Near infrared spectroscopy offers a promising technological platform for continuous glucose monitoring in the human body. NIR measurements can be performed in vivo with an implantable single-chip based optical NIR sensor. However, the application of NIR spectroscopy for accurate estimation of the analyte concentration in highly scattering biological systems still remains a challenge. For instance, a thin tissue layer may grow in the optical path of the sensor. As most biological tissues allow only a small fraction of the collimated light to pass, this might result in a large reduction of the light throughput. To quantify the effect of presence of a thin tissue layer in the optical path, the bulk optical properties of tissue samples grown on sensor dummies which had been implanted for several months in goats were characterized using Double Integrating Spheres and unscattered transmittance measurements. The measured values of diffuse reflectance, diffuse transmittance and collimated transmittance were used as input to Inverse Adding-Doubling algorithm to estimate the bulk optical properties of the samples. The estimates of absorption and scattering coefficients were then used to calculate the light attenuation through a thin tissue layer. Based on the lower reduction in unscattered transmittance and higher absorptivity of glucose molecules, the measurement in the combination band was found to be the better option for the implantable sensor. As the tissues were found to be highly forward scattering with very low unscattered transmittance, the diffuse transmittance measurement based sensor configuration was recommended for the implantable glucose sensor.
Diabetes is a fast growing metabolic disease, where the patients suffer from disordered glucose blood levels. Monitoring
the blood glucose values in combination with extra insulin injection is currently the only therapy to keep the glucose
concentration in diabetic patients under control, minimizing the long-term effects of elevated glucose concentrations and
improving quality of life of the diabetic patients. Implantable sensors allow continuous glucose monitoring, offering the
most reliable data to control the glucose levels. Infrared absorption spectrometers offer a non-chemical measurement
method to determine the small glucose concentrations in blood serum. In this work, a spectrometer platform based on
silicon photonics is presented, allowing the realization of very small glucose sensors suitable for building implantable
sensors. A proof-of-concept of a spectrometer with integrated evanescent sample interface is presented, and the route
towards a fully implantable spectrometer is discussed.
The CMOS IC industry thrives on the down-scaling drive for ever smaller transistors, leading to faster, smaller and more complex digital systems. These ICs are interconnected by electrical tracks running on Printed Circuit Boards. Due to different frequency-dependent sources of signal degradation, the performance of these electrical interconnects lags behind the IC performance. As the electrical interconnect bottleneck increasingly impacts overall system performance, the interest in optical interconnects at the inter-chip level is growing. An important question to answer is how and where such optical interconnects should be implemented. Therefore, we first discuss the weaknesses of electrical interconnects and the potential benefits of optical interconnects. From this we then consider the implications on the introduction of optical interconnects and we argue why integration is of key importance for the successful introduction of optical interconnects at this level. Finally we describe how we have implemented optical inter-chip interconnects in a demonstrator system and go into more detail on the different levels of integration in this demonstrator system.
Ronny Bockstaele, Michiel De Wilde, Wim Meeus, Olivier Rits, Hannes Lambrecht, Jan Van Campenhout, Johan De Baets, Peter Van Daele, Eric van den Berg, Michaela Klemenc, Sven Eitel, Richard Annen, Jan Van Koetsem, Gilles Widawski, Jacques Goudeau, Baudouin Bareel, Patrick Le Moine, Reto Fries, Peter Straub, Francois Marion, Julien Routin, Roel Baets
This paper describes a complete technology family for parallel optical interconnect systems. Key features are the two-dimensional on-chip optical access and the development of a complete optical pathway. This covers both chip-to-chip links on a single boards, chip-to-chip links over an optical backpanel, and even system-to-system interconnects. Therefore it is a scalable technology. The design of all parts of the link, and the integration of parallel optical interconnect systems in the design flow of electronic systems is presented in this paper.
An overview of planar resonant-cavity light-emitting diodes is presented. Letting spontaneous emission happen in a planar cavity will in the first place affect the extraction efficiency. The internal intensity distribution is not longer isotropic due to interference effects (or density of states effects). The basics of dipole emission in planar cavities will be shortly reviewed using a classical approach valid in the so called weak-coupling regime. The total emission enhancement or Purcell factor, although small in planar cavities, will be explained. The design of a GaAs/AlGaAs RCLED is discussed. We review the state-of-the-art devices in different semiconductor material systems and at different wavelengths. Some advanced techniques based on gratings or photonic crystals to improve the efficiency of these devices are discussed. RCLEDs are not the only candidates that can be used as high-efficiency light sources in communication and non-communication applications. They compete with other high-efficiency LEDs and with VCSELs. The future prospects of RCLEDs are discussed in view of this competition.
In this paper, a novel way for the fabrication of opto-electronic transceiver modules is proposed. These modules are characterized by the use of MT-RJ connectors, low-cost fabrication tools, highly efficient opto-electronic components such as VCSELs and CMOS integrated detectors, and an easy fabrication scheme. The module is based on the direct alignment technique; this means that the fiber and the photon detector and laser diode are self and directly aligned with respect to each other, without the need for optical lenses. Cost are expected to be low, since the transceiver module can be fabricated using existing mass volume fabrication technqiues.
In order to satisfy the increasing demand for interchip interconnect bandwidth, a number of current research projects are concentrating on the use of waveguided optical interconnect arrays to span PCB-range distances. To accelerate system design and technology development, CAD tools for the design and the simulation of the interconnects are indispensable. We are developing a design methodology for optical inter-chip interconnects, to produce a tool for assisting system designers on deciding on product and parameter options for the different interconnect building blocks. A mandatory first step in this methodology development concerns the investigation of the combined impact of individual product and parameter variations on system-level interconnect system properties. Accurately predicting some interconnect properties requires analog simulation of the full electrical-optical-electrical links. Detailed models for the link building blocks involving geometrical calculations are much too slow for this purpose. Circuit-level simulation tools, with appropriate model descriptions, are much more suitable. In this paper, we describe our framework for the joint simulation of the entire optical interconnect with a mixed analog/digital system. We discuss in detail a number of issues that are involved with the implementation of circuit-level simulation models in the analog modelling language Verilog-AMS, and show a link simulation example.
Architectural studies have identified field-programmable gate arrays (FPGA) as a class of general-purpose very large scale integration components that could benefit from the introduction at the logic level of state-of-the-art massively parallel optical inter-chip interconnections. In this paper, we present a small-scale optoelectronic multi-FPGA demonstrator in which three optoelectronic enhanced FPGAs are interconnected by 2D Plastic Optical Fiber (POF) ribbon arrays. The full-custom FPGA chips consisting of an 8 X 8 array of very simple programmable logic cells are equipped with two optical sources and two receivers per FPGA cell yielding a maximum of 256 optical links per chip. The optical links are designed for signaling rates of 80 to 100 Mbit/s (160 to 200 Mbaud using Manchester coded data) compatible with the maximum clock frequency of the, in 0.6 micrometers CMOS implemented, FPGA chips. The results of parallel link experiments between such modules with both VCSELs and LEDs as sources will be shown. A large scale parallel bit error rate experiment at 90 Mbit/s/channel between two half-populated VCSEL-based FPGA modules with 112 of their 128 channels operational at bit error rates below 10-13 on all active channels (approximately equals 10 Gbit/s/chip) proves the feasibility of this approach. We first briefly discuss the general architecture and the realization of the optoelectronic FPGA demonstrator system. We then present measurement results on the available modules, followed by some conclusions on this work.
It is our goal to demonstrate the viability of massively parallel optical interconnections between electronic VLSI chips. This is done through the development of the technology necessary for the realization of such interconnections, and the definition of a systems architecture in which these interconnections play a meaningful role. Field-programmable gate arrays (FPGA) have been identified as a class of general-purpose very large scale integration components that could benefit from the massive introduction of state-of-the-art optical inter-chip interconnections at the logic level. In this paper, we present the realization of a small-scale optoelectronic FPGA with 8 X 8 logic cells, containing two optical sources and two receivers per FPGA cell yielding a total of 256 links per chip. These FPGA chips designed to operate with information rates of 80 Mbit/s/link will be used in a three- chip demonstrator system as a test bed for the concepts above. We first identify the reason why we think optical interconnects can provide added value in FPGAs. The next sections briefly discuss the general architecture of our demonstrator system and the realization of the optoelectronic FPGA. We then present first measurement results followed by ongoing work and conclusions.
Current developments in computer technology give rise to increasing data communication over relatively short distances at backplane- and inter MCM interconnect level. It is foreseen that electrical interconnect will not be able to accommodate the necessary data traffic in advanced data processing systems in the future and hence a bottleneck will be created. A potential remedy for this interconnect problem is the use of parallel optical datalinks. In this paper we propose small diameter step index plastic optical fiber ribbons in combination with high efficient resonant cavity LED's as a cheap and feasible option for these optical links. A design for such an optical link is presented with special attention for the optical pathway. Experimental results on the optical properties of the used POF are shown. We describe the development of RCLED's at 850 nm specially designed for efficient coupling into POF. We measured a RCLED to POF coupling efficiency up to 40%. Additionally we report on the technologies used for the fabrication and assembly of the optical pathways and finally some experiments were carried out on the first realized assemblies.
Planar Resonant Cavity LEDs (RCLEDs) are suitable light sources for parallel interchip interconnect links, due to their high efficiency, zero-threshold, low voltage, high reliability and high speed characteristics. The through- substrate emitting RCLEDs, optimized for Polymer Optical Fiber (POF) coupling, consist of an InGaAs quantum sandwiched between a metal mirror and a distributed Bragg reflector. The RCLEDs are arranged in 8 X 8 arrays with 250 um pitch. The arrays have been mounted onto glass carriers, and the coupling efficiency into POF, the far- field pattern and the modulation characteristics are measured. The overall quantum efficiency of the devices with 50 um diameter was found to be 13.4%, the QE into POF was 3.7%. The large-signal transient behavior of the devices has been investigated. Using a high-speed pulse source, nanosecond rise and fall times have been measured. Wide open eye diagrams at 1 Gbit/s were obtained using voltage pulse drivers. These data were compared to theoretical results based on a non-linear rate equations model.
Low-power consumption, high efficiency and high bandwidth surface emitting semiconductor optical sources are critical elements in the development of future photonic systems for space and civil nuclear applications. In this paper, we report on preliminary high total dose experiments performed on two types of recently developed microcavity emitters: VCSELs and microcavity (or resonant cavity) LEDs. We gamma irradiated a total of twelve commercially available packaged VCSELs and two home-made flip-chipped 2 X 2 microcavity LED arrays. For doses between 5(DOT)106 Gy and 1.3(DOT)107 Gy the VCSELs show a threshold current increase lower than 20% and an output power decrease lower than 10%. These values are even smaller if the VCSEL is operated at a higher temperature. At a dose of 3.14(DOT)107 Gy, one VCSEL still showed satisfactory operation. The microcavity LEDs suffered from a burn-in after radiation but recovered quickly when biased. Their output power decrease is comparable to that of the VCSELs, while their quantum efficiency is not much affected. The specifications of both types of devices are not substantially altered by high gamma doses and can therefore be considered for application in enhanced radiation environments.
We simulate and compare optical transmission efficiencies, throughputs and interconnection lengths of free-space and POF-based guided-wave optical interconnection systems for different types of microcavity emitters.
Parallel optical data links using high efficiency Microcavity LEDs and small diameter POF ribbons are proposed. MCLED performance, coupling efficiencies, alignment tolerances, POF end facet termination techniques and first link experiments are studied.
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