Valerie Baukens

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.

Low-cost microoptical modules for MCM level optical interconnections

A multichannel free-space microoptical module for dense MCM-level optical interconnections has been designed and fabricated. Extensive modeling proves that the module is scalable with a potential for multi-Tb/s/spl middot/cm/sup 2/ aggregate bit rate capacity while alignment and fabrication tolerances are compatible with present-day mass replication techniques. The microoptical module is an assembly of refractive lenslet-arrays and a high-quality microprism. Both components are prototyped using deep lithography with protons and are monolithically integrated using a vacuum casting replication technique. The resulting 16-channel high optical-grade plastic module shows optical transfer efficiencies of 46% and inter-channel cross talks as low as -22 dB, sufficient to establish workable multichannel MCM-level interconnections. This microoptical module was used in a feasibility demonstrator to establish intra-chip optical interconnections on a 0.6 /spl mu/m CMOS optoelectronic field programmable gate array. This optoelectronic chip combines fully functional digital logic, driver and receiver circuitry and flip-chipped VCSEL and detector arrays. With this test-vehicle multichannel on-chip data-communication has been achieved for the first time to our knowledge. The bit rate per channel was limited to 10 Mb/s because of the limited speed of the chip tester.

Fast optical thresholding with an array of optoelectronic transceiver elements

In this letter, we present an optoelectronic system for fast gray-level image decomposition into binary slices. To perform thresholding, we are making use of the differential nature of optical thyristors and compare the light level of the image pixels to that of a reference intensity. As input a gray-level image was generated using a nematic liquid crystal spatial light modulator (SLM) and as a reference intensity a VCSEL light source combined with a diffractive fan-out element was used. We also introduced a compact, large field of view telecentric optical system based on gradient refractive index lenses to image between the SLM and the array. A frame rate decomposition of a six gray-level image has been obtained at 1.8 kHz. Future prospects for system improvements are discussed.

Free-space optical interconnect and processing demonstrators with arrays of light-emitting thyristors

The significant progress which as been made in the development of differential pairs and arrays of differential pairs of light-emitting thyristors has made the construction of optical computing systems with high speed interconnections a realistic possibility. In this paper we review our work on the practical implementation of these optoelectronic transceiver devices in systems and demonstrate most of the basic functionalities necessary to build a primitive digital parallel optical processor. We demonstrate the transcription of digital optical data between cascaded single elements and between 8 by 8 arrays of completely- depleted optical thyristor differential pairs. We also show results of digital optical logic NAND, NOR, AND, OR, NOT operations, logic plane to logic plane imaging with a diffractive fan-out and parallel digital data input with a computer controlled liquid crystal micro- display. As an example of a sub-system module which has reasonable complexity we focus on a demonstrator platform which combines optical thyristor logic planes, polarization- selective diffractive optical elements, liquid crystal variable retarders and large diameter gradient index lenses, and successfully demonstrate dynamically reconfigurable nearest neighbor interconnects. We conclude by discussing the future system performances in the light of system scalability.

Free-space optical interconnection modules for two-dimensional photonic very large scale integration circuitry based on microlenses and gradient-refractive-index lenses

We present different configurations for a compact free-space optical interconnection module by combining two radial gradientrefractive- index lenses and/or two arrays of refractive microlenses. Based on our findings with ray tracing and radiometric analysis, we discuss how we have selected the proper optical system configurations and how we have chosen the different design parameters to optimally accommodate different types of optoelectronic emitters such as LEDs, microcavity LEDs, and vertical-cavity surface-emitting lasers. We focused on maximizing optical coupling efficiencies and misalignment tolerances while minimizing interchannel crosstalk.

Free-space micro-optical intra-MCM interconnection modules: performances, potentialities and limitations

We design and realize a scalable multi-channel free-space interconnection prototype with the potential for Tb/s.cm2 aggregate bit rate capacity over inter- and intra-MCM interconnection distances. The component is prototyped in a high quality optical plastic, PMMA, using deep lithography with protons. At present data communication is achieved at 622 Mb/s per channel with a BER smaller than 10-13 for the 16 channels with inter-channel cross-talks as low as -22dB. We perform a sensitivity analysis for misalignments and study the impact of fabrication errors on the performance of the interconnection module in case injection moulding would be the preferred mass-fabrication technique. We provide evidence that these modules can be mass-fabricated with the required precision in optical plastics suited for heterogeneous integration with semiconductor materials.

Free-space optical interconnection modules for 2D photonic-VLSI circuitry based on microlenses and GRINs

In this paper we present different configurations for a compact free-space optical interconnection (FSOI) module by combining two radial gradient refractive index lenses (GRIN) and/or two arrays of refractive microlenses. Based on our finding with ray-tracing and radiometric analysis we discuss how we have selected the proper optical system configurations and how we have chosen the different design parameters to optimally accommodate different types of opto- electronic emitters such as LEDs, micro-cavity LEDs and VCSELs. We hereby focused on maximizing optical coupling efficiencies and misalignment tolerances while minimizing inter-channel cross-talk. Furthermore we discuss the experimental optical characteristics of two such prototype modules that we completed together with the first experimental results of their use in parallel data communication demonstrator systems.

Design and optimization of VCSEL-based micro-optical relay systems: bringing optical information to silicon chips

We analyze the potentialities of microlens-based free-space optical pathway blocks for on-chip interconnects. To assess the promises of these modules, researchers typically make use of simple analytic Gaussian beam propagation (GBP). Although this approach leads to a first order layout of a microlens system it does not include aberrations. Aberrations however and -- spherical aberrations in particular -- become important when lenses with a small focal number are implemented. This is especially true when surface emitting lasers with a relative high beam divergence such as e.g. VCSELs are used. In this paper we evaluate how these aberrations affect the performances of such optical interconnection systems and we verify the validity of the GBP method. We enter various GBP layouts in the photonics design software SOLSTIS, which traces real rays or propagates spatially coherent optical beams through the system. We model and compare the performances of different microlens-relay system configurations and we focus on optical efficiency and scalability issues of these micro-optical interconnection components. To conclude we relate optical pathway lengths to minimum microlens diameters and to maximum achievable channel densities.

Multi-channel free-space intra-chip optical interconnections: combining plastic micro-optical modules and VCSEL based OE-FPGA.

We fabricated and replicated in semiconductor compatible plastics a multichannel free-space optical interconnection module designed to establish intra-chip interconnections on an Opto-Electronic Field Programmable Gate Array (OE-FPGA). The micro-optical component is an assembly of a refractive lenslet-array and a high-quality microprism. Both components were prototyped using deep lithography with protons and were monolithically integrated using a vacuum casting replication technique. The resulting 16-channel module shows optical transfer efficiencies of 50% and interchannel crosstalks as low as -22 dB. These characteristics are sufficient to establish multichannel intra-chip interconnects with OE- FPGAs. The OE-FPGA we used was designed within a European co- founded MEL-ARI consortium, working towards a manufacturable solution for optical interconnects between CMOS ICs. The optoelectronic chip combines fully functional FPGA digital logic with the drivers, receivers and flip-chipped optoelectronic components. It features 2 optical inputs and 2 optical outputs per FPGA cell, amounting to 256 photonic I/O links based on multimode 980-nm VCSELs and InGaAs detectors.

Microlens arrays fabricated by deep lithography with protons and their characterization

In this paper we present our latest results on the fabrication and characterization of plastic microlenslet arrays using Deep Lithography with Protons (DLP) and highlight their geometrical dimensions, their surface profile and their uniformity. We also present quantitative information on their optical characteristics such as focal length and spherical aberration as measured with a Mach-Zehnder interferometer. Furthermore we demonstrate the flexibility of the DLP technology to fabricate arrays of microlenses that feature different pitches and different sags. Although the DLP technology is a valuable tool to rapidly prototype refractive micro-optical components, the approach is unpractical for mass-fabrication. We therefore introduce a replication technique, called vacuum casting, which is very appropriate when only a few tens of copies have to be made, and we bring forward the first quantitative characteristics of these microlens replicas.