This letter concerns the mode-competition effect for compound-cavity l
asers. Considering the mode properties of such a system we show, that
the side cavity mode having the same threshold gain as the lasing one
may correspond to either stable or unstable mode of laser operation. I
n the last case the mode competition leads to locking of the lasing an
d side modes yielding high-frequency self-pulsations in some range of
system parameters. This effect can be used for the design of self-puls
ating SLs generating optical pulses in microwave region without intrac
avity saturable absorber.