Photonic crystals offer strong confinement of light, as well as control over the group velocity. We compare the resulting enhancement to that available in cavities and show that the group velocity can be controlled over a large spectral range, thus giving access to nonlinear functions. We show how coupled cavities allow tuning of the slowdown factor and present a very compact (5 μm long) optical switch based on slow light concepts.

Integrating electronic and photonic functions onto a single silicon-based chip using techniques compatible with mass-production CMOS electronics will enable new design paradigms for existing system architectures and open new opportunities for electro-optic applications with the potential to dramatically change the management, cost, footprint, weight, and power consumption of today's communication systems. While broadband analog system applications represent a smaller volume market than that for digital data transmission, there are significant deployments of analog electro-optic systems for commercial and military applications. Broadband linear modulation is a critical building block in optical analog signal processing and also could have significant applications in digital communication systems. Recently, broadband electro-optic modulators on a silicon platform have been demonstrated based on the plasma dispersion effect. The use of the plasma dispersion effect within a CMOS compatible waveguide creates new challenges and opportunities for analog signal processing since the index and propagation loss change within the waveguide during modulation. We will review the current status of silicon-based electrooptic modulators and also linearization techniques for optical modulation.

Multilevel thin film processing, global planarization and advanced photolithography enables the ability to integrate complimentary materials and process sequences required for high index contrast photonic components all within a single CMOS process flow. Developing high performance photonic components that can be integrated with electronic circuits at a high level of functionality in silicon CMOS is one of the basic objectives of the EPIC program sponsored by the Microsystems Technology Office (MTO) of DARPA. Our research team consisting of members from: BAE Systems, Alcatel-Lucent, Massachusetts Institute of Technology, Cornell University and Applied Wave Research reports on the latest developments of the technology to fabricate an application specific, electronic-photonic integrated circuit (AS_EPIC). Now in its second phase of the EPIC program, the team has designed, developed and integrated fourth order optical tunable filters, both silicon ring resonator and germanium electro-absorption modulators and germanium pin diode photodetectors using silicon waveguides within a full 150nm CMOS process flow for a broadband RF channelizer application. This presentation will review the latest advances of the passive and active photonic devices developed and the processes used for monolithic integration with CMOS processing. Examples include multilevel waveguides for optical interconnect and germanium epitaxy for active photonic devices such as p-i-n photodiodes and modulators.

We report on the development of single-chip, monolithically-integrated 40 Gbps transceivers built in a 130 nm SOI CMOS process as part of Phase II of the DARPA EPIC program. In this talk we give an overview of the system architecture, including the transmit and receive paths as well as the control systems. We report on the performance of the individual building blocks, and discuss a scaling to 100 Gbps and beyond single-chip transceivers built in CMOS photonics.

Photonic Analog-to-Digital Conversion (ADC) has a long history. The premise is that the superior noise performance of femtosecond lasers working at optical frequencies enables us to overcome the bottleneck set by jitter and bandwidth of electronic systems and components. We discuss and demonstrate strategies and devices that enable the implementation of photonic ADC systems with emerging electronic-photonic integrated circuits based on silicon photonics. Devices include 2-GHz repetition rate low noise femtosecond fiber lasers, Si-Modulators with up to 20 GHz modulation speed, 20 channel SiN-filter banks, and Ge-photodetectors. Results towards a 40GSa/sec sampling system with 8bits resolution are presented.

We describe our approach to the monolithic integration of Ge photodetectors in a photonics-enabled CMOS technology. Ge waveguide photodetectors allow fast and efficient conversion of optical signals in the near infrared (1.55μm) to the electrical domain thus enabling the fabrication of compact, high speed (10Gbps) receivers.

The vision of longwave silicon photonics articulated in the Journal of Optics A, vol. 8, pp 840-848, 2006 has now come into sharper focus. There is evidence that newly designed silicon-based optoelectronic circuits will operate at any wavelength within the wide 1.6 to 200 μm range. Approaches to that LWIR operation are reviewed here. A long-range goal is to manufacture LWIR OEIC chips in a silicon foundry by integrating photonics on-chip with CMOS, bipolar, or BiCMOS micro-electronics. A principal LWIR application now emerging is the sensing of chemical and biological agents with an OE laboratory-on-a-chip. Regarding on-chip IR sources, the hybrid evanescent-wave integration of III-V interband-cascade lasers and quantum-cascade lasers on silicon (or Ge/Si) waveguides is a promising technique, although an alternative all-group-IV solution is presently taking shape in the form of silicon-based Ge/SiGeSn band-to-band and inter-subband lasers. There is plenty of room for creativity in developing a complete suite of LWIR components. Materials modification, device innovation, and scaling of waveguide dimensions are needed to implement microphotonic, plasmonic and photonic-crystal LWIR devices, both active and passive. Such innovation will likely lead to significant LIO applications.

A Si ridge waveguide integrated with a lateral p-i-n diode forms a basic optical amplitude and phase modulator. An efficient Si modulator is expected to establish a carrier concentration in the waveguide with a minimum amount of electrical drive power. We show that P⁺ and N⁺ doping sections that are recessed below the slab lead to lower power consumption. This configuration is compared with alternative doping section arrangements. The optimum arrangement results in less Si active area and reduced carrier recombination.

Circular grating resonators could lead to the development of very advanced silicon-on-insulator (SOI) based nano-photonic devices clearly beyond state of the art in terms of functionality, size, speed, cost, and integration density. The photonic devices based on the circular grating resonators are computationally designed and studied in their functionality using finite-difference time-domain (FDTD) method. A wide variety of critical quantities such as transmission and field patterns are calculated. Due to their computational size some of these calculations have to be performed on a supercomputer like a massive parallel Blue Gene machine. Using the computational design parameters the devices are fabricated on SOI substrates consisting of a buried oxide layer and a 340-nm-thick device layer. The devices are defined by electron-beam lithography and the pattern transfer is achieved in a inductively coupled reactive-ion etch process. Then the devices are characterized by coupling light in from a tunable laser with a lensed fiber. As predicted the measured transmission spectra exhibit a wide range of different type of resonances with Q-factors over 1000 which compares very well with the computations.

Silicon Photonics has the potential to revolutionise a whole raft of application areas. Currently, the main focus is on various forms of optical interconnects as this is a near term bottleneck for the computing industry, and hence this application area is high profile. However, adoption of silicon photonics for such a mass production area would also significantly benefit a range of other application areas. One of the key components that will enable silicon photonics to flourish in all of the potential application areas is a high performance optical modulator. Therefore we will propose what is in our view the need for optical modulation in silicon on insulator, the concept of optical modulation in silicon and its principles, and we discuss different devices, as well as how they evolved, in order to achieve the required target driven by high integration.

Photonic integration is one of the important ways to realize low cost and small form factor optical transceivers for future high-speed high capacity I/O applications in computing systems. The photonic integration on silicon platform is particularly attractive because of the CMOS photonics and electronics process compatibility. In this paper, we present design and fabrication of a silicon photonic integrated circuit that is capable of transmitting data at hundreds gigabits per second. In such an integrated chip, 8 high-speed silicon optical modulators with a 1:8 wavelength demultiplexer and an 8:1 wavelength multiplexer are fabricated on a single silicon-on-insulator (SOI) substrate. We review the recent results of individual silicon modulator based on electric-field-induced carrier depletion in a SOI waveguide containing a reverse biased pn junction. We characterize the individual multiplexer/demultiplexer as well as the integrated chip. The basic functionality of the photonic integration is demonstrated.

Modeling of p⁺np⁺ CMOS Si LED structures show that by utilizing a short linear increasing E-field in the p⁺n reverse biased junction with a gradient of approximately 5 × 10⁵ V.cm^-1. μm^-1, and facing an injecting p⁺n junction, has the potential to enhance photonic emissions in the 2.2 and 2.8 eV (450-750nm ) regime. Latest new designs utilize reach-through techniques in p⁺np⁺ avalanche-injection control structures and p⁺np⁺ poly-Si gated structures and show positive realizations of this model. Areas in the devices show marked increases in emission efficiency of factors of up to 50 - 100 as compared to previous realizations utilizing no reach-through and injection techniques. The current devices operated in the 6-8V, 1uA - 2mA regime and emit at levels of up to ~10nW /μm². The developed devices have been realized using standard 0.35 μm CMOS design rules and fabrication technology, and have particular technological significance for future all-silicon CMOS opto-elctronic circuits and systems. The current emission levels are about three orders higher than the low frequency detectability limit of CMOS p-i-n detectors of corresponding area.

A MOS-LED and a p-n LED emitting based on the dislocation-related luminescence (DRL) at 1.5 micron were already demonstrated by the authors. Here we report recent observation of the Stark effect for the DRL in Si. Namely, a red/blue-shift of the DRL peak positions was observed in electro- and photo-luminescence when the electric field in the pn-LED was increased/lowered. Fitting the experimental data yields a strong characteristic coefficient of 0.0186 meV/(kV/cm)². This effect may allow realization of a novel Si-based emitter and modulator combined in a single device.

Light emitting diodes (LEDs) based on a metal-oxide-semiconductor-like (MOS-like) structure with Si nanocrystals (nc-Si) embedded in SiO₂ have been fabricated with low-energy ion implantation. Under a negative gate voltage as low as ~-5 V, both visible and infrared (IR) electroluminescence (EL) have been observed at room temperature. The EL spectra are found to consist of four Gaussian-shaped luminescence bands with their peak wavelengths at ~460, ~600, ~740, and ~1260 nm, in which the ~600-nm band dominants the spectra. The EL properties have been investigated together with the current transport properties of the Si⁺-implanted SiO₂ films. A systematic study has been carried out on the effect of the Si ion implantation dose and the energy on both the current transport and EL properties. The mechanisms of the origin of the four different EL bands have been proposed and discussed.

Both isolated Si nanocrystals (nc-Si) dispersedly distributed in a SiO₂ matrix and densely stacked nc-Si layers embedded in SiO₂ have been synthesized with the ion implantation technique followed by high temperature annealing. The dielectric functions of the isolated nc-Si and densely-stacked nc-Si layer embedded in SiO₂ have been determined with spectroscopic ellipsometry (SE) in the photon energy range of 1.1-5 eV. The dielectric functions of these two different Si nanostructures were successfully extracted from the SE fitting based on a multi-layer fitting model that takes into account the distribution of nc-Si in SiO2 and a five phase model (i.e., air/SiO₂ layer/densely-stacked nc-Si layer/SiO₂ layer/Si), respectively. The dielectric spectra of isolated nc-Si distributed in SiO₂ present a two-peak structure, while the dielectric spectra of densely-stacked nc-Si layer show a single broad peak, being similar to that of amorphous Si. The dielectric functions of these two Si nanostructures both show significant suppressions as compared with bulk crystalline Si. However, it has been observed that the densely stacked nc-Si layer exhibits a more significant suppression in the dielectric spectra than the isolated nc-Si dispersedly embedded in SiO₂. This is probably related to the two factors: (i) the nc-Si size (~3 nm) of the densely stacked nc-Si layer is smaller than that (~4.5 nm) of the isolated nc-Si embedded in SiO₂ matrix, and (ii) the densely stacked nc-Si layer has an amorphous phase.

We present a monolithic integrated low-threshold Raman silicon laser based on silicon-on-insulator (SOI) rib waveguide ring cavity with an integrated p-i-n diode. The laser cavity consists of a race-track shaped ring resonator connected to a straight bus waveguide via a directional coupler which couples both pump and signal light into and out of the cavity. Reverse biasing the diode with 25V reduces the free carrier lifetime to below 1 ns, and stable, single-mode, continuous-wave (CW) Raman lasing is achieved with threshold of 20mW, slope efficiency of 28%, and output power of 50mW. With zero bias voltage, a lasing threshold of 26mW and laser output power >10mW can be obtained. The laser emission has high spectral purity with a side-mode suppression of >80dB and laser linewidth of <100 kHz. The laser wavelength can be tuned continuously over 25 GHz. To demonstrate the performance capability of the laser for gas sensing application, we perform absorption spectroscopy on methane at 1687 nm using the CW output of the silicon Raman laser. The measured rotationally-resolved direct absorption IR spectrum agrees well with theoretical prediction. This ring laser architecture allows for on-chip integration with other silicon photonics components to provide an integrated and scaleable monolithic device. By proper design of the ring cavity and the directional coupler, it is possible to achieve higher order cascaded Raman lasing in silicon for extending laser wavelengths from near IR to mid IR regions.

We have achieved continuous-wave electrically-injected lasing operation at room-temperature in InP-based microdisks heterogeneously integrated on a SOI nanophotonic circuit. The microdisks were evanescently coupled with sub-micron SOI wire waveguides, resulting in up to 10 μW waveguide-coupled unidirectional output power, with a measured slope efficiency up to 20 μW/mA. A tunnel junction was used for efficient electrical injection with low optical absorption. The measured laser performance agrees well with calculations based on a standard laser model. This model suggests that considerable improvement in laser performance is possible.

Recently, AlGaInAs-silicon evanescent lasers have been demonstrated as a method of integrating active photonic devices on a silicon based platform. This hybrid waveguide architecture consists of III-V quantum wells bonded to silicon waveguides. The self aligned optical mode leads to a bonding process that is manufacturable in high volumes. Here give an overview of a racetrack resonator laser integrated with two photo-detectors on the hybrid AlGaInAs-silicon evanescent device platform. Unlike previous demonstrations of hybrid AlGaInAs-silicon evanescent lasers, we demonstrate an on-chip racetrack resonator laser that does not rely on facet polishing and dicing in order to define the laser cavity. The laser runs continuous-wave (c.w.) at 1590 nm with a threshold of 175 mA, has a maximum total output power of 29 mW and a maximum operating temperature of 60 C. The output of this laser light is directly coupled into a pair of on chip hybrid AlGaInAs-silicon evanescent photodetectors used to measure the laser output.

Microphotonic devices employing strong confinement of light are of growing importance for key applications such as telecommunication and optical interconnects. They have unique and desirable characteristics but their extreme sensitivity to dimensional variations makes them difficult to successfully implement. Here, we discuss strategies towards the successful realization of strong confinement devices. We leverage what planar fabrication technology does best: replicating structures. Although the absolute dimensional control required for successful fabrication of many strong confinement devices is all but impossible to achieve, we show that surprisingly-high relative dimensional accuracy can be obtained on structures in proximity of one another on a wafer. This provides an advantage to schemes that are based on multiple copies of low-complexity structures. These copies can be made nearly identical or with precise relative-dimensional offsets to achieve the desired function. We quantify the achievable relative dimensional control and discuss the first demonstration of multistage filters, integrated polarization diversity, and high-order microring-filter banks.

Recent research progresses in slot waveguide have shown that it is possible to achieve photon confinement in low-refractive index region with nm thickness. To utilize this photon confinement, we propose a multilayer waveguide that could be the optimum design for future silicon light emission devices. Our device consists of multiple alternating layers of Si and SiO₂ with nm thickness, which can be easily fabricated. Both transfer matrix method (TMM) and FDTD simulation are used to simulate the performance of this device. We calculated the propagation mode index, and photon confinement in SiO₂ layers. Birefringence as high as 0.8 is achieved with moderate design parameters, although a homogeneous slab waveguide also shows some birefringence, it cannot account for the high birefringence we have calculated. Thus it indirectly indicates that for TM polarization photons are actually confined in SiO₂ layers, where the refractive index is lower. Also our photon confinement simulation shows that, for a structure with multilayer region thickness of 0.52 μm, photon confinement in SiO₂ layers as high as 75% can be achieved with Si/SiO₂ layer thickness ratio close to 1. We fabricated a few multilayer samples with different Si/SiO₂ thickness ratios and performed M-line measurement to measure the propagation mode index. The measurement results agrees well with our simulate results, indicates that for TM polarization photons can be strongly confined in SiO₂ layers in this multilayer structure. Thanks to this high confinement in SiO₂ layers, this structure could be an excellent choice for future silicon light emitting devices.

We report a novel technique for the fabrication of an all-silicon channel waveguide using direct proton beam writing and subsequent electrochemical etching. A focused beam of high energy protons is used to selectively inhibit porous silicon formation in the irradiated regions. By over-etching beyond the ion range, the irradiated region becomes surrounded by porous silicon cladding. Waveguide characterization carried out at 1550 nm on the proton irradiated waveguide shows that the propagation losses improve significantly from 20±2 dB/cm to 9±2 dB/cm after vacuum annealing at 800°C for 1 hour.

In this paper we report a novel fabrication technique for silicon photonic waveguides with sub-micron dimensions. The technique is based upon the Local Oxidation of Silicon (LOCOS) process widely utilised in the fabrication of microelectronics components. This approach enables waveguides to be fabricated with oxide sidewalls with minimal roughness at the silicon/SiO₂ interface. It is also sufficiently flexible to enable the depth of the oxidised sidewall to be varied to control the polarisation performance of the waveguides. We will present preliminary results on submicron waveguide fabrication and loss characteristics (less than 1 dB/cm), as well as effects of varying waveguide width on modal properties of the waveguides. We consider the ease of fabrication, as well as the quality of the devices produced in preliminary experimental fabrication results, and compare the approach to the more conventional requirements of high resolution photolithographically produced waveguides. We also discuss preliminary optical results, as measured by conventional means. Issues such as the origins of loss are discussed in general terms, as are the fabrication characteristics such as waveguide wall roughness and waveguide profile. We will discuss further work that will help to establish the potential of the technique for future applications.

Mid-infrared wavelength region is interesting for several application areas including sensing, communications, signal processing, and imaging. Its importance stems from the two atmospheric windows and the fact that nearly all important molecular gases have strong absorption lines in the mid-infrared. In this paper, we discuss the design, fabrication and propagation loss measurements of three silicon waveguide structures that can find applications in the mid-infrared region.

In this study, we theoretically investigate the leakage behavior of SOI slot waveguides at a wavelength of 1.55 μm. First, the dependence of the substrate leakage of vertical and horizontal wire-type slot waveguides on their geometry is shortly summarized. The main part is devoted to the lateral leakage in perfectly symmetric and asymmetric rib-type slot waveguides, which is caused by coupling between the TM-like slot mode and the TE slab modes outside the rib. The influence of the geometry parameters on the leakage behavior and the impact of structural deviations caused by the fabrication process are studied in depth. A semi-analytical criterion for the design of leakproof rib-type slot waveguides is derived and compared with full-vectorial numerical methods employing a commercial FEM solver and a recently developed variational mode-matching 2D eigenmode solver.

We show that optical soliton can be realized in very short waveguides (5 mm long) fabricated on silicon-on-insulator (SOI) wafers. By tailoring their zero-dispersion wavelength and launching optical pulses at only sub pico-joule energy level close to this wavelength, we have observed significant spectral narrowing due to the pulse reshaping during the formation of optical soliton, which is in strong contrast to previous measurements. The extent of spectral narrowing depends on the carrier wavelength of the input pulse in the normal dispersion region and spectral broadening is observed in normal dispersion region. We simulate femto-second pulses' propagation in such waveguide. Simulation results show the evolution of the pulse shape in both time domain and frequency domain when the pulse energy is increased from very low level, when nonlinear effects are negligible, to the energy level we used in our experiment. The simulation results agree well with our observation. To be best of our knowledge, this is the first report on soliton in silicon waveguides.

We present vertically-integrated multimode interferometers that optically couple between waveguide layers of a three-dimensional photonic circuit. Coupling between these layers can be restricted to certain regions by selectively fabricating a silicon channel between them, resulting in an isolated multimode waveguide section. Simulations reveal that complete coupling between two waveguides that are 2 μm square is achieved over a length of 236 μm, when the separating silicon channel is 1 μm thick. Standard photolithography and etching techniques are used to fabricate a proof-of-concept device consisting of one waveguide coupling into a silicon waveguide that is vertically multimode.

In this paper we present the design, fabrication and characterization of waveguide-coupled corner-cut square resonators. The square resonators are attractive for multiple applications including sensors, filters and lasers. We use two- and three- dimensional finite difference time domain (FDTD) methods to optimize the performance of the square resonator. We show that the dropping efficiency for these type of microcavities depends on the gap between the waveguide and the cavity and the corner-cut length, which is defined as a distance c away from the cavity sidewalls. Fabrication of these corner-cut square-resonators is performed on Silicon-on-Insulator (SOI) by conventional E-beam lithography and dry etching. These processes were optimized to achieve vertical and smooth sidewalls in order to decrease scattering losses and they will be discussed in details below. Characterization of these corner-cut square resonators shows good performance and excellent agreement with the rigorous electromagnetic simulation. We will also discuss the potential application of using this design in combination with dispersion based Photonic Crystals (PhCs) to achieve lasing.

We propose a design of an optical switch on a silicon chip comprising a 5 × 5 array of cascaded waveguide-crossing-coupled microring resonator-based switches for photonic networks-on-chip applications. We adopt our recently demonstrated design of multimode-interference (MMI)-based wire waveguide crossings, instead of conventional plain waveguide crossings, for the merits of low loss and low crosstalk. The microring resonator is integrated with a lateral p-i-n diode for carrier-injection-based GHz-speed on-off switching. All 25 microring resonators are assumed to be identical within a relatively wide resonance line width. The optical circuit switch can employ a single wavelength channel or multiple wavelength channels that are spaced by the microring resonator free spectral range. We analyze the potential performance of the proposed photonic network in terms of (i) light path cross-connections loss budget, and (ii) DC on-off power consumption for establishing a light path. As a proof-of-concept, our initial experiments on cascaded passive silicon MMI-crossing-coupled microring resonators demonstrate 3.6-Gbit/s non-return-to-zero data transmissions at on- and off-resonance wavelengths.

The emerging class of multicore architectures and chip multiprocessors (CMPs) has fundamentally shifted the impact of communications on computing systems performance. Global communications at all scales is playing a central and dominant role in the ultimate realization of CMP system performance as it falls increasingly on the efficiency of the information exchange among the vastly growing number of compute and memory resources. In this new communication-bound paradigm, the realization of a system-wide scalable communications infrastructure that can meet the enormous bandwidths, capacities, and stringent latency requirements in an energy efficient manner is a key goal for scaling future computation performance. We explore how recent extraordinary advances in nanoscale silicon photonic technologies can be exploited for developing optical interconnection networks that address the critical bandwidth and power challenges presented across several levels of the CMP computing system communications infrastructure. Unlike prior generations of photonic technologies, the remarkable capabilities of nanoscale "CMOS photonics" offer the possibility of creating highly integrated platforms for generating and receiving optical signals with fundamentally superior power efficiencies. Optical interconnection network architectures employing these silicon nanophotonic building blocks are uniquely co-developed and explored in the context of bandwidth-driven computing models. The design of an on-chip optical interconnection network that employs nanoscale CMOS photonic devices and enables seamless off-chip communications to other CMP computing nodes and to external memory is described.

We review recent work on low-dose high-energy helium ion implantation into silicon-on-insulator (SOI) optical waveguides. The important role of free carriers generated by two-photon absorption (TPA) in nonlinear silicon waveguide devices is discussed and a generalized definition of the nonlinear effective length which takes into account the presence of nonlinear losses is proposed. We describe experimental studies and simulations of helium ion implantation for carrier lifetime reduction to increase the nonlinear effective lengths of silicon waveguides. Helium ion implantation can also enhance the photodetection responsivity of silicon at below-bandgap wavelengths. We review our work on a possible application of the helium ion implanted waveguides for in-line optical power monitors (ICPM) which monitor the output from erbium doped fiber amplifiers (EDFA) and, when combined with silicon variable optical attenuators, can perform EDFA gain tilt and gain transient compensation.

This paper reports theoretical and experimental investigations of germanium photodetectors integrated in silicon on insulator waveguides for metal-semiconductor-metal (MSM) photodetectors integrated in a slightly etched rib waveguide. Experimental characteristics of germanium on silicon photodetectors have been obtained using time measurements with femtosecond pulses and opto-RF experiments. For MSM structure with 1μm electrode spacing, the measured bandwidth under 6V bias is 25 GHz at 1.55 μm wavelength with a responsivity as high as 1 A/W and the bandwidth reaches 30GHz for 0.7μm electrode spacing under 1V bias.

We present hybrid silicon evanescent photodetectors that utilize silicon waveguides and offset AlGaInAs quantum wells. The light in the hybrid waveguide is absorbed by the AlGaInAs quantum wells under reverse bias. The first demonstrated photodetector had an internal quantum efficiency of >90 % over the 1.5 μm wavelength regime. This detector structure has the same structure as silicon evanescent lasers and amplifiers leading to easy integration for power monitors and preamplified receivers. A pre-amplified receiver implementing a hybrid silicon evanescent amplifier and a hybrid silicon evanescent waveguide photodetector is also presented in this paper. The integrated device operates at 1550 nm with a responsivity of 5.7 A/W and a receiver sensitivity of -17.5 dBm at 2.5 Gb/s.

Atomic spectroscopy relies on photons to probe the energy states of atoms, typically in a gas state. In addition to providing fundamental scientific information, this technique can be applied to a number of photonic devices including atomic clocks, laser stabilization references, slow light elements, and eventually quantum communications components. Atomic spectroscopy has classically been done using bulk optics and evacuated transparent vapor cells. Recently, a number of methods have been introduced to dramatically decrease the size of atomic spectroscopy systems by integrating optical functionality. We review three of these techniques including: 1) photonic crystal fiber based experiments, 2) wafer bonded mini-cells containing atomic vapors and integrated with lasers and detectors, and 3) hollow waveguides containing atomic vapors fabricated on silicon substrates. In the context of silicon photonics, we will emphasize the hollow waveguide platform. At the heart of these devices is the anti-resonant reflecting optical waveguide (ARROW). ARROW fabrication techniques will be described for both hollow and solid core designs. Solid-core waveguides are necessary to direct light on and off the silicon chip while confining atomic vapors to hollow-core waveguides. We will also discuss the methods and challenges of attaching rubidium vapor reservoirs to the chip. Experimental results for optical spectroscopy of rubidium atoms on a chip will be presented.

Results of a hydrogen sensor based on light scattering from a porous silicon surface coated with a thin palladium film are discussed. Reflected light scattered from the rough surface of porous silicon surface with a thin palladium film is compared before and after exposure to hydrogen gas. After exposure to hydrogen gas the sensor's optical reflectance is decreased indicating the presence of hydrogen.

We review our recent progress in bringing fluorescent correlation spectroscopy (FCS) of single molecules on a silicon optofluidic platform. Starting from basic concepts and applications of FCS we move to a description of our integrated optofluidic device, briefly outlining the physics behind its function and relevant geometrical characteristics. We then derive an FCS theoretical model for our sensor geometry, which we subsequently apply to the examination of molecular properties of single fluorophores and bioparticles. The model allows us to extract the diffusion coefficient, translational velocity and local concentration of particles in question. We conclude with future directions of this research.

Two different applications that take advantage of integrated planar waveguides will be shown. The first example is a silicon chips for capillary electrochromatography (CEC), where the fluidic part contains electrically insulated channels with an injection cross and a chromatography column of microfabricated pillars, while the optical part consists of ultraviolet transparent planar waveguides for absorbance detection in the plane of the chip and fiber couplers for easy connection to an external light source and a photodetector. Electrochromatographic separations have been performed using hydrophobic octyl chains (C-8) immobilized onto the pillar sidewalls as a stationary phase. This is the first time capillary electro-chromatography has been shown on a chip with integrated waveguides for detection. In another chip, an array of pillars inside a microfluidic column that is designed for electrochromatography is used as an optofluidic filter (1 D photonic crystal) for on-column label-free refractive index detection. Conventional planar waveguides are furthermore integrated for coupling light in and out of the structure.

We demonstrate Mach-Zehnder interferometer and ring resonator evanescent field sensors fabricated on the silicon-on-insulator material platform. These devices exploit the strong evanescent field of the transverse magnetic mode of a high index contrast, submicron dimension waveguide to obtain strong interaction of the guided mode with biomolecules adsorbed to the waveguide surface. We utilize the extremely small bend radius achievable with silicon photonic wire waveguides to fabricate spiral and folded waveguide sensors that maintain the high sensitivity of a long waveguide, while providing compact footprint. These devices offer a suitable geometry for the development of sensor arrays and provide compatibility with commercial spotting functionalization systems. We demonstrate sensors containing waveguides of up to 5.5 mm length that are contained within a 150 μm × 150 μm area.

The increasing demand for portable devices to detect and identify pathogens represents an interdisciplinary effort between engineering, materials science, and molecular biology. Automation of both sample preparation and analysis is critical for performing multiplexed analyses on real world samples. This paper selects two possible components for such automated portable analyzers: modified silicon structures for use in the isolation of nucleic acids and a sheath flow system suitable for automated microflow cytometry. Any detection platform that relies on the genetic content (RNA and DNA) present in complex matrices requires careful extraction and isolation of the nucleic acids in order to ensure their integrity throughout the process. This sample pre-treatment step is commonly performed using commercially available solid phases along with various molecular biology techniques that require multiple manual steps and dedicated laboratory space. Regardless of the detection scheme, a major challenge in the integration of total analysis systems is the development of platforms compatible with current isolation techniques that will ensure the same quality of nucleic acids. Silicon is an ideal candidate for solid phase separations since it can be tailored structurally and chemically to mimic the conditions used in the laboratory. For analytical purposes, we have developed passive structures that can be used to fully ensheath one flow stream with another. As opposed to traditional flow focusing methods, our sheath flow profile is truly two dimensional, making it an ideal candidate for integration into a microfluidic flow cytometer. Such a microflow cytometer could be used to measure targets captured on either antibody- or DNA-coated beads.

Micro-total-analysis-systems and lab-on-chip are more than promises in lot of social interest applications such as clinical diagnostic or environmental monitoring. There is an increasing demand of new and customized devices with better performances to be used in very specific applications. Nanostructured Porous silicon is a functional material and a versatile platform for the fabrication of integrated optical microsystems to be used in biochemical analysis. Our research activity is focused on the design, the fabrication and the characterization of several photonic porous silicon based structures, which are used in the sensing of specific molecular interactions. To integrate the porous silicon based optical transducer in biochip devices we have modified standard micromachining processes, such as anodic bonding and photo-patterning, in order to make them consistent to the utilization of biological probes.

A silicon-on-insulator (SOI) rib waveguide integrated with a Bragg grating and nickel chromium heating elements has been fabricated. The heaters enable tuning of the Bragg wavelength through a thermo-optic effect. As the temperature is increased, the Bragg wavelength also increases due to the increasing silicon refractive index and effective mode index of the guide. The device is designed so that an additional processing step can remove the buried oxide beneath the grating to form a suspended waveguide. This structure would further decrease the power input required to tune the filter, and would allow the waveguide to buckle at a critical temperature. In this work the un-released structure is fabricated and mounted in a standard dual in-line pin (DIP) package to allow optical and electrical characterization. Test results demonstrating thermo-optic tuning show a 1 nm shift in Bragg wavelength with a power input of 58 mW.

In this paper we excite the surface of porous silicon with incoherent, broad band white light and observe the spectrum of colors reflected from the surface. Using an atomic force microscope images from red and green porous silicon samples are collected. In this paper we relate the optical color of the surface to the size of scattering features on the textured surface. From image segmentation using the watershed transform the height distributions of the optical scattering features are determined. The heights of these surface features are then used as input variables to a computer simulation of a reflective grating. The computer predicted color is compared to the measured color. In this manner, by inspection of the reflected color from the textured porous silicon surface the physical size of the surface features can be estimated.

β-FeSi₂ has been attracting a great deal of attention because of its compatibility with Si-based light-emitting diodes (LEDs). It has also been reported that Β-FeSi₂ thin film undergoes a direct transition with a band gap of about 0.85 eV. However, some authors have reported that β-FeSi₂ has an indirect band gap structure on the basis of several first principles calculations. This difference is thought to be induced by the stress of the β-FeSi₂ interface acting on Si by lattice mismatch, which affects the band structure of the β-FeSi₂ thin film. To investigate the effect, we evaluated the optical properties of β-FeSi₂ grown on lattice matched Si (001) substrate 8°off toward the <110> direction. All samples were formed by depositing Fe on the Si substrate to grow β-FeSi₂ thin film by electron beam deposition. From Raman measurements, it was observed that the samples prepared on inclined substrate shifted to higher wave numbers. From the optical absorption measurement, we observed that the band structure was changed by the Si off substrate. Additionally, the PL intensity at about 0.8 eV for the samples grown on the Si off substrate was increased.

It is now established that defects introduced via ion implantation may act as generating centers in silicon waveguide structures and consequently enhance photosensitivity at wavelengths in the region of 1550 nm. Although several integrated p-i-n waveguide photodiode structures have been presented which exploit this behavior, no attempt has been made to model the generation process and thus optimize device design. We report a model that has been implemented using SILVACO's ATLAS software, and reproduces the observed behavior in the aforementioned device structures. By varying parameters such as the dimensions of the device and the implantation conditions, the responsivity can be maximized. In particular, we have designed an integrated structure centered on a 3 µm wide waveguide created by the LOCOS (Local Oxidation of Silicon) technique on lightly p-doped Silicon-on-Insulator. A self aligned n+ polysilicon contact is placed above the ridge, causing the majority of the depletion to overlap with the optical mode. Symmetric p+ regions are placed on either side of the waveguide, separated by a distance selected to optimize responsivity without causing excess loss. This presents a vast improvement over previous structures of its size, having a predicted responsivity in excess of 50 mA/W at a 2V reverse bias.