The fabrication of epitaxial compound semiconductors and optoelectronic devices at Tampere University of Technology is described. First, we determine the bandgap energies of technologically important quaternary alloys GaxIn1-xAsyP1-y, grown by gas-source molecular beam epitaxy, which are lattice-matched to InP and GaAs throughout the entire composition ranges. Second, we discuss state-of-the art aluminum-free laser diodes intended for pumping light at λ = 980 nm into erbium-doped optical fiber amplifiers. Third, principles of a new kind of avalanche photodetector (APD), a "unipolar" APD, are discussed. Our attempt is to develop a compound semiconductor detector that could detect an event of single-photon absorption. Finally, we present a photovoltaic fiber optical power converter. This device is comprised of a series of photovoltaic cells and an integrated 980-nm data laser. It is designed to convert the fiber-coupled optical power launched by a transmitter laser at 780<λ<850 nm into electrical power.