PurposeThe purpose of this paper is to present a novel manufacturing process that aims to pattern metal tracks onto polyimide at atmospheric pressure and ambient environment. The process can be scaled up for industrial applications.Design/methodology/approachFrom a thorough literature survey, different approaches were carried out for processing polyimide. Following a design of experiments for the processing and various characterisation techniques, a micro‐coil was manufactured as a test demonstrator.FindingsThe characteristics of some main formaldehyde‐based electroless copper baths were compared. The quality of the sidewalls was characterised and the performance of the process was assessed.Originality/valueThis paper demonstrates a high‐value manufacturing technique that is mass manufacturable, low cost and suitable for use on 3D surfaces. Criteria required for the development of a direct‐writing process have been described. The issues surrounding electroless plating on polyimide have been explained.

Conductive micro-patterned copper tracks were fabricated by UV direct-writing of a nanoparticle silver seed layer followed by selective electroless copper deposition. Silver ions were first incorporated into a hydrolyzed polyimide surface layer by wet chemical treatment. A photoreactive polymer coating, methoxy poly(ethylene glycol) (MPEG) was coated on top of the substrate prior to UV irradiation. Electrons released through the interaction between the MPEG molecules and UV photons allowed the reduction of the silver ions across the MPEG/doped polyimide interface. The resultant silver seed layer has a cluster morphology which is suitable for the initiation of electroless plating. Initial results showed that the deposited copper tracks were in good agreement with the track width on the photomask and laser direct-writing can also fabricate smaller line width metal tracks with good accuracy. The facile fabrication presented here can be carried out in air, at atmospheric pressure, and on contoured surfaces.

We have previously developed a direct UV-laser-writing technique and custom photo-polymer optimised to form multimode polymer waveguides and embedded 45deg out-of-plane mirrors. In the IeMRC funded ldquoIntegrated Optical and Electronic Interconnect PCB Manufacturingrdquo (OPCB) project the key aim is to explore how these techniques can be extended to suit real-world optical backplane applications - both in the context of scale and manufacturability. In particular, we are assessing the viability of the technique for writing polymer optical waveguides of approximately 50 times 50 mum in cross-section over large metre-scale areas and the compatibility of this optical interconnect approach with existing PCB manufacturing processes.

In this paper, we describe a series of improvements that have been made to our direct laser writing waveguide/microfluidic fabrication technology. We demonstrate significant increases in the writing speed ( measured in micrometres of written structure per second) by both the use of customized photopolymers containing light emitting polymer and the inclusion of a diffractive optical element to enable the writing of multiple channels in a single pass.

A qualitative comparison is made between laser direct writing and laser ablation as enabling technologies for the structuring of multimode waveguides (50x50μm2) and 45° micro-mirrors into an optical layer. A small demonstrator is fabricated that allows us to couple light vertically from a transmitter into an optical layer and from the optical layer to a receiver. The optical layer, a multifunctional acrylate-based photo-polymer, is applied on an FR4-substrate. Multimode waveguides, that carry signals in the plane of the optical layer, are fabricated by means of laser direct writing, a technology that is available at HWU. The 45° micro-mirrors, that provide out-of-plane coupling, are ablated with the laser ablation set-up available at UGent. This set-up contains a KrF-excimer laser (248nm) that can be tilted, which eases the definition of angled facets. Surface roughness measurements are performed on both the optical layer and the micro-mirrors with a non-contact optical profiler. Loss measurements are performed on both the waveguides and the micro-mirrors.

This paper describes work on the development of a two-level lightwave circuit containing multimode polymer waveguides with 45/spl deg/ out-of-plane turning mirrors to communicate between the layers. The polymer waveguides and mirror structures are produced using a direct laser-writing system. The system is based on a He-Cd (325 nm) UV laser and a vertically mounted slotted base-plate which is used to align the polarising, routing and focussing optics that guide and focus three beams (at normal and /spl plusmn/45/spl deg/ angles) onto a computer controlled XY translation stage.

Direct laser writing is a good alternative to photolithography for rapid prototyping as it is a maskless process. Here we describe different polymer structures and passive devices fabricated using a direct laser-writing system based on a He-Cd (325 nm) UV laser. This has been used to fabricate structures in polymer such as bumps, micro-via, mechanical guides for fibre alignment and passive devices such as beam splitters and combiners which can be used for incoherent light sources such as LEDs. A custom multifunctional acrylate photo-polymer with good thermal and mechanical properties was used to fabricate the structures.

The devices and the integration platform for the assembly of a 4 × 4 optoelectronic crosspoint switch have been described. We will report on the performance of the mirror structures and bumps, and on the progress made in the assembly, and testing of the switch.

An adaptive alignment scheme for packaging two-dimensional (2D) arrays of optoelectronic systems interconnected by free-space optics is presented. A method of using three quadrant detectors to detect alignment errors in six degrees of freedom is described. However, the complexity of this system increases due to the interactions among the detected error signals. A novel control algorithm is presented to eliminate the interaction and simplify the design of the closed-loop feedback control. A computer simulation compares different algorithms and shows the effectiveness of the proposed algorithm. An experimental closed-loop feedback system demonstrated the principle of the error detection and correction of the proposed system with initial errors in multiple degrees of freedom

We theoretically analyze the effect of current-directionality induced dichroism of fundamental absorption in III–V semiconductors with a high nonequilibrium carrier density. Band filling is shown to provide giant values of relative absorption difference for two orthogonal polarizations near the transparency point. Self-adjustment of the transparency point to the incident photon energy due to absorption saturation at high incident optical powers leads to large absorption dichroism in a broad spectral range. The situation we model is relevant to polarization modulation in vertical-cavity surface-emitting laser diodes. A specialized laser construction to achieve this purpose is proposed.

The performance of a novel multifunctional acrylate based photo-polymer is presented. Rapid direct writing of multimode (50 μm square core) cladded waveguides, compliant bumps for flip-chip bonding and 45° total internal reflection mirrors for out of plane coupling have been realised using a high-power 325 nm He:Cd laser with high precision and repeatability. The losses are measured to be less than 0.17 dB/cm at 850 nm and less than 0.5 dB/cm at 1300 nm by cutback method. This custom multifunctional acrylate co-polymer has been found to be thermally stable up to a temperature of 300° as determined using DTA–TG analysis.

3D imaging is an important tool for metrology and reverse engineering of components and structures in a wide variety of contexts, from automobile and aeroplane manufacture to the creative media and architectural surveying. In this article, we review briefly the principal methods in current use for 3D imaging, then present a new method for time of flight depth measurement, which is more accurate and sensitive than the current techniques. To illustrate its potential, we show a number of examples of 3D data acquired from both small and large objects, taking examples from cars, planes and archaeological artefacts.

We theoretically analyse the effect of current-induced dichroism in degenerate semiconductors. The use of this effect for dynamic control of polarisation properties of purpose-built vertical-cavity surface-emitting lasers is proposed and its potential evaluated.

We theoretically analyze the effect of current-induced polarization dependence of absorption (fundamental and intersubband) and gain in degenerate semiconductors. The sign of the currentinduced polarization selectivity of absorption is shown to depend on the energy of the initial (or final) state of the transition with respect to the Fermi level and, therefore, on the photon energy. The effect is predicted to be important for understanding and, potentially, engineering polarization properties of devices such as vertical-cavity surface-emitting lasers.

Development of a novel multifunctional acrylate based photo-polymer for photonic integration is presented. A 325 nm He:Cd laser has been used for direct writing of 50 mum square core mull-mode waveguides, compliant lumps for flip-chip bonding and 45 degrees total internal reflection mirrors for out of plane coupling. The transmission losses are measured to be 0.17 dB/cm at 850 nm and 0.5 dB/cm at 1300 nm by cutback method. Partially halogenated versions show losses around 1dB/cm at 1550 run. DTA TG analysis shows that this multifunctional acrylate co-polymer is thermally stable up to a temperature of 270 degreesC.

The physical limit on electronic data communication rates between silicon chips is projected to be of the order of Tbit/s over cm-scale connections. The semiconductor industry predicts that this level of i/o is likely to be required in the near future. Free-space optical connections to silicon VLSI are potentially able to offer much higher: data-rates than electrical interconnects and are promising for future high-performance electronic systems. We have assembled the components of an optoelectronic 15 Gbit/s crossbar switch designed to include, internally, an optical data rate to a hybrid InGaAs/silicon chip in the Tbit/s regime. Input to the demonstrator is by-an 8x8 VCSEL array operating at 250Mbit/s/channel, and these 64 channels are fanned out 8x8 times to give the high data rate onto the hybrid chip. This chip includes an array of 4096 InGaAs-based detectors flip chip bonded to silicon CMOS. The custom-designed CMOS performs packet routing under the control of an optical clock and the routed signals are output via differential modulator pairs, interlaced between the detectors on the InGaAs chip.

The performance of selected, commercially available InGaAs/InP avalanche photodiodes operating in a photon-counting mode at an incident wavelength of 1.55 microm is described. A discussion on the optimum operating conditions and their relationship to the electric field distribution within the device is presented.

The concept of adaptive optics for improving the cost-performance of free-space optoelectronic interconnects is discussed. Adaptive optics as a design option for optical interconnect systems is presented and discussed. A practical demonstrator that performs low-order correction was built and tested. Slowly varying misalignments, including thermal effects, were compensated for in a 622-Mbit/s free-space optical data link.

We propose and analyze a promising surface-normal optical modulator for use in optical interconnects. The device is based on n-AlGaAs materials, operating with red light, and is therefore fully compatible with silicon photodetectors. The operation principle is based on current-induced electron heating, with redistribution of carriers between conduction band valleys playing a significant part. Calculations predict efficient absorption modulation with operating voltages <1 V and switching times of units of picoseconds.