Low self-starting threshold polarization-maintaining Er-doped fiber optical frequency comb

We report the development of an all-fiber polarization maintaining (PM) optical frequency comb using a mode-locked figure-9 laser with a low self-starting pump threshold. We have achieved self-starting mode-lock for repetition rates ( fr ) from 70 MHz to 109 MHz. At a repetition rate of 109 MHz, mode-locking can be achieved for a pump power ranging from 187 mW to 880 mW. To the best of our knowledge, this is the lowest pump power reported for PM figure-9 erbium fiber lasers with repetition rate over 100 MHz. By optimizing the pump power to 238 mW, we have achieved an output power of 5 mW, center wavelength of 1566.2 nm, and 3-dB spectral bandwidth of 20.5 nm. The repetition rate has a high signal-to-noise ratio of 95 dB at a resolution bandwidth of 300 Hz. We have studied the spectral characteristics of the laser under different cavity lengths and pump powers. Additionally, we have stabilized the repetition rate using a GPS-Rb disciplined RF reference. The fractional instability of the repetition rate is measured to be 4.67×10-12 at 1 s and 9.22×10-13 at 10 s over a measurement of 11 h. Our findings demonstrate that the developed figure-9 comb is robust, compact and has the advantage of high stability and low power consumption. It offers a cost effective solution for future outdoor comb applications.