The conventional vertical-cavity surface-emitting lasers (VCSELs) are designed to have a very short resonant cavity.
Therefore, the longitudinal mode of the VCSELs is intrinsically single; and the VCSELs are expected to be an excellent
instrument for many precision measurements that demand high-purity single-wavelength light sources. However, the
laser facet of the conventional VCSELs is relatively large, around 10 μm, which admits the emission of multi-transverse
modes. Accordingly, conducting a single transverse mode from VCSELs is an important research topic. In this research,
the beam-profile-adapted optical feedback (BPAF) method was investigated by a single-mode fiber cavity (SMFC), in
which the beam profile of the multimode-VCSEL's output was adapted to the fundamental-transverse mode of an optical
fiber to feedback into the laser's cavity. The operational principle and performance of BPAF will be presented. The
experimental results successfully demonstrated that BPAF can efficiently conduct multimode VCSELs to stably lase the
fundamental transverse mode with a wide tuning range of about 1090 GHz, or 2.62 nm, and a spectrum purity around 20
dB. Some precision spectrum measurements will be exhibited. These results will help to extend the application of the
VCSELs in many precision measurements.