Fiber grating laser: a performance study on coupling efficiency of fiber microlens and the Bragg reflectivity

摘要

The λ=1.55 μm fiber grating lasers (FGLs), comprised of an uncoated tapered hemispherical-end fiber (THEF) microlens for strong coupling the fiber grating external cavity and the HR/AR-coated diode laser, have been investigated in four different combinations of coupling efficiency (η) and Bragg reflectivity (R_(g)). The FGL of higher η=72% and R_(g)=0.52 has a stronger resonant feedback as the spectral output shows a single longitudinal mode (SMSR >45 dB), high output power (>5 mW), and lower threshold current. However, for the case of R_(g)=0.35 and η=68%, the FGL exhibits more stable SMSR against pumping current and temperature. We have also performed numerical simulation on the SMSR at different η and R_(g) for the FGLs. The calculated SMSR shows an excellent agreement with the measured data for the FGLs of higher η.