This PDF file contains the front matter associated with SPIE Proceedings Volume 7607, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In this paper we present a computing system that uniquely leverages the bandwidth, density, and latency advantages of silicon photonic interconnects to enable highly compact supercomputerscale systems. We present the details of an optically enabled "macrochip" which is a set of contiguous, optically-interconnected chips that deploy wavelength-division multiplexed (WDM) enabled by silicon photonics. We describe the system architecture and the WDM point-to-point network implementation of a "macrochip" providing bisection bandwidth of 10 TBps and discuss system and device level challenges, constraints, and the critical technologies needed to implement this system. We present a roadmap to lowering the energy-per-bit of a silicon photonic interconnect and highlight recent advances in silicon photonics under the UNIC program that facilitate implementation of a "macrochip" system made of arrayed chips.

The Ultra-performance Nanophotonic Intrachip Communication (UNIC) project aims to achieve unprecedented high-density, low-power, large-bandwidth, and low-latency optical interconnect for highly compact supercomputer systems. This project, which has started in 2008, sets extremely aggressive goals on power consumptions and footprints for optical devices and the integrated VLSI circuits. In this paper we will discuss our challenges and present some of our first-year achievements, including a 320 fJ/bit hybrid-bonded optical transmitter and a 690 fJ/bit hybrid-bonded optical receiver. The optical transmitter was made of a Si microring modulator flip-chip bonded to a 90nm CMOS driver with digital clocking. With only 1.6mW power consumption measured from the power supply voltages and currents, the transmitter exhibits a wide open eye with extinction ratio >7dB at 5Gb/s. The receiver was made of a Ge waveguide detector flip-chip bonded to a 90nm CMOS digitally clocked receiver circuit. With 3.45mW power consumption, the integrated receiver demonstrated -18.9dBm sensitivity at 5Gb/s for a BER of 10^-12. In addition, we will discuss our Mux/Demux strategy and present our devices with small footprints and low tuning energy.

We report a very compact (1.6μmx10μm) and low dark current (20nA) Germanium p-i-n photodetector integrated on 0.25μm thick silicon-on-insulator (SOI) waveguides. A thin layer of Germanium was selective-epitaxially grown on top of SOI waveguides. Light is evanescently coupled into Germanium layer from the bottom SOI waveguide. The device demonstrates superior performance with demonstrated responsivity of 0.9A/W and 0.56A/W at wavelength of 1300nm and 1550nm, respectively, and dark current less than 20nA at -0.5V bias. The 3dB bandwidth of the device is measured to be 23GHz at -0.5V bias.

An add/drop filter based on coupled vertical gratings is presented on silicon. We analyze the device theoretically and experimentally and show that the concept is easily extended to multi-channel add/drop filters. We demonstrate tunability of the device bandwidth and operation wavelength. The free spectral range of the device exceeds the bandwidth used in wavelength division multiplexing systems, which makes it ideally suited for use in such systems.

A major breakthrough to alleviating the interconnect bottleneck in intra cabinet system in HPC may happen by bringing optics directly to the processor package. In order to do so efficient and compact optical interconnect subassembly modules that utilize simple optical and electrical interfacing schemes are needed. In our current work the development of a novel 10-channel, miniature 7mm(W)x1.8mm(L)x3mm(H), optical interconnect transmitter subassembly module is described. The module consists of a high precision molded optical alignment unit with integrated microlens arrays, highspeed coplanar waveguide (CPW) electrical interfaces and a VCSEL (Vertical Cavity Surface Emitting Laser) array chip which is flip chip mounted. The module is designed to uniquely interface vertically with high-speed electrical I/O lines on a microprocessor style package or a motherboard to convert electrical signals to optical for transmission to other similar units using a standard (Multi-Terminal) MT style optical connector. We report on optical coupling efficiency, misalignment tolerance and high-speed electrical and optical measurements of the module. We have measured 40Gb/s electrical eye for the CPW interfaces on the module and 20Gb/s clear optical eyes for VCSEL assembled module from all the 10 channels to produce an aggregate transmitter bandwidth of 200Gb/s. We also measured 30Gb/s electrical and 20Gb/s optical eyes for the optical subassembly module that is bonded onto a microprocessor style package substrate.

We report the fabrication and properties of 850nm wavelength AlGaAs/GaAs-based transceiver chips, in which vertical-cavity surface-emitting lasers (VCSELs) and photodiodes are monolithically integrated. Various types of devices allow half- and full-duplex bidirectional optical interconnection at multiple Gbit/s data rates over a single butt-coupled glass or polymer-clad silica optical fiber with core diameters of 100 or 200 μm. Whereas metal-semiconductor-metal (MSM) photodiodes are employed for these large-area fibers, we also investigate the integration of PIN-type photodiodes which appear more promising in combination with standard 62.5 or 50 μm core diameter graded-index multimode fibers. This interconnect solution based on two identical chips is attractive owing to lower volume, weight, and cost. Applications will be found in home, in-building, industrial, or automotive networks and potentially within computer clusters or central offices.

Ring waveguide resonating structures with high quality factors are the key components in the silicon photonics portfolio boosting up its functionality and circuit performance. Due to a number of manufacturing reasons their peak wavelengths are often prone to deviate from designed values. In order to keep the ring resonator operating as specified, its peak wavelength then needs to be corrected in a reliable and power efficient way. We demonstrate the performance of the thermally tunable mux/demux filter ring structures fabricated in the commercial 130 nm SOI CMOS line.

We experimentally demonstrate a Mach-Zehnder modulator based on electro-optic (EO) polymer (AJ-CKL1/PMMA) infiltrated photonic crystal slot waveguide. The modulator design combines the advantage of excellent optical confinement in silicon slot waveguide, slow light enhancement in photonic crystal waveguide, and strong electro-optical response in EO polymer. This design allows us to achieve electro-optic modulation in active region only 352μm long. Matching the mode profile and group velocity between strip and photonic crystal slot waveguide enables coupling into slow light regime. The modulator shows a 22V switching voltage and an improved in-device EO coefficient of 51pm/V as compared to recently reported value.

In last decades various approaches have been investigated within frame of photonics research activities. From hybrid assembly to monolithically integration including III-V and CMOS technologies, the main challenges remained: cost effective, high bandwidth, high-density devices, components and subsystems. This paper will review basic photonics packaging approaches/concepts which have been developed over years in different research projects and platforms. Furthermore, targeting the converging technologies the demands on future heterogeneous integration perspective will be discussed with respect to high bandwidth interconnects.

Electrical-optical integration is a rapidly growing field with a strong potential for applications in a wide spectrum covering optical sensors, data & telecom, respectively. The driving forces are bandwidth demand, power efficiency and increased channel density. For higher degrees of integration thin glass substrates provide very suitable properties. The technology of the "glassPack" concept relies on the realization of the passive single mode and multi mode optical waveguides within the thin glass substrates and benefits of the excellent optical, electrical, and thermal properties of glass itself. Suitable technologies are ion-exchange and direct optical butt coupling by laser fusion. The planar integrated single- or multi-mode waveguide is characterized by a graded refractive index profile. The laser fused fiber interconnect shows a determinate coupling loss. Also, planar waveguide array coupling elements of very flexible design can be applied for optical coupling and 90 degree light deflection. Novel innovative features are added to this packaging technique to leverage its generic usage. For electrical wiring thin film technologies and through glass vias have been demonstrated to address high integrate photonic System-in-packaging solutions. All together makes glass to the perfect platform for optical as well as electrical interconnects on board and module level. Multi-mode interconnects in thin glass layers of an EOCB as well as a glass based transceiver module show the integration potential of that approach. The demonstrated development goes hand in hand with ongoing trends in the area of silicon photonics to provide a suitable packaging and interconnection platform. Also the gap between single mode fiber interconnects and single mode SoI (silicon-on-insulator) waveguides in ICs (integrated circuit) can be bridged by the glass based interconnects on board and module level. The paper presents the glass packaging state-of-the art and discusses solutions to overcome demands in future.

This paper presents the latest results on the development of a thin flexible package of commercially available optoelectronics with polymer multimode waveguides. The GaAs VCSELs and Photodiodes are thinned down to 20 μm thickness, resulting in packages which can be bended to a bending radius of 2 mm with high reliability. With these actives, also waveguides and out-of-plane coupling structures are embedded inside the foil. Flexible Polyimide micromirrors were fabricated, characterized and embedded inside the foil. An embedded VCSEL to Photodiode optical waveguide link was demonstrated at a speed of 1.2 Gbs with open eye diagram. Temperature (-40 to 125 degrees Celsius) and humidity (85 rh/85 °C for 1000 hours) reliability was tested with good results. The total thickness of the completed foil containing actives, waveguides and coupling elements is only 145 μm.

The "Modulation-Enabled Tapered Remote Coupler" (METRoC) is introduced targeting the integration of on-chip and off-chip optical interconnects. With Moore's law scaling of CMOS critical dimensions, the computing power of modern microprocessors has grown rapidly. Future multi-core chips will demand aggregate on- and off-chip bandwidths in the TBytes/sec regime. However, metal on-chip global interconnections and off-chip communications do not scale commensurately with the CMOS device sizes, resulting in challenges to meet the growing bandwidth requirements within acceptable power budgets. Optics is a potential solution to replace the fundamentally limited electrical interconnects. Recent advancements in optical and optoelectronic component fabrication and manufacturing processes may enable implementation of optical interconnects at the chip-scale. An optical solution that seamlessly integrates the two domains is highly desirable. The METRoC is proposed as a compact optical interconnect fabric that obviates the need for opto-electronic and electrooptic conversions when signals propagate between the on-chip and off-chip domains. Multiple quantum well (MQW) devices are chosen as the optical modulators and photodetectors. The key aspect of METRoC is the modulationenhanced prismatic structures embedded in waveguides, which enable the direct coupling from the integrated MQW devices to the intra-chip guided-wave fabrics. Additionally, tapered remote couplers can provide free-space interconnections between chips or remote regions on-chip. Both coupling structures have small footprint areas and hence are projected to provide high bandwidth densities. The fabrication process is compatible with silicon CMOS processes. The coupling fabric can also be used to optically interconnect two silicon die within a multichip module.

We present the heterogeneous integration of a 3.8 μm thick InGaAs/GaAs edge emitting laser that was metal-metal bonded to SiO₂/Si and end-fire coupled into a 2.8 μm thick tapered SU8 polymer waveguide integrated on the same substrate. The system was driven in pulsed mode and the waveguide output was captured on an IR imaging array to characterize the mode. The waveguide output was also coupled into a multimode fiber, and into an optical head and spectrum analyzer, indicating lasing at ~997 nm and a threshold current density of 250 A/cm².

The design, implementation and characterisation of an electro-optical backplane and an active pluggable optical connector technology are presented. The connection architecture adopted allows line cards to mate and unmate from a passive electro-optical backplane with embedded polymeric waveguides. The active connectors incorporate photonics interfaces operating at 850 nm and a mechanism to passively align the interface to the embedded optical waveguides. A demonstration platform has been constructed to assess the viability of embedded electro-optical backplane technology in dense data storage systems. The electro-optical backplane is comprised of both copper layers and one polymeric optical layer, whereon waveguides have been patterned by a direct laser writing scheme. The optical waveguide design includes arrayed multimode waveguides with a pitch of 250 μm, multiple cascaded waveguide bends, non-orthogonal crossovers and in-plane connector interfaces. In addition, a novel passive alignment method has been employed to simplify high precision assembly of the optical receptacles on the backplane. The in-plane connector interface is based on a two lens free space coupling solution, which reduces susceptibility to contamination. The loss profiles of the complex optical waveguide layout has been characterised and successful transfer of 10.3 Gb/s data along multiple waveguides in the electro-optical backplane demonstrated.

For the realization of a polymer waveguide based optical backplane link for computing applications, we developed a method to passively align multiple layers of polymer waveguide flex sheets in a single MT compatible ferrule. The minimal feature forming the backplane is a 192 channel link. This link is equipped with four MT connector at each end, and is performing a shuffling of the channels. We describe the passive alignment used to realize the connectors. The achieved accuracy demonstrated in a 48 channels connector consisting of 4 polymer sheets carrying 12 waveguides each, is shown to be better than ±5μm. The connection losses between a 48 channel MT fiber connector and the realized polymer waveguide connector were found to be about 2dB. Compared to fiber connectors, the presented concept using polymer waveguides has several advantages. The most relevant are that only few assembly steps are needed, it is based on a totally passive alignment scheme and it can easily be executed by standard pick and place tools.

We report on the co-packaging of electrical CMOS transceiver and VCSEL chip arrays on a flexible electrical substrate with optical polymer waveguides. The electro-optical components are attached to the substrate edge and butt-coupled to the waveguides. Electrically conductive silver-ink connects them to the substrate at an angle of 90°. The final assembly contacts the surface of a package laminate with an integrated compressible connector. The module can be folded to save space, requires only a small footprint on the package laminate and provides short electrical high-speed signal paths. With our approach, the electro-optical package becomes a compact electro-optical module with integrated polymer waveguides terminated with either optical connectors (e.g., at the card edge) or with an identical assembly for a second processor on the board. Consequently, no costly subassemblies and connectors are needed, and a very high integration density and scalability to virtually arbitrary channel counts and towards very high data rates (20+ Gbps) become possible. Future cost targets of much less than US$1 per Gbps will be reached by employing standard PCB materials and technologies that are well established in the industry. Moreover, our technology platform has both electrical and optical connectivity and functionality.

The increasing demand for planar polymer optical waveguides integrated into electrical printed circuit boards (PCB) calls for mass production capabilities: Hence, appropriate materials, systems, assembly concepts and production technologies become vital, in order to guarantee a high reproducibility and quality of the waveguides. The manufacturing and assembly costs have to be kept on a low level, while the integration of the highly sensible waveguides into the rough environment of PCB's with their cheap and non-ideal substrates is a particular challenge. The present paper describes an assembly and manufacturing technology for electro-optical circuit boards which meets these requirements. First, the manufacturing and characterization of multimode polymer waveguides is presented and the process for layer deposition and structuring is described. Specific attention is given to the reproducibility of these processes ensuring the high optical quality of the waveguides. Additionally, some problems arising from the integration of the waveguides into the PCB's are discussed. Second, various light coupling concepts are presented. In particular, a novel mirror element based on parabolic reflectors is described. The optical design was calculated analytically and optimized using computer simulations. The mirror element was fabricated using injection molding in a reproducible manner at high quantities and lowest cost. To allow for a wider tolerance in the subsequent assembly steps our novel electro-optical transceivers concept facilitates the use of conventional SMD- placement machines for mounting which makes the process very cost effective. This concept was demonstrated successfully and is also described within the third section. In the last part the practical use of this building set is illustrated with different successfully realized applications in the field of ICT and optical sensor technology.

An optical transceiver formed onto a conventional low-cost printed circuit board with integrated optical waveguides is presented. The transceiver incorporates an optical multimode polymer Y-splitter formed directly on a low-cost singlelayered FR4 substrate enabling duplex transmission along a single optical fibre. The transmitter and receiver assemblies are mounted onto the board using methods common to conventional PCB manufacturing. Simple through-board connectors, compatible with pick-and-place assembly technology, are used to interface the electrical and optical layers of the board. This approach allows end-fired optical coupling between the active devices and optical waveguides on the board. The demonstrated transceiver, intended as a board-level optical network unit, achieves error-free data transmission for both Tx and Rx modules at 10 Gb/s.

In this paper, 3-to-3 metallic hard mold for optical bus waveguide with opposite 45° micro-mirrors was successfully fabricated using electroplating method. The optical bus waveguide pre-mold with 45° surfaces before electroplating was prepared using photopolymer SU-8 through tilted exposure process under de-ionized water. Metal nickel was electroplated into SU-8 defined bus waveguide trenches. The 45° slant angles can be well controlled through titled exposure, which have deviations of 0.15° and 0.27° for SU-8 pre-mold and Ni hard mold, respectively. This metallic hard mold provides a convenient way to fabricate the polymeric optical bus waveguide devices through imprint technique.

A platform for video data link between FPGA microprocessors based on an optical printed-circuit board (OPCB) was implemented. Optimized compact size of 9.5 x 10.5 x 1.0 mm³ Tx/Rx modules were prepared and applied for the optical link of the platform. A low insertion loss of 0.42 dB and stable optical fiber-layer integrated with connectors was embedded in FR4 board for the implementation of the OPCB. The platform shows that embedding the optical fiber-layer with connectors can improve the degree of freedom for packaging as well as optical and physical characteristics. Real time video image from a charge-coupled-device (CCD) camera was successfully transmitted to a monitor through optical link between FPGA microprocessors of the platform. The captured image was successfully saved in a static random access memory (SRAM) and clearly shown on the monitor. This study shows that chip-to-chip optical interconnection technology based on fiber-layer embedded OPCB can be applied for the CPU-to-CPU/memory optical interconnections.

In this paper, we presented fabrication of nickel based metal mold with 45° tilted surfaces on both ends of the channel waveguide through electroplating process. To obtain a precise 45° tilted angle, a 50μm thick SU-8 layer was UV exposed under de-ionized water, with repeatable error control of 0.5°. The polymeric waveguide array with 45° micromirrors, which is formed by a UV imprinting method with the fabricated metallic mold, shows total insertion losses around 4dB, propagation loss around 0.18dB/cm and 75% coupling efficiency.

Optical and electrical hybrid flexible printed circuit boards with unique photo-defined polymer waveguide layers have been investigated. The photo-defined waveguides are made by simple pattering process, known as "Photo-addressing". In the process, only ultraviolet irradiation through a photo mask over photosensitive dry film is carried out to form entire waveguide patterns, and any additional steps like etching or developing are not required. We are now giving high priority to further process development how to integrate them with conventional flexible printed circuit boards, and gathering data of basic characteristics, properties and reliabilities of those kinds of hybrid product.

The success of optical interconnection for practical use is strongly dependent on the development of a sophisticated packaging and coupling technology capable of both high coupling efficiency and easy alignment. We have developed the photomask transfer method applying UV curable resin. This technology enables fabrication of arrayed M x N optical patterns at one shot of UV light. It is also possible to fabricate very precise patterns by a conventional photomask. The length/thickness of the fabricated patterns can be controlled by the thickness between the photomask and the substrate. The maximum length reaches over 1,000μm. As applications using this method, two original devices are reviewed. One is a chip optical device which consists of a VCSEL (vertical cavity surface emitting laser), optical rods as cores, and a surrounding clad layer. These optical rods can be accurately fabricated on the emitting spot of the VCSEL. This VCSEL device enables flexible packaging on OE-PWBs (opto-electric printed wiring boards). Another is a 90-degree light path conversion device for coupling to an optical wiring on OE-PWBs. It features in hybrid comb-clad consisting of air and polymer parts. This device has a large refractive index difference between the core and hybrid comb-clad, and enables downsizing.

This paper proposes a low-loss and thermally stable waveguide component for optical printed-circuit board (OPCB) applications. The proposed waveguide component is formed using silica fiber as a waveguide medium and seamlessly linking the 90°-bent parts to the planar optical layer. The component was designed through considerations of optical loss, mechanical failure, thermal stability, module packaging, and applicability in PCB system in determination of fiber-core-diameter, bending radius, waveguide-mounting epoxy material, and packaging structure. In the experiment, we used a multimode fiber with 100μm-core-diameter, a MT-ferrule component to hold the 90°-bent fiber and to package the surface modules, and a 353ND thermo-curable epoxy resin to mount the ferrule parts on planar fiber layer. The optimized bending radius was selected near 3mm to avoid mechanical failure. The measured average value of the insertion loss for the whole waveguide component was as low as -0.145dB. In the thermal test similar to the PCB lamination process, the loss characteristics were not significantly degraded. In the packaging of optical transmitter (Tx) and receiver (Rx) modules, we used a ceramic lid on which optical devices and IC chips were integrated and guide holes were formed. The optical Tx/Rx modules assembled on the waveguide plate showed a successful data transmission up to 8Gbps. The results demonstrate that our proposed waveguide component can be applied for a simple fabrication of OPCBs.

Quantum dot-based diode comb lasers can provide a single multi-channel-laser source for short-reach, high-speed WDM interconnects. In this paper, we review the technology and demonstrate for the first time a 15 channel, low RIN comb laser with 80 GHz channel spacing. We show that each of the Fabry-Perot (FP) modes can be externally modulated at 10 Gb/s or all modes directly modulated, at 3.2 Gb/s so far. The latter indicates that the comb laser may be an ideal broadband light source in WDM-PON applications. We further demonstrate that the whole comb laser spectrum can be amplified by a quantum dot SOA without increasing relative density noise (RIN) of the individual channels. The small signal amplification factor was measured up to 30dB and the saturated output power was as high as 15 dBm.

A Y-branch directional coupler modulator based on electro-optic (EO) polymer with domain-inversion is designed, fabricated, and characterized. The functional core material is LPD-80 chromophore in amorphour-polycarbonate (APC) host polymer which is cladded between UV15-LV and UFC-170A. The switching voltage of 4.4V and the electro-optic coefficient (r₃₃) of 90pm/V are measured from 4-domain directional coupler modulator and Mach-Zehnder modulator, respectively. A two-tone test of domain-inversed directional coupler modulator demonstrates the spurious-free dynamic range (SFDR) of 119dB/Hz^2/3, which is enhanced by 11dB compared with the conventional Mach-Zehnder modulator. The SFDR of Mach-Zehnder modulator shows good agreement with simulation result but the directional coupler modulator shows approximately 10dB lower value than simulation result, which is mainly due to the high sensitivity of directional coupler structure to the fabrication error. Further improvement can be achieved with completion of fabrication precision.

A key requirement for the success of future microphotonic devices will be the ability to integrate such devices into current mainstream semiconductor technologies. The ability to create silicon-based light sources in a standard CMOS process is therefore very appealing. It is known that avalanche silicon LED efficiency can be increased using reach- and punch-through mechanisms. This paper reveals a technique for improving the operational performance of a silicon light source by increasing the external quantum efficiency and relaxing the separation requirements for the light source operating under the mentioned reach- or punch-through mechanisms in a standard unmodified local oxidation of silicon (LOCOS) CMOS process.

Silicon-based electro-optic (EO) modulator is an indispensable building block for integrated lightwave circuits. In this paper, we report an EO modulator that incorporates a heterojunction bipolar transistor (HBT) with Ge composition graded base. The emitter is n-type doped silicon with a doping concentration of 10²¹/cm³. The width of the emitter strip is 0.2μm and the thickness of the emitter layer is 0.16μm. The base has a thickness of 40nm with varying Ge composition from zero at the emitter-base junction side to 20% at the base-collector junction side. Raised extrinsic base is incorporated for base contact. The intrinsic base is p-type doped with a concentration of 4×10¹⁹/cm³. The HBT is biased at V_CE = 0.5 V whereas VBE is switched between -1.0V and 1.0V. The carrier distribution at "ON" state of the EO modulator and the transient analysis are performed by MEDCI simulation. The changes of the refractive indices of the HBT are computed from the carrier density in all regions, and then the refractive index map is imported into an optical mode solver (RSoft BeamProp). The HBT EO modulator that supports only one optical mode is ideal, but a trade-off between modal property and device speed is observed. For current design, we achieved a π-phase modulation length of less than 600μm, and a switching delay less than 62ps.

This paper describes hybrid assembly of a wavelength selective switch using laser-formed glass bumps. Recently, a process was developed for forming raised bumps on IR-absorbing glass substrates using a focused laser beam. Glass bumps with heights exceeding 90 μm have been formed with an accuracy of ~100 nm using multiple laser shots. Proper selection of materials permits the bump height to be raised or lowered via subsequent laser shots by adjusting laser power. Processes are described for precision alignment of planar AWG components to a pedestal-mounted planar SOA array by forming three glass laser bumps beneath the AWG components. While the iterative process of bump formation and component position assessment was performed manually, this work demonstrates that the process is predictable and well-suited for automation.

Change in resistance of interconnect traces on flexible substrates is dependent on material properties and mechanical stress imposed by tensile strain. Dedicated test structures and a mechanical flexing / data collection system were designed and fabricated to collect time to failure data based on cyclic loading to different radii of curvature. We propose a life-stress model based on an inverse power law relationship defining the characteristic life of a Weibull life distribution.

In this paper, we present the results of the design and fabrication of a 12 channel nano-membrane-based optical phased array that allows for large angle beam steering operating at wavelength=1.55μm. Our device is fabricated on silicon-oninsulator using standard CMOS process. By implementing unequally spaced waveguide array elements, we can relax the half-wavelength spacing requirement for large angle beam steering, thereby avoiding the optical coupling between adjacent waveguides and reducing the side-lobe-level of the array radiation pattern. 1D beam steering of tranverseelectric polarized single mode light is designed to be achieved thermo-optically through the use of thin film metal phase shifters.

Silicon MEMS cantilever-based photoacoustic technology allows for the sensing of ultra low gas concentrations with very wide dynamic range. The sensitivity enhancement is achieved with a cantilever microphone system in which the cantilever displacement is probed with an optical interferometer providing a pico-meter resolution. In the gas sensor, the silicon cantilever microphone is placed in a two-chamber differential gas cell. By monitoring differential pressure changes between the two chambers, the differential cell operates as a differential infra-red detector for optical absorption signals through a measurement and reference path. The differential pressure signal is proportional to gas concentration in the optical measurement path. We have designed, implemented and tested a differential photo-acoustic gas cell based on Low Temperature Co-fired Ceramic (LTCC) multilayer substrate technology. Standard LTCC technology enables implementation of 2.5D structures including holes, cavities and channels into the electronic substrate. The implemented differential photoacoustic gas cell structure includes two 10 mm long cylindrical cells, diameter of 2.4 mm. Reflectance measurements of the cell showed that reflectivity of the substrate material can be improved by a factor 15 - 90 in the 3 - 8 μm spectral region using gold or silver paste coatings. A transparent window is required in the differential gas cell structure in order to probe the displacement of the silicon cantilever. The transparent sapphire window was sealed to the LTCC substrate using two methods: screen printed Au80/Sn20 solder paste and pre-attached glass solder paste (Diemat DM2700P/H848). Both methods were shown to provide hermetic sealing of sapphire windows to LTCC substrate. The measured He-leak rate for the 10 sealed test samples implemented using glass paste were under 2.0 ×10^-9 atm×cm3/s, which meets the requirement for the leak rate according to MIL-STD 883. The achieved hermeticity level suggests that the proof-of-principle packaging demonstrator paves the way for implementing a novel differential photoacoustic gas cell for a future miniature gas sensor module. The future module consisting of a sample gas cell and immersion lens IR LEDs together with interferometric probing of the cantilever microphone is expected to be capable of measuring ultra low concentrations of a wide range of gases with their fundamental absorption bands at 3 - 7 μm wavelength, such as CO, CO₂ and CH₄.

Micro-optics packaging provides a practical and cost-effective approach for controlling the spatial field distributions of structured laser beams in a variety of photonics applications. Structured laser beams (SLBs) are playing an increasingly important role in ultrahigh resolution microscopy, biophotonics, optical micromanipulation and trapping, laser pumping, materials processing and microfabrication, quantum information, and optical communications. It is shown that the limited aperture sizes, as well as the distortions introduced by micro-optics components during the integration phase, may influence field formation of the structured laser beams, and may alter their spatial characteristics. To avoid the undesirable changes to the field shape of the structured beams during micro-optics design and packaging phases, detailed analysis of the beam propagation characteristics along the optical path is required.

Photonic technologies have found widespread applications in high-speed longhaul and metro transmission networks for decades. Introducing similarly advanced optical technologies into access networks must respect the strict requirements for simple deployment and operations as well as ease of system migration and network maintenance. The large number of optical ports and fiber links to be provided and operated at lowest cost make access networks special as compared to their longhaul and metro networks counterparts. The paper provides a view on the status and on potential future evolution paths of optical access network technologies.

The paper deals with the application of methods and approaches of the engineering mechanics to fiber optics systems. The emphasis is on fiber optics interconnects. We address traditional problems of the mechanical behavior of optical fiber interconnects subjected to mechanical and/or thermally induced loading, as well as the application of nanotechnology in optical fiber engineering. Particularly, we elaborate on the application of a newly developed advanced nano-particle material (NPM) as an attractive substitute for the existing optical fiber coatings and perhaps even claddings. The solutions to the majority of the examined problems were obtained using analytical ("mathematical") modeling, i.e., methods of classical structural analysis.

We derive analytical formulations for the output phase profile of symmetrically excited one-to-N multimode interference couplers. We show that the output phase increases quadratically from the middle of the MMI waveguide, which needs to be taken into account for phase-dependent applications such as optical phased arrays.

In this work, an optimum frequency is found for the operation of single cavity photonic switches. At this optimum point, the transmission contrast of ON and OFF states takes its highest value, while keeping the device power threshold relatively low and the device speed acceptably high. Then, the dynamic behavior of a typical single cavity all optical switch is investigated in the optimum operation point through temporal Coupled Mode Theory. Switching speed and power are discussed, and the device is shown to be applicable for telecommunication and data processing applications. The analysis is quite general, and can be used for resonant structures, such as photonic crystals and microring resonators, in both side coupled and direct coupled configurations.

Cosite interference can be roughly defined as the unintentional degradation of receiver functionality as a result of close proximity to a powerful in-band transmission source; for instance receivers located on modern cellular communication towers often suffer as a result of co-site interference introduced through space limitations and overcrowding. The Opto- Cancellation system was designed as a novel approach to mitigate the problem of co-site interference. The system accomplishes interference cancellation through the integration of traditional EO telecommunications devices into an otherwise wholly RF communications system. This paper will discuss the integration of EO components into an RF communications system as well as the non-traditional integration of EO components to perform co-site interference mitigation. To date the system has performed cancellation up to 80 dB reduction of a narrowband signal and 45 dB reduction of a 100 MHz bandwidth signal without affecting the receiver's signal of interest. The system is able to perform extremely wide-band interference cancellation by utilizing the large instantaneous bandwidth inherent in a fast EO modulator, largely addressing the limitations of traditional RF interference cancellation/mitigation techniques such as digital sampling and filtering.

An analog-type high-speed serializer/deserializer (SerDes) has been designed for optical links especially between CPU and memory. The circuit uses a system clock and its phases to multiplex data to the serial link which avoids the need for a PLL-based high frequency clock generation used in serializing parallel data as in conventional SerDes design. The multiplexed link combined with the de-serializing clock is used as a reference signal for de-serialization. The SerDes is being designed in a 0.13 μm Si-CMOS technology. The fabricated serializer has a core chip size of 360 x750 μm². Power dissipation for the SerDes is 71.4 mW operating up to 6.5 Gbps.