We report on recent theoretical and experimental results on n-i-p-i based smart pixels. We present first results on dynamical switching in these devices. In particular, we present 1.9 ns switching times at an optical power of 880 W for the photoconductive switch. This corresponds to a total switching energy of 1.7 pJ or 2.4 fJ/m2 relative to the device area. A contrast of the electronic output signal larger than iO and a maximum dc gain exceeding 106 is achieved. For an optical NOR gate -composed of a photoconductive switch and an electroabsorptive n-i-p-i modulator -we were able to demonstrate operation at optical switching energies of 2 pJ and switching times of 1 ts. This corresponds to an opto-optical gain (fan out) of 750. The switching contrast of the optical output signal is 4.5 : 1.
We present a novel smart pixel composed of an optoelectronic threshold switch with gain and a vertical cavity surfaceemiuing laser (VCSEL). In this smart pixel two surface-normal input optical beams control an output optical beam emitted by the VCSEL. In its present hybrid version the VCSEL-based smart pixel is capable of opto-optical switching with an output contrast ratio in excess of 30 dB at an optical output power of about 1.5 mW. For quasi-stationary operation we achieve an optical gain of up to 3 x iO. We also report drastic improvements on the switching dynamics. Operating the receiver with an optical input power of 130 pW we achieve bitrates of up to 160 Mbitls and an optical gain of 1 1, while optical inputs of 410 iW result in a maximum bitrate of 400 Mbit/s and an optical gain of 3.6. The minimum input optical energy required for switching is 765 IJ, the AC output contrast ratio is 9 dB. Optically performed NAND and NOR logic operations are demonstrated at 40 Mbitls with a fan-out of 7.6. We further show that the functionality of this smart pixel can easily be extended to electric read-out of input optical data and to direct electric control of the VCSEL within the smart pixel configuration. In particular, we demonstrate conversion of electric input to optical output data at 1 Gbitls.
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