Hadi Baghsiahi

FirstLight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers

The protocol data rate governing data storage devices will increase to over 12 Gb/s by 2013 thereby imposing unmanageable cost and performance burdens on future digital data storage systems. The resulting performance bottleneck can be substantially reduced by conveying high-speed data optically instead of electronically. A novel active pluggable 82.5 Gb/s aggregate bit rate optical connector technology, the design and fabrication of a compact electro-optical printed circuit board to meet exacting specifications, and a method for low cost, high precision, passive optical assembly are presented. A demonstration platform was constructed to assess the viability of embedded electro-optical midplane technology in such systems including the first ever demonstration of a pluggable active optical waveguide printed circuit board connector. High-speed optical data transfer at 10.3125 Gb/s was demonstrated through a complex polymer waveguide interconnect layer embedded into a 262 mm × 240 mm × 4.3 mm electro-optical midplane. Bit error rates of less than 10-12 and optical losses as low as 6 dB were demonstrated through nine multimode polymer wave guides with an aggregate data bandwidth of 92.8125 Gb/s.

Integrated optical and electronic interconnect PCB manufacturing research

Purpose – The purpose of this paper is to provide an overview of the research in a project aimed at developing manufacturing techniques for integrated optical and electronic interconnect printed circuit boards (OPCB) including the motivation for this research, the progress, the achievements and the interactions between the partners.Design/methodology/approach – Several polymer waveguide fabrication methods were developed including direct laser write, laser ablation and inkjet printing. Polymer formulations were developed to suit the fabrication methods. Computer‐aided design (CAD) tools were developed and waveguide layout design rules were established. The CAD tools were used to lay out a complex backplane interconnect pattern to meet practical demanding specifications for use in a system demonstrator.Findings – Novel polymer formulations for polyacrylate enable faster writing times for laser direct write fabrication. Control of the fabrication parameters enables inkjet printing of polysiloxane waveguides...

Polymer optical waveguide fabrication using laser ablation

Due to their inherent bandwidth capacity, optical interconnects are replacing copper as bottlenecks begin to appear within the various interconnect levels of electronic systems. Current optical interconnect solutions found in industry are based upon optical fibres and are capable of providing a suitable platform for inter-board applications. However, to allow high bit rate digital interconnects between components and within systems, optically enabled printed circuit boards containing waveguides are essential. One way in which this can be accomplished is through the integration of polymer optical waveguides into traditional printed circuit boards (PCBs). There are a number of routes to accomplish this including photolithography and laser direct imaging, however, this paper explores laser ablation using UV and IR sources namely: 248 nm Excimer, 355 nm UV Nd:YAG and 10.6 µm CO2, to form waveguide structures in optical polymer materials. The paper presents the process route and initial results of trials conducted to fabricate waveguides and indicates the difference between the structures formed by the different lasers. The demonstration of the use of these three lasers for optical waveguide fabrication may provide a route to the rapid deployment of this technology into the PCB industry through the use of existing infrastructure.

Optical Waveguide End Facet Roughness and Optical Coupling Loss

This paper investigates the end facet roughness of multimode polymer channel waveguides fabricated on FR4 printed circuit boards, PCBs, when cut at right angles to their optical axis by milling routers for optical butt-coupling connectors and compares it with that resulting from dicing saws and polishing and proposes a novel end facet treatment. RMS surface roughness of waveguide end facets, measured by AFMs, are compared for a range of rotation speeds and translation speeds of a milling router. It was found that one-flute routers gave significantly less rough surfaces than two or three-flute routers. The best results were achieved for a one-flute router when the milling bit was inserted from the PCB side of the board with a rotation speed of 15,000 rpm and a translation speed of 0.25 m/min which minimized the waveguide core end facet RMS roughness to 183 ± 13 nm and gave input optical coupling loss of 1.7 dB ± 0.5 B and output optical coupling loss of 2.0 dB ± 0.7 dB. The lowest RMS roughness was obtained at chip loads of 16 μm/revolution. High rotation speeds should be avoided as smearing of the end facet occurs possibly due to polymer heating and softening. For the first time to our knowledge, channel waveguide optical insertion loss is shown to be linearly proportional to the ratio of the waveguide core end facet RMS roughness to its autocorrelation length. A new fabrication technique for cut waveguide end facet treatment is proposed and demonstrated which reduces the insertion loss by 2.60 dB ± 1.3 dB which is more than that achieved by the closest available index matching fluid which gave 2.23 dB ± 1.2 dB. The new fabrication method gives a more robust end facet for use in commercial products.

Photolithographically manufactured acrylate polymer multimode optical waveguide loss design rules

This paper describes how design rules are established for photolithographically manufactured acrylate polymer optical multimode waveguide components by optical experimental measurements made on the manufactured waveguide component. The loss of individual waveguide components, such as straight sections, 90deg bends, crossings, tapers and tapered bends must be known so that the combined loss of a cascade of such elements can be found to determine whether the interconnectionpsilas optical power budget is sufficient to achieve a good bit error rate. However, the loss depends on several factors: the materials: the polymer used for the core and for the cladding, the fabrication technique: e.g. the photolithographic procedure and the precise temperature baking regime used, and the measurement technique: the optical source lateral size and angular divergence and precise position relative to the entrance of the waveguide, the output detector lateral size, its angular acceptance angle (if any) and its precise position relative to the exit of the waveguide. The experiments reported on photolithographically manufactured acrylate polymer multimode waveguide were performed at room temperature. A new technique for measure the transmitted power at waveguide crossings is reported for the first time.

Design and implementation of an electro-optical backplane with pluggable in-plane connectors

The design, implementation and characterisation of an electro-optical backplane and an active pluggable optical connector technology are presented. The connection architecture adopted allows line cards to mate and unmate from a passive electro-optical backplane with embedded polymeric waveguides. The active connectors incorporate photonics interfaces operating at 850 nm and a mechanism to passively align the interface to the embedded optical waveguides. A demonstration platform has been constructed to assess the viability of embedded electro-optical backplane technology in dense data storage systems. The electro-optical backplane is comprised of both copper layers and one polymeric optical layer, whereon waveguides have been patterned by a direct laser writing scheme. The optical waveguide design includes arrayed multimode waveguides with a pitch of 250 μm, multiple cascaded waveguide bends, non-orthogonal crossovers and in-plane connector interfaces. In addition, a novel passive alignment method has been employed to simplify high precision assembly of the optical receptacles on the backplane. The in-plane connector interface is based on a two lens free space coupling solution, which reduces susceptibility to contamination. The loss profiles of the complex optical waveguide layout has been characterised and successful transfer of 10.3 Gb/s data along multiple waveguides in the electro-optical backplane demonstrated.

Laser scanning based autostereoscopic 3D display with pupil tracking

An autostereoscopic 3D display based on direct-view RGB laser projection via a transparent display screen is presented. Dynamic exit pupils are formed at the target eye locations with the help of a pupil tracker.

Innovative Optical and Electronic Interconnect Printed Circuit Board Manufacturing research

An overview of the pound1.3 million EPSRC and company matched funded Innovative electronics Manufacturing Research Centre (IeMRC) Flagship project between 3 UK universities and 10 companies entitled ldquointegrated optical and electronic interconnect PCB manufacturingrdquo. The project aims to develop of optical waveguide design rules, layout software, fabrication methods compatible with commercial production, characterisation techniques and optical connector design to provide a supply chain for Polymer Multimode Optical Waveguide Printed Circuit Boards (OPCB) for 10 Gb/s board-to-board interconnections.

Light engine and optics for HELIUM3D auto-stereoscopic laser scanning display

This paper presents a laser-based auto-stereoscopic 3D display technique and a prototype utilizing a dual projector light engine. The solution described is able to form dynamic exit pupils under the control of a multi-user head-tracker. A prototype completed recently is able to provide a glasses-free solution for a single user at a fixed position. At the end of the prototyping phase it is expected to enable a multiple user interface with an integration of the pupil tracker and the spatial light modulator.

Photolithographically manufactured acrylate multimode optical waveguide translation and rotation misalignment tolerances

This paper reports numerous experimental measurements and modelling result of the loss caused by various amounts of translation and rotation misalignment in the optical backplane system. Combinations of VCSEL as the light source and waveguides of various widths have been input in the system. The source has been moved away from the centre of a channel waveguide in the horizontal and vertical direction gradually to find out the translation and rotation tolerance. Offsets between VCSEL-waveguide and waveguide-receiver have been studied to find the translation and rotation tolerance.