This PDF file contains the front matter associated with SPIE Proceedings Volume 7220, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We devised a silicon photonic circuit with polarization diversity. The circuit consists of polarization splitters and rotators. The splitter is based on simple 10-micrometer-long directional couplers. The polarization extinction ratio is 23 dB and excess loss is less than 0.5 dB. The rotator consists of a silicon waveguide embedded in an off-axis siliconoxynitride waveguide. A 35-micrometer-long rotator gives a rotation angle of more than 72 degrees and excess loss of about 1 dB. Both devices can be made by using planar fabrication technology and do not require a complex structure such as three-dimensional forming. Using these devices, we developed a polarization diversity circuit for a ringresonator wavelength filter. The polarization dependent loss of the filter with polarization diversity is about 1 dB. A 10- Gbps data transmission with scrambled polarization is demonstrated.

There is currently considerable research interest in all-optical signal processing for telecommunication applications. In this paper it is shown that a range of all-optical signal processing functions may be carried out using passive waveguides and phase-shifting elements as basic building blocks. Two types of multimode interference (MMI) photonic circuits, based on silicon-on-insulator (SOI) technology, are discussed in detail. In the first type, phase-shifting elements are added to the ports of MMI couplers. In the second type, the waveguide structure of the MMI coupler itself is modified to achieve a range of signal processing functions. Designs are verified using 2D and 3D simulations.

We propose the V-groove waveguide as a novel silicon nanophotonic structure. By anisotropic etching of a monocrystalline silicon layer, angled photonic wires with isosceles-trapezoidal cross section can be realized. Placing two such wires side by side results in a waveguiding structure consisting of two highly coupled wires separated by an acute angled V-shaped nano groove. By choosing proper geometry parameters, the light is concentrated near the bottom of the groove. In this work, we theoretically study the dependence of the light confinement characteristics on the waveguide geometry parameters and demonstrate the suitability of the Vgroove waveguide as a versatile platform for surface sensing, for exploiting nonlinear optical effects in low index materials, and for realizing nanowire lasers.

We report on new types of sub-wavelength grating gradient index structures for efficient mode coupling in high index contrast slab waveguides. Using sub-wavelength gratings (SWGs), an adiabatic transition can be formed at the interface between slab waveguides of different core thicknesses. The SWG transition region minimizes both mode mismatch loss and coupling to higher order modes. By creating the adiabatic gradient effective index region in the direction of propagation, we demonstrate that vertical mode size transformation is readily achieved in structures that can be fabricated using a single etch step. Using 3D finite-difference time-domain simulations we study the loss, polarization dependence and the higher order mode excitation for two types (triangular and triangular-transverse) of SWG transition regions between silicon-on-insulator slab waveguides of different core thicknesses. We also demonstrate two solutions to mitigate polarization dependent loss, namely using a partial transverse SWG and a SWG in the region between the triangular teeth. Our mode transformer designs are optimized for applications in polarization compensator in echelle grating and arrayed waveguide grating (AWG) multiplexers and a gradient index interface between the ridge waveguide and the slab combiner region in a curved waveguide grating demultiplexer.

We investigate the effects of silicon ion irradiation on free carrier lifetime and propagation loss in silicon rib waveguides, and thus its ability to reduce the density of two-photon-absorption (TPA) generated free carriers, an undesired effect of the Raman process in crystalline silicon. Our experimental results show that free carrier lifetime can be reduced significantly by silicon ion implantation. Associated excess optical absorption from the implanted silicon ions can be kept low if irradiation energy and dose are correctly chosen. Simulations of Raman amplification in silicon rib waveguides suggest that net gain can be achieved in certain cases without the need for an integrated diode in reverse bias to sweep out the photo-generated free carriers.

A number of active elements have been demonstrated using the hybrid silicon evanescent platform, including lasers, amplifiers and detectors. In this paper, two types of hybrid silicon modulators, fulfilling the building blocks in optical communication on this platform, will be presented. A hybrid silicon electroabsorption modulator, suitable for high speed interconnects, with 10 dB extinction ratio at -5 V and 16 GHz modulation bandwidth is demonstrated. In addition a hybrid silicon Mach-Zehnder modulator utilizing carrier depletion in multiple quantum wells is proved with 2 V-mm voltage-length product, 150 nm optical bandwidth and a large signal modulation up to 10 Gb/s.

Silicon photonics have generated an increasing interest in the recent year, mainly for optical telecommunications or for optical interconnects in microelectronic circuits. The rationale of silicon photonics is the reduction of the cost of photonic systems through the integration of photonic components and an IC on a common chip, or in the longer term, the enhancement of IC performance with the introduction of optics inside a high performance chip. In order to build a Opto-Electronic Integrated circuit (OEIC), different European project has been launched in Europe. The PICMOS project demonstrated the full optical link on a silicon circuit with InP bonded devices. The following WADIMOS project goes a step further with the demonstration of an optical network on chip with WDM µlaser for on-chip intraconnection between IC cores. The UK silicon photonics project and the European HELIOS project are focalized on telecommunications devices with the aim of photonics and electronics integration which can be done either by wafer bonding of an SOI photonic circuit or by low temperature fabrication of a photonic layer at the metallization levels. Recent development on building blocks will be reported such as low loss couplers, Si and InP µdisk modulators, high speed Ge or InGaAs photodetectors.

Sampling rates of high-performance electronic analog-to-digital converters (ADC) are fundamentally limited by the timing jitter of the electronic clock. This limit is overcome in photonic ADC's by taking advantage of the ultra-low timing jitter of femtosecond lasers. We have developed designs and strategies for a photonic ADC that is capable of 40 GSa/s at a resolution of 8 bits. This system requires a femtosecond laser with a repetition rate of 2 GHz and timing jitter less than 20 fs. In addition to a femtosecond laser this system calls for the integration of a number of photonic components including: a broadband modulator, optical filter banks, and photodetectors. Using silicon-on-insulator (SOI) as the platform we have fabricated these individual components. The silicon optical modulator is based on a Mach-Zehnder interferometer architecture and achieves a V_πL of 2 Vcm. The filter banks comprise 40 second-order microring-resonator filters with a channel spacing of 80 GHz. For the photodetectors we are exploring ion-bombarded silicon waveguide detectors and germanium films epitaxially grown on silicon utilizing a process that minimizes the defect density.

We present an improvement of monolithically integrated photodiodes in a p-type substrate of a commercial high-speed 0.35μm SiGe heterojunction bipolar transistor (HBT) BiCMOS technology. These photodetectors (PDs) combine low capacitance with high bandwidth and responsivity. Slight process modifications of the standard HBT process have been introduced in order to decrease leakage currents and enhance reach-through stability of the PDs. These modifications have been chosen carefully in order not to alter any other transistor parameters as shown in [1]. To enable low capacitances of the PDs very lightly p-doped epitaxially grown layers of different thicknesses over highly p-doped substrates have been investigated. The improvement becomes manifest, e.g. in a bandwidth of 557MHz and a responsivity of 0.19A/W of a finger photodiode at blue light and a reverse bias voltage of 4V in a 10μm cathode digit-spacing configuration. The capacitance of this finger photodiode is 150fF, overtopping the regular PIN photodiode published in [2] for the same light-sensitive area with a capacitance of 225fF. Results of detectors with interdigitated cathode distances of 5μm, 10μm, 15μm and 30μm are presented over the wide spectrum of technologically significant optical wavelengths from near-infrared to blue and ultraviolet. These detectors fulfil the requirements demanded by photodiode integrated circuits for universal backward compatible optical storage systems.

In wavelength-division multiplexing systems, it is important to develop various wavelength-selective components to have flexible and reconfigurable nodes. When using conventional optical waveguides with low index contrast, the sizes of these wavelength-selective components are usually several cm², which is too large to integrate more components in a single wafer or chip. In order to improve the integration density and reduce the cost, it is desirable to minimize the component sizes. In our case, two kinds of strongly-confined optical waveguides on silicon wafer are considered for compact wavelength-selective devices. One is the popular silicon-on-insulator (SOI) nanowire and the other is SU-8 strip optical waveguide with an air cladding and a SiO₂ insulator layer on a Si substrate. In this paper, we give a review of our recent work on wavelength-selective photonic integrated devices based on these two kinds of silicon-based optical waveguides with strong-confinements. Arrayed-waveguide grating (AWG) and microring resonator (MRR), which are two typical wavelength-selective components are included. First we give a review for several new layouts for SOI-nanowire AWG to have a further size-reduction and our novel designs for diminishing the polarization dependency of AWGs. Secondly we present the design and fabrication of multimode interference (MMI) couplers for MRRs. A novel design method for tapered MMI couplers is presented and the diminishment of polarization in a MMI coupler is proposed by optimizing the tapered MMI section. We also present our experimental results on optical sensor combining MRRs and micro-fluid channel. The measured sensitivity is about 180nm/RIU.

This paper reports on fabrication and characterization of two kinds of photodetectors: surface illuminated and waveguide integrated vertical PIN Ge/Si photodetectors for operation at optical telecommunication wavelengths. The measured -3dB bandwidth of surface illuminated photodetectors is 40 GHz under 5 V reverse bias at 1.53 µm wavelength. For waveguide integrated photodetectors, the measured -3dB bandwidth at 1.53 µm wavelength under 4 V reverse bias is 42 GHz.

CMOS Geiger avalanche photodiodes (GPD), and parallel arrays of GPDs - a solid-state photomultiplier - are high-gain, high-sensitivity, versatile light sensors. Applications include readout of scintillation materials for nuclear detection and gamma ray imaging, scanning of biological fluorescence including flow cytometry, and as LIDAR sensors. Manufacturing such devices in CMOS provides the possibility of direct integration of signal processing and readout electronics monolithically with the sensor. Recently, RMD has fabricated SSPM arrays with pixel-level conditioning. For example, comparators at the pixel level are used, as described in this work, to condition the signal. These active pixel elements provide active quenching of the Geiger avalanche, increase dynamic range, and can suppress afterpulsing by the application of a long gate. A conditioned signal can also isolate the output from the temperature fluctuations that are often associated with silicon devices. We examine the performance of these integrated circuits at the pixel level and at the level of the whole sensor. Preliminary results show that sources of electronic noise are drastically reduced. The resulting isolation of the processed signals from bias and temperature fluctuations is presented.

We report reconfigurable optofluidic photonic crystal components in silicon-based membranes by controllably infiltrating and removing fluid from holes of the photonic crystal lattice. Systematic characterizations of our fluidically defined microcavities are presented, corresponding with the capability to increase or decrease the span of the fluid-filled regions and thus alter their optical properties. We show initial images of single-pore fluid infiltration for holes of diameter 265 nm. Furthermore, the infiltration process may employ a large range of optical fluids, adding more flexibility to engineer device functionality. We discuss the great potential offered by this optofluidic scheme for integrated optofluidic circuits, sensing, fluorescence and plasmonic applications.

We have achieved the design, fabrication and packaging of microfluidic networks with photonic sensors for novel labon- chip platforms which incorporate the on-chip biosensing detection. As sensors, we used an integrated Mach-Zehnder interferometer (MZI) based on TIR waveguides (Si/SiO₂/Si₃N₄) of micro/nanodimensions for evanescent field detection of biomolecular interactions onto the sensing areas. For the lab-on-a-chip development, the biosensors have been integrated with a 3D microfluidic polymer network. In addition, we have developed a novel hybrid device for coupling light into the waveguides of the Mach-Zehnder sensor. The coupling hybrid device is composed of a thin film of diffraction gratings fixed to a polydimethylsiloxane film. The optical characterization has shown the excellent compatibility and integration between fabrication technologies of silicon MZI, SU-8 polymer microfluidic network and mountable grating couplers.

Silicon photonic technology has incredible potential to transform multiplexed bioanalysis on account of the scalability of device fabrication, which maps favorably to a myriad of medical diagnostic applications. The optical properties of CMOS-fabricated microring resonators are incredibly responsive to changes in the local dielectric environment accompanying a biological binding event near the ring surface. Arrays of high-Q microrings were designed to be individually addressable both in surface derivitization, using well-established microarraying technologies, and in optical evaluation. The optical response of each ring can be determined in near real time allowing multiple biomolecular interactions to be simultaneously monitored. We describe a stable and robust measurement platform that allows sensitive visualization of small molecule surface chemical derivitization as well as monitoring of biological interactions, including the detection of proteins and nucleic acids. We also present recent results demonstrating multiplexed measurement of cancer markers. These demonstrations establish a pathway to higher level multiparameter analysis from real-world patient samples; a development that will enable individualized disease diagnostics and personalized medicine.

We present several nanophotonic biosensors on silicon-on-insulator: ring resonator based devices, slotted ring resonators to increase the interaction between light and the sample, and finally devices based on nanoplasmonic interferometers.

We present a potential high sensitive label-free optical bio-sensing system based on biophotonic sensing cells, which can be fabricated and interrogated at wafer or disposable chip level. The key benefits rely on the holistic approach that combines bio-photonic resonant micro-nano cavities and advanced sub-micron spot size optical interrogation technologies. The proposed optical sensing system will be tremendously sensitive to refractive index variations by means of the observation of the reflectivity profile of three complementary enhanced sub-micron spot size optical technologies simultaneously (Reflectometry, Spectrometry and Ellipsometry based techniques), and the magnification due to the biophotonics resonant sensing cells, making possible to determine with more reliability and sensitivity the biomolecular interaction with the receptor biomolecules. This novel sensing system also offers an inexpensive solution for integration and packaging because it overcomes the need for using complex systems for light coupling such as inverted tapers or grating couplers, usually used in planar micro-nano photonic devices, because the sensor evaluation is done measuring vertically collecting the reflected light of the bio-photonic resonant sensing cells. The sensing system may use a tightly focused beam which allows measuring in situ micron/sub-micron size geometries, making the routine screening more cost-effective and suitable to perform hundreds of measurements on a single or several samples for multi-single or multiparameter measurements. The simultaneous used of the three different optical techniques will allow the systems to achieve a high throughput and productivity in comparison with other established analytical techniques. The levels of sensitivity expected are in the order of 10^-6/10^-7 refractive index units (RIU).

We have investigated the fabrication and emission characteristics of InGaAs/GaAs quantum dot microtubebased coherent light sources on GaAs and Si, which are formed by self-rolling of pseudomorphically strained semiconductor bilayers through controlled release from the substrate. Tailoring of the optical modes is achieved by engineering the shape of the microtube ring resonators. Using substrate-to-substrate transfer method, we have also achieved, for the first time, three-dimensionally confined quantum dot microtube optical ring resonators on Si, that are relatively free of dislocations. Sharp polarized and regularly spaced optical modes, with an intrinsic Q-factor of ~ 3,000, were measured at 77 K.

In the continual drive toward improved microprocessor performance, power efficiency has emerged as a prime design consideration. At the chip scale, the trend toward multi-core architectures and chip multiprocessors (CMPs) for driving performance-per-watt via increases in the number of parallel computational cores is dominating new commercial releases. The role of the interconnect and associated global communication infrastructure is becoming central to the chip and ultimately computing system performance. On-chip photonic communication has been recently explored to address the communication requirements in future high-performance CMPs. We have developed a photonic network simulation environment that uniquely incorporates physical layer silicon photonic device models. We report on the design optimization of the network micro-architecture layout and photonic switching fabric organization. The event-driven network simulator establishes physical layer metrics for the silicon photonic devices and provides a measure of the network performance-per-Watt requirements derived from device characteristics.

We review the progress and challenges in scaling computing systems; discuss the potential benefits and challenges for achieving optical-interconnects to the chip via the native integration of silicon photonics components with VLSI electronics; and introduce the "macrochip" - a collection of contiguous silicon chips enabled by optical proximity communication

Achieving on-chip optical signal isolation is a fundamental difficulty in integrated photonics [1]. The need to overcome this difficulty, moreover, is becoming increasingly urgent, especially with the emergence of silicon nano-photonics [2- 4], which promise to create on-chip optical systems at an unprecedented scale of integration. In spite of many efforts, there have been no techniques that provide complete on-chip signal isolation using materials or processes that are fundamentally compatible with silicon CMOS process. Here we introduce an isolation mechanism based on indirect interband photonic transition. Photonic transition, as induced by refractive index modulation [5], has been recently observed experimentally in silicon nanophotonic structures [6]. Here we show that a linear, broad-band, and nonreciprocal isolation can be accomplished by spatial-temporal modulations that simultaneously impart frequency and wavevector shifts during the photonic transition process. We further show that non-reciprocal effect can be accomplished in dynamically-modulated micron-scale ring-resonator structures.

Third order ring resonators are designed and their resonance frequency deviations are analyzed experimentally by processing them with E-beam lithography and ICP etching in a CMOS nano-Fabrication laboratory. We developed a reliable method to identify and reduce experimentally the degree of deviation of each ring resonance frequency before completion of the fabrication process. The identified deviations can be minimized by the way to be presented in this paper. It is expected that this method will provide a significant clue to make a high order multi-channel ring resonators.

As Silicon Photonics is developing further towards integration on a single platform, the need for precise fabrication is paramount and no matter how developed a technology is, there is always potential for error at the wafer and chip level. In combination with Focused Ion Beam (FIB) technology, we present direct write methods to fabricate and tailor Silicon Photonic devices to offer the potential of prototyping, testing and correction in a post-processing environment. However, inherent in most FIB processing is the introduction of large optical loss due to damage and implantation of Gallium, because Gallium is typically the gas species used in FIBs. Therefore, methods of processing to minimise potential loss and changes to the original device design will be presented alongside results and a discussion offering a comparison with other potential methods.

Tunable silicon microring filters are used to demonstrate CMOS-compatible on-chip wavelength control of Er+ doped fiber-lasers. The filter uses a 10 μm-diameter microring resonator based on single-mode silicon-on-insulator (SOI) strip waveguides operating around the telecom range of 1.55 μm. A piece of Er+ doped fiber (EDF) serves as the gain media which is pumped by a 980 nm laser diode. An on-chip Ni-Cr micro-heater consuming up to 38 mW is capable of tuning the Si microring filter by 2.3 nm with a lasing linewidths narrower than 0.02 nm. This approach enables arbitrary multiple wavelength generation on a silicon chip. Possible applications include on-chip and chip-to-chip densewavelength division multiplexed communications, telecommunications and optical sensor interrogation.