Optical interconnects based on high-contrast all-dielectric nano-post arrays.

In this paper, we present a compact solution for optical interconnects in optoelectronic integrated neural networks using high-contrast all-dielectric nano-post arrays. The nano-post arrays are made of amorphous silicon, which has a high refractive index and high transmittance in the near infrared. The radius of each post is changed to generate different phase delays. Deflection and convergence of the light are realized by proper design of the phase profile of the nano-post array. Connection efficiencies are calculated by numerical simulations and compared with those of zone plate interconnects. Simulation results show that the proposed nano-post arrays can have superior performance over zone plates in applications that require short focal length and high efficiency.

Design, fabrication, and testing of zone-plate interconnects for a compact optoelectronic integrated neural coprocessor.

We have designed, fabricated, and tested a set of scalable compact optical elements for use in the compact optoelectronic integrated neural (COIN) coprocessor. The COIN coprocessor is an implementation of a feed-forward neural network that uses optical interconnects to transmit information from one layer of neurons to the next. Optical interconnection elements based on Fresnel-zone-plate concepts have been fabricated using standard lithographic processes, thereby allowing large arrays to be fabricated with a single exposure. This paper discusses the design trade-offs that must be considered for effective use of such elements in a COIN coprocessor, and the fabrication and testing of a set of such optical interconnection elements. It was found that the behavior of the fabricated zone plates correlated well with the design simulation, and that this type of optical element is indeed suitable for use in the COIN coprocessor.

Evaluation of organic light-emitting diodes as light sources for a compact optoelectronic integrated neural coprocessor.

Organic light-emitting diodes (OLEDs) are a most promising candidate for light sources of the compact optoelectronic integrated neural (COIN) coprocessor because of their easy integration with the silicon electronics. However, the optical properties of OLEDs are different from those of vertical-cavity surface-emitting lasers, which were previously used in the COIN system. The interconnect behavior of the COIN coprocessor is unknown if OLEDs are employed. In this paper, we build a mathematical model of the interconnect scheme of the COIN coprocessor and investigate the influence of the spectral bandwidth, light-emitting area, and angular emission profile of OLEDs by numerical simulations. The simulation results show that OLEDs with properly selected properties can be used as the light sources for the COIN coprocessor.

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.

Preparation, characterization, and heat resistance studies of a holographic photopolymer based on SU-8 epoxy resin.

A holographic photopolymer based on SU-8 epoxy resin as the binder and trimethylolpropane ethoxylate triacrylate as the monomer with an iodonium salt photoinitiator was studied. A diffraction efficiency of 93% and a refractive index modulation (Delta n) of 1.3 x 10(-2) were obtained from a 16 microm thick sample with write beam intensities of 50 mW/cm(2) at a wavelength of 514.5 nm, an exposure time of 60 s, and a postbaking at 65 degrees C for 1 h. The material exhibits good heat resistance in the range from 40 degrees C to 160 degrees C and long projected life.

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.

Imaging multispectral polarimetric sensor: single-pixel design, fabrication, and characterization.

A discrete-component approach was taken to establish the operational feasibility of a novel, imaging, midinfrared, multispectral, polarimetric sensor for remote-sensing application. The sensor is designed to exploit the spectral and polarimetric characteristics of the scene as discriminants. Pixelated multispectral filters and polarization filters were designed and fabricated on sapphire and Si substrates, respectively, and both were characterized. A single-pixel spectropolarimetric composite filter was characterized by use of a Fourier transform infrared spectrometer and a Pt-Si thermal-imaging camera. The experimental results show excellent agreement with theoretical predictions.