Modelling of the effects of thermal gradients on optical propagation in polymer multimode tapered waveguides in optical backplanes

Finite difference beam propagation modelling (FD-BPM) calculates the effect of thermal gradients in an optical backplane on the optical field propagation in a polymer multimode linearly tapered waveguide. Compared to straight waveguides, tapered entrances offer improved power coupling for a wide range of optical source lateral offset misalignments. However, surface temperature gradients of 0.5 degrees C/um across the taper were found to degrade this benefit due to the thermo-optic effect of the polymer. Higher surface temperature gradients improve power coupling in two discrete ranges of lateral source offset but the original tolerance to a wide range of source offsets is not recovered

Integrated optical and electronic PCB manufacturing: invited plenary talk

In high speed digital systems the signals travel through copper track interconnections in Printed Circuit Boards (PCBs) but suffer loss, radiation, cross-talk, electromagnetic interference (EMI), and corruption limiting the maximum speed and interconnect distance so costly low loss dielectrics, pulse pre-emphasis, adaptive equalization and high levels of Forward Error Correction (FEC) must be used. This paper describes a lower cost approach using optical interconnections for the highest speed interconnects, This optical approach is scalable to large area PCBs and bit rates in excess of 10 Gb/s and makes use of multimode polymer waveguides butt coupled via dismountable, self aligning connectors to VCSEL laser and PIN photodiode arrays. The optical PCB (OPCB) 3 university and 10 company consortium, formed and led by the speaker constitutes a supply chain including waveguide modeling, OPCB layout, polymer manufacturing, OPCB manufacturing with route to exploitation in storage system, aerospace and optical sensor markets. The consortium’s research is reviewed including the establishment of waveguide design rules by measurement and simulation to build into PCB layout tools enabling the easy widespread adoption of this disruptive technology. Manufacturing technologies studied for acrylate and polysiloxane waveguides include photolithography, laser ablation, laser direct write, embossing, extrusion and ink jet printing

Opto-electronic high order feedback neural network

A novel neural network design, in which nonlinearities are created by feedback, is described. It is called the HOFNET. The design is suitable for optical implementation because it is tolerant of the limited dynamic ranges present in optical systems. An optical system with electronic feedback was constructed and its operation is described

A high order feedback net (HOFNET) with variable non-linearity

Most neural networks proposed for pattern recognition sample the incoming image at one instant and then analyse it. This means that the data to be analysed is limited to that containing the noise present at one instant. Time independent noise is therefore, captured but only one sample of time dependent noise is included in the analysis. If however, the incoming image is sampled at several instants, or continuously, then in the subsequent analysis the time dependent noise can be averaged out. This, of course, assumes that sufficient samples can be taken before the object being imaged, has moved an appreciable distance in the field of view. High speed sampling requires parallel image input and is most conveniently carried out by optoelectronic neural network image analysis systems. Optical technology is particularly good at performing certain operations, such as Fourier Transforms, correlations and convolutions while others such as subtraction are difficult. So for an optical net it is best to choose an architecture based on convenient operations such as the high order neural networks

High-dynamic-range imaging optical detectors

Imaging spectrometers allowing spatially resolved targets to be spectrally discriminated are valuable for remote sensing and defense applications. The drawback of such instruments is the need to quickly process very large amounts of data. In this paper we demonstrate two imaging systems which detect a dim target in a bright background, using the coherence contrast between them, generating much less data but only operating over a limited optical bandwidth. Both systems use a passband filter, a Michelson interferometer, coupling optics and a CCD camera. The first uses the interferometer in a spatial mode, by tilting one of the mirrors to create a set of line fringes on the CCD array. The visibility of these fringes is proportional to the degree of coherence. The interferogram is displayed spatially on the CCD array, as a function of the path differences. The second system uses the interferometer in a temporal mode. A coherent point target and an extended background are imaged through the interferometer onto the CCD array, and one of the interferometer's mirrors is scanned longitudinally to vary the path difference in time. In both cases the coherent target is detected over a large dynamic range down to negative signal-to-background power ratios (in dB). The paper describes an averaging technique to improve the signal-to-noise ratio and correction techniques required to extract interferograms from the images. The spatial technique developed has the advantage of using no moving parts