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A d i f f u d junction GaAs diode has been developed for use as a fast, higheefficlency, infrared source. The diode is forward biased with the light being generated by the recombination of minority carriers in the semiconductor bulk. The device is a P+-N structure with a spaced contact covering a minor portion of the N-type face of the wafer through which the radiation is emitted. less than band gap (E gap = 1.43ev at 300' K) and a broad peak at &outThe infrared radiation is characterized by a sharply defined peak at sli htlyplate, i.e., the intensity decreases as the cosine of the angle {om the normal.The measure,d radiation pattern closely follows that ex ected of a flatThe diode V.1 curve is characterized by exp (qV/2kT) at low current (up to 1 ma), exp (qV/kT) at moderate current (5.50 ma) and series IR drop at high current (above 200 ma).Data will be presented for the electron to photon conversion efficiency, the photon emission efficiency and the overdl energy efficiency of the GaAs infrared source as a function of current level and temperature.constructed by optically coupling a GaAs infrared source and a silicon photo A four terminal device which exhibits significant power gain has been transistor. A discussion of this device and the speed of response of the GaAs infrared source will also be presented.A brief review of the electroeoptic effect in crystals as applied to light modulation will be given, then followed by a description of the technique developed at our laboratories for single4deband modulation of light by this effect. Aside from applications to superheterodyne optical communications, this technique can be used to shift, by a specified amount, the inherently fixed frequency of a laser beam without introducing, additional frequency components.One method uses two electro.optic crystals in a tandem arrangement and is capable of shifting about 45% of the input light energy onto a sideband when a sinusoidal voltage is applied. The remainin energy is absorbed in the device. Principles of operation will be analyzed an% the evolution of a simpler embodiment, which uses only one crystal, will be discussed. This latter device can completely convert an incident beam to a sideband and is easily adaptable to broadband operation far into the microwave region.These modulators were demonstrated with coherent light obtained from a heliumaeon gas laser using audio-frequency modulating signals. Two tone teats showing the expected intensity envelopes and confirming singlesideband suppressedcarrier modulation will be described. 96

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