  We stabilized the frequency of a compact planar-waveguide external cavity
laser (ECL) on a Fabry-P\'erot cavity (FPC) through a Pound-Drever-Hall scheme.
The residual frequency stability of the ECL is 1E-14, comparable to the
stability achievable with a fiber laser (FL) locked to a FPC through the same
scheme. We set up an optical link of 100 km, based on fiber spools, that
reaches 1E-19 relative stability, and we show that its performances using the
ECL or FL are comparable. Thus ECLs could serve as an excellent replacement for
FLs in optical links where cost-effectiveness and robustness are important
considerations.
