Low-noise narrow-linewidth fiber laser at 1550 nm (June 2003)

We present a compact integrated fiber laser with more than 200 mW of output power. It combines polarized fiber output with very narrow linewidth of less than 2 kHz. The coherence length of the laser is measured to be longer than 5 km. The laser features high mode stability of less than +/-10 MHz over hours. The relative intensity noise (RIN) spectrum is dominated by a peak at the relaxation oscillation frequency and is shot-noise limited otherwise. The RIN peak at 1 MHz is reduced to similar to -130 dB/Hz by integrating a negative feedback circuit. In addition to thermal wavelength tuning, the laser frequency can be modulated at a bandwidth of up to 10 kHz via the piezoelectric effect.