This PDF file contains the front matter associated with SPIE Proceedings Volume 6477, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

While investment in sub-wavelength silicon photonics research has gained popularity, Kotura has forged significant customer traction with first generation silicon-photonics products by focusing on manufacturable designs and processes. This paper reviews recent gains in engineering developments where mature monolithic and hybrid methods are integrated to form high-performance manufacturable products with proven long-term reliability. Components and methods are described that lead to photonic modules and subsystems suitable for automated manufacturing techniques.

Highly-efficient, low-voltage organic light emitting diodes (OLEDs) are well suitable for post-processing integration onto the top metal layer of CMOS devices. This has been proven for OLED microdisplays so far. Moreover, OLEDon- CMOS technology may also be excellently suitable for various optoelectronic sensor applications by combining highly efficient emitters, use of low-cost materials and cost-effective manufacturing together with silicon-inherent photodetectors and CMOS circuitry. The use of OLEDs on CMOS substrates requires a top-emitting, low-voltage and highly efficient OLED structure. By reducing the operating voltage for the OLED below 5V, the costs for the CMOS process can be reduced, because a process without high-voltage option can be used. Red, orange, white, green and blue OLED-stacks with doped charge transport layers were prepared on different dualmetal layer CMOS test substrates without active transistor area. Afterwards, the different devices were measured and compared with respect to their performance (current, luminance, voltage, luminance dependence on viewing angle, optical outcoupling etc.). Low operating voltages of 2.4V at 100cd/m² for the red p-i-n type phosphorescent emitting OLED stack, 2.5V at 100cd/m² for the orange phosphorescent emitting OLED stack and 3.2V at 100cd/m² for the white fluorescent emitting OLED have been achieved here. Therefore, those OLED stacks are suitable for use in a CMOS process even within a regular 5V process option. Moreover, the operating voltage achieved so far is expected to be reduced further when using different top electrode materials. Integrating such OLEDs on a CMOS-substrate provide a preferable choice for silicon-based optical microsystems targeted towards optoelectronic sensor applications, as there are integrated light barriers, optocouplers, or lab-onchip devices.

Among the major challenges confronting the current initiatives to incorporate optical interconnect capabilities for chip to chip I/O is to define, develop and implement the necessary components required for a complete pipeline from source to receiver. For next generation integrated circuits, the need for multifunctionality and multidimensional integration has resulted in new demands on interface technology to yield massively parallel data and clock lines. At this point, such methods are primarily limited to static reflectors, filters and gratings for interface and optical routing. One of the crucial elements is to develop a high performance and flexible optical network to transform an incoming optical pulse train into a widely distributed set of optical signals whose direction, alignment and power can be independently controlled. This coupling can be achieved using several methods including active (primarily, MEMS-based) beam steering arrays. For chip to chip applications, the overwhelming majority of the recent research and development effort has been focused on source and detector technologies, but less attention has been devoted to flexible, reconfigurable beam steering modalities. A variety of approaches for such beam steering and distribution of both timing and data lines has been examined. This paper will present an overview of active, silicon components under development at the College of Nanoscale Science and Engineering for arraybased I/O management with an emphasis on reconfigurable diffractive devices and adjustable, porous silicon- based components which combine optical beam steering, filtering and focusing capabilities. Design details along with initial performance data from prototype components will be presented.

Silicon-based, monolithically-integrated optical receivers offer the potential of lowering the cost of optical interconnects through simplified packaging and leveraging established Si-manufacturing technology, in addition to enabling new applications such as inter- and intra-chip optical links that will require large-scale receiver arrays. Silicon photodetectors have progressed, and integrated receivers have been demonstrated to operate above 10 Gb/s; however, the poor efficiency of silicon in detecting 850-nm light results in fundamental tradeoffs in performance and/or operating voltage. In contrast, using Ge as the detector material opens the possibility of producing fast, efficient, and low-voltage photodiodes compatible with CMOS processing. We have fabricated planar, interdigitated Ge-on-SOI photodiodes in Ge absorption layers grown directly on SOI wafers. Devices with 10 x 10 μm² square active areas, biased at -2 V, with an electrode spacing of 0.6 to 0.8 μm, exhibit dark currents less than 10 nA, bandwidths in excess of 23 GHz, and external quantum efficiencies of 52 % (0.35 A/W) at a wavelength of 850 nm. We have built and characterized three different optical receivers using 0.13-μm CMOS ICs: 1) a 15-Gb/s high-gain full receiver (transimpedance amplifier, limiting amplifier, and output driver); 2) a 10-Gb/s, low-power full receiver (powered by a single 1.1-V supply); 3) a 19-Gb/s high-speed receiver front-end (transimpedance amplifier only). These receivers achieve the highest operating speed, highest sensitivity at > 10 Gb/s rates, lowest-voltage single-supply operation, and lowest power consumption for any all-silicon-based receivers reported to-date, and illustrate the performance that can be attained through combining Ge detectors with CMOS analog circuitry.

This paper reports on fabrication and characterization of two kinds of photodetectors: interdigited metal-germanium on silicon-metal photodetectors (Metal-Semiconductor-Metal or MSM) and pin germanium photodiodes for operation at optical telecommunication wavelengths. For both 1.31 micron and 1.55 micron wavelengths, the measured -3dB bandwidth of interdigited MSM photodetectors is 35 GHz under 2V bias for electrode spacing equal to 0.5 micron. For pin diodes at 1.55 micron wavelength, the measured -3dB bandwidth under -3V bias ranges from 9 to 29 GHz for mesa diameters from 20 to 7 microns, respectively.

A monolithically integrated, high speed optical front-end for optical sensing application in standard 0.35-micron CMOS technology is reported. The proposed receiver consists of an integrated photodiode, a transimpedance amplifier, a mixer, an IF amplifier and an output buffer. By treating the n-well in standard CMOS technology as a screening terminal to block the slow photo-generated bulk carriers and interdigitizing shallow p^- junctions as the active region, the integrated photodiode operates up to several gigahertz with no process modification. With multi-inductive-series peaking technique, the improved regulated cascade (RGC) transimpedance amplifier achieves an experimentally measured -3 dB bandwidth of more than 6 GHz and a transimpedance gain of 51 dB(omega), which is the fastest reported TIA in CMOS 0.35-micron technology. The 5 GHz broadband mixer produces a conversion gain of 13 dB which greatly minimizes the noise contribution from the IF amplification stage. The optical front-end of the active pixel demonstrates a -3 dB bandwidth of 4.9 GHz while consuming a current of 40 mA from 3.3 V power supply. This work presents the highest bandwidth for fully integrated CMOS optical receivers reported to date.

Silicon photonic-wire waveguide is one of the most promising platforms in constructing compact optical devices, since the waveguide can be bent with a radius of less then several microns. Recently, we have demonstrated various optical devices based on silicon photonic-wire waveguides, which include a directional coupler, a tunable optical add-drop multiplexer, and some ultra-compact 1 x N optical switches. The optical coupling length of the directional coupler was just around 10 microns, due to its high coupling efficiency. The tunable optical add-drop multiplexer was constructed with Bragg grating waveguides. It was about 700-μm-long, and was controlled through thermo-optic effect. The maximum center-wavelength shift of the tunable optical add-drop multiplexer was 6.6 nm, which was obtained at a tuning power of 0.82 W. The 1 x N optical switches were Mach-Zehnder interferometer types and were also thermally controlled. The 1 x 2 switch was compact with a footprint of 85 x 30 µm2. Its maximum extinction ratio exceeded 30 dB. The switching power and switching time was about 90 mW and 100 μsec, respectively. The 1 x 4 optical switch was constructed based on the 1 x 2 switch. Its operation was successfully demonstrated. The 1 x 4 optical switch was believed to be the smallest switch in the world. A 1 x 8 optical switch was also demonstrated with its switching operations. Further, we are fabricating a compact packaged switch module with a size of 15 x 8 x 5 (height) mm³, which includes a 1 x 4 optical switch and the input and output fiber couplers assembly.

Silicon-on-Insulator (SOI) has emerged as promising material choice for various integrated optoelectronic devices. Two issues make SOI attractive for complex optical systems: the cost reduction due to compatibility with CMOS technology and high refractive index contrast between core and cladding, which is an important property for good confinement of light and efficient guiding and coupling in sub-micron waveguides. However, for those devices that are intended to be part of broadband optical networks, for example multiplexers and de-multiplexers, it is desirable to demonstrate a high selectivity and a tunable response. Thus, it is necessary to provide wavelength selective elements with the ability to filter input data streams producing a large Free Spectral Range (FSR), a small Full Width at Half Maximum (FWHM), and a high quality factor (Q), all conditions set by communication standards. Owing to the generic and adaptable operation, ring-resonator-types of filters in SOI are often considered as candidates to meet these demands. Herein two different designs are investigated from both experimental and modelling standpoints in order to tailor the filter transfer function. These are mutually coupled (Vernier) resonators and cascaded resonators based on small SOI photonic wires. Fabricated filters designed to provide a large FSR and a polarisation independent (PI) response are analysed and improvements proposed. Issues associated with temperature control of the transfer function have also been addressed.

Microspheres possess high quality factor morphology-dependent resonances, i.e., whispering gallery modes. These whispering gallery modes can be used in resonant cavity enhanced applications of optoelectronic devices such as, filters, detector, modulators and switches. Feasibility of silicon microsphere device at Mid-IR frequencies is studied. The high quality factor morphology dependent resonances have repetitive channel separations of 0.124 μm in silicon microspheres with a radius of 50 microns at wavelengths between 9.8 μm and 10.6 μm.

We review the design considerations and experimental results of a novel design of polarization insensitive ring resonators in silicon-on-insulator (SOI) ridge waveguides. The polarization insensitive coupling is achieved using a multi-mode-interference (MMI) coupler. Cladding stress-induced birefringence is used to correct the round trip phase difference between the TE and TM polarizations. Experimental demonstration is presented for such ring resonators fabricated on SOI with 1.5 ?m Si waveguide core layer. For resonators with radius R = 200 ?m, polarization insensitive operation is achieved in both the resonance wavelength and linewidth over a ~ 4 nm wavelength range using a 7.5 ?m × 84 ?m MMI coupler and 0.8 ?m thick oxide cladding with -250 MPa stress, with the resonance wavelength shifts between TE and TM polarizations less than 3 pm. The quality factor Q of ~ 15,000 and free-spectral range (FSR) of 0.46 nm is measured. For resonators with a smaller radius of 50 ?m, similar FRS of 1.3 nm and extinction of 13 dB are observed for TE and TM, although the resonance wavelengths are shifted, in agreement with the theoretical prediction. By choosing the proper combination of the cladding stress and thickness, zero-birefringence condition can be achieved for resonators of different cavity lengths.

In this paper we report two novel fabrication techniques for silicon photonic circuits and devices. The techniques are sufficiently flexible to enable waveguides and devices to be developed for telecommunications wavelengths or indeed other wavelength ranges due to the inherent high resolution of the fabrication tools. Therefore the techniques are suitable for a wide range of applications. In the paper we discuss the outline fabrication processes, and discuss how they compare to conventional processing. We compare ease of fabrication, as well as the quality of the devices produced in preliminary experimental fabrication results. We also discuss preliminary optical results from fabricated waveguide devices, as measured by conventional means. In these preliminary results we discuss fundamental properties of the waveguides such as loss and spectral characteristics, as it is these fundamental characteristics that will determine the viability of the techniques. Issues such as the origins of the loss are discussed in general terms, as resulting fabrication characteristics such as waveguide surface roughness (and hence loss), or waveguide profile and dimensions may be traded off against cost of production for some applications. We also propose further work that will help to establish the potential of the technique for future applications.

Recent deployments of fiber-to-the-home (FTTH) represent the fastest growing sector of the telecommunication industry. The emergence of the silicon-on-insulator (SOI) photonics presents an opportunity to exploit the wide availability of silicon foundries and high-quality low-cost substrates for addressing the FTTH market. We have now demonstrated that a monolithically integrated FTTH demultiplexer can be built using the SOI platform. The SOI filter comprises a monolithically integrated planar reflective grating and a multi-stage Mach-Zehnder interferometer that were fabricated using a CMOS-compatible SOI process with the core thickness of 3.0 ?m and optically insulating layer of silica with a thickness of 0.375 ?m. The Mach-Zehnder interferometer was used to coarsely separate the 1310 nm channel from 1490 and 1550 nm channels. Subsequently, a planar reflective grating was used to demultiplex the 1490 and 1550 nm channels. The manufactured device showed the 1-dB bandwidth of 110 nm for the 1310 nm channel. For the 1490 nm and 1550 nm channels, the 1-dB bandwidth was measured to be 30 nm. The adjacent channel isolation between the 1490 nm and 1550 nm channels was better than 32 dB. The optical isolation between the 1310 nm and 1490 and 1550 nm channels was better than 45 dB. Applications of the planar reflective gratings in the FTTH networks are discussed.

Waveguide birefringence almost always exists, except for cases where the two orthogonally polarized modes are incidentally degenerate. Birefringence is in general undesirable as it causes an unwanted polarization dependent phase shift and wavelength shift in all interferometric devices such as spectrometers, Mach-Zehnder interferometers, and ring resonators. The birefringence due to the waveguide core geometry in high-index-contrast material systems such as silicon-on-insulator can significantly increase with decreasing core dimensions. One solution is to separate the two orthogonally polarized TE and TM components of the optical signal and process them individually. Waveguide polarization splitters/filters are the key elements in this polarization diversity approach. In this work, novel passive polarization splitters/filters in the SOI platform using a geometrically balanced Mach- Zehnder interferometer configuration are demonstrated experimentally. Polarization splitting/filtering functions are achieved by modifying the birefringence in one arm of the interferometer using a stressed cladding film. Only one additional fabrication step is required for patterning a stressed cladding film on top of the silicon ridge waveguides. A broadband polarization splitting performance was observed with an average extinction ratio of 10 dB in each of the output ports over the entire C-Band from 1530 to 1565nm. The device size is 2.5 mm x 16 μm. This work represents the first reported use of stress engineering for making SOI polarization splitters/filters.

In this paper, the design of effective microprism based on the subwavelength periodic lattices is proposed. The microprism is realized by using a two-dimensional photonic crystal (PhC) structure with a periodic lattice of air-holes. In order to behave as a homogeneous and isotropic microprism, the PhC structure with a hexagonal lattice should be operated in the low frequency. By monolithically integrating the effective microprism in the bending area of an optical waveguide, its wavefront of eigenmode could be tilted correctly to suppress the radiation loss in wide-angle bent waveguides. In order to demonstrate the feasibility of proposed microprism for low-index-contrast waveguides, an example of bent waveguide with the eigenmode nearly compatible to the single mode fiber is adopted to design the PhC microprism. The transmission efficiency as high as 92% for the proposed structure with the bending angle of 12.96° and the bending radius of 89.09 μm is achieved.

Silicon-on-insulator (SOI) is a widely recognized as a very promising material for high-index integrated photonic chips because of its compatibility with complementary metal oxide semiconductor (CMOS) technologies. One challenge in integrating many photonic devices on a single chip is to realize compact waveguide bends and splitters, particularly for rib waveguide geometries. We report compact SOI rib waveguide 90° bends and splitters with SU8-filled trenches based on total internal reflection (TIR). We use the two-dimensional finite difference time domain (2D-FDTD) method to numerically calculate bend and splitter efficiencies. The maximum bend efficiency is 98.0%. The splitter efficiency is 49.0% for transmission and 48.9% for reflection with an 80 nm wide SU8-filled trench. Electron beam lithography (EBL) is used to accurately position the trench interface relative to the waveguides and to pattern the 80 nm wide trench. Inductively coupled plasma reactive ion etching (ICP RIE) is used to achieve a vertical sidewall. For fabricated bends the measured bend loss is 0.32±0.02 dB/bend (93% bend efficiency) for TE polarization at a wavelength of 1.55 microns, which is the lowest SOI rib waveguide 90° bend loss reported in literature. The initial measured splitter efficiency is 54.6% for transmission and 29.2% for reflection. This can be improved by avoiding defects in fabricated structures.

We describe a novel non-destructive technique to measure the sidewall roughness induced scattering loss of SOI ridge waveguides using an integrated 5x17 star coupler. The accuracy of our technique is independent of the coupling efficiency. In our technique, we capture the near field images of the full output waveguides array with varying width ranging from 0.2 to 2.0 micron and use the intensity maps of these images to produce normalized intensity profiles, from which the relative scattering losses of output waveguides are extracted. Using our technique, we have studied and compared the scattering and polarization dependent losses of three different sets of SOI waveguide samples fabricated by different processes. We have determined the root-mean-square roughness and autocorrelation length of these samples using scanning electron microscopy (SEM). Relating the loss and roughness analysis, we have showed that the process utilizing negative e-beam photoresist and Cr-hardmask with inductively coupled plasma (ICP) etching produced the smoothest waveguide sidewalls and lowest scattering losses. We have also successfully modeled the measured ridge waveguide losses as a function of waveguide width and demonstrated that the theoretical sidewall roughness is in reasonable agreement with the measured roughness from SEM. Our technique is capable of studying roughness induced scattering loss and thus provides an efficient way of optimizing and monitoring process parameters that affect sidewall roughness.

In this paper, the guide-mode resonance (GMR) devices based on a suspended membrane structure is designed and experimentally demonstrated. The presented membrane structure possesses a simple structure for resonance excitation and is capable of improving the spectral response. The results of resonance excitation, improving the sideband and low oscillatory spectrum are presented. Due to the utilization of silicon-based materials, the proposed filter is also potential candidates to be integrated with other optoelectronic devices for further applications.

The Local Oxidation of Silicon (LOCOS) technique is used to define optical rib waveguides in silicon-on-insulator (SOI) material. This process, commonly used for device isolation in purely microelectronic CMOS processes, results in a nearly planar surface suitable for integrating optical and electronic components on the same chip. Optical mode simulation was used to determine rib geometries suitable for single-mode propagation and minimizing birefringence in the 1550 nm optical telecommunications band. Test devices were then fabricated in SOI material with a Si film thickness near 3 microns. Growth of a 1 micron field oxide by wet oxidation yielded a 0.5 micron rib height. As-drawn rib widths ranged from 3 microns to 5 microns, giving final rib widths ranging from 2 microns to 4 microns after oxidation. Cutback optical testing of 3 microns drawn width ribs showed the loss to be less than 1 dB/cm at 1555 nm. Unbalanced Mach-Zehnder interferometers with Y-splitter junctions were also fabricated and tested with input wavelength swept from 1470 to 1580 nm and showed an extinction of 6-10 dB, demonstrating the ability of the LOCOS rib technique to produce more complex waveguide devices.

While many parallel computers have been built, it has generally been too difficult to program them. Now, all computers are effectively becoming parallel machines. Biannual doubling in the number of cores on a single chip, or faster, over the coming decade is planned by most computer vendors. Thus, the parallel programming problem is becoming more critical. The only known solution to the parallel programming problem in the theory of computer science is through a parallel algorithmic theory called PRAM. Unfortunately, some of the PRAM theory assumptions regarding the bandwidth between processors and memories did not properly reflect a parallel computer that could be built in previous decades. Reaching memories, or other processors in a multi-processor organization, required off-chip connections through pins on the boundary of each electric chip. Using the number of transistors that is becoming available on chip, on-chip architectures that adequately support the PRAM are becoming possible. However, the bandwidth of off-chip connections remains insufficient and the latency remains too high. This creates a bottleneck at the boundary of the chip for a PRAM-On-Chip architecture. This also prevents scalability to larger "supercomputing" organizations spanning across many processing chips that can handle massive amounts of data. Instead of connections through pins and wires, power-efficient CMOS-compatible on-chip conversion to plasmonic nanowaveguides is introduced for improved latency and bandwidth. Proper incorporation of our ideas offer exciting avenues to resolving the parallel programming problem, and an alternative way for building faster, more useable and much more compact supercomputers.

This paper will briefly outline the technology related to CMOS photonics, and will then discuss systems design aspects and experimental results from the construction of a 4 wavelength WDM transceiver with each channel running at 10Gbps. Optics including mux/demux, modulation and optical monitoring taps were monolithically integrated into the 0.13 micron CMOS die, alongside the PMD circuitry used for modulator drivers and receiver amplification. A BER of 10^-12 was achieved on all 4 channels.

Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse trains that show jitter on the level of a few femtoseconds over tens of milliseconds and over seconds if referenced to atomic frequency standards. These low jitter sources can be used to perform opto-electronic analog to digital conversion that overcomes the bottleneck set by electronic jitter when using purely electronic sampling circuits and techniques. Electronic Photonic Integrated Circuits (EPICs) may enable in the near future to integrate such an opto-electronic analog-to-digital converters (ADCs) completely. This presentation will give an overview of integrated optical devices such as low jitter lasers, electro-optical modulators, Si-based filter banks, and high-speed Si-photodetectors that are compatible with standard CMOS processing and which are necessary for the implementation of EPIC-chips for advanced opto-electronic ADCs.

The complete integration of photonic devices into a CMOS process flow will enable low cost photonic functionality within electronic circuits. BAE Systems, Lucent Technologies, Massachusetts Institute of Technology, Cornell University, and Applied Wave Research are participating in a high payoff research and development program for the Microsystems Technology Office (MTO) of DARPA. The goal of the program is the development of technologies and design tools necessary to fabricate an application specific, electronic-photonic integrated circuit (AS-EPIC). The first phase of the program was dedicated to photonics device designs, CMOS process flow integration, and basic electronic functionality. We will present the latest results on the performance of waveguide integrated detectors, and tunable optical filters.

We report on an increase in emission intensity of up to 10 nW / microns² that has been realized with a new novel two junction, diagonal avalanche control and minority carrier injection silicon CMOS light emitting device. The device utilizes a four terminal configuration with two shallow n⁺p junctions, embedded in a p substrate. One junction is kept in deep avalanche and light emitting mode, while the other junction is forward biased and minority carrier electrons are injected into the avalanching junction. The device has been realized using standard 0.35 micron CMOS design rules and fabrication technology and operates at 9V in the current range 0.1 - 3mA. The optical emission intensity is anout two orders higher than that for previous single junction n⁺ p light emitting junctions. The optical output is about three orders higher than the low frequency detectivity limit of silicon p-i-n detectors of comparable dimensions. The realized characteristics may enable diverse opto-electronic applications in standard CMOS silicon technology based integrated circuitry.

1.278μm laser emission has been observed in a SOI structure which has been nanopatterned to contain an array of nanopores. The optical transition is known to be associated with phononless recombination mediated by the bistable, carbon-related G-center. A physical model is proposed to explain the enhanced optical activity of the G-centers in the presence of the nanopore array. The effects of the SOI, strain, dielectric modification and breaking of phonon k-selection rules on the optical properties of the nanopatterned silicon are addressed. Temperature limitations are discussed.

Ge/SiGe quantum well electroabsorption modulators grown on silicon through relaxed SiGe buffers had shown strong quantum-confined Stark effect (QCSE), even though Ge is an in-direct band gap semiconductor. The absorption characteristic near the direct band gap edge can be tuned by applying an electric field. QCSE is the most efficient optical modulation mechanism through direct light absorption and promising for reducing the device size and power consumption. The device fabrication here is based on Ge-rich SiGe technology, which is also commonly used for various silicon photonics applications. Here we will discuss Ge QCSE electroabsorption modulators as well as the consideration of SiGe process integration for optical interconnects.

We demonstrate methods to enhance electro-optical effect in silicon. In the first method, a tunable PhC device is proposed to consist of the self-guiding region and the tunable region. The tunable lattice is designed such that it has a band gap and the self-guiding frequency is located at its bottom band edge of the conduction band. Therefore, the device output can be tuned by injecting free carriers into the tunable region to slightly reduce its effective index to pull up the band gap. In the second method we design a self-guiding PhC cavity. Using this cavity, we could switch output light on and off with an extinction ratio of 17.5 dB by changing only 1e-3 of the effective refractive index of the silicon background. The third method utilizes a 12-fold symmetric quasi- photonic crytal cavity to enhance electro-optical effect in silicon. The designed cavity supports whispering gallery modes and one of such modes is found to have Q value of 2.3e4.

An ultra-compact silicon Mach-Zehnder interferometer (MZI) modulator featuring p-i-n-diode-embedded photonic crystal waveguides has been fabricated. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density (~10⁴A/cm²) exists for achieving gigahertz modulation in the widely employed p-i-n diode configuration. Electrical simulations have been performed to design and analyze the device. The device interaction length was reduced by one order of magnitude compared to the conventional waveguide based MZI modulators by taking advantage of the slow group velocity exhibited by photonic crystal waveguides (PCWs). A maximum modulation depth of 93% has been obtained under an injected current of 7.1 mA. High-speed optical modulation at 1 Gbit s^-1 in the 1.55 micron wavelength region was experimentally demonstrated. To our knowledge, this is the fastest speed ever achieved for a p-i-n diode based integrated silicon MZI modulator.

High-speed silicon optical modulator is one of key components for integrated silicon photonic chip aiming at Tb/s data transmission for next generation communication networks as well as future high performance computing applications. In this paper we review the recent development of the silicon modulator. In particular, we present a high-speed and highly scalable silicon optical modulator based on the free carrier plasma dispersion effect. The fast refractive index modulation of the device is due to electric-field-induced carrier depletion in a Silicon-on-Insulator waveguide containing a reverse biased pn junction. To achieve high-speed performance, a traveling-wave design is employed to allow co-propagation of electrical and optical signals along the waveguide. We demonstrate high-frequency modulator optical response with 3 dB bandwidth of ~20 GHz and data transmission up to 30 Gb/s. We also highlight the future device optimization for 40 Gb/s and beyond.

Effective carrier lifetimes of Si modulators based upon a lateral p-i-n structure were measured using the reverse-recovery method. Modulators of two different waveguide dimensions were characterized using this approach. Two additional lifetime measurement methods were used to check against this method and showed consistent results. Finally the physical meaning of this measured effective carrier lifetime was discussed in reference to its relationship with the diode transit time, surface recombination velocity and the bulk carrier lifetime.

We report the development and characterization of 2-D photonic crystal (PC) microcavity devices on silicon on insulator. The transmission of light through a 2-D PC microcavity near resonance can be switched on and off by modulating the refractive index of the PC. Because silicon has poor electro-optical properties, it is advantageous to insert electro-optic materials inside the air holes. In this work, we report the design, fabrication, and characterization of such hybrid PC microcavity switches using liquid crystals as the electro-optic material. In addition, we demonstrate an electrode geometry that eliminates electric field screening by the more conducting silicon host, and thus enables switching. fabrication.

The requirement of a precise and controllable reflection interface in total internal reflection type optical switches is widely acknowledged. When these switches are based upon carrier injection such as those fabricated in silicon-oninsulator the ability to set up a precise reflection interface becomes difficult due to the diffusion of carriers. This diffusion of carriers across the reflection interface creates a refractive index gradient which is likely to cause the input light to be imperfectly reflected into the output port, which is obviously less efficient than reflection from a precise interface in terms of loss due to the absorption by the free carriers and the directivity of the reflected wave. In our work we propose the use of a barrier positioned along the reflection interface, and around a completely enclosed injection region to prevent diffusion of carriers, and therefore set up a precise reflection interface. The barrier will also improve the injection efficiency since the carriers are being injected into a much smaller volume. This will, in turn, lead to a reduced switching current and faster switching speeds. This paper reports the modeling of the device and predicts the bandwidth performance for one specific switch design.

In this work we show that integrated silicon hollow core AntiResonant Reflecting Optical Waveguide (ARROW) can be used as a basic tool for the realization of optical sensors. ARROW waveguides, with hollow core, permit to confine the light in a low refractive index liquid core, by means of two cladding layers designed to form a high reflectivity Fabry- Perot antiresonant cavity. This arrangement allows to realize microchannels that can simultaneously act as microfluidic networks and optical waveguides with a strong advantage in the integration and with an increased interaction efficiency between the light and the liquid substance that can be very useful in sensing applications (fluorescence, absorption spectroscopy, etc.). Another ARROW waveguides advantage is the ability to tailor the wavelength response of the device. In fact, the waveguide propagation losses strongly depend on the change of the resonant condition inside the interference cladding. In this paper we report three sensing applications of hollow core ARROW waveguide. A long path absorbance cell for colorimetric protein assay, a high sensitivity integrated refractometer and a micro flow cytometer for cell/particles analysis. The proposed devices have been realized in standard silicon technology by using two silicon wafers bonded together.

The combination of integrated optics and microfluidics in planar optofluidic devices carries the potential for novel compact and ultra-sensitive detection in liquid and gaseous media. Single molecule fluorescence detection sensitivity in planar beam geometry was recently demonstrated in liquid-core antiresonant reflecting optical waveguides (ARROWs) fabricated on a silicon chip. A key component of a fully integrated single-molecule sensor is the addition of an optical filtering capability to separate excitation beams from much weaker generated fluorescence or scattering signals. This capability will eventually allow for integration of the photodetector on the same chip as the optofluidic sensing part. It has been theoretically shown that the wavelength-dependent transmission of liquid-core ARROWs can be tailored to efficiently separate excitation and fluorescence. Here, we present the wavelength dependent transmission of air-core ARROW waveguides, using a highly nonlinear photonic crystal fiber to generate a broadband excitation spectrum, and the design of liquid-core ARROW waveguides with integrated filter function. The air-core waveguide loss shows pronounced wavelength dependence in good agreement with the design, demonstrating the potential of tailoring the optical properties of liquid-core waveguides to accommodate single-molecule sensing on a chip. We also present an ARROW design to produce wavelength-dependent transmission that is optimized for fluorescence resonance energy transfer (FRET) studies with high transmission at 573 nm and 668nm, and low transmission at 546 nm.

Porous silicon is a suitable host material for biosensing applications due to its high surface area to volume ratio, which enables substantial infiltration of biomolecules. Resonant waveguides can be fabricated from porous silicon based on a two layer porous silicon structure. Light is coupled into the waveguide only at a particular angle of incidence. Biomolecular binding inside the pores induces an increase in the effective porous silicon refractive index and causes a change in the angle at which light is coupled into the waveguide. A biosensor for DNA detection based on a porous silicon waveguide has been fabricated. Detection of DNA at concentrations on the level of ~μM is reported. Simulations suggest significantly lower detection levels are possible.

We show that thin silicon-on-insulator (SOI) microphotonic waveguides offer significant advantages over other material platforms for the applications of biological and chemical sensing. The high index contrast inherent to SOI waveguides allow an extremely large yet highly localized electric field to be supported in the evanescent tail of the waveguide mode, ideal for the probing of thin biological layers. Various sensing geometries including Mach-Zehnder interferometers and high quality factor ring resonators have been designed and fabricated and their performance is presented. SOI sensors are shown to be capable of providing higher intrinsic sensitivity over comparable sensor designs reported in all other lower index contrast planar waveguide material systems. Finally, the device design conditions for optimized sensitivity are examined for the sensing of both bulk solutions and thin adsorbed biomolecular layers.

Silicon-on-Insulator (SOI) is a very interesting material system for highly integrated photonic circuits. The high refractive index contrast allows photonic waveguides and waveguide components with submicron dimensions to guide, bend and control light on a very small scale so that various functions can be integrated on a chip. Moreover, SOI offers a flexible platform for integration with surface plasmon based components which in turn allows for even higher levels of miniaturization. Key property of both waveguide types is the mode distribution of the guided modes: a high portion of the light is concentrated outside of the core material, thus making them suitable for sensitive detection of environmental changes. We illustrate chemical and label-free molecular biosensing with SOI microring resonator components. In these microring resonator sensors, the shift of the resonance wavelength is measured. A ring of radius 5 micron is capable of detecting specific biomolecular interaction between the high affinity protein couple avidin/biotin down to a few ng/ml avidin concentration. We describe the integration of surface plasmon waveguides with SOI waveguides and discuss the principle of a highly sensitive and compact surface plasmon interferometric sensor suitable for biosensing. The device is two orders of magnitude smaller than current integrated SPR sensors, and has a highly customizable behavior. We obtain a theoretical limit of detection of 10^-6 RIU for a component of length 10 microns. We address material issues and transduction principles for these types of sensors. Besides in chemical sensors, the SOI microring resonators can also be used in physical sensors. We demonstrate a strain sensor in which the shift of the resonance wavelength is caused by mechanical strain. We have experimentally characterized the strain sensors by performing a bending test

Deflection of a microcantilever caused by any kind of biochemical reaction occurring on its surface can be detected with subangstrom resolution if an appropriate detection technique is exploited. This kind of transducers has become widely used in biological research since a few years ago. Usually, for the readout of the nanomechanical response of the micro beams to bio-specific interactions, a technique similar to one used in the atomic force microscopy is employed. The optical read-out method has some disadvantages, such as low degree of integration and difficulties in work with arrays of cantilevers. In the technique presented in this work the cantilever itself is an optical waveguide butt-coupled with another one. The device is fabricated as an array of 20 waveguide cantilever channels which allows for higher integration level. The analysis of the capabilities of the device, the problems associated with the design and the fabrication of the device, the choice of the material and the technology for the fabrication of very flat cantilevers have been successfully addressed. The characterisation of the device was done, showing that the resolution of the device is comparable with the one using the optical lever read-out. Results of the simulations and experimental data on the optical cantilevers coated with an absorbent material will be presented. The choice of the appropriate thickness of the absorbent material on the cantilever surface allows for acceptable losses, for single mode behaviour and adjustment of the initial displacement of the cantilever.

In order to solve the drawbacks of sensitivity and portability in optical biosensors we have developed ultrasensitive and miniaturized photonic silicon sensors able to be integrated in a "lab-on-a-chip" microsystem platform. The sensors are integrated Mach-Zehnder interferometers based on TIR optical waveguides (Si/SiO₂/Si₃N₄) of micro/nanodimensions. We have applied this biosensor for DNA testing and for detection of single nucleotide polymorphisms at BRCA-1 gene, involved in breast cancer development, without target labeling. The oligonucleotide probe is immobilized by covalent attachment to the sensor surface through silanization procedures. The hybridization was performed for different DNA target concentrations showing a lowest detection limit at 10 pM. Additionally, we have detected the hybridization of different concentrations of DNA target with two mismatching bases corresponding to a mutation of the BRCA-1 gene. Following the way of the lab-on-a-chip microsystem, integration with the microfluidics has been achieved by using a novel fabrication method of 3-D embedded microchannels using the polymer SU-8 as structural material. The optofluidic chip shows good performances for biosensing.