  In a wide range of quantum technology applications, ranging from atomic
clocks to the creation of ultracold or quantum degenerate samples for atom
interferometry, optimal laser sources are critical. In particular, two
phase-locked laser sources with a precise difference frequency are needed for
efficient coherent population trapping (CPT) clocks, gray molasses laser
cooling, or driving Raman transitions. Here we show how a simple cost-effective
laser diode can selectively amplify only one sideband of a
fiber-electrooptically-modulated seed laser to produce moderate-power
phase-locked light with sub-Hz relative linewidth and tunable difference
frequencies up to $\approx 15\,$GHz. The architecture is readily scalable to
multiple phase-locked lasers and could conceivably be used for future on-chip
compact phase-locked laser systems for quantum technologies.
