz/Hz.νrms ranges from 26dBHz/Hz at 1 kHz to 2dBHz/Hz at 1 MHz, with a sharp peak at the relaxation oscillation frequency. Below 1 kHz 1/f noise is observed in νrms. Negative feedback to the pump laser from the fiber laser output power is found to eliminate the relaxation oscillation noise peaks both from RIN and νrms spectra. By comparing measured intensity and frequency fluctuations at the relaxation oscillation frequency, we estimate the linewidth broadening factor of two investigated lasers to be 2.1 and 3.6, as compared to typically between 3 and 7 for semiconductor lasers.