  We report on a design of a compact laser system composed of an extended
cavity diode laser with high passive stability and a pre-filter Fabri-Perot
cavity. The laser is frequency stabilized relative to the cavity using a
serrodyne technique with a correction bandwidth of $\geq 6$ MHz and a dynamic
range of $\geq 700$ MHz. The free running laser system has a power spectral
density (PSD) $\leq 100$ Hz$^{2}$/Hz centered mainly in the acoustic frequency
range. A highly tunable, $0.5-1.3$ GHz copy of the spectrally pure output beam
is provided, which can be used for further stabilization of the laser system to
an ultra-stable reference. We demonstrate a simple one-channel lock to such a
reference that brings down the PSD to the sub-Hz level. The tuning, frequency
stabilization and sideband imprinting is achieved by a minimum number of key
elements comprising a fibered EOM (electro-optic modulator), AOM (acousto-optic
modulator) and a NLTL (non-linear transmission line). The system is easy to
operate, scalable, and highly applicable to atomic/molecular experiments
demanding high spectral purity, long-term stability, and robustness.
