In-cavity soliton self-frequency shift ultrafast fiber lasers

Lasing wavelengths are generally limited at the gain bands of active materials. In this Letter, we propose and demonstrate a new concept of ultrafast fiber laser based on in-cavity soliton self-frequency shift (SSFS). Benefiting from SSFS, the wavelength of ultrafast fiber lasers can be beyond the gain band of active fibers. SSFS was previously stimulated by transmitting pulses in passive fibers. Triggering SSFS inside a laser cavity has never been reported. We successfully stimulate SSFS in a laser by employing a piece of dispersion-shifted fiber. In-cavity SSFS is expected to be implemented in various ultrafast lasers and is conducive to develop compact wavelength versatile laser sources.