Abstract: An optical signal repeater where an upstream modulator is configured to generate an optical upstream output signal by modulating an optical carrier signal, and to transmit the optical upstream output signal to an upstream fibre-optic output port. A downstream modulator is also configured to generate an optical downstream output signal by modulating an optical carrier signal and to transmit the optical downstream output signal to a downstream fibre-optic output port. By ensuring that the wavelengths of the optical carrier signals are equal or substantially equal, the wavelength drift in the upstream direction can be kept equal to the drift in the downstream direction. These repeaters can be used for time and frequency synchronization in long-distance fibre-optic networks.

Abstract: Grinding head for surfacing and polishing stone, marbles and other hard materials including a rotating housing supporting a number of oscillating grinding blocks which during rotation of said housing are pressed against the surface to be treated during simulataneous supply of water to the working zone of said grinding blocks. The apparatus includes a new excenter mechanism for imparting to said grinding blocks an oscillatory tangential movement with respect to said grinding head during rotation thereof. The apparatus also renders possible a forced self-lubrication of bearing surfaces.