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A high dynamic range (HDR) CMOS image sensor architecture based on spiking pixel cells and its first implementation, a linear 128-pixel sensor, is presented. The pulse rate of the pixel cell is proportional to the local light intensity. The pixel cell features a pixel-level analog-to-digital (A/D) conversion by pulse counting. It allows one to tradeoff conversion precision versus frame rate. Sample sensor chips have been manufactured using a 0.8-/spl mu/m double metal CMOS technology, and the test results confirming the feasibility of the chosen approach are reported.

We present results from In/sub 0.35/Ca/sub 0.65/As-GaAs 4 QW lasers whose Al/sub 0.8/Ga/sub 0.2/As binary short-period superlattice (SPSL) cladding layers were grown at either 700/spl deg/C or 620/spl deg/C. The threshold current densities (J/sub th/) are /spl sim/3 times smaller for the lasers whose AlGaAs cladding layers were grown at 620/spl deg/C. At the same time, the internal differential quantum efficiency (/spl eta//sub i/) increases from 60% to 70%. We attribute the lower J/sub th/ and increased /spl eta//sub i/ to a significant decrease in the concentration of point defects in the MQW active region, consistent with the observed improvement of the diode ideality factor. Temperature-dependent photoluminescence (PL) results suggest that these nonradiative recombination centers are related to point defects recently observed with Raman scattering. Ridge lasers grown with low-temperature SPSL Al/sub x/Ga/sub 1-x/As have achieved 3-dB modulation bandwidths of 24 GHz at record low bias currents of only 25 mA. >

We present a systematic theoretical investigation of the influence of p-doping on the gain characteristics of strained In/sub 0.35/Ga/sub 0.65/As/GaAs multiple-quantum-well (MQW) lasers, and compare the results with those obtained experimentally from devices with record 30 GHz modulation bandwidths. Experimentally, the combination of p-doping and strain has been found to lead to only a small increase in the differential gain, /spl part/g//spl part/n, but a large decrease in the non-linear gain coefficient, /spl epsiv/; this behaviour has been theoretically accounted for by a doping-induced decrease in the intraband relaxation time, /spl tau//sub in/. The theoretical investigations reveal that the assumption of a constant intraband relaxation time is not sufficient to describe the role of p-doping in the above devices, and highlight the importance of utilizing an appropriate lineshape function for the modeling of high speed laser modulation behaviour. >

We demonstrate record direct modulation bandwidths from MBE-grown In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers with undoped active regions and with the upper and lower cladding layers grown at different growth temperatures. Short-cavity ridge waveguide lasers achieve CW direct modulation bandwidths up to 40 GHz for 6/spl times/130 /spl mu/m/sup 2/ devices at a bias current of 155 mA, which is the damping limit for this structure. We further demonstrate large-signal digital modulation up to 20 Gb/s (limited by the measurement setup) and linewidth enhancement factors of 1.4 at the lasing wavelength at threshold of /spl sim/1.1 /spl mu/m for these devices.

The addition of strain and p-doping in high-speed GaAs-based MQW lasers are assessed experimentally in terms of their potential for both increasing the differential gain, /spl part/g//spl part/N, and reducing the modulus of the differential refractive index, |/spl part/n//spl part/N|, in order to decrease the linewidth enhancement factor, /spl alpha/. The increased differential gain with strain alone is found to be offset by a corresponding increase of |/spl part/n//spl part/N|. The further addition of p-doping, on the other hand, simultaneously increases /spl part/g//spl part/N and decreases |/spl part/n//spl part/N|, yielding a substantial reduction in /spl alpha/. >