Abstract: An optical transmission apparatus is operable without being effected by ambient temperature by combining the control over output light of a semiconductor light emitting element, which constitutes a semiconductor laser unit, and the control over the temperature of the light emitting element. The apparatus is usable in an extended range of ambient temperatures.

Abstract: In an optical isolator device using a Faraday rotator for permitting a forward light beam to pass therethrough but for preventing a reverse light beam from passing therethrough, two Faraday rotators are used in a cascade-connection in order to improve the temperature characteristic of the isolation over a wide temperature range. One of two Faraday rotators is prepared to have the Faraday rotation angle of 45.degree. for a wavelength shorter than the intended wavelength .lambda..sub.0, while the other having the Faraday rotation angle of 45.degree. for a wavelength longer than .lambda..sub.0. A polarizer and an analyzer are disposed on opposite ends of one of the rotators at a rear stage and prevent the reverse light beam from passing therethrough. Another polarizer and another analyzer can further be disposed at opposite ends of the other front stage rotator so that two isolators are arranged in a cascade-connection.

Abstract: An integrated light amplifier in which a stripe laser is formed over a substrate and then a vertical phototransistor is formed over the laser. Electrodes are attached to the back of the substrate and to the top of the phototransistor with the phototransistor electrode being formed with a hole so that incident light can reach the phototransistor. Before formation of the substrate electrode, the substrate can be ground to the desired thickness. Photocarriers are detected and multiplied in the phototransistor and injected into the stripe laser. Additional electrodes may be provided over the laser in order to bias the laser independently of the incident light.