Monolithic pnpn injection laser optical repeater

Abstract

A monolithic PNPN injection laser diode operating as an optical repeater is comprised of a direct band-gap semiconductor material, such as essentially GaAs, epitaxially grown in five layers with the first, third and fifth layers of GaAsAl and the second and fourth layers of GaAs, and all layers suitably doped to effectively form two complementary transistors interconnected for regenerative feedback between them with the second layer forming the base of one transistor and the collector of the other transistor, and the third layer forming the base of the other transistor and the collector of the one transistor. The PNPN laser diode thus produced has a V-I negative resistance characteristic. The second and fourth layers produce coherent laser beams in response to a light pulse received while the laser diode is biased off with its load line below its breakover voltage, thus switching the laser diode on. An externally stored charge is then discharged through the laser diode to produce the coherent laser beams until the discharging current is reduced below a threshold level. The laser diode is then cut off and the charge is restored in preparation for responding to another light pulse.