In this work, we demonstrated a practical means to construct wafer-level optical interconnects in commercial BiCMOS electronics. Through modifying the layout and design of commercially available SiGe Heterojunction Bipolar Transistors (HBT) through MOSIS^TM foundry, we obtained high performance SiGe Heterojunction Phototransistors (HPT) that utilize the SiGe Base and Collector junction for photo-detection and the transistor action for the amplified photocurrent. Responsivities of 2.4A/W and 0.2A/W were achieved for the phototransistor detecting light of 850nm and 1060nm, respectively. The external quantum efficiency of 350% was obtained. The photocurrent gain was shown to be 78. Furthermore, we investigated the integration of optical waveguides and elements with the SiGe commercial platform to demonstrate an effective approach of the wafer-level optical interconnects. The leaky-mode waveguide routed on the chip surface can couple the light laterally from the input fiber to the buried photodetection region. A 20% coupling efficiency is obtained in the SiGe layer, and provides a response about 40 times higher than that of the vertical illumination. The integrated on-chip waveguides and photodetectors in the commercial platform offer efficient optical-to-electrical conversion and a low-loss routing scheme useful for on-chip computational architectures.

The increasing complexity of silicon integrated circuits are making global interconnects more difficult to achieve. It is predicted that, even at the high clock rates envisaged in future generations of chips, the propagation delays across the whole chip will amount to multiples of the clock period. Clock distribution and data transfer via optical waveguides offer a solution to this global interconnect problem. This paper examines the optical waveguide structures that would be suitable for these applications.

The present paper describes Si microphotonics and its current status of electronics and photonics convergence on Si platform based on monolithic integration using CMOS (Complementary Metal Oxide Semiconductor) technologies. The Si CMOS platform is advantageous over III-V semiconductor based platform because of a short time-lag between basic research and commercialization in terms of the standardized materials and processes. To implement photonic devices on the Si CMOS platform, it is important to reduce materials diversity in current photonics devices. Low loss SiNx waveguides with sharp bends, high performance strained Ge photodetectors for C+L band, and demultiplexer/multiplexer for WDM (wavelength division multiplexing) have been successfully implemented on the Si CMOS platform. The current targets are cost-effective OADMs (optical add-drop multiplexers) for optical communication and optical clocking for Si LSIs beyond Cu-low k technologies.

A prototype Silicon CMOS Optical Integrated Circuit (Si CMOS OEIC) was designed and simulated using standard 0.8 micron Bi-CMOS silicon integrated circuit technology. The circuit consisted of an integrated silicon light emitting source, an optical wave-guiding structure, two integrated optical detectors and two high-gain CMOS transimpedance analogue amplifiers. Simulations with MicroSim PSpice software predict a utilizable bandwidth capability of up to 220 MHz for the trans-impedance amplifier for detected photo-currents at the input of the amplifier in the range of 1 nA to 100 nA and driving a 10mV to 1 V signal into a 100 kΩ load. First iteration OEIC structures were realised in 1.2 micron CMOS technology for various source-waveguide-detector arrangements. Current signal ranging from 1nA to 1 micro-amp was detected at detectors. The technology seems favorable for first-iteration implementation for digital communications on chip up to 200Mbps.

We present design, fabrication, and testing of a high-speed all-silicon optical phase modulator in silicon-on-insulator (SOI). The optical modulator is based on a novel silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. We show that, under the accumulation condition, the drive voltage induced charge density change in the silicon waveguide having a MOS capacitor can be used to modulate the phase of the optical mode due to the free-carrier plasma dispersion effect. We experimentally determined the phase modulation efficiency of the individual phase shifter and compared measurements with simulations. A good agreement between theory and experiment was obtained for various phase shifter lengths. We also characterized both the low- and high-frequency performance of the integrated Mach-Zehnder interferometer (MZI) modulator. For a MZI device containing two identical phase shifters of 10 mm, we obtained a DC extinction ratio above 16 dB. For a MZI modulator containing a single-phase shifter of 2.5 mm in one of the two arms, the frequency dependence of the optical response was obtained by a small signal measurement. A 3-dB bandwidth exceeding 1 GHz was demonstrated. This modulation frequency is two orders of magnitude higher than has been demonstrated in any silicon modulators based on current injection in SOI.

This paper describes methods to control and manipulate birefringence in SiliconOxyNitride waveguides and devices. Each method is demonstrated by measurements on example devices. The methods and devices that will be covered are: Reduction of heater induced birefringence in a dynamic gain equalizer by heater design or etched trenches. Reduction of polarization mode dispersion in a tunable dispersion compensator by UV trimming of residual waveguide birefringence. Polarization conversion using integrated optical half-wave-plates, fabricated by etching trenches at one side of a waveguide. Polarization splitting using waveguide sections with specified birefringence, obtained by etched trenches at both sides of the waveguide.

We show that stress engineering can be used to adjust the SOI waveguide birefringence to the stringent polarization tolerances expected of commercial devices, using only standard silicon processes. With decreasing device dimensions and high index contrast the waveguide birefringence becomes increasingly sensitive to device geometry. As a result, it is almost impossible to eliminate waveguide birefringence by adjusting waveguide profile alone. This paper presents, for the first time, a systematic study of the stress-induced birefringence of SOI waveguides. Through full-vectorial finite-element simulations, we investigate the variation of stress-induced birefringence with waveguide core and cladding geometries. It is found that the stress-induced birefringence is determined by the waveguide cross-section, the upper cladding layer thickness, and film stress levels. We develop a waveguide model that predicts the total waveguide birefringence and guides the post-fabrication processing steps. An experimental demonstration of a polarization insensitive SOI arrayed waveguide grating (AWG) demultiplexer is presented. The polarization dependent wavelength shifts measured experimentally agree well with the simulations.

In an effort to determine low-cost alternatives for components currently used in DWDM, optical ring resonators are currently being investigated. The well-known microfabrication techniques of silicon, coupled with the low propagation loss of single crystal silicon, make SOI an attractive material. Laterally coupled racetrack resonators utilising rib waveguides have been fabricated and preliminary results are discussed. An extinction ratio of 15.9 dB and a finesse of 11 have been measured.

There is a trend in photonic circuits to move to smaller device dimensions for improved cost efficiency and device performance. However, the trend also comes at some cost to performance, notably in the polarisation dependence of the circuits, the difficulty in coupling to the circuits, and in some cases, in increased device complexity. This paper discusses a range of Silicon-on-Insulator (SOI) based optical devices, and the advantages and disadvantages in moving to smaller waveguide dimensions. In particular optical phase modulators based upon the plasma dispersion effect and ring resonators are considered, together with a device for coupling to small waveguides, the so-called Dual Grating Assisted Directional Coupler (DGADC). The advantages of moving to small dimensions are considered, and some preliminary experimental results are given. In particular, progress of the DGADC is evaluated in the light of promising experimental results.

Xerox Corporation has developed a technology platform for on-chip integration of latching MEMS optical waveguide switches and Planar Light Circuit (PLC) components using a Silicon On Insulator (SOI) based process. To illustrate the current state of this new technology platform, working prototypes of a Reconfigurable Optical Add/Drop Multiplexer (ROADM) and a l-router will be presented along with details of the integrated latching MEMS optical switches. On-chip integration of optical switches and PLCs can greatly reduce the size, manufacturing cost and operating cost of multi-component optical equipment. It is anticipated that low-cost, low-overhead optical network products will accelerate the migration of functions and services from high-cost long-haul markets to price sensitive markets, including networks for metropolitan areas and fiber to the home. Compared to the more common silica-on-silicon PLC technology, the high index of refraction of silicon waveguides created in the SOI device layer enables miniaturization of optical components, thereby increasing yield and decreasing cost projections. The latching SOI MEMS switches feature moving waveguides, and are advantaged across multiple attributes relative to alternative switching technologies, such as thermal optical switches and polymer switches. The SOI process employed was jointly developed under the auspice of the NIST APT program in partnership with Coventor, Corning IntelliSense Corp., and MicroScan Systems to enable fabrication of a broad range of free space and guided wave MicroOptoElectroMechanical Systems (MOEMS).

We show the design, fabrication and testing of micro/nanobiosensor devices based on optical waveguides in a highly sensitive interferometric configuration and by using evanescent wave detection. The devices are fabricated by standard Silicon CMOS microelectronics technology after a precise design for achieving a high sensitivity for biosensing applications. Two integrated Mach-Zehnder interferometric (MZI) devices, using two technologies, have been developed: (a) a MZI Microdevice based on ARROW waveguide (b) a MZI Nanodevice based on TIR waveguide. Direct biosensing with both sensors has been tested, after a specific receptor coupling to the surface device using nanometer scale immobilization techniques. Further integration of the microoptical sensors, the microfluidics, the photodetectors and the CMOS electronics will render in a lab-on-a-chip microsystem.

High surface area mesoporous silicon microcavities are investigated for direct detect optical biosensor applications. Device quality is reported as a function of fabrication parameters. A dilute KOH etch process is utilized to modify the intrinsic 3D microstructure to enable enhanced pore infiltration of large biomolecules. Results suggest that the KOH etch mechanism is a two step process consisting of a fast step where high surface area nanostructures are rapidly removed. This is followed by a slower step where silicon is removed from the pore channel walls. The enzyme, Glutathione-S-Transferase (50kDa), is utilized to probe pore infiltration. Results from a solid phase immobilized enzyme assay support our conclusions on the impact the KOH etch step has on modifying the porous silicon microstructure. Preliminary findings point to trade-offs that exists between optimizing microstructure with microcavity operation mode and device sensitivity.

We describe a new method for doping high-quality porous silicon microcavities with erbium using ion implantation, where the erbium is confined to the spacer layer of the structure. This method involves fabricating porous silicon microcavities from a crystalline silicon wafer that has been implanted with erbium to a depth that coincides with a spacer layer of the microcavity. Using this technique erbium doped microcavities with Q-factors in excess of 1500 have been demonstrated. From low temperature photoluminescence measurements we observe a strong modification of the spontaneous emission spectrum of the erbium doped PSi, where the emission is enhanced 25 times at the resonance and suppressed elsewhere. Temperature dependent photoluminescence exhibited strong thermal quenching and excitation power dependent photoluminescence measurement showed saturation at high excitation powers. Both of these trends are characteristically similar to luminescent erbium centres in crystalline silicon. In addition we discuss the merits of localising the erbium in the crystalline part of the PSi and its potential for reducing the effects of Auger recombination and energy back-transfer, which limit the performance of the structures at room high temperatures.

The area of integrated optical circuits has been undergoing rapid development due to the important applications of fiber communication systems and optical interconnects. A significant challenge of photonic circuits is to increase circuit density and to miniaturize these devices. The vertical integration of stacked waveguides for photonic circuits onto a single substrate is a promising configuration to enable the dense monolithic integration of three-dimensional photonic devices. Application of high-index-contrast waveguides, such as silicon-on-insulator waveguides, is another important way to increase the density of optical circuits due to their small sizes. These waveguides produce high confinement in the guiding layers and have the advantages of compactness and immunity of cross-talk between different waveguides. It is thus expected that efficient coupling of light between vertically integrated waveguides where no direct field-overlap of guided modes exists is a key issue. We propose a compact double-grating coupler to realize efficient coupling through radiation modes between two vertically stacked SOI waveguides. The grating is strong enough to be considered as a onedimensional photonic bandgap structure which facilitates a very short coupling length. Simulations suggest that a 22% efficiency is achievable in coupling light from one waveguide to another with a 12.9μm long grating. We find that the coupling efficiency is enhanced by Fabry-Perot resonance between two gratings. Coupling efficiency can be dramatically increased by incorporating a reflective under-layer structure or using blazed grating.

The RF-propagation characteristics of the Metal-Insulator-Semiconductor (MIS) type microstrip line, such as effective index (or slowing factor) and attenuation, show large variation with optically generated carrier concentration and frequency. For a typical MIS line on silicon substrate of dielectric constant 11.8 and thickness 190μm with an insulating (SiO₂) layer of thickness 0.3μm and dielectric constant 4.5, the effective index varies from 3.43 under no illumination to 53 under large illumination. Hence, the propagation of narrow pulses through such lines forms an interesting study. We studied the effect of illumination on the propagation of a Gaussian pulse of unit amplitude through such a 10mm line. The propagation delay can be varied from 0.1ns to a maximum value of 1.6ns by controlled optical illumination. Dispersion and attenuation result in pulse distortion and reduced amplitude with propagation. We also obtained analytical expressions for pulse delay and amplitude of a Gaussian pulse modulated on a carrier of frequency 1GHz for propagation in such a line where both effective index and attenuation are frequency dependant. The analysis concludes that a true time delay can be obtained at microwave frequencies by optical control of a MIS line on silicon.

Dielectric microspheres are used to resonantly couple light from a half optical fiber coupler to a silicon photodetector. Dielectric microspheres posses high quality factor morphology dependent resonances, i.e., whispering gallery modes. The observed resonances have a channel spacing of 0.14 nm and a linewidth of 0.06 nm. These resonances provide the necessary narrow linewidths, that are needed for high resolution optical spectroscopy applications. Optical communication and biological detection applications of this optoelectronic system are studied experimentally and theoretically.

Complementary metal-oxide-semiconductor-compatible tunable Fabry-Perot microcavities filled with liquid crystals (LCs) were realized and studied in the near-infrared region. The microcavities were produced by chip bonding technique, which allows one to infill LC between two [SiO₂/Si]n λ/4 (λ = 1.5 μm) Dielectric Bragg Reflectors separated by 950 nm thick SiO₂ posts. The Dielectric Bragg reflectors were realized on Si or SiO₂ substrates Liquid crystals with positive and negative dielectric anisotropy were used, i.e. MerckE7 (Δε=13.8) and Merck-6608 LC (Δε=-4.2). Mirror-integrated electrodes allow an external bias to induce an electrical field and to tune the LC properties and, hence, the microcavity resonance. Electric-field-induced shifts of the second-order cavity modes of ~120 nm and ~50 nm were obtained for Merck-E7 and Merck-6608 LC, with driving potentials of 5 V and 10 V, respectively. The transmittance at the cavity resonance is typically in the order of 10%. Simulation of cavities allows to identify surface roughness of the Dielectric-Bragg-Reflectors as the major origin of the transmission losses. The switching behavior of microcavities filled with E7 were studied as function of applied fields. Both switch-on t_on and switch-off t_off times were measured and were found to be lower than 5 ms.

Photoluminescence and electroluminescence of boron and phosphorus implanted silicon have been studied as a function of temperature. Phosphorus implantation is found to have a similar effect on light emission as boron implantation. An increase of the band-to-band luminescence intensity by one order of magnitude is observed upon rising the temperature from 80 K to 300 K. Defect luminescence arising from the implanted layer is found only at low temperatures. The remarkable band-to-band luminescence is attributed to a high Shockley-Read-Hall lifetime caused by the gettering action of implantation defects.