Ths paper reviews benefits for the integration of optical components into Photonic Light Circuits (PLC's), with a particular emphasis on the integration of optical switching elements. The requirements for the optical switches in these circuits will be discussed and the suitability of various switching technologies for meeting these requirements will be considered.

Even if a lot of applications are today focused on optical communications, other industrial fields can also take benefit from the advantages offered by MOEMS solutions. Many Optical MEMS are based on electro-mechanical devices providing optical function, for example moving micro-mirrors for optical switches, attenuators or scanners. But LETI and a few other labs have also developed an original MOEMS technology by combining on the same substrate integrated optical planar waveguides with micro-mechanical structures. To reach this aim, a specific 'silica micro-machining' technology has been developed. Based on the moving waveguide technology, LETI have fabricated a micro-vibration sensor for the surveillance of rotating machines in electrical generators and optical switches for optical network protection and reconfiguration. Other devices are also based on silica micro-machining technology since they use moving silica optical structures, for example micro-lenses for micro-scanners. After general ideas on definitions and Optical MEMS applications, the paper continues with a short overview of the state of the art of Optical MEMS based on moving waveguides. Then it is more focused on silica on silicon technology. Specific technological problems are presented and the discussion is illustrated by the work carried out by LETI in this area.

Agilent Technologies' approach to photonic cross-connect switching combines a silica-based planar lightwave circuit chip with a silicon-based actuator chip. The former contains two intersecting arrays of waveguides, with trenches etched into each crosspoint. The latter contains a matching pattern of electrically addressed resistive elements, and the two chips are hermetically sealed together. In the default state, the trenches, along with the rest of the sealed space between the two chips, are filled with a liquid whose index matches the waveguides. Optical signals passing along any guide simply pass on through. However, by activating a resistive element, a bubble can be created at that crosspoint, so that total internal reflection occurs at the side wall of the corresponding trench, and switching is achieved. Recent performance data of prototype 32x32 optical switches, including insertion loss, polarization dependent loss, switching time, and vibration sensitivity will be presented. Some of the intrinsic advantages of our technology will be discussed. One example is the built-in alignment of the waveguides and the trench walls at which switching occurs, which means that no optical realignments are necessary during operation. Another example is the potential for very low crosstalk, characteristic of the underlying phenomenon of total internal reflection.

For optical applications using a silicon platform (e.g. optical interconnects), passive and especially active components made of silicon need to be developed. Unfortunately, the optical properties of silicon are not sensitive to electric fields, which makes active elements difficult to fabricate. In this work, we demonstrate electrically tunable mirrors that consist of a porous silicon microcavity resonator. Liquid crystal molecules are uniformly infiltrated into the porous silicon matrix to allow tuning of the microcavity resonance with an electric field. The applied electric field causes the liquid crystal molecules to change orientation, creating a change in the value of their refractive index and a shift of the resonance wavelength of the microcavity resonator. Simulations show devices could be built that exhibit a resonance with a full width at half maximum value of 2nm. The resonance can be shifted to achieve a change in reflectivity from ~0% to ~100%. Thus, the application of a small ac voltage should lead to a complete modulation of the reflected light.

A technique for fabricating aperiodic Bragg gratings in rib waveguides on Silicon-On-Insulator (SOI) is presented. The technique allows flexibility in defining various characteristics of aperiodic gratings so that a full range of optical grating filters can be realized. The fabrication process comprises optical and electron-beam (e-beam) lithography followed by a liftoff and a single Reactive Ion Etch (RIE) to simultaneously produce the waveguide and the embedded grating structure.

The implementation of efficient Si-based optical functions has attracted a considerable interest in the last years since it would allow the use of the Si technology for the realization of integrated optoelectronic devices. We have fabricated and characterized a novel Si-based light modulator working at the standard communication wavelength of 1.54 micrometers . It consists of a three terminal Bipolar Mode Field Effect Transistor integrated with a silicon RIB waveguide on epitaxial Si wafers. The optical channel of the modulator is embodied within its vertical electrical channel. Light modulation is obtained through the formation of a plasma of carriers, inside the optical channel, that produces an increase of the absorption coefficient. Fast modulation is achieved by moving the plasma inside and outside the optical channel by properly biasing the control electrode. The devices have been fabricated using clean room processing. Detailed electrical characterization and device simulation confirm that strong conductivity modulation and plasma formations in the channel are achieved. The plasma distribution in the device under different bias conditions has been directly derived from Emission Microscopy analysis. The expected device performances in terms of modulation depth and speed will be presented and discussed.

Optical modulation in silicon photonics is performed either via the plasma dispersion effect, or by thermal means. Both are relatively slow processes when utilized in large (multi micron) waveguide structures. However, modulators based on the plasma dispersion effect become much faster in smaller waveguides, but coupling to such waveguides is then inefficient. In this paper we discuss both the operation of small waveguide modulators and a potentially more efficient means of coupling to such waveguides. A number of design parameters of the modulators are discussed including the optimum configuration of a three terminal p-i-n diode around a rib waveguide, and the optimization of both the power efficiency and the operating speed of the device. Operating speed is theoretically increased by as much as 7400% with respect to devices in the literature. The problem of coupling to these waveguides is addressed via gratings. All work is theoretical, but sets the groundwork for subsequent fabrication.

Multi-terminal silicon CMOS light emitting diode structures are described where the light emission intensity from the reverse biased pn junctions is modulated by gate voltages applied to overlapping polysilicon gates. Linear arrays, as well as two-dimensional arrays of Si LED's were realized in combination with a grid of overlapping resistive polysilicon gates. The gate voltages applied to the resistive gate grid at different points modulated the pn junction breakdown, and thus the reverse avalanche current through the diodes. A novel structure where the light pattern can be changed from two point sources to a single line source using one MOS control gate has also been realized. A linear relationship exists between reverse current and light intensity, but due to the nonlinear variation of breakdown voltage with applied MOS gate voltage, the light intensity varies approximately with the square root of the applied voltage. This nonlinear behavior may facilitate electro-optical signal processing. The resistive gate grid voltages can be used to generate different breakdown voltages at different positions in the LED array. The result is that the array emission pattern is a function of the applied gate voltages. Spatial modulation of the light emission pattern is demonstrated for several device structures.

We report the direct injection of precise clock signals into standard CMOS circuits using short optical pulses by a novel receiverless scheme that eliminates the delay, skew and jitter of a typical receiver. To accomplish the optical injection we designed small silicon detectors along-side standard 0.25micrometers CMOS-circuits. Due to the low intrinsic capacitance of the detectors, the photogenerated carriers can directly generate voltage swings that are comparable with CMOS voltage levels if the detectors are loaded with high-impedance circuits. As a first step to implement this scheme we characterized various detectors built in the CMOS process for their high-frequency response. In a test set-up the silicon detectors are sampled with on-chip samplers that only present a small capacitive loading to the detector node. We present the high-frequency high-impedance response measured with this scheme together with capacitance measurements and DC responsivities of various types and sizes of detectors. The characterized long tails typically observed with silicon detectors allowed us to set up a model for the power penalty we have to take into account for precise clock detection. Finally, as a proof-of-principle demonstration we present the first results of this receiverless scheme in which a totem-pole of silicon detectors directly drives an on-chip CMOS inverter.

The need for tunable optical transmitters in optical networking is growing at a rapid rate. A tunable optical transmitter is the combination of a tunable laser, an isolator, and a modulator. Although today lasers and modulators could be integrated together on a single chip, an integrated component of this type would not be useful because the absence of an isolator between the two elements would cause optical reflections to reach the laser, leading to a high level of frequency chirp and relaxation oscillations. Therefore discrete external modulators are used, and lasers are coupled to them through discrete optical isolators. We report on recent developments in integrated active, thermo-optic, magneto-optic and electro-optic technologies that enable the production of a fully integrated tunable transmitter. This transmitter consists of a planar polymer waveguide circuit that is built on a silicon chip and in which films of a variety of materials are embedded. This subsystem on a chip includes a laser chip coupled to a thermo-optically tunable planar polymeric filter resulting in a tunable external cavity laser; an integrated magneto-optic isolator consisting of a planar polymer waveguide with inserted thin films of yttrium iron garnet for Faraday rotation, crystal ion sliced LiNbO₃ for half-wave retardation, and polarizers; and an electro-optic modulator consisting of a crystal ion sliced LiNbO₃ thin film patterned with a Mach-Zehnder interferometer and grafted into the polymer circuit, capable of operating with less than 5 Volts at modulation speeds up to 40 Ghz.

The ever-increasing performance and economy of operation requirements placed on commercial and military transport aircraft are resulting in very complex systems. As a result, the use of fiber optic component technology has lead to high data throughput, immunity to EMI, reduced certification and maintenance costs and reduced weight features. In particular, in avionic systems, data integrity and high data rates are necessary for stable flight control. Fly-by-Light systems that use optical signals to actuate the flight control surfaces of an aircraft have been suggested as a solution to the EMI problem in avionic systems. Current fly-by-light systems are limited by the lack of optically activated high-power switching devices. The challenge has been the development of an optoelectronic switching technology that can withstand the high power and harsh environmental conditions common in a flight surface actuation system. Wide bandgap semiconductors such as Silicon Carbide offer the potential to overcome both the temperature and voltage blocking limitations that inhibit the use of Silicon. Unfortunately, SiC is not optically active at the near IR wavelengths where communications grade light sources are readily available. Thus, we have proposed a hybrid device that combines a silicon based photoreceiver model with a SiC power transistor. When illuminated with the 5mW optical control signal the silicon chip produces a 15mA drive current for a SiC Darlington pair. The SiC Darlington pair then produces a 150 A current that is suitable for driving an electric motor with sufficient horsepower to actuate the control surfaces on an aircraft. Further, when the optical signal is turned off, the SiC is capable of holding off a 270 V potential to insure that the motor drive current is completely off. We present in this paper the design and initial tests from a prototype device that has recently been fabricated.

Ordered Si nanocrystals showing a strong room temperature luminescence are prepared using a novel SiO/SiO2 superlattice approach fully compatible to Si technology. This enables independent control of particle size as well as particle density and particle position. Size control is demonstrated for nanocrystal sizes of 3.8 nm to 2 nm. A size-dependent blue shift of the luminescence from 900 to 750 nm and a luminescence intensity comparable to porous Si are observed. Experiments using high power excitation show a saturation behavior, a blue shift of the PL peak position by 61-87 meV and an increase in full width at half maximum depending on size. A blue shift by around 60 meV is found for luminescence at 5 K. Erbium doping of the superlattice structure for photonic applications is discussed.

Terahertz (far-infrared) intersubband electroluminescence is reported in p-type Si/SiGe quantum wells and quantum cascade structures. Surface-normal emission (without the aid of a surface grating) from light hole - heavy hole intersubband transitions has been observed for the first time in a quantum cascade device. Edge-emission measurements have also been performed, which show emission from both heavy hole - heavy hole and light hole - heavy hole transitions, and have allowed demonstration of the polarisation dependence of the emitted power, according to the selection rules for the intersubband interactions. The electroluminescence is visible up to temperatures of ~150K, in the multiple quantum well structures, and >=77K in the quantum cascade structure.

We report that electroluminescence (EL) at Si bandgap energy is significantly enhanced from the nano-structured metal- oxide-semiconductor (MOS) devices on silicon. The nano- structure is constructed by inserting SiO₂ nanoparticles with the size of 12 nm in the oxide layer. The measured EL efficiency of the nano-structured MOS devices is enhanced to be near 10^-4, which exceeds the limitation imposed by the indirect bandgap nature of silicon. We also observed the nearly lasing behaviors such as the threshold and resonance modes in the EL characteristics. The enhanced EL efficiency is attributed to simultaneous localization of electrons and holes to form exciton by nano-structure. This causes the process of the phonon-assisted radiative recombination of electron-hole pair more like two-particle (exciton-phonon) collision than three-particle (electron- hole-phonon) collision.

Efficient silicon-based light emitting diodes have been fabricated using a recently developed approach - dislocation engineering. Crucially this technique uses entirely conventional ULSI processes. The devices were fabricated by conventional low energy boron implantation into silicon substrates followed by high temperature rapid thermal annealing. Strong silicon band edge luminescence was observed. Electroluminescence emissions with an efficiency greater than 2 X 10^-4 at rom temperature were measured; the device lifetime was found to be approximately 18 microsecond(s) . The luminescence integrated intensity varied with the device fabrication conditions. In this paper we discuss the influence of processing conditions on the luminescence emissions.

The development of Schottky barrier technology for creation of IR-photodetectors is caused by reduction of a potential barrier height used by formation of heavily-doped thin layer near to the semiconductor surface. We propose for this aim to form heavily-doped nanolayer in p-Si by recoil implantation of boron. Boron nm-thick film was deposited on the Si sample surfaces by cathode sputtering. After that the samples were irradiated by high intensity Al⁺ beams extracted from pregenerated explosion-emission plasma. The samples are examined by secondary ion mass-spectrometry (SIMS). It is experimental established that profile of impurity distribution in surface layer is exponential. The doping concentration at the silicide/silicon interface is 10¹⁸-10²⁰ cm^-3 and thickness of surface layer is 8 - 12 nm. The energy band diagrams of a PtSi - p- Si Schottky barrier with high-doped surface layer formed by recoil implantation were calculated for different parameters of barrier. It is shown, that effective barrier heights in PtSi-Si with recoil implantation formed surface 10 nm layer at surface concentration order 10²⁰ cm^-3 is reduced to 0.13 eV, corresponding to a cutoff wavelength of 9.5 micrometers . Thus, the cutoff wavelength of the PtSi Schottky infrared detectors has been extended to the long wavelength infrared region by incorporating a p⁺ doping layer with exponential profile of impurity distribution at the silicide/silicon interface.

Silicon Carbide is a potentially useful compound for use in silicon based photonics because cubic silicon carbide (3C- SiC), possesses a first order electro-optic (Pockels) effect, something absent in pure silicon. This means the material is potentially suitable for high speed optical modulation. Furthermore, the wide bandgap (2.2 eV) of 3C-SiC makes the devices suitable for use over the visible and near infrared spectrum range as well as the longer communication wavelengths, and also means the material can tolerate high temperatures. However, relatively little work has been carried out in SiC for photonics applications. In this paper we will discuss design and fabrication of both SiC waveguides and modulators for silicon based photonics. The fabrication process utilizes ion implantation of oxygen into SiC to form the lower waveguide boundary. Subsequently, ribs are etched and contacts are added to form the optical modulators. Consideration of both Pockels modulators and plasma dispersion modulators has been made, and both will be discussed here. These devices have potential for optical modulation, but are also compatible with silicon processing technology. We have demonstrated waveguiding in 3C-SiC, established a processing recipe for the SiC wafers which enables fabrication of 3-dimensional devices, and demonstrated optical modulation. Performance of the resultant devices is compared to other silicon based devices in terms of operating speed and efficiency.

We were investigated photoluminescence, cathodoluminescence and photosensitivity properties of porous silicon (PS) and PS capsulated by Al₂O₃ thin film. This film was deposited by RF magnetron sputtering in argon - oxygen atmosphere and had crystalline structure. PS was processed in hydrogen under the high pressure. Light-emission and photosensitivity spectra such double structures in visible and infrared region were investigated. The process of light emitting had tendency to decrease. The cathodoluminescence decay for Al₂O₃3-PS-silicon substrate heterostructure was lower then for PS-silicon substrate.

A novel low-power thermo-optic MMI-MZI switch is presented. It consists of two different MMI couplers and phase shifting arms between them. It has been designed to utilize a modal phase shift of 90-degrees one each arm at every switching in turn and hence a half driving power of previous switches with similar device structures. This could be achieved by making the phase of input signals to the arms identical. The switching speed is also expected to be much faster due to the reduced power consumption.