This PDF file contains the front matter associated with SPIE Proceedings Volume 9367 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We have demonstrated a bidirectional wavelength division (de)multiplexer (WDM) on the silicon-on-insulator platform. An excellent match of the peak transmission wavelength of each channel between the two AMMIs was achieved. This type of device is ideal for integrated optical transceivers where the transmission wavelengths are required to match with the receiving wavelengths. The device also benefits from simple fabrication (as only a single lithography and etching step is required), improved convenience for the transceiver layout design, a reduction in tuning power and circuitry, and efficient use of layout space.

We investigate the improvement of an insertion loss in silicon arrayed waveguide grating (AWG), by analyzing the multimode generation due to the field-mismatching effect. 8 channel silicon AWGs on a 6” SOI wafer are fabricated with an ultra-shallow etching structure and various aperture size of arrayed WGs. Our experimental results demonstrate the improved insertion loss and crosstalk characteristics. The fabricated AWG shows an insertion loss less than 1 dB with a crosstalk of -23.2 ~ -25.6 dB, exhibiting ~2.5 dB improvement of insertion loss and ~5 dB improvement of crosstalk, compared to our reported result.

Microring resonators are important elements in a wide variety of optical systems, ranging from optical switches and tunable filterbanks to optical sensors. In these structures, the resonant frequencies are normally controlled by tuning the effective index of refraction. In optical switches and filters, this has traditionally been achieved through electro-optic or thermo-optic effects. In sensors, the effective refractive index is changed by the presence of the measurand. Adding a mechanical degree of freedom to these optical systems allows additional evanescent frequency tuning. In particular, the presence of a cantilever in the near-field of the optical mode can tune the effective refractive index. A specific cantilever displacement can therefore induce a desired resonant frequency shift. Alternatively, a measured shift in the resonant frequency can be associated with a cantilever displacement, and be used for pressure or acceleration sensing. In this paper, we explore a geometry that can be used for controlling the resonant frequency of a microring resonator through evanescent field perturbation, using a cantilever defined in the same silicon layer as the optical waveguides, in a silicon-on-insulator platform. The effects of the lateral gap size between the optical waveguide and the cantilever, and the cantilever vertical displacement, on both the resonant frequency and quality factor of the resonator, are evaluated through finite-difference timedomain computations for wavelengths centered at 1550 nm. The presence of the cantilever in the near-field of the optical mode changes the effective refractive index, resulting in frequency tuning, but also lowers the quality factor due to additional coupling into the membrane.

We demonstrate non-invasive light observation in silicon photonics with a ContactLess Integrated Photonics Probe (CLIPP), neither introducing appreciable perturbations of the optical field nor requiring photon tapping from the waveguide. Light monitoring with sensitivity down to -30 dBm, across 40 dB dynamic range, in few tens of microseconds, on TE and TM polarizations, and on monomode and multimode waveguides is achieved. Moreover, we show wavelength tuning, locking and swapping of high-Q resonators assisted by the CLIPP that is integrated inside the microring. CLIPP readout and feedback control is managed by a CMOS microelectronic circuit bridged to the silicon photonic chip.

We propose and demonstrate a unique suspended slot-waveguide structure supported by a thin slab to realize high-quality air-clad silicon slotted microring resonators (SMRs) on the silicon-on-insulator platform, based on a fabrication process consisting of two-step electron beam lithography and inductively-coupled-plasma reactive-ion- etching. Our SMRs can achieve an intrinsic optical quality factor (Q) above 10⁵ operating at the telecom band, which is the highest value for silicon SMRs reported to date. The demonstrated high-quality air-clad silicon SMRs enable great potential for broad applications in biosensing, nonlinear photonics, and cavity optomechanics.

Long and yet compact spiral waveguides based on micron-scale silicon strip waveguides has been enabled very recently by the introduction of the Euler bends. By ensuring effective broadband single mode operation of otherwise highly multimodal waveguides, these bends can have very low losses (<0.01 dB/90°) even with effective radii of a few microns. Together with the low propagation losses (< 0.15 dB/cm) of micron-scale strip waveguides, these bends enable centimeter-long delay lines with negligible losses and very small foot-print (< 1 mm2). In particular, interferometers delayed by ≈ 1 cm long spirals on one of the two arms have been fabricated on SOI wafers with both 3 um- and 4 umthick silicon layer, based on the well assessed process developed by VTT. The full devices have footprint smaller than 1.5 mm², and they have been measured to have extinction ratios < 15 dB (reaching up to 21 dB) and about 3 dB excess losses. Functional characterization of the delayed interferometers at about 10 Gbps through demodulation of pseudorandom Differential Phase Shift Keying signals led to clearly opened eye diagrams with Q factor of 8.6 and bit error rates lower than 10^-15.

Total internal reflection (TIR) mirrors represent an ultra-compact and flexible method to turn light in a photonic integrated circuit (PIC). These can also have very broadband and polarisation independent operation. This paper presents results from 90 degree strip waveguide turning mirrors with novel geometry on a 3 μm SOI waveguide platform. The new TIR mirrors have record-low insertion loss of 0.08 dB/mirror. They are compared with previous designs that have demonstrated insertion losses down to 0.15 dB/mirror. The test structures consisted of up to 96 consecutive mirrors and were fabricated in a multi-project wafer run. The multi-moded test devices only propagate light in the fundamental mode. The mirrors can be used in single-mode PICs that combine low losses, small polarisation dependency, wide bandwidth and small footprint.

Latest computational and experimental studies on high-speed monolithic silicon-based Mach-Zehnder optical modulators are studied in the light of photonic integrated circuits for digital coherent communication at a bit rate as fast as 128 Gb/s per wavelength channel. Lateral PN-junction rib-waveguide phase shifters are elaborated with experimental characteristics of DC phase shifter response in comparison with computational characteristics. High-speed response in refractive-index dynamics including electron and hole transport in the PN junction is simulated to study speed limit of the phase shifters. The performance in quadrature phase-shift keying signal generation is characterized in experimental and computational constellation diagrams. Silicon waveguides for polarization-division multiplexing are designed in common design rules with the rib-waveguide phase shifters. Long-haul transmission in polarization-multiplexed quadrature phase-shift keying in 1000-km single-mode fiber link is confirmed with a monolithic silicon Mach-Zehnder modulator assembled with modulator drivers in a ceramic-based metal package.

In this paper, we communicate on the design, fabrication, and testing of optical modulators for Silicon-based photonic integrated circuits (Si-PICs) in the O-band (1.31 μm), targeting the 100GBASE-LR4 norm (4 wavelengths at 25 Gbit/s). The modulators have been conceived to be later coupled with hybrid-III-V/Si lasers as well as echelle grating multiplexer, to create a hetero-integrated optical transmitter on a silicon-on-insulator (SOI) platform. The devices are based on a Mach-Zehnder Interferometer (MZI) architecture, where a p-n junction is implanted to provide optical modulation through carrier depletion. A detailed study focusing on the best doping scheme for the junction, aimed at optimizing the overall transmitter performance and power-efficiency is presented. In detail, the trade-off between low optical losses and high modulation efficiency is tackled, with a targeted CMOS-compatible voltage drive of 2.5 V. Process simulations of the junction are realized for the doping profile optimization. Modulators of different lengths are also investigated to study the compromise between extinction ratio, insertion losses and bandwidth. Furthermore, coplanar-strip (SGS) travelling-wave electrodes are designed to maximize the bandwidth, to reach the targeted bit rate of 25 Gbit/s. Measurements show modulation efficiencies up to 19 °/mm (or 2.4 V.cm) for a 2.5 V input voltage, with doping-related losses below 1 dB/mm, in line with theoretical estimates, and well-suited to enhance the Si-PIC transmission and power-efficiency. Finally, an electro-optical (EO) bandwidth at 1.25 V bias is measured above 28 GHz.

The bandgap tuning of sub-micron wide Germanium (Ge) waveguides by selective epitaxial growth (SEG) method with a SiO2 mask has been demonstrated. SEG-grown Ge waveguides on Si substrate are designed to show various compressive strain depending on the growth parameters, such as the width and thickness of Ge waveguides and SiO₂ masks. X-Ray Diffraction (XRD) verifies that -0.25% (compressive) strain is induced in a 0.6μm-wide Ge waveguide with SiO₂ mask of 20μm width and 1.0μm thickness. The strained Ge waveguide should show the absorption edge wavelength of ~1.55μm. Furthermore, compressive strain can be tuned between -0.03% and -0.25% by changing the lateral structure of the device, which correspond to the absorption edge wavelength of 1.548~1.568μm. It means that only one epitaxial growth with specific lateral design of the electro-absorption modulator can modulate light in the wavelength range.

Modulation format is a key determinant to the performance of an optical communication network. In this work, we study a silicon phase shifter arranged around rib waveguide topologies and explore its potential to be applied in quadraturephase- shift-keying (QPSK) optical modulators. Optical QPSK is implemented with four silicon phase shifters embedded in a nested Mach-Zehnder waveguide. Modulated QPSK signal is simulated by calculating the interference between light beams pass through each phase shifter. The constellation diagram of modulated QPSK signal is calculated after coherent demodulation.

We present SiCloud (Silicon Photonics Cloud), the first free, instructional web-based research and education tool for silicon photonics. SiCloud’s vision is to provide a host of instructional and research web-based tools. Such interactive learning tools enhance traditional teaching methods by extending access to a very large audience, resulting in very high impact. Interactive tools engage the brain in a way different from merely reading, and so enhance and reinforce the learning experience. Understanding silicon photonics is challenging as the topic involves a wide range of disciplines, including material science, semiconductor physics, electronics and waveguide optics. This web-based calculator is an interactive analysis tool for optical properties of silicon and related material (SiO2, Si3N4, Al2O3, etc.). It is designed to be a one stop resource for students, researchers and design engineers. The first and most basic aspect of Silicon Photonics is the Material Parameters, which provides the foundation for the Device, Sub-System and System levels. SiCloud includes the common dielectrics and semiconductors for waveguide core, cladding, and photodetection, as well as metals for electrical contacts. SiCloud is a work in progress and its capability is being expanded. SiCloud is being developed at UCLA with funding from the National Science Foundation’s Center for Integrated Access Networks (CIAN) Engineering Research Center.

Slow light effect based rib silicon waveguide structures are studied in this paper to enhance modulation efficiency of an optoelectronic carrier plasma dispersion effect based phase modulator. Center frequency to achieve desired slow down factor and band width limitations of the structures are investigated through finite element method simulations. Optical modulation efficiency is modeled and the effects of doping, bias voltage and slow light on its performance are studied.

We report the silicon photonic receivers based on the hybrid-integrated vertical-illumination-type germanium-on-silicon photodetector and CMOS amplifier circuit, for optical interconnects. The high-speed vertical-illumination-type Ge-on-Si photodetector is defined on a bulk-silicon wafer, and the CMOS amplifier chip was designed with 65nm ground rule. The PCB-packaged 4 channel 25 Gb/s photoreceiver exhibits a resposivity of 0.68A/W. The sensitivity measured at a BER of 10⁻¹² is -8.3 dBm and -2.4dBm for 25Gb/s and 32Gb/s, respectively. The energy efficiency is 2.19 pJ/bit at 25 Gb/s. The single-channel butterfly-packaged photoreceiver exhibits the sensitivity of -11dBm for 25 Gb/s at a BER of 10^−12. The energy efficiency is 2.67 pJ/bit at 25 Gb/s.

We provide an alternative architecture for the next generation datacenters by employing electronic and photonic switching cores. The capacity of electronic packet switching (EPS) cores is not enough for the bandwidth requirements of next generation datacenters. On the other hand, it is prohibitively costly to build pure photonic packet switching (OPS) core which is capable of switching native Ethernet frames in nanoseconds. We propose a low-cost hybrid OPS/EPS platform which significantly increases the switching capacity of datacenters for all traffic patterns while using the existing EPS cores. Our proposed architecture is a fat-tree hierarchy consisting of servers, top-of-racks (TOR), aggregation switches, and core switches. The aggregation switches are interconnected to the core hybrid OPS/EPS switch. Since the traffic inside datacenters is typically bimodal, the hybrid switch core becomes feasible by switching short and long packets using EPS and OPS cores, respectively. In order to prepare long packets for photonic switching, they undergo packet contention resolution, compression, and bitwise scrambling. Afterwards, a photonic destination label is added to the long packets, and they are sent out through an optical transmitter. For compressing the long packets, the clock rate is raised on the output of the physical layer. Packet compression increases inter-packet gap to insert the photonic label. Also, it provides more time for photonic switch connection set-up and receiver synchronization at the destination aggregation switch. We developed a test bed for our architecture and used it to transmit real-time traffic. Our experiments show successful transmission of all packets through OPS.

We review recent progress of an effort led by the Stojanović (UC Berkeley), Ram (MIT) and Popović (CU Boulder) research groups to enable the design of photonic devices, and complete on-chip electro-optic systems and interfaces, directly in standard microelectronics CMOS processes in a microprocessor foundry, with no in-foundry process modifications. This approach allows tight and large-scale monolithic integration of silicon photonics with state-of-the-art (sub-100nm-node) microelectronics, here a 45nm SOI CMOS process. It enables natural scale-up to manufacturing, and rapid advances in device design due to process repeatability. The initial driver application was addressing the processor-to-memory communication energy bottleneck. Device results include 5Gbps modulators based on an interleaved junction that take advantage of the high resolution of the sub-100nm CMOS process. We demonstrate operation at 5fJ/bit with 1.5dB insertion loss and 8dB extinction ratio. We also demonstrate the first infrared detectors in a zero-change CMOS process, using absorption in transistor source/drain SiGe stressors. Subsystems described include the first monolithically integrated electronic-photonic transmitter on chip (modulator+driver) with 20-70fJ/bit wall plug energy/bit (2-3.5Gbps), to our knowledge the lowest transmitter energy demonstrated to date. We also demonstrate native-process infrared receivers at 220fJ/bit (5Gbps). These are encouraging signs for the prospects of monolithic electronics-photonics integration. Beyond processor-to-memory interconnects, our approach to photonics as a “More-than- Moore” technology inside advanced CMOS promises to enable VLSI electronic-photonic chip platforms tailored to a vast array of emerging applications, from optical and acoustic sensing, high-speed signal processing, RF and optical metrology and clocks, through to analog computation and quantum technology.

Here, I review the development of a polysilicon photonic platform that is optimized for integration with electronics fabricated on bulk silicon wafers. This platform enables large-scale monolithic integration of silicon photonics with microelectronics. A single-polysilicon deposition and lithography mask were used to simultaneously define the transistor gate, the low-loss waveguides, the depletion modulators, and the photodetectors. Several approaches to reduce optical scattering and mitigate defect state absorption are presented. Waveguide propagation loss as low as 3 dB/cm could be realized in front-end polysilicon with an end-of-line loss as low as 10 dB/cm at 1280nm. The defect state density could be enhanced to enable all-silicon, infrared photodetectors. The resulting microring resonant detectors exhibit over 20% quantum efficiency with 9.7 GHz bandwidth over a wide range of wavelengths. A complete photonic link has been demonstrated at 5 Gbps that transfers digital information from one bulk CMOS photonics chip to another.

Silicon photonics provides the ability to construct complex photonic circuits that act on the amplitude and phase of multiple optical channels. Many applications of silicon photonics depend on maintenance of optical coherence among the various waveguides and structures on the chip. Other applications can depend on the modal structures of the waveguides. All these application require the ability to characterize the amplitude and phase of individual optical channels. Fourier imaging with high numerical aperture microscope objectives has been used to image the intensity of individual channels of photonic structures in both real and Fourier space. In other work, holographic imaging of multimode fibers has allowed modal decomposition. In this work we use interferometric microscopy to image the amplitude and phase of a variety of silicon photonic structures. These include a multimode interference splitter and a multimode waveguide under various excitation conditions.

We design and discuss an impedance matching solution for a hybrid silicon mode-locked laser diode (MLLD) to improve peak optical power coming from the device. In order to develop an impedance matching solution, a thorough measurement and analysis of the MLLD as a function of bias on each of the laser segments was carried out. A passive component impedance matching network was designed at the operating frequency of 20 GHz to optimize RF power delivery to the laser. The hybrid silicon laser was packaged together in a module including the impedance matching circuit. The impedance matching design resulted in a 6 dB (electrical) improvement in the detected modulation spectrum power, as well as approximately a 10 dB phase noise improvement, from the MLLD. Also, looking ahead to possible future work, we discuss a Step Recovery Diode (SRD) driven impulse generator, which wave-shapes the RF drive to achieve efficient injection. This novel technique addresses the time varying impedance of the absorber as the optical pulse passes through it, to provide optimum optical pulse shaping.

In this paper we present SOI, suspended Si, and Ge-on-Si photonic platforms and devices for the mid-infrared. We demonstrate low loss strip and slot waveguides in SOI and show efficient strip-slot couplers. A Vernier configuration based on racetrack resonators in SOI has been also investigated. Mid-infrared detection using defect engineered silicon waveguides is reported at the wavelength of 2-2.5 μm. In order to extend transparency of Si waveguides, the bottom oxide cladding needs to be removed. We report a novel suspended Si design based on subwavelength structures that is more robust than previously reported suspended designs. We have fabricated record low loss Ge-on-Si waveguides, as well as several other passive devices in this platform. All optical modulation in Ge is also analyzed.

Ge_1-xSn_x/Ge thin films and Ge/Ge_1-xSn_x/Ge n-i-p double heterostructure (DHS) have been grown using commercially available reduced pressure chemical vapor deposition (RPCVD) reactor. The Sn compositional material and optical characteristics have been investigated. A direct bandgap GeSn material has been identified with Sn composition of 10%. The GeSn DHS samples were fabricated into LED devices. Room temperature electroluminescence spectra were studied. A maximum emission power of 28mW was obtained with 10% Sn LED under the injection current density of 800 A/cm².

Si based Ge1-xSnx photoconductors, with Sn incorporation of 0.9, 3.2, and 7%, were fabricated using a CMOS-compatible process. Temperature dependent study was conducted from 300 to 77 K. The first generation device (standard photoconductor, PD) shows long wavelength cut-off beyond 2.1 μm for 7%-Sn devices at room temperature. The peak responsivity and D* of the 7% Sn device at 1.55 μm were obtained at 77K as 0.08 A/W and 1×10⁹ cm*Hz^1/2*W^-1, respectively. Improved responsivity and specific detectivity (D*) were observed on second generation devices by a newly designed electrode structure (photoconductor with interdigitated electrodes, IEPD). The enhancement factor of responsivity was up to 15 at 77 K.

We experimentally demonstrate transmission characteristics of a W1 photonic crystal waveguide in silicon on sapphire at mid infrared wavelength of 3.43 m. Devices are studied as a function of lattice constant to tune the photonic stop band across the single wavelength of the source laser. The shift in the transmission profile as a function of temperature and refractive index is experimentally demonstrated. In addition to zero transmission in the stop gap, high transmission was observe for the characteristic of the waveguiding behavior of photonic crystal line defect modes.

Silicon photonics has become in the past years an important technology adopted by a growing number of industrial players to develop their next generation optical transceivers. However most of the technology platforms established in CMOS fabrication lines are kept captive or open to only a restricted number of customers. In order to make silicon photonics accessible to a large number of players several initiatives exist around the world to develop open platforms. In this paper we will present imec’s silicon photonics active platform accessible through multi-project wafer runs.

Silicon-on-sapphire devices are attractive for the mid-infrared optical applications up to 5 microns due to the low loss of both silicon and sapphire in this wavelength band. Designing efficient couplers for silicon-on-sapphire devices presents a challenge due to a highly confined mode in silicon and large values of refractive index of both silicon and sapphire. Here, we present design, fabrication, and measurements of a mode-converting coupler for silicon-on-sapphire waveguides. We utilize a mode converter layout that consists of a large waveguide that is overlays a silicon inverse tapered waveguide. While this geometry was previously utilized for silicon-on-oxide devices, the novelty is in using materials that are compatible with the silicon-on-sapphire platform. In the current coupler the overlaying waveguide is made of silicon nitride. Silicon nitride is the material of choice because of the large index of refraction and low absorption from near-infrared to mid-infrared. The couplers were fabricated using a 0.25 micron silicon-on-sapphire process. The measured coupling loss from tapered lensed silica fibers to the silicon was 4.8dB/coupler. We will describe some challenges in fabrication process and discuss ways to overcome them.

We have designed and for the first time experimentally verified a topology optimized mode (de)multiplexer, which demultiplexes the fundamental and the first order mode of a double mode photonic wire to two separate single mode waveguides (and multiplexes vice versa). The device has a footprint of ~4.4 μm x ~2.8 μm and was fabricated for different design resolutions and design threshold values to verify the robustness of the structure to fabrication tolerances. The multiplexing functionality was confirmed by recording mode profiles using an infrared camera and vertical grating couplers. All structures were experimentally found to maintain functionality throughout a 100 nm wavelength range limited by available laser sources and insertion losses were generally lower than 1.3 dB. The cross talk was around -12 dB and the extinction ratio was measured to be better than 8 dB.

For a multi mode fiber optical link, a high speed silicon photonics receiver based on a highly alignment tolerant vertically illuminated germanium photodiode was developed. The germanium photodiode has 20 GHz bandwidth and responsivity of 0.5 A/W with highly alignment tolerance for passive optical assembly. The receiver achieves 25 Gbps error free operation after 100 m multi mode fiber transmission.

We report our recent progress on reconfigurable optical true time delay lines (RTTDL) and optical switches. The RTTDL is composed of 8 stages of MZIs connected by 7 waveguide pairs with an incremental length difference. Variable optical attenuators are inserted in the delay waveguides to suppress crosstalk caused by the residual signals from noise paths. Transmission of a 25 Gbps PRBS signal confirms the signal fidelity after a maximum of 1.27 ns delay. The optical switch is based on a Benes architecture with Mach-Zehnder interferometers (MZI) as the switching elements. Both p-i-n diodes and silicon resistive micro-heaters are integrated in the MZI arms for electrical tuning and phase correction, respectively. The measured on-chip insertion loss of the 4×4 switch is < 8 dB. Transmission of a 50 Gb/s quadrature phase shift keying (QPSK) optical signal verifies its switching functionality.

Recently, grating couplers (GCs) have been extensively reported as a promising device for optical coupling between Siwire waveguides and standard single mode optical fibers. In this paper, we report the feasibility study of Si-wire type GCs fabricated by the 248-nm KrF lithography process on a 200-mm silicon-on-insulator (SOI) wafer with a 220-nmthick Si layer. We report a 1D-GC for a transmitter that operates only with TE mode and a 2D-GC for a receiver that splits arbitrary polarization from a single mode fiber operating at a wavelength of 1550 nm. We investigated the fundamental feasibility with the simple design. Especially, the wafer uniformity in inter-dies of 1D and 2D-GC is mainly examined on a 200-mm SOI wafer. Additionally, we experimentally clarify the fundamental characteristics of the 1DGC from the viewpoint of an insertion loss and a 1-dB fiber misalignment tolerance. As for the 2D-GC, in addition to the same aspects with the 1D-GC, an optical crosstalk and a polarization dependent loss will also be discussed around 1550 nm wavelength. Also, the center wavelength against a grating period of the 1D-GC and a circular hole diameter of the 2D-GC will be characterized.

In view of high volume manufacturing of silicon based photonic-integrated-circuits (Si-PICs), CMOS compatible low-cost fabrication processes as well as simplified packaging methods are imperatively needed. Silicon-onInsulator (SOI) based grating couplers (GCs) have attracted attention as the key components for providing optical interfaces to Si-PICs due their fabrication simplicity compared to the edge coupling alternatives. GCs based on perfectly vertical coupling scheme become essential by introducing substantial savings in the packaging cost as no angular configurations are required but at the expense of high coupling efficiency values due to the second order diffraction. In this context, research efforts concentrated on designing GCs with minimized back reflection into the waveguide yet employing more than one etching steps or rather complex fabrication processes. Herein, we propose a fully etched CMOS compatible non-uniform one-dimensional (1D) GC for perfectly vertical coupling with low back reflected optical power by means of numerical simulations. A particle-swarm-optimization (PSO) algorithm was deployed in conjunction with a commercially available 2D finite-difference-time-domain (FDTD) method to maximize the coupling efficiency to a SMF fiber for TM polarization. The design parameters were restricted to the period length and the filling factor while the minimum feature size was 80 nm. A peak coupling loss of 4.4 dB at 1553 nm was achieved with a 1-dB bandwidth of 47 nm and a back reflection of -20 dB. The coupling tolerance to fabrication errors was also investigated.

We present a scheme for on-chip optical mode conversion in a hybrid photonic-phononic waveguide. Both propagating optical and acoustic wave can be tightly confined in the hybrid waveguide, and the acoustooptical interaction can be enhanced to realize optical mode conversion within a chip-scale size. The theoretical model of the acousto-optic interaction is established to explain the mode conversion. The numerical simulation results indicate that the high efficient mode conversion can be achieved by adjusting the intensity of the acoustic wave. We also show that the mode conversion bandwidth can be dramatically broadened to 13 THz by adjusting the frequency of the acoustic wave to match phase condition of the acousto-optic interaction. This mode converter on-chip is promising in order to increase the capacity of silicon data busses for on-chip optical interconnections.

1x1 optical resonators have been designed based on multi-mode interference (MMI) splitters of different splitting ratios (85:25 and 73:27) and different types of back-reflectors as feedback mechanism. They are basically 2x2 MMIs of uneven splitting ratios with one of the ports from both sides ending in a reflector. The chosen reflectors include metal-dielectric mirrors, waveguide loops and MMI reflectors. The remaining two ports play the role of input and thru port respectively. The resonant wavelengths are reflected back in the input port, hence acting also as output port in reflection. The devices have been fabricated on SOI wafers with a 3 μm-thick silicon layer. In all cases, the quality factors of the resonances of a given resonator have been found to significantly change form peak to peak. This can be attributed to wavelength dependent losses in the feedback mechanisms, that is wavelength dependent reflectivity of the back-reflectors. Through a suitable transfer matrix model, we have found that best performing devices correspond to reflectivity as high as 92% for the metal/dielectric mirrors and 88% for the MMI reflectors, corresponding to a resonator finesse of 13.1 and 9.9 respectively. The free spectral ranges of the resonators vary from about 3 nm to about 1 nm, depending on the cavity length, which is constrained by the lengths of both the MMIs and the reflectors. When suitably combined with gain elements, the proposed resonators are promising candidates as fabrication tolerant wavelength selective reflectors for external cavity lasers.

Integrated laser sources compatible with microelectronics represent currently one of the main challenges for silicon photonics. Using the Smart Cut^TM technology, we have fabricated for the first time 200 mm optical Germanium-On-Insulator (GeOI) substrates which consist of a thick layer of germanium (typically greater than 500 nm) on top of a thick buried oxide layer (around 1 µm). From this, we fabricated suspended microbridges with efficient Bragg mirror cavities. The high crystalline quality of the Ge layer should help to avoid mechanical failure when fabricating suspended membranes with amounts of tensile strain high enough to transform Ge into a direct bandgap material. Optical GeOI process feasibility has successfully been demonstrated, opening the way to waferscale fabrication of new light emitting devices based on highly-tensely strained (thanks to suspended membranes) and/or doped germanium.

In the context of 3D-integrated circuit (3DIC) integration of photonic and electronic components on vertical stacks covering different domains (digital, analog, RF, optical and MEMS), the control and minimization of adverse thermal effects on the behavior of the different parts of the microsystem is a major concern. Solutions based on passive athermal design are good candidates for enabling operation of optical components over electronic ICs with variable temporal and spatial thermal load while at the same time, minimizing energy loss on thermal biasing resistive loads. In this work, an improved athermal design method and the corresponding validating fabricated prototype are presented with the aim of extending the spectral athermal operating range of a Mach-Zehnder interferometer (MZI) over a wide thermal range with minimal temperature sensitivity. The proposed approach is demonstrated with a CMOS compatible silicon-on-insulator process flow fabrication run. The fabricated MZIs have a temperature sensitivity of around 20 pm/K over a spectral range larger than 60 nm for operating temperatures in the range of 20°C to 60°C. These devices are suitable for future optical and electronic 3D IC integration.

In this paper, we present experimental and theoretical studies on the bending induced resonance shift of a photonic crystal cavity. The photonic crystal devices are fabricated on a 2cm x 2cm large-area single crystal SiNM which is transferred defect-freely onto a Kapton substrate with an SU-8 bottom cladding. Photonic crystal tapers are implemented at the strip-photonic crystal waveguide interfaces, which lowers the coupling loss and enables operation closer to the band edge. Subwavelength grating (SWG) couplers are employed at the input and output of the device in order to enable device characterization. The device is mounted on the two jaws of a caliper and it can be buckled up and down through sliding one of the jaws. The bending radius at the top of the curvature can be estimated with the length of the specimen and the distance between the two jaws. A minimum bending radius of 5 mm is achieved. Finite element method (FEM) is used to simulate the deformation and the strain of the nanomembrane. The results are used as the input of finite difference time-domain (FDTD) simulation. The analysis shows that the strain sensitivities are 0.673 pm/με, 0.656 pm/με, 0.588 pm/με, and 0.591 pm/με, for longitudinal face-out, longitudinal face-in, transverse face-out, and transverse face-in bending, respectively.

A compact silicon arrayed waveguide grating router (AWGR) for optical interconnects is experimentally demonstrated. The design, fabrication and characterization of this 4×4 AWGR with a 1250 GHz channel spacing and a 5 THz free spectral range are discussed. The loss of the AWGR varies from 2.5 dB to 5.5 dB and the crosstalk is better than -18 dB. The functionality of the AWG as a router and its good rotation property are also presented. This device has a compact footprint of 0.46×0.26mm2.

In this work we show that integrated Hybrid Silicon-PDMS Antiresonant Reflecting Optical Waveguide (H-ARROW) can be applied for the realization of optofluidic devices. H-ARROW is constituted by the optofluidic channel of a conventional ARROW, sealed with a thin PDMS layer. This layout simplifies the integration of microfluidic parts to manipulate liquid samples, which can be easily fabricated in the PDMS layer. Hybrid ARROWs have been fabricated and used in order to design complex devices like an integrated hybrid liquid core optofluidic ring resonator (h-LCORR) and a hybrid optofluidic platform for fluorescence measurements.

Silicon Carbide (SiC) provides the unique property of near-perfect visible blindness and very high signal-to-noise ratio due to the high quantum efficiency and low dark current even at high temperature. These features make SiC the best available material for the manufacturing of visible blind semiconductor ultraviolet (UV) light detectors. Thanks to their properties, SiC detectors have been extensively used in fact for flame detection monitoring, UV sterilization and astronomy. Here we report on the electrical and optical performance of patterned thin metal film NiSi/4H-SiC vertical Schottky photodiodes with different semiconductor exposed area suitably designed for UV light monitoring.

Monolithically integrated Ge lasers on Si have long been one of the biggest challenges for electronic and photonic integration on Si Complementary Metal Oxide Semiconductor (CMOS) platform. The “last one mile” is to reduce the threshold current of the electrically pumped Ge-on-Si laser. We have studied the growth of heavily doped n type (n⁺) Ge and analyzed its photoluminescence (PL) characteristics of Ge with a Si cap and thermal oxide layers. It is found that the PL intensity of n⁺ Ge was significantly reduced by the cap and etching off the cap showed a ~100% recovery to the intensity of n⁺ Ge without the cap. Thermally oxidized n⁺ Ge, on the other hand, showed a ~50% increase in the PL intensity of uncapped n⁺ Ge. These finding indicated that capping of n⁺ Ge introduces non-radiative recombination centers due to defects (dislocations) to reduce the PL intensity, while oxidation passivates surface defects remained even on uncapped n⁺ Ge. Considering these, we have designed and fabricated an electrically pumped n⁺ Ge light emitting diode with no Si cap layer but oxidation. A broad luminescence of Ge at 1500-1700 nm has been demonstrated but yet lasing not observed.

Photo-voltaic (PV) and conventional power (CP) stations of 500MW power are compared. An evaluation between CP and PV stations is carried out according to physical properties, economic indicators and electrical characteristics. It is shown, that for many parameters PV plant efficiencies exceed those of CP ones. An impact of introducing large PV stations is also discussed.

We report the fabrication and characterization of GeSn waveguide structures on Si substrates grown by molecular beam epitaxy for efficient light-detection and emission. For photodetectors, GeSn waveguide structures exhibit a higher optical response compared to a reference Ge device as revealed by the photocurrent experiments. For light-emission, room-temperature photoluminescence experiments show a redshifted emission wavelength for the GeSn samples compared to the Ge reference sample due to the Sn incorporation. Besides, we observe ripple characteristics in the amplified spontaneous emission spectrum of the GeSn waveguide structure, which are attributed to the waveguide modes. Those results suggest that GeSn waveguide structures are promising for high-performance Si-based lightdetectors and emitters integrable with Si electronics.

We analyzed Ge- and GeSn/Ge multiple quantum well (MQW) light emitting diodes (LEDs). The structures were grown by molecular beam epitaxy (MBE) on Si. In the Ge LEDs the active layer was 300 nm thick. Sb doping was ranging from 1×10¹⁸ to 1×10²⁰ cm^-3. An unintentionally doped Ge-layer served as reference. The LEDs with the MQWs consist of ten alternating GeSn/Ge-layers. The Ge-layers were 10 nm thick and the GeSn-layers were grown with 6 % Sn and thicknesses between 6 and 12 nm. The top contact of all LEDs was identical. Accordingly, the light extraction is comparable. The electroluminescence (EL) analysis was performed under forward bias at different currents. Sample temperatures between <300 K and 80 K were studied. For the reference LED the direct transition at 0.8 eV dominates. With increasing current the peak is slightly redshifted due to Joule heating. Sb doping of the active Ge-layer affects the intensity and at 3×10¹⁹ cm^-3 the strongest emission appears. It is ~4 times higher as compared to the reference. Moreover a redshift of the peak position is caused by bandgap narrowing. The LEDs with undoped GeSn/Ge-MQWs as active layer show a very broad luminescence band with a peak around 0.65 eV, pointing to a dominance of the GeSn-layers. The light emission intensity is at least 17 times stronger as compared to the reference Ge-LED. Due to incorporation of Sn in the MQWs the active layer should approach to a direct semiconductor. In indirect Si and Ge we observed an increase of intensity with increasing temperature, whereas the intensity of GeSn/Ge-MQWs was much less affected. But a deconvolution of the spectra revealed that the energy of indirect transition in the wells is still below the one of the direct transition.

We demonstrate Silicon-only near-infrared (NIR) photodetectors (sensitive up to 2000 nm) that meet large-scale ultralow-cost fabrication requirements. For the detection of infrared photons, we use metal nanoislands that form Schottky contact with Silicon. NIR photons excite plasmon resonances at metal nanoislands and plasmons decay into highly energetic charge carriers (hot electrons). These hot electrons get injected into Silicon (internal photoemission), resulting in photocurrent. Several groups have studied plasmonic nanoantennas using high resolution lithography techniques. In this work, we make use of randomly formed nanoislands for broad-band photoresponse at NIR wavelengths. We observe photoresponse up to 2000 nm wavelength with low dark current density about 50 pA/µm² . The devices exhibit photoresponsivity values as high as 2 mA/W and 600 µA/W at 1.3 µm and 1.55 µm wavelengths, respectively. Thin metal layer was deposited on low-doped n-type Silicon wafer. Rapid thermal annealing results in surface reconstruction of the metal layer into nanoislands. Annealing conditions control the average size of the nanoislands and photoresponse of the devices. An Al-doped Zinc Oxide (AZO) layer was deposited on the nanoislands using thermal atomic layer deposition (ALD) technique to acts as a transparent conductive oxide (TCO) and patterned using photolithography. AZO film creates electrical connection between the nanoislands and also makes a heterojunction to Silicon. Simple and scalable fabrication on Si substrates without the need for any sub-micron lithography or high temperature epitaxy process make these devices good candidates for ultra-low-cost broad-band NIR imaging and spectroscopy applications.

Slot waveguide based ring resonators filled with atomic layer deposited (ALD) aluminum oxide (Al₂O₃) were fabricated and characterized. Our results demonstrate that ALD can be used to create slot waveguide ring resonators with relatively high Q-factors, which opens new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

A simple analytical model is developed to estimate the power loss and time delay in photonic integrated circuits fabricated using SOI standard wafers. This model is simple and can be utilized in physical verification of the circuit layout to verify its feasibility for fabrication using certain foundry specifications. This model allows for providing new design rules for the layout physical verification process in any electronic design automation (EDA) tool. The model is accurate and compared with finite element based full wave electromagnetic EM solver. The model is closed form and circumvents the need to utilize any EM solver for verification process. As such it dramatically reduces the time of verification process and allows fast design rule check.

In this work we report the results of both theoretical and experimental strain analysis of Silicon waveguides and couplers. Simulations of induced stress and strain distributions on photonic structures (waveguides with 450 × 220 nm cross section) have been performed taking into account a ~375 nm thick Si₃N₄ straining layer. The Convergent Beam Electron Diffraction (CBED) technique has also been employed to provide locally accurate strain measurements on fabricated silicon rib and coupling structures across the nitride-to-silicon interface, showing a good match between multiphysics simulations and measurements along the rib cross-section, resulting in notable attained strain levels.

In this work we model the effects of depositing gold nanospheres of varying radii and spatial separations onto a 500nm film of silicon in an effort to couple more light into silicon through the localized surface plasmon resonance (LSPR) of the nanoparticles. To further enhance the field at the interface, we study the effect of embedding the spheres within the dielectrics air, NBK7, and titanium dioxide (TiO₂). The modeling is done through finite element analysis via COMSOL over the radiation spectrum (0.4μm 1.5μm) of the sun. A positive size dependency of the light coupled into silicon and the radii of the spheres is found and analyzed. Use of dielectrics greater than air, NBK7 and TiO₂, results in greater field enhancement at the silicon interface.

Although the development of a monolithically-integrated, silicon-compatible light source has been traditionally limited by the indirect band gaps of Group IV materials, germanium-tin (Ge_1-xSn_x) is predicted to exhibit direct band gap behavior. In pseudomorphic conditions with materials of smaller lattice constant, the accumulation of compressive strain in Ge_1-xSn_x counteracts this behavior to prevent the direct band gap transition. One possible approach to compensate for this compressive strain is to introduce tensile strain into the system, which can be achieved by applying an external stressing agent to post-fabricated devices. We describe a suspended Ge_0:922Sn_0:078 multiple quantum well microdisk resonator cavity strained by 140 nm of highly compressively stressed silicon nitride. Raman shifts and photoluminescence redshifts indicate that an additional 0.23-0.30% strain can be induced in these microdisks with this approach. The ability to tune the optical performance of these resonator structures by strain engineering has the potential to enable the development of low threshold Ge_1-xSn_x-based lasers on Si.

The IBM Silicon Nanophotonics technology enables cost-efficient optical links that connect racks, modules, and chips together with ultralow power single-die optical transceivers. I will give an overview of its historical development, technology differentiators, current status and a roadmap.