  We experimentally observed self-injection locking regime of the gain-switched
laser to high-Q optical microresonator. We revealed that comb generated by the
gain-switched laser experiences a dramatic reduce of comb teeth linewidths in
this regime. We demonstrated the Lorentzian linewidth of the comb teeth of
sub-kHz scale as narrow as for non-switched self-injection locked laser. Such
setup allows generation of high-contrast electrically-tunable optical frequency
combs with tunable comb line spacing in a wide range from 10 kHz up to 10 GHz.
The characteristics of the generated combs were studied for various modulation
parameters - modulation frequency and amplitude, and for parameters, defining
the efficiency of the self-injection locking - locking phase, coupling
efficiency, pump frequency detuning.
