Logic circuits employ photoresponsive GaAs field effect transistors to directly drive GaAs laser diodes to provide optical output signals in response to optical input signals. Since the only electrical inputs are DC bias voltages, each such circuit can be readily decoupled, such as for use in electrically noisy environments. The optical output represents a predetermined logic condition in response to a predetermined operating current applied to the laser diode as a result of the operation of the photoresponsive device. Two photoresponsive devices may be used to apply two different operating current magnitudes to the laser diode to produce two different optical output signals.
An optical operational memory device comprises a light-emitting device, a first and second phototransistors, and a load resistor. The light-emitting device and the first phototransistor are connected electrically in series to form an optical bistable switch based on optical positive feedback. The second phototransistor is connected in parallel to the optical bistable switch, and the load resistor is connected in series to the optical bistable switch. The time constant given by the product of the current gain of the second phototransistor, the base-collector capacitance of the second phototransistor, and the resistance of the load resistor is larger than the period required for recombination of the excess majority carriers in the base of the first phototransistor. A single optical beam modulated with pulse signals is input to the first and the second phototransistors simultaneously. The optical pulse with a peak power in a predetermined range turns the optical bistable switch on, and the pulse with higher peak power turns the optical bistable switch off.
A complete set of optical logic gates and circuits based upon direct polarization switching, and various types of optical flip-flops based upon polarization bistability, in semiconductor lasers are described. By operating the laser in the direct polarization switchable mode, logic gates and circuits such as inverter, AND, NAND, OR and NOR can be provided with two optoelectronic switches or photodetectors. With the laser being operated in the polarization bistable mode, clocked optical flip-flops are operable with a few optoelectronic switches or photodetectors.
An opto-electronic XOR gate includes a pair of diode type light sources connected back to back in parallel by a pair of input leads to which first and second electronic logic signals are applied. With only one logic signal in the high state, one of the diode-type light sources is forward biased while the other is reverse biased. With both logic signals high or low neither diode-type light source emits. A two to one fiber optic combiner (FOC) provides a single optical output which is on only when only one electrical signal is high. If an electronic output is desired, a single photodetector converts the output of the FOC to an electronic logic signal. For performing the exclusive OR operation on optical input signals, a pair of photodetectors and buffer amplifiers and connected to the input leads. For 10 to 12 GHz switching speeds laser diodes are used as the diode-type light sources. When lower switching speeds are satisfactory, light emitting diodes can be used as the diode-type light sources.
A semiconductor laser device has a package which contains inside a laser diode which outputs light according to an applied voltage and a protective element. The protective element has a control terminal and is connected in parallel with the laser diode, and its impedance is significantly smaller than that of the laser diode when no voltage is applied to the control terminal and is significantly larger when a specified voltage is applied to the control terminal. The protective element may be a depletion mode FET connected in parallel with the laser diode between its drain and source, its gate serving as the control terminal. A photoelectric conversion IC for converting a received light signal into an electrical signal may also be contained inside the package and containing the protective element.
The photo-sensor cell comprises two optical flip-flop sensors having two different light intensity thresholds, respectively , under imbalanced load offset conditions, two logic cells for latching only two different binary level signals from the two optical sensor respectively, without latching two of the same binary level signals from the two optical sensors due to a high or low pulsed power supply, and an output logic cell for generating an output binary signal from the time when light intensity rises beyond a higher threshold to the time when it drops below a lower threshold. Since all the elements are standardized in an IC manufacturing process and further no synchronizing clock signals are required between cells and signal processing logic owing to latch operations when a number of cells are connected in series or parallel, it is possible to realize a compact digital photo-sensor cell assembly with hysteresis activated by a pulsed power supply.
