Bart Volckaerts

Plastic microoptical interconnection modules for parallel free-space interand intra-MCM data communication

We design and fabricate a prototype scalable multichannel free-space interconnection module with the potential for Tb/s/spl middot/cm/sup 2/ aggregate bit-rate capacity over inter- and intra-MCM interconnection distances. The component is fabricated in a high quality optical plastic, PMMA, using deep proton lithography, an ion-based rapid prototyping technology. As a feasibility demonstration, data communication is achieved at 622 Mb/s per channel with a bit error rate smaller than 10/sup -13/ for 16 channels with an interchannel crosstalk lower than -22 dB. We perform a sensitivity analysis for misalignments and fabrication errors and study the fabrication issues of these components with injection molding techniques. Finally, we provide evidence that these modules can be mass fabricated with the required precision.

Two-dimensional plastic microlens arrays by deep lithography with protons: fabrication and characterization

We present a quantitative study of the fabrication process of two-dimensional plastic microlens arrays fabricated using deep lithography with protons. Our process involves the proton irradiation of a PMMA (poly(methyl methacrylate)) sample in regions with a circular footprint followed by a diffusion of MMA vapour into the bombarded zones to cause a lens-shaped volume expansion. In the first part of this paper we give a detailed description of our fabrication technique and of the calibration procedure that goes with it. We demonstrate the flexibility of our approach with the fabrication of different types of array: highly uniform microlens arrays and arrays of microlenses with varying sags (maximum height of the spherical lenscap) and pitches. All lenses under test feature diameters of 200 ± 2µm, root-mean-square (RMS) roughnesses on the top of the lenses of λ/30 @ 632 nm and lens sags ranging from 10 to 70 µm. We also present the optical performances and the aberrations of the microlenses, measured using a dedicated transmission Mach–Zehnder interferometer. The focal lengths of the lenses under study range from 166 to 1444 µm, corresponding to a range of sags between 9.77 and 69.73 µm and to focal numbers between 0.83 and 7.22. Typical values for the RMS and peak-to-valley aberrations of 0.209λ and 1.057λ respectively were observed. To conclude, we analyse and discuss the strengths and weaknesses of this fabrication method.

Deep proton writing: a rapid prototyping polymer micro-fabrication tool for micro-optical modules

One of the important challenges to deploying the emerging breed of nanotechnology components is interfacing them with the external world, preferably accomplished with low-cost micro-optical devices. In our labs at the Vrije Universiteit Brussel (VUB), we are therefore focusing on the continuous development of a rapid prototyping technology for the fabrication of micro-optical modules. In this technology, which we call deep proton writing (DPW), we bombard polymer samples with swift protons, which will result after chemical processing steps in high quality micro-optical components. The strength of the DPW micro-machining technology is the ability to fabricate monolithic building blocks that include micro-optical and mechanical functionalities which can be precisely integrated into more complex photonic systems. The DPW technology is furthermore compatible with low-cost mass-replication techniques such as micro-injection moulding and hot embossing. In this paper we give an overview of the process steps of the technology and the characteristic qualities we can expect from the components made by DPW. The general overview of the technology is followed by three case studies of different micro-optical components that were fabricated at our labs: (i) two-dimensional fibre connectors, (ii) out-of-plane couplers for optical waveguides embedded in printed circuit boards (PCBs), (iii) intra multi-chip-module (MCM) level optical interconnection via free space optical modules.

Plastic Microlens Arrays by Deep Lithography with Protons: Fabrication and Characterization

In this paper, we present the state-of-the-art of deep lithography with protons (DLP), a technology that we have adopted and optimized to rapidly prototype three-dimensional micro optical components and high-aspect-ratio micro mechanical structures in poly(methyl methacrylate). In particular, we focus on the fabrication of individual plastic refractive microlenses featuring a wide range of numerical apertures, diameters and pitches and on their 2-dimensional arrays. We provide a detailed description of the microlens fabrication technique and its calibration procedure. We highlight the quantitative geometrical and optical characteristics of these DLP microlenses and we demonstrate the reproducibility of their fabrication process. We also illustrate the prototyping flexibility of DLP by fabricating arrays featuring microlenses with different sags, pitches and diameters. As a conclusion, we analyze and discuss the strengths and weaknesses of this technology.

The Munich ion microprobe: Characteristics and prospect

Abstract The newly developed ion microprobe SNAKE (superconducting nanoscope for applied nuclear (Kern-) physics experiments) has gone into routine operation at the Munich 14 MV tandem accelerator. It focuses ion beams, from protons to uranium, with energies that are about 10 times larger than they are available at standard nuclear microprobes. Lateral resolutions of Δ x =1.6 μm and Δ y =1.2 μm for x - and y -direction at full aperture and as low as Δ x =600 nm and Δ y =150 nm for a pencil beam have been achieved so far. The latter values are limited by positional drifts and 50 Hz oscillating fields which have become obvious in time resolved measurements. SNAKE opens new possibilities for analysis of microstructured materials as well as materials modifications. The highlights are three dimensional hydrogen analysis using proton proton scattering, high resolution transmission energy loss measurements utilizing a magnetic spectrograph and materials modification with available high energy proton and heavy ion beams. Standard techniques like particle induced X-ray emission, elastic and inelastic scattering are also used for imaging. The paper summarizes some of the prospects using the enlarged range of available ion beams and ion energies.

SPAD arrays and micro-optics: towards a real single photon spectrometer

This study aims at proving that single photon sensing can be made accessible in the form of cheap off-the-shelf micro-devices with micro-optical/micro-mechanical coupling systems. In order to achieve this challenging goal, use is made of different micro-technologies, not yet fully established but promising and innovative in and of themselves. It is planned to combine them into a more challenging micro-technology capable of making single photon handling off-the-shelf. Moreover, the technology to be implemented should make it possible to provide photonic sensors in a ready-to-go fashion.

Optomechanical Monte Carlo Tolerancing Study of a Packaged Free-Space Intra-MCM Optical Interconnect System

We report on the performance of an intra-multichip-module free-space optical interconnect that integrates microlenses and a deflection prism above a dense optoelectronic chip, under various fabrication and assembly errors. This paper describes the results of a combination of mechanical Monte Carlo analysis and optical simulations. Both the technological requirements to ensure a high process yield, and the specifications of the technology we use at our laboratories to fabricate the microoptical and micromechanical components, deep lithography with protons (DLP), are discussed. Therefore, we first conduct a sensitivity analysis that is subsequently used to set the variances of the random perturbations of the Monte Carlo simulation. By scaling these variances, we are able to investigate the effect of a technology accuracy enhancement on the fabrication and assembly yield. We estimate that 40% of the systems fabricated with DLP will show an optical transmission efficiency above -4.32 dB, which is -3.02 dB below the theoretical obtainable value. In this paper, we also discuss our efforts to implement an optomechanical Monte Carlo simulator. It allows us to deal with specific issues not directly related with the microoptical or DLP components, such as the influence of gluing layers and structures that allow for self-alignment, by combining mechanical tolerancing algorithms with optical simulation software. In particular, we determine that DLP provides ample accuracy to meet the requirements of a high manufacturing yield (around 91% meet an optical transmission that is -0.75 dB below the theoretical maximum). The adhesive bonding of optoelectronic devices in their package, however, is subject to further improvement to enhance the tilt accuracy of the devices with respect to the optical interconnect modules

Ion micro-beam diagnostics with photodetectors

We have developed two techniques for microscopic ion beam imaging and profiling, both based on scintillators, particularly suitable for applications in deep lithography with protons (DLP) or with heavier ions. The first one employs a scintillating fiberoptic plate and a CCD camera with suitable lenses, the second makes use of a small scintillator optically coupled to a compact photomultiplier. We have proved the possibility of spanning from single beam particles counting up to several nA currents. Both the devices are successfully exploited for on-line control of proton beams, down to a beam size of less than 50 μm, in the framework of DLP application.

Rapid Prototyping of Polymer Micro-Opto-Mechanical Components with Deep Proton Writing

We present Deep Proton Writing as a flexible rapid prototyping technology for the fabrication of a wide variety of three dimensional refractive micro-optical components and high-aspect-ratio micro-mechanical structures with applications in telecom, datacom and biophotonics.

Diagnostic Tools For Low Intensity Ion Micro‐Beams

We have developed two techniques for microscopic ion beam imaging and profiling, both based on scintillators, particularly suitable for applications in Deep Lithography with Protons (DLP) or with heavier ions. The first one employs a scintillating fiberoptic plate and a CCD camera with suitable lenses, the second makes use of a small scintillator optically coupled to a compact photomultiplier. We have proved the possibility of spanning from single beam particles counting up to several nA currents. Both devices are successfully being exploited for on‐line control of low and very low intensity proton beams, down to a beam size of less than 50μm.