  Narrow-linewidth lasers have high spectral purity, long coherent length and
low phase noise, so they have important applications in cold atom physics,
quantum communication, quantum information processing and optical precision
measurement. We inject transmitted laser from a narrow-linewidth (15 kHz)
flat-concave Fabry-Perot (F-P) cavity made of ultra-low expansion (ULE) optical
glass into 852-nm distributed-Bragg-reflector type laser diode (DBR-LD), of
which the comprehensive linewidth of 1.67 MHz for the free running case. With
the increase of self-injection power, the laser linewidth is gradually
narrowed, and the inject-locking current range is gradually increased. The
narrowest linewidth measured by the delayed frequency-shifted self-heterodyne
(DFSSH) method is 263 Hz. Moreover, to characterize the laser phase noise, we
use a detuned F-P cavity to measure the conversion signal from laser phase
noise to intensity noise for both the free running case and self-injection lock
case. Laser phase noise for the self-injection lock case is significantly
suppressed in the analysis frequency range of 0.1-10 MHz compared to the free
running case. Especially, the phase noise is suppressed by more than 30dB at
the analysis frequency of 100 kHz.
