Monolithic PNPN injection laser optical repeater

An optical repeater comprising a monolithic PNPN injection laser having a V-I negative resistance characteristic, said laser comprising a crystal of direct band-gap semiconductor material, said crystal having at least four planar layers of P-type and N-type material arranged to provide three rectifying junctions, one polarity for two of said rectifying junctions separated by the third rectifying junction of opposite polarity, and said crystal having a pair of optically flat and parallel faces normal to said planar layers, means for reverse biasing said third junction between the first and second junctions at a predetermined voltage below the breakover voltage of said V-I negative resistance characteristic selected to hold off current through said layers in series while forward biasing said two p-n junctions on both sides of said third junction, means coupled to said biasing means for storing a predetermined quantity of charge to be discharged through said layers in series once conduction through said third junction is initiated, and means for coupling a light pulse of predetermined minimum amplitude into said planar layers to cause photocurrent through said third junction, thereby injecting carriers and lowering the breakover voltage of the negative resistance characteristic of said PNPN injection laser below said predetermined voltage, a sufficient portion of said carriers flowing through the N-type and P-type layers of said third junction to maintain current flow independent of said light pulse for discharge of said stored charge and the balance of said carriers recombining radiatively to provide, through at least one of said optically flat faces, an output laser pulse the duration of which is determined only by the time required for said stored charge to be discharged to a point where current flow can no longer be maintained through said third junction above a lasing threshold level independent of said light pulse coupled into said layers.

A monolithic PNPN optical pulses repeater comprising a crystal of direct band-gap semiconductor material having a pair of parallel optically flat faces, said crystal being epitaxially grown in planar layers on a substrate consisting essentially of GaAs, at least four of said layers being doped alternately for negative and positive carrier type to provide a structure having three junctions, two end junctions of one polarity, p-n, and a current junction of opposite polarity, n-p, said structure having active regions where charge carriers recombine radiatively, means for biasing said central junction below its breakover voltage, thus forward biasing said end junctions for conduction when said central junction conducts, means for storing current for discharge through said junctions when said central junction conducts, means for coupling a light pulse into said reverse biased central junction to produce photocurrent through said central junction and to trigger conduction through the device which sustains current flow as long as said stored charge provides sufficient current through said central junction to hold said central junction conducting, thus discharging said stored charge through said three junctions in response to said light pulse, said current flow causing population inversion in said structure, and means for restoring said stored charge automatically once sufficient current is no longer sustained to hold said central junction conducting.