Abstract: In an integrated optical semiconductor device wherein a stripe geometry laser diode is separated from a photodetector by an etched groove, the stripe region has a smaller width, such as 2 to 3 microns, than a carrier generating region of the photodetector. The stripe region is preferably rendered thicker than the carrier generating region, in which case the carrier generating region is more preferably made of a seimconductor material having a narrower band gap than the material of the stripe region. The stripe region may be defined by a buried mesa structure. Alternatively, the stripe region may be bounded transversely of a pair of heterojunctions therefor by a pair of channel-shaped regions of a semiconductor material having a wider bank gap than the material of the stripe region. In this event, the carrier generating region is divided into three parts by extensions of the channel-shaped regions.

Abstract: There is disclosed a bidirectional optical fiber transmission system. This system includes first and second light transmitter-receiver sets and a single strand of optical fibers. The light transmitter-receiver sets each comprise (a) a light receiver, (b) a light transmitter whose light source is a light emitting diode, and (c) means to isolate downstream and upstream light from each other. The optical fibers connect the light-transmitter-receiver sets through the light isolating means. The emission spectra of the light emitting diodes at least partly overlap each other and the isolating means have wavelength pass bands which do not substantially overlap each other.

Abstract: A multichannel light switch including a cylindrical-shaped light-focusing transmission body having a length equal to an odd multiple of one quarter of the pitch of light beam undulation within the body and having a total reflection coating applied to one end face thereof, which is normal to the axis of the transmission body. A stationary optical fiber bundle is arranged opposite to the other end face of the transmission body and is in parallel to the axis thereof. For light-path switching between the optical fibers, the transmission body is adapted to be displaced in a radial direction or to be rotated in a plane normal to the axis thereof.

Abstract: A light branching and coupling device, having a light focusing transmission body, in which the refractive index distribution of the body gradually decreases from the center towards the periphery of the body in a cross-section thereof, said cross-section being perpendicular to the center axis of the body. The light focusing transmission body has a length substantially equal to a positive integral multiple of 1/4 pitch with a reflective surface positioned from an end face of the body at a predetermined distance substantially equal to an odd number multiple of 1/4 pitch. Light incident on one of two end faces perpendicular to the center axis of the body propagates undulatingly to the other end face at a predetermined pitch.