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A comprehensive investigation of real-time temperature-induced resonance shift cancellation for silicon wire based biosensor arrays is reported for the first time. A reference resonator, protected by either a SU8 or SiO(2) cladding layer, is used to track temperature changes. The temperature dependence of resonators in aqueous solutions, pertinent to biosensing applications, is measured under steady-state conditions and the operating parameters influencing these properties are discussed. Real-time measurements show that the reference resonator resonances reflect the temperature changes without noticeable time delay, enabling effective cancellation of temperature-induced shifts. Binding between complementary IgG protein pairs is monitored over 4 orders of magnitude dynamic range down to a concentration of 20 pM, demonstrating a resolvable mass of 40 attograms. Reactions are measured over time periods as long as 3 hours with high stability, showing a scatter corresponding to a fluid refractive index fluctuation of ± 4 × 10(-6) in the baseline data. Sensor arrays with a SU8 protective cladding are easy to fabricate, while oxide cladding is found to provide superior stability for measurements involving long time scales.

We demonstrate a terahertz bandwidth silicon nanowire based radio-frequency spectrum analyzer using cross-phase modulation. We show that the device provides accurate characterization of 640Gbaud on-off-keyed data stream and demonstrate its potential for optical time-division multiplexing optimization and optical performance monitoring of ultrahigh speed signals on a silicon chip. We analyze the impact of free carrier effects on our device, and find that the efficiency of the device is not reduced by two-photon or free-carrier absorption, nor its accuracy compromised by free-carrier cross-chirp.

We present an ultra-compact comb filter using an add-drop ring resonator with an Archimedean spiral cavity. The cavity consists of two interleaved spiral branches which are connected in the center using arcs of circle of a radius that causes minimum bend loss. We describe the design procedure and examine the physical parameters governing the resonator performance. As an example, we demonstrate experimentally a comb filter with a 25 GHz channel spacing made of silicon photonic wires and only occupies an area of 80 × 90 µm2, approximately a 70 fold size reduction compared to a racetrack resonator. The filter transmission is free of spurious reflections, attesting to the smooth transition between different sections of the resonator cavity. Over a 40 channel wavelength span, the filter exhibits a quality factor Q > 35,000, extinction ratios > 10 dB, and an excellent power uniformity with variations < 0.5 dB for both the through and drop ports.

We analyzed the properties of the two factors determining the resonant-tunneling transport: the one- dimensional carrier energy distribution factor, which monotonically decreases with energy and increases with temperature, and the transmission probability peak, which decreases with bias and temperature, and we determined a criterion for current resonance. Our conclusions are quite different from those in commonly used descriptions. Calculations of the resonant tunneling versus temperature with constant E F , μ, and m * cannot give a decrease of peak currents with temperature

We report on several new types of sub-wavelength grating (SWG) gradient index structures for efficient mode coupling in high index contrast slab waveguides. Using a SWG, an adiabatic transition is achieved at the interface between silicon-on-insulator waveguides of different geometries. The SWG transition region minimizes both fundamental mode mismatch loss and coupling to higher order modes. By creating the gradient effective index region in the direction of propagation, we demonstrate that efficient vertical mode transformation can be achieved between slab waveguides of different core thickness. The structures which we propose can be fabricated by a single etch step. Using 3D finite-difference time-domain simulations we study the loss, polarization dependence and the higher order mode excitation for two types (triangular and triangular-transverse) of SWG transition regions between silicon-on-insulator slab waveguides of different core thicknesses. We demonstrate two solutions to reduce the polarization dependent loss of these structures. Finally, we propose an implementation of SWG structures to reduce loss and higher order mode excitation between a slab waveguide and a phase array of an array waveguide grating (AWG). Compared to a conventional AWG, the loss is reduced from -1.4 dB to < -0.2 dB at the slab-array interface.

We present experimental and theoretical results of label-free molecular sensing using the transverse magnetic mode of a 0.22 mum thick silicon slab waveguide with a surface grating implemented in a guided mode resonance configuration. Due to the strong overlap of the evanescent field of the waveguide mode with a molecular layer attached to the surface, these sensors exhibit high sensitivity, while their fabrication and packaging requirements are modest. Experimentally, we demonstrate a resonance wavelength shift of approximately 1 nm when a monolayer of the protein streptavidin is attached to the surface, in good agreement with calculations based on rigorous coupled wave analysis. In our current optical setup this shift corresponds to an estimated limit of detection of 0.2% of a monolayer of streptavidin.

We present the design and numerical simulation results for a silicon waveguide modulator based on carrier depletion in a linear array of periodically interleaved PN junctions that are oriented perpendicular to the light propagation direction. In this geometry the overlap of the optical waveguide mode with the depletion region is much larger than in designs using a single PN junction aligned parallel to the waveguide propagation direction. Simulations predict that an optimized modulator will have a high modulation efficiency of 0.56 V.cm for a 3V bias, with a 3 dB frequency bandwidth of over 40 GHz. This device has a length of 1.86 mm with a maximum intrinsic loss of 4.3 dB at 0V bias, due to free carrier absorption. (C) 2009 Optical Society of America

We demonstrate efficient, low power, continuous-wave four-wave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20nm. We show theoretically that the characteristic low dispersion enables phase-matching over a tuning range > 160nm.

We propose a silicon waveguide-fiber grating coupler that uses a subwavelength microstructure to achieve a continuously variable grating strength yet can be fabricated using only a single etch step. By adjusting the subwavelength microstructure at every point along the grating, the grating coupler can be optimized to give high field overlap with the optical fiber mode and also minimize backreflections along the incident waveguide path. Our design example is optimized for quasi-TM mode in a silicon photonic-wire waveguide, as required for waveguide evanescent-field-sensing applications. A field overlap of up to 94% with a standard single-mode optical fiber (SMF-28) is achieved by coupler apodization. Backreflection from the grating is reduced to ~0.1%, and the total predicted photonic wire to fiber coupling efficiency is 50%.

We demonstrate folded waveguide ring resonators for biomolecular sensing. We show that extending the ring cavity length increases the resonator quality factor, and thereby enhances the sensor resolution and minimum level of detection, while at the same time relaxing the tolerance on the coupling conditions to provide stable and large resonance contrast. The folded spiral path geometry allows a 1.2 mm long ring waveguide to be enclosed in a 150 microm diameter sensor area. The spiral cavity resonator is used to monitor the streptavidin protein binding with a detection limit of approximately 3 pg/mm(2), or a total mass of approximately 5 fg. The real time measurements are used to analyze the kinetics of biotin-streptavidin binding.

For Si1-xGex/Si hole and Ga1-xAlxAs/GaAs electron double barrier resonant tunneling devices (RTDs), we have studied the negative differential resistance (NDR). The current peak-to-valley ratio (PVR) was investigated as function of the temperature T for different device parameters and the dependence of the maximum working temperature Tm on material parameters and device parameters was determined. The results show that by narrowing well and barrier width, decreasing barrier height, and decreasing the doping concentration in the spacer layer, the RTDs have improved temperature characteristics, and have higher peak current Jp and larger PVR at high temperature. The RTDs with larger well width, and wide and high barriers nave quite large PVR, and are favorable to use at low temperature. Ga1-xAlxAs/GaAs electron RTDs are estimated to work at room temperature for a wide range of device parameters, while the device parameter design of Si1-xGex/Si hole RTDs is much more critical to work at same temperature. These results are consistent with the tendency of recently published experiments. On the basis of calculated PVR curves we can optimize RTD parameters to increase the working temperature and current peak-to-valley ratio.

Studies of current-voltage (I-V) characteristics and their temperature dependence show that the current transport in MBE-grown Si1-xGex/Si diodes is closely related to the epitaxial film quality. It is mainly controlled by two different mechanisms at low and high temperature. The ideality factor n of the diodes increases as the temperature is reduced, and n increases faster for the diodes which have larger n at room temperature. From comparisons with calculated results, it is proposed that the transport mechanism is diffusion controlled at high temperature and defect-assisted tunneling controlled at low temperature. The results from ? irradiation studies also support this suggestion. Due to the existence of band-offsets, the shift of the I-V curve with temperature of p+-Si1-xGex/n-Si diodes is much smaller than that in n+-Si1-xGex/p-Si diodes, when the current is diffusion controlled. The band-offsets are estimated from these shifts, and the results are in agreement with values measured by another method.

We present the implementation of a novel wavelength independent polarization splitter on a silicon-on-insulator platform. The waveguide splitter is based on a zero-order arrayed waveguide grating (AWG) configuration. The splitting function is realized by employing cladding stress-induced birefringence. The device demonstrated a TE to TM splitting ratio better than -15 dB over a 20 nm tuning range centered around lambda=1550 nm and better than -10 dB over our entire accessible wavelength range from lambda=1465 nm to 1580 nm. The highest splitting extinction ratio achieved was -20 dB. To our knowledge, this is the first reported passive broadband polarization splitter based on AWG.

A ring resonator in SOI photonic wire waveguides is demonstrated using a compact MMI coupler with 3mum x 9 mum footprint as the coupling element. We achieved high bandwidth of 0.25 nm, and a quality factor Q of ~ 6000 for rings with a radius of 50 mum. Unlike directional coupler based rings, these resonators have a wavelength independent Q and extinction ratio over more than 30 nm wavelength range, and there is no loss penalty for increasing the bandwidth. Compared to their directional coupler based counterparts, these resonators also have less demanding fabrication requirements and are compatible with high speed signal processing and optical delay lines.

We propose a new waveguide resonator device with a mirror cavity and a multimode interference (MMI) coupler. We present simulation results for the silicon wire MMI coupler with suppressed reflections and its use as a coupling element in the resonator cavity, built on the silicon-on-insulator waveguide platform. Tapering structures used in the reflection suppression were optimized, and the wavelength dependency of a conventional MMI was compared to that of the MMI with reflection suppression. Equations relating the power transfer of the two-mirror MMI-coupled resonator and quality factor were derived. The device was also studied using finite difference time domain simulation by both pulse and continuous wave excitation. The resonator does not require bend waveguides, it has the advantages of having no bend loss and a compact layout. The resonator device has a very small footprint of 3 mum x 30 mum, and a quality factor of 516.

We demonstrate a 50-channel high-resolution arrayed waveguide grating microspectrometer with a 0.2 nm channel spacing on a silicon-on-insulator (SOI) platform. The chip size is 8 mm x 8 mm. High channel density and spectral resolution are achieved using high aspect ratio 0.6 mum x 1.5 mum waveguide apertures to inject the light into the input combiner and to intercept different spectral channels at the output combiner focal region. The measured crosstalk is

We present an analysis of Fourier-transform arrayed waveguide gratings in the Fresnel diffraction regime. We report a distinct spatial modulation of the interference pattern referred to as the Moiré-Talbot effect. The effect and its influence in a FT AWG device is explained by deriving an original analytical expression for the modulated field, and is also confirmed by numerical simulations using the angular spectrum method to solve the Fresnel diffraction integral. We illustrate the retrieval of spectral information in a waveguide Fourier-transform spectrometer in the presence of the Moiré-Talbot effect. The simulated device comprises two interleaved waveguide arrays each with 180 waveguides and the interference order of 40. It is designed with a Rayleigh spectral resolution of 0.1 nm and 8 nm bandwidth at wavelength lambda approximately 1.5 mum. We also demonstrate by numerical simulations that the spectrometer crosstalk is reduced from -20 dB to -40 dB by Gaussian apodization.

Concept, theory and simulations of a new type of waveguide device, a multiaperture Fourier-transform planar waveguide spectrometer, are presented. The spectrometer is formed by an array of Mach-Zehnder interferometers generating a wavelength dependent spatial fringe pattern at the array output. The input light spectrum is calculated using a discrete Fourier transformation of the output spatial fringes. The multiaperture input significantly increases the optical throughput (étendue) compared to conventional single input spectrometers. Design rules for the arrayed spectrometer are deduced from performance specifications such as wavelength range and spectral resolution. A design example with spectral resolution 0.025 nm and range 2.5 nm is presented, where the optical throughput is increased by a factor of 200 compared to a single input device.

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Optically-pumped long-wavelength vertical-cavity surface-emitting lasers (VCSELs) have been fabricated exhibiting more than 2mW over 20–70°C, and 1.25mW at 85°C. Small-signal modulation measurements on the VCSEL at 20°C indicate a 3dB bandwidth of 14.8GHz at an output power of 2mW. The VCSELs have a narrow spectral width suitable for data transmission over single-mode fiber. The good temperature performance of the VCSEL is maintained in a suspended configuration that would allow monolithic integration.

We describe the design, fabrication, and characterization of an optical modulator in silicon-on-insulator (SOI). The modulator is based upon a rib waveguide, with a transverse p–i–n diode being used to produce a refractive index change through the plasma dispersion effect. Measurements of optical modulation show submicrosecond transition times and confirm that electronic switching dominates over thermal effects.

Novel AlGaInAs VCSELs have been fabricated for coarse wavelength division multiplexing over multimode fibre at wavelengths of 1275, 1300, 1325 and 1350 nm. Efficient monomode lasing (>2.0 mW power, 31% efficiency) and multimode lasing (up to 9 mW power, 39% efficiency) are reported, along with 3.125 and 10 Gbit/s modulation to 85°C.

The measurement and analysis of I‐V characteristics from molecular beam epitaxially grown Si0.9Ge0.1/Si p‐n diodes are presented. When a diode is forward biased the current transport is mainly injection diffusion of the holes and defect recombination within the depletion region of the n side. At reverse bias, the current comes from tunneling of holes from the top of the p‐type valence band to the n‐type conduction band, and also to the interface states followed by multistep recombination tunneling via defect states in the depletion region of the n side. The forward voltage drop was found to be much lower than that of Si diodes. Electron irradiation damages have opposite effects on the forward‐biased I‐V characteristics of Si0.9Ge0.1/Si diodes as compared to the effects observed for Si diodes.

In this work the anomalous formation kinetics of old thermal donors (TD) observed in the initial stage of formation in pre-heat-treated carbon-rich samples are studied. Computer simulations applying a reaction scheme where the TD-complexes are subsequently formed by single oxygen diffusion reveal that the experimental results can only be acounted for if the pre-existing TD-core involves three oxygen atoms and has a concentration in the range 1013-1014 cm−3. Carbon is found to have a major influence on the production rate of pre-existing cores.

This work is devoted to an \"old\" defect and its annealing characteristics, namely the divacancy center in Si. IR spectroscopy is applied to study the annealing kinetics of divacancy-related absorption peaks in electron-irradiated Czochralski-grown samples doped with B. In all specimens the kinetics show an exponential decay (first-order process) and a model taking into account both diffusion and dissocn. as annihilation mechanisms gives excellent quant. agreement with the exptl. results. Activation energy values extd. for diffusion and dissocn. are 1.28 eV and 1.71 eV, resp. In highly B-doped samples (0.1 Wcm), a strong dependence of the absorption bands on the Fermi-level position is obsd. during annealing .ltorsim.200 Deg and concurrently, a change of the divacancy charge state from neutral to singly pos. takes place. [on SciFinder (R)]