Linear polarization and narrow-linewidth external-cavity semiconductor laser based on birefringent Bragg grating optical feedback.

• The external laser based on femtosecond-written birefringent fiber Bragg grating (FBG) achieves excellent linewidth characteristics. • The hybrid laser based on ridge waveguide emission gain chip and femtosecond-written birefringent FBG attains high integration and low cost. • Linear polarization output is realized by the orthogonal polarization eigenmode and effective external cavity mode selection of the birefringent FBG. We demonstrate an external-cavity semiconductor laser (ECSL) with linear polarization and a narrow linewidth. A birefringent Bragg grating prepared by a femtosecond laser point-by-point technique in a polarization-maintaining fiber (PMF) is used to provide external-cavity feedback, and its polarization-dependent characteristics enable selection of the main polarization mode and linewidth narrowing of the ridge waveguide emission gain chip (GC). This compact and robust ECSL achieves an output power of > 60 mW and a polarization extinction ratio (PER) of > 30 dB. We simulate and calculate the linewidth and injection current, while a Lorentz linewidth of 2.58 kHz is obtained based on delayed self-heterodyne beat frequency measurement. This flexible and cost-effective solution allows realization of a compact ECSL with linear polarization and a narrow linewidth. [ABSTRACT FROM AUTHOR]