Passively mode-locked fiber laser is a flexible source of ultrafast optical pulses duo to its advantages of compact size, high stability and simple configuration. One approach to achieve mode-locking is nonlinear polarization rotation (NPR) effect. Because of the induced polarizer, the output pulses always possess fixed linear polarization, which is known as scalar solitons. The other approach is material saturable absorber (SA) based mode-locking. SA materials with ideal polarization-independent feature can support vector solitons generation. Vector and scalar solitons both play an important role in many theoretical researches and scientific applications, such as three-dimensional display and polarization division multiplexing transmission, etc. So far, all passively mode-locked fiber lasers have been generally outputted with either vector or scalar solitons after pulse propagation within the cavity.

Prof. Songnian Fu, Prof. Ming Tang, Ph.D student Zhichao Wu with the Wuhan National Lab for Optoelectronics, Huazhong University of Science and Technology designed a novel laser cavity where vector soltions and scalar solitons co-exist, indicating that transitions between them are possible. The experimental results agree well with our numerical simulation.

Fig.1. Schematic illustration of the experimental setup including both the laser cavity and polarization resolved measurement.


Fig.2. Experimental optical spectra of the two orthogonal axes from the OC1 (left) and OC2 (right).

After experimental characterization, the co-existence of vector and scalar solitons is demonstrated. For very large local birefringence, the laser approaches the operation regime of vector soliton lasers, while it approaches scalar soliton lasers under the condition of very small birefringence.

The paper was published at Optics Express (Vol.24, No.16, pp.18764-18771, 2016) and this work was supported in part by National Key Scientific Instrument and Equipment Development Project (2013YQ16048702), National Natural Science Foundation of China (61275109, 61275069, 61331010), and Open project funding of the Jiangsu Key Laboratory of Advanced Laser Materials and Devices, Jiangsu Normal University (KLALMD-2015-02)