RESUMO
We have fabricated high-speed Si metal-semiconductor-metal photodetectors using(19) F(+) ion implantation in low-doped Si. Bandwidths in excess of 6 GHz have been obtained that represent more than an order-of-magnitude improvement over unimplanted counterparts. Measurements with short optical pulses show that the increase in bandwidth is due primarily to a shorter carrier lifetime in implanted devices. In the absence of implantation, the response under short optical pulse excitation has a long decay with a time constant of ~0.35 ns. We carried out an optical fiber transmission experiment using a GaAs (lambda ~ 0.85 mum) laser source and the implanted Si photodetector. Error-free transmission (bit error rate < 10(-11)) with good receiver sensitivity was obtained at 2 Gbits/s. These results demonstrate that implanted Si can be used as a detector for short-wavelength fiber-optic communication systems for speeds to a few gigabits per second. Monolithic integration of this detector technology with conventional Si processing offers the potential for low-cost receiver designs.
RESUMO
We extend our recent general discussion of electroabsorption and refraction in multiple-quantum-well modulators to determine the optimum modulator design for smart-pixel applications. In addition to the optimum operating wavelength shift, from that of the zero-voltage exciton, we determine the optimum number of quantum wells, and we calculate the reflectivity change and the contrast ratio obtainable. This analysis is undertaken for both simple detectors and modulators, meaning that they are antireflection coated, as well as for devices that include Fabry-Perot resonators. The optimization is performed on a figure of merit that is inversely proportional to the incident optical read energy required on a device to switch another, downstream device. We maximize the figure of merit to minimize the optical read energy. An interesting result is that there should be no significant improvement in our smart-pixel circuit figure of merit with the use of Fabry-Perot resonant modulators and detectors. Our results are, of course, material-system specific, but for the 850-nm AlGalAs/GaAs quantum-well system the optimum wavelength shift from the exciton location is approximately 6 nm. The general trends and approach are applicable to other material systems.
RESUMO
We demonstrate that GaAs/AlGaAs smart pixels can be operated with picosecond and subpicosecond laser pulses. Switching times as short as 200 ps are measured. Our results confirm the theoretical prediction that input mode-locked pulses are more advantageous than the more typical square-wave pulses. They also suggest that use of picosecond mode-locked pulses for optical output could produce operating speeds in the gigahertz range.
RESUMO
Optically bistable symmetric self-electro-optic-effect devices that use an asymmetric Fabry-Perot resonator are demonstrated and assessed. Contrast ratios exceeding 30 for low bias levels (under 6 V) are measured for low intensities. The Fabry-Perot self-electro-optic-effect device is also shown to saturate readily with intensity, with the contrast ratio decreasing by a factor of 3 for an irradiance of 10 microW/microm(2). Wavelength sensitivity measurements and calculations are also presented.
RESUMO
Using a 6 X 6 array of integrated quantum-well self-electro-optic-effect devices, we demonstrate an optically addressed spatial light modulator able to convert a visible, incoherent image into coherent infrared (IR) light. Depending on the IR wavelength used, the output is either a positive, binary-thresholded version of the input (bistable mode) or its linear, negative (self-linearized) mode. This device can also function as a dynamic bistable memory that can retain its internal state without power for times as long as 30 sec.
