Browsing by Subject "Optical interconnects"
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Item Centralized optical backplane bus using holographic optical elements for high performance computing(2007) Bi, Hai, 1975-; Chen, Ray T.Optical communication is distinguished for its enormous interconnect capacity over long distance. As the cost of optical components drops, high bandwidth optical systems were successfully employed into local area network and computer racks because electrical counterparts are not able to deal with the data rate demands for these applications. With the popularity of multi-core CPU in High Performance Computers, the board-to-board interconnects exclusive based on electrical technology in backplane applications become insufficient because of not only bandwidth crises, but also wiring congestions. Many researches have projected that the progress of optical technology will further push down the boundary demarcating electrical and optical domains in the interconnect hierarchy. Accordingly, backplane or even board-to-board level interconnects will benefit from the complement of optical interconnect. From architecture point of view, an optical bus implementation of the optical interconnect has the potential advantage of both huge bandwidth and elimination of wiring congestion. In contrast, optical waveguide and free-space interconnects although provide high bandwidth capacity, are essentially point-to-point technology which requires routing to a central switch on the backplane. The centralized approach that was based on substrate guided optical interconnects is the only way known that fulfills a uniform fan-out for different nodes in a bus architecture, which allows medium sharing among nodes. In this dissertation, innovative bit-interleaved optical backplane bus architecture is created based on centralized substrate-guide optical interconnect, which allows the tremendous bandwidth capacity to be shared by retaining the share bus architecture. Therefore, a secure and reliable high speed transmission channel could be established by distributing copies of confidential information separately. The feature provided by this innovative design cannot be fulfilled using electrical interconnects or other optical point-to-point technology without causing wiring congestions. In this dissertation, the optical characteristics of the centralized optical bus such as bandwidth and alignment tolerance are analyzed so that multi-channel implementation are successful on the fabricated optical interconnect layer. A 3-board-16-channel computer server using optical backplane board demonstrator using centralized optical bus was built upon the simulation, design and packaging work.Item Fan-out equalized shared optical backplane bus(2003) Han, Xuliang; Chen, Ray T.Optics is distinguished for its interconnect capability. A variety of optical interconnect technologies have been successfully employed in the real applications where the conventional implementations that are exclusively based on electrical interconnects have become insufficient, and the boundary demarcating the electrical and optical domain is being further pushed down in the interconnect hierarchy. Many researches have projected an imminent bottleneck throttling the board-to-board data transfers. Accordingly, an opportunity exists for the continuing exploitation of optics to complement or even replace the conventional electrical backplanes. The most prominent benefit of utilizing optics is the tremendous gain in the bandwidth capacity. From the architecture point of view, however, three fundamental optical methodologies, optical waveguide interconnects, free-space optical interconnects, and substrate-guided optical interconnects, have a huge discrepancy in how effectively the obtained bandwidth gain would improve the overall system performance. The approaches that are based on optical waveguide or free-space interconnects provide only the point-to-point topology, in turn the various proposed architectures are essentially an optical point-to-point switched backplane. In contrast, the approaches that are based on substrate-guided optical interconnects can effectively fulfill the shared bus topology, and thus an optical backplane bus can be implemented. In this dissertation, the comparative examinations specifically point out that optical backplane bus has many considerable advantages over optical point-to-point switched backplane. An innovative optical backplane architecture, optical centralized shared bus, is created based on substrate-guided optical interconnects, which utilizes the beneficial physical characteristics of optics while retaining the desirable architectural properties of the shared bus topology. Therefore, it is projected that the bandwidth gain would be maximized. Superior to other optical shared bus architectures, this innovatively designed optical backplane bus can accomplish equalized fan-outs across the entire architecture in an elegant manner. This significant merit can substantially ease the overall system integration. In this dissertation, the equalized bus fan-outs are successfully established on the fabricated optical interconnect layer. To further verify the feasibility of optical centralized shared bus architecture in the practical scenarios, two research prototypes, a microprocessor-to-memory interconnect demonstrator and a centralized shared-memory multiprocessing emulator, are constructed with the physically characterized optical centralized shared bus.Item Highly integrated polymer photonic switching and interconnects(2006) Wang, Xiaolong; Chen, Ray T.Benefited from its tremendous gain in bandwidth, optics is taking the leader role instead of electronics in many communication systems for the past three decades, and is expected to continue this trend irresistibly in the predictable future. From the architecture point of view, most optical communication systems provide only the point-to-point topology. The interconnection among the distributed nodes still has to rely on the electronic exchanger, which is becoming an imminent bottleneck throttling the overall system bandwidth. In contrast, all optical exchange networks employing optical switches will skip the heavy-loaded data conversion and achieve a prominent bandwidth enhancement and cost reduction. In the first part of this dissertation, a planar lightwave circuit (PLC) based polymer optical switch utilizing total internal reflection (TIR) effect was proposed and fabricated. The optimized device obtained many desired features, such as low insertion loss, low cross talk, low power consumption and wavelength insensitivity. The application of the TIR optical switch was extended to provide true time delays (TTD) for phased array antennas (PAA). A fully integrated 4-bit TTD device composed of TIR switches and waveguide delay lines successfully delivered the 16 delay values required by a PAA system. As we move from long-distance network to short distance reach, optics encounters increasing difficulties in terms of packaging, reliability and system cost. However, with the rapid increasing speed and complexity of VLSI technology, electrical interconnects will fail to provide sufficient bandwidth beyond 10GHz after 2012. There does exist an opportunity for the continuing exploration of optics to complement or even replace the conventional board level electrical interconnects. An innovative approach with a fully embedded structure is anticipated to overcome the technical and cost barriers that prohibit the realization of optical interconnects in board levels. In the second half of this dissertation, technology efforts projected to relieve the concerns of low cost, high performance optical layers, as well as the system integration issues were carried out. The research accomplishments include a 51cm long molded waveguide array with 150GHz optical bandwidth, 85% coupling efficiency surface normal micro-mirror and system integration with laser diodes and photo detectors.Item Integration of thin film GaAs MSM photodetector in fully embedded board-level optoelectronic interconnects(2004) Lin, Lei; Chen, Ray T.Technology in 21 century has developed in an accelerated rate. As a technology indicator of modern era, computer has developed from its early age to ubiquitous equipment in every day life. The driven force for faster computer has become even stronger. Together with the fast-evolved high-speed Internet, faster computes are processing huge amount of data. Electrical interconnect between CPU and memory has become the bottleneck of data processing in computer. The foreseeable solution to address this bottleneck is to use optical interconnect replacing electrical interconnect. However, before this substation becomes reality, many difficulties to integrate optics into VLSI system have to be addressed. In this dissertation, a fully embedded optical interconnect system is proposed. The main attribute of optical interconnect system with fully embedded form is the high degree of reliability. Together with the high bandwidth, low power consumption, the optical interconnect system is fully compatible with VLSI circuit and fully fulfill the request of bandwidth between CPU and memory. The fully embedded optical interconnect system includes three main components: thin film VCSEL (vertical cavity surface emitting laser) as optical transmitter, thin film GaAs MSM (metal-semiconductor-metal) photodetector as optical receiver and flexible polymer waveguide as optical transmitting media. Thin film MSM photodetector array is fabricated and integrated with channel waveguide array. The whole system integration among thin film array of photodetector and VCSEL and thin film flexible waveguide is presented.Item Investigation of polymer waveguides for fully embedded board-level optoelectronic interconnects(2004) Liu, Yujie; Chen, Ray T.We proposed a fully embedded board-level optoelectronic interconnect structure utilizing polymer waveguides and 45-degree micro mirror light couplers. This structure is expected to provide high-speed, large bandwidth, low power dissipation, as well as compatibility to conventional PCB fabrication process, ease of optical alignment and packaging. High performance polymer waveguide with 45 degree micro mirror coupler is one key component to enable all these advantages. The performance analyses indicate that the polymer waveguide can provide low loss link for optical data and high channel density can be achieved without inducing significant crosstalk. Waveguide intersections and bends can be employed in the waveguide circuitry design to improve the design flexibility and interconnection density. 45 degree mirror couplers can provide high input and output surface-normal coupling efficiency. The fully embedded system features high tolerance to the linear and angular misalignments due to the possible fabrication imperfection. Ultradel 9000 series polyimides are used to form the waveguide and mirror couplers. Fabrication techniques are developed and discussed in detail. Waveguide array and mirror couplers with good quality have been fabricated and characterized. Preliminary integration of polymer waveguide array with MSM photodetector array through 45-degree micro mirror couplers is demonstrated and shows an aggregate bandwidth of 32GHz for a 1×12 channel array. Further integration is under development. An optoelectronic interconnect layer (OIL) will be developed and laminated with the other layers of PCB to improve system performance without inducing manufacturing difficulties.Item On-chip silicon photonic waveguide devices for biochemical sensing and optical interconnects(2017-09-15) Yan, Hai, Ph. D.; Chen, Ray T.; Wang, Zheng; Ben-Yakar, Adela; Yeh, Hsin-Chih; Chakravarty, SwapnajitOn-chip photonic devices based on waveguides receives significant attention for its capability in realizing great performance with high integration density. Two of the most representative area of application are biochemical sensing and optical interconnects. Micro- and nano-scale photonic biosensor has become a fast growing research topic driven by the need of portable bio-detection systems with high sensitivity, high throughput, real-time and label-free detection. Various structures, especially those based on silicon-on-insulator (SOI) substrate, have been demonstrated in research, some of which have been developed into commercially available product. In terms of optical interconnect, extensive research and development is underway to try to break the bottleneck in traditional copper interconnect in modern electronics facilities and devices, from local area network to short-reach data links and even down to on-chip interconnect. Silicon photonics is currently the most promising solution to optical interconnect primarily due to its mature processing technologies. Yet other materials, including electro-optic (EO) polymers, are also widely used in specific applications (e.g. EO modulators) for the benefits of high speed and low energy consumption. In this dissertation, various photonic waveguide devices for biochemical sensing and optical interconnect will be presented. First, biosensors based on photonic crystal (PC) microcavities will be demonstrated. A bandpass filter will be introduced to combine multiple PC microcavity sensors into an array. Array of PC biosensors with different parameters was formed to give a wide dynamic range of detection range. The detection of antibiotics and heavy metals will be covered. Then, a novel structure -- subwavelength grating waveguides (SWG) based biosensors will be introduced and its unique thickness-independent surface sensitivity will be analyzed and demonstrated. Thirdly, I will show a novel one-dimensional PC slot waveguide. It offers a simple, high-efficiency and low-loss phase shifter design for silicon-polymer hybrid EO modulators. Strained silicon waveguide for the generation of mid-infrared wave through difference frequency generation will be covered at last. It will show the potential application of chemical sensing with integrated photonic devices.Item Optical clock signal distribution and packaging optimization(2002-05) Wu, Linghui; Chen, Ray T.Polymer-based waveguides for optoelectronic interconnects and packagings were fabricated by a fabrication process that is compatible with the Si CMOS packaging process. An optoelectronic interconnection layer (OIL) for the high-speed massive clock signal distribution for the Cray T-90 supercomputer board employing optical multimode channel waveguides in conjunction with surface-normal waveguide grating couplers and a 1-to-2 3 dB splitter was constructed. Equalized optical paths were realized using an optical H-tree structure having 48 optical fanouts. This device could be increased to 64 without introducing any additional complications. A 1-to-48 fanout H-tree structure using Ultradel 9000D series polyimide was fabricated. The propagation loss and splitting loss have been measured as 0.21 dB/cm and 0.4 dB/splitter at 850 nm. The power budget was discussed, and the H-tree waveguide fully satisfies the power budget requirement. A tapered waveguide coupler was employed to match the mode profile between the singlemode fiber and the multimode channel waveguides of the OIL. VII A thermo-optical based multimode switch was designed, fabricated, and tested. The finite difference method was used to simulate the thermal distribution in the polymer waveguide. Both stable and transient conditions have been calculated. The thermo-optical switch was fabricated and tested. The switching speed of 1 ms was experimentally confirmed, fitting well with the simulation results. Thermo-optic switching for randomly polarized light at wavelengths of 850 nm was experimental confirmed, as was a stable attenuation of 25 dB. The details of tapered waveguide fabrication were investigated. Compressionmolded 3-D tapered waveguides were demonstrated for the first time. Not only the vertical depth variation but also the linear dimensions of the molded waveguides were well beyond the limits of what any other conventional waveguide fabrication method is capable of providing. Molded waveguides with vertical depths of 100 µm at one end and 5µm at the other end and lengths of 1.0 cm were fabricated using a photolime gel polymer. A propagation loss of 0.5 dB/cm was achieved when light was coupled from the 5 µm x 5 µm end to the 100 µm x 100 µm end and that of 1.1 dB/cm was observed when light was coupled from the 100 µm x 100 µm end to the 5 µm x 5 µm. By confining the energy to the fundamental mode when coupling from the large end to the small end, lowloss packaging can be achieved bi-directionally. 3-D compression-molded polymeric waveguides present a promising solution to bridging the huge dynamic range of different optoelectronic device-depths varying from a few microns to several hundred microns.Item Polymer based nano- and micro-photonic devices for three-dimensional optical interconnects(2010-12) Dou, Xinyuan; Chen, Ray T.; Bank, Seth R.; Banerjee, Sanjay K.; Lee, Jack C.; Park, Chanro; Wang, AlanThe demand for higher bandwidth and higher speed driven by semiconductor technology development draws a great deal of research efforts devoted to the development of high speed data communication. Challenges on electrical copper interconnects at high frequency make optical interconnect technologies become a promising alternative to conventional electrical interconnects at different levels. This doctoral dissertation describes polymer based nano- and micro-photonic devices for three-dimensional optical interconnects. Two areas are focused, (1) polymer based two-dimensional (2D) and three-dimensional (3D) photonic crystal fabrication and simulation for laser beam steering applications, (2) polymer based optical waveguide array and shared bus waveguide with embedded 45° micro-mirrors for board level optical interconnects. A three-dimensional (3D) face-centered cubic (FCC) type polymer based photonic crystal using the polymer material SU-8 was simulated and successfully fabricated using a polygonal prism based holographic fabrication method. The theoretical study of polymer based photonic crystals was carried out for laser beam steering, which is based on the superprism effect. Horizontally stacked two-dimensional (2D) photonic crystal was fabricated by a double exposure holographic interference method. The k-vector superprism effect, the principle for beam steering, was studied in detail through EFC (Equi-frequency Contour) analysis. A polymer based optical waveguide array with embedded 45° micro-mirrors for board level optical interconnects was prepared using a Ni metal hard mold by a UV imprint technique. A nickel based metal mold with 45º tilted surfaces on both ends of the channel waveguide was prepared through the electroplating process. To obtain a precise 45º tilted angle, a 50µm thick SU-8 layer was exposed under de-ionized water. High speed optical testing (10Gb/s) was carried out on the polymeric optical waveguide array with embedded 45º micro-mirrors on flexible substrate for out-of-plane optical interconnects. A polymer based 3-to-3 shared optical bus waveguide with opposite 45º micro-mirrors was designed and fabricated using the metallic hard mold method. The Ni metal hard mold was successfully prepared using the Ni electroplating method. This metallic hard mold provides a convenient way to fabricate the polymeric optical bus waveguide devices through the imprint technique.Item Silicon - polymer hybrid integrated microwave photonic devices for optical interconnects and electromagnetic wave detection(2015-05) Zhang, Xingyu, 1986-; Chen, Ray T.; Willson, Grant; Alu, Andrea; Akinwande, Deji; Poggio, EnricoThe accelerating increase in information traffic demands the expansion of optical access network systems that require high-performance optical and photonic components. In short-range communication links, optical interconnects have been widely accepted as a viable approach to solve the problems that copper based electrical interconnects have encountered in keeping up with the surge in the data rate demand over the last decades. Low cost, ease of fabrication, and integration capabilities of low optical-loss polymers make them attractive for integrated photonic applications to support futuristic data communication networks. In addition to passive wave-guiding components, electro-optic (EO) polymers consisting of a polymeric matrix doped with organic nonlinear chromophores have enabled wide-RF-bandwidth and low-power active photonic devices. Beside board level passive and active optical components, on-chip micro- or nano-photonic devices have been made possible by the hybrid integration of EO polymers onto the silicon platform. In recent years, silicon photonics have attracted a significant amount of attentions, because it offers compact device size and the potential of complementary metal–oxide–semiconductor (CMOS) compatible photonic integrated circuits. The combination of silicon photonics and EO polymers can enable miniaturized and high-performance hybrid integrated photonic devices, such as electro-optic modulators, optical interconnects, and microwave photonic sensors. Silicon photonic crystal waveguides (PCWs) exhibit slow-light effects which are beneficial for device miniaturization. Especially, EO polymer filled silicon slotted PCWs further reduce the device size and enhance the device performance by combining the best of these two systems. The potential applications of these silicon-polymer hybrid integrated devices include not only optical interconnects, but also optical sensing and microwave photonics. In this dissertation, the design, fabrication, and characterization of several types of silicon-polymer hybrid photonic devices will be presented, including EO polymer filled silicon PCW modulators for on-chip optical interconnects, antenna-coupled optical modulators for electromagnetic wave detections, and low-loss strip-to-slot PCW mode converters. In addition, some polymer-based devices and silicon-based photonic devices will also be presented, such as traveling wave electro-optic polymer modulators based on domain-inversion directional couplers, and silicon thermo-optic switches based on coupled photonic crystal microcavities. Furthermore, some microwave (or RF) components such as integrated broadband bowtie antennas for microwave photonic applications will be covered. Some on-going work or suggested future work will also be introduced, including in-device pyroelectric poling for EO polymer filled silicon slot PCWs, millimeter- or Terahertz-wave sensors based on EO polymer filled plasmonic slot waveguide, low-loss silicon-polymer hybrid slot photonic crystal waveguides fabricated by CMOS foundry, logic devices based on EO polymer microring resonators, and so on.Item Thin-film VCSEL and optical interconnection layer fabrications for fully embedded board level optical interconnects(2003) Choi, Chulchae; Chen, Ray T.Semiconductor technology has been splendid evolved. As a consequence of, massive data traffic is required in system level. However copper based interconnection reached the upper limit of data transfer rate and can not provide enough bandwidth for high performance system. Copper based interconnection in long haul application was replaced to optical fiber. Optical interconnection in system level is generally considered as an alternative to provide high bandwidth. However, unlike long haul application, optical interconnection in system level encountered many problems such as compatibility, robustness and packaging difficulty. The compatibility to current electrical board system and packaging difficulty must be solved. This dissertation describes a fully embedded board level optical interconnection, which can solve many problems, components fabrication and hybrid integration with electrical layers. Thin-film VCSEL array and flexible optical waveguide are demonstrated. The optical interconnection layer integrated with thin-film VCSEL and photo-detector arrays is demonstrated.