Photodetector arrays and architectures for acousto-optical signal processing

Photodetectors and photodetector arrays for optical processing

“…3 The same requirements must be considered for serial arrays. In serial-addressed-array AO systems the signal compression can be at the photodetector, prior to the multiplexer, and/or after the multiplexer, depending on the dynamic range of each component.…”

“…Photodetectors fabricated in GaAs can be easily integrated with FET amplifiers on the same chip.48 56 57 58 High bandwidth and low Johnson noise are attractive features of GaAs FET amplifiers. 3 The high 1/f noise of GaAs FETs,59 however, is a potential limitation.3 Several detector concepts using GaAs and other compound-semiconductor quantum-well-superlattice structures have been proposed and/or demonstrated. These include avalanche photodetectors based on a GaAs/AlGaAs superlattice structure,° 61 62 avalanche photodetectors with a graded bandgap superlattice,62 63 a detector concept using effective mass filtering to achieve gain,TM and heterostructure bipolar devices.…”

“…First, it is difficult to use a true integrating detector in some system applications because of the high dynamic range and short pulse requirements. 3 The detector typically is operated as an integrating detector at low signal levels and as an instantaneous detector at high signal levels. To retain amplitude information when the detector is in the instantaneous mode, a peak detector must be used prior to the multiplexer.…”

<title>Acousto-optic compressing photodetector approach for cw signals</title>

“…(15) of Chamberlain and Lee.3 The resulting expression for the total number of carriers in the imaging gate region, NT, for the subthreshold operations is NT (CnV/q)ln((I + 'P)/('L + Ipexp[-(IL + IP)tI/(CnVT)})), (1) where VT is the thermal voltage (kT/q = 0.26 V), C is the capacitance of the storage region, n is the subthreshold parameter, 'L is the leakage current, Ip is the photocurrent, t1 is the integration period, k is the Boltzmann constant, T is the absolute temperature, and q is the electronic charge. Figure 2 shows the calculated transfer functions obtained from Eq.…”

Compressing photodetectors for long optical pulses using a lateral blooming drain structure

“…T applications such as machine vision and acousto-optical (AO) spectrum analysis cannot be met with conventional integrating photodetector arrays [ 11- [ 141. To meet these dynamic range requirements-which may be as high as 80 dB ( lo8) in optical power, with the maximum useful optical power being as low as 300 pW or less-photodetector circuits with a compressing transfer Characteristic are usually required [3], [5]. A compressing transfer function reduces the effective quantization noise at low optical power levels for a given analog-to-digital (A/D) converter resolution.…”