Full recess integration of small diameter low threshold VCSELs within Si-CMOS ICs.

Oxide-aperture vertical-cavity surface-emitting lasers (VCSELs) have been integrated as individual device pills within the dielectric stacks of commercially produced silicon integrated circuits and monolithically connected electrically with the underlying circuitry using technology compatible with wafer-scale processing. The 55 microm diameter, 8 microm tall device pills were bonded in recesses etched to reveal buried contact/bond pads included in the IC layout; the surface was replanarized, contact vias formed, and interconnect metal deposited and patterned. The typical CW threshold current, 1 to 2.5 mA, was the same before and after integration, and integrated devices had thermal impedances similar to devices on their native GaAs substrates.

Optimizing stochastic gradient descent algorithms for serially addressed adaptive-optics wavefront modulators.

High-resolution adaptive-optical systems with thousands to millions of pixels will most likely have to employ serial- or matrix-addressed spatial light modulators (e.g., microelectromechanical-system-on-VLSI spatial light modulators). We compare parallel gradient descent adaptive-optics algorithms with serial gradient descent algorithms running on serially addressed modulators. While serial algorithms have previously been shown to require more iterations than parallel algorithms, we show that, because of the limitations of the databus, each serial iteration of the algorithm on a serial modulator requires significantly less time to complete than a parallel iteration, thereby favoring the serial algorithm when time to convergence is used as the performance metric. Thus, such high-resolution serially addressed devices are generally better matched to the serial-update wavefront correction algorithm owing to the data load penalty imposed by the bandwidth-limited databus of these modulators.