Proceedings Volume 6126

Photonics Packaging and Integration VI

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Proceedings Volume 6126

Photonics Packaging and Integration VI

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Volume Details

Date Published: 10 February 2006
Contents: 6 Sessions, 25 Papers, 0 Presentations
Conference: Integrated Optoelectronic Devices 2006 2006
Volume Number: 6126

Table of Contents

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Table of Contents

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  • Optical Interconnects I
  • Materials in Advanced Packaging
  • Optical Interconnects II
  • Packaging for Communication Components
  • Alignment/Packaging/Fabrication
  • Optical Interconnects/Micro-Optics
Optical Interconnects I
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Ultra-high-speed transmission of polymer-based multimode interference devices for board-level high-throughput optical interconnects
Multimode interference (MMI) devices operating at high data rates are important for integrated optics and optical networks. Their 1×N splitting provides a basic functionality in these applications. Ultra-high speed data transmission at 40Gb/s per channel with a total bandwidth of 320Gb/s for all 8 output ports is demonstrated for the first time on a 1 × 8 photo-definable polymer-based MMI power splitter. The transmission integrity is confirmed by the bit-error-rate (BER) testing. To further determine the speed limitations of MMI devices, ultra-short pulse response of these devices is quantified. For example, for 20fs Gaussian input pulses into a 1×8 polymer-based MMI splitter, the output pulses are severely degraded in coupling efficiency (47%) and completely broken up in time and in space primarily due to inter-modal and intra-modal (waveguide) dispersions.
Holographic optical elements for optical backplane bus targeted at high speed data transfer
Jonathan Ellis, Robert Mays Jr., Dale Griffiths, et al.
The primary technical challenge for optical backplanes involve the alignment and optical isolation of multiple data channels. Since most backplanes require data transfer rates greater than a single optical channel can costeffectively provide, multiple data channels is the common solution for higher aggregate transfer rates. Established optical alignment and isolation techniques include spatial separation of optical channels, use of lensing elements to focus specific transmitter outputs to specific receiver areas, use of differing wavelengths for adjacent channels with appropriate frequency filtering on receivers, and the use of "light guide tubes" for each channel. This presentation will examine another promising option, the use of "matched" Holographic Optical Elements (HOEs) to provide both cross channel optical isolation and to significantly relax traditional optical alignment requirements. Matched HOEs can both induce upon a transmitted optical stream, and then filter upon a received optical stream, a number of distinguishing characteristics such as wavelength, polarization, phase, and amplitude. Thus the use of a unique "matched HOE" pair with each transmitterreceiver pair of multiple optical data channels can provide an efficient mechanism to isolate individual data streams even when they may be physically coincident, such as in a length of fibre optic or when multiple free space data transmitters illuminate several channel's receiver elements. Thus, the alignment issue is relaxed from the usual constraint of attempting to physically separate channels to one where, as long as the receiver is within the optical cone of it's matched transmitting element, cross channel interference can be effectively eliminated.
Development of a fabrication technology for integrating low cost optical interconnects on a printed circuit board
Geert Van Steenberge, Nina Hendrickx, Peter Geerinck, et al.
We present a fabrication technology for integrating polymer waveguides and 45° micromirror couplers into standard electrical printed circuit boards (PCBs). The most critical point that is being addressed is the low-cost manufacturing and the compatibility with current PCB production. The latter refers to the processes as well as material compatibility. Multimode waveguides are patterned by KrF excimer laser ablation in acrylate polymers with 0.13 dB/cm propagation loss at 850 nm. Single mode waveguides using inorganic-organic hybrid polymers show an attenuation loss of 0.62 ± 0.08 dB/cm at 1.3 μm. A process for embedding metal coated 45° micromirrors in optical waveguiding layers is developed. Mirrors are selectively metallized using a lift-off process. Filling up the angled via without the presence of air bubbles and providing a flat surface above the mirror is only possible by enhancing the cladding deposition process with ultrasound agitation. Initial single mode coupling loss measurements at 1.3 μm show an excess mirror loss of 1.55 dB. Multimode coupling loss measurements will improve this excess loss, because of the lower surface roughness of the mirrors using the acrylate polymers for multimode waveguides.
Bit-interleaved optical bus for high-speed secure multiboard system
Optical backplane bus based on glass substrate with volume holographic gratings on top surface possesses a great ability to broadcast information. This feature is utilized to accomplish a bit-interleaved optical interconnect system. In this system, each daughter board sends only one bit per round and the bit pulses from different boards can cascade in a designed series when the transmitters are distributed in an appropriate manner. In this way, even slow electronic chips can be coordinated to generate an aggregate bandwidth up to 10Gbps, which is impossible to achieve with a multi-drop electrical bus. Besides the benefits of high data rate and low crosstalk, such a bit-interleaved architecture provides a secure data storage method. Each daughter board only stores a quarter bits of any byte, so that no single board has the entire information and security is enhanced. Alignment tolerance and power budget of the proposed optical interconnect system is theoretically calculated and experimentally verified. With collimating lenses, the packing density of transceivers is more than 4/cm2, and thus the signal density can be above 40Gbps/cm2/board. The insertion loss due to misalignment and beam divergence is measured to be approximately 3dB. The bit error rate (BER) of 10Gbps receivers with -12dBm sensitivity is estimated to be below 10-12.
Materials in Advanced Packaging
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Advanced packaging materials for optical applications: bridging the gap between nm-size structures and large-area panel processing
Ruth Houbertz, Herbert Wolter, Peter Dannberg, et al.
During the last two decades, nano-materials have been intensively investigated due to their wide range of properties, resulting in a variety of applications. In order to serve as advanced packaging material, from an industrial point of view emphasis has also to be on cost reduction either for the materials, the processes, or for both. Materials are searched for which enable processing and integration from a nm up to a cm scale. A particular class of low-cost nanoscale materials fulfilling this requirement are inorganic-organic hybrid polymers (ORMOCER®)1 which are synthesized by catalytically controlled hydrolysis/polycondensation reactions, resulting in storage-stable resins. Due to the variety of chemical and physical parameters, the material and processing properties which directly influence the resulting structure and thus the physical properties, can be varied over wide ranges. Upon synthesis, functional organic groups are introduced into the material which allows one to photochemically pattern the resins. The materials are capable to be patterned on a nm up to a cm scale, employing a variety of different micro- and nanopatterning methods such as, UV lithography, UV replication/lithography, laser-direct writing, or two-photon polymerization, in order to generate micro- and nano-optical components. While for most of the techniques the patterning has to be repeated several times in order to achieve multi-functional layers, the latter method allows one to directly write arbitrary 3D structures into the hybrid polymer material. The combination of chemically designed low-cost materials with tunable material parameters such as low optical absorption, tunable refractive index, good processibility, and high chemical, thermal and mechanical stability, is very attractive for (integrated) optical applications. Examples for application of the materials for microoptics as well as for optical back-planes generated by large-area processing will be given.
Fiber optics structural mechanics and nanotechnology-based new generation of fiber coatings
This paper consists of two parts - review and extension. The review part deals with typical fiber optics structures (bare, single- and dual-coated fibers; fibers experiencing low temperature micro-bending; fibers soldered into ferrules or adhesively bonded into capillaries; role of the non-linear stress-strain relationship, etc.) subjected to thermally induced and/or mechanical loading in bending, tension, compression, or to various combinations of such loadings. The emphasis is on the state-of-the-art in the area of optical fiber coatings and the functional (optical), mechanical and environmental problems that occur in polymer-coated or metallized fibers. The solutions to the examined problems are obtained using analytical methods (predictive models) of structural mechanics. The review is based primarily on the author's research conducted at Bell Laboratories, Murray Hill, NJ, during his eighteen years tenure with this company. The extension part addresses a new generation of optical fiber coatings and deals with the application of a newly developed (by the ERS/Siloptix Co.) nano-particle material (NPM) that is used as an attractive substitute for the existing optical fiber coatings. This NPM-based coating has all the merits of polymer and metal coatings, but is free of their shortcomings. The developed material is an unconventional inhomogeneous "smart" composite material, which is equivalent to a homogeneous material with the following major properties: low Young's modulus, immunity to corrosion, good-to-excellent adhesion to adjacent material(s), non-volatile, stable properties at temperature extremes (from -220°C to +350°C), very long (practically infinite) lifetime, "active" hydrophobicity - the material provides a moisture barrier (to both water and water vapor), and, if necessary, can even "wick" moisture away from the contact surface; ability for "self-healing" and "healing": the NPM is able to restore its own dimensions, when damaged, and is able to fill existing or developed defects (cracks and other "imperfections") in contacted surfaces; very low (near unity) effective refractive index (if needed). NPM can be designed, depending on the application, to enhance those properties most important. NPM properties have been confirmed through testing. The tests have demonstrated the outstanding mechanical reliability, extraordinary environmental durability and, in particular applications, improved optical performance of the light guide.
Versatile coupling of a plastic optical fibre bundle to an avalanche photodiode array
With the increasing use of optical fibre in both the telecommunications and home networking areas, the packaging and alignment of various optoelectronic devices has never been more critical. In particular coupling of Plastic Optical Fibre (POF) to detectors has become an important area of research. Most off-the-shelf POF has a core diameter of 980 micron, while a typical photodiode may have an active area diameter of 50 micron. Hence without some kind of physical alignment losses may become unmanageable. This paper describes efforts to couple Plastic Optical Fibres to an avalanche photodiode (APD) array. An imaging POF fibre-bundle is used to connect to the array in a low cost versatile manner. An array of up to ten fibres is used to form the bundle. Mechanical guide systems both on the substrate of the chip and on the package housing itself are used to align each individual fibre to a corresponding photodiode. The results from several focusing techniques are presented to overcome coupling losses encountered while focusing the beam from the POF onto the smaller detector active area. A multi fibre connector is used to connect other instruments at the opposite end of the fibre bundle. The primary application of this technology will enable the use of arrays of photon counting detectors in astronomy.
Lithography-grade tungsten-copper substrates for wafer level packaging
Bob Cronk, Greg Rudd
Wafer-level packaging can result in significant yield improvement, cost savings, and other improvements in function. For power devices, mismatch between coefficients of thermal expansion (CTE's) between the device and the mounting substrate or package can induce stress that reduces reliability. Adapting CTE-matched composite materials to wafer-level packaging schemes would be beneficial. We describe processes and show data for tungsten-copper substrates that meet wafer specifications for form and finish.
Optical Interconnects II
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Three-dimensional chip-scale optical interconnects and switches with self-organized wiring based on device-embedded waveguide films and molecular nanotechnologies
Tetsuzo Yoshimura, Yoshiyuki Suzuki, Noriyuki Shimoda, et al.
We review our strategy toward chip-scale optical interconnect/switching with nano-scale packaging. A threedimensional optoelectronic (3-D OE) platform "System in S-FOLM" consisting of stacked OE films with embedded thin-film devices provides multilayer OE boards, 3-D stacked OE LSIs, 3-D optical switching systems, and so on. OE Amplifier/Driver-Less Substrate (OE-ADLES), where E-O and O-E conversions are respectively carried out by light modulators directly-driven by LSI output and by photodetectors directly-generating LSI input, reduces power dissipation and increases data rate in the platform. To realize the 3-D OE platform, waveguide films with surface-normal mirrors, resource-saving heterogeneous integration, 3-D optical wiring, and nano optical ICs and their mass production processes are required. These will be achieved our five original core technologies: the built-in mask method, PL-Pack with SORT, SOLNET, the molecular-controlled growth, and MND. The FDTD simulation reveals that in nano optical ICs of photonic crystals ~0.6-ps delay arises to complete lightwave interferences and confine lightwaves into waveguide regions. In addition, the molecular-controlled growth may enable future molecular transistor circuits.
Progress toward optical interconnects for intrachip global communication
Michael W. Haney, Muzammil Iqbal, Michael J. McFadden, et al.
Microprocessor performance is now limited by the poor delay and bandwidth performance of the on-chip global wiring layers. Although relatively few in number, the global metal wires have proven to be the primary cause of performance limitations - effectively leading to a premature saturation of Moore's Law scaling in future Silicon generations. Building upon device-, circuit-, system- and architectural-level models, a framework for performance evaluation of global wires is developed aimed at quantifying the major challenges faced by intrachip global communications over the span of six technology generations. This paper reviews the status of possible intra-chip optical interconnect solutions in which the Silicon chip's global metal wiring layers are replaced with a high-density guided-wave or free-space optical interconnection fabric. The overall goal is to provide a scalable approach that is compatible with established silicon chip fabrication and packaging technology, and which can extend the reach of Moore's Law for many generations to come. To achieve the required densities, the integrated sources are envisioned to be modulators that are optically powered by off-chip sources. Structures for coupling dense modulator arrays to optical power sources and to free-space or guide-wave optical global fabrics are analyzed. Results of proof-of-concept experiments, which demonstrate the potential benefits of ultra-high-density optical interconnection fabrics for intra-chip global communications, are presented.
A novel free-space optical interconnect employing vertical-cavity surface emitting laser diodes and InGaAs metal-semiconductor-metal photodetectors for Gbit/s RF/microwave systems
Emerging technologies and continuing progress in research are making way for novel, high speed forms of optical data transfer. Vertical-cavity surface emitting laser (VCSEL) diodes operating at 1550nm have only recently become commercially available, while metal-semiconductor-metal (MSM) photodetectors are pushing the limits of contact lithography with interdigitated electrode widths reaching sub micron levels. We propose a novel, free-space optical interconnect operating up to 1Gbit/s utilizing commercially available 1550nm VCSEL diodes and newly fabricated InGaAs MSM photodetectors with functionality for both chip level and board level applications. We report on development, progress, and current work. Analyses of the divergent behavior and of the normalized frequency response of VERTILAS GmbH 1550nm VCSEL diodes for coupling to MSM photodetectors with a 50μm by 50μm active area are presented. The MSM photodetectors are fabricated on a pseudomorphic In0.9Ga0.1P-InP-InGaAs heterostructure and have gold interdigitated Shottky contacts with varying electrode width and spacing on the order of 1 to 3 microns. We discuss the calculated response of these MSM photodetectors as well as the fabrication and characterization of the devices. A report on bit error rate (BER) characteristics of the VCSEL diodes coupled to commercially available high-speed photodetectors and successively coupled to the novel MSM photodetectors integrated with commercially available transimpedance amplifiers (TIA) follows. The work accounted here will lead to the formation and characterization of a fully integrated 1Gbit/s free-space optical interconnect applying VCSEL diodes and MSM photodetectors operating at 1550nm for RF/microwave digital systems.
Application of parallel optical axis converting waveguide to optoelectronic-PWB
T. Tanaka, H. Nanai, H. Sakamoto, et al.
We demonstrate for the first time a high-speed parallel optical signal transmission using multi-channel optical axis converter having U-shape optical paths (AXC-U), which has been developed to apply to optical printed wiring board (OPWB). AXC-U developed here contains 4-channel multimode waveguides, which have vertical waveguides and 45-degree mirrors connected at both ends of horizontal waveguides using to form U-shape optical paths. The AXC-U accommodates VCSEL and PD arrays, which are surface-mounted on each end to perform optical coupling to vertical waveguides in a manner of passive alignment and flip-chip bonding. The waveguides in AXC-U have a horizontal waveguide length of 2 cm, a vertical waveguide length of 100 μm, a cross section of 40x40 μm, a numerical aperture of 0.25 and an insertion loss of less than 2.5 dB. We performed a parallel optical signal transmission experiment using this AXC-U and succeeded in 4-channel parallel transmission at a data rate of 10 Gb/s/ch.
High channel density optical interconnects using photonic crystal fibers
Terence J. Shepherd, Charlotte R. Bennett, David M. Taylor, et al.
Demanding real-time data processing applications are driving the need for high-throughput programmable logic. Improvements to computing speed from reduction of processor feature sizes are predicted, but these are expected to be hampered within the next 2-5 years by the limitations of metallic interconnects between processors. Optical interconnect alternatives have been attempted, but independent optical channel densities are, at present, restricted by conventional fiber dimensions. In this paper a novel solution to this problem is presented employing a multi-core microstructured fiber. In this type of fiber, a photonic crystal fiber (PCF), the core is a solid silica region surrounded by air holes shot through the length of the fiber. This is created by stacking capillaries and solid canes of silica to create a preform, with the structure preserved after drawing down; a core may be created by replacing an air hole by a solid cane. The criteria for the fiber design are discussed: a bit error rate restriction leads to an upper limit for cross-coupling between cores and hence the distance (or number of air holes) between each channel. Modeling indicates a final fiber design containing 37 cores 31.25 microns apart, equivalent to a density of 1150 independent channels per millimeter squared. Details of an optical transmitting/receiving system utilizing four of the channels and arrays of VCSELs as transmitters and receivers are described. Future improvements to the system are discussed.
Packaging for Communication Components
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Efficient optical communications using multibit differential signaling
We present an alternative signaling method for multi-channel fiber ribbon based optical links. The method is based on a hybrid of differential signaling and single-ended channels. Channels are grouped into code blocks of n-bits. Each code word transmitted in the block is restricted to conform to an n choose m rule. Electrical drivers steer current between m active VCSELS with no dummy loads. A virtual reference is synthesized from the received signals and used for differential discrimination. This signaling method approaches the signal-to-noise characteristics of fully differential signaling but can be implemented with significantly lower channel overhead, giving as much as a 33% reduction in fiber count and a 44% reduction in power. Further, code utilization rates on these links can be as low as 51%, leaving substantial code space available for ECC or channel management functions. In this paper, we describe the signaling method and present a prototype transceiver chip. The transceiver is implemented in 0.25um UTSi Silicon-on-Sapphire technology with flip-chip bonded VCSEL and photodetector arrays. The design demonstrates a pin-compatible alternative to the POP4-MSA transceiver standard with 125% greater data throughput and 25% better power efficiency.
Multimode fibers with integrated optical mode field adapters for 40Gbit/s optical ethernet systems
In this paper we present the fabrication of optical mode field adaptors at the end of single mode and multimode optical fibers, which act as a micro lens, for fiber optical communications devices, capable up to 40Gbit/s data. The mode field adaptors were used to focus the optical output field (1550nm wavelength) of the fiber to receiver and transmitter OEICs. Based on the measurement of a singlemode fiber in accordance with ITU Recommendation G.652 the optical mode fields are measured in a new set-up, which is demonstrated and discussed in comparison to conventional methods. The work was performed in cooperation with the Heinrich-Hertz-Institute in Berlin.
Highly integrated plastic package transceiver modules for large core fiber systems
Flora Ho, Wai Hung, Sing Cheng, et al.
We have developed fiber optic transceivers (FOT) based on leadframe and plastic molding technology for large core POF and PCS fiber systems. The leadframe style package exhibits a compact small size of 9.7mm x 6.2mm x 3.6mm. For PCS fiber system, the VCSEL based fiber optic transceivers have an operating wavelength at 850nm. The transmitter has an internal control circuit to stabilize the optical output of VCSEL and an integrated coupling optics to provide loose alignment tolerances of ±70μm in lateral axis for a working distance of 500μm to PCS optical fibers. The optical coupling power from the transmitter to the PCS fiber has a variation within 1dB over the wide ambient temperature range from -40oC to +105oC. Eye diagrams of the transceivers at 50Mbps are wide open over the normal operating temperature range from -40oC to +105oC. With a pair of VCSEL transmitter and MSM-PD receiver we achieve 1.25Gb/s transmission over 10m of PCS fiber. In a POF transmission system of 40m, over an operating temperature range from -40oC to +85oC, the fiber output power variation with the green LED transmitter is 1.5dB less than that with a similar red LED transmitter. The eye-diagrams of the green LED transmitter at 20Mbps are captured at back-to-back transmission and after 40m POF transmission.
Alignment/Packaging/Fabrication
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Advanced integration schemes for high-functionality/high-performance photonic integrated circuits
James W. Raring, Matthew N. Sysak, Anna Tauke-Pedretti, et al.
The evolution of optical communication systems has facilitated the required bandwidth to meet the increasing data rate demands. However, as the peripheral technologies have progressed to meet the requirements of advanced systems, an abundance of viable solutions and products have emerged. The finite market for these products will inevitably force a paradigm shift upon the communications industry. Monolithic integration is a key technology that will facilitate this shift as it will provide solutions at low cost with reduced power dissipation and foot-print in the form of highly functional optical components based on photonic integrated circuits (PICs). In this manuscript, we discuss the advantages, potential applications, and challenges of photonic integration. After a brief overview of various integration techniques, we present our novel approaches to increase the performance of the individual components comprising highly functional PICs.
2D scalable optical controlled phased-array antenna system
A novel optoelectronically-controlled wideband 2-D phased-array antenna system is demonstrated. The inclusion of WDM devices makes a highly scalable system structure. Only (M+N) delay lines are required to control a M×N array. The optical true-time delay lines are combination of polymer waveguides and optical switches, using a single polymeric platform and are monolithically integrated on a single substrate. The 16 time delays generated by the device are measured to range from 0 to 175 ps in 11.6 ps. Far-field patterns at different steering angles in X-band are measured.
Recent advances in photonics packaging materials
There are now over a dozen low-CTE materials with thermal conductivities between that of copper (400 w/m-K) and over 4X copper (1700 W/m-K). Most have low densities. For comparison, traditional low-CTE packaging materials like copper/tungsten have thermal conductivities that are little or no better than that of aluminum (200 W/m-K) and high densities. There are also low-density thermal insulators with low CTEs. Some advanced materials are low cost. Most do not outgas. They have a wide range of electrical properties that can be used to minimize electromagnetic emissions or provide EMI shielding. Several are now in commercial and aerospace applications, including laser diode packages; light-emitting diode (LED) packages; thermoelectric cooler bases, plasma displays; power modules; servers; laptops; heat sinks; thermally conductive, low-CTE printed circuit boards; and printed circuit board cold plates. Advanced material payoffs include: improved thermal performance, reliability, alignment and manufacturing yield; reduced thermal stresses and heating power requirements; simplified thermal design; enablement of hard solder direct attach; weight savings up to 85%; size reductions up to 65%; and lower cost. This paper discusses the large and increasing number of advanced packaging materials, including properties, development status, applications, increasing manufacturing yield, cost, lessons learned and future directions, including nanocomposites.
Edge termination effects on finite aperture polarizers for polarimetric imaging applications at mid-wave IR
A. A. Cruz-Cabrera, S. A. Kemme, J. R. Wendt, et al.
Polarimetric imaging applications at the 2 to 5 μm or Mid-Wave Infrared (MWIR) range use large pixel-count focal plane arrays (FPA) with small pixel size. This project is centered in designing, fabricating and testing micropolarizers that work in that wavelength regime and intended for that type of FPAs. The micro-polarizers will be used in conjunction with a FPA in snapshot mode and will be in the near field of the imaging device. The pixel pitches for some commercial FPAs are small enough that the finite apertures of the polarizing devices may significantly affect their performance given that their aperture size varies between 3 and 5 waves. We are interested in understanding the effect on extinction ratio due to variations in the edge terminations of a polarizer with a small aperture. Edge terminations are the spaces between the first or last wire with the perimeter of the aperture of the polarizer. While this parameter has negligible effects on a larger polarizer, it will be significant for apertures that are about 3 to 5 waves. We will present data that indicates significant variation in performance due to edge terminations.
Optical Interconnects/Micro-Optics
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Fabrication of a hybrid electrical-optical printed circuit board (EO-PCB) by lamination of an optical printed circuit board (O-PCB) and an electrical printed circuit board (E-PCB)
We report on the results of our work on the fabrication of a hybrid electrical-optical printed circuit board (EOPCB) by lamination of an optical printed circuit board (O-PCB) and an electrical printed circuit board (EPCB). This is a part of our work on the micro/nano-scale design, fabrication and integration of optical waveguide arrays and devices for optical printed circuit board (O-PCBs) and VLSI micro/nano-photonic integrated circuit application. The integrated circuit layers form the O-PCB, which is to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards. The OPCBs consist of an optical layer containing planar circuits and arrays of waveguides and photonic devices of various dimensions and characteristics and an electrical layer containing electrical circuits of various functions. Here, we laminate the two layers to form an O-PCB. The advantages include the processing simplification, cost reduction, fabrication of compact devices, and reduction of alignment problem among others. The VLSI micro/nano-photonic integrated circuits perform similar functions on a chip scale. We describe the lamination process and examine the characteristics of the laminated EO-PCBs.
Low-cost plastic micro-optics for board-level optical interconnections
One of the grand challenges in solving the interconnection bottlenecks at the Printed Circuit Board (PCB) and Multi-Chip-Module (MCM) level, is to adequately replace the PCB and intra-MCM galvanic interconnects with high-performance, low-cost, compact and reliable micro-photonic alternatives. In our labs at the Vrije Universiteit Brussel we are therefore focusing on the continuous development of a rapid prototyping technology for micro-optical interconnect modules, which we call Deep Proton Writing (DPW).The special feature of this prototyping technology is that it is compatible with commercial low-cost mass replication techniques such as micro injection moulding and hot embossing. We will address more specifically in this paper the following components: 1) out-of-plane couplers for optical wave-guides embedded in PCB, 2) peripheral fiber ribbons and two dimensional single- and multimode fiber connectors for high-speed parallel optical connections, and 3) intra-MCM level optical interconnections via free-space optical modules. We furthermore give special attention to the optical tolerancing and the opto-mechanical integration of the components. We use both a sensitivity analysis to misalignment errors and Monte Carlo simulations. It is our aim to investigate the whole component integration chain from the optoelectronic device to the micro-opto-mechanical components constituting the interconnect module.
Integrated waveguide micro-optic elements for 3D routing in board-level optical interconnects
Alexei L. Glebov, Michael G. Lee, Shigenori Aoki, et al.
Planar waveguides and embedded microelements such as 45o vertical mirrors, lateral mirrors, bends, and microlenses comprise main building blocks of the waveguide-based optical printed circuit boards (PCB) for board-level optical interconnects (OI). These microelements enable a variety of three dimensional (3D) routing architectures which are required to support high density interconnects in optical boards. Optical polymers have proved to be the materials of choice for large-scale OI modules with propagation dimensions exceeding 100 mm. In order to meet the loss budget available for the integrated OI modules, the polymers are expected to have optical losses less than 0.05 dB/cm. Both channel and slab waveguides can be used to transmit the signals between the input and output ports. In the case of channel waveguides, the critical issues are the waveguide core shaping, propagation losses and ability to form various passive elements such as bends, crossings and reflective mirrors. In the case of slab waveguides, two dimensional waveguide microlenses have to be designed to collimate the light beams for propagation at longer distances with the controllable beam divergences. The 45o micromirrors can be used to couple the light signal in and out of the waveguiding layer and enable 3D routing of the optical signal in the waveguiding layers. In this work, we present the experimental and computational results on the development of different waveguide devices and microelements for the board level OI.
Hyperboloid sol gel microlens array fabricated by soft-lithography for optical coupling
Miao He, Jing Bu, Xiaocong Yuan, et al.
It is known that the best way to correct spherical aberrations is the use of aspheric microlenses in optical systems, where a single aspheric microlens can be employed to replace a compound of spherical microlenses in a compact design. However the fabrication of aspheric microlenses is often complex because expensive high-energy beam-sensitive (HEBS) gray scale mask is needed in the fabrication process. In this paper, we reported a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate hyperboloid refractive microlens arrays (MLAs) in the inorganic-organic hybrid SiO2-ZrO2 sol-gel material. The fabrication procedures involved two basic steps. Firstly, a master of hyperboloid MLA was made in photoresist by the sample-inverted reflow technique. Secondly, a negative mold of the master was built by casting polydimethylsiloxane (PDMS) to a silicone elastomer against the master, and then the profile was impressed onto the sol-gel glass. As a result, the fabricated sol-gel MLAs have been obtained with excellent smooth profiles, having negligible discrepancies from the profiles of the ideal hyperboloid MLAs. The root-mean-square roughness values (Rq) of the surface of MLA were measured as 1.2 nm in the central areas and 2.1 nm in the outskirts of the lens. In an application of coupling a laser diode (LD) to a single-mode fibre (SMF), we proposed a two-MLA coupling scheme where two revolved-hyperboloid MLAs were back to back introduced between the LD and the SMF. In this configuration, the coupling efficiency has achieved 83.4% (-0.79 dB).
Fabrication of SIL array of glass by surface-tension mold technique
Tetsuo Kishi, Shuichi Shibata, Tetsuji Yano
A preparation of microlens array of the super-spherical glasses by a combination of the photolithography and the Surface-tension Mold (StM) techniques is shown. A super-spherical lens has been gathering much attention because of its function as a Solid Immersion Lens (SIL) with the super-resolution, which circumvents the optical diffraction limit. StM technique enables the preparation of a micrometer-sized SIL (μ-SIL) with the desirable shape, and the obtained SILs realize the optical function. In order to develop the optical micro-devices composed of SILs, μ-SIL array module, the micro-fabrication technique of photolithography is combined with StM technique. Na2O-CaO-SiO2 glass film is attached to glassy-carbon, and etched into glass tiles after the formation of masks by the photolithography. They are heated up to 800oC to self-organize into the super-spherical form of the glass droplets. The obtained lens array is found to be composed of the μ-SILs with the uniform radius and thickness.