This PDF file contains the front matter associated with SPIE Proceedings Volume 9753, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

To meet the increasing demand for board level high speed data transmission in the area of high performance computing, much attention has been paid to employ high performance polymer optical waveguide. So far, optical interconnects have been considered to have advantages over electronic solutions in various aspects, such as lower power consumption, larger information carrying capacity and immunity to crosstalk. It is one of the advantages that waveguides are possible to be curved and crossed light paths in the same circuit plane. GI-core polymer waveguides are capable of confining the signal light around the core center more tightly, by which the GI-core waveguides exhibit low propagation loss, low crosstalk, and low modal dispersion. Therefore, GI-core reduces the loss in meshed waveguide compared to SI-core meshed waveguides. The material of our GI-core polymer waveguide is Polynorbornene. The varnish for both core and cladding is prepared and coated onto a substrate then the coated layers are exposed to a UV light through a photomask and heated at a certain temperature. After heating, index profile changes and GI-core waveguide is formed. This is our original photo-addressing method. We confirm that extremely low crossings loss is observed in both 90-degree (0.53 dB/500 crosses) and 45-degree (1.55 dB/500 crosses). Also, we succeed high-speed data transmission. We expect that this ultra low crossing loss GI-core waveguide will be one of the promising components giving a strong impact on high performance computing systems in near future.

Multimode polymer waveguides are being increasingly considered for use in short-reach board-level optical interconnects as they exhibit favourable optical properties and allow direct integration onto standard PCBs with conventional methods of the electronics industry. Siloxane-based multimode waveguides have been demonstrated with excellent optical transmission performance, while a wide range of passive waveguide components that offer routing flexibility and enable the implementation of complex on-board interconnection architectures has been reported. In recent work, we have demonstrated that these polymer waveguides can exhibit very high bandwidth-length products in excess of 30 GHz×m despite their highly-multimoded nature, while it has been shown that even larger values of > 60 GHz×m can be achieved by adjusting their refractive index profile. Furthermore, the combination of refractive index engineering and launch conditioning schemes can ensure high bandwidth (> 100 GHz×m) and high coupling efficiency (<1 dB) with standard multimode fibre inputs with relatively large alignment tolerances (~17×15 μm²). In the work presented here, we investigate the effects of refractive index engineering on the performance of passive waveguide components (crossings, bends) and provide suitable design rules for their on-board use. It is shown that, depending on the interconnection layout and link requirements, appropriate choice of refractive index profile can provide enhanced component performance, ensuring low loss interconnection and adequate link bandwidth. The results highlight the strong potential of this versatile optical technology for the formation of high-performance board-level optical interconnects with high routing flexibility.

Polymer waveguides (PWGs) are used within photonic interconnects as inexpensive and versatile substitutes for traditional optical fibers. The PWGs are typically aligned to silica-based optical fibers for coupling. An epoxide elastomer is then applied and cured at the interface for index matching and rigid attachment. Self-written waveguides (SWWs) are proposed as an alternative to further reduce connection insertion loss (IL) and alleviate marginal misalignment issues. Elastomer material is deposited after the initial alignment, and SWWs are formed by injecting ultraviolet (UV) light into the fiber or waveguide. The coupled UV light cures a channel between the two differing structures. A suitable cladding layer can be applied after development. Such factors as longitudinal gap distance, UV cure time, input power level, polymer material selection and choice of solvent affect the resulting SWWs. Experimental data are compared between purely index-matched samples and those with SWWs at the fiber-PWG interface. It is shown that < 1 dB IL per connection can be achieved by either method and results indicate lowest potential losses associated with a fine-tuned self-writing process. Successfully fabricated SWWs reduce overall processing time and enable an effectively continuous low-loss rigid interconnect.

This paper focuses on latest progress in experimental and theoretical studies on silicon-based carrier-depletion PN-junction phase shifters in terms of high modulation efficiency for energy-efficient photonic networks of high transmission capacity. Modulation efficiency of rib-waveguide phase shifters having various PN-junction configuration are characterized with respect to DC figure of merit defined for phase shifters using carrier-plasma dispersion as the physical principle of refractive-index modulation. In addition, RF drive voltage required for 10-Gb/s on-off keying is characterized for rib-waveguide phase shifters including lateral and vertical PN-junction configurations.

We report on an ultra-compact co-integrated transmitter and receiver in SiGe BiCMOS technology for short reach optical interconnects. A fully integrated EPIC transceiver chip on silicon photonics technology is described. The chip integrates all photonic and electronic devices for an electro-optic transceiver and has been designed to be testable on wafer-scale. A node-matched diode modulator based on carrier injection is a key building block in the chip design. Its operation performance is presented with respect to insertion loss, signal-to-noise-ratio and power consumption at a 25.78125 Gbit/s in NRZ operation. A novel SiGe based photodetector exhibits a -3 dB bandwidth of up to 70 GHz and a responsivity of >1 A/W. Details are given about the process technology of co-integration of photonic and electronic integrated circuits using both silicon-on-insulator and bulk silicon. The implemented co-integration process requires only few additional process steps, leading to only a slight increase in complexity compared to conventional CMOS and BiCMOS baselines.

We experimentally and theoretically investigate the use of silicon germanium (SiGe) on silicon substrate as a new platform for optical interconnects. The system composed of Germanium (Ge) rich Si_1-xGe_x guiding layer on a graded SiGe layer is showed to be suitable for the realization of all main building blocks of passive optical circuitry. We show experimentally at a wavelength of 1550nm that sharp 12μm radius bends can be obtained by light confinement tuning. Mach-Zehnder interferometer with more than 10 dB extinction ratio is also demonstrated. Moreover, Ge-rich Si_1-xGe_x based passive components are very interesting for their native integration with Ge-rich active optical devices. Hence, by using this new platform for optical integrated circuits, lattice mismatch between silicon and germanium is no longer a major constraint for the integration of Ge-rich active photonic components on silicon.

In this paper we benchmark various interconnect technologies including electrical, photonic, and plasmonic options. We contrast them with hybridizations where we consider plasmonics for active manipulation devices, and photonics for passive propagation integrated circuit elements, and further propose another novel hybrid link that utilizes an on chip laser for intrinsic modulation thus bypassing electro-optic modulation. Link benchmarking proves that hybridization can overcome the shortcomings of both pure photonic and plasmonic links. We show superiority in a variety of performance parameters such as point-to-point latency, energy efficiency, capacity, ability to support wavelength division multiplexing, crosstalk coupling length, bit flow density and Capability-to-Latency-Energy-Area Ratio.

We propose and experimentally demonstrate a new type of silicon total-internal-reflection (TIR) optical switch by embedding of pn junction providing both function of a reflector and a thermo-optic heater simultaneously. The TIR switch is composed of asymmetrically y-branched multimode waveguides with a waveguide width of 5 μm for a switching node. The incident light is tapered from singlemode waveguides for the fundamental mode propagation and normally reflected without bias at the pn diode based on free carrier plasma dispersion effect. The switching operation is achieved by thermo-optic effect which can compensate the decreased refractive index at the doped region based on reverse breakdown of pn junction. At the rest of switch, extinction ratio of 8 dB and insertion loss of 5.6 dB are achieved with a 3° and 1-μm-thick reflector, By applying -50 V to pn diode, we achieved the perfect switching operation with an extinction ratio of 11.6 dB, an insertion loss of -4.1 dB and a thermal heating power of 152.5 mW.

We present a vision for the hybrid integration of advanced transceivers at 1.3 μm wavelength, and the progress done towards this vision in the EU-funded RAPIDO project. The final goal of the project is to make five demonstrators that show the feasibility of the proposed concepts to make optical interconnects and packet-switched optical networks that are scalable to Pb/s systems in data centers and high performance computing. Simplest transceivers are to be made by combining directly modulated InP VCSELs with 12 μm SOI multiplexers to launch, for example, 200 Gbps data into a single polymer waveguide with 4 channels to connect processors on a single line card. For more advanced transceivers we develop novel dilute nitride amplifiers and modulators that are expected to be more power-efficient and temperatureinsensitive than InP devices. These edge-emitting III-V chips are flip-chip bonded on 3 μm SOI chips that also have polarization and temperature independent multiplexers and low-loss coupling to the 12 μm SOI interposers, enabling to launch up to 640 Gbps data into a standard single mode (SM) fiber. In this paper we present a number of experimental results, including low-loss multiplexers on SOI, zero-birefringence Si waveguides, micron-scale mirrors and bends with 0.1 dB loss, direct modulation of VCSELs up to 40 Gbps, ±0.25μm length control for dilute nitride SOA, strong band edge shifts in dilute nitride EAMs and SM polymer waveguides with 0.4 dB/cm loss.

Industrial and military requirements for optics dictate the ability to operate reliably over a myriad of extreme environmental conditions such as extended temperature, increased shock and vibration, high particulate environments, etc. While it is paramount that the transceiver be able to maintain performance over these extreme conditions, considerations for the optical interconnects in the signal path are often overlooked. In general, optical performance tends to degrade as the operating temperature drifts from nominal conditions. Likewise, optical connector performance degrades at higher shock and vibration levels. As a result, optical products are generally limited to operating at case temperatures between 0 °C – 70 °C and struggle at high shock and vibration levels. In this paper we demonstrate the performance of the Samtec 12 channel FireFly^TM at 10 Gbps, -40 °C and 85 °C case temperature coupled with the expanded beam MXCTM connector from US Conec. Optical eye diagrams and receiver sensitivity for a link that includes 100 m of OM3 fiber, reliability results for transmitters operating at extended temperature, and shock and vibration data are presented.

A novel method for fabricating a single mode optical interconnection platform is presented. The method comprises the miniaturized assembly of optoelectronic single dies, the scalable fabrication of polymer single mode waveguides and the coupling to glass fiber arrays providing the I/O’s. The low cost approach for the polymer waveguide fabrication is based on the nano-imprinting of a spin-coated waveguide core layer. The assembly of VCSELs and photodiodes is performed before waveguide layers are applied. By embedding these components in deep reactive ion etched pockets in the silicon substrate, the planarity of the substrate for subsequent layer processing is guaranteed and the thermal path of chip-to-substrate is minimized. Optical coupling of the embedded devices to the nano-imprinted waveguides is performed by laser ablating 45 degree trenches which act as optical mirror for 90 degree deviation of the light from VCSEL to waveguide. Laser ablation is also implemented for removing parts of the polymer stack in order to mount a custom fabricated connector containing glass fiber arrays. A demonstration device was built to show the proof of principle of the novel fabrication, packaging and optical coupling principles as described above, combined with a set of sub-demonstrators showing the functionality of the different techniques separately. The paper represents a significant part of the electro-photonic integration accomplishments in the European 7th Framework project “Firefly” and not only discusses the development of the different assembly processes described above, but the efforts on the complete integration of all process approaches into the single device demonstrator.

Embedded optical waveguide technology for optical printed circuit boards (OPCBs) has advanced considerably over the past decade both in terms of materials and achievable waveguide structures. Two distinct classes of planar graded index multimode waveguide have recently emerged based on polymer and glass materials. We report on the suitability of graded index polymer waveguides, fabricated using the Mosquito method, and graded index glass waveguides, fabricated using ion diffusion on thin glass foils, for deployment within future data center environments as part of an optically disaggregated architecture. To this end, we first characterize the wavelength dependent performance of different waveguide types to assess their suitability with respect to two dominant emerging multimode transceiver classes based on directly modulated 850 nm VCSELs and 1310 silicon photonics devices. Furthermore we connect the different waveguide types into an optically disaggregated data storage system and characterize their performance with respect to different common high speed data protocols used at the intra and inter rack level including 10 Gb Ethernet and Serial Attached SCSI.

A glass optical waveguide process has been developed for fabrication of electro-optical circuit boards (EOCB). Very thin glass panels with planar integrated single-mode waveguides can be embedded as a core layer in printed circuit boards for high-speed board-level chip-to-chip and board-to-board optical interconnects over an optical backplane. Such singlemode EOCBs will be needed in upcoming high performance computers and data storage network environments in case single-mode operating silicon photonic ICs generate high-bandwidth signals [1]. The paper will describe some project results of the ongoing PhoxTroT project, in which a development of glass based single-mode on-board and board-to-board interconnection platform is successfully in progress. The optical design comprises a 500 μm thin glass panel (Schott D263Teco) with purely optical layers for single-mode glass waveguides. The board size is accommodated to the mask size limitations of the fabrication (200 mm wafer level process, being later transferred also to larger panel size). Our concept consists of directly assembling of silicon photonic ICs on cut-out areas in glass-based optical waveguide panels. A part of the electrical wiring is patterned by thin film technology directly on the glass wafer surface. A coupling element will be assembled on bottom side of the glass-based waveguide panel for 3D coupling between board-level glass waveguides and chip-level silicon waveguides. The laminate has a defined window for direct glass access for assembling of the photonic integrated circuit chip and optical coupling element. The paper describes the design, fabrication and characterization of glass-based electro-optical circuit board with format of (228 x 305) mm².

We report on the functionality and key performance properties of 50 μm x 50 μm flexible graded index silicone polymer waveguides. The materials show low optical propagation losses of < 0.04 dB/cm @ 850 nm over 1 m lengths as well as stability to 2000 hours 85°C/85% relative humidity and 5 cycles of 260°C solder wave reflow testing. Methods to fabricate large area panels are demonstrated for scaled manufacturing of polymer based optical printed wiring boards. The polymer waveguides are terminated with a passive direct fiber attach method. Fully MPO connectorized waveguide panels are realized and their optical performance properties assessed.

We discuss light emitters and modulators in silicon photonic interconnects. In particular, we experimentally demonstrate resonant luminescence from Ge quantum dots embedded in a photonic crystal ring resonator (PCRR) at room temperature. Six sharp resonant peaks are observed, which correspond to the resonant modes supported by the PCRR. We further study a high speed silicon-graphene nanobeam modulator, and a silicon spatial light modulator. These devices show great potential in future high density and high capacity interconnection systems.

In recent decades, silicon photonics has attracted intensive research interest in optical communications due to its advantageous compact dimensions and high-volume manufacturability. Particularly, micro-ring resonators on silicon-oninsulator (SOI) platform have been widely exploited as a basic building block for a vast range of applications such as switches, modulators, and sensors. A majority of these applications involve light-matter interaction, which can be substantially enhanced by the high quality factor micro-ring resonators. However, conventional strip waveguide based micro-ring resonators suffer from the intrinsic dilemma in achieving high light confinement and strong light-matter interaction simultaneously. Subwavelength grating (SWG) waveguides, comprised of periodically interleaved high and low refractive index materials with a pitch less than one wavelength, have been demonstrated as a promising alternative. For SWG waveguides built on SOI wafers, the ratio of silicon and cladding materials can be engineered microscopically to achieve desired macroscopic properties. The control of these properties could potentially lead to significant performance improvements compared with conventional micro-ring resonators based photonic devices, such as filters and sensors. However, SWG waveguide based micro-ring resonators (SWGMRs) that have been demonstrated so far can only provide a moderate quality factor (~5600) with a large radius (e.g. 15 μm), which greatly jeopardize the wide spread research efforts in this area. In this paper, we propose to use trapezoidal silicon pillars to reduce the bend loss of SWGMRs to improve the quality factor. For the first time, we experimentally demonstrate the smallest SWGMR (the micro-ring radius equals to 5 μm) with an applicable quality factor as high as 11,500. This approach also can be applied to SWGMRs with larger radii for higher quality factors. We also experimentally demonstrated a 10 μm radius SWGMR that can provide a quality factor up to 45,000. Compared to SWGMRs built with conventional rectangular silicon pillars, the quality factors is increased by 4.6 times from a 5 μm radius SWGMR and 3 times from a 10 μm SWGMR radius, respectively.

Ultracompact thermooptically tuned photonic crystal waveguide (PCW) based Mach–Zehnder interferometers (MZIs) working in silicon-on-sapphire in mid-infrared regime have been proposed and demonstrated. We designed and fabricated a PCW based silicon thermo-optic (TO) switch operating at 3.43 μm. Both steady-state and transient thermal analyses were performed to evaluate the thermal performance of the TO MZIs. The required π phase shift between the two arms of the MZI has been successfully achieved within an 80 μm interaction distance. The maximum modulation depth of 74% was demonstrated for switching power of 170 mW.

Data center (DC) and high performance computing (HPC) applications have traditionally used a combination of copper, multimode fiber and single-mode fiber interconnects with relative percentages that depend on factors such as the line rate, reach and connectivity costs. The balance between these transmission media has increasingly shifted towards optical fiber due to the reach constraints of copper at data rates of 10 Gb/s and higher. The percentage of single-mode fiber deployed in the DC has also grown slightly since 2014, coinciding with the emergence of mega DCs with extended distance needs beyond 100 m. This trend will likely continue in the next few years as DCs expand their capacity from 100G to 400G, increase the physical size of their facilities and begin to utilize silicon-photonics transceiver technology. However there is a still a need for the low-cost and high-density connectivity, and this is sustaining the deployment of multimode fiber for links ≤ 100 m. In this paper, we discuss options for single-mode and multimode fibers in DCs and HPCs and introduce a reduced diameter multimode fiber concept which provides intra-and inter-rack connectivity as well as compatibility with silicon-photonic transceivers operating at 1310 nm. We also discuss the trade-offs between single-mode fiber attributes such as bend-insensitivity, attenuation and mode field diameter and their roles in capacity and connectivity in data centers.

Multicore fiber enables a parallel optic data link with a single optical fiber, thus providing an attractive way to increase the total throughput and the integration density of the interconnections. We study and present photonics integration technologies and optical coupling approaches for multicore transmitter and receiver subassemblies. Such optical engines are implemented and characterized using multimode 6-core fibers and multicore-optimized active devices: 850-nm VCSEL and PD arrays with circular layout and multi-channel driver and receiver ICs. They are developed for bit-rates of 25 Gbps/channel and beyond, i.e. <150 Gbps per fiber, and also optimized for ruggedized transceivers with extended operation temperature range, for harsh environment applications, including space.

We propose two low-cost and robust optical fiber systems based on the photonic lantern (PL) technology for operating at 635 nm and 1550 nm. The PL is an emerging technology that couples light from a multi-mode (MM) fiber to several single-mode (SM) fibers via a low-loss adiabatic transition. This bundle of SM fibers is observed as a MM fiber system whose spatial modes are the degenerate supermodes of the bundle. The adiabatic transition allows that those supermodes evolve into the modes of the MM fiber. Simulations of the MM fiber end structure and its taper transition have been performed via functional mode solver tools in order to understand the modal evolution in PLs. The modelled design consists of 7 SM fibers inserted into a low-index capillary. The material and geometry of the PLs are chosen such that the supermodes match to the spatial modes of the desired step-index MM fiber in a moderate loss transmission. The dispersion of materials is also considered. These parameters are studied in two PL systems in order to reach a spectral transmission from 450 nm to 1600 nm. Additionally, an analysis of the geometry and losses due to the mismatching of modes is presented. PLs are typically used in the fields of astrophotonics and space photonics. Recently, they are demonstrated as mode converters in telecommunications, especially focusing on spatial division multiplexing. In this study, we show the use of PLs as a promising interconnecting tool for the development of miniaturized spectrometers operating in a broad wavelength range.

Optical networking is evolving from classical service-provider base data-center centric (DCC) internetworking environment with massive capacity, hence demanding novel optical switching and interconnecting technologies. The traditional telecom networks are under a flattening transformation to meet challenges from DCC networks for massive capacity serving in order of multi-Pb/s. We present proposed distributed and concentric data center based networks and the essential optical interconnection technologies, from the photonic kernels to electronic and optoelectronic server clusters, in both passive and active structures. Optical switching devices and integrated matrices are proposed composing of tunable (bandwidth and center wavelength) optical filters and switches as well as resonant microring modulators (μRM)(switching and spectral demux/mux) for multi-wavelength flexible-bandwidth optical channels of aggregate capacity reaching Ebps. The design principles and some experimental results are also reported.

Traffic in data centers networks (DCNs) is steadily growing to support various applications and virtualization technologies. Multi-tenancy enabling efficient resource utilization is considered as a key requirement for the next generation DCs resulting from the growing demands for services and applications. Virtualization mechanisms and technologies can leverage statistical multiplexing and fast switch reconfiguration to further extend the DC efficiency and agility. We present a novel high performance flat DCN employing bufferless and distributed fast (sub-microsecond) optical switches with wavelength, space, and time switching operation. The fast optical switches can enhance the performance of the DCNs by providing large-capacity switching capability and efficiently sharing the data plane resources by exploiting statistical multiplexing. Benefiting from the Software-Defined Networking (SDN) control of the optical switches, virtual DCNs can be flexibly created and reconfigured by the DCN provider. Numerical and experimental investigations of the DCN based on the fast optical switches show the successful setup of virtual network slices for intra-data center interconnections. Experimental results to assess the DCN performance in terms of latency and packet loss show less than 10^-5 packet loss and 640ns end-to-end latency with 0.4 load and 16- packet size buffer. Numerical investigation on the performance of the systems when the port number of the optical switch is scaled to 32x32 system indicate that more than 1000 ToRs each with Terabit/s interface can be interconnected providing a Petabit/s capacity. The roadmap to photonic integration of large port optical switches will be also presented.

Polymer photonic device fabrication usually relies on the utilization of clean-room processes, including photolithography, e-beam lithography, reactive ion etching (RIE) and lift-off methods etc, which are expensive and are limited to areas as large as a wafer. Utilizing a novel and a scalable printing process involving ink-jet printing and imprinting, we have fabricated polymer based photonic interconnect components, such as electro-optic polymer based modulators and ring resonator switches, and thermo-optic polymer switch based delay networks and demonstrated their operation. Specifically, a modulator operating at 15MHz and a 2-bit delay network providing up to 35.4ps are presented. In this paper, we also discuss the manufacturing challenges that need to be overcome in order to make roll-to-roll manufacturing practically viable. We discuss a few manufacturing challenges, such as inspection and quality control, registration, and web control, that need to be overcome in order to realize true implementation of roll-to-roll manufacturing of flexible polymer photonic systems. We have overcome these challenges, and currently utilizing our inhouse developed hardware and software tools, <10μm alignment accuracy at a 5m/min is demonstrated. Such a scalable roll-to-roll manufacturing scheme will enable the development of unique optoelectronic devices which can be used in a myriad of different applications, including communication, sensing, medicine, security, imaging, energy, lighting etc.

We demonstrate, for the first time to our knowledge, a SiN-assisted in-plane adiabatic coupler between SiPh and onboard glass waveguides. Our numerical study is founded on an actual graded index glass waveguide developed by Fraunhofer-IZM. The Silicon taper profile and the optimal length are extracted employing the supermode theory and the adiabatic theorem. Fabrication and assembly issues are investigated, resulting to an optimized coupler design that exhibits a theoretical Si-to-glass loss below 0.1dB over the entire C-band. The proposed solution can be realized utilizing standard passive flip-chip assembly equipment and is, therefore, cost-effective, easy to be fabricated, and well-suited for compact packaging.

This paper proposes and tests a design of electro-thermal bimorph actuators for alignment of flexible photonic waveguides fabricated in 16 µm thick SiO₂. The actuators are for use in a novel alignment concept for multi-port photonic integrated circuits (PICs), in which the fine alignment is taken care of by positioning of suspended, mechanically flexible waveguide beams on one or more of the PICs. The design parameters of the bimorph actuator allow to tune both the initial relative position of the waveguide end-facets, and the motion range of the actuators. Bimorph actuators have been fabricated and characterized. The maximum out-of-plane deflection of the bimorph actuator (with 720 μm-long poly-Si) can reach 18:5 μm with 126:42mW, sufficient for the proposed application.

We study the optical performances of microring resonator modulators fabricated on 200 mm SOI wafers to select the ring resonator modulators for targeted ONoC and optical interposer applications. Counter-doped ring resonator modulators were fabricated to guarantee the absence of unexpected p-i-n junctions in the ring waveguide due to overlay misalignments inherent to successive fabrication steps. The fabricated add-drop ring resonator modulators showed good DC performances with a VπL at 1.55 V.cm. Finally, ultra-low loss waveguides were realized to allow long distance data transport on photonic chips.

Here we show the results of an experimental analysis dedicated to investigate the impact of optical non linear effects, such as two-photon absorption (TPA), free-carrier absorption (FCA) and free-carrier dispersion (FCD), on the performance of integrated micro-resonator based filters for application in WDM telecommunication systems. The filters were fabricated using SOI (Silicon-on-Insulator) technology by CEA-Leti, in the frame of the FP7 Fabulous Project, which aims to develop low-cost and high-performance integrated optical devices to be used in new generation passive optical- networks (NG-PON2). Different designs were tested, including both ring-based structures and racetrack-based structures, with single-, double- or triple- resonator configuration, and using different waveguide cross-sections (from 500 x 200 nm to 825 x 100 nm). Measurements were carried out using an external cavity tunable laser source operating in the extended telecom bandwidth, using both continuous wave signals and 10 Gbit/s modulated signals. Results show that the use 100-nm high waveguide allows reducing the impact of non-linear losses, with respect to the standard waveguides, thus increasing by more than 3 dB the maximum amount of optical power that can be injected into the devices before causing significant non-linear effects. Measurements with OOK-modulated signals at 10 Gbit/s showed that TPA and FCA don’t affect the back-to-back BER of the signal, even when long pseudo-random-bit-sequences (PRBS) are used, as the FCD-induced filter-detuning increases filter losses but “prevents” excessive signal degradation.

We present new scheme for chip-level photonic I/Os, based on monolithically integrated vertical photonic devices on bulk silicon, which increases the integration level of PICs to a complete photonic transceiver (TRx) including chip-level light source. A prototype of the single-chip photonic TRx based on a bulk silicon substrate demonstrated 20 Gb/s low power chip-level optical interconnects between fabricated chips, proving that this scheme can offer compact low-cost chip-level I/O solutions and have a significant impact on practical electronic-photonic integration in high performance computers (HPC), cpu-memory interface, 3D-IC, and LAN/SAN/data-center and network applications.

InAs quantum dot (QD) laser heterostructures are grown by molecular beam epitaxy (MBE) system on GaAs substrates and fabricated. The InAs QD lasers exhibit comparable properties of the state-of-the-art QD lasers with the threshold current density J_th and efficiency η_i of 475A/cm² and 72.6%, respectively, at room temperature. The quantum dot laser emission is butt-joint coupled into silicon photonics waveguides by aligning the laser and silicon photonics chips with two translation stages. Due to the optical feedback to the laser cavity at the air/Si interface, the laser power self-pulsation and reduced threshold current density are observed. And the effective facet reflectivity, R_eff, of 62.7% is obtained from the theoretically analysis of the laser characteristics. Furthermore, the silicon photonics waveguides interface is coated with the SiO₂/TiO₂ antireflection (AR) coating layers, and no laser performance interference is observed owing the reduced optical feedback.

We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB.

Subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to its freedom to tune a few important waveguide properties such as dispersion and refractive index. Devices based on SWG waveguide have demonstrated impressive performances compared to those of conventional waveguides. However, the large loss of SWG waveguide bends jeopardizes their applications in integrated photonics circuits. In this work, we propose that a predistorted refractive index distribution in SWG waveguide bends can effectively decrease the mode mismatch noise and radiation loss simultaneously, and thus significantly reduce the bend loss. Here, we achieved the pre-distortion refractive index distribution by using trapezoidal silicon pillars. This geometry tuning approach is numerically optimized and experimentally demonstrated. The average insertion loss of a 5 μm SWG waveguide bend can be reduced drastically from 5.58 dB to 1.37 dB per 90° bend for quasi-TE polarization. In the future, the proposed approach can be readily adopted to enhance performance of an array of SWG waveguide-based photonics devices.

Silicon photonics has taken great importance owing to the applications in optical communications, ranging from short reach to long haul. Originally dedicated to telecom wavelengths, silicon photonics is heading toward circuits handling with a broader spectrum, especially in the short and mid-infrared (MIR) range. This trend is due to potential applications in chemical sensing, spectroscopy and defense in the 2-10 μm range. We previously reported the development of a MIR photonic platform based on buried SiGe/Si waveguide with propagation losses between 1 and 2 dB/cm. However the low index contrast of the platform makes the design of efficient grating couplers very challenging. In order to achieve a high fiber-to-chip efficiency, we propose a novel grating coupler structure, in which the grating is locally suspended in air. The grating has been designed with a FDTD software. To achieve high efficiency, suspended structure thicknesses have been jointly optimized with the grating parameters, namely the fill factor, the period and the grating etch depth. Using the Efficient Global Optimization (EGO) method we obtained a configuration where the fiber-to-waveguide efficiency is above 57 %. Moreover the optical transition between the suspended and the buried SiGe waveguide has been carefully designed by using an Eigenmode Expansion software. Transition efficiency as high as 86 % is achieved.

We simulate and test a new structure for light coupling from silicon strip waveguide to plasmonic slot waveguide. The conventional approach of simply using a taper-funnel structure for the mode matching between two types of waveguides is typically insufficient for high coupling efficiency. Here we propose the use of an additional silicon strip-to-slot mode converter, which has a low insertion loss itself and achieves better mode matching. The experimental results show the new design, with slot width fixed at 200nm, achieves a higher coupling efficiency than conventional one. The newly implemented design has 1.5 dB less loss than the conventional taper-funnel coupler, with a theoretical coupling loss of 2.18 dB/coupler and an experimentally measured loss of 3 dB/coupler at 1640nm wavelength.

In this research, subwavelength grating (SWG) nanostructures with different periodic configurations are designed on a slab dielectric waveguide and theoretically studied for creating beam splitting, position-shifting, and focusing effects, using Comsol Multiphysics as the simulation tool. Su8 with a refractive index (n) of 1.585 is considered as the core material for the dielectric waveguide, which has a lateral and longitudinal dimension of 3 and 6 um, respectively. Uniform and nonuniform rows and columns of nanoholes with diameters of 90 nm are considered as the diffractive design elements. We took advantage of the multimode interference (MMI) phenomenon caused by periodic arrays of nanoholes as SWG structures, which are engineered to induce the desired effects. The power transmission efficiencies of the SWG-designed MMI waveguides are calculated in the wavelength range of 500-1200 nm. The efficiencies are high for the major part of the studied spectrum and reach a maximum of ~97% at 1200 nm for some designs. Also, the refractive index contrasts between the effective index (n_eff) and the ideal parabolic model (n_par) are shown for the conventional MMI SU8 waveguide within a wavelength range of 700-1000 nm. It can be clearly seen that the contrast is minimum for λ = 700nm, and increases with wavelength, showing the multimode interference effect is optimum at 700 nm and deteriorates as the wavelength increases. Modal phase error (MPE) estimated for m=5 and different wavelengths revealed that the MMI device can have a fairly high performance within the whole studied wavelength range for a maximum mode number of 3. Additionally, the field intensity distributions calculated for the design with the beam splitting effect for different wavelengths reflected that the effect has a broadband characteristic.

We present high performance vertical-illumination type Ge-on-Si avalanche photodetectors and photoreceiver modules operating up to 25 Gb/s. The Ge avalanche photodetectors were grown on a bulk-silicon wafer by RPCVD, and fabricated with CMOS-compatible process. The fabricated devices show a -3dB bandwidth greater than 13 GHz at operational biases (gain> 20) for λ ~ 1550 nm. The measured maximum gain-bandwidth (GB) product is ~ 493 GHz. Two types of Ge-on-Si APD receiver modules exhibit high sensitivities of better than –20.7 dBm for a 25 Gb/s operation at a BER = 10^-12 and λ ~ 1310 nm, and –27.75 dBm for a 10 Gb/s operation at a BER = 10^-12 and λ ~ 1550nm, respectively.

A binary Fresnel Zone Axilens (FZA) is designed for the infinite conjugate mode and the phase profile of a refractive axicon is combined with it to generate a composite Diffractive Optical Element (DOE). The FZA designed for two focal lengths generates a line focus along the propagation direction extending between the two focal planes. The ring pattern generated by the axicon is focused through this distance and the radius of the ring depends on the propagation distance. Hence, the radius of the focused ring pattern can be tuned, during the design process, within the two focal planes. The integration of the two functions was carried out by shifting the location of zones of FZA with respect to the phase profile of the refractive axicon resulting in a binary composite DOE. The FZAs and axicons were designed for different focal depth values and base angles respectively, in order to achieve different ring radii within the focal depth of each element. The elements were simulated using scalar diffraction formula and their focusing characteristics were analyzed. The DOEs were fabricated using electron beam direct writing and evaluated using a fiber coupled diode laser. The tunable ring patterns generated by the DOEs have prospective applications in microdrilling as well as microfabrication of circular diffractive and refractive optical elements.

A new optical backplane solution is proposed for high-capacity ICT apparatus. A modular, scalable and full-mesh bandwidth-upgradable optical interconnection between optoelectronic boards is guaranteed thanks to an optimized layout of standard MM 12-fiber ribbons which divides the overall backplane into several independent optical sub-circuits. The novel automated assembly procedure of fiber ribbons inside sub-circuits with a robotic work-cell is described. System validation of the optical backplane performed with commercially available MM 12-fiber transceivers @10Gb/s proved the feasibility of the proposed solution for future optical interconnections with terabit overall capacity.