We introduced the vertical cavity surface emitting laser (VCSEL) as the laser diode in tour external cavity system.
Because VCSELs are now commercially available, and the External cavity diode laser (ECDL) systems using
them are expected to improve their frequency stability, we have replaced a Fabry-Perot type laser diode with a
VCSEL, and examined its oscillation-frequency stability. Therefore we were able to expect that the VCSELs with
our double optical feedback system have good oscillation frequency stability. The obtained VCSEL's
oscillation-frequency stability, i.e., the square root of Allan variance σ was 4×10<sup>-10</sup>, at an averaging time of τ=1