This PDF file contains the front matter associated with SPIE Proceedings Volume 8990 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Silicon photonics has attracted extensive attention in recent years as a promising solution for next generation high-speed, low energy consumption, and low cost data transmission systems. Although a few experiments indicated board-level and long haul communication capability, major and near-future application of silicon photonics is commonly seen as Ethernet at 100Gb/s and beyond, such as interconnects in data centers, where O-Band (near 1310 nm wavelength) has been standardized for its low fiber dispersion. However, almost all silicon photonics devices demonstrated up to date operate at C-Band (1530 nm to 1560 nm), the fiber loss and erbium amplification window, probably due to the wider availability of lasers and testing apparatus at this wavelength. Typical C-Band devices cannot operate at O-Band, thus the whole device library needs to be redesigned and recalibrated for O-Band applications. In this paper, we present an ultra compact, low loss, and low crosstalk waveguide crossing operating at O-Band. It is designed using the finite difference time domain method coupled with a particle swarm optimization. Device footprint is only 6 μm × 6 μm. The measured insertion loss is 0.19±0.02 dB across an 8-inch wafer. Cross talk is lower than -35 dB. We also report a second waveguide crossing with a 9 μm × 9 μm footprint with 0.017±0.005 dB insertion loss. Finally we summarize the performance of our overall O-Band device library, including low-loss waveguides, high-speed modulators, and photodetectors.

Silicon photonics is a rapidly growing R&D field where universities, institutes and companies are all involved and the business expectations for the next few years are high. One of the key enabling elements that led to the present success of silicon photonics is ePIXfab. It is a consortium of institutes that has together offered multi-project wafer (MPW) runs, packaging services, training, and feasibility studies. These services have significantly lowered the barrier of various research groups and companies to start developing silicon photonics. Until now the MPW services have been offered by the ePIXfab partners IMEC, CEA-Leti and IHP, which all use CMOS-type silicon photonics technology with a typical silicon-on-insulator (SOI) waveguide thickness of 220 nm. In November 2013 this MPW offering was expanded by the ePIXfab partner VTT that opened the access to its 3 μm SOI waveguide platform via ePIXfab MPW runs. This technology platform is complementary to the mainstream silicon photonics technology (220 nm) and it offers such benefits as very low losses, small polarization dependency, ultrabroadband operation and low starting costs

We present our recent breakthrough for high density integration in micron-scale thick semiconductor platforms. The novel bend concept is presented from a theoretical point of view and supported by experimental results on silicon strip waveguides, including the smallest low-loss bends ever reported for an optical waveguide. Some experimental example applications to resonators, spirals, and Mach-Zehnder interferometers are also presented, along with envisaged applications to other semiconductor platforms. A special focus will be dedicated to potential applications in III-V platforms, where the novel bend could lead to unprecedented dense integration of devices as well as to novel concepts for active components.

We have recently characterized spirals waveguides based on 4 μm thick strip waveguides with suitably designed lowloss micron scale bends. Different bends and different lengths have been tested to extrapolate propagation losses and bending losses. In particular lowest bending losses have been found to be smaller than 0.01 dB per turn, while propagation losses are about 0.15 dB/cm. Very small footprint is achieved thanks to a novel bend concept combined to waveguide pitches of a few microns. The unique properties of our waveguides make our platform the ideal one for low loss long spiral waveguides with very small footprint.

In response to the optical packaging needs of a rapidly growing silicon photonics market, Chiral Photonics, Inc. (CPI) has developed a new generation of ultra-dense-channel, bi-directional, all-optical, input/output (I/O) couplers that bridge the data transport gap between standard optical fibers and photonic integrated circuits. These couplers, called Pitch Reducing Optical Fiber Arrays (PROFAs), provide a means to simultaneously match both the mode field and channel spacing (i.e. pitch) between an optical fiber array and a photonic integrated circuit (PIC). Both primary methods for optically interfacing with PICs, via vertical grating couplers (VGCs) and edge couplers, can be addressed with PROFAs. PROFAs bring the signal-carrying cores, either multimode or singlemode, of many optical fibers into close proximity within an all-glass device that can provide low loss coupling to on-chip components, including waveguides, gratings, detectors and emitters. Two-dimensional (2D) PROFAs offer more than an order of magnitude enhancement in channel density compared to conventional one-dimensional (1D) fiber arrays. PROFAs can also be used with low vertical profile solutions that simplify optoelectronic packaging while reducing PIC I/O real estate usage requirements. PROFA technology is based on a scalable production process for microforming glass preform assemblies as they are pulled through a small oven. An innovative fiber design, called the “vanishing core,” enables tailoring the mode field along the length of the PROFA to meet the coupling needs of disparate waveguide technologies, such as fiber and onchip. Examples of single- and multi-channel couplers fabricated using this technology will be presented.

Silicon-on-insulator grating coupler is a crucial passive device that enables the coupling of light into and out of a submicron, silicon-based photonic integrated circuit. In particular, a grating coupler with completely vertical emission is vital for interfacing surface-emitting/receiving optoelectronic devices, and can largely reduce the packaging cost and complexity due to off-normal configuration. Unfortunately, for a grating coupler with completely vertical emission, it inevitably induces the second-order diffraction that significantly degrades the coupling efficiency and enhances the backreflection. In this work, we propose and study a new concept for making a high-performance grating coupler with completely vertical emission. Following our design strategy, we numerically show that a 1.1 dB total coupling loss, a - 24.4 dB backreflection, and a 20 nm spectral linewidth can be achieved at the same time (without full optimization), when our grating coupler is butt-coupled to a standard single-mode fiber operating around 1310 nm wavelengths. Compared to the previous proposals such as slant grating, polymer wedge, and entrance mirror made by slit or chirped grating, our approach requires only CMOS process compatible elements and does not involve complex numerical methods to reach the desired performances. The design methodology and optimization procedure will also be discussed.

Test points are essential in allowing optical circuits on a wafer to be autonomously tested after selected manufacturing steps, hence allowing poor performance or device failures to be detected early and to be either repaired using direct write methods, or a cessation of further processing to reduce fabrication costs. Grating couplers are a commonly used method for efficiently coupling light from an optical fibre to a silicon waveguide. They are relatively easy to fabricate and they allow light to be coupled into/out from any location on the device without the need for polishing, making them good candidates for an optical test point. A fixed test point can be added for this purpose, although traditionally these grating devices are fabricated by etching the silicon waveguide, and hence this permanently adds loss and leads to a poor performing device when placed into use after testing. We demonstrate a similar device utilising a refractive index change induced by lattice disorder. Raman data collected suggests this lattice damage is reversible, allowing a laser to subsequently erase the grating coupler.

In this paper we present a uniform fully-etched TM-mode grating coupler for vertical coupling of light into SOI photonic integrated circuits and a chirped alternative to increase its bandwidth by using the same fabrication steps and maintaining its coupling efficiency. The first design refers to a uniform grating consisting of 22 periods with 670 nm period length, exhibiting 5.6 dB coupling losses at 1564 nm and a 3dB bandwidth of 32 nm. The 3dB bandwidth is extended from 32 to 76 nm by adding a chirped section at the front end of the uniform section in the second design. The ultra-wideband coupler can be used across all C-band as well as in S and L bands, it is realized at no expense of fabrication complexity while coupling efficiency is maintained. The coupling efficiency can be improved if the grating gap is decreased below 80 nm yet increasing fabrication resolution requirements. Theoretical and experimental analysis is presented for the coupling efficiency versus structure period and gap width while angle alignment tolerance is also investigated.

Silicon is considered a promising platform for photonic integrated circuits as they can be fabricated in state-of-the-art electronics foundaries with integrated CMOS electronics. While much of the existing work on CMOS photonics has used directional couplers for power splitting, multimode interference (MMI) devices may have relaxed fabrication requirements and smaller footprints, potentially energy efficient designs. They have already been used as 1x2 splitters, 2x1 combiners in Quadrature Phase Shift Keying modulators, and 3-dB couplers among others. In this work, 3-dB, butterfly and cross MMI couplers are realized on bulk CMOS technology. Footprints from around 40um² to 200 um² are obtained. MMI tolerances to manufacturing process and bandwidth are analyzed and tested showing the robustness of the MMI devices.

Integration density, channel scalability, low switching energy and low insertion loss are the major prerequisites for on-chip WDM systems. A number of device geometries have already been demonstrated that fulfill these criteria, at least in part, but combining all of the requirements is still a difficult challenge. I will present our recent work on photonic crystal enhanced light sources, modulators and detectors for silicon photonics, that promise to give the ultimate in low energy and area consumption.

The angled multimode interferometer (AMMI) was recently demonstrated as a wavelength division (de)multiplexing (WDM) structure employing the phenomenon of dispersive self-imaging in a multimode planar waveguide. It has distinct advantages including very low insertion loss, ease of fabrication and good tolerance to fabrication error. Here, we first demonstrated a further optimized single 4-channel AMMI on the silicon-on-insulator (SOI) platform with a low insertion loss of < 1 dB, a low cross talk of < -23 dB and a non-uniformity of < 0.5 dB. However, a single AMMI is limited to have small channel count with a relatively large channel spacing in order to maintain high-performance WDM functionality. Therefore we subsequently demonstrated two structures derived from a single AMMI on the SOI platform: An 8-channel WDM comprising of two 4-channel AMMIs interleaved by an imbalanced Mach-Zehnder interferometers (MZIs) was fabricated. Low-insertion-loss and low-cross-talk operation was achieved without active tuning structures.

We present the first characterization results of some cascaded interleavers that we have recently fabricated on 4 μm thick Silicon on Insulator (SOI) wafers. The filters are based on strip waveguides, micron-scale bends and compact MMIs, all components with low loss and high tolerance to fabrication errors, due to the high mode confinement in the silicon region. A thorough comparison of the found results with the theoretical model will be presented, taking into account fabrication limitations. The fabricated filters will be used in the optical RAM circuits of the RAMPLAS project funded by the European Commission.

Modern optical communication systems require tunable optical delay lines for synchronization of data packages. Chirped fiber grating are typically used as a dispersive element for this application. Fiber-based schemes, however, suffer from bulkiness, slow response and/or low time resolution. Integrated photonics on silicon is one alternative approach. Several more advanced device architectures have been subsequently demonstrated on silicon, including ringresonator and photonic crystal (PhC) line-defect waveguide types. The coauthors of this paper have recently proposed a novel class of tunable optical delay lines based on apodized grating waveguides. It was shown that high bit-rate operation is achievable by cascading two complementary (inward and outward) apodized gratings. In this paper, we have experimentally demonstrated our proposed approach and studied performance of the fabricated delay lines for optical telecommunication applications. The bit-rate was extracted from broadening of transform-limited input pulses of the measured dispersion of the delay lines. Characterization of the compact delay lines shows that the single grating devices offer true-time delays as long as 164 ps, tuning range of ~ 81 ps, and a minimum bit rate of ~ 15 Gb/s. The cascaded scheme offer true-time delays of 82 ps and tuning range of 32 ps and can potentially operate at bit rates as high as 107 Gb/s.

We demonstrate several building blocks of true-time-delay (TTD) network, including subwavelength grating couplers, photonic crystal waveguide TTD lines, and multimode interferometer (MMI) power splitters fabricated on silicon nanomembrane (SiNM) transferred onto unconventional substrates, such as glass, Kapton. Bending tests performed on flexible gratings demonstrate operation even at ~15mm bending radius, with about 5dB loss. The 1×16 cascaded multimode interference (MMI) based power splitter demonstrates uniformity of 0.96dB across all the 16 output channels, and an insertion loss of 0.56dB.The photonic crystal waveguides are designed to provide large time delay values within a short length. Photonic crystal tapers are implemented at the strip-photonic crystal waveguide interfaces to minimize loss and provide larger time delay values. A large group index of ~28.5 is calculated from the measurement data, thus indicating achievability of time delay larger than 58ps per millimeter length of the delay line within a tuning range of 20nm. The demonstrated building blocks present a viable path for obtaining scalable TTD modules on unconventional substrates.

Silicon-on-insulator (SOI) is fast becoming a popular technology platform for silicon photonic devices as well as RFand nanoelectronics, while the field of nanoscale silicon structures remains an active topic in optoelectronic research. Silicon light sources with an active material only a couple of nanometers in dimension has several distinct advantages for enhanced light emission due to carrier confinement and improved external light extraction efficiency when compared to bulk CMOS light sources. This work focuses on these inherent advantages, where the design of nanoscale silicon light source arrays implemented in a custom SOI process, is presented utilizing hot carrier luminescence generated by avalanching pn-junctions. SOI light sources have shown an improvement in electroluminescent power emitted through various techniques inducing carrier confinement effects. These techniques are typically applied by either thinning the silicon active material in one or two dimensions. Conventional nanoscale SOI LEDs usually depend on recombination in forward-biased junctions. The wavelengths of interest are consequently in the near-infrared range around the band gap energy. In contrast, the device structures presented in this paper is based on hot carrier electroluminescence utilizing reach-through and punch-through techniques. We present the power spectral densities of the structures over a very wide spectral range also covering the visible wavelengths. The spectral characteristics of the SOI light sources were investigated and the dominant light generation mechanisms were identified. This work compares various device structures and light source architectures and the results presented exemplify the possibilities of SOI light sources for future applications.

Graded junction, carrier energy and momentum engineering concepts have been utilized to realize a high intensity 100 nW 5GHz Silicon Avalanche based LED (Si Av LED). A silicon 0.35 micron RF bi-polar process was used as design and processing technology. Particularly, the carrier momentum and energy distributions were modeled in graded junction Silicon p+-i-n structures, and utilized to increase optical yield. Best performance are up to 750nW emission in a 7 micron square active area at 10 V and 1mA. The device show up to 5 GHz modulation bandwidth. The spectral range is from 450 nm to 850 nm with an emphasized components in the white spectral region. The process is greatly CMOS compatible. The technology is particularly suitable for application in futuristic on- chip micro-photonic systems, lab-on chip systems, silicon- based micro display systems, on chip optical links, and optical inter-connects systems.

Hybrid integration on Silicon-on-Insulator (SOI) has emerged as a practical solution for compact and high-performance Photonic Integrated Circuits (PICs). It aims at combining the cost-effectiveness and CMOS-compatibility benefits of the low-loss SOI waveguide platform with the versatile active optical functions that can be realized by III-V photonic materials. The utilization of SOI, as an integration board, with μm-scale dimensions allows for an excellent optical mode matching between silicon rib waveguides and active chips, allowing for minimal-loss coupling of the pre-fabricated IIIV components. While dual-facet coupling as well as III-V multi-element array bonding should be employed to enable enhanced active on-chip functions, so far only single side SOA bonding has been reported. In the present communication, we present a novel integration scheme that flip-chip bonds a 6-SOA array on 4-μm thick SOI technology by coupling both lateral SOA facets to the waveguides, and report on the experimental results of wavelength conversion operation of a dual-element Semiconductor Optical Amplifier – Mach Zehnder Interferometer (SOA-MZI) circuit. Thermocompression bonding was applied to integrate the pre-fabricated SOAs on SOI, with vertical and horizontal alignment performed successfully at both SOA facets. The demonstrated device has a footprint of 8.2mm x 0.3mm and experimental evaluation revealed a 12Gb/s wavelength conversion operation capability with only 0.8dB power penalty for the first SOA-MZI-on-SOI circuit and a 10Gb/s wavelength conversion operation capability with 2 dB power penalty for the second SOA-MZI circuit. Our experiments show how dual facet integration can significantly increase the level of optical functionalities achievable by flip-chip hybrid technology and pave the way for more advanced and more densely PICs.

Recently there has been a growing interest in mid-infrared (mid-IR) photonic technology with a wavelength of operation approximately from 2-14 μm. Among several established mid-IR photonic platforms, silicon nanophotonic platform could potentially offer ultra-compact, and monolithically integrated mid-IR photonic devices and device arrays, which could have board impact in the mid-IR technology, such as molecular spectroscopy, and imaging. At room temperature, silicon has a bandgap ~ 1.12 eV resulting in vanishing two-photon absorption (TPA) for mid-IR wavelengths beyond 2.2 μm, which, coupled with silicon’s large nonlinear index of refraction and its strong waveguide optical confinement, enables efficient nonlinear processes in the mid-IR. By taking advantage of these nonlinear processes and judicious dispersion engineering in silicon waveguides, we have recently demonstrated a handful of silicon mid-IR nonlinear components, including optical parametric amplifiers (OPA), broadband sources, and a wavelength translator. Silicon nanophotonic waveguide’s anomalous dispersion design, providing four-wave-mixing (FWM) phase-matching, has enabled the first demonstration of silicon mid-IR optical parametric amplifier (OPA) with a net off-chip gain exceeding 13 dB. In addition, reduction of propagation losses and balanced second and fourth order waveguide dispersion design led to an OPA with an extremely broadband gain spectrum from 1.9-2.5 μm and >50 dB parametric gain, upon which several novel silicon mid-IR light sources were built, including a mid-IR optical parametric oscillator, and a supercontinuum source. Finally, a mid-IR wavelength translation device, capable of translating signals near 2.4 μm to the telecom-band near 1.6 μm with simultaneous 19 dB gain, was demonstrated.

Recent progress on the development of optofluidic-nanoplasmonic BioNEMS is reviewed in this proceeding. Following a brief summary of the fundamental limitations in current lab-on-chip platforms, optofluidic-nanoplasmonic BioNEMS are discussed in detail and means to overcome mass transport limitations are shown. Finally, nanofluidic approach is extended to a cross fluidic scheme for efficiently isolation of rare circulating tumor cells.

A platform for multiplexed detection of several biomolecular events, simultaneously at the same instant of time, is highly desirable in biomolecular diagnostics. Silicon Photonics is ideally suited for the above requirement. Our biosensor comprises a PC microcavity coupled to a PC waveguide. High sensitivities were achieved by slow light engineering which reduced the radiation loss and increased the stored energy in the photonic crystal microcavity resonance mode. Resonances with high quality factor Q~26,760 coupled with larger optical mode volumes allowed enhanced interaction with the analyte biomolecules which resulted in sensitivities down to 3.35pg/ml. We have multiplexed up to 64 PC microcavities in series and parallel for high throughput multiplexing using silicon integrated photonic components such as multimode interference power splitters combined with advanced group index engineering.

A novel Si-based detector, having a low noise and a high sensitivity, up to a single photon detection, was used for a biosensor application. It is a Silicon photomultiplier (SiPM), a device formed by avalanche diodes operating in Geiger mode, in parallel connections. Arrays with different dimensions were electro-optically characterized (5×5; 10×10 and 20×20 pixels) in order to identify the best geometry to be used in terms of signal-to-noise ratio, for our purposes. The SiPM array was used to study both traditional and innovative fluorophores. CY5 was chosen as “reference” marker. It has an absorption peak at 649 nm and an emission peak at 670 nm. Ru(bpy)₃[Cl]₂ was identified as innovative fluorophore, since it has absorption and emission peaks at 455 and 630 nm, respectively. Measurements were carried out in both functional regimes: continuous and pulsed. Emission spectra in the range 550–750 nm were measured with both traditional photomultipliers tubes (PMT) and SiPM operating at room temperature in continuous mode. More interestingly, fluorophore lifetimes were monitored showing that SiPM can measure lifetimes as short at 1 ns (CY5 lifetime), well below the lowest PMT limit (23 ns). Ru(bpy)₃[Cl]₂ lifetime characterization was performed with both PMT and SiPM (being in the hundreds of ns range), as a function of the solvent and after deposition and drying on glass substrates.

We demonstrate light-weight, conformal, and high-performance flexible sensors fabricated on a large area (>2 cm × 2 cm) silicon nanomembrane transferred onto a flexible substrate. Linear L13 photonic crystal microcavities are designed to provide high quality factors on the flexible platform. Subwavelength grating (SWG) couplers are employed in order to enable efficient light coupling to the device using a single mode fiber. Photonic crystal tapers are implemented at the strip-photonic crystal waveguide interfaces to minimize loss. Preliminary chemical sensing data suggests a sensitivity of 75nm/RIU. Bending tests are further performed in order to demonstrate sensitivityindependent operation.

Here, we present an integrated Lab-on-a-Chip (LOC) system based on silicon microring resonator devices. The system comprises of an electrical tracing-assisted silicon dual-microring sensor which requires a low-cost broadband light source instead of a bulky and expensive tunable laser therefore allows the development of cost-effective point-of-care (POC) diagnostic device. Highly efficient and fast nucleic acids detection with silicon microring device is demonstrated using an isothermal solid-phase amplification/detection (ISAD) technique. The integrated LOC system consists of dualmicroring sensors and microfluidic device for sample processing together with ISAD technique offers true realization of POC device for human disease diagnosis.

This article presents work on a Silicon-On-Insulator (SOI) compact sensing platform based on Micro Ring Resonators (MRRs). In order to enable correction for variations in environmental conditions (temperature, mechanical stress etc), a study has been performed on the performance of uncoated sensing MRRs, and of SU8- and SiO₂-covered reference MRRs. Excellent shielding for both cover materials has been obtained, however, water permeation into the SU8 causes a slow drift in sensor response. We believe that a user-friendly, low-cost and robust way for optical interfacing to MRR sensor chips is required for practical application in Point-Of-Care diagnostics, and that the cost and complexity of optical-electrical read-out systems must decrease. We have taken first steps to realize that vision, by building a prototype free-space optical coupling set-up, which enables non-photonic experts to characterize surface activation processes using MRRs. Moreover, we present our first steps towards on-chip read-out systems.

A chip integrated infrared spectrometer for in situ sensing and spectroscopic identification of VOCs in water probing large absorption cross sections of VOCs in the mid-infrared is desired. Preliminary strip and slot waveguide devices fabricated in silicon-on-sapphire for operation at 3.4μm wavelength experimentally demonstrated propagation loss of 2.1dB/cm for strip waveguides and 11dB/cm for slot waveguide. VOC are extracted from water using PDMS for solid phase micro-extraction and enables absorbance measurements independent from the strong absorbance of water. Absorbance of xylene as a typical VOC is determined on chip from the difference in transmitted intensity in the presence and absence of xylene.

We compared different on-chip silicon waveguide based absorption sensors for the detection of xylene in water in nearinfrared with detection limit down to 1ppb. Strip waveguide, slot waveguide and PC-based chip integrated optical absorption spectroscopy devices are compared in near-infrared. PCW utilizes slow light effect to enhance absorbance and is most sensitive while slot waveguide strengthens light-matter interaction in a narrow low index slot by a factor up to 10 and performs better than a strip waveguide. The results provide a route for enhanced sensitivity via absorption spectroscopy while retaining device miniaturization.

A monolithically integrated silicon-based optical modulator is reviewed with respect to design and high-speed performance. The integrated silicon-based optical modulator consists of nested in-phase/quadrature Mach-Zehnder modulator operated in quadrature phase-shift keying formats. Design and performance of high-speed silicon ribwaveguide phase shifters and high-frequency coplanar-waveguide traveling-wave electrode are presented as key modulator elements which allow high-speed zero-chirp operation of the integrated optical modulator in the quadrature phase-shift keying formats. Transmission performance of the integrated optical modulator in differential quadrature phase-shift keying format is characterized in direct-detection constellation-diagram and bit-error-rate measurements towards 44.6-Gbit/s optical-fiber transmission. High-speed quadrature phase-shift keying operation is characterized in coherent-detection constellation-diagram measurements in C and L bands, and QPSK at bit rates up to 64-Gbit/s is presented. A partial-rib-waveguide polarization rotator, which is essential for 128-Gbit/s small-footprint silicon-based optical modulator for digital coherent communication, is described and high-extinction ratio low-loss polarization conversion over C and L bands is evidenced.

Silicon-based optical modulator devices have experienced dramatic improvements over the last decade with data rates up to 50Gbps for On-Off-Keying (OOK) consuming ultra low power in fJ/bit [1-3]. The ability to fully understand the performances of these plasma dispersion effect-based devices from a simulation standpoint could be further improved especially in the coupling of high-speed electrical and optical effects. Here, we report an accurate methodology to study high-speed eye diagrams from the electrical and optical simulation data of individual silicon modulators. In particular, we demonstrate the capacity of this simulation methodology by applying it to the current state-of-the-art experimental demonstrated silicon optical modulator using OOK at 50Gbps [3].

We present 40 Gbit/s optical modulators based on different types of phase shifters (lateral pn, pipin, and interleaved pn junction phase). Those structures were processed both on 200 and 300mm SOI wafers, available in large-scale microelectronic foundries. Both Ring Resonators (RR) and Mach Zehnder (MZ) modulators were fabricated. As an example, MZ modulator based on 0.95 mm long interleaved pn junction phase shifter delivered a high ER of 7.8 dB at 40 Gbit/s with low optical loss of only 4 dB. Ring modulator was also fabricated and characterized at high-speed, exhibiting 40 Gbit/s.

Fiber optics is well established today due to the high capacity and speed, unrivaled flexibility and quality of service. However, state of the art optical elements and components are hardly scalable in terms of cost and size required to achieve competitive port density and cost per bit. Next-generation high-speed coherent optical communication systems targeting a data rate of 100-Gb/s and beyond goes along with innovations in component and subsystem areas. Consequently, by leveraging the advanced silicon micro and nano-fabrication technologies, significant progress in developing CMOS platform-based silicon photonic devices has been made all over the world. These achievements include the demonstration of high-speed IQ modulators, which are important building blocks in coherent optical communication systems. In this paper, we demonstrate silicon photonic QPSK modulator based on a metal-oxide-semiconductor (MOS) capacitor structure, address different modulator configuration structures and report our progress and research associated with highspeed advanced optical modulation in silicon photonics

GeSi based photodetectors and avalanche photodetectors on silicon photonics platform have been widely studied in the past decade due to its low cost nature and compatibility with CMOS fabrication process. Conventionally, high-quality Ge on Si is obtained by a direct epitaxy growth or by a wafer/die bonding technique, which complicates the possible on-chip integration with CMOS electronics such as transimpedance amplifier, equalizer and limiting amplifier etc. Recently, rapid-melt growth of Ge on insulator emerged as a new method to produce high-quality Ge stripes. In this paper, we present our effort in making waveguide based photodetectors and avalanche photodetectors using Ge rapid-melt growth. First, we demonstrate a high-performance, high-speed GeSi heterojunction photodiode by a self-aligned microbonding technique utilizing surface tension. Such a method is subsequently extended to fabricate a novel butt-coupled, high-speed metal-semiconductor-metal Ge photodetector. At the same time, we study the possibility of operating GeSi avalanche photodetectors at a low bias voltage to be compatible with standard CMOS IC power supply. Based on the theoretical and numerical results, a new type of GeSi avalanche photodetector in three-terminal configuration is proposed and demonstrated, reaching the lowest possible operation bias voltage constrained by Zener tunneling breakdown.

A new detector technology was developed, particularly suitable for low-cost radioactivity monitoring in radwaste storage sites. It consists of a scintillating optical fiber coupled at each end to a silicon photomultiplier (SiPM). The single photon sensitivity of the SiPM, along with the left-right coincidence constraint, allows to achieve a reasonable sensitivity to gamma radiation even though using a thin 1mm diameter plastic scintillating fiber. Simulation results are in perfect agreement with the measured behavior, and several implementations are under way. The possibility of choosing the fiber length and shape makes them very flexible both conceptually and mechanically. Any improvement in the SiPM development technology reflects immediately into an improvement in the detector performance.

Functional Near Infrared Spectroscopy (fNIRS) uses near infrared sources and detectors to measure changes in absorption due to neurovascular dynamics in response to brain activation. The use of Silicon Photomultipliers (SiPMs) in a fNIRS system has been estimated potentially able to increase the spatial resolution. Dedicated SiPM sensors have been designed and fabricated by using an optimized process. Electrical and optical characterizations are presented. The design and implementation of a portable fNIRS embedded system, hosting up to 64 IR-LED sources and 128 SiPM sensors, has been carried out. The system has been based on a scalable architecture whose elementary leaf is a flexible board with 16 SiPMs and 4 couples of LEDs each operating at two wavelengths. An ARM based microcontroller has been joined with a multiplexing interface, able to control power supply for the LEDs and collect data from the SiPMs in a time-sharing fashion and with configurable temporal slots. The system will be validated by using a phantom made by materials of different scattering and absorption indices layered to mimic a human head. A preliminary characterization of the optical properties of the single material composing the phantom has been performed using the SiPM in the diffuse radial reflectance measurement technique. The first obtained results confirm the high sensitivity of such kind of detector in the detection of weak light signal even at large distance between the light source and the detector.

We report on the design and the electro-optical characterization of a novel class of 4H-SiC vertical Schottky UV detectors, based on the pinch-off surface effect and obtained employing Ni2Si interdigitated strips. We have measured, in dark conditions, the forward and reverse I–V characteristics as a function of the temperature and the C–V characteristics. Responsivity measurements of the devices, as a function of the wavelength (in the 200 – 400 nm range), of the package temperature and of the applied reverse bias are reported. We compared devices featured by different strip pitch size, and found that the 10 μm device pitch exhibits the best results, being the best compromise in terms of full depletion and space-strip width ratio.

The Silicon Photomultiplier (SiPM) is a novel pixelated photon detector able to detect single photon arrival with good timing resolution and high gain. In this work we present a complete study of the performances of different SiPMs produced by STMicroelectronics. Their potentialities and limits were identified using experimental measurements and electrical simulations performed both on single pixel and SiPM having up to ∼4000 pixels. SiPM was tested in different experiments such as photoluminescence emission measurement, lifetime measurement of semiconductor materials and light diffusion in highly scattering material in the near infrared spectrum showing its aptitude to replace PMT in those applications.

We report on our Signal-to-Noise Ratio (SNR) measurements carried out, in the continuous wave regime, at different frequencies and at various temperatures, on a novel class of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon p-type substrate. SNR of SiPMs is given by the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square (RMS) deviation of the same current. In our measurements, we have employed a 10 Hz equivalent noise bandwidth, around the lock-in amplifier reference frequency. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current, while background light is not present in our setup. We have found that the SNR is independent from frequency in the evaluated range 1 - 100 kHz. Our measurements highlight a quasi-flat trend of the SiPM SNR up to an overvoltage of about 5 V (with respect to the breakdown voltage of 28.0 V). At higher overvoltages (OV), we have observed a SNR decrease, mainly because of the strong increase of the shot noise. We have also performed a comparison between the SiPM and the PhotoMultiplier Tube (PMT) SNR as a function of the temperature of the SiPM package and at different bias voltages. Our results show the outstanding performance of this novel class of SiPMs even without the need of any cooling system. Indeed, their SNR is only a few dBs below the PMT SNR at room temperature. Furthermore, cooling the SiPM at a package cell temperature of 3 °C, it reaches the PMT SNR values at room temperature despite the SiPM is biased in the range 28.7 – 33.5 V, while the PMT has a bias value up to 950 V.

The keystone to realize a monolithic integrated source on silicon with germanium is to optimize tensile strain and n-doping. In order to realize an integrated compact source, we demonstrate highly strained n-doped germanium microdisks obtained by two approaches using initially compressed silicon nitride (SiN) deposition. In the first approach, the microdisks are fabricated from relaxed Ge. In a second approach, we use tensile-strained Ge grown on a mismatched buffer layer, thus increasing the global strain in the Ge volume and lowering its gradient. A photoluminescence red-shift up to 450 nm is observed, corresponding to more than 1% biaxial strain.

We present flatband, low-loss and low-crosstalk characteristics of Si-nanowire-based 5^th-order coupled resonator optical waveguides (CROW) fabricated by ArF-immersion lithography process on a 300-mm silicon-on-insulator (SOI) wafer. We theoretically specified why phase controllability over Si-nanowire waveguides is prerequisite to attain desired spectral response, discussing spectral degradation by random phase errors during fabrication process. It was experimentally demonstrated that advanced patterning technology based on ArF-immersion lithography process showed extremely low phase errors even for Si-nanowire channel waveguides. As a result, the device exhibited extremely low loss of <0.2dB and low crosstalk of <-40dB without any external phase compensation. Furthermore, fairly good spectral uniformity for all fabricated devices was found both in intra-dies and inter-dies. The center wavelengths for box-like drop channel responses were distributed within 0.4 nm in the same die. This tendency was kept nearly constant for other dies on the 300-mm SOI wafer. In the case of the inter-die distribution where each die is spaced by ~3cm, the deviation of the center wavelengths was as low as ±1.8 nm between the dies separated by up to ~15 cm. The spectral superiority was reconfirmed by measuring 25 Gbps modulation signals launched into the device. Clear eye openings were observed as long as the optical signal wavelengths are stayed within the flat-topped passband of the 5^th-order CROW. We believe these high-precision fabrication technologies based on 300-mm SOI wafer scale ArF-immersion lithography would be promising for several kinds of WDM multiplexers/demultiplexers having much complicated configurations and requiring much finer phase controllability.

We demonstrate evanescent coupling between a photonic crystal (PhC) waveguide and a PhC embedded microring resonator on the silicon-on-insulator platform. The mode converter comprises 6 linearly chirped air holes that adiabatically couple the light between the silicon waveguide mode and the PhC mode. Three-dimensional finitedifference time-domain simulations reveal a coupling bandwidth of >100nm. From our experiment, the optical spectra show a photonic bandgap located below ~1590nm. At the resonances in the slow-light regime, a loaded quality factor as high as ~2500 was measured and a group index of ~16 in the PhC embedded microring resonator was estimated from the non-uniform free spectral ranges.

We investigate the optical signal processing capability of self-coupled optical waveguide (SCOW) resonators. Benefited from the double-notch resonance feature in transmission, a variety of optical pulse shaping functions can be implemented. A Gaussian input pulse can be transformed to a flat-top square-like pulse or in reverse. The separate and merged notches can perform first- and second-order differentiations to the input pulse. Odd-symmetry Hermite-Gaussian (OS-HG) waveforms are generated from the differentiation. Numerical simulation and preliminary experimental results are given.

An evanescently-coupled, hybrid InGaAsP-Si laser operating at 1.55 μm is presented by selective area metal bonding (SAMB). The III-V laser, fabricated on a p-InP substrate with a semi-insulating InP:Fe buried heterostructure (BH), serves to provide optical gain. On the SOI wafer, a 3-μm wide and 500-nm high Si waveguide is formed and the bonding metal (AuSn alloy) is selectively deposited in the regions 6 μm away from the Si waveguide on each side. The InGaAsP gain structure is flip-chip bonded onto the patterned SOI wafer using SAMB method which separates laterally the optical coupling area and the metal bonding area to avoid strong light absorption by the bonding metal. The hybrid laser runs with a maximum single-sided output power of 9 mw at room temperature. The slope efficiency of the hybrid laser is about 0.04 W/A, 4 times that of the laser before bonding which indicates that the light confinement is improved after the bonding. The hybrid laser has achieved 10 °C contimuous wave (CW) lasing. A near-field image of the hybrid laser is studied. As the inject current increases, the light spot markedly shifts down to the Si waveguide and covers the Si waveguide region, which demonstrates that the light generated in the III-V active region is coupled into the Si waveguide. This method allows for different III-V devices to be bonded onto any desired places on a SOI substrate. The simplicity and flexibility of the fabrication process and high yield make the hybrid laser a promising light source.

SOI-based microring resonators (MRRs) have attracted extensive attentions as ultra-compact sensors. Recently, a new structure design combining a ring and a Mach-Zehnder interferometer (MZI) was proposed as sensors for biomedical applications, and as modulators for communications applications. In this design, the MZI uses two identical couplers, where one arm is formed by connecting the access waveguide of the couplers, while the other arm is part of the microring. Such a device may have only one major resonance with a high extinction ratio in a very broad wavelength span (quasi-free spectral range, quasi-FSR), which offers a very large measurement range for sensing applications. 2×2 multimode interference (MMI) couplers are used to couple the microring and the bus waveguides as MMI couplers have broader wavelength responses. We present the first experimental demonstration of the MMI-coupled MZI racetrack microrings for sensing applications. Two types of MMI-coupled MZI racetrack microrings are discussed: one with wire waveguides, and the other using slotted waveguides. For the MZI racetrack microring using wire waveguides, we achieve a quasi-FSR of 34.3 nm near the wavelength of 1520 nm. The corresponding major resonance of the MZI racetrack microring demonstrates a high extinction ratio of ~22.4 dB with a full-width-half-maximum (FWHM) of 1.94 nm, and a quality factor Q of ~800. On the other hand, the quasi-FSR of the MZI racetrack microring with slot waveguides is 23.2 nm near the wavelength of 1540 nm; and the extinction ratio of the major resonance is ~24.5 dB with λ_FWHM=0.82 nm and Q=~1,900. To demonstrate the uses for sensing applications, we measure the resonance shifts corresponding to the concentration change of the ambient aqueous solutions of sucrose. DI water is used as the reference for calibration to avoid any other variations, e.g. temperature change. Experiments show that the sensitivities of the MZI racetrack microring sensors with wire and slot waveguides are 101.7 nm/RIU and 166.7 nm/RIU, respectively.