9 optical isolators, optical switches, optical couplers, optical connectors, optical circulators, polarized beam splitters, non-polarized beam splitters, [ band pass filters, ] faraday rotation elements, spherical-ended fibers, oblique-ended fibers, collimated fibers, [ chip carriers, ] laser diode receptacles, heat sinks, optical fiber ferrules, sleeves, [ can-types header for laser diode, ] optical amplifier modules, magneto-optical sensors, optical multi-demulti-plexors, optical waveguides, optical fiber assemblies, spherical lens assemblies, laser diode modules, optical receiver module assemblies, plug assemblies; electro-acoustic transducers, electric vibrators, electric buzzers